Patent Publication Number: US-10788078-B2

Title: Outer joint member of constant velocity universal joint

Description:
TECHNICAL FIELD 
     The present invention relates to a method of manufacturing an outer joint member of a constant velocity universal joint, an outer joint member, a shaft member, and to a cup member. 
     BACKGROUND ART 
     In a constant velocity universal joint, which is used to construct a power transmission system for automobiles and various industrial machines, two shafts on a driving side and a driven side are coupled to each other to allow torque transmission therebetween, and rotational torque can be transmitted at a constant velocity even when each of the two shafts forms an operating angle. The constant velocity universal joint is roughly classified into a fixed type constant velocity universal joint that allows only angular displacement, and a plunging type constant velocity universal joint that allows both the angular displacement and axial displacement. In a drive shaft configured to transmit power from an engine of an automobile to a driving wheel, for example, the plunging type constant velocity universal joint is used on a differential side (inboard side), and the fixed type constant velocity universal joint is used on a driving wheel side (outboard side). 
     Irrespective of the plunging type and the fixed type, the constant velocity universal joint includes, as a main component, an outer joint member including a cup section having track grooves formed in an inner peripheral surface thereof and engageable with torque transmitting elements, and a shaft section that extends from a bottom portion of the cup section in an axial direction. In many cases, the outer joint member is constructed by integrally forming the cup section and the shaft section by subjecting a rod-like solid blank (bar material) to plastic working such as forging and ironing or processing such as cutting work, heat treatment, and grinding. 
     Incidentally, as the outer joint member, an outer joint member including a long shaft section (long stem) may sometimes be used. In order to equalize lengths of a right part and a left part of an intermediate shaft, the long stem is used for an outer joint member on the inboard side that corresponds to one side of the drive shaft. The long stem is rotatably supported by a rolling bearing. Although varied depending on vehicle types, the length of the long stem section is approximately from 300 mm to 400 mm in general. In the outer joint member, the long shaft section causes difficulty in integrally forming the cup section and the shaft section with high accuracy. Therefore, there is known an outer joint member in which the cup section and the shaft section are formed as separate members, and both the members are joined through friction press-contact. Such a friction welding technology is described in, for example, Patent Document 1. 
     An overview of the friction welding technology for the outer joint member described in Patent Document 1 is described with reference to  FIG. 29  and  FIG. 30 . An intermediate product  71 ′ of an outer joint member  71  includes a cup member  72  and a shaft member  73 , which are joined through the friction welding. As illustrated in  FIG. 29 , burrs  75  are generated in at least one of inner and outer diameter portions on a joining portion  74  along with the friction welding. In order to mount a rolling bearing (see  FIG. 1 ) to a shaft section of the intermediate product  71 ′ of the outer joint member  71 , as illustrated in  FIG. 30 , it is necessary to remove the burrs  75  on the radially outer side of the joining portion  74  through processing such as turning. Although illustration is omitted, the intermediate product  71 ′ is processed into a finished product of the outer joint member  71  through machining of a spline, snap ring grooves, and the like, and through heat treatment, grinding, and the like. Therefore, the outer joint member  71  and the intermediate product  71 ′ have slight differences in shape, but illustration of the slight differences in shape is omitted in  FIG. 30  to simplify the description, and the outer joint member  71  being the finished product and the intermediate product  71 ′ are denoted by the reference symbols at the same parts. The same applies to the description below. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     Patent Document 1: JP 2012-57696 A 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The burrs  75  on the joining portion  74  generated due to the friction welding described above are quenched by friction heat and cooling that follows the friction heat. Thus, the burrs  75  have a high hardness and a distorted shape extended in a radial direction and an axial direction. Therefore, as illustrated in  FIG. 30 , when removing the burrs  75  on the radially outer side through the turning, a tip for turning is liable to be significantly abraded due to the high hardness and cracked due to the distorted shape. Therefore, it is difficult to increase the turning speed. In addition, the cutting amount per pass of the tip for turning is decreased, and hence the number of passes is increased, which causes a problem in that the cycle time is increased to increase the manufacturing cost. 
     Further, in order to inspect a joining state of the joining portion  74  of the outer joint member  71 , when ultrasonic flaw detection, which enables flaw detection at high speed, is to be performed, an ultrasonic wave is scattered due to the burrs  75  remaining on the radially inner side of the joining portion  74 , and hence the joining state cannot be checked. Therefore, there occurs a problem in that total inspection through the ultrasonic flaw detection cannot be performed after the joining. 
     In view of the above-mentioned problems, when the components are joined through laser welding or electron beam welding, the surfaces of the joining portion may be prevented from being increased in thickness unlike the case of the friction welding. However, when the cup member  72  and the shaft member  73  as illustrated in  FIG. 31  are brought into abutment against each other to be welded, a gas pressure in a hollow cavity portion  76  is increased due to processing heat during the welding, and after completion of the welding, the pressure is decreased. Due to the variation in the internal pressure of the hollow cavity portion  76 , blowing of a molten material occurs. Thus, a recess is formed on radially outer surfaces of the welded portion, poor welding in terms of depth occurs, and air bubbles are generated inside the welded portion, thereby degrading the welding state. As a result, the strength of the welded portion is not stable, which adversely affects quality. 
     In addition, the cup member  72  and the shaft member  73 , which are joined through the friction welding as illustrated in  FIG. 29  and  FIG. 30  or joined by welding as illustrated in  FIG. 31  as described above, are joined at an intermediate position on the entire shaft section having a shape and dimensions different for each vehicle type. Accordingly, as described later, it was proved that there is also a problem in terms of cost reduction achieved through enhancement of productivity and standardization of a product type of the cup member. 
     In addition, through the laser welding and the electron beam welding, a weld bead can be prevented from being increased in thickness, and hence the total inspection through the ultrasonic flaw detection can be performed. However, the inventors of the present invention have focused on the fact that the outer joint member is a component of the constant velocity universal joint being a mass-produced product for automobiles and the like, thereby being essential to enhance accuracy and operability in inspection on the welded portion. 
     The present invention has been proposed in view of the above-mentioned problems, and has an object to provide a method of manufacturing an outer joint member, a shaft member, and a cup member, which are capable of increasing strength of a welded portion and quality, enhancing accuracy and operability in inspection, reducing welding cost, achieving cost reduction through enhancement of productivity and standardization of a product type, and reducing a burden of production management. 
     Solution to Problems 
     In order to achieve the above-mentioned object, the inventors of the present invention have diligently conducted research and verification to arrive at the following findings. Based on the findings from multiple aspects, the inventors of the present invention have conceived a novel manufacturing concept in consideration of mass-productivity to achieve the present invention. 
     (1) In terms of production technology in laser welding and electron beam welding, when the cup member and the shaft member are welded to each other under a state in which the cup member and the shaft member are placed in a sealed space and the hollow cavity portion as well as the sealed space becomes the vacuum, blowing of a molten material and generation of air bubbles are suppressed. 
     (2) Further, in terms of productivity, when welding is performed on the cup member and the shaft member after being subjected to heat treatment such as quenching and tempering in order to enhance productivity, a temperature of a peripheral portion is increased by heat generated during the welding, which causes a risk of reduction in hardness of a region subjected to heat treatment. To address this problem, the inventors of the present invention have focused on a joining method involving steps capable of achieving highest efficiency and greatest cost reduction without affecting the joint function through change in the order of the welding step. For example, the following steps are adopted. In a case of a cup member and a shaft member having no risk of thermal effect during the welding, the cup member and the shaft member in a finished state after being subjected to heat treatment that involves quenching and tempering are welded to each other. In a case of a cup member and a shaft member having a risk of thermal effect, on the other hand, the cup member and the shaft member are subjected to heat treatment after the welding. As in this example, the inventors of the present invention have found a concept of adopting optimum steps depending on shapes, specifications, and the like of the cup member and the shaft member. 
     (3) Still further, in terms of productivity and standardization of the product type, the inventors of the present invention have found the following problem with the cup member  72  illustrated in  FIG. 29  to  FIG. 31 . That is, the cup member  72  has a short shaft section formed by forging or the like to have a diameter smaller than that of the bottom portion of the cup section. This short shaft section is prepared based on the shape and dimensions of the shaft member  73 , and is joined to the shaft member  73  at an intermediate position on the entire shaft section. Depending on a vehicle to which the shaft member  73  is assembled, the shaft member  73  is required to have a variety of shaft diameters and outer peripheral shapes in addition to differences in types such as a general length stem type and a long stem type. Therefore, when the short shaft section of the cup member  72  is prepared based on the shape and dimensions of the shaft member  73 , and is joined to the shaft member  73  at the intermediate position on the entire shaft section, a cup member  72  dedicated to one type of the shaft member  73  is required due to differences both in shaft diameter (joining diameter) and in shape and length (joining position) of the short shaft section of the cup member  72  to be joined to the shaft member  73 . Therefore, it was proved that there is a problem also in terms of cost reduction achieved through enhancement of productivity and standardization of a product type of the cup member. 
     (4) In addition, the inventors of the present invention have found that, in order to practically achieve the novel manufacturing concept for the outer joint member of the constant velocity universal joint being a mass-produced product for automobiles and the like, it is necessary to elaborate an ultrasonic flaw detection-inspection method and a shape of the welded portion so that accuracy and operability in inspection on the welded portion can be enhanced. 
     As a technical measure to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a method of manufacturing an outer joint member of a constant velocity universal joint, which is constructed by forming, through use of separate members, a cup section having track grooves formed at an inner periphery of the cup section and engageable with torque transmitting elements, and a shaft section formed at a bottom portion of the cup section, and by welding a cup member forming the cup section and a shaft member forming the shaft section, the method comprising: forming the cup member and the shaft member of medium carbon steel; preparing, as the cup member, a cup member having a cylindrical portion and a bottom portion integrally formed by forging, and a joining end surface formed on an outer surface of the bottom portion in a machining step after the forging; preparing, as the shaft member, a shaft member having a joining end surface to be joined to the bottom portion of the cup member, which is formed in a machining step; bringing the joining end surface of the cup member and the joining end surface of the shaft member into abutment against each other; welding the cup member and the shaft member by radiating a beam from an outer side of the cup member to an abutment portion between the cup member and the shaft member in a radial direction of the cup member, the joining end surface of the cup member having an outer diameter set to an equal dimension for each joint size, the welding being performed under a state in which a welding depth checking chamfer is formed on a radially inner side of any one of the joining end surface of the cup member and the joining end surface of the shaft member; and performing, after the welding, ultrasonic flaw detection-inspection from a surface side of any one of the cup member and the shaft member, which has the any one of the joining end surface of the cup member and the joining end surface of the shaft member. 
     With the above-mentioned configuration, it is possible to achieve the method of manufacturing an outer joint member and the outer joint member, which are capable of increasing the strength of the welded portion and the quality, reducing the welding cost, enhancing the accuracy and the operability in the inspection on the welded portion, achieving the cost reduction through the enhancement of productivity of the cup member and the shaft member and through the standardization of a product type of the cup member, and reducing the burden of production management. 
     The any one of the joining end surface of the cup member and the joining end surface of the shaft member may comprise, in addition to the welding depth checking chamfer, an excessive welding depth checking chamfer formed on a radially inner side with respect to the welding depth checking chamfer. In this case, determination as to whether or not the welding depth is kept within a satisfactory range of being not insufficient or not excessive can be made. Thus, it is possible to prevent excess of the welding depth, further reduce the welding cost, and achieve satisfactory operability in the inspection. 
     It is preferred that the welding depth checking chamfer and the excessive welding depth checking chamfer be formed into the same shapes for each joint size. With this configuration, the welding depth checking chamfer and the excessive welding depth checking chamfer can be standardized for each joint size. As a result, enhancement of accuracy in inspection of the welding depth and productivity, and the standardization of a product type of the cup member can be further promoted. 
     In this case, in Claims and Specification of the present invention, setting the outer diameter of the joining end surface of the cup member to an equal dimension for each joint size, and forming the welding depth checking chamfer and the excessive welding depth checking chamfer into the same shapes for each joint size are not limited to preparing one type of the cup member for one joint size, that is, not limited to preparing the cup member assigned with a single product number. For example, the present invention encompasses preparing cup members of a plurality of types (assigned with a plurality of product numbers, respectively) for one joint size based on different specifications of a maximum operating angle, setting the outer diameter of the joining end surface of each of the cup members to an equal dimension, and forming the welding depth checking chamfer and the excessive welding depth checking chamfer into the same shapes. In addition, the present invention encompasses, for example, preparing cup members of a plurality of types (assigned with a plurality of product numbers, respectively) for one joint size in order to achieve management of the cup members in a plurality of forms including intermediate components before heat treatment and finished components after heat treatment in consideration of the joint function, the circumstances at the manufacturing site, the productivity, and the like, setting the outer diameter of the joining end surface of each of the cup members to an equal dimension, and forming the welding depth checking chamfer and the excessive welding depth checking chamfer into the same shapes. 
     Further, in Claims and Specification of the present invention, setting the outer diameter of the joining end surface of the cup member to an equal dimension for each joint size, and forming the welding depth checking chamfer and the excessive welding depth checking chamfer into the same shapes for each joint size may be applied also to different types of constant velocity universal joints. For example, the present invention encompasses setting outer diameters of the joining end surfaces of a tripod type constant velocity universal joint and a double-offset constant velocity universal joint to equal dimensions, and forming the welding depth checking chamfer and the excessive welding depth checking chamfer into the same shapes on the inboard side, and encompasses setting outer diameters of the joining end surfaces of a Rzeppa type constant velocity universal joint and an undercut-free type constant velocity universal joint to equal dimensions, and forming the welding depth checking chamfer and the excessive welding depth checking chamfer into the same shapes on the outboard side. Further, the present invention also encompasses setting the outer diameters of the joining end surfaces of the constant velocity universal joints on the inboard side and the outboard side to equal dimensions, and forming the welding depth checking chamfers and the excessive welding depth checking chamfers into the same shapes on the inboard side and the outboard side. 
     It is preferred that the ultrasonic flaw detection-inspection comprise inputting an ultrasonic wave from an angle probe. In this case, when the welding depth checking chamfer and the excessive welding depth checking chamfer are formed in a direction perpendicular to a transmission pulse, the accuracy and the operability in the inspection can be enhanced. Further, at the time of ultrasonic flaw-detection inspection on the welded portion, when the ultrasonic wave from the angle probe is input from the surface side of the shaft member having a small shaft diameter, the flaw-detection inspection can be facilitated. 
     The outer joint member may have a protruding surface protruding to a radially inner side with respect to an inner diameter of the any one of the joining end surface of the cup member and the joining end surface of the shaft member, the protruding surface being formed on a radially inner side of another one of the joining end surface of the cup member and the joining end surface of the shaft member without the welding depth checking chamfer and the excessive welding depth checking chamfer. With this configuration, the accuracy in the inspection of the welding depth can be further enhanced. 
     At least one of the cup member or the shaft member before the welding may be prepared as an intermediate component without performing heat treatment. In this case, the heat treatment and finishing such as grinding and quenched-steel cutting work are performed after the welding. Thus, this configuration is suited to a cup member and a shaft member having such shapes and specifications that the hardness of the heat-treated portion may be affected by temperature rise at the periphery due to heat generated during the welding. The intermediate component is assigned with a product number for management. 
     Further, at least one of the cup member or the shaft member before the welding may be prepared as a finished component subjected to heat treatment. With the at least one of the cup member or the shaft member prepared as the finished component subjected to the heat treatment and the finishing such as grinding after the heat treatment or quenched-steel cutting work, it is possible to obtain the cup member prepared as the finished component for common use for each joint size, and the shaft member having a variety of specifications of the shaft section for each vehicle type. Thus, the cup member and the shaft member are each assigned with a product number for management. Therefore, the cost is significantly reduced through the standardization of a product type of the cup member, and the burden of production management is significantly alleviated. Further, the cup member prepared for common use and the shaft member having a variety of specifications of the shaft section can be manufactured separately until the cup member and the shaft member are formed into the finished components subjected to the finishing such as forging, turning, heat treatment, grinding, and quenched-steel cutting work. Further, as well as reduction of setups and the like, the enhancement of productivity is achieved. However, the cup member and the shaft member as the finished components are not limited to members subjected to finishing such as the grinding after the heat treatment or the quenched-steel cutting work as described above. The cup member and the shaft member according to the present invention encompass members assuming a state after completion of heat treatment but before being subjected to the finishing. 
     The above-mentioned welding comprises electron beam welding. Thus, burrs are not generated on the joining portion. Reduction of manufacturing cost through omission of the number of steps of post-processing for the joining portion can be reliably achieved, and further, total inspection on the joining portion through ultrasonic flaw detection can be more reliably performed. Further, deep penetration can be obtained by electron beam welding, thereby being capable of increasing welding strength and reducing thermal strain. 
     It is desired that the cup member and the shaft member be welded to each other under a state in which the cup member and the shaft member are placed in a sealed space to keep a pressure equal to or less than an atmospheric pressure. Accordingly, the blowing of a molten material and the generation of air bubbles are suppressed, thereby enhancing the strength and quality of the welded portion. 
     It is desired that a hardness of a welded portion between the cup member and the shaft member range from 200 Hv to 500 Hv. When the hardness is lower than 200 Hv, it is difficult to secure the strength required in terms of a product function, which is undesirable. On the other hand, when the hardness exceeds 500 Hv, there may occur cracking due to phase transformation and degradation of fatigue strength due to changes in toughness, which are undesirable. 
     The any one of the shaft member and the cup member, which comprises the welding depth checking chamfer and the excessive welding depth checking chamfer, is suited to mass-production of the outer joint member. 
     According to one embodiment of the present invention for an outer joint member, there is provided an outer joint member of a constant velocity universal joint, comprising: a cup section having track grooves formed at an inner periphery of the cup section and engageable with torque transmitting elements; and a shaft section formed at a bottom portion of the cup section, the outer joint member being constructed by forming the cup section and the shaft section through use of separate members, and by welding a cup member forming the cup section and a shaft member forming the shaft section, the cup member and the shaft member being formed of medium carbon steel, the cup member having a cylindrical portion and a bottom portion integrally formed by forging, and a joining end surface formed on an outer surface of the bottom portion by machining, the shaft member having a joining end surface to be joined to the bottom portion of the cup member, which is formed by machining, the joining end surface of the cup member and the joining end surface of the shaft member being welded in abutment against each other, the outer joint member comprising a welded portion between the cup member and the shaft member, which comprises a bead formed by a beam radiated from an outer side of the cup member in a radial direction of the cup member, the joining end surface of the cup member having an outer diameter set to an equal dimension for each joint size, the outer joint member comprising an excessive welding depth checking chamfer formed on a radially inner side of any one of the joining end surface of the cup member and the joining end surface of the shaft member. 
     With the above-mentioned configuration, it is possible to achieve the outer joint member capable of increasing the strength of the welded portion and the quality, reducing the welding cost, enhancing the accuracy and the operability in the inspection on the welded portion, achieving the cost reduction through the enhancement of productivity of the cup member and the shaft member and through the standardization of a product type of the cup member, and reducing the burden of production management. In particular, it is possible to achieve the outer joint member capable of preventing the excess of the welding depth, further reducing the welding cost, and achieving satisfactory operability in the inspection. 
     Effects of the Invention 
     According to the method of manufacturing an outer joint member of a constant velocity universal joint and the outer joint member of the present invention, it is possible to achieve the method of manufacturing an outer joint member, the outer joint member, the shaft member, and the cup member, which are capable of increasing the strength of the welded portion and the quality, reducing the welding cost, enhancing the accuracy and the operability in the inspection on the welded portion, achieving the cost reduction through the enhancement of productivity of the cup member and the shaft member and through the standardization of a product type of the cup member, and reducing the burden of production management. When the joining end surface comprises, in addition to the welding depth checking chamfer, the excessive welding depth checking chamfer formed on the radially inner side with respect to the welding depth checking chamfer, the determination as to whether or not the welding depth is kept within a satisfactory range of being not insufficient or not excessive can be made. Thus, it is possible to achieve the method of manufacturing an outer joint member and the outer joint member, which are capable of preventing excess of the welding depth, further reducing the welding cost, and achieving satisfactory operability in the inspection. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view for illustrating the entire structure of a drive shaft to which an outer joint member according to a first embodiment of the present invention is applied. 
         FIG. 2 a    is an enlarged partial vertical sectional view for illustrating the outer joint member of  FIG. 1 . 
         FIG. 2 b    is an enlarged view for illustrating a welded portion of  FIG. 2   a.    
         FIG. 2 c    is an enlarged view for illustrating a shape before welding in  FIG. 2   b.    
         FIG. 3  is a diagram for illustrating an overview of manufacturing steps for the outer joint member of  FIG. 1 . 
         FIG. 4 a    is a vertical sectional view for illustrating a cup member before welding and after ironing. 
         FIG. 4 b    is a vertical sectional view for illustrating the cup member before welding and after turning. 
         FIG. 5 a    is a front view for illustrating a shaft member before welding, that is, a billet obtained by cutting a bar material. 
         FIG. 5 b    is a partial vertical sectional view for illustrating the shaft member before welding and after forging. 
         FIG. 5 c    is a partial vertical sectional view for illustrating the shaft member before welding and after turning and spline processing. 
         FIG. 6  is a view for illustrating an overview of a welding step. 
         FIG. 7  is a view for illustrating an overview of the welding step. 
         FIG. 8  is a front view for illustrating an overview of an ultrasonic flaw detection-inspection apparatus. 
         FIG. 9  is a plan view for illustrating the overview of the ultrasonic flaw detection-inspection apparatus. 
         FIG. 10  is a front view for illustrating the overview of the ultrasonic flaw detection-inspection apparatus. 
         FIG. 11  is a plan view for illustrating the overview of the ultrasonic flaw detection-inspection apparatus. 
         FIG. 12 a    is a partial enlarged view as viewed from the arrow F-F of  FIG. 10 , for illustrating a case of a non-defective welded product. 
         FIG. 12 b    is a partial enlarged view as viewed from the arrow F-F of  FIG. 10 , for illustrating a defective welded product. 
         FIG. 13  is a view for illustrating findings in the course of development. 
         FIG. 14  is a front view for illustrating a shaft member assigned with a different product number. 
         FIG. 15  is a partial vertical sectional view for illustrating an outer joint member that is manufactured using the shaft member illustrated in  FIG. 14 . 
         FIG. 16  is a diagram for illustrating an example of standardization of a product type of the cup member. 
         FIG. 17  is a vertical sectional view for illustrating a modification of the outer joint member according to the first embodiment, specifically, illustrating the entirety of a cup member before welding. 
         FIG. 18  is an enlarged view for illustrating a state of ultrasonic flaw-detection inspection after welding of the cup member of  FIG. 17 . 
         FIG. 19 a    is a partial vertical sectional view for illustrating another modification of the outer joint member according to the first embodiment. 
         FIG. 19 b    is an enlarged view for illustrating a welded portion of  FIG. 19   a.    
         FIG. 19 c    is an enlarged view for illustrating a shape before welding in  FIG. 19   b.    
         FIG. 20  is a vertical sectional view for illustrating the entirety of a cup member of  FIG. 19   c.    
         FIG. 21  is a diagram for illustrating an overview of a method of manufacturing an outer joint member according to a second embodiment of the present invention. 
         FIG. 22  is a diagram for illustrating an overview of a method of manufacturing an outer joint member according to a third embodiment of the present invention. 
         FIG. 23  is a partial vertical sectional view for illustrating a constant velocity universal joint using an outer joint member according to the second embodiment of the present invention. 
         FIG. 24 a    is a partial vertical sectional view for illustrating the outer joint member of the  FIG. 23 . 
         FIG. 24 b    is an enlarged view for illustrating a welded portion of  FIG. 24   a.    
         FIG. 24 c    is an enlarged view for illustrating a shape before welding in  FIG. 24   b.    
         FIG. 25 a    is a partial vertical sectional view for illustrating an outer joint member according to a third embodiment of the present invention. 
         FIG. 25 b    is an enlarged view for illustrating a welded portion of  FIG. 25   a.    
         FIG. 25 c    is an enlarged view for illustrating a shape before welding in  FIG. 25   b.    
         FIG. 26 a    is an enlarged view for illustrating a state of ultrasonic flaw-detection inspection on a welded portion (non-defective welded product) illustrated in  FIG. 25 b   , specifically, illustrating a state of inspection as to whether or not the welding depth is insufficient. 
         FIG. 26 b    is an enlarged view for illustrating a state of ultrasonic flaw-detection inspection on the welded portion (non-defective welded product) illustrated in  FIG. 25 b   , specifically, illustrating a state of inspection as to whether or not the welding depth is excessive. 
         FIG. 27 a    is an enlarged view for illustrating states of ultrasonic flaw-detection inspection in cases of a defective welded product and an excessively welded product, specifically, illustrating a state of inspection on the defective welded product having an insufficient welding depth. 
         FIG. 27 b    is an enlarged view for illustrating states of ultrasonic flaw-detection inspection in the cases of the defective welded product and the excessively welded product, specifically, illustrating a state of inspection on the excessively welded product. 
         FIG. 28  is a view for illustrating a welding depth checking chamfer and an excessive welding depth checking chamfer. 
         FIG. 29  is a vertical sectional view for illustrating an outer joint member according to a related art. 
         FIG. 30  is a vertical sectional view for illustrating the outer joint member according to the related art. 
         FIG. 31  is a vertical sectional view for illustrating an outer joint member according to a related art. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Now, description is made of embodiments of the present invention with reference to the drawings. 
       FIG. 3  to  FIG. 16  are views for illustrating a method of manufacturing an outer joint member of a constant velocity universal joint according to a first embodiment of the present invention, and  FIG. 1  and  FIG. 2  are views for illustrating an outer joint member according to the first embodiment of the present invention. First, the outer joint member according to the first embodiment is described with reference to  FIG. 1  and  FIG. 2 , and subsequently, the method of manufacturing an outer joint member according to the first embodiment is described with reference to  FIG. 3  to  FIG. 16 . 
       FIG. 1  is a view for illustrating the entire structure of a drive shaft  1  using an outer joint member  11  according to the first embodiment. The drive shaft  1  mainly comprises a plunging type constant velocity universal joint  10  arranged on a differential side (right side of  FIG. 1 : hereinafter also referred to as “inboard side”), a fixed type constant velocity universal joint  20  arranged on a driving wheel side (left side of  FIG. 1 : hereinafter also referred to as “outboard side”), and an intermediate shaft  2  configured to couple both the constant velocity universal joints  10  and  20  to allow torque transmission therebetween. 
     The plunging type constant velocity universal joint  10  illustrated in  FIG. 1  is a so-called double-offset type constant velocity universal joint (DOJ). The constant velocity universal joint  10  comprises the outer joint member  11  comprising a cup section  12  and a long shaft section (hereinafter referred to also as “long stem section”)  13  that extends from a bottom portion of the cup section  12  in an axial direction, an inner joint member  16  housed along an inner periphery of the cup section  12  of the outer joint member  11 , balls  41  serving as torque transmitting elements that are arranged between track grooves  30  and  40  of the outer joint member  11  and the inner joint member  16 , and a cage  44  having a spherical outer peripheral surface  45  and a spherical inner peripheral surface  46  that are fitted to a cylindrical inner peripheral surface  42  of the outer joint member  11  and a spherical outer peripheral surface  43  of the inner joint member  16 , respectively, and being configured to retain the balls  41 . A curvature center O 1  of the spherical outer peripheral surface  45  and a curvature center O 2  of the spherical inner peripheral surface  46  of the cage  44  are offset equidistantly from a joint center O toward opposite sides in the axial direction. 
     An inner ring of a support bearing  6  is fixed to an outer peripheral surface of the long stem section  13 , and an outer ring of the support bearing  6  is fixed to a transmission case with a bracket (not shown). The outer joint member  11  is supported by the support bearing  6  in a freely rotatable manner, and when the support bearing  6  as described above is provided, vibration of the outer joint member  11  during driving or the like is prevented as much as possible. 
     The fixed type constant velocity universal joint  20  illustrated in  FIG. 1  is a so-called Rzeppa type constant velocity universal joint, and comprises an outer joint member  21  comprising a bottomed cylindrical cup section  21   a  and a shaft section  21   b  that extends from a bottom portion of the cup section  21   a  in the axial direction, an inner joint member  22  housed along an inner periphery of the cup section  21   a  of the outer joint member  21 , balls  23  serving as torque transmitting elements that are arranged between the cup section  21   a  of the outer joint member  21  and the inner joint member  22 , and a cage  24 , which is arranged between an inner peripheral surface of the cup section  21   a  of the outer joint member  21  and an outer peripheral surface of the inner joint member  22 , and is configured to retain the balls  23 . Note that, as the fixed type constant velocity universal joint  20 , an undercut-free type constant velocity universal joint may sometimes be used. 
     The intermediate shaft  2  comprises splines  3  for torque transmission (including serrations; the same applies hereinafter) at outer peripheries both end portions thereof. The spline  3  on the inboard side is spline-fitted to a hole portion of the inner joint member  16  of the plunging type constant velocity universal joint  10 . Thus, the intermediate shaft  2  and the inner joint member  16  of the plunging type constant velocity universal joint  10  are coupled to each other to allow torque transmission therebetween. Further, the spline  3  on the outboard side is spline-fitted to a hole portion of the inner joint member  22  of the fixed type constant velocity universal joint  20 . Thus, the intermediate shaft  2  and the inner joint member  22  of the fixed type constant velocity universal joint  20  are coupled to each other to allow torque transmission therebetween. Although the solid intermediate shaft  2  is illustrated, a hollow intermediate shaft may be used instead. 
     Grease is sealed inside both the constant velocity universal joints  10  and  20  as a lubricant. To prevent leakage of the grease to an outside of the joint or entry of a foreign matter from the outside of the joint, bellows boots  4  and  5  are respectively mounted to a portion between the outer joint member  11  of the plunging type constant velocity universal joint  10  and the intermediate shaft  2  and a portion between the outer joint member  21  of the fixed type constant velocity universal joint  20  and the intermediate shaft  2 . 
     The outer joint member according to the first embodiment is described with reference to  FIG. 2 .  FIG. 2  are enlarged views for illustrating the outer joint member  11  according to this embodiment.  FIG. 2 a    is a partial vertical sectional view.  FIG. 2 b    is an enlarged view for illustrating a circle “A” of  FIG. 2 a   .  FIG. 2 c    is a view for illustrating a shape before welding. The outer joint member  11  comprises the bottomed cylindrical cup section  12  that is opened at one end and has the cylindrical inner peripheral surface  42  and the plurality of track grooves  30 , on which the balls  41  (see  FIG. 1 ) are caused to roll, formed equiangularly on the inner peripheral surface, and the long stem section  13  that extends from the bottom portion of the cup section  12  in the axial direction and comprises a spline Sp serving as a torque transmitting coupling portion formed at an outer periphery on an end portion thereof on an opposite side to the cup section  12 . In this embodiment, the outer joint member  11  is formed by welding a cup member  12   a  and a shaft member  13   a  to each other. 
     The cup member  12   a  illustrated in  FIG. 2 a    to  FIG. 2 c    is an integrally-formed product being made of medium carbon steel, such as S 53 C, containing carbon of from 0.40 wt % to 0.60 wt %, and having a cylindrical portion  12   a   1  and a bottom portion  12   a   2 . The cylindrical portion  12   a   1  has the track grooves  30  and the cylindrical inner peripheral surface  42  formed at an inner periphery thereof. A projecting portion  12   a   3  is formed at the bottom portion  12   a   2  of the cup member  12   a . A boot mounting groove  32  is formed at an outer periphery of the cup member  12   a  on the opening side thereof, whereas a snap ring groove  33  is formed at an inner periphery of the cup member  12   a  on the opening side thereof. A bearing mounting surface  14  and a snap ring groove  15  are formed at an outer periphery of the shaft member  13   a  on the cup member  12   a  side, whereas the spline Sp is formed at an end portion of the shaft member  13   a  on an opposite side. 
     The shaft member  13   a  is made of medium carbon steel, such as S 40 C, containing carbon of from 0.30 wt % to 0.55 wt %. A joining end surface  50  formed at the projecting portion  12   a   3  of the bottom portion  12   a   2  of the cup member  12   a  and a joining end surface  51  formed at an end portion of the shaft member  13   a  on the cup member  12   a  side are brought into abutment against each other, and are welded to each other by electron beam welding performed from an outer side of the cup member  12   a  in a radial direction. As illustrated in  FIG. 2 a    and  FIG. 2 b   , a welded portion  49  is formed of a bead, which is formed by a beam radiated from a radially outer side of the cup member  12   a . Although detailed description is made later, outer diameters B of the joining end surface  50  and the joining end surface  51  (see  FIG. 4 b    and  FIG. 5 c   ) are set to equal dimensions for each joint size. However, the outer diameter B of the joining end surface  50  of the cup member  12   a  and the outer diameter B of the joining end surface  51  of the shaft member  13   a  need not be set to equal dimensions. In consideration of, for example, a state of the weld bead, a dimensional difference may be given as appropriate in such a manner that the outer diameter B of the joining end surface  51  is set slightly smaller than the outer diameter B of the joining end surface  50 . The description “the outer diameters B of the joining end surface  50  and the joining end surface  51  are set to equal dimensions for each joint size” herein refers to a concept encompassing a case where the dimensional difference is given as appropriate between the outer diameter B of the joining end surface  50  and the outer diameter B of the joining end surface  51 . 
     The welded portion  49  is formed on the joining end surface  51  located on the cup member  12   a  side with respect to the bearing mounting surface  14  of the shaft member  13   a , and hence the bearing mounting surface  14  and the like can be processed in advance so that post-processing after welding can be omitted. Further, due to the electron beam welding, burrs are not generated at the welded portion. Thus, post-processing for the welded portion can also be omitted, which can reduce manufacturing cost. Still further, total inspection on the welded portion through ultrasonic flaw detection can be performed. Note that, features of this embodiment reside in an ultrasonic flaw detection-inspection method and a shape of the welded portion, which are capable of enhancing accuracy and operability in inspection on the welded portion in order to practically achieve the novel manufacturing concept for the outer joint member of the constant velocity universal joint being a mass-produced product. Details thereof are described later. 
     As illustrated in  FIG. 2 c   , a welding depth checking chamfer  51   a  is formed on a radially inner side of the joining end surface  51  of the shaft member  13   a . An inner diameter D of the joining end surface  50  of the cup member  12   a  and an inner diameter E of the joining end surface  51  of the shaft member  13   a  (inner diameter of the welding depth checking chamfer  51   a ) are set to equal dimensions. In such a state, the cup member  12   a  and the shaft member  13   a  are welded to each other. In this embodiment, the welding depth checking chamfer  51   a  is formed into the same shape for each joint size. 
     Next, the manufacturing method according to the first embodiment of the present invention is described with reference to  FIG. 3  to  FIG. 16 . Before description of details of the features of the manufacturing method of this embodiment, that is, an ultrasonic flaw detection-inspection step for the welded portion, an overview of manufacturing steps (processing steps) is described.  FIG. 3  is an illustration of the overview of the manufacturing steps for the outer joint member. In this embodiment, as illustrated in  FIG. 3 , the cup member  12   a  is manufactured through manufacturing steps comprising a bar material cutting step S 1   c , a forging step S 2   c , an ironing step S 3   c , and a turning step S 4   c . On the other hand, the shaft member  13   a  is manufactured through manufacturing steps comprising a bar material cutting step S 1   s , a turning step S 2   s , and a spline processing step S 3   s . Intermediate components of the cup member  12   a  and the shaft member  13   a  thus manufactured are each assigned with a product number for management. 
     After that, the cup member  12   a  and the shaft member  13   a  are subjected to a welding step S 6 , an ultrasonic flaw detection-inspection step S 6 K, a heat treatment step S 7 , and a grinding step S 8  so that the outer joint member  11  is completed. A machining step described in Claims refers to the turning step S 4   c  and the turning step S 2   s  among the above-mentioned manufacturing steps, and to a grinding step S 5   s  described later (see  FIG. 22 ). 
     An overview of each step is described. Each step is described as a typical example, and appropriate modification and addition may be made to each step as needed. First, the manufacturing steps for the cup member  12   a  are described. 
     [Bar Material Cutting Step S 1   c ] 
     A bar material is cut into a predetermined length in accordance with a forging weight, thereby producing a billet. 
     [Forging Step S 2   c ] 
     The billet is subjected to forging so as to integrally form the cylindrical portion, the bottom portion, and the projecting portion as a preform of the cup member  12   a.    
     [Ironing Step S 3   c ] 
     Ironing is performed on the track grooves  30  and the cylindrical inner peripheral surface  42  of the preform, thereby finishing the inner periphery of the cylindrical portion of the cup member  12   a.    
     [Turning Step S 4   c ] 
     In the preform after ironing, the outer peripheral surface, the boot mounting groove  32 , the snap ring groove  33 , the joining end surface  50 , and the like are formed by turning. In this embodiment, after the turning step S 4   c , the cup member  12   a  in the form of an intermediate component is assigned with a product number for management. 
     Next, the manufacturing steps for the shaft member  13   a  are described. 
     [Bar Material Cutting Step S 1   s ] 
     A bar material is cut into a predetermined length in accordance with the total length of the shaft section, thereby producing a billet. After that, the billet may be forged into a rough shape by upset forging depending on the shape of the shaft member  13   a.    
     [Turning Step S 2   s ] 
     The outer peripheral surface of the billet (bearing mounting surface  14 , snap ring groove  15 , minor diameter of the spline, end surface, and the like) and the joining end surface  51 , the welding depth checking chamfer  51   a , and the like of the billet at the end portion on the cup member  12   a  side are formed by turning. 
     [Spline Processing Step S 3   s ] 
     The spline is formed by rolling in the shaft member after turning. Note that, the method of processing the spline is not limited to the rolling, but press working or the like may be adopted instead as appropriate. In this embodiment, after the spline processing, the shaft member  13   a  in the form of an intermediate component is assigned with a product number for management. 
     Next, the manufacturing steps in the process of completing the outer joint member  11  from the cup member  12   a  and the shaft member  13   a  are described. 
     [Welding Step S 6 ] 
     The joining end surface  50  of the cup member  12   a  and the joining end surface  51  of the shaft member  13   a  are brought into abutment against and welded to each other. 
     [Ultrasonic Flaw Detection-Inspection Step S 6   k ] 
     The welded portion  49  between the cup member  12   a  and the shaft member  13   a  is inspected by the ultrasonic flaw-detection method. 
     [Heat Treatment Step S 7 ] 
     Induction quenching and tempering are performed as heat treatment on at least the track grooves  30  and the cylindrical inner peripheral surface  42  of the cup section  12  after welding and a necessary range of the outer periphery of the shaft section  13  after welding. Heat treatment is not performed on the welded portion. A hardened layer having a hardness of approximately from 58 HRC to 62 HRC is formed on each of the track grooves  30  and the cylindrical inner peripheral surface  42  of the cup section  12 . Further, a hardened layer having a hardness of approximately from 50 HRC to 62 HRC is formed in a predetermined range of the outer periphery of the shaft section  13 . 
     [Grinding Step S 8 ] 
     After the heat treatment, the bearing mounting surface  14  of the shaft section  13  and the like are finished by grinding. Thus, the outer joint member  11  is completed. 
     In the manufacturing steps of this embodiment, the heat treatment step is provided after the welding step, and hence the manufacturing steps are suited to a cup member and a shaft member having such shapes and specifications that the hardness of the heat-treated portion may be affected by temperature rise at the periphery due to heat generated during the welding. 
     Next, main constituent features of the manufacturing method of this embodiment are described in detail.  FIG. 4 a    is a vertical sectional view for illustrating a state after ironing of the cup member  12   a .  FIG. 4 b    is a vertical sectional view for illustrating a state after turning. In a preform  12   a ′ for the cup member  12   a , a cylindrical portion  12   a   1 ′, a bottom portion  12   a   2 ′, and a projecting portion  12   a   3 ′ are integrally formed in the forging step S 2   c . After that, the track grooves  30  and the cylindrical inner peripheral surface  42  are formed by ironing in the ironing step S 3   c  so that the inner periphery of the cylindrical portion  12   a   1 ′ is finished as illustrated in  FIG. 4   a.    
     After that, in the turning step S 4   c , the outer peripheral surface, the boot mounting groove  32 , the snap ring groove  33 , and the like of the cup member  12   a  as well as the joining end surface  50  of the projecting portion  12   a   3  of the bottom portion  12   a   2  and the joining end surface  50  having the outer diameter B and the inner diameter D are formed by turning as illustrated in  FIG. 4   b.    
       FIG. 5  are illustrations of states of the shaft member  13   a  in the respective processing steps.  FIG. 5 a    is a front view for illustrating a billet  13   a ″ obtained by cutting a bar material.  FIG. 5 b    is a partial vertical sectional view for illustrating a preform  13   a ′ obtained by forging the billet  13   a ″ into a rough shape by upset forging.  FIG. 5 c    is a partial vertical sectional view for illustrating the shaft member  13   a  after turning and spline processing. 
     The billet  13   a ″ illustrated in  FIG. 5 a    is produced in the bar material cutting step S 1   s . The preform  13   a ′ is produced by increasing, if necessary, the shaft diameter of the billet  13   a ″ in a predetermined range and forming a recessed portion  52  at a joining-side end portion (end portion on the cup member  12   a  side) by upset forging as illustrated in  FIG. 5   b.    
     After that, in the turning step S 2   s , the outer diameter portion of the shaft member  13   a , the bearing mounting surface  14 , the snap ring groove  15 , an inner diameter portion  53  (inner diameter E) of the recessed portion  52 , the joining end surface  51  the welding depth checking chamfer  51   a , and the joining end surface  50  having the outer diameter B of the joining-side end portion are formed by turning as illustrated in  FIG. 5 c   . In the spline processing step S 3   s , the spline Sp is processed at the end portion on the opposite side to the recessed portion  52  by rolling or press forming. 
     The outer diameter B of the joining end surface  50  located at the projecting portion  12   a   3  of the bottom portion  12   a   2  of the cup member  12   a  illustrated in  FIG. 4 b    is set to an equal dimension for one joint size. Further, in the shaft member  13   a  illustrated in  FIG. 5 c   , which is used as a long stem shaft, the outer diameter B of the joining end surface  51  located at the end portion on the cup member  12   a  side is set to an equal dimension to the outer diameter B of the joining end surface  50  of the cup member  12   a  irrespective of the shaft diameter and the outer peripheral shape. Still further, the joining end surface  51  of the shaft member  13   a  is located at the position on the cup member  12   a  side with respect to the bearing mounting surface  14 . The outer diameter B and the welding depth checking chamfer  51   a  of the joining end surface  51  are set to equal dimensions for each joint size. Through the setting of dimensions as described above, the outer joint member  11  compatible with various vehicle types can be manufactured in such a manner that, while the cup member  12   a  is prepared for common use, only the shaft member  13   a  is manufactured to have a variety of shaft diameters, lengths, and outer peripheral shapes depending on vehicle types, and both the members  12   a  and  13   a  are welded to each other. Details of the preparation of the cup member  12   a  for common use and the welding depth checking chamfer  51   a  are described later. 
     Next, a method of welding the cup member  12   a  and the shaft member  13   a  is described with reference to  FIG. 6  and  FIG. 7 .  FIG. 6  and  FIG. 7  are views for illustrating an overview of a welding apparatus.  FIG. 6  is an illustration of a state before welding.  FIG. 7  is an illustration of a state during welding. As illustrated in  FIG. 6 , a welding apparatus  100  mainly comprises an electron gun  101 , a rotation device  102 , a chuck  103 , a center hole guide  104 , a tailstock  105 , workpiece supports  106 , a center hole guide  107 , a case  108 , and a vacuum pump  109 . 
     The cup member  12   a  and the shaft member  13   a  being workpieces are placed on the workpiece supports  106  arranged inside the welding apparatus  100 . The chuck  103  and the center hole guide  107  arranged at one end of the welding apparatus  100  are coupled to the rotation device  102 . The chuck  103  grips the cup member  12   a  to rotate the cup member  12   a  under a state in which the center hole guide  107  has centered the cup member  12   a . The center hole guide  104  is integrally mounted to the tailstock  105  arranged at the other end of the welding apparatus  100 . Both the center hole guide  104  and the tailstock  105  are configured to reciprocate in the axial direction (lateral direction of  FIG. 6  and  FIG. 7 ). 
     A center hole of the shaft member  13   a  is set on the center hole guide  104  so that the shaft member  13   a  is centered. The vacuum pump  109  is connected to the case  108  of the welding apparatus  100 . A “sealed space” herein refers to a space  111  defined by the case  108 . In this embodiment, the cup member  12   a  and the shaft member  13   a  are entirely received in the sealed space  111 . The electron gun  101  is arranged at a position corresponding to the joining end surfaces  50  and  51  of the cup member  12   a  and the shaft member  13   a . The electron gun  101  is configured to approach the workpieces up to a predetermined position. 
     Next, the operation of the welding apparatus  100  constructed as described above and the welding method are described. The cup member  12   a  and the shaft member  13   a  being workpieces are stocked at a place different from the place of the welding apparatus  100 . The respective workpieces are taken out by, for example, a robot, are conveyed into the case  108  of the welding apparatus  100  opened to the air as illustrated in  FIG. 6 , and are set at predetermined positions on the workpiece supports  106 . At this time, the center hole guide  104  and the tailstock  105  are retreated to the right side of  FIG. 6 , and hence a gap is formed between the joining end surfaces  50  and  51  of the cup member  12   a  and the shaft member  13   a . After that, a door (not shown) of the case  108  is closed and the vacuum pump  109  is activated to reduce the pressure in the sealed space  111  defined in the case  108 . Thus, the pressures in an inner diameter portion  50   b  of the cup member  12   a  and the recessed portion  52  and the inner diameter portion  53  of the shaft member  13   a  are reduced as well. 
     When the pressure in the sealed space  111  is reduced to a predetermined pressure, the center hole guide  104  and the tailstock  105  are advanced to the left side as illustrated in  FIG. 7  to eliminate the gap between the joining end surfaces  50  and  51  of the cup member  12   a  and the shaft member  13   a . Thus, the cup member  12   a  is centered by the center hole guide  107  and fixed by the chuck  103 , whereas the shaft member  13   a  is supported by the center hole guide  104 . After that, the workpiece supports  106  are moved away from the workpieces. At this time, the distance between the workpiece supports  106  and the workpieces may be infinitesimal, and hence illustration of this distance is omitted from  FIG. 7 . As a matter of course, the welding apparatus  100  may have such a structure that the workpiece supports  106  are retreated downward greatly. 
     Although illustration is omitted, the electron gun  101  is then caused to approach the workpieces up to a predetermined position and the workpieces are rotated to start pre-heating. As a pre-heating condition, unlike the welding condition, the temperature is set lower than the welding temperature by, for example, radiating an electron beam under a state in which the electron gun  101  is caused to approach the workpieces so as to increase the spot diameter. Through the pre-heating, the cooling rate after welding is reduced, thereby being capable of preventing a quenching crack. When a predetermined pre-heating time has elapsed, the electron gun  101  is retreated to a predetermined position, and radiates the electron beam from the outer side of the workpieces in the radial direction to start welding. When the welding is finished, the electron gun  101  is retreated and the rotation of the workpieces is stopped. 
     Although illustration is omitted, the sealed space  111  is then opened to the air. Then, the center hole guide  104  and the tailstock  105  are retreated to the right side and the chuck  103  is opened under a state in which the workpiece supports  106  are raised to support the workpieces. After that, for example, the robot grips the workpieces, takes the workpieces out of the welding apparatus  100 , and places the workpieces into alignment on a cooling stocker. In this embodiment, the cup member  12   a  and the shaft member  13   a  are entirely received in the sealed space  111 , and hence the configuration of the sealed space  111  defined in the case  108  can be simplified. 
     Specifically, the cup member  12   a  having a carbon content of from 0.4% to 0.6% and the shaft member  13   a  having a carbon content of from 0.3% to 0.55% were used and welded to each other in the above-mentioned welding apparatus  100  under the condition that the pressure in the sealed space  111  defined in the case  108  was set to 6.7 Pa or less. In order to prevent the cup member  12   a  and the shaft member  13   a  from being cooled rapidly after the welding to suppress increase in hardness of the welded portion, the joining end surfaces  50  and  51  of the cup member  12   a  and the shaft member  13   a  were soaked by pre-heating to have a temperature of from 300° C. to 650° C., and then electron beam welding was performed. As a result, a welded portion having a projecting height from the welded surface (0.5 mm or less), which imposed no adverse effect on a product function, was obtained. Further, through the soaking by pre-heating, the hardness of the welded portion after completion of the welding was able to be kept within a range of from 200 Hv to 500 Hv, thereby being capable of attaining high welding strength and stable welding state and quality. Still further, the cup member  12   a  and the shaft member  13   a  were welded to each other under the condition that the pressure in the sealed space  111  of the welding apparatus  100  was set to an atmospheric pressure or less, thereby being capable of suppressing the change in pressure in the hollow cavity portion during the welding. As a result, the blowing of a molten material and the entry of the molten material toward the radially inner side were able to be prevented. 
     Following the above description of the overview of the manufacturing steps (processing steps) of this embodiment, the features of this embodiment, that is, the ultrasonic flaw detection-inspection step for the welded portion is described with reference to  FIG. 8  to  FIG. 13 .  FIG. 8  is a front view for illustrating an overview of an ultrasonic flaw detection-inspection apparatus as viewed from the arrow I-I of  FIG. 9 .  FIG. 9  is a plan view for illustrating the ultrasonic flaw detection-inspection apparatus. In each of the states illustrated in  FIG. 8  and  FIG. 9 , the outer joint member after welding is placed in the ultrasonic flaw detection-inspection apparatus.  FIG. 10  is a front view for illustrating a state during inspection as viewed from the arrow H-H of  FIG. 11 .  FIG. 11  is a plan view for illustrating the state during inspection. 
     As illustrated in  FIG. 8  and  FIG. 9 , an ultrasonic flaw detection-inspection apparatus  120  mainly comprises a water bath  122  mounted at the center of a base  121 , a workpiece support  123 , a workpiece holding member  124 , a rotary drive device  125  configured to rotate an intermediate product  11 ′ of the outer joint member  11  (hereinafter also referred to as “workpiece  11 ”), a pressing device  135  configured to press an axial end of the workpiece  11 ′, and a drive positioning device  136  (see  FIG. 9 ) for a probe. 
     As illustrated in  FIG. 8 , the workpiece support  123  comprises rollers  126  and  127  configured to allow the workpiece  11 ′ to be placed thereon in a freely rotatable manner. As illustrated in  FIG. 9 , the rollers  126  and  127  are arranged in pairs so that the shaft section  13  of the workpiece  11 ′ can be stably supported. The rollers  126  are located at a portion close to the welded portion, and the rollers  127  are located at a center portion of the shaft section  13 . The rollers  126  and  127  are capable of adjusting the placement position of the workpiece  11 ′ as appropriate in the axial direction (lateral direction of  FIG. 9 ) and the radial direction (vertical direction of  FIG. 9 ) in consideration of a joint size, dimensions, and weight balance of the workpiece  11 ′. 
     Further, the workpiece holding member  124  is mounted to the workpiece support  123  at a position displaced from an axial line of the workpiece  11 ′ in a horizontal direction (see  FIG. 9 ). The workpiece holding member  124  comprises a lever  128 , and a workpiece holding roller  129  is arranged at an end portion of the lever  128 . The lever  128  is pivotable in the plane, and is vertically movable. 
     The workpiece support  123  is mounted to a support  134  through intermediation of a linear-motion bearing  130  comprising rails  131  and linear guides  132 , and is movable in the axial direction (lateral direction of  FIG. 8  and  FIG. 9 ). The support  134  is mounted to the base  121 . A rod  133  is coupled to an end portion (left end portion of  FIG. 8  and  FIG. 9 ) of the workpiece support  123  so that the workpiece support  123  is driven to be positioned by an actuator (not shown) on an outside of the water bath  122 . 
     The rotary drive device  125  comprises a rotary shaft  143  having a rotary disc  144  mounted thereto, and this rotary shaft  143  is driven to rotate by a motor (not shown) on the outside of the water bath  122 . 
     As illustrated in  FIG. 8 , a mounting base  137  is arranged on an upper side of the ultrasonic flaw detection-inspection apparatus  120 . A base plate  145  for the pressing device  135  configured to press the axial end of the workpiece  11 ′ is mounted to the mounting base  137  through intermediation of a linear-motion bearing  138  comprising a rail  139  and a linear guide  140  so that the pressing device  135  is movable in the axial direction (lateral direction of  FIG. 8  and  FIG. 9 ). A rod  142  of a pneumatic cylinder  141  is coupled to an end portion of the base plate  145  for the pressing device  135  so that the pressing device  135  is driven. A free bearing  146  is mounted to a portion to be held in abutment against the axial end of the shaft section  13  of the workpiece  11 ′ so that the axial end can be pressed in a freely rotatable manner. 
     As illustrated in  FIG. 9 , the drive positioning device  136  for a probe is arranged at a position displaced from an axial line of the workpiece  11 ′ in the horizontal direction. This drive positioning device  136  comprises actuators for the X-axis direction (lateral direction of  FIG. 9 ) and the Y-axis direction (vertical direction of  FIG. 9 ) so that a probe  147  is driven to be positioned in the X-axis and Y-axis directions. An actuator  148  for the X-axis direction and an actuator  149  for the Y-axis direction are each an electric ball-screw type (electric cylinder), which is capable of performing positioning with high accuracy. Reference symbol  150  represents a rail for a linear-motion bearing. The drive positioning device  136  is arranged on the outside of the water bath  122 , and the probe  147  and a holder  151  therefor are arranged in the water bath  122 . 
     Next, the operation of the ultrasonic flaw detection-inspection apparatus  120  and the ultrasonic flaw detection-inspection step S 6   k  are described. As illustrated in  FIG. 8  and  FIG. 9 , the workpiece  11 ′ after welding is placed on the workpiece support  123  by a loading device (not shown). At this time, in order that the workpiece  11 ′ is loaded, the workpiece support  123  is located at an appropriate interval from the rotary drive device  125  in the axial direction of the workpiece  11 ′, and the workpiece holding member  124  raises and pivots the lever  128  thereof so as to be substantially parallel to the axial line of the workpiece  11 ′. Further, the pressing device  135  and the drive positioning device  136  for a probe wait at retreated positions. 
     After that, the lever  128  of the workpiece holding member  124  is pivoted so as to be substantially perpendicular to the axial line of the workpiece  11 ′, and then lowered to hold the workpiece  11 ′ from above (see  FIG. 10 ). Then, water is supplied to the water bath  122 . In the ultrasonic flaw detection-inspection apparatus  120  according to this embodiment, flaw detection is performed under water, and hence ultrasonic waves are satisfactorily propagated. Thus, inspection can be performed with high accuracy. 
     Next, as illustrated in  FIG. 10  and  FIG. 11 , the pneumatic cylinder  141  is driven to cause the pressing device  135  to be advanced and pressed against the axial end of the workpiece  11 ′, thereby pressing the opening rim of the cup section  12  of the workpiece  11 ′ against the rotary disc  144  of the rotary drive device  125 . In conjunction with the advance of the pressing device  135 , the workpiece support  123  is also moved toward the rotary drive device  125 . Thus, the workpiece  11 ′ is positioned in the radial direction and the axial direction. In this state, the motor (not shown) of the rotary drive device  125  is rotated, thereby rotating the workpiece  11 ′. 
     As illustrated in  FIG. 11 , the drive positioning device  136  is moved in the X-axis direction, and then moved in the Y-axis direction, thereby positioning the probe  147  at a flaw detection position (in  FIG. 10 , the probe  147  in this state is indicated by the broken line). Then, the flaw-detection inspection is performed. After the flaw-detection inspection, the water is drained, and the workpiece  11 ′ is unloaded from the ultrasonic flaw detection-inspection apparatus  120  by the loading device (not shown). As described above, the inspection is sequentially repeated on the workpieces  11 ′. 
     In the ultrasonic flaw detection-inspection apparatus  120  according to this embodiment, in order to reduce the cycle time of the inspection, time-consuming supply and drainage of water are performed simultaneously with the operations of the devices and the members, or at other timings in accordance therewith. Further, some of the operations of the devices and the members may be performed simultaneously with each other or in different orders as appropriate. 
     Details of the ultrasonic flaw-detection inspection are described with reference to  FIG. 12 a   ,  FIG. 12 b   , and  FIG. 13 . All of  FIG. 12 a   ,  FIG. 12 b   , and  FIG. 13  are views as viewed from the arrow F-F of  FIG. 10 .  FIG. 12 a    is an illustration of a non-defective welded product, and  FIG. 12 b    is an illustration of a defective welded product.  FIG. 13  is an illustration of findings in the course of development. 
     The probe  147  is positioned at the flaw detection position away from the welded portion  49  by a predetermined distance. The flaw detection position is preset for each joint size. A target welding depth is denoted by the reference symbol Wa, and a minimum acceptable welding depth is denoted by the reference symbol Wmin. Workpieces having a depth equal to or larger than the minimum acceptable welding depth Wmin are determined as non-defective welded products, and workpieces having a depth smaller than the minimum acceptable welding depth Wmin are determined as defective welded products. When a transmission pulse G is transmitted at an incident angle θ 1  from the probe  147 , the transmission pulse G is refracted by the surface of the shaft section  13 , and advances at a refraction angle θ 2 . The ultrasonic flaw-detection inspection of this embodiment is performed under the condition that the incident angle θ 1  is approximately 20°, and the refraction angle θ 2  is approximately 45°. During the flaw-detection inspection, the workpiece  11 ′ is kept rotated by the rotary drive device  125  (see  FIG. 10 ). 
     The probe  147  positioned at the flaw detection position away from the welded portion  49  by the predetermined distance collects data of the entire periphery of the workpiece  11 ′. Specifically, in consideration of tolerance for displacement of the welding position, at the above-mentioned flaw detection position, first, data of a single rotation (360°) of the workpiece  11 ′ is collected. Then, the probe  147  is sequentially shifted in the axial direction at a minute pitch (for example, 0.5 mm) to collect data of a plurality of rotations (for example, five rotations). Based on those pieces of data, non-defective/defective determination is made. A threshold of a reflected echo to be used in the non-defective/defective determination is determined based on a welding pattern corresponding to the minimum acceptable welding depth Wmin. 
     Next, advantages to be obtained by the shape of the welded portion of this embodiment are described. As described above, the welding depth checking chamfer  51   a  is formed on the radially inner side of the joining end surface  51  of the shaft member  13   a  (see  FIG. 12 b   ). The inner diameter D of the joining end surface  50  of the cup member  12   a  and the inner diameter E of the joining end surface  51  of the shaft member  13   a  are set to equal dimensions. In such a state, the cup member  12   a  and the shaft member  13   a  are welded to each other. The welding depth checking chamfer  51   a  is formed into the same shape for each joint size. 
     Details of the advantages to be obtained by the shape of the above-mentioned welded portion are described by way of an example of cases of the non-defective welded product and the defective welded product. In the case of the non-defective welded product, when the transmission pulse G from the probe  147  is input as illustrated in  FIG. 12 a   , a reflected echo of the transmission pulse G scattered by a boundary surface of a back bead  49   a  at the depth equal to or larger than the minimum acceptable welding depth Wmin is generated. A part of the reflected echo is transmitted as a reflected echo R 1  in the direction of the transmission pulse G, and is received by the probe  147 . In this embodiment, the inventors of the present invention have focused on the fact that the part of the reflected echo which is generated by the transmission pulse G scattered by the boundary surface of the back bead  49   a  is transmitted as the reflected echo R 1  in the direction of the transmission pulse G, and the reflected echo R 1  is relatively weak. In the case of the non-defective welded product, the intensity of the reflected echo R 1  is equal to or less than the threshold of the non-defective/defective determination. Thus, determination that the welded product is non-defective is made. 
     Meanwhile, in the case of the defective welded product, as illustrated in  FIG. 12 b   , a distal end of the bead  49   a  does not reach the minimum acceptable welding depth Wmin, and hence the welding depth checking chamfer  51   a  remains. In this state, when the transmission pulse G from the probe  147  is input, the transmission pulse G is reflected by the welding depth checking chamfer  51   a . The welding depth checking chamfer  51   a  is formed in a direction perpendicular to the transmission pulse G, and hence a reflected echo R 2  that is not affected by scattering of the transmission pulse G and remains strong is received by the probe  147 . As a result, the intensity of the reflected echo R 2  is more than the threshold of the reflected echo for the non-defective/defective determination, and hence determination that the welded product is defective is made. 
     As for the shape of the welded portion of this embodiment, the inventors of the present invention have focused on the fact that, as described above, in the case of the non-defective welded product, the part of the reflected echo which is generated by the transmission pulse G scattered by the back bead  49   a  is received by the probe  147 , and in the case of the defective welded product, the reflected echo is received by the probe  147  without being affected by the scattering of the transmission pulse G due to the welding depth checking chamfer  51   a . Thus, the features of the present invention resides in that the determination as to whether the welded product is non-defective or defective is made through discrimination between the intensities of the reflected echoes. 
     The findings in the course of the development to arrive at the shape of the welded portion of this embodiment are illustrated in  FIG. 13 .  FIG. 13  is an illustration of a defective welded product that does not comprise the welding depth checking chamfer on the radially inner side of the joining end surface  51  of the shaft member  13   a  and has a welding depth smaller than the minimum acceptable welding depth Wmin. When the transmission pulse G from the probe  147  is input, a reflected echo which is generated by the transmission pulse G scattered by the joining end surface  51  and a normal chamfered portion is generated. A part of the reflected echo is transmitted as a reflected echo R 3  in the direction of the transmission pulse G, and is received by the probe  147 . Thus, also in the case of the defective welded product, the reflected echo is scattered. For this reason, the intensity of the above-mentioned reflected echo R 3  is equal to or less than the threshold of the above-mentioned non-defective/defective determination. As a result, it was proved that the determination as to whether the welded product was non-defective or defective was difficult. Based on those findings, the inventors of the present invention arrived at the shape of the welded portion of this embodiment. 
     Dimensions of the welding depth checking chamfer  51   a  are set to such dimensions that the welding depth checking chamfer  51   a  is eliminated by a width of the back bead  49   a  in the axial direction at the minimum acceptable welding depth Wmin as illustrated in  FIG. 12 a   . Thus, the intensities of the reflected echoes can be discriminated from each other, and hence the determination as to whether the welded product is non-defective or defective can be made with high accuracy. 
     As described above, the ultrasonic flaw detection-inspection apparatus  120  according to this embodiment mainly comprises the water bath  122  mounted at the center of the base  121 . In the water bath  122 , the workpiece support  123 , the workpiece holding member  124 , the rotary disc  144  of the rotary drive device  125  configured to rotate the workpiece  11 ′, the free bearing  146  of the pressing device  135  configured to press the axial end of the workpiece  11 ′, and the probe  147  mounted to the drive positioning device  136  are arranged. With this configuration, the operation of loading the workpiece  11 ′, the supply and drainage of water, the flaw-detection inspection, and the operation of unloading the workpiece  11 ′ can be performed in conjunction with each other, and the ultrasonic flaw-detection inspection can be automated. Thus, accuracy, operability, and efficiency in the inspection can be enhanced, which is suited to the inspection on the welded portion of the outer joint member of the constant velocity universal joint being a mass-produced product. 
     Further, the outer diameter B of the joining end surface  50  of the cup member  12   a  of this embodiment is set to an equal dimension for each joint size. Also with this configuration, in the ultrasonic flaw-detection inspection, setup operations with respect to the outer joint members  11  having the different product numbers are simplified. Thus, the efficiency in the inspection can be further enhanced. 
     Still further, flaw detection is performed under water, and hence ultrasonic waves are satisfactorily propagated. Thus, inspection can be performed with much higher accuracy. In addition, through employment of the shape of the welded portion, in which the welding depth checking chamfer  51   a  is formed on the radially inner side of the joining end surface  51 , the intensities of the reflected echoes can be discriminated from each other. Thus, the determination as to whether the welded product is non-defective or defective can be made with high accuracy. 
     To summarize the manufacturing concept, standardization of a product type of the cup member is additionally described while exemplifying a shaft member having a product number different from that of the above-mentioned shaft member  13   a  of the long stem type illustrated in  FIG. 5 . A shaft member  13   b  illustrated in  FIG. 14  and  FIG. 15  is used as a general stem type on the inboard side. The shaft member  13   b  has the joining end surface  51  to be brought into abutment against the joining end surface  50  (see  FIG. 4 b   ) of the bottom portion  12   a   2  (projecting portion  12   a   3 ) of the cup member  12   a . The outer diameter B and the inner diameter E of the joining end surface  51  are set to the equal dimensions to the outer diameter B and the inner diameter E of the joining end surface  51  of the shaft member  13   a  of the long stem type illustrated in  FIG. 5 . Also in this case, the welding depth checking chamfer  51   a  is formed on the radially inner side of the joining end surface  51  of the shaft member  13   b . In such a state, the cup member  12   a  and the shaft member  13   b  are welded to each other. 
     The shaft member  13   b  is used as the general stem type on the inboard side. Accordingly, the shaft member  13   b  comprises a shaft section with a small length, and a sliding bearing surface  18  formed on an axial center portion thereof, and a plurality of oil grooves  19  are formed in the sliding bearing surface  18 . The spline Sp and a snap ring groove  48  are formed in an end portion of the shaft member  13   b  on the side opposite to the cup member  12   a  side. As described above, even when there are differences in types, such as the general length stem type and the long stem type, and shaft diameters and outer peripheral shapes vary in each vehicle type, the diameter B of the joining end surface  51  of the shaft member  13   a  or  13   b  is set to an equal dimension. 
     The outer diameter B of the joining end surface  50  of the cup member  12   a  and the joining end surface  51  of the shaft member  13   a  or  13   b  is set to an equal dimension for each joint size. Thus, the cup member prepared for common use for each joint size, and the shaft member having a variety of specifications of the shaft section for each vehicle type can be prepared in a state before heat treatment. Further, the intermediate component of each of the cup member  12   a  and the shaft member  13   a  or  13   b  can be assigned with a product number for management. Even when standardizing product types of the cup member  12   a , various types of the outer joint members  11  satisfying requirements can be produced quickly through combination of the cup member  12   a  and the shaft member  13   a  or  13   b  having a variety of specifications of the shaft section for each vehicle type. Therefore, standardization of a product type of the cup member  12   a  can reduce cost and alleviate a burden of production management. 
     The standardization of the product type of the cup member is described above by taking the differences in types, such as the general length stem type and the long stem type, as an example for easy understanding, but the present invention is not limited thereto. The same applies to standardization of the product type of the cup member for shaft members having a variety of specifications of the shaft section for each vehicle type among the general length stem types, and for shaft members having a variety of specifications of the shaft section for each vehicle type among the long stem types. 
     As a summary of the above description,  FIG. 16  is a diagram for illustrating an example of standardization of a product type of the cup member according to this embodiment. As illustrated in  FIG. 16 , the cup member is prepared for common use for one joint size, and is assigned with, for example, a product number C 001  for management. In contrast, the shaft member has a variety of specifications of the shaft section for each vehicle type, and is assigned with, for example, a product number S 001 , S 002 , or S(n) for management. For example, when the cup member assigned with the product number C 001  and the shaft member assigned with the product number S 001  are combined and welded to each other, the outer joint member assigned with a product number A 001  can be produced. Thus, owing to standardization of a product type of the cup member, it is possible to reduce cost and to alleviate a burden of production management. In the standardization of a product type, the cup member is not limited to one type for one joint size, that is, not limited to one type assigned with a single product number. For example, the cup member comprises cup members of a plurality of types (assigned with a plurality of product numbers, respectively) that are prepared for one joint size based on different specifications of a maximum operating angle, and are each prepared so that the outer diameter B of the joining end surface of each of those cup members has an equal dimension. 
     A first modification of the outer joint member according to the first embodiment is described with reference to  FIG. 17  and  FIG. 18 .  FIG. 17  is a vertical sectional view for illustrating the entirety of a cup member before welding, and  FIG. 18  is an illustration of a state of the ultrasonic flaw-detection inspection as viewed from the arrow F-F of  FIG. 10 . An inner diameter dimension of a joining end surface of the cup member of this modification is different from that in the first embodiment, and other features are the same as those in the first embodiment. Thus, parts that have the same function are denoted by the same reference symbols (except for the subscripts), and only main points are described. 
     As illustrated in  FIG. 17  and  FIG. 18 , an inner diameter D 1  of a joining end surface  50   1  of a cup member  12   a   1  is set smaller than the inner diameter E of the joining end surface  51  of the shaft member  13   a . On the joining end surface  50   1  of the cup member  12   a   1 , a protruding surface  50   a   1  protruding to the radially inner side with respect to the inner diameter E of the joining end surface  51  of the shaft member  13   a  is formed. In such a state, the cup member  12   a   1  and the shaft member  13   a  are welded to each other. Although illustration is omitted, as in the first embodiment, the welding depth checking chamfer  51   a  is formed on the radially inner side of the joining end surface  51  of the shaft member  13   a.    
       FIG. 18  is an illustration of a case of a non-defective welded product. When the transmission pulse G from the probe  147  is input as illustrated in  FIG. 18 , the transmission pulse G enters a cup section  12   1  through the back bead  49   a  at the depth equal to or larger than the minimum acceptable welding depth Wmin, and travels straight as it is. Alternatively, the transmission pulse G is transmitted to the cup section  12   1  side by being reflected due to the inner diameter D 1  of the cup section  12   1 . In those cases, the probe  147  does not receive a reflected echo. This is because, as described above, on the joining end surface  50   1  of the cup member  12   a   1 , the protruding surface  50   a   1  protruding to the radially inner side with respect to the inner diameter E of the joining end surface  51  of the shaft member  13   a  is formed. Thus, even when the transmission pulse G enters the back bead  49   a , the boundary surface of the back bead  49   a , which is perpendicular to the transmission pulse G, does not exist. For this reason, a reflected echo having such an intensity as to cause a detection error of the probe  147  is not generated. The intensity of the reflected echo is equal to or less than the threshold of the non-defective/defective determination, and hence determination that the welded product is non-defective is made. 
     Although illustration is omitted, in the case of the defective welded product, as in the case of the first embodiment, the transmission pulse G is reflected by the welding depth checking chamfer  51   a . Thus, the intensity of the reflected echo R 2  that is not scattered is more than the threshold of the non-defective/defective determination. As a result, determination that the welded product is defective is made. 
     As described above, the welding depth checking chamfer  51   a  and the protruding surface  50   a   1  are formed on the joining end surface  51  and on the radially inner side of the joining end surface  50 , respectively. Thus, the discrimination between the non-defective welded product and the defective welded product can be positively made based on presence/absence of the reflected echo. As a result, the operability and the efficiency in the inspection as to whether the welded product is non-defective or defective can be further enhanced. 
     A second modification of the outer joint member according to the first embodiment is described with reference to  FIG. 19  and  FIG. 20 .  FIG. 19 a    is a partial vertical sectional view for illustrating an outer joint member of this modification,  FIG. 19 b    is an enlarged view for illustrating a circle “A” of  FIG. 19 a   , and  FIG. 19 c    is a view for illustrating a state before welding in  FIG. 19 b   .  FIG. 20  is a vertical sectional view for illustrating the entirety of a cup member before welding. A form of a protruding surface formed on a joining end surface of the cup member of this modification is different from that in the first modification described above, and other features are the same as those in the first modification. Thus, parts that have the same function are denoted by the same reference symbols (except for the subscripts), and only main points are described. 
     As illustrated in  FIG. 19 c    and  FIG. 20 , a joining end surface  50   2  formed on a projecting portion  12   a   3   2  of a bottom portion  12   a   2   2  of a cup member  12   a   2  is formed by annular turning. In this case, a diameter D 2  of the joining end surface  50   2  on the radially inner side corresponds to the inner diameter D 1  of the joining end surface  50   1  of the cup member  12   a   1  of the first modification. Thus, as illustrated in  FIG. 19 c   , a portion on the radially inner side with respect to the inner diameter E of the shaft member  13   a  corresponds to a protruding surface  50   a   2 . The cup member  12   a   2  of this modification can be formed by turning an end surface of the projecting portion  12   a   3 ′ of the preform  12   a ′ for the above-mentioned cup member after ironing, which is illustrated in  FIG. 4 a   , at only a portion corresponding to the joining end surface  50   2  on the radially outer side of the projecting portion  12   a   3   2  as illustrated in  FIG. 20 . Thus, the time for the turning can be reduced. Note that, the present invention is not limited thereto, and a projecting surface portion  50   b   2  on the radially inner side with respect to the joining end surface on the radially inner side of  FIG. 20  may be subjected to turning. In this modification, as in the first modification, the reflected echo to the probe is not generated in the case of the non-defective welded product. 
     Other features and advantages, that is, details of the overview of the respective steps, the states of the cup member and the shaft member in the main processing steps, the preparation of the cup member for common use, the welding method, the ultrasonic flaw detection-inspection method, the standardization of the product type, the configuration of the outer joint member, and the like as described above in the first embodiment on the manufacturing method are the same as those of the first embodiment. Therefore, all the details of the first embodiment are applied in the first and second modifications to omit redundant description. 
       FIG. 21  is an illustration of a manufacturing method according to a second embodiment of the present invention. In the manufacturing steps of this embodiment, the heat treatment step for the cup member, which is involved in the heat treatment step S 7  in  FIG. 3  as described above in the first embodiment, is provided before the welding step S 6  in the sequence and named “heat treatment step S 5   c ”, to thereby prepare the cup member as a finished product. Details of other aspects of the second embodiment than this aspect, that is, details of the overview of the respective steps, the states of the cup member and the shaft member in the main processing steps, the preparation of the cup member for common use, the welding method, the ultrasonic flaw detection-inspection method, the standardization of the product type, the configuration of the outer joint member, and the like as described above in the first embodiment on the manufacturing method are the same as those of the first embodiment. Therefore, all the details of the first embodiment are applied in this embodiment, and only the difference is described. 
     As illustrated in  FIG. 4 b   , the cup member  12   a  has a shape extending from the joining end surface  50  to the large-diameter cylindrical portion  12   a   1  via the bottom portion  12   a   2 , and the portions to be subjected to heat treatment that involves quenching and tempering are the track grooves  30  and the cylindrical inner peripheral surface  42  located at the inner periphery of the cylindrical portion  12   a   1 . Therefore, the cup member  12   a  generally has no risk of thermal effect on the heat-treated portion during the welding. For this reason, the cup member  12   a  is subjected to heat treatment before the welding to be prepared as a finished component. The manufacturing steps of this embodiment are suitable in practical use. 
     In the manufacturing steps of this embodiment, the cup member  12   a  is subjected to heat treatment for preparing the cup member  12   a  as a finished product, and is therefore assigned with a product number indicating a finished product for management. Thus, the standardization of the product type of the cup member  12   a  remarkably reduces the cost and alleviates the burden of production management. Further, the cup member  12   a  can be manufactured solely until the cup member  12   a  is completed as a finished product through the forging, turning, and heat treatment. Thus, the productivity is enhanced by virtue of reduction of setups and the like as well. 
     In this embodiment, in  FIG. 16  for illustrating the example of standardization of the product type of the cup member as described above in the first embodiment, only the product number of the cup member in  FIG. 16  is changed to the product number indicating a finished product, whereas the product numbers of the shaft member and the outer joint member are the same as those of the first embodiment. Therefore, description thereof is omitted herein. 
       FIG. 22  is an illustration of a manufacturing method according to a third embodiment of the present invention. In the manufacturing steps of this embodiment, the heat treatment steps for the cup section and the shaft section, which are involved in the heat treatment step S 7  in  FIG. 3  as described above in the first embodiment, and the grinding step S 8  for the shaft section in  FIG. 3  are provided before the welding step S 6  in the sequence and named “heat treatment step S 5   c  for cup member”, “heat treatment step S 4   s  for shaft member”, and “grinding step S 5   s ”. Thus, both the cup member and the shaft member are prepared as finished products. Details of other aspects of the third embodiment than this aspect, that is, details of the overview of the respective steps, the states of the cup member and the shaft member in the main processing steps, the preparation of the cup member for common use, the welding method, the ultrasonic flaw detection-inspection method, the standardization of the product type, the configuration of the outer joint member, and the like as described above in the first embodiment on the manufacturing method are the same as those of the first embodiment. Therefore, all the details of the first embodiment are applied in this embodiment, and only the difference is described. 
     After the spline processing step S 3   s , a hardened layer having a hardness of approximately from 50 HRC to 62 HRC is formed in a predetermined range of the outer peripheral surface of the shaft member by induction quenching in the heat treatment step S 4   s . Heat treatment is not performed on a predetermined portion in the axial direction, which includes the joining end surface  51 . The heat treatment for the cup member, the assignment of the product number, and the like are the same as those of the second embodiment on the manufacturing method, and redundant description is therefore omitted herein. 
     After the heat treatment step S 4   s , the shaft member is transferred to the grinding step S 5   s  so that the bearing mounting surface  14  and the like are finished. Thus, the shaft member is obtained as a finished product. Then, the shaft member is assigned with a product number indicating a finished product for management. The manufacturing steps of this embodiment are suitable in a case of a cup member and a shaft member having shapes and specifications with no risk of thermal effect on the heat-treated portion during the welding. 
     In the manufacturing steps of this embodiment, both the cup member and the shaft member can be assigned with product numbers indicating finished products for management. Thus, the standardization of the product type of the cup member further remarkably reduces the cost and alleviates the burden of production management. Further, the cup member and the shaft member can be manufactured independently of each other until the cup member and the shaft member are completed as finished products through the forging, turning, heat treatment, grinding after heat treatment, and the like. Thus, the productivity is further enhanced by virtue of reduction of setups and the like as well. 
     In this embodiment, in  FIG. 16  for illustrating the example of standardization of the product type of the cup member as described above in the first embodiment, the product numbers of the cup member and the shaft member in  FIG. 16  are changed to the product numbers indicating finished products. The product number of the outer joint member is the same as that of the first embodiment. Therefore, description thereof is omitted herein. Note that, the cup member and the shaft member to be prepared as finished components are not limited to the cup member and the shaft member subjected to finishing such as the above-mentioned grinding after heat treatment or quenched-steel cutting work, but encompass a cup member and a shaft member in a state in which the heat treatment is completed while the finishing is uncompleted. 
     As described in the standardization of the product type, the cup member is not limited to one type for one joint size, that is, not limited to one type assigned with a single product number. Specifically, as described above, the cup member encompasses, for example, cup members of a plurality of types (assigned with a plurality of product numbers, respectively) that are prepared for one joint size based on different specifications of a maximum operating angle, and are also prepared so that the outer diameters B of the above-mentioned joining end surfaces of the cup members are set to equal dimensions. In addition, the cup member encompasses, for example, cup members of a plurality of types (assigned with a plurality of product numbers, respectively) that are prepared for one joint size in order to achieve management of the cup members in a plurality of forms including intermediate components before heat treatment and finished components in consideration of the joint function, the circumstances at the manufacturing site, the productivity, and the like, and are also prepared so that the outer diameters B of the above-mentioned joining end surfaces of the cup members are set to equal dimensions. 
     Next, an outer joint member according to a second embodiment of the present invention is described with reference to  FIG. 23  and  FIG. 24 . In this embodiment, parts that have the same function as those of the outer joint member according to the first embodiment are denoted by the same reference symbols, and only main points are described. 
     A plunging type constant velocity universal joint  10   3  illustrated in FIG.  23  is a tripod type constant velocity universal joint (TJ), and comprises an outer joint member  11   3  comprising a cup section  12   3  and the long stem section  13  that extends from a bottom portion of the cup section  12   3  in the axial direction, an inner joint member  16   3  housed along an inner periphery of the cup section  12   3  of the outer joint member  11   3 , and rollers  19  serving as torque transmitting elements that are arranged between the outer joint member  11   3  and the inner joint member  16   3 . The inner joint member  16   3  comprises a tripod member  17  comprising three equiangular leg shafts  18  on which the rollers  19  are externally fitted. 
     Similarly to the outer joint member according to the first embodiment, the inner ring of the support bearing  6  is fixed to the outer peripheral surface of the long stem section  13 , and the outer ring of the support bearing  6  is fixed to the transmission case with the bracket (not shown). The outer joint member  11   3  is supported by the support bearing  6  in a freely rotatable manner, and thus the vibration of the outer joint member  11   3  during driving or the like is prevented as much as possible. 
       FIG. 24  are partial vertical sectional views for illustrating the outer joint member  11   3 . As illustrated in  FIG. 24 , the outer joint member  11   3  comprises a bottomed cylindrical cup section  12   3  that is opened at one end and has inner peripheral surfaces  31   3  and the track grooves  30   3 , on which the rollers  19  (see  FIG. 23 ) are caused to roll, formed at three equiangular positions on an inner peripheral surface of the cup section  12   3 , and the long stem section  13  that extends from a bottom portion of the cup section  12   3  in the axial direction and comprises the spline Sp serving as the torque transmitting coupling portion formed at the outer periphery of the end portion on the opposite side to the cup section  12   3  side. The outer joint member  11   3  is formed by welding the cup member  12   a   3  and the shaft member  13   a  to each other. 
     As illustrated in  FIG. 24 , the cup member  12   a   3  is an integrally-formed product having a cylindrical portion  12   a   1   3  and a bottom portion  12   a   2   3 . The cylindrical portion  12   a   1   3  has the track grooves  30   3  and the inner peripheral surfaces  31   3  formed at the inner periphery thereof. A projecting portion  12   a   3   3  is formed at the bottom portion  12   a   2   3  of the cup member  12   a   3 . The boot mounting groove  32  is formed at an outer periphery of the cup member  12   a   3  on the opening side thereof. The bearing mounting surface  14  and the snap ring groove  15  are formed at the outer periphery of the shaft member  13   a  on the cup member  12   a   3  side, whereas the spline Sp is formed at the end portion on the opposite side to the cup member  12   a   3  side. 
     A joining end surface  50   3  formed at the projecting portion  12   a   3   3  of the bottom portion  12   a   2   3  of the cup member  12   a   3  and the joining end surface  51  formed at the end portion of the shaft member  13   a  on the cup member  12   a   3  side are brought into abutment against each other, and are welded to each other by electron beam welding performed from the radially outer side. The welded portion  49  is formed of a bead, which is formed by a beam radiated from the radially outer side of the cup member  12   a   3 . Similarly to the outer joint member of the first embodiment, the outer diameters B of the joining end surface  50   3  and the joining end surface  51  are set to equal dimensions for each joint size. The welded portion  49  is formed on the joining end surface  51  located on the cup member  12   a   3  side with respect to the bearing mounting surface  14  of the shaft member  13   a , and hence the bearing mounting surface  14  and the like can be processed in advance so that post-processing after welding can be omitted. Further, due to the electron beam welding, burrs are not generated at the welded portion. Thus, post-processing for the welded portion can also be omitted, which can reduce the manufacturing cost. 
     The details of the outer joint member and the method of manufacturing the outer joint member according to this embodiment are the same as the details of the outer joint member according to the first embodiment, the modifications thereof, and the manufacturing method according to the first to third embodiments as described above. Therefore, all of those details are applied in this embodiment to omit redundant description. 
     Next, an outer joint member according to a third embodiment and a manufacturing method according to a fourth embodiment of the present invention are described with reference to  FIG. 25  to  FIG. 28 . Features of the outer joint member and the method of manufacturing the outer joint member of those embodiments reside in that, in addition to the welding depth checking chamfer formed on the joining end surface, an excessive welding depth checking chamfer is formed on the radially inner side with respect to the welding depth checking chamfer. In those embodiments, determination as to whether or not the welding depth is kept within a satisfactory range of being not insufficient or not excessive can be made. Thus, it is possible to achieve the outer joint member and the method of manufacturing the outer joint member, which are capable of preventing excess of the welding depth, further reducing welding cost, and achieving satisfactory operability in the inspection. 
     The details of the outer joint member according to the third embodiment are described with reference to  FIG. 25 .  FIG. 25 a    is a partial vertical sectional view for illustrating the outer joint member,  FIG. 25 b    is an enlarged view for illustrating a circle “A” of  FIG. 25 a   , and  FIG. 25 c    is an enlarged view for illustrating a shape before welding in  FIG. 25 b   . A cup section  12   2  and the cup member  12   a   2  of an outer joint member  114  according to this embodiment are the same as the cup section  12   2  and the cup member  12   a   2  of the second modification of the first embodiment, respectively. Thus, parts of the cup section  12   2  and the cup member  12   a   2  according to this embodiment, which have the same function as those in the second modification of the first embodiment, are denoted by the same reference symbols to omit redundant description. 
     A shaft member  13   a   1  is described with reference to  FIG. 25 c   . On a joining end surface  51   1  of the shaft member  13   a   1 , the welding depth checking chamfer  51   a  is formed similarly to the shaft members  13   a  and  13   b  of the embodiments and the modifications described above. Further, in the shaft member  13   a   1  according to this embodiment, in addition to the welding depth checking chamfer  51   a , an excessive welding depth checking chamfer  51   b  is formed on the radially inner side with respect to the joining end surface  51   1 . The excessive welding depth checking chamfer  51   b  is formed to determine whether or not the welding depth is excessive. 
       FIG. 25 b    is an illustration of a non-defective welded product welded to an extent that the welding depth checking chamfer  51   a  does not remain and having a welding depth equal to or larger than the minimum acceptable welding depth Wmin, whereas the excessive welding depth checking chamfer  51   b  remains. 
     Next, the manufacturing method according to the fourth embodiment of the present invention is described with reference to  FIG. 26  to  FIG. 28 .  FIG. 26  are enlarged views for illustrating states of ultrasonic flaw-detection inspection on the welded portion (non-defective welded product) illustrated in  FIG. 25 b   .  FIG. 26 a    is an illustration of a state of inspection as to whether or not the welding depth is insufficient, and  FIG. 26 b    is an illustration of a state of the inspection as to whether or not the welding depth is excessive. 
     As illustrated in  FIG. 26 a   , when the transmission pulse G from the probe  147  is input at a flaw detection position corresponding to the welding depth checking chamfer, the transmission pulse G travels straight as it is to the cup section  12   2  side. Thus, the probe  147  does not receive a reflected echo. 
     After that, when the probe  147  is shifted in the axial direction, and the transmission pulse G from the probe  147  is input at a flaw detection position corresponding to the excessive welding depth checking chamfer as illustrated in  FIG. 26 b   , the transmission pulse G is reflected by the excessive welding depth checking chamfer  51   b . The excessive welding depth checking chamfer  51   b  is formed in the direction perpendicular to the transmission pulse G, and hence a reflected echo R 4  that is not scattered and remains strong is received by the probe  147 . 
     As described above, in the case of the non-defective welded product, when the transmission pulse G from the probe  147  is input at each of the two flaw detection positions corresponding to the welding depth checking chamfer  51   a  and the excessive welding depth checking chamfer  51   b , the reflected echo R 4  is solely received. Thus, determination can be made. 
     Next, states of ultrasonic flaw-detection inspection in the case of the defective welded product (having an insufficient welding depth) and a case of a product having an excessive welding depth are described.  FIG. 27 a    is an illustration of a defective welded product, and  FIG. 27 b    is an illustration of the product having an excessive welding depth. As illustrated in  FIG. 27 a   , in the case of the defective welded product having an insufficient welding depth, as in  FIG. 12 b    for illustrating the manufacturing method according to the first embodiment, the distal end of the bead  49   a  does not reach the minimum acceptable welding depth Wmin, and hence the welding depth checking chamfer  51   a  remains. The transmission pulse G from the probe  147  at this flaw detection position is input and reflected by the welding depth checking chamfer  51   a . The welding depth checking chamfer  51   a  is formed in the direction perpendicular to the transmission pulse G, and hence the reflected echo R 2  that is not scattered and remains strong is received by the probe  147 . Although illustration is omitted, in this embodiment, after that, the probe  147  is shifted in the axial direction, and the probe  147  receives the second strong reflected echo R 4  (see  FIG. 26 b   ) at the flaw detection position corresponding to the excessive welding depth checking chamfer  51   b . When the two strong reflected echoes R 2  and R 4  are received as described above, determination that the welded product has an insufficient welding depth and hence is defective is made. 
     As illustrated in  FIG. 27 b   , in the case of the product having an excessive welding depth, welding is performed to an extent that none of the welding depth checking chamfer  51   a  and the excessive welding depth checking chamfer  51   b  remains. Thus, at any of the flaw detection position corresponding to the welding depth checking chamfer  51   a  and the flaw detection position corresponding to the excessive welding depth checking chamfer  51   b , the probe  147  does not receive the reflected echo. When no reflected echo is received as described above, determination that the welding depth is excessive is made. 
     As described above, in this embodiment, through the ultrasonic flaw-detection inspection, determination that the welded product has an insufficient welding depth and hence is defective is made when the probe  147  receives the two reflected echoes, determination that the welded product is non-defective is made when the probe  147  receives the one of the reflected echoes, and determination that the welding depth is excessive is made when the probe  147  receives none of the reflected echoes. Note that, the excessively welded product is not necessarily defective when determination that a beam intensity during welding is high, determination that duration of the welding is long, or other determination may be made. When over quality is suppressed and such welding conditions are changed as appropriate, cost reduction and other advantages can be obtained. 
     The welding depth checking chamfer  51   a  and the excessive welding depth checking chamfer  51   b  are summarized with reference to  FIG. 28 . The minimum acceptable welding depth Wmin corresponds to a welding depth under the state in which the welding depth checking chamfer  51   a  is eliminated, and an excessive-welding determination depth Wmax corresponds to a start end of the excessive welding depth checking chamfer  51   b . A region J from an outer periphery of the shaft member  131  to the minimum acceptable welding depth Wmin corresponds to the defective welded product, a region K between the minimum acceptable welding depth Wmin and the excessive-welding determination depth Wmax corresponds to the non-defective welded product, and a region L on the radially inner side with respect to the excessive-welding determination depth Wmax corresponds to the excessively welded product. 
     All the details of the overview of the respective steps, the states of the cup member and the shaft member in the main processing steps, the preparation of the cup member for common use, the welding method, the ultrasonic flaw detection-inspection method, the standardization of the product type, the configuration of the outer joint member, and the like as described above in the first embodiment on the manufacturing method are applied to the outer joint member according to the third embodiment and the manufacturing method according to the fourth embodiment to omit redundant description. 
     In the above-mentioned embodiments and the above-mentioned modifications, the case where the welding depth checking chamfer and the excessive welding depth checking chamfer are formed on the radially inner side with respect to the joining end surface of the shaft member is exemplified. However, conversely, the welding depth checking chamfer and the excessive welding depth checking chamfer may be formed on the radially inner side with respect to the joining end surface of the cup member. In this case, there are no problems as long as the ultrasonic flaw-detection inspection is performed from a surface side of the cup member. 
     In the above-mentioned embodiments and the above-mentioned modifications, the case to which electron beam welding is applied is described, but laser welding is also similarly applicable. 
     In the outer joint member according to the embodiments and the modifications described above, the cases where the present invention is applied to the double-offset type constant velocity universal joint as the plunging type constant velocity universal joint  10 , and to the tripod type constant velocity universal joint as the plunging type constant velocity universal joint  10  are described. However, the present invention may be applied to an outer joint member of another plunging type constant velocity universal joint such as a cross-groove type constant velocity universal joint, and to an outer joint member of a fixed type constant velocity universal joint. Further, in the above, the present invention is applied to the outer joint member of the constant velocity universal joint, which is used to construct the drive shaft. However, the present invention may be applied to an outer joint member of a constant velocity universal joint, which is used to construct a propeller shaft. 
     The present invention is not limited to the above-mentioned embodiments and the above-mentioned modifications. As a matter of course, various modifications can be made thereto without departing from the gist of the present invention. The scope of the present invention is defined in Claims, and encompasses equivalents described in Claims and all changes within the scope of claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  drive shaft 
               2  intermediate shaft 
               3  spline 
               4  boot 
               5  boot 
               6  support bearing 
               10  plunging type constant velocity universal joint 
               11  outer joint member 
               12  cup section 
               12   a  cup member 
               12   a   1  cylindrical portion 
               12   a   2  bottom portion 
               13  long shaft section 
               13   a  shaft member 
               14  bearing mounting surface 
               16  inner joint member 
               17  tripod member 
               19  torque transmitting element (roller) 
               20  fixed type constant velocity universal joint 
               21  outer joint member 
               22  inner joint member 
               23  torque transmitting element (ball) 
               24  cage 
               30  track groove 
               31  inner peripheral surface 
               40  track groove 
               41  torque transmitting element (ball) 
               42  cylindrical inner peripheral surface 
               49  welded portion 
               50  joining end surface 
               50   a  protruding surface 
               51  joining end surface 
               51   a  welding depth checking chamfer 
               51   b  excessive welding depth checking chamfer 
               52  recessed portion 
               100  welding apparatus 
               101  electron gun 
               108  case 
               109  vacuum pump 
               111  sealed space 
               120  ultrasonic flaw detection-inspection apparatus 
               121  base 
               122  water bath 
               123  workpiece support 
               124  workpiece holding member 
               125  rotary drive device 
               135  pressing device 
               136  drive positioning device for probe 
               147  probe 
             B outer diameter 
             D inner diameter 
             E inner diameter 
             G transmission pulse 
             R reflected echo 
             O joint center 
             O 1  curvature center 
             O 2  curvature center 
             Sp spline