Patent Description:
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 fixed type and the plunging type, the constant velocity universal joint includes, as main components, an inner joint member, an outer joint member, and torque transmission members. The outer joint member includes a cup section and a shaft section. The cup section has track grooves formed in an inner peripheral surface thereof and configured to allow the torque transmission members to roll thereon. The shaft section extends from a bottom 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, that is, a round bar to plastic working such as forging and ironing or processing such as cutting work, heat treatment, and grinding (see <FIG> and <FIG> of Patent Literature <NUM>).

In Patent Literature <NUM>, there is disclosed steps of manufacturing an outer joint member, which integrally includes a cup member and a shaft member, through forging. The forging is described with reference to <FIG>. First, a rod-like blank, that is, a billet <NUM> (<FIG>) is subjected to forward extrusion molding so that a preform <NUM> (<FIG>), which includes a shaft section <NUM> and a solid main body section <NUM>, is obtained. Next, the solid main body section <NUM> is subjected to upsetting so that an intermediate preform <NUM> (<FIG>), which is constructed by the shaft section <NUM> and a solid large-diameter section <NUM>, is obtained. Next, the solid main body section <NUM> is subjected to backward extrusion and formed into a cup section <NUM>, which is literally opened at one end, so that a preforged product <NUM> (<FIG>) is obtained. After that, the cup section <NUM> of the preforged product <NUM> is subjected to ironing so that an ironed product <NUM> (<FIG>) that is finished with high accuracy is obtained. In the course of the backward extrusion and ironing, on an inner side of the cup section, there are formed track grooves <NUM> serving as rolling surfaces for torque transmission balls in the case of a ball type constant velocity universal joint, and there are formed track grooves (not shown) in the case of a tripod type constant velocity universal joint.

The shaft section <NUM> molded by the forward extrusion (<FIG>) is retained by a lower portion molding die (not shown) throughout all of subsequent steps of upsetting (<FIG>), backward extrusion (<FIG>), and ironing (<FIG>). Further, the upsetting is performed in a single step (<FIG>).

Incidentally, an outer joint member (long stem type) including a shaft section longer than a standard may sometimes be used. For example, in order to equalize lengths of a right part and a left part of the drive shaft, the long stem type is used for a constant velocity universal joint on the inboard side that corresponds to one side of the drive shaft. In this case, the shaft section is rotatably supported by a support bearing. Although varied depending on vehicle types, the length of the shaft section of the long stem type is approximately from <NUM> to <NUM> in general. The outer joint member of the long stem type has a long shaft section, and hence there is a 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 (Patent Literature <NUM>).

An overview of the friction press-contact technology for the outer joint member described in Patent Literature <NUM> is described below. First, as illustrated in <FIG>, a cup member <NUM> and a shaft member <NUM> are joined through the friction press-contact to form an intermediate product <NUM>'. Next, burrs <NUM> on a radially outer side of a joining portion <NUM> are removed, and hence an outer joint member <NUM> as illustrated in <FIG> is obtained. The burrs <NUM> are generated on the joining portion <NUM> of the intermediate product <NUM>' along with the press-contact. The burrs <NUM> on the radially outer side of the joining portion <NUM> are removed through processing such as turning. Accordingly, a support bearing (rolling bearing <NUM>: see <FIG>) to a shaft section of the outer joint member <NUM>.

Although illustration is omitted, the intermediate product <NUM>' is processed into a finished product of the outer joint member <NUM> through machining of a spline, snap ring grooves, and the like, and through heat treatment, grinding, and the like. Therefore, the outer joint member <NUM> and the intermediate product <NUM>' have slight differences in shape. However, illustration of the slight differences in shape is omitted in <FIG> and <FIG> to simplify the description, and the outer joint member <NUM> being the finished product and the intermediate product <NUM>' are denoted by the reference symbols at the same parts. The same applies to the description below. A further outer joint member of a constant velocity universal joint and a method of manufacturing it is disclosed in Patent Literature <NUM>, which form the basis for the preamble of claim <NUM>.

The burrs <NUM> on the joining portion <NUM>, which are generated due to the friction press-contact, not only are quenched by friction heat and cooling that follows the friction heat to have a high hardness but also have a distorted shape extended in an axial direction and a radial direction. Therefore, when removing the burrs <NUM> 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, a 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 <NUM> of the outer joint member <NUM>, when ultrasonic flaw detection, which enables flaw detection at high speed, is to be performed, an ultrasonic wave is scattered due to the burrs <NUM> remaining on the radially inner side of the joining portion <NUM>, 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 welding through use of high energy intensity beam such as laser welding or electron beam welding is employed, it is conceivable that the surfaces of the joining portion may be prevented from being increased in thickness unlike the case of the friction press-contact (see Patent Literature <NUM>). However, when the cup member <NUM> and the shaft member <NUM> as illustrated in <FIG> are brought into abutment against each other to be welded, a hollow cavity portion <NUM> having a relatively large volume is formed. Then, a pressure in the hollow cavity portion <NUM> is increased due to processing heat during the welding, and after completion of the welding, the pressure is decreased. Due to such variation in the internal pressure of the hollow cavity portion <NUM>, blowing of a molten material occurs. Thus, there arise defects such as formation of a recess on a surface of the welded portion, poor penetration depth, and generation of air bubbles 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.

Further, in consideration of the case where members (workpieces) constructing the outer joint member of the constant velocity universal joint are to be welded, the workpieces employ medium to high carbon steel having a high carbon content to secure strength. Thus, when the workpieces are welded to each other as they are, the welded portion is significantly hardened, and becomes more liable to be cracked. Therefore, for the purpose of reducing the hardness and securing the toughness, pre-heating is performed to reduce the cooling rate after welding. However, when the workpieces each having a solid shaft shape are butt-welded as they are, a large volume in the periphery of the welded portion may cause a long time for pre-heating to be required. Thus, the cycle time is increased to increase the manufacturing cost.

Further, in the case of a joint-type outer joint member manufactured by joining the cup member and the shaft member through welding, when, in particular, center segregation of the rod-like blank being a blank for the cup member enters the welded portion, impurities may reduce strength of the joined portion and increase the percent defective. Herein, the segregation is a phenomenon of causing uneven distribution of alloying elements or impurities, or such a state (JIS G <NUM> Terms used in iron and steel (Heat Treatment)). Further, the center segregation represents occurrence of segregation at a center portion of a steel material due to segregation of components in a solidifying step of steel (see JIS G <NUM> Macroscopic examination method for steel).

The outer joint member disclosed in Patent Literature <NUM> is of a type integrally including the cup section and the shaft section. Thus, the problems which may arise in the case of welding the cup section and the shaft section are not considered. However, when the upsetting is performed in a single step as in the forging disclosed in Patent Literature <NUM>, the section reduction rate or the height reduction rate is increased. There is a limit in the lateral expansion in a billet end surface due to friction with a die or a punch, and hence a center portion of the billet in a height direction is laterally expanded (increased in diameter). As a result, the center segregation also moves toward the radially outer side. There is a fear in that the center segregation having moved toward the radially outer side in such a manner may interfere with the joined portion in the case of the joint-type outer joint member. The interference of the center segregation with the joined portion may cause poor strength and defective welding. Thus, elaboration of confining the center segregation within the radially inner side is required in the step of forging so as to prevent the interference of the center segregation with the welded portion. The section reduction rate is represented by <NUM>×(A<NUM>-A)/A, where a sectional area before molding of a material is A<NUM>, and a sectional area after molding is A. Further, the height reduction rate is a percentage calculated by <NUM>×(H<NUM>-H)/H, where the height of a material portion, which is to be subjected to upsetting, before processing is Ho, and the height after processing is H (JIS B <NUM> Terms of forging).

It is conceivable to use a material having a high cleanliness. However, the use of such material increases the cost. Further, when a stem having a small diameter is not to be employed to avoid the interference of the center segregation, the design is limited at the time of considering a stem shape of the joint-type outer joint member, which is not preferred.

It is an object of the present invention to eliminate the above-mentioned problems of the above-mentioned related art, and to improve strength and quality of a welded portion of an outer joint member of a constant velocity universal joint which is manufactured by joining a cup member and a shaft member through welding.

The invention is defined by the features of claim <NUM>. In order to solve the above-mentioned problem, according to one embodiment of the present invention, there is provided an outer joint member of a constant velocity universal joint, comprising: a cup member; and a shaft member, the outer joint member being manufactured by joining the cup member and the shaft member, the cup member having a bottomed cylindrical shape that is opened at one end, and comprising a cylindrical portion, a bottom portion, and a short shaft section protruding from the bottom portion, the short shaft portion having a solid shaft shape, and comprising a joining end surface at an end portion thereof, the shaft member having a solid shaft shape, and comprising a joining end surface at one end thereof, the joining end surface of the cup member and the joining end surface of the shaft member being brought into abutment against each other and welded to form a welded portion having an annular shape, to prevent interference of center segregation with the welded portion.

The welded portion is formed into an annular shape, and hence the welded portion is positioned on a radially outer side with respect to the center segregation. Thus, the problem caused by the interference of the center segregation with the welded portion is eliminated. The range of the center segregation is not determined geometrically. However, herein, the range of the center segregation in the radial direction is assumed to be within the range of one-half of the diameter of the blank, and such range is determined based on the impact test piece location of a round bar defined by JIS G <NUM> (Steel and Steel Products - Location and Preparation of Samples and Test Pieces for mechanical testing) and with expectation for safety.

The welded portion is a generic name of a portion including a welded metal and a heat-affected portion. The welded metal is metal which forms part of the welded portion and is molten and solidified during welding. The heat-affected portion is a portion which is changed in structure, metallurgical property, mechanical property, and the like by heat of welding and is unmolten part of a base material (JIS Z <NUM>-<NUM> Welding Terms - Section <NUM>: General).

Herein, the term "solid shaft shape" is intended to exclude a shaft having a hollow cavity penetrating in an axial direction, or a shaft having an elongated hollow cavity portion extending from a joining end surface in the axial direction (see Patent Literatures <NUM> and <NUM>). The cup member has a bottomed cylindrical shape as a whole, but the short shaft section having the joining end surface formed thereon does not have a through hole and an elongated hollow cavity portion extending from the joining end surface in the axial direction. Thus, at least the short shaft section has a solid shaft shape.

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, when the above-mentioned outer joint member of a constant velocity universal joint is to be manufactured, the method comprising: forming the cup member by forging, the forging comprising: upsetting a billet having a columnar shape successively in a plurality of stages; extruding the cylindrical portion and the short shaft portion; and ironing the cylindrical portion; and bringing a joining end surface of the cup member and a joining end surface of the shaft member into abutment against each other and welding the joining end surfaces to form a welded portion having an annular shape.

In the outer joint member of a constant velocity universal joint according to the present invention, the welded portion has an annular shape. Thus, even when the center segregation occurs in the blank, the interference of the center segregation with the welded portion can be avoided as much as possible. Therefore, welding quality for the joint-type outer joint member including the cup member and the shaft member joined through welding is improved, thereby being capable of securing strength of the welded portion.

With the method of manufacturing an outer joint member of a constant velocity universal joint according to the present invention, the center segregation near the joining end surface of the cup member is confined within the radially inner side, thereby being capable of avoiding the interference of the center segregation with the welded portion as much as possible, suppressing the reduction in strength of the welded portion, and reducing the percent defective. Further, the interference of the center segregation with the welded portion can be avoided as much as possible. Thus, the method is applicable also to the case of the cup member having a relatively small diameter, and hence the degree of freedom in design of the outer joint member may be attained.

In welding with a high energy intensity beam, a bead width is small, and deep penetration can be obtained in a short period of time, thereby being capable of increasing the strength of the welded portion and reducing thermal strain. Further, burrs are not generated, and hence post-processing for the joining portion can be omitted. As a result, the manufacturing cost can be reduced. Further, there is no scattering of ultrasonic waves caused by the burrs, which is a problem raised in the case of joining through the friction press-contact. Thus, total inspection through ultrasonic flaw detection can be performed to stably secure high welding quality. Further, in general, the electron beam welding is performed in vacuum. Therefore, the problems such as the blowing of a molten material and the generation of air bubbles are eliminated.

As is clear from the description above, according to the method of butt-welding of the present invention, the strength and quality of the welded portion can be improved. Further, when the present invention is applied to manufacturing of an outer joint member of a constant velocity universal joint having the cup member and the shaft member joined through butt-welding, the outer joint member improved in strength and quality of the welded portion can be provided.

Now, description is made of embodiments of the present invention with reference to the drawings.

First, a first embodiment of an outer joint member is described with reference to <FIG> and <FIG>, and subsequently, a first embodiment of a method of manufacturing the outer joint member is described with reference to <FIG>.

<FIG> is a view for illustrating the entire structure of a drive shaft <NUM>. The drive shaft <NUM> mainly comprises a plunging type constant velocity universal joint <NUM>, a fixed type constant velocity universal joint <NUM>, and an intermediate shaft <NUM> configured to couple both the joints <NUM> and <NUM>. The plunging type constant velocity universal joint <NUM> is arranged on a differential side (right side of <FIG>: hereinafter also referred to as "inboard side"), and the fixed type constant velocity universal joint <NUM> is arranged on a driving wheel side (left side of <FIG>: hereinafter also referred to as "outboard side").

The plunging type constant velocity universal joint <NUM> is a so-called double-offset type constant velocity universal joint (DOJ), and mainly comprises an outer joint member <NUM>, an inner joint member <NUM>, a plurality of balls <NUM> serving as torque transmitting elements, and a cage <NUM> configured to retain the balls <NUM>.

The outer joint member <NUM> comprises a cup section <NUM> and a long shaft section (hereinafter also referred to as "long stem section") <NUM> that extends from a bottom of the cup section <NUM> in an axial direction. The inner joint member <NUM> is housed in the cup section <NUM> of the outer joint member <NUM>. Track grooves <NUM> formed along an inner periphery of the cup section <NUM> of the outer joint member <NUM> and track grooves <NUM> formed along an outer periphery of the inner joint member <NUM> form pairs, and the balls <NUM> are arranged between the track grooves <NUM> and <NUM> of respective pairs. The cage <NUM> is interposed between the outer joint member <NUM> and the inner joint member <NUM>, and is held in contact with a partially cylindrical inner peripheral surface <NUM> of the outer joint member <NUM> at a spherical outer peripheral surface <NUM> and held in contact with a spherical outer peripheral surface <NUM> of the inner joint member <NUM> at a spherical inner peripheral surface <NUM>. A curvature center O<NUM> of the spherical outer peripheral surface <NUM> and a curvature center O<NUM> of the spherical inner peripheral surface <NUM> of the cage <NUM> are offset equidistantly from a joint center Q toward opposite sides in the axial direction.

An inner ring of a support bearing <NUM> is fixed to an outer peripheral surface of the long stem section <NUM>, and an outer ring of the support bearing <NUM> is fixed to a transmission case with a bracket (not shown). As described above, the outer joint member <NUM> is supported by the support bearing <NUM> in a freely rotatable manner, and hence vibration of the outer joint member <NUM> during driving or the like is prevented as much as possible.

The fixed type constant velocity universal joint <NUM> is a so-called Rzeppa type constant velocity universal joint, and mainly comprises an outer joint member <NUM>, an inner joint member <NUM>, a plurality of balls <NUM> serving as torque transmitting elements, and a cage <NUM> configured to retain the balls <NUM>. The outer joint member <NUM> comprises a bottomed cylindrical cup section 21a and a shaft section 21b that extends from a bottom of the cup section 21a in the axial direction. The inner joint member <NUM> is housed in the cup section 21a of the outer joint member <NUM>. The balls <NUM> are arranged between the cup section 21a of the outer joint member <NUM> and the inner joint member <NUM>. The cage is interposed between an inner peripheral surface of the cup section 21a of the outer joint member <NUM> and an outer peripheral surface of the inner joint member <NUM>.

Note that, as the fixed type constant velocity universal joint, an undercut-free type constant velocity universal joint may sometimes be used.

The intermediate shaft <NUM> comprises spline (including serrations; the same applies hereinafter) shafts <NUM> on both end portions thereof. The spline shaft <NUM> on the inboard side is inserted to a spline hole of the inner joint member <NUM> of the plunging type constant velocity universal joint <NUM>. Thus, the intermediate shaft <NUM> and the inner joint member <NUM> of the plunging type constant velocity universal joint <NUM> are coupled to each other to allow torque transmission therebetween. Further, the spline shaft <NUM> on the outboard side is inserted to a spline hole of the inner joint member <NUM> of the fixed type constant velocity universal joint <NUM>. Thus, the intermediate shaft <NUM> and the inner joint member <NUM> of the fixed type constant velocity universal joint <NUM> are coupled to each other to allow torque transmission therebetween. Although the example of the solid intermediate shaft <NUM> is illustrated, a hollow intermediate shaft may also be used.

Grease is sealed inside both the constant velocity universal joints <NUM> and <NUM> as a lubricant. To prevent leakage of the grease or entry of a foreign matter, bellows boots <NUM> and <NUM> are respectively mounted to a portion between the outer joint member <NUM> of the plunging type constant velocity universal joint <NUM> and the intermediate shaft <NUM>, and a portion between the outer joint member <NUM> of the fixed type constant velocity universal joint <NUM> and the intermediate shaft <NUM>.

Next, details of the outer joint member <NUM> are described with reference to <FIG>.

The outer joint member <NUM> comprises the cup section <NUM> and the long stem section <NUM>. The outer joint member <NUM> is manufactured by joining the cup member 12a and the shaft member 13a through butt welding, and manufacturing steps are described later in detail.

The cup section <NUM> has a bottomed cylindrical shape that is opened at one end, and the inner peripheral surface <NUM> has the plurality of track grooves <NUM> that are formed equidistantly in a circumferential direction, thereby forming a partially cylindrical shape. The balls <NUM> (see <FIG>) roll on the track grooves <NUM>.

The cup member 12a is an integrally-formed product being made of medium carbon steel, e.g., S53C, containing carbon of from <NUM> wt% to <NUM> wt%, and having a cylindrical portion 12a1 and a bottom portion 12a2. The cylindrical portion 12a1 has the track grooves <NUM> and the inner peripheral surface <NUM> described above. A boot mounting groove <NUM> is formed at an outer periphery of the cup member 12a on the opening side thereof, whereas a snap ring groove <NUM> is formed at an inner periphery. The bottom portion 12a2 has a shaft section having a solid shaft shape protruding toward the shaft member 13a side, that is, a short shaft section 12a3, and a joining end surface <NUM> (<FIG>) is formed at the short shaft section 12a3.

The joining end surface <NUM> is finished by turning. Herein, a recessed portion 50b is formed on a radially inner side of the joining end surface <NUM>, and as a result, the annular joining end surface <NUM> is formed on a radially outer side of the recessed portion 50b. The reference symbol D denotes an inner diameter of the joining end surface <NUM>. The recessed portion 50b may be formed during forging, or may be formed by cutting. When the recessed portion 50b is formed during forging, the number of steps can be reduced. Further, the joining end surface <NUM> is formed into an annular shape, and hence time required for turning can be reduced.

The long stem section <NUM> is a solid shaft that extends from the bottom portion 12a2 of the cup section <NUM> in the axial direction. A bearing mounting surface <NUM> and a snap ring groove <NUM> are formed at an outer periphery of the long stem section <NUM> on the cup member 12a side, whereas a spline shaft Sp serving as a torque transmission coupling portion is formed at an end portion on a side opposite to the cup section <NUM>.

The shaft member 13a is made of medium carbon steel, e.g. , S40C, containing carbon of from <NUM>. <NUM> wt% to <NUM> wt%. A joining end surface <NUM> (<FIG>) is formed at an end portion on the cup member 12a side. The joining end surface <NUM> has a recess <NUM>, and as a result, is formed into an annular surface. The reference symbol E denotes an inner diameter of the joining end surface <NUM>. <FIG> and <FIG> are illustrations of an example in which the recess <NUM> is formed during forging and in which the inner diameter portion <NUM> is formed in the joining end surface <NUM> by cutting. Thus, it appears as if the recess <NUM> and the inner diameter portion <NUM> are formed into a hole having stages. However, the inner diameter portion <NUM> may be an inner diameter portion of the joining end surface <NUM>, or may be an inner diameter portion of the recess <NUM>. The recess <NUM> may maintain a forged surface. In that case, the inner diameter portion <NUM> that can be clearly distinguished from the recess <NUM> does not appear as illustrated.

The recess <NUM> has a shallow bottom, that is, is very shallow with respect to an outer diameter of the joining end surface <NUM>. As an example of the depth, a lower limit is approximately <NUM>. That is intended to secure a straight portion having a length in the axial direction necessary to perform ultrasonic flaw detection for defectiveness in dimension in the radial direction (penetration depth) of the welded portion <NUM>. The above-mentioned lower limit is a value in view of the ultrasonic flaw detection. In view of reducing the pre-heating time through reduction of a volume near the joining portion, a corresponding depth of the recess <NUM> is desired.

In the case of forming the recessed portion during forging, an upper limit of the depth of the recess <NUM> is approximately a limit value formed through forging (reference)×<NUM>. Excessively deep recess <NUM> may cause increase in forging load, degradation of die lifetime, and increase in processing cost. Even in the case of forming through cutting, excessively deep recess <NUM> may cause longer processing time and poor material yield.

The inner diameter portion <NUM> of the joining end surface <NUM>, while being dependent on the outer diameter of the shaft member 13a, is presupposed to secure a radial width of the welded portion <NUM> to be formed on the outer diameter side of the recess <NUM>. The term "diameter" of the inner diameter is generally associated with a circular shape. However, a contour of the recess <NUM> as viewed from a plane perpendicular to the axial line of the shaft member 13a is not limited to have a circular shape, and the shape may be, for example, a polygon or an irregular shape.

Welding is performed by bringing the joining end surface <NUM> of the cup member 12a and the joining end surface <NUM> of the shaft member 13a into abutment against each other and irradiating an electron beam from an outer side of the cup member 12a in the radial direction (<FIG>). The welded portion <NUM>, as is well known, comprises metal that is molten and solidified during welding, that is, a molten metal and a heat-affected portion in a periphery of the molten metal. In <FIG>, the broken parallel oblique lines schematically represent an assumed range S of the center segregation. As illustrated in <FIG>, the assumed range S of the center segregation is confined within the radially inner side to prevent the interference with the welded portion <NUM>. With regard to the shaft member 13a, illustration of the assumed range of the center segregation is omitted. This is because, even in the case of molding the recess <NUM> at an end portion through forging such as upset forging (see <FIG>), the recess <NUM> is as shallow as counter boring as described above, and hence the section reduction rate and the height reduction rate are small, with the result that the recess <NUM> is not increased in diameter to such an extent that the assumed range of the center segregation interferes with the welded portion.

Although detailed description is made later, outer diameters B of the joining end surfaces <NUM> and <NUM> (see <FIG> and <FIG>) are set to equal dimensions for each joint size. However, the outer diameter B of the joining end surface <NUM> of the cup member 12a and the outer diameter B of the joining end surface <NUM> of the shaft member 13a need not be set to equal dimensions. In consideration of, for example, a state of the bead, a dimensional difference may be given as appropriate in such a manner that the outer diameter B of the joining end surface <NUM> is set slightly smaller than the outer diameter B of the joining end surface <NUM> or the like. The dimensional relationship between the outer diameter B of the joining end surface <NUM> and the outer diameter B of the joining end surface <NUM> is the same throughout the Description.

The welded portion <NUM> is formed on the cup member 12a side with respect to the bearing mounting surface <NUM> of the shaft member 13a, and hence the bearing mounting surface <NUM> and the like can be processed in advance before welding so that post-processing after welding can be omitted. Further, in the electron beam welding, burrs are not generated at the welded portion. Thus, also on this point, 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.

As illustrated in <FIG>, an inner diameter D of the joining end surface <NUM> of the cup member 12a is set smaller than an inner diameter E of the joining end surface <NUM> of the shaft member 13a. As a result, the joining end surface <NUM> of the cup member 12a partially protrudes to a radially inner side with respect to the joining end surface <NUM> having the inner diameter E. This protruding portion is referred to as a protruding surface 50a. The joining end surfaces <NUM> and <NUM> having such a shape are brought into abutment against each other, and the cup member 12a and the shaft member 13a are joined by welding. The protruding surface 50a is formed to be the same for each joint size.

Next, the manufacturing method of the above-mentioned outer joint member is described with reference to <FIG>. Before description of details of each manufacturing step, an overview of manufacturing steps is described.

As illustrated in <FIG>, the cup member 12a is manufactured through manufacturing steps comprising a bar material cutting step S1c, a forging step S2c, an ironing step S3c, and a turning step S4c. The forging step S2c and the ironing step S3c are illustrated as separate steps. However, in general, the forging operation is classified variously, and there is a case where the steps including upsetting, extruding, and ironing are collectively referred to as forging (see <FIG> and corresponding description).

Meanwhile, the shaft member 13a is manufactured through manufacturing steps comprising a bar material cutting step S1s, a turning step S2s, and a spline processing step S3s.

The cup member 12a and the shaft member 13a thus manufactured are each assigned with a product number for management. After that, the cup member 12a and the shaft member 13a are subjected to a welding step S6, an ultrasonic flaw detection step S6k, a heat treatment step S7, and a grinding step S8 so that the outer joint member <NUM> is completed.

An overview of each step is described below. Each step is described as a typical example, and appropriate modification and addition may be made as needed.

First, the manufacturing steps for the cup member 12a are described.

A bar material (round bar) is cut into a predetermined length in accordance with a forging weight, thereby producing a columnar billet.

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 12a.

Ironing is performed on the track grooves <NUM> and the cylindrical surface <NUM> of the preform, thereby finishing the inner periphery of the cylindrical portion of the cup member 12a.

In the preform after ironing, the outer peripheral surface, the boot mounting groove <NUM>, the snap ring groove <NUM> and the like, and the joining end surface <NUM> are formed by turning. After the turning step S4c, the cup member 12a in the form of an intermediate component is assigned with a product number for management.

Next, the manufacturing steps for the shaft member 13a are described.

A bar material is cut into a predetermined length in accordance with an entire length of the shaft section, thereby producing a columnar billet. After that, the billet is forged into a rough shape by upset forging depending on the shape of the shaft member 13a.

The outer peripheral surface of the billet (bearing mounting surface <NUM>, snap ring groove <NUM>, minor diameter of the spline, end surface, and the like) and the joining end surface <NUM> of the billet at the end portion on the cup member 12a side are formed by turning.

The spline shaft is formed by processing splines in the shaft member through rolling after turning. Note that, the method of processing the spline is not limited to the rolling, and press working or the like may be adopted instead as appropriate. After the spline processing, the shaft member 13a 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 <NUM> from the cup member 12a and the shaft member 13a in the form of the intermediate component obtained in the manner described above are described.

The joining end surface <NUM> of the cup member 12a and the joining end surface <NUM> of the shaft member 13a are brought into abutment against and welded to each other. This welding step is described later in detail.

The welded portion <NUM> between the cup member 12a and the shaft member 13a is inspected by ultrasonic flaw detection. This ultrasonic flaw detection step is also described later in detail.

High frequency quenching and tempering are performed as heat treatment on at least the track grooves <NUM> and the inner peripheral surface <NUM> of the cup section <NUM> after welding and a necessary range of the outer periphery of the shaft member <NUM> after welding. Heat treatment is not performed on the welded portion <NUM>. A hardened layer having a hardness of approximately from <NUM> HRC to <NUM> HRC is formed on each of the track grooves <NUM> and the inner peripheral surface <NUM> of the cup section <NUM> by the heat treatment. Further, a hardened layer having a hardness of approximately from <NUM> HRC to <NUM> HRC is formed in a predetermined range of the outer periphery of the shaft section <NUM>.

After the heat treatment, the bearing mounting surface <NUM> of the shaft member <NUM> and the like are finished by grinding. Thus, the outer joint member <NUM> is completed.

As described above, 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.

Main constituent features of the above-mentioned method of manufacturing the outer joint member are described more in detail.

<FIG> are illustrations of the forging step for the cup member 12a. <FIG> are sectional views, but illustrations of sections of the billet and the forged workpiece are omitted. Further, as already described in relation to <FIG>, those are schematic illustrations of the assumed range S of the center segregation with the broken parallel oblique lines. Further, the two-dotted chain lines represent a contour of the billet and the forged workpiece in the previous stage.

First, a rod-like blank (billet) <NUM> illustrated in <FIG> is inserted into a cavity of a forging die (hereinafter referred to as "die") 62A. Then, as illustrated in <FIG>, a punch 66A is lowered to upset the billet <NUM> in the die 62A. At this time, an upper portion of the billet <NUM>, that is, a region corresponding to an opening side of the cup member 12a is laterally expanded (increased in diameter) until an outer diameter is regulated by an inner peripheral surface of the die 62A.

Meanwhile, a lower portion of the billet <NUM>, that is, a region corresponding to a bottom side of the cup member 12a is narrowed in the die 62A and reduced in diameter. In order to achieve the narrowing, an inner diameter of the die is gradually reduced as approaching the bottom side (lower side in <FIG>) of the cup member 12a. Specifically, as illustrated in <FIG>, the shapes of the inner peripheral surfaces of the dies 62A to 62C in sectional view are formed into, for example, an arc shape 64A (<FIG>), a taper shape 64B (<FIG>), or a combined shape 64C (<FIG>) of those. The narrowing is not limited to a single step, and may be performed for a plurality of times depending on design of steps. When the narrowing is performed in such a manner, in the region corresponding to the bottom side of the cup member 12a, a force toward a center is applied to the material through the course of upsetting (<FIG>), and hence movement of the material toward the radially outer side is suppressed.

As described above, in the dies <NUM> (62A to 62C) to be used in the course of upsetting, an inner diameter is larger than an outer diameter of the billet <NUM> in a first region corresponding to the opening side of the cup member 12a, and an inner diameter is gradually reduced in a second region corresponding to the bottom side of the cup member 12a. Through sequential use of the plurality of dies 62A to 62C gradually increased in inner diameter in the first region, the region of the billet <NUM> corresponding to the opening side of the cup member 12a is increased in diameter in the course of upsetting, thereby narrowing the region corresponding to the bottom side of the cup member 12a.

<FIG> are illustrations of an example of performing the upsetting in three steps. As illustrated in <FIG>, the inner diameters of the dies 62A to 62C and the outer diameters of the punches 66A to 66C are sequentially increased. When the upsetting is performed in a plurality of steps, an increase in the friction resistance due to shortage of lubricant is avoided, thereby being capable of promoting the lateral expansion of the material. Thus, a billet edge can be moved to the radially outer side as much as possible. Through movement of the billet edge toward the radially outer side as much as possible, the billet edge portion can be removed at the time of subjecting the end surface on the opening side of the cup member to finishing.

Next, as illustrated in <FIG>, combination extrusion is performed. That is, a short shaft portion 12a3 of the cup member 12a is molded by the forward extrusion, and a cylindrical portion 12a1 of the cup member 12a is molded by the backward extrusion. At that time, the narrowed region corresponding to the bottom side of the cup member 12a is retained as an original shape of the short shaft portion 12a3, and the backward extrusion is performed for the region of the cylindrical portion 12a1 corresponding to the opening side of the cup member 12a while suppressing the lateral expansion (increase in diameter) as much as possible. In other words, a fiber flow in the axial direction is formed in the short shaft portion 12a3. This step may be performed for a plurality of times depending on the design of steps.

After that, as illustrated in <FIG>, the cylindrical portion 12a1 of the cup member 12a is subjected to cold ironing so that an ironed product is obtained. The ironed product is subjected to turning as needed and formed into the cup member 12a being a forged product (see <FIG>).

<FIG> are schematic illustrations of shapes the workpiece which are assumed in the case of performing normal forging through upsetting, extruding, and ironing without the narrowing described in relation to <FIG>, for comparison with <FIG>.

<FIG> is an illustration of a state after ironing of the cup member 12a. <FIG> is an illustration of a state after turning. In a preform 12a' for the cup member 12a, there are integrally formed a cylindrical portion 12a1', a bottom portion 12a2', and a short shaft section 12a3' in the forging step S2c (upsetting of <FIG>). After that, the track grooves <NUM> and the cylindrical surface <NUM> are formed by ironing in the ironing step S3c (<FIG>) so that the inner periphery of the cylindrical portion 12a1' is finished as illustrated in <FIG>. After that, in the turning step S4c, the outer peripheral surface, the boot mounting groove <NUM>, the snap ring groove <NUM>, and the like of the cup member 12a as well as the joining end surface <NUM> of the short shaft section 12a3 and the outer diameter B and the inner diameter D of the joining end surface <NUM> are formed by turning as illustrated in <FIG>.

<FIG> are illustrations of states of the shaft member 13a in the respective processing steps. That is, <FIG> is an illustration of a billet 13a" obtained by cutting a bar material. <FIG> is an illustration of a preform 13a' obtained by forging the billet 13a" into a rough shape by upset forging. <FIG> is an illustration of the shaft member 13a after turning and spline processing.

The billet 13a" illustrated in <FIG> is formed in the bar material cutting step S1s. The preform 13a' is formed by increasing, if necessary, the shaft diameter of the billet 13a" in a predetermined range and forming a recess <NUM> at a joining-side end portion (end portion on the cup member 12a side) by upset forging as illustrated in <FIG>. As described above, <FIG> is an illustration of an example of forming the recess <NUM> during forging and forming the inner diameter portion <NUM> in the opening end portion by turning. However, the recess <NUM> may maintain a forged surface. In that case, the recess <NUM> and the inner diameter portion <NUM> are integrally formed, and hence may not be clearly distinguished from each other.

After that, in the turning step S2s, the outer diameter of the shaft member 13a, the bearing mounting surface <NUM>, the snap ring groove <NUM>, an inner diameter portion <NUM> (inner diameter E), the joining end surface <NUM>, and the outer diameter B thereof are formed by turning, as illustrated in <FIG>. Further, in the spline processing step S3s, the spline shaft Sp is processed at the end portion on the opposite side to the recess <NUM> by rolling or press forming.

The outer diameter B of the joining end surface <NUM> of the cup member 12a illustrated in <FIG> is set to an equal dimension for one joint size. Further, in the shaft member 13a illustrated in <FIG>, which is used for a long stem shaft type, the outer diameter B of the joining end surface <NUM> located at the end portion on the cup member 12a side is set to an equal dimension to the outer diameter B of the joining end surface <NUM> of the cup member 12a irrespective of the shaft diameter and the outer peripheral shape. Still further, the joining end surface <NUM> of the shaft member 13a is located at the position on the cup member 12a side with respect to the bearing mounting surface <NUM>.

Through the setting of dimensions as described above, the outer joint member <NUM> compatible with various vehicle types can be manufactured in such a manner that, while the cup member 12a is prepared for common use, only the shaft member 13a is manufactured to have a variety of shaft diameters, lengths, and outer peripheral shapes depending on vehicle types, and both the members 12a and 13a are welded to each other. Details of the preparation of the cup member 12a for common use are described later.

Next, welding of the cup member 12a and the shaft member 13a is described with reference to <FIG> and <FIG>. <FIG> is a schematic elevation view of a welding apparatus for illustrating a state before welding, and <FIG> is a schematic plan view of the welding apparatus for illustrating a state during welding.

As illustrated in <FIG>, a welding apparatus <NUM> mainly comprises an electron gun <NUM>, a rotation device <NUM>, a chuck <NUM>, a center <NUM>, a tailstock <NUM>, workpiece supports <NUM>, a center <NUM>, a case <NUM>, and a vacuum pump <NUM>.

The cup member 12a and the shaft member 13a being workpieces are placed on the workpiece supports <NUM> arranged inside the welding apparatus <NUM>. The chuck <NUM> and the centering jig <NUM> arranged at one end of the welding apparatus <NUM> are coupled to the rotation device <NUM>. The chuck <NUM> grips the cup member 12a to rotate the cup member 12a by the rotation device <NUM> under a state in which the center <NUM> has centered the cup member 12a. The center <NUM> is integrally mounted to the tailstock <NUM> arranged at another end of the welding apparatus <NUM>. Both the center <NUM> and the tailstock <NUM> are configured to reciprocate in the axial direction (lateral direction of <FIG>).

A center hole of the shaft member 13a is set on the center <NUM> so that the shaft member 13a is centered. The vacuum pump <NUM> is connected to the case <NUM> of the welding apparatus <NUM>. A "sealed space" herein refers to a space <NUM> defined by the case <NUM>. The cup member 12a and the shaft member 13a are entirely received in the sealed space <NUM>. The electron gun <NUM> is arranged at a position corresponding to the joining end surfaces <NUM> and <NUM> of the cup member 12a and the shaft member 13a. The electron gun <NUM> is configured to be approachable to and separable from the workpieces.

The operation of the welding apparatus <NUM> constructed as described above and the welding method are described below.

The cup member 12a and the shaft member 13a being workpieces are stocked at a place different from the place of the welding apparatus <NUM>. The respective workpieces are taken out by, for example, a robot, are conveyed into the case <NUM> of the welding apparatus <NUM> opened to the air as illustrated in <FIG>, and are set at predetermined positions of the workpiece supports <NUM>. At this time, the center <NUM> and the tailstock <NUM> are retreated to the right side of <FIG>, and hence a gap is formed between the joining end surfaces <NUM> and <NUM> of the cup member 12a and the shaft member 13a.

After that, a door (not shown) of the case <NUM> is closed, and the vacuum pump <NUM> is activated to reduce the pressure in the sealed space <NUM> defined in the case <NUM>. Thus, the pressures in the recessed portion 50b of the cup member 12a and the recessed portions <NUM> and <NUM> of the shaft member 13a are reduced as well.

When the pressure in the sealed space <NUM> is reduced to a predetermined pressure, the center <NUM> and the tailstock <NUM> are advanced to the left side as illustrated in <FIG> to eliminate the gap between the joining end surfaces <NUM> and <NUM> of the cup member 12a and the shaft member 13a. Thus, the cup member 12a is centered by the center <NUM> and fixed by the chuck <NUM>, whereas the shaft member 13a is centered and supported by the center <NUM>. After that, the workpiece supports <NUM> are moved away from the workpieces (12a and 13a). At this time, the distance between the workpiece supports <NUM> and the workpieces (12a and 13a) may be infinitesimal, and hence illustration of this distance is omitted from <FIG>. As a matter of course, the welding apparatus <NUM> may have such a structure that the workpiece supports <NUM> are retreated downward greatly.

Although illustration is omitted, the electron gun <NUM> is then caused to approach the workpieces (12a and 13a) up to a predetermined position, and the workpieces (12a and 13a) 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 <NUM> is caused to approach the workpieces (12a and 13a) so as to increase the spot diameter. Through the pre-heating, the cooling rate at the welded portion after welding is reduced, thereby being capable of preventing a quenching crack. When a predetermined pre-heating time has elapsed, the electron gun <NUM> is retreated to a predetermined position, and radiates the electron beam from the outer side of the workpieces (12a and 13a) in the radial direction to start welding. When the welding is finished, the electron gun <NUM> is retreated, and the rotation of the workpieces (12a and 13a) is stopped.

Although illustration is omitted, the sealed space <NUM> is then opened to the air. Then, the center <NUM> and the tailstock <NUM> are retreated to the right side in the drawing sheet and the chuck <NUM> is opened under a state in which the workpiece supports <NUM> are raised to support the workpieces. After that, for example, the robot grips the workpieces (12a and 13a), takes the workpieces out of the welding apparatus <NUM>, and places the workpieces into alignment on a cooling stocker. In this embodiment, the cup member 12a and the shaft member 13a are entirely received in the sealed space <NUM>, and hence the configuration of the sealed space <NUM> defined in the case <NUM> can be simplified.

Specific conditions for welding are exemplified below. The cup member 12a having a carbon content of from <NUM>% to <NUM>% and the shaft member 13a having a carbon content of <NUM>% to <NUM>% were used and welded to each other in the welding apparatus <NUM> under the condition that the pressure in the sealed space <NUM> defined in the case <NUM> was set to <NUM>. <NUM> Pa or less. In order to prevent rapid cooling after the welding to suppress excessive increase in hardness of the welded portion, a periphery including the joining end surfaces <NUM> and <NUM> of the cup member 12a and the shaft member 13a were soaked by pre-heating with the electron beam to have a temperature of from <NUM> to <NUM>, and then electron beam welding was performed. As a result, the pre-heating time was able to be reduced to approximately one-half or less as compared to the case where the recess is not formed in the joining end surface, and a favorable welded portion satisfying the required strength was able to be obtained.

As a result, a welded portion having a projecting height from the welded surface (<NUM> 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 <NUM> HV to <NUM> HV, thereby being capable of attaining high welding strength and stable welding state and quality. Still further, welding was performed under the condition that the pressure in the sealed space <NUM> defined in the welding apparatus <NUM> was set to an atmospheric pressure or less, thereby being capable of suppressing the change in pressure in a 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. For example, a ventilation hole communicating with an inside of the cup member 12a and with the recess <NUM> may be formed, and the space inside the cup member 12a may be drawn to vacuum to the pressure of <NUM> Pa, and thereafter the joining surfaces may be brought into abutment against each other for welding.

Next, the ultrasonic flaw detection step is described with reference to <FIG>.

Herein, <FIG> and <FIG> are a front view and a plan view, respectively, of an ultrasonic flaw-detection apparatus having a welded outer joint member mounted thereto. <FIG> corresponds to an illustration as viewed from the direction of the arrow VIII-VIII of <FIG>. <FIG> and <FIG> are a front view and a plan view, respectively, of the ultrasonic flaw-detection apparatus during the ultrasonic flaw detection. <FIG> corresponds to an illustration as viewed from the direction of the arrow X-X of <FIG>.

As illustrated in <FIG> and <FIG>, an ultrasonic flaw-detection apparatus <NUM> mainly comprises a base <NUM>, a water bath <NUM>, a workpiece support <NUM>, a workpiece holding member <NUM>, a rotary drive device <NUM>, a pressing device <NUM>, and a drive positioning device <NUM> (see <FIG>). The water bath <NUM> is mounted at the center of the base <NUM>. The rotary drive device <NUM> is configured to rotate an intermediate product <NUM>' (hereinafter also referred to as "workpiece <NUM>'") of the outer joint member <NUM>. The pressing device <NUM> is configured to press an axial end of the workpiece <NUM>'. The drive positioning device <NUM> is configured to drive and position a probe.

The workpiece support <NUM> comprises support rollers <NUM> and <NUM> configured to allow the workpiece <NUM>' to be placed thereon in a freely rotatable manner. The support rollers <NUM> are arranged at a position close to the welded portion. The support rollers <NUM> are arranged near a center portion of the shaft section <NUM>. As is apparent from <FIG>, the support rollers <NUM> and <NUM> are constructed by pairs of rollers provided on both sides in the axial line of the shaft section <NUM> so that the shaft section <NUM> of the workpiece <NUM>' can be stably supported. The support rollers <NUM> and <NUM> are capable of adjusting the placement position of the workpiece <NUM>' in the axial direction (lateral direction of <FIG>) and the radial direction (vertical direction of <FIG>) in consideration of a joint size, dimensions, and weight balance of the workpiece <NUM>'.

Further, the workpiece holding member <NUM> is mounted to the workpiece support <NUM> at a position displaced in a plane of <FIG> from an axial line of the workpiece <NUM>'. The workpiece holding member <NUM> comprises a lever <NUM>, and a workpiece holding roller <NUM> is arranged at an end portion of the lever <NUM>. The lever <NUM> is pivotable in the plane of <FIG>, and is movable in the vertical direction of <FIG>.

The workpiece support <NUM> is mounted to a support <NUM> through intermediation of a linear-motion bearing <NUM> comprising rails <NUM> and linear guides <NUM>, and is movable in the axial direction (lateral direction of <FIG> and <FIG>). The support <NUM> is mounted to the base <NUM>. The workpiece support <NUM> can be driven to be positioned at a desired position by an actuator (not shown) arranged on an outside of the water bath <NUM> through intermediation of a rod <NUM> coupled to an end portion (left end portion of <FIG> and <FIG>).

The rotary drive device <NUM> comprises a rotary shaft <NUM> having a rotary disc <NUM> mounted thereto, and this rotary shaft <NUM> is driven to rotate by a motor (not shown) arranged on the outside of the water bath <NUM>.

A mounting base <NUM> is arranged on an upper side of the ultrasonic flaw-detection apparatus <NUM>. A base plate <NUM> for the pressing device <NUM> is mounted to the mounting base <NUM> through intermediation of a linear-motion bearing <NUM> comprising a rail <NUM> and a linear guide <NUM> so that the base plate <NUM> of the pressing device <NUM> is movable in the axial direction (lateral direction of <FIG> and <FIG>). A rod <NUM> of a pneumatic cylinder <NUM> is coupled to an end portion of the base plate <NUM> so that the base plate <NUM> is driven, that is, axially moved by the pneumatic cylinder <NUM>. The pressing device <NUM> is held in abutment against the axial end of the shaft section <NUM> of the workpiece <NUM>' through a free bearing <NUM>.

As viewed in the plane of <FIG>, the drive device <NUM> for a probe is arranged at a position displaced in the axial line of the workpiece <NUM>'. This drive device <NUM> comprises actuators for the X-axis direction and the Y-axis direction so that a probe <NUM> is driven to be positioned in the X-axis direction and the Y-axis direction. An actuator <NUM> for the X-axis direction and an actuator <NUM> for the Y-axis direction are each an electric ball-screw type (ROBO cylinder), which is capable of performing positioning with high accuracy. The reference symbol <NUM> denotes a rail for a linear-motion bearing. The drive device <NUM> is arranged on the outside of the water bath <NUM>, and the probe <NUM> and a holder <NUM> therefor are arranged in the water bath <NUM>.

Next, the operation of the ultrasonic flaw-detection apparatus <NUM> having the above-mentioned configuration and the ultrasonic flaw detection step S6k are described below.

First, the workpiece <NUM>' after welding is placed on the workpiece support <NUM> by a loader (not shown) (see <FIG> and <FIG>). At this time, the workpiece support <NUM> is located at an appropriate interval from the rotary drive device <NUM> in the axial direction of the workpiece <NUM>', and the workpiece holding member <NUM> raises and pivots the lever <NUM> thereof so as to be substantially parallel to the axial line of the workpiece <NUM>'. Further, the pressing device <NUM> and the drive device <NUM> for a probe wait at retreated positions.

After that, the lever <NUM> of the workpiece holding member <NUM> is pivoted so as to be substantially perpendicular to the axial line of the workpiece <NUM>', and then lowered to hold the workpiece <NUM>' from above (see <FIG>). Then, water is supplied to the water bath <NUM>. As described above, the ultrasonic flaw-detection apparatus <NUM> has the configuration of performing flaw detection under water, and hence ultrasonic waves are satisfactorily propagated. Thus, inspection can be performed with high accuracy.

Next, as illustrated in <FIG> and <FIG>, the pneumatic cylinder <NUM> is driven to cause the pressing device <NUM> to be advanced and pressed against the axial end of the workpiece <NUM>', thereby pressing the opening rim of the cup section <NUM> of the workpiece <NUM>' against the rotary disc <NUM> of the rotary drive device <NUM>. In conjunction with the advance of the pressing device <NUM>, the workpiece support <NUM> is also moved toward the rotary drive device <NUM>. Thus, the workpiece <NUM>' is positioned in the axial direction and the radial direction. In this state, the motor (not shown) of the rotary drive device <NUM> is activated, thereby rotating the workpiece <NUM>'.

As illustrated in <FIG> with the outlined arrow, the drive device <NUM> is moved in the X-axis direction, and then moved in the Y-axis direction, thereby positioning the probe <NUM> at a flaw detection position. The probe <NUM> in this state is indicated by the broken line in <FIG>. Then, the ultrasonic flaw detection is performed. After the completion of the ultrasonic flaw detection, water is drained from the water bath <NUM>, and the workpiece <NUM>' is delivered from the ultrasonic flaw-detection apparatus <NUM> by the loader (not shown). In such a manner, the ultrasonic flaw detection is sequentially repeated on the workpiece <NUM>'.

In order to reduce the cycle time of the ultrasonic flaw detection, it is desired that time-consuming supply and drainage of water be performed simultaneously with 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 are described with reference to <FIG>, and <FIG>. All of <FIG>, and <FIG> are views as viewed from the arrow XII-XII of <FIG>. <FIG> is an illustration of a non-defective welded product. <FIG> is an illustration of a defective welded product. <FIG> is a view for illustrating findings in the course of development.

The probe <NUM> is positioned at a flaw detection position away from the welded portion <NUM> by a predetermined distance. The flaw detection position is preset for each joint size. A transmission pulse G from the probe <NUM> is caused to obliquely enter from a surface of the workpiece <NUM>'. A reflected echo having been received is displayed as waveforms, and the waveforms may be observed to determine a presence or absence of defectiveness (angle beam flaw detection method). The reference symbol θ1 denotes an incident angle, and the reference symbol θ2 denotes a refraction angle. In the case of the embodiment, the incident angle θ1 is about <NUM>°, and the refraction angle θ2 is about <NUM>°.

Herein, a presence or absence of the penetration defectiveness is mainly detected through detection of a position of a back bead. That is, workpieces having a penetration depth equal to or larger than a determination reference Wmin to reach a radially inner side are determined as non-defective welded products, and workpieces having a penetration depth smaller than the determination reference Wmin to terminate on a radially outer side are determined as defective welded products. In the illustrated example, the inner diameter portion <NUM> of the recess <NUM> formed in the joining end surface <NUM> is matched with the determination reference Wmin. The reference symbol E denotes an inner diameter of (the inner diameter portion <NUM> of) the recess <NUM>, and also denotes an inner diameter of the joining end surface <NUM>. The reference symbol Wa denotes a target penetration depth. Incidentally, after the welding, the welded portion <NUM> is formed on the radially outer side of the recess <NUM>. As a result, a closed cavity is formed on the radially inner side of the welded portion <NUM>. Thus, a back bead <NUM> cannot be visually confirmed from outside.

During the ultrasonic flaw detection, the workpiece <NUM>' is driven by the rotary drive device <NUM> to rotate. The probe <NUM> positioned at the flaw detection position away from the welded portion <NUM> by the predetermined distance collects data of the entire periphery of the workpiece <NUM>'. In consideration of tolerance for displacement of the welding position, at the above-mentioned flaw detection position, first, data of a single rotation (<NUM>°) of the workpiece <NUM>' is collected. Then, the probe <NUM> is sequentially shifted in the axial direction at a minute pitch (for example, <NUM>) 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 determination reference Wmin.

As already described above, in the joining end surface <NUM> of the cup member 12a, there is formed the protruding surface 50a which protrudes toward the radially inner side with respect to the inner diameter E of the joining end surface <NUM> of the shaft member 13a. With the above-mentioned shape, the following advantages in the ultrasonic flaw detection can be obtained.

For easy understanding of the above-mentioned advantages, description is preferentially made of findings in the course of development, that is, the case in which an inner diameter D' of the joining end surface <NUM> of the cup member 12a is set to an equal dimension to the inner diameter E of the joining end surface <NUM> of the shaft member 13a as illustrated in <FIG>. In this case, the penetration depth is equal to or larger than the determination reference Wmin to reach the radially inner side, and hence the workpiece is to be determined as a non-defective welded product. However, when the transmission pulse G enters from the probe <NUM>, due to the boundary surface of the back bead <NUM>, which is perpendicular to the transmission pulse G, a reflected echo R reflected by this boundary surface is received by the probe <NUM>. Although reflected echoes from the back bead <NUM> are scattered, the reflected echo R has a large echo height exceeding the threshold of the reflected echo for the non-defective/defective determination. Thus, determination that the welded product is defective is made. For this reason, it was proved that the determination as to whether the welded product was non-defective or defective was difficult.

Thus, in the embodiment, a measure is taken by forming the protruding surface 50a, which protrudes toward the radially inner side with respect to the inner diameter E of the joining end surface <NUM> of the shaft member 13a, in the joining end surface <NUM> of the cup member 12a.

As illustrated in <FIG>, the non-defective welded product has sufficient penetration. In this case, the transmission pulse G from the probe <NUM> enters the cup section <NUM> through the back bead <NUM> having reached the radially inner side beyond the determination reference Wmin, and travels straight as it is. Alternatively, the transmission pulse G travels to the cup section <NUM> side by being reflected due to the inner diameter D of the cup section <NUM>. Therefore, the probe <NUM> does not receive a reflected echo. That is, even when the transmission pulse G enters the back bead <NUM>, the boundary surface of the back bead <NUM>, which is perpendicular to the transmission pulse G, does not exist. Therefore, although a slightly-scattered reflected echo is generated, the reflected echo which may cause the detection error is not generated. Thus, the echo height of the reflected echo received by the probe <NUM> is equal to or less than the threshold, and hence determination that the welded product is non-defective is made.

As described above, when the protruding surface 50a is formed on the joining end surface <NUM> of the cup member 12a, the echo height of the reflected echo becomes lower. Thus, the accuracy in the inspection can be enhanced.

In the case of the defective welded product, as illustrated in <FIG>, a distal end of the bead <NUM> does not reach the determination reference Wmin due to the defective penetration. Thus, the transmission pulse G is reflected by the joining end surface <NUM> and a chamfered portion 51a, and the scattered reflected echo R is received by the probe <NUM>. The reflected echo R exceeds the threshold of the reflected echo for the non-defective/defective determination, and hence determination that the welded product is defective is made.

As described above, the protruding surface 50a is formed on the joining end surface <NUM>, and hence the echo heights of the reflected echoes can be clearly discriminated from each other. Thus, the determination as to whether the welded product is non-defective or defective can be made with high accuracy.

Dimensions of the protruding surface 50a are set so that a relationship of S≥Q is established, where S [S=(E-D) /<NUM>] is a width of the protruding surface 50a in a radial direction, and where Q is a height of the back bead <NUM> from the inner diameter E of the joining end surface <NUM> as illustrated in <FIG>. When this relationship is satisfied, the heights of the reflected echoes can be clearly discriminated from each other. Thus, the determination as to whether the welded product is non-defective or defective can be made with high accuracy. As long as the relationship of S≥Q is maintained, the dimensions of the protruding surface 50a may be set as appropriate. The inner diameter E of the joining end surface <NUM> is also an inner diameter (of the inner diameter portion <NUM>) of the recess <NUM>.

In the ultrasonic flaw-detection apparatus <NUM>, the operation of loading the workpiece <NUM>', the supply and drainage of water, the ultrasonic flaw detection, and the operation of unloading the workpiece can be performed in conjunction with each other, and the ultrasonic flaw detection 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, in the ultrasonic flaw detection, with the base configuration in which the outer diameter B of the joining end surface <NUM> of the cup member 12a is set to an equal dimension for each joint size, setup and replacement operations with respect to the outer joint members <NUM> having the different product numbers are reduced. 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 protruding surface 50a is formed on the joining end surface <NUM>, the echo heights of the reflected echoes can clearly 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.

Next, 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 13a of the long stem type illustrated in <FIG>.

A shaft member 13b illustrated in <FIG> is used as a general stem type on the inboard side. The shaft member 13b has the joining end surface <NUM> to be brought into abutment against the joining end surface <NUM> (see <FIG>) of the bottom portion 12a2 (short shaft section 12a3) of the cup member 12a. The outer diameter B and the inner diameter E of the joining end surface <NUM> are set to the equal dimensions to the outer diameter B and the inner diameter E of the joining end surface <NUM> of the shaft member 13a of the long stem type illustrated in <FIG>.

Also in this case, the inner diameter D of the joining end surface <NUM> of the cup member 12a is set smaller than the inner diameter E of the joining end surface <NUM> of the shaft member 13b. As a result, on the joining end surface <NUM> of the cup member 12a, the protruding surface 50a protruding to the radially inner side with respect to the inner diameter E of the joining end surface <NUM> of the shaft member 13b is formed. The joining end surfaces <NUM> and <NUM> having such shape are brought into abutment against each other to be welded so that the cup member 12a and the shaft member 13b are joined to each other.

The shaft member 13b is used as the general stem type on the inboard side. Accordingly, the shaft member 13b comprises a shaft section with a small length, and a sliding bearing surface <NUM> formed on an axial center portion thereof, and a plurality of oil grooves <NUM> are formed in the sliding bearing surface <NUM>. The spline shaft Sp and the snap ring groove <NUM> are formed in an end portion on the side opposite to the cup member 12a 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 outer diameter B of the joining end surface <NUM> of the shaft member 13a or 13b is set to an equal dimension.

The outer diameter B of the joining end surface <NUM> of the cup member 12a and the joining end surface <NUM> of the shaft member 13a or 13b 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 12a and the shaft member 13a or 13b can be assigned with a product number for management. Even when standardizing product types of the cup member 12a, various types of the outer joint members <NUM> satisfying requirements can be produced quickly through combination of the cup member 12a and the shaft member 13a or 13b having a variety of specifications of the shaft section for each vehicle type. Therefore, standardization of a product type of the cup member 12a 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.

An example of standardization of a product type of the cup member is illustrated in <FIG>.

As illustrated in <FIG>, the cup member is prepared for common use for one joint size, and is assigned with, for example, a product number C001 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 S001, <NUM>, or S(n) for management. For example, when the cup member assigned with the product number C001 and the shaft member assigned with the product number <NUM> are combined and welded to each other, the outer joint member assigned with a product number A001 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.

Next, a second embodiment of the outer joint member is described with reference to <FIG> and <FIG>.

<FIG> is a partial sectional front view of the outer joint member. <FIG> is an enlarged view of a portion "b" of <FIG> is a view for illustrating a state before welding in <FIG>. <FIG> is a vertical sectional view for illustrating the cup member before welding. <FIG> correspond to <FIG>. As is clear from comparison of <FIG> and <FIG>, the second embodiment is different from the above-mentioned first embodiment in the form of the radially inner side of the joining end surface of the cup member. Other configurations are the same as those in the first embodiment. Thus, parts that have the same function as those of the first embodiment are denoted by the same reference symbols except for the subscripts, and redundant description is omitted. As a matter of course, as illustrated in <FIG> with the broken parallel oblique lines, the second embodiment is also the same as the first embodiment in that an assumed range S<NUM> of the center segregation is confined within the radially inner side to prevent the interference with the welded portion <NUM>.

As illustrated in <FIG> and <FIG>, a joining end surface <NUM><NUM> formed on a short shaft section 12a3<NUM> of a cup member 12a<NUM> is annular, and a projecting portion 50b<NUM> is formed on the radially inner side. In this case, a diameter D<NUM> of the annular joining end surface <NUM><NUM> on the radially inner side corresponds to the inner diameter D of the joining end surface <NUM> of the cup member 12a of the first embodiment of the outer joint member. A portion of the joining end surface <NUM><NUM> on the radially inner side protrudes toward the radially inner side with respect to the inner diameter E of the joining end surface <NUM> of the shaft member 13a. This protruding portion is referred to as a protruding surface 50a<NUM> as in the first embodiment. As in the first embodiment, the shaft member 13a has the recess <NUM> on the radially inner side of the joining end surface <NUM>. In order to prevent hindrance in abutment of the joining end surfaces <NUM><NUM> and <NUM>, the height of the projecting portion 50b<NUM> of the cup member 12a<NUM>, that is, a distance from the joining end surface <NUM><NUM> to the end surface of the projecting portion 50b<NUM> is set smaller than the depth of the recess <NUM>.

The cup member 12a<NUM> can be formed by turning an end surface of the short shaft section 12a3' of the preform 12a' (<FIG>) for the cup member of the first embodiment after ironing at only a portion of the joining end surface <NUM><NUM> on the radially outer side. Thus, the time for the turning can be reduced, with good material yield. As a matter of course, the projecting portion 50b<NUM> on the radially inner side can also be subjected to turning. However, the number of steps can be reduced by maintaining the forged surface as it is.

Other configurations and operations, that is, 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, the standardization of the product type, the configuration of the outer joint member, and the like as described above in relation to the first embodiment of the outer joint member are also applicable to the second embodiment of the outer joint member.

<FIG> is an illustration of a second embodiment of a manufacturing method of the outer joint member.

In the second embodiment, the heat treatment step for the cup member, which is involved in the heat treatment step S7 in <FIG>, is provided before the welding step S6 and named "heat treatment step S5c", to thereby prepare the cup member as a finished product. Other than this point, the matters described above in relation to the first embodiment of the manufacturing method, that is, 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, the standardization of the product type, the configuration of the outer joint member, and the like are also applicable to the second embodiment.

As illustrated in <FIG>, the cup member 12a has a shape extending from the joining end surface <NUM> to the large-diameter cylindrical portion 12a1 via the bottom portion 12a2, and the portions to be subjected to heat treatment that involves quenching and tempering are the track grooves <NUM> and the cylindrical inner peripheral surface <NUM> located at the inner periphery of the cylindrical portion 12a1. Therefore, the cup member 12a generally has no risk of thermal effect on the heat-treated portion during the welding. For this reason, the cup member 12a is subjected to heat treatment before the welding to be prepared as a finished product. Such manufacturing steps are suitable in practical use.

The cup member 12a is subjected to heat treatment for preparing the cup member 12a 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 12a remarkably reduces the cost and alleviates the burden of production management. Further, the cup member 12a can be manufactured solely until the cup member 12a 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.

With regard to <FIG> for illustrating the example of standardization of the product type of the cup member described above in relation to the first embodiment of the manufacturing method, only the product number of the cup member in <FIG> 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 of the manufacturing method. Therefore, description thereof is omitted herein.

<FIG> is an illustration of a third embodiment of a manufacturing method of the outer joint member.

In the third embodiment, the heat treatment steps for the cup section and the shaft section, which are involved in the heat treatment step S7 in <FIG> described above in relation to the first embodiment, and the grinding step S8 for the shaft section in <FIG> are provided before the welding step S6 in the sequence and named "heat treatment step S5c for cup member", "heat treatment step S4s for shaft member", and "grinding step S5s". Thus, both the cup member and the shaft member are prepared as finished products. Other matters, that is, 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, the standardization of the product type, the configuration of the outer joint member, and the like described in relation to the first embodiment are also applicable to the third embodiment.

After the spline processing step S3s, a hardened layer having a hardness of approximately from <NUM> HRC to <NUM> HRC is formed in a predetermined range of the outer peripheral surface of the shaft member by induction quenching in the heat treatment step S4s. Heat treatment is not performed on a predetermined portion in the axial direction, which includes the joining end surface <NUM>. 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 S4s, the shaft member is transferred to the grinding step S5s so that the bearing mounting surface <NUM> 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 the third 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 the third 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 the case of the third embodiment of the manufacturing method, with regard to <FIG> for illustrating the example of standardization of the product type of the cup member described above in relation to the first embodiment, the product numbers of the cup member and the shaft member in <FIG> are changed to the product numbers indicating finished products. The outer joint member is the same as that of the first embodiment of the manufacturing method. Therefore, description thereof is omitted herein. Note that, the cup member and the shaft member to be prepared as finished products are not limited to the cup member and the shaft member subjected to finishing such as the above-mentioned grinding after heat treatment or cutting after quenching, and 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 with regard to 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. 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, a third embodiment of the outer joint member is described with reference to <FIG> and <FIG>.

Herein, parts that have the same function as those of the first embodiment of the outer joint member are denoted by the same reference symbols, and only main points are described.

A plunging type constant velocity universal joint <NUM><NUM> illustrated in <FIG> is a tripod type constant velocity universal joint (TJ), and comprises an outer joint member <NUM><NUM>, an inner joint member <NUM><NUM>, and rollers <NUM> serving as torque transmitting elements. The outer joint member <NUM><NUM> comprises a cup section <NUM><NUM> and the long stem section <NUM> that extends from a bottom of the cup section <NUM><NUM> in the axial direction. The inner joint member <NUM><NUM> comprises a tripod member <NUM> comprising three equiangular leg shafts <NUM> configured to support the rollers <NUM> in a freely rotatable manner, and is housed along an inner periphery of the cup section <NUM><NUM> of the outer joint member <NUM><NUM>. The rollers <NUM> are arranged between the outer joint member <NUM><NUM> and the inner joint member <NUM><NUM>, and configured to transmit torque therebetween.

Similarly to the first embodiment of the outer joint member, the inner ring of the support bearing <NUM> is fixed to the outer peripheral surface of the long stem section <NUM>, and the outer ring of the support bearing <NUM> is fixed to the transmission case with the bracket (not shown). The outer joint member <NUM><NUM> is supported by the support bearing <NUM> in a freely rotatable manner, and thus the vibration of the outer joint member <NUM><NUM> during driving or the like is prevented as much as possible.

As illustrated in <FIG>, the outer joint member <NUM><NUM> comprises a cup section <NUM><NUM> and the long stem section <NUM>. The cup section <NUM><NUM> has a bottomed cylindrical shape that is opened at one end, and has track grooves <NUM><NUM>, on which the rollers <NUM> are caused to roll, formed at three equiangular positions on an inner peripheral surface <NUM><NUM>. The long stem section <NUM> extends from the bottom of the cup section <NUM><NUM> in the axial direction and comprises the spline shaft Sp serving as the torque transmitting coupling portion formed at the outer periphery of the end portion on the side opposite to the cup section <NUM><NUM>.

The outer joint member <NUM><NUM> is formed by welding the cup member 12a<NUM> serving as the cup section <NUM><NUM> and the shaft member 13a serving as the long stem section <NUM> to each other.

The cup member 12a<NUM> is an integrally-formed product having a cylindrical portion 12a1<NUM> and a bottom portion 12a2<NUM>, and has track grooves <NUM> and an inner peripheral surface <NUM> formed at the inner periphery of the cylindrical portion 12a1<NUM>. A short shaft section 12a3<NUM> is formed at the bottom portion 12a2<NUM>. A boot mounting groove <NUM> is formed at an outer periphery of the cup member 12a<NUM> on the opening side.

In the shaft member 13a, the bearing mounting surface <NUM> and the snap ring groove <NUM> are formed at the outer periphery on the cup member 12a<NUM> side, and the spline shaft Sp is formed at an end portion on the side opposite to the cup member 12a<NUM>.

A joining end surface <NUM><NUM> formed at the short shaft section 12a3<NUM> of the cup member 12a<NUM> and the joining end surface <NUM> formed at the end portion of the shaft member 13a on the cup member 12a<NUM> side are brought into abutment against each other, and are welded to each other by radiating an electron beam from the radially outer side. As is well known, the welded portion <NUM> comprises metal that is molten and solidified during welding, that is, the molten metal, and the heat-affected portion in the periphery thereof.

Similarly to the first embodiment of the outer joint member, the outer diameters B of the joining end surface <NUM><NUM> and the joining end surface <NUM> are set to equal dimensions for each joint size. The welded portion <NUM> is formed on the cup member 12a<NUM> side with respect to the bearing mounting surface <NUM> of the shaft member 13a, and hence the bearing mounting surface <NUM> 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 matters described in relation to the first and second embodiments of the outer joint member and the first to third embodiments of the manufacturing method are also applicable to the third embodiment of the outer joint member.

Herein, with regard to setting of the outer diameters B of the joining end surface <NUM>, <NUM><NUM>, or <NUM><NUM> of the cup member 12a, 12a<NUM>, or 12a<NUM> and the protruding surfaces 50a and 50a<NUM> to the equal dimension for each joint size, the cup member 12a, 12a<NUM>, or 12a<NUM> 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 encompasses 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 of the above-mentioned joining end surfaces of the cup members are set to equal dimensions and that the protruding surfaces are formed into the same shape.

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 after heat treatment 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 of the above-mentioned joining end surfaces of the cup members are set to equal dimensions and that the protruding surfaces are formed into the same shape.

Further, setting the outer diameter B of the joining end surface <NUM>, <NUM><NUM>, or <NUM><NUM> of the cup member 12a, 12a<NUM>, or 12a<NUM> to an equal dimension for each joint size, or forming the protruding surfaces 50a and 50a<NUM> into the same shape for each joint size may be applied also to different types of constant velocity universal joints.

For example, 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 protruding surface into the same shape on the inboard side are also encompassed. Further, setting outer diameters of the joining end surfaces of a Rzeppa type constant velocity universal joint and an undercut-free constant velocity universal joint to equal dimensions, and forming the protruding surface into the same shape on the outboard side are also encompassed. Further, 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 protruding surface into the same shape on the inboard side and the outboard side are also possible.

At least one of the cup member 12a, 12a<NUM>, or 12a<NUM> and the shaft member 13a or 13b 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 welding. Thus, this configuration is suited to the cup members 12a, 12a<NUM>, and 12a<NUM> and the shaft members 13a and 13b 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 welding after heat treatment. The intermediate component is assigned with a product number for management.

Further, at least one of the cup member 12a, 12a<NUM>, or 12a<NUM> and the shaft member 13a or 13b before the welding may be prepared as a finished component subjected to heat treatment. The finished component subjected to heat treatment is a finished component subjected to the heat treatment and the finishing such as grinding after the heat treatment or quenched-steel cutting work. In this case, it is possible to obtain the cup member 12a, 12a<NUM>, or 12a<NUM> prepared as the finished component for common use for each joint size, and the shaft members having a variety of specifications of the shaft section for each vehicle type. Thus, the cup members and the shaft members can each be assigned with a product number for management. Therefore, the cost is significantly reduced through the standardization of a product type of the cup members 12a, 12a<NUM>, and 12a<NUM>, and the burden of production management is significantly alleviated.

Further, the cup members 12a, 12a<NUM>, and 12a<NUM> prepared for common use and the shaft members 13a and 13b having a variety of specifications of the shaft section can be manufactured separately until the cup members and the shaft members 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 members 12a, 12a<NUM>, and 12a<NUM> and the shaft members 13a and 13b 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 members 12a, 12a<NUM>, and 12a<NUM> and the shaft members 13a and 13b assuming a state after completion of heat treatment and before being subjected to the finishing are encompassed.

The effects of the above-mentioned embodiments of the present invention are summarized and described below.

The outer joint member <NUM>, <NUM><NUM>, or <NUM><NUM> of the embodiment is an outer joint member of a constant velocity universal joint, which is manufactured by joining the cup member 12a, 12a<NUM>, or 12a<NUM> and the shaft member 13a or 13b.

The cup member 12a, 12a<NUM>, or 12a<NUM> has a bottomed cylindrical shape that is opened at one end, and comprises the cylindrical portion 12a1, 12a1<NUM>, or 12a1<NUM>, the bottom portion 12a2, 12a2<NUM>, or 12a2<NUM>, and the short shaft portion 12a3, 12a3<NUM>, or 12a3<NUM> protruding from the bottom portion 12a2, 12a2<NUM>, or 12a2<NUM>. The short shaft portion 12a3, 12a3<NUM>, or 12a3<NUM> has a solid shaft shape and comprises the joining end surface <NUM>, <NUM><NUM>, or <NUM><NUM> at an end portion thereof. The shaft member 13a or 13b has a solid shaft shape and comprises the joining end surface <NUM> at one end thereof. The joining end surface <NUM>, <NUM><NUM>, or <NUM><NUM> of the cup member 12a, 12a<NUM>, or 12a<NUM> and the joining end surface <NUM> of the shaft member 13a or 13b are brought into abutment against each other and welded through radiation of a high energy intensity beam from the radially outer side to form the annular welded portion <NUM>. With this, the interference of the center segregation with the welded portion <NUM> is prevented. Through formation of the welded portion <NUM> into an annular shape, the welded portion <NUM> can be arranged on the radially outer side avoiding the center segregation. Thus, the strength and welding quality are improved.

According to the inventive manufacturing method, when the outer joint member <NUM>, <NUM><NUM>, or <NUM><NUM> of a constant velocity universal joint is to be manufactured, the cup member 12a, 12a<NUM>, or 12a<NUM> is formed through forging. The forging comprises: upsetting the billet <NUM> having a columnar shape successively in a plurality of stages; extruding the cylindrical portion 12a1, 22a1<NUM>, or 12a1<NUM> and the short shaft portion 12a3, 12a3<NUM>, or 12a3<NUM>; and ironing the cylindrical portion 12a1, 12a1<NUM>, or 12a1<NUM>. The joining end surface <NUM>, <NUM><NUM>, or <NUM><NUM> of the cup member 12a, 12a<NUM>, or 12a<NUM> and the joining end surface <NUM> of the shaft member 13a or 13b are brought into abutment against each other and welded through radiation of a high energy intensity beam from the radially outer side to form the welded portion <NUM> having an annular shape. Through the upsetting in the plurality of stages, the billet edge can be moved to the radially outer side as much as possible.

In the die <NUM> to be used in the course of the upsetting, an inner diameter is larger than an outer diameter of the billet <NUM> in a first region corresponding to an opening side of the cup member 12a, 12a<NUM>, or 12a<NUM>, and an inner diameter is gradually reduced in a second region corresponding to a bottom side of the cup member 12a, 12a<NUM>, or 12a<NUM>. Then, a plurality of dies gradually increased in inner diameters in the first region are sequentially used. With this, in the course of the upsetting, the billet <NUM> is increased in diameter in the region corresponding to the opening side of the cup member 12a, 12a<NUM>, or 12a<NUM>, and the region corresponding to the bottom side of the cup member 12a, 12a<NUM>, or 12a<NUM> is narrowed. Through the narrowing, a flow of the material toward the radially outer side is prevented, thereby being capable of confining the center segregation of the billet within the radially inner side.

With regard to the second region of the die <NUM>, the gradually reduced diameter is, as a specific example, a recessed arc shape 64A, a taper shape 64B, or a combined shape 64C of the arc and the taper in sectional view.

The extruding comprises the forward extrusion for forming the short shaft portion 12a3, 12a3<NUM>, or 12a3<NUM> and the backward extrusion for forming the cylindrical portion 12a1, 12a1<NUM>, or 12a1<NUM>. At this time, when the second region narrowed in the course of the upsetting is to be subjected to the forward extrusion to form the short shaft portion 12a3, 12a3<NUM>, or 12a3<NUM>, the fiber flow in the axial direction is formed. With this, an increase in diameter (lateral expansion) is suppressed as much as possible, thereby being capable of confining the narrowed center segregation within the center portion.

The outer joint member of a constant velocity universal joint manufactured by the above-mentioned method is improved in strength and welding quality of the welded portion.

The embodiments of the present invention are described above with reference to the attached drawing. However, the present invention is not limited to the embodiments described herein and illustrated in the attached drawings. The present invention can be carried out with various modifications within the range of not departing from the scope of claims.

The case of employing the electron beam welding is described as an example. However, the present invention is applicable not only to the case of the electron beam welding but also to the case of employing laser welding or other welding through use of a high energy intensity beam.

Claim 1:
A method of manufacturing an outer joint member (<NUM>) of a constant velocity universal joint, the method comprising:
joining a cup member (12a); and a shaft member (13a) to form the outer joint member (<NUM>), wherein
the cup member (12a) has a bottomed cylindrical shape that is opened at an end on one side in an axial direction, and comprises a cylindrical portion (12a1), a bottom portion (12a2), and a short shaft portion (12a3) protruding from the bottom portion (12a2) toward the other side in the axial direction, and the short shaft portion (12a3) has a solid shaft shape, and comprises an annular joining end surface at an end portion thereof,
the shaft member (13a) has a solid shaft shape, and comprises a joining end surface at one end thereof, and
the joining end surface (<NUM>) of the cup member (12a) and the joining end surface (<NUM>) of the shaft member (13a) are brought into abutment against each other and welded to form a welded portion having an annular shape, wherein the method comprising:
forming the cup member (12a) by forging and interference of center segregation of the cup member (12a) with the welded portion is prevented for welding, characterized in that the forging comprising:
upsetting a billet (<NUM>) having a columnar shape successively in a plurality of stages;
extruding the cylindrical portion (12a1) and the short shaft portion (12a3); and
ironing the cylindrical portion (12a1),
the welded portion is formed on the cup member (12a) side with respect to a bearing mounting surface (<NUM>) of the shaft member (13a),
the bearing mounting surface (<NUM>) is processed in advance before welding so that post-processing of the bearing mounting surface (<NUM>) after welding can be omitted.