Abstract:
A method whereby magnetic and nonmagnetic materials can be joined together firmly and having their joining areas freed from embrittlement and with a minimum of deformation is disclosed. Applied to the process of fitting a ring of nonmagnetic material into an annular space formed between an inner and an outer member each made of magnetic material, the method includes bringing an inner and an outer peripheral surface of the ring of nonmagnetic material each into a semi-molten state and bringing the inner and outer peripheral surfaces of the ring of nonmagnetic material into pressure contact with the inner and outer members, respectively, to join the inner and outer peripheral surfaces to the inner and outer members, respectively, by interfacial fusion.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of joining together magnetic and nonmagnetic materials, namely a magnetic material such as carbon steel for machine construction and a nonmagnetic material such as stainless steel or aluminum. 
   2. Description of the Prior Art 
   Such a magnetic and a nonmagnetic material are both metals, and for joining such dissimilar metals together, techniques has so far been known including a mechanical joining method, e.g., press fitting or calking, and also brazing, adhesive bonding, spot welding, friction welding and electron-beam welding methods. 
   Of these prior-art techniques, the mechanical joining methods present a problem of deformation during joining and are also hard to ensure sealing. The brazing method offers only a limited bonding strength and, relying on partial heating along a joining line, entails the problem that deformation is produced by the partial heating. The adhesive bonding method gives rise to problems in bonding strength and reliability of joining. In the methods such as spot welding, friction welding and electron-beam welding that require fusion to join, not only is the problem encountered that a brittle intermetallic compound formed at a weld prevents joining with reliability, but also it becomes the problem that depending on temperatures at which the weld is heated and cooled and time durations in which it is then held, respectively, its metallographic structure may be caused to change adversely so that the weld is cracked or becomes brittle. Especially in the electron-beam welding process, the problem of deformation by heating as in the brazing process is left unresolved together with the problem that excess weld metal portions must be cut for removal. 
   BRIEF SUMMARY OF THE INVENTION 
   In view of the foregoing, it is an object of the present invention to provide a method of joining magnetic and nonmagnetic materials together whereby the problems in the prior art mentioned above can be resolved. 
   In order to achieve the object mentioned above, there is provided in accordance with the present invention a method of joining magnetic and nonmagnetic materials together in a process wherein an annular space formed between an inner member and an outer member each made of magnetic material is fitted with a ring of nonmagnetic material, characterized in that the method comprises the steps of: bringing an inner and an outer peripheral surface of the ring of nonmagnetic material each into a semi-molten state; and bringing the inner and outer peripheral surfaces of the ring of nonmagnetic material into pressure contact with the inner and outer members, respectively, to join the inner and outer peripheral surfaces to the inner and outer members, respectively, by interfacial fusion. 
   According to the joining method of the present invention mentioned above whereby a ring of nonmagnetic material in the annular space has its respective mating surfaces with the inner and outer members of magnetic material interfacially fused with them, the magnetic and nonmagnetic materials are prevented from embrittlement in their joining areas and can be joined together firmly. 
   In a specific form of implementation of the joining method mentioned above, the ring of nonmagnetic material is heated to a temperature sufficient to make it semi-molten and the semi-molted ring of nonmagnetic material is then fitted into the annular space under pressure. In an alternative specific implementation of the mentioned above, the ring of nonmagnetic material is fitted under pressure into the annular space and thereafter is heated by high-frequency induction heating to a temperature sufficient to make it semi-molten and is then compressed under pressure. 
   According to such a specific joining method of the invention whereby a ring of nonmagnetic material heated until it is semi-molten is press-fitted into or compressed under pressure in the annular space between the inner and outer members of magnetic material, deformation of these members of magnetic material while they are being joined with the ring of magnetic nonmagnetic material is minimized. 
   In another specific form of implementation of the joining method mentioned above, the ring of nonmagnetic material is fitted under pressure into the annular space and thereafter a rotating body is pressed against an end face of the ring of nonmagnetic material whereby a frictional heat then generated heats the ring of nonmagnetic material to a temperature sufficient to make it semi-molten. 
   According to this specific joining method of the invention whereby a ring of nonmagnetic material is heated by the frictional heat to a temperature sufficient to make it semi-molten in the annular space between the inner and outer members of magnetic material, deformation of these members of magnetic material while they are being joined with the ring of magnetic nonmagnetic material is minimized. Also, the temperature of the ring of nonmagnetic material can be easily controlled by changing rotation number or pressure of the rotation body. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention as well as other manners of its implementation will become more readily apparent, and the invention itself will also be better understood, from the following detailed description when taken with reference to the drawings attached hereto showing certain illustrative forms of implementation of the present invention. In the drawings: 
       FIG. 1  is a cross sectional view illustrating an electromagnetic coupling to which the present invention is being applied; 
       FIGS. 2A to 2C  are a series of cross sectional views illustrating a process of forming an output shaft material in which it is formed from a disc shaped material; 
       FIGS. 3A to 3E  are a series of cross sectional views illustrating another process of forming an output shaft material in which it is formed from a tubular material; 
       FIGS. 4A to 4E  are like views illustrating a process of forming a casing material in which it is formed from a disc shaped material; 
       FIGS. 5A to 5C  are like views illustrating another process of forming a casing material in which it is formed from a tubular material: 
       FIGS. 6A to 6D  are like views illustrating a further process of forming a casing material in which it is formed by spinning a disc shaped material; 
       FIGS. 7A and 7B  are like views illustrating an alternative process of forming a casing material in which it is formed by spinning a perforated disc material; 
       FIG. 8  is a view illustrating a first form of implementation of the joining method according to the present invention; 
       FIG. 9  is a view illustrating a second form of implementation of the joining method according to the present invention; 
       FIG. 10  is a view illustrating a third form of implementation of the joining method according to the present invention; and 
       FIG. 11  is a view illustrating a fourth form of implementation of the joining method according to the present invention. 
   

   DETAILED DESCRIPTION 
   An explanation is first given below in respect of a first form of implementation of the present invention with reference to the Drawing Figures.  FIG. 1  shows an electromagnetic coupling to which the present invention is being applied. In  FIG. 1 , there are shown an input shaft  1  that is connected to an engine (not shown) side, an output shaft  2  for transmitting power to rear wheels, and a main clutch  3  for connecting and disconnecting the input shaft  1  to and from the output shaft  2 . The main clutch  3  comprises inner plates  3   a  whose inner diametrical sides are coupled in spline engagement with the outer periphery of the input shaft  1  and outer plates  3   b  whose outer diametrical sides are coupled in spline engagement with the inner periphery of a casing  2   a  united to the output shaft  2  in a manner to be described later, the inner and outer plates  3   a  and  3   b  being alternately positioned. A fixed plate  4  is fastened to an end of the casing  2   a  and a thrust means  5  has a push plate  6  such that pressing the inner and outer plates  3   a  and  3   b  against the fixed plate  4  with the push plate  6  under a pressure engages the input shaft  1  with the output shaft  2  and removing the pressure or thrust disengages the output shaft  2  from the input shaft  1 . 
   The thrust means  5  comprises the abovementioned push plate  6 , a backing plate  7  disposed behind the push plate  6 , and a thrust generating mechanism  8  for actuating the push plate  6  to push with the backing plate  7  via balls disposed between them. 
   The inner diametrical side of the push plate  6  is coupled in spline engagement with the outer periphery of the input shaft  1 . And, the backing plate  7  with its end face supported by a thrust bearing  16  is supported rotatably relative to a boss section  2   b  of the output shaft  2  and has its inner diametrical side fitted with the outer periphery of the input shaft  1  so that it can be rotated while in sliding contact with the latter. Further, this backing plate  7  is coupled via an electromagnetic clutch (sub-clutch)  9  lying outwards thereof to the casing  2   a  united with the output shaft  2  so that it can engage with and disengage from the casing  2   a  in a direction in which it is rotated. 
   In the electromagnetic clutch  9 , a retaining ring  10  is axially inserted into an annular space formed between the outer periphery of the backing plate  7  and an inner periphery of the casing  2   a  so that it can be axially moved in sliding contact with these peripheries in that space to an extent that it comes into contact with a stop ring  17 . And, between the retaining ring  10  and a rotor section  2   a ′ of the casing  2   a  there are positioned alternately clutch plates  9   a  whose inner diametrical sides are coupled in spline engagement with the outer periphery of the backing plate  7  and friction discs  9   b  whose outer diametrical sides are coupled in spline engagement with the inner periphery of the casing  2   a . And, axially rearwards (at the left hand side as shown) of the rotor section  2   a ′ of the casing  2   a  there is provided a ring-shaped electromagnetic coil  11  for electromagnetically attracting the retaining ring  10  towards the rotor section  2   a ′ of the casing  2   a  to bring the clutch plates  9   a  and the friction discs  9   b  into pressure contact with one another, thereby turning the electromagnetic clutch  9  into its engaged state. 
   The electromagnetic coil  11  is disposed in a coil accommodating chamber  12  formed by a stepped recess formed in the casing  2   a  and an outer periphery of the boss section  2   b  of the output shaft  2  and arranged therein so that it is juxtaposed with the electromagnetic clutch  9  across the rotor section  2   a ′. And, this electromagnetic coil  11  is supported from a covering member  13  which is securely connected to a frame (not shown) and which is fitted over and rotatably coupled to the output shaft  2  via a bearing  18 . 
   Between the rotor section  2   a ′ of the casing  2   a  and a flange section  2   b ′ of the boss section  2   b  of the output shaft  2  there lies a ring of nonmagnetic material  14  that is composed of stainless steel as a nonmagnetic material for preventing a magnetic force on a magnetic loop  15  of the electromagnetic coil  11  from short-circuiting. Thus, the output shaft  2  and the casing  2   a  which are separate members are united together via this ring of nonmagnetic material  14 . While it was customary to form these members by mechanically machining a body formed by cold or hot forging, the present inventors formed such members by drawing or spinning as shown in  FIGS. 2 to 7  with the advantage of an improved process yield, hence reduced material and working costs compared with forming them customarily by both forging and mechanical machining. 
     FIGS. 2A to 2C  show a process of forming an output shaft material  22  in which a plate material  21  made of a disc-shaped steel plate is axially drawn out by drawing successively. 
     FIGS. 3A to 3E  shows a process of forming an output shaft material  22  in which a tubular material  23  made of a steel tube such as an electro-resistance-welded tube is drawn while being reduced in diameter successively by spinning. 
     FIGS. 4A to 4E  shows a process of forming a casing material  25  by axially drawing a plate material  24  made of a disc shaped steel plate in which  FIG. 4B  indicates a deep drawing step,  FIG. 4C  indicates a step of trimming a flange  26  by a press,  FIG. 4D  indicates a step of forming spline lines  27  wherein a drawn plate is loaded with a spline die in its inside and a spinning roller is applied to its outside to reduce its diameter, and  FIG. 4E  indicates a step wherein its bottom  28  is trimmed by the press 
     FIGS. 5A to 5C  shows process steps whereby a tubular material  29  made of a steel tube such as an electro-resistance-welded tube is drawn while being reduced in diameter with a spinning roll to form a casing material  25  having spline grooves  27 . 
     FIGS. 6A to 6D  shows process steps wherein a plate material  24  made of a disc-shaped steel plate is drawn successively by spinning to form a casing material  25  in which  FIG. 6C  indicates a step wherein a bottom  28  is trimmed by a press. 
     FIGS. 7A and 7B  indicates a case that an apertured disc plate  24   a  with a hole preformed is used to omit the step of trimming of the bottom in spinning to form the casing material  25 . 
   Next, the outer peripheral surface of the flange of the output shaft material  22  so formed and the inner peripheral surface of the open bottom of the casing material  25  so formed as mentioned above are each surface-finished so that a ring of nonmagnetic material  14  can be inserted between those materials  22  and  25  with its inner and outer peripheral surfaces tightly fitted with those outer and inner peripheral surfaces. Then, the peripheral surfaces are finished so that the finishing stock removal gives rise to a dimensional tolerance of their tight fit with the inner and outer peripheral surfaces of the ring of nonmagnetic material  14 . 
   Thereafter, the output shaft material  22  and the casing material  25  are placed on a platen so that the flange section of the former and the open bottom of the latter rest thereon coaxially. In this state, the ring of nonmagnetic material  14  is heated by high-frequency induction heating or the like to a temperature sufficient to bring it into a semi-molten state and is fitted under pressure into the annular or ring shaped space between the output shaft material  22  and the casing material  25 . Then, while the inner and outer peripheral surfaces of the ring of nonmagnetic material  14  are each in a semi-molten state, the materials  22  and  25  is practically at a room or ordinary temperature. 
   The ring of nonmagnetic material  14  is brought into semi-molten state at a temperature of 1350 to 1450° C. if it is composed of stainless steel (SUS304), at a temperature of 560 to 660° C. if it is of aluminum and at a temperature of 980 to 1080° C. if it is of copper. 
   Thus, the inner and outer peripheral surfaces of the ring of nonmagnetic material  14  fitted under pressure into the annular space between the two materials  22  and  25  are joined with the outer peripheral surface of the output shaft material  22  and the inner peripheral surface of the casing member  25 , respectively, by interfacial fusion, and the ring of nonmagnetic material  14  is thereby firmly anchored in this annular space. 
     FIG. 9  shows a second form of implementation of the present invention. In the second form of implementation of the invention, as illustrated in  FIG. 9  the ring of nonmagnetic material  14  is fitted under pressure at a room temperature into the annular space between the output shaft material  22  and the casing material  25 , and is thereafter heated by high-frequency induction heating to a temperature sufficient to bring it into a semi-molten state and is then compressed under pressure. In this manner, the inner and outer peripheral surfaces of the ring of nonmagnetic material  14  are joined with the outer peripheral surface of the output shaft material  22  and the inner peripheral surface of the casing member  25 , respectively, by interfacial fusion, and the ring of nonmagnetic material  14  is thereby firmly anchored in this annular space. 
     FIG. 10  shows a third form of implementation of the present invention. In this form of implementation of the invention, as shown in  FIG. 10  the ring of nonmagnetic material  14  is fitted under pressure at a room temperature into the annular space between the output shaft material  22  and the casing material  25 . Thereafter, a plurality of pins  31  embedded on an end face of a rotary body  30  along a circle corresponding to that of the ring  14  are brought under pressure into contact with or pressed against the open end face of the ring of nonmagnetic material  14  while the rotary body  30  is being rotated. 
   This causes the ring of nonmagnetic material  14  to be heated from its open end face by the frictional heat that develops between the end face and the pins  31 . And, this heating operation is continued until the ring of nonmagnetic material is heated to a temperature sufficient to bring it into a semi-molten state. Thus, the ring of nonmagnetic material  14  comes to be heated over its entire body gradually to a temperature sufficient to make it semi-molten due to the circumferential movements of the pins  31  relative to the ring  14  in pressure contact therewith. In this way, the inner and outer peripheral surfaces of the ring of nonmagnetic material  14  are joined with the outer peripheral surface of the output shaft material  22  and the inner peripheral surface of the casing member  25 , respectively, by interfacial fusion, and the ring of nonmagnetic material  14  is thereby firmly anchored in this annular space. 
     FIG. 11  shows a fourth form of implementation of the present invention. In this form of implementation of the invention, as shown in  FIG. 11  the ring of nonmagnetic material  14  is fitted under pressure into the annular space between the output shaft material  22  and the casing material  25 . Thereafter, a pair of rotating pins  32   a  and  32   b  are brought into pressure contact with or pressed against the upper and lower end faces of the ring  14 , respectively, while they are being moved annularly or along the annular end faces of the ring of nonmagnetic material  14 , respectively, to cause the ring of nonmagnetic material  14  to be heated from its opposite end faces by the frictional heat to a temperature sufficient to make it semi-molten. Then, relative to the rotating pins  32   a  and  32   b , the materials  22  and  25  joined together may be rotated. Thus, the ring of nonmagnetic material  14  comes to be heated over its entire body gradually to a temperature sufficient to make it semi-molten due to the circumferential movements of the pins  32   a  and  32   b  relative to the ring  14  in pressure contact therewith. In this way, the inner and outer peripheral surfaces of the ring of nonmagnetic material  14  are joined with the outer peripheral surface of the output shaft material  22  and the inner peripheral surface of the casing member  25 , respectively, by interfacial fusion, and the ring of nonmagnetic material  14  is thereby firmly anchored in this annular space. 
   Although the present invention has hereinbefore been set forth with respect to certain illustrative embodiments thereof, it will readily be appreciated to be obvious to those skilled in the art that many alterations thereof, omissions therefrom and additions thereto can be made without departing from the essences and scope of the present invention. Accordingly, it should be understood that the invention is not intended to be limited to the specific embodiments thereof set forth above, but to include all possible embodiments that can be made within the scope with respect to the features specifically set forth in the appended claims and to encompass all the equivalents thereof.