Device for cold-forming deep holes

Abstract: The objective of the present invention is to provide a cold deep hole forming device capable of forming, by the method of cold forging, deep hole for involute spline, etc. with high accuracy and in simple way, even in member to be formed partially different in thickness, comprising a supporting base 1A for supporting the member W to be formed and a punch 1B for forming deep hole H in the member W to be formed, realized in such a way that a clamp holder 3 is provided on the outer circumference of the punch 1B for forming deep hole in the member to be formed, that a clamp 2 composed by circumferentially disposing a plurality of split clamping pieces 21 is disposed in the clamp holder, and that, when forming deep hole H in the member W to be formed with the punch 1B, the clamping pieces 21 are made to move to the direction of the center under a fluid pressure, so as to constrain the member W to be formed at its outer circumference of the small diameter portion WT.

Description: BACKGROUND OF THE INVENTION The present invention relates to a cold deep hole forming device, especially a cold deep hole forming device used for forming, by the method of cold forging, deep hole for involute spline, etc., in member to be formed partially different in thickness. Conventionally, formation of deep hole for involute spline, etc., in a member to be formed partially different in thickness is made with a method comprising the steps of supporting the member to be formed on a supporting base, lowering a punch for forming deep hole for involute spline, etc. on the member to be formed from above and press fitting the punch in a prepared hole roughly formed in advance in the member to be formed, to form a deep hole for involute spline, etc. in prescribed shape in the member to be formed. By the way, a problem with said conventional cold deep hole forming device was that, since it is designed in a way to press fit the punch in a prepared hole roughly formed in advance in the member to be formed, in the state in which the member to be formed is supported on a supporting base, it is impossible to form a deep hole for involute spline, etc. uniform from end face (inlet of hole) to inner part of the member W to be formed, as shown in Fig. 3 (B) (Fig. 3 (B), which indicates changes of BBD (Between Ball Diameter) from end face to inner part of the member W to be formed of an involute spline formed by said conventional cold deep hole forming device, shows that the involute spline formed is of poor accuracy, deviating from the upper and lower limit values of BBD, in the range of effective length of the spline), especially in the case where the object member W to be formed is partially different in thickness as shown in Fig. 1 and Fig. 2, thus making it impossible to obtain formed pieces of high accuracy. On the other hand, efforts are being made to solve this problem with a method which consists in press fitting the punch in a prepared hole roughly formed in advance in the member to be formed, in the state in which the member to be formed is inserted in a die and constrained at its outer circumference, so as to form a deep hole for involute spline, etc. in prescribed shape in the member to be formed. However, this method also presented problems such as accidents of seizure between the punch and the member to be formed, impossibility of extraction of formed piece from inside the die, etc., because there is no way to control the restraining force on the outer circumference of the member to be formed at proper value. SUMMARY OF THE INVENTION The objective of the present invention is to provide a cold deep hole forming device capable of forming, in a simple way, by cold forging, a deep hole for involute spline, etc. with high accuracy, even if the member to be formed has partially different thickness, in view of the problems of the said conventional cold deep hole forming device. To achieve said objective, the cold deep hole forming device according to the present invention is a cold deep hole forming device comprised of a supporting base to support the member to be formed and a punch for forming a deep hole in the member to be formed, characterized in that a clamp holder is provided on the outer circumference of said punch, that a clamp composed by circumferentially disposing a plurality of split clamping pieces is disposed in said clamp holder, and that, when forming a deep hole in the member to be formed with said punch, said clamping pieces are made to move in the direction of the center under fluid pressure, so as to constrain said member to be formed at its outer circumference. According to the cold deep hole forming device of the present invention, realized in such a way as to move, when forming deep hole with the punch in the member to be formed supported on a support base, a plurality of clamping pieces disposed in a clamp holder provided on the outer circumference of the punch in the direction of the center under fluid pressure and restraining the member to be formed at its outer circumference, it is possible to form a deep hole for involute spline, etc. uniformly from the end face to the inner part of the member to be formed, even if the member to be formed has a partially different thickness, and thus obtain highly-accurate formed pieces. In this case, since the movement of the clamping pieces are made with fluid pressure, it becomes possible to easily control the restraining force on the outer circumference of the member to be formed at a proper value, thus improving the durability of the device without causing any friction between the punch and the member to be formed. Moreover, after the forming, the restraint by the clamping pieces of the outer circumference of the member to be formed can be released with a simple cancellation of fluid pressure, thus making it possible to form, by cold forging method, a deep hole for involute spline, etc. in a simple and efficient way, without causing accidents such as extracting formed pieces from inside the die, etc., as they occur in conventional cold deep hole forming devices. In this case, (the cold deep hole forming device according to the present invention) may be constructed in such a way to move said clamping pieces in the direction of the center, by forming the outer face of said clamping pieces on a sloped face, forming the inner circumferential face of the clamp holder with which the outer face of the clamping pieces comes in contact on a similar sloped face, and moving said clamping pieces, through a fluid pressure piston, on the clamp holder formed on the sloped face. This makes it possible to uniformly constrain the outer circumference of the member to be formed, by means of a plurality of the disposed clamping pieces, in the clamp holder, in such a way as to surround the outer circumference of the member to be formed, and obtain highly-accurate formed pieces. Furthermore, the inner face of the clamping pieces which come in contact with the outer face of the member to be formed may be formed on a sloped face. This makes it possible to perform forming considering distortion produced on the formed pieces in subsequent processes such as carbo-hardening, etc. to be made after the forming, and thus obtaining formed pieces of high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing an embodiment of the cold deep hole forming device according to the present invention, the drawing in the right half showing the state in which the punch is raised and the drawing in the left half showing the state in which the punch is press fit in the member to be formed. Fig. 2 (A) is a sectional view showing a clamp holder in which is disposed a clamp, the drawing in the left half showing the state in which the outer circumference of the member to be formed is constrained with clamping pieces and the drawing in the right half showing the state in which that constraint is released. Fig. 2 (B) is a plan view showing the state of arrangement of clamping pieces. Fig. 3 indicates changes of BBD (Between Ball Diameter) from end face to inner part of a member to be formed of an involute spline formed on the member to be formed, (A) showing a case of forming made by using the cold deep hole forming device according to the present invention, and (B) showing a case of forming made by using a conventional cold deep hole forming device, respectively. DETAILED DESCRIPTION OF THE INVENTION The cold deep hole forming device according to the present invention will be explained hereafter with reference to drawings. Fig. 1 and Fig. 2 indicate an embodiment of the deep hole forming device according to the present invention. This cold deep hole forming device is constructed by comprising, for example, a supporting base 1A for supporting the lower part of the member W to be formed partially different in thickness and a punch 1B for forming deep hole H for involute spline, etc. in this member W to be formed, and concentrically disposing clamp holder 3 on the outer circumference of the punch 1B and also disposing clamp 2 composed by circumferentially disposing a plurality of split clamping pieces 21 in this clamp holder 3. In this case, the supporting base 1A is fixed on a base 4. On the other hand, the punch 1B is concentrically disposed over the supporting base 1A, by providing a punch clamp holder 12, through a mounting bracket 9, at the center position of a lift stand 8 attached to a ram 7, and fixing to this punch clamp holder 12 by means of a box-nut shaped mounting fixture 13. This makes it possible to lower the punch 1B from above on the member W to be formed supported on the supporting base 1A by driving the ram 7, and form deep hole H for involute spline, etc. of prescribed shape in the member W to be formed, by press fitting the punch 1B in the prepared hole H0 roughly formed in advance in the member W to be formed. Moreover, the clamp holder 3 is concentrically disposed on the outer circumference of the punch 1B by hanging at the bottom end of a hanging bolt 11 guided in a way to go up and down by a supporting guide 10 disposed on the outer circumference of the mounting bracket 9 attached to the lift stand 8. On this clamp holder 3 is placed a clamp 2 constructed by circumferentially disposing a plurality of split clamping pieces 21. In this embodiment, the clamp 2 is composed of clamping pieces 21 split into 8 parts, but the dividing number of the clamp 2 is not restricted to this number but may also be set for optional number such as 6 split parts, etc., for example. The clamping pieces 21 are disposed in a clamp holding mechanism 30 in circular shape formed by the clamp holder 3 and a flange 6 fixed to the bottom face of this clamp holder 3 with a bolt 6B. This clamp holding mechanism 30 is formed with a dimension D in axial direction (direction of height in Fig. 2 (A)) larger than the thickness T of the clamping pieces 21, and constructed in such a way that the clamping pieces 21 may move up and down in the range of a distance C in Fig. 2 (A) in the clamp holding mechanism 30. In this case, the clamping pieces 21 are arranged to be urged by a spring 3S1 interposed between the clamping pieces 21 and the flange 6. Furthermore, to the clamping pieces 21 is fastened a bolt 3B which is inserted in a slit 3H provided in vertical direction in the clamp holder 3, to thereby prevent the clamping pieces 21 from circumferentially moving in the clamp holding mechanism 30, while a spring 3S2 disposed on the shaft of the bolt 3B keeps the outer side face 2T1 of the clamping pieces 21 in a state in contact with the inner circumferential face 3T of the clamp holder 3. And, the outer side face 2T1 of the clamping pieces 21 is formed on a downward slope face, and the inner circumferential face 3T of the clamp holder 3 to be in contact with the outer side face 2T1 of the clamping pieces 21 is also formed on a downward slope face. Still more, at the top of the clamp holder 3, forming a clamp holding mechanism 30, is formed an operating fluid chamber 3R in circular shape, and disposed on a piston 5. This makes it possible to feed operating fluid to the operating fluid chamber 3R through a port 3P, when forming a deep hole H for involute spline, etc. in the member W to be formed supported on the supporting base 1A by punch 1B, to thereby move the piston 5 in the downward direction in Fig. 2 (A), and move the clamping pieces 21 downward along the inner circumferential face 3T of the clamp holder 3 formed on a slope face, to the direction of the center, so as to constrain the outer circumference of the small diameter portion WT of the member W to be formed. In case the supply of operating fluid to the operating fluid chamber 3R is interrupted, the clamping pieces 21 move in the radial direction (direction to get away from the center), while moving upward along the inner circumferential face 3T of the clamp holder 3 formed on a slope face, under the action of the spring 3S1 interposed between the clamping pieces 21 and the flange 6 and the spring 3S2 disposed on the shaft of the bolt 3B fastened to the clamping pieces 21, thus making it possible to cancel the constraint by clamping pieces 21 on the outer circumference of the small diameter portion WT of the member W to be formed. Yet more, on the body frame F is disposed a stopper 14 for controlling ascent of the clamp holder 3 when the clamp holder 3 is at the down position. This stopper 14 is designed in such a way that, as operating fluid is fed to an operating fluid chamber 14R formed inside the stopper body 14A fixed to the body frame F, the stopper pin 14P juts out and the tip of the stopper pin 14P is caught in the notch 3K formed at the top of the clamp holder 3, to thereby control ascent of the clamp holder 3. Thanks to this stopper 14, it becomes possible to control ascent of the clamp holder 3, by engaging the tip of the stopper pin 14P with the notch 3K formed at the top of the clamp holder 3, when extracting the punch 1B from the member W to be formed by making the ram 7 go up after forming a deep hole H for involute spline, etc. of prescribed shape in the member W to be formed with the punch 1B, and extract the punch 1B smoothly from the member W to be formed by preventing the member W to be formed from going up together with the clamp holder 3 (in this embodiment, the bottom face of the clamping pieces 21 disposed on the clamp 3 holder gets in contact with the member W to be formed). The stopper pin 14P is constructed in a way to be stored in the stopper body 14A, when the supply of operating fluid to the operating fluid chamber 14R is stopped, under the action of the spring 14S disposed on the shaft of the stopper pin 14P, to allow ascent of the clamp holder 3 and its descent in the subsequent process. The actions of the cold deep hole forming device according to the present invention will be explained hereafter. This member W to be formed, which is formed in prescribed shape in advance by the method of forging, etc., and having a prepared hole H0 roughly formed on it, is supported on a supporting base 1A (right half drawing in Fig. 1). Next, the ram 7 is lowered, to thereby concentrically dispose the clamp holder 3 hung at the bottom end of the hanging bolt 11 guided in a way to go up and down by a supporting guide 10 disposed on the outer circumference of the mounting bracket 9 attached to the lift stand 8, on the outer circumference of the small diameter portion WT of the member W to be formed. In this state, operating fluid is fed to the operating fluid chamber 3R of the clamp holder 3 through the port 3P, to thereby move the piston 5 in the downward direction, and move the clamping pieces 21 downward along the inner circumferential face 3T of the clamp holder 3 formed on a slope face, to the direction of the center, so as to constrain the outer circumference of the small diameter portion WT of the member W to be formed (left half drawing in Fig. 2 (A)). And, by further lowering the ram 7, in the state in which the outer circumference of the small diameter portion WT of the member W to be formed is constrained by the clamping pieces 21, the punch 1B is made to come down from above on the member W to be formed supported on the supporting base 1A and press fit in the prepared hole H0 roughly formed in advance in the member W to be formed, to form a deep hole H for involute spline, etc. of prescribed shape in the member W to be formed with the punch 1B (left half drawing in Fig. 1). As described above, by forming deep hole H for involute spline, etc. of prescribed shape in the state in which the outer circumference of the small diameter portion WT of the member W to be formed is constrained, it becomes possible for form deep hole H for involute spline, etc. uniformly from end face to inner part of the member W to be formed even in the case where the member W to be formed is partially different in thickness. Fig. 3 (A) indicates changes of BBD (Between Ball Diameter) from end face to inner part of a member W to be formed of an involute spline formed by using the cold deep hole forming device according to the present invention, showing that the involute spline formed remains between the upper and lower limit values of BBD, in the range of effective length of the spline, thus ensuring high accuracy. And, as the supply of operating fluid to the operating fluid chamber 3R is interrupted, the clamping pieces 21 move in the radial direction (direction to get away from the center), while moving upward along the inner circumferential face 3T of the clamp holder 3 formed on a slope face, under the action of the spring 3S1 interposed between the clamping pieces 21 and the flange 6 and the spring 3S2 disposed on the shaft of the bolt 3B fastened to the clamping pieces 21, to thereby cancel the constraint by clamping pieces 21 on the outer circumference of the small diameter portion WT of the member W to be formed (right half drawing in Fig. 2 (A)). In this way, after forming deep hole H for involute spline, etc. of prescribed shape in the member W to be formed with the punch 1B, the ram 7 is made to go up to extract the punch 1B from the member W to be formed. At that time, as operating fluid is fed to the operating fluid chamber 14R formed inside the stopper body 14A of the stopper 14 fixed to the body frame F, the tip of the stopper pin 14P is caught in the notch 3K formed at the top of the clamp holder 3, to thereby control ascent of the clamp holder 3 and prevent the member W to be formed from going up, through the clamp holder 3, to extract the punch 1B from the member W to be formed. After extraction of the punch 1B from the member W to be formed, the supply of operating fluid to the operating fluid chamber 14R formed in the stopper body 14A of the stopper 14 is stopped, and the stopper pin 14P is stored in the stopper body 14A, to cancel control of ascent of the clamp holder 3, while the ram 7 is raised to make the clamp holder 3 to go up and return to its initial state. The member W to be formed in which is formed deep hole H for involute spline, etc. supported on the supporting base 1A is taken out, to complete the forming process. By the way, the shapes of the component parts such as supporting base 1A, punch 1B and clamping pieces 21 composing clamp 2, etc. to be installed on this cold deep hole forming device are not restricted to those indicated in the present embodiment, but other shapes suitable to the shape of the member W to be formed may also be used as required. In addition, the inner side face 2T2 of the clamping pieces 21 to be in contact with the outer circumferential face of the small diameter portion WT of the member W to be formed may be formed on a slope, as required, thus making it possible to perform forming considering distortion produced on the formed pieces in the subsequent processes such as carbo-hardening, etc. to be made after the forming of the member W to be formed and obtain formed pieces of high accuracy. Especially, in the case where the object member W to be formed is partially different in thickness as shown in Fig. 1 and Fig. 2, it is desirable to form in such a way that the end face side of the small diameter portion WT of the member W to be formed is slightly larger, to compensate for the distortion produced on the formed pieces in the subsequent processes such as carbo-hardening, etc. to be made after the forming of the member W to be formed, but this can be achieved easily by forming the inner side face 2T2 of the clamping pieces 21 on a downward slope.

Claims: A cold deep hole forming device comprised of a support base (1A) to support the member (W) to be formed and a punch (1B) for forming a deep hole (H) in the member to be formed, characterised in that a clamp holder (3) is provided on the outer circumference of said punch (1B), that a clamp (2) composed by circumferentially disposing a plurality of split clamping pieces (21) is disposed in said clamp holder (3), and that , when forming a deep hole in the member (W) to be formed with said punch (18), said clamping pieces (21) are made to move in the direction of the center under fluid pressure, so as to constrain said member (W) to be formed at its outer circumference. A cold deep hole forming device as defined in Claim 1, wherein the outer face of said clamping pieces (21) is formed on a sloped face, while the inner circumferential face of the clamp holder (3) with which the outer face of the clamping pieces (21) comes in contact is formed on a similar sloped face, to move said clamping pieces along the inner circumferential face of the clamp holder formed on the sloped face, through a fluid pressure piston (5), in the direction of the center. A cold deep hole forming device as defined in Claim 1 or 2, wherein the inner side face of the clamping pieces (21), to be in contact with the outer circumference of the member (W) to be formed, is formed on a sloped face.

Inventors: KATO MUTSUMI, OKUMURA TADASHI, KATO,MUTSUMI, OKUMURA,TADASHI
Applicants: GOHSYU CORP, GOHSYU CORPORATION
Application year: 1999
Main classification: B21J5
IPC codes: B21J5, B21K1, B21J9, B21J13