METHOD AND APPARATUS OF PRODUCING A STEPPED HOLLOW ARTICLE

Abstract: A solid slug (2) provided with a disc portion (2a) and a projecting portion (2b) is placed in a rigid cylindrical recess formed between a counter punch (12) and a hollow mold (11). An annular upper surface (2e) of the disc portion (2a) and the side surface (2f) of the projecting portion (2b) are pre-compressed by an outer punch (16) so as to restrain the outer periphery of the solid slug. A closed-base hole is formed in the center of the solid slug (2) by the plastic deformation caused by an inner punch (17), thereby a stepped hollow component is obtained.

Description: The present invention relates to a cold forming method and apparatus of producing a stepped hollow component such as a gear blank, according to the first portion of claim 1 (method) and 4 (apparatus), respectively. A conventional method of producing a stepped hollow component is given in "Impact Machining" by Verson Co., translated by Akio Takahashi and Ko Muramatsu, and published by Corona-Sha, particularly in Fig. 3.19, page 57. This method employs 6 press steps between a first step of cutting a metal bar and a final coining step. At least two annealing steps and three lubrication treatments are necessary during the process. Furthermore, a press with a large capacity is needed to bear the heavy processing load, particularly during rearward and forward extrusion steps, but this means that the service life of the molds is inconveniently reduced by the high pressure applied to them. The excessive number of steps in the process tends to reduce the dimensional accuracy of the stepped hollow component which is produced. From the US-A- 3 589 164, as closest prior art, it is known a method and apparatus for producing a stepped hollow article. A cleaned and annealed solid slug provided with a radial flange and an axially projecting portion is disposed in a cylindrical recess of a press. On the upper annular surface of the flange acts an outer ring punch for restraining the outer periphery of the flange portion and the side surface of the projecting portion. Said outer ring punch is fixed and cannot move upwardly during the following forming operation of a hole by pressing an inner movable plug in the center of the slug. For this reason cracks will occur in the projecting portion when the inner punch approaches its lower dead point. Further a very high pressure load is necessary for the plastic deformation of the slug. An object of the invention is to provide a method and an apparatus of producing stepped hollow components, which is improved so as to reduce the processing load while reducing the number of process steps. Said object will be solved by the features of claim 1 (method) and claim 4 (apparatus), respectively. The method and the apparatus of the invention enables the production of stepped hollow component with a high dimensional accuracy, but by using a minimum of processing steps and a low load by cold forming. Namely, according to the invention since plastic flow takes place not uniaxially but biaxially in the radial and axial directions, the working pressure is reduced to ensure a high-precision process. Brief description of the drawings: Fig. 1 is a perspective view of a cylindrical metallic member; Fig. 2 is a perspective view of a solid slug formed from the metallic member shown in Fig. 1; Fig. 3 is a perspective view of a slug with a central closed hole, formed from the solid slug shown in Fig. 2; Fig. 4 is a perspective view of a stepped hollow component; Fig. 5 is a vertically sectioned view of a preferred embodiment of a cold forming apparatus; Fig. 6 is an enlarged view of essential parts of the apparatus of Fig. 5; and Figs. 7 and 8 are illustrations of a method of producing a stepped hollow component in accordance with another embodiment of the invention. Detailed Description of the Preferred Embodiment Figs. 1 to 6 illustrate a method of producing a stepped hollow component in accordance with an embodiment of the invention. Referring first to Fig. 1 which is a perspective view of a cylindrical metallic member, the cylindrical metallic member 1 is cut from a round metallic bar so that it has a predetermined volume (or weight), and upper and lower end surfaces 1a and 1b parallel to each other. Fig. 2 is a partly-sectioned perspective view of a solid slug formed from the cylindrical metallic member of Fig. 1. The solid slug 2 is mounted in a manner as shown in the left-hand part of a portion held by a hollow mold 11 of Fig. 5, and is formed as shown in right-hand part of Fig. 5. This process is shown in an enlarged sectioned view in Fig. 6, the result is that a slug 3 with a central closed hole 3e, as shown in Fig. 3, is obtained. A stepped hollow component 4 shown in Fig. 4 is formed by punching out the base of the slug 3 by a press. A description will now be made of the cold forming apparatus and process used in the production of the stepped hollow component 4. Fig. 3 is a perspective view of a slug with a central closed hole, formed from the solid slug of Fig. 2. In this figure, the front portion of the slug is cutaway. The slug 3 has a disc-like flange portion 3a and a boss portion 3b in the form of an annular projection. A closed hole 3e is formed in the center of the boss portion 3b. Reference numerals 3c, 3d, and 3g denote, respectively, the upper end surface of the boss portion 3b, the lower surface of the flangeportion 3a, and the upper surface of the flange portion 3a. This slug is formed by the apparatus shown in Fig. 5. Fig. 5 is a vertically sectioned view of a cold forming apparatus. A hard plate 13 is fixed into a central bore formed in a pedestal 14 mounted on a rigid base 30, and a counterpunch 12 is mounted within the hard plate 13. A hollow mold 11 is placed on top of the hard plate 13, and is secured to the pedestal 14 by fastening members 15 which are screwed onto the pedestal 14. The solid slug 2 of Fig. 2 is positioned in the recess formed by the hollow mold 11 and the upper surface of the counterpunch 12 fitting in the central bore. A movable pressurizing portion 10 is installed above the hollow mold 11. The pressure in the oil passage 22 provided in the cylinder block 20 is increased by pressure control member (not shown) to lower a piston block 21 so that the lower end of an outer punch 16 attached to the lower end of the piston block 21 is made to come into contact with the annular upper surface 2e of the solid slug 2 and the side surface 2f of the projecting portion, thereby the solid slug is restrained. Subsequently, as a pressure-receiving member 19 of a cylindrical member positioned within the central bore of the cylinder block 20 via a holder 18 is depressed, the lower end of an inner punch 17 comes into contact with the solid slug 2 so that it pushes the boss portion 3b backward while forming the flange portion 3a. Namely, plastic flow takes place not uniaxially but biaxially in the radial and axial directions. Fig. 6 is an enlarged view of the essential parts of Fig. 5. While the hydraulically-operated outer punch 16 imparts a force δ o to the annular upper surface 2e of the solid slug 2, the material of this region flows in the direction of the arrows as a result of the lowering of the inner punch 17, because the lower surface 2c is prevented from moving by the counterpunch 12. Consequently, the outer configuration of the flange portion 3a of the slug 2 is changed from a barrel shape to a cylindrical shape, while the boss portion 2b is elongated upward, so that the slug has the shape shown in Fig. 3. The pressure applied to the annular upper surface 2e through the outer punch 16 is adjustable. The outer punch is arranged to be moved upward so as to absorb the excessive force caused in the axial direction of the boss portion by the plastic flow of the material when the inner punch is lowered, thereby the region between the upper surface of the flange portion and the side surface of the boss portion is free from the generation of cracks. Thereafter, the force applied to the pressure receiving surface 19 is relaxed to allow the cylinder block 20 to move upward to separate the outer punch 16 and the inner punch 17 from the slug 3, and the slug 3 is removed as the counterpunch 12 is raised by a push rod provided in the central bore in the base. The slug 3 can be removed from the hollow mold 11 without much difficulty if an application of oil and a punch treatment are performed before the solid slug 2 is placed in the hollow mold 11. Fig. 4 is a perspective view of the stepped hollow slug which is to be obtained. In this figure, the slug is illustrated with its front portion cut away to show the shape of its hole. A punched-out portion 4b in the lower part of a hole 4a is a region from which a waste part 5 has been removed, it has a smooth surface although an annular line remains. The punching out of this hole bottom can be done easily by a simple press. Annealing is conducted thereafter to remove residual stresses and obtain the stepped hollow component 4 which is suitable for use as a gear blank in which teeth are cut in the flange portion. According to the method of producing a stepped hollow component of this embodiment, a slug with a flange portion and a boss portion can easily be obtained by a process comprising the steps of placing in a rigid cylindircal recess a solid slug provided with a disc portion and a projecting portion in the form of a cylindrical bar, restraining the annular upper surface of the disc portion and the side surface of the projecting portion by the annular edge of an outer punch, and driving an inner punch into the center of the projecting portion. From this slug, a stepped hollow component can easily be obtained simply by punching out the base of the hole into which the inner punch was driven. This production method offers the following advantages over that of the prior art. (1) The flange portion 3a and the boss portion 3b of the stepped hollow component with a central closed hole can be formed simultaneously in one action by the cold forming apparatus shown in Fig. 5, so that the production efficiency can be improved markedly. In the conventional method which employs a plurality of steps, as stated before a plurality of annealings and a plurality of bonderizing treatments are required. In contrast, according to the method of the present invention, the annealing and the bonderizing treatment are conducted only once each. (2) In the method of the embodiment described, since the component can be formed by a single press operation, the number of the molds is reduced and the pressure force can be adjusted to the minimum level required. Namely, since plastic flow takes place not uniaxially but biaxially in the radial and axial directions, the working pressure is reduced to ensure a high-precision process. Figs. 7 and 8 show a method of producing a stepped hollow slug in accordance with another embodiment of the invention. In this case, boss portions are formed on the upper and lower sides of the flange portion, so that the slug of this embodiment differs from that of Fig. 3 in that a boss portion 6c is also formed on the lower surface 3d. In the same way, a closed hole 6d is formed by the inner punch 17 from above. The upper surface of counterpunch 12 used in this embodiment is provided with a recess receiving the boss portion 6c. In this embodiment, the slug is formed by the same process as that which produced the slug 3 of Fig. 3, using the cold forming apparatus 10 of Fig. 5. Fig. 8 is a perspective view of a stepped hollow slug produced by punching out the base of the hole in the slug shown in Fig. 7, so that a stepped hollow component 7 can be obtained by punching out the base of hole 6d from a simple slug 6. Reference numeral 7a designates the hole, 7b the punched portion, and 8 the punched-out waste. According to the method of this embodiment for producing a stepped hollow component with boss portions on both sides thereof, the component can be produced with a high efficiency and with a good structural accuracy by using a counterpunch of the same type as that used in the first embodiment, but which is provided in the upper surface thereof with a recess receiving the lower boss portion.

Claims: A method of producing a stepped hollow article, comprising the steps of: placing a solid slug (2) having a disc portion (2a) and an axially projecting portion (2b) on a counterpunch (12) at a prescribed position in such a manner that the disc portion (2a) of the slug (2) is disposed on said counterpunch (12); pressing an annular end surface (2e) of the disc portion (2a) by an outer punch (16) while restraining the side face of the projecting portion (2b) to avoid outward expansion; and pressing the projecting portion (2b) by an inner punch (17) to form a blind hole (3e) in a central portion of the projecting portion (2b) through plastic deformation which causes the material of the solid slug (2) to flow in radial and axial directions of the solid slug (2), whereby a slug (3) having a disc-like flange portion (3a) and a boss portion (3b) in which a blind hole (3e) is formed is produced, characterized in that the formation of said boss portion (3b) is carried out by moving the inner punch (17) in an axial direction while allowing the outer punch (16) restraining the outward expansion of the projecting portion (2b) to move axially in an opposite direction to the axial movement of the inner punch (17) so as to absorb excessive force caused in an axial direction by the plastic flow of the material of the solid slug (2). Method according to claim 1, wherein the solid slug (2) is formed from a cylindrical metallic member (1), and the formed solid slug not subjected to annealing is subjected to the press-forming of said slug (3). Method according to claims 1 or 2 further including the steps of punching out a base portion of the slug (3). An apparatus for producing a stepped hollow component, comprising: -- a cylindrical counterpunch (12) for supporting a solid slug (2), said slug (2) having a disc portion (2a) and a projecting portion (2b) axially projecting from an end (2e) of the disc portion (2a); a hollow mold (11) for accomodating the counterpunch (12) and for positioning the disc portion (2a) of the slug (2) to place the slug (2) on the upper endface of said counterpunch (12) at a predetermined position, a hollow-cylindrical outer punch (16) guided in the hollow mold (11), so that the projection portion (2b) of the slug (2) is slidably inserted in said outer punch (16), for pressing against the upper end (2e) of the disc portion (2a) while restraining a side surface (2f) of the projecting portion (2b) of the slug (2); an inner punch (17) slidingly inserted in said hollow-cylindrical outer punch (16) with an annular spacing therebetween, for pressing a central portion of the projection portion (2b) to form a closed-base hole (3e) through plastic deformation of material of the slug (2), characterized by driving means (20, 21, 22) for driving said cylindrical outer punch (16) independently of said inner punch (17), said driving means (20, 21, 22) allowing said cylindrical outer punch (16) to move in an opposite direction to the pressing direction of said inner punch (17) when said inner punch (17) is axially moved to form the closed-base hole (3e). The apparatus according to claim 4, wherein said driving means (20, 21, 22) is a means for hydraulically driving said hollow cylindrical outer punch (16).

Inventors: KANAMARU, HISANOBU, OKU, MASAHARU, SAWAHATA, KAZUO
Applicants: HITACHI, LTD.
Application year: 1984
Main classification: B21K21
IPC codes: B21J5, B21K21, B21K23, B21J13, B21K1