PROCESS FOR MANUFACTURING A PART HAVING A TOOTH PROFILE AND BOSS

Abstract: The present invention relates to a process for the manufacture of parts having a tooth profile and boss by means of a press machine. The process of the present invention comprises a blank (3) with a boss, which is produced in a prior operation by machining, cold forging, warm forging or other method, being positioned on a female die (2) having a tooth profile formed thereon on a mirrored surface, said female die having a 20-­ 150° taper at its inlet, and having a shape conforming to the bottom configuration of said blank, and wherein an ironing process is performed by means of a punch (1) having a shape conforming to the top configuration of said blank.

Description: The present invention relates to a process for manufacturing a finished part having a tooth profile and a boss from a blank according to the precharacterizing clause of claim 1. A part having a tooth profile also commonly has a boss. In conventional manufacturing processes of such a part by cold-press forming, for example as disclosed in JP-B-58 47 929, stretch-forming is performed using a finishing die following extrusion molding using a rough-forming die. The tooth profile of the finishing die conforms to the major diameter of the blank to be worked. However, in such a process a large-scale press machine is required. The major diameter of the punch to which high pressure is applied becomes worn within a short period, so that toothed parts having the required quality cannot be manufactured over a long period. This causes a severe limitation of the service life of the punch. Furthermore, processes employing precision punch-pressures require expensive, specialized press machines. The service life of the punches used in such machines is limited, and a degree of closure is produced on the top and bottom of the toothed part. Whereas according to JP-B-58 47 929 the blank is pressed into a female die through the same opening through which it is removed from the die afterwards, JP-A- 59 76 639 discloses a process according to the precharacterizing clause of claim 1, i.e. a process during which a blank is pressed through a female die, entering same through an inlet opening and leaving it through an oppositely arranged outlet opening. However, according to this method three press cycles are needed for obtaining a finished product in the form of a gear with a tooth profile and a boss. First, an intermediate product part is inserted through the through hole of a container into the die hole by a first press stroke. Then a second intermediate product part is similarly inserted therein in the same direction by a second press stroke. Thereafter, a third intermediate product part is similarly inserted, whereafter the press punch is lowered a third time. The pressure of the press punch is applied to the part which was press-fitted as first into the die hole via the second and third parts which have been press-fitted afterwards, so that said first part is extruded and dropped as a finished product from the die hole. This complicated method is practically cumbersome and will yield poor productivity. JP-A-49 79 945 discloses a method of cold-forming a spline shaft. With this method, however, apart having a tooth profile and a boss cannot be produced because a cylindrical material being properly smaller than the inside diameter of the die is pressed into the die by a pressure ram from above whereby a spline tooth profile is formed on the outer surface of the cylindrical material. Thereafter, the formed spline shaft is ejected through the same opening of the die through which it was pressed into the die before. US-A-3,258,834 discloses a process of forging a metal gear having a body and a plurality of gear teeth integral with the body. However, the temperature of the formed blank prior to an impact blow is in the range of 1800°F to 2000°F, and thus a high temperature furnace and a heating step are required. Consequently a method according to this publication suffers from the fact that manufacturing costs are high and production efficiency is low. Therefore it is an object of the present invention to provide a process by which a part having a tooth profile and a boss can be manufactured without using a specialized, large-scale or expensive press machine and which, at the same time, extends the service life of the used punch and female die and allows to obtain finished parts having a high quality. For this purpose the present invention provides a process for manufacturing a finished part having a tooth profile and a boss from a blank according to the precharacterizing clause of claim 1 which further comprises the steps of using a female die with a mirrored inlet surface and having also a taper at its opposite inlet, both tapers being in the range of 20° to 150°, and of pressing said blank a second time through said female die in a direction opposite to the direction of said first pressing step by means of a counter which, at its end engaging said blank, has a shape conforming to the respective configuration of said blank. According to the aforesaid construction, the pressure applied to the punch and female die is reduced, thus extending the service life span of said punch and female die as well as reducing the occurence of cracks in the finished part. Since the punch is provided with a shape which conforms to the top configuration of the blank, it is effective in producing an adequate flow of material in the direction of the teeth. Friction generated in the contact area between the blank and the female die is reduced due to the provision of a taper at the inlet to the female die and due to the mirrored surface provided to improve sliding, the rough surface of the toothed part thus becoming smooth. Also, the blank can be processed at a reduced forming pressure applied to the punch and female die because the pressure is dispersed by the taper. The service life of the punch is further extended by the reduction of the pressure exerted by the punch on the surface in opposition. According to a first embodiment of the present invention, the aforesaid punch is provided with a tooth profile. When the clearance between the punch and the female die is minimal, punch debris from the blank at the bottom of the punch is ejected and a suitable tooth profile is formed on the blank because the shape of the punch itself conforms to the minor diameter shape of the female die which is provided with a tooth profile. Without additional measures a trimming taper is produced on the blank on the underside by the female die and on the top by the punch because the inlet to the female die has a taper provided thereon. Toothed parts which do not require high precision forming can be completed in a single operation comprising a single combined cycle of descending and ascending strokes of the press. However, if high precision toothed parts are to be produced, according to a second embodiment of the invention said trimming taper is removed by reversing the top-to-bottom orientation of the blank by 180° and performing the stamping operation a second time. This has the advantage of effectively improving the precision of the obtained part because all trimming taper is removed from the interior minor diameter, the major diameter, and the pitch circle produced by the female die at the stamping process. According to a further embodiment of the present invention, the aforesaid punch is a round punch having no tooth profile formed thereon. When the toothed part requires a modular or fine tooth profile this has the advantage of further extending the service life of the punch. According to still a further embodiment of the present invention, the aforesaid punch does not have a tooth profile formed thereon and an excess thickness recess is provided on the counter and said punch. Even in the case of parts production using a punch having a tooth profile formed thereon, buildup will be produced on the punch side at the clearance between the punch and the female die, or excess thickness will be produced. The excess thickness and buildup which are thus produced can be removed in a secondary process by means of a machining or grinding process, but when a greater degree of precision is required, the trimming taper is removed in a secondary stamping process as described with respect to the aforesaid second embodiment. When a toothed part having excess thickness, excluding buildup, undergoes a secondary stamping process, it is desirable to provide beforehand an excess thickness recess in the counter and punch in order to allow a reduction in the press-forming pressure. In all these embodiments the blank is preferably clamped between the punch and the counter during the first down-going pressing stroke as well as during the second up-going pressing stroke. Further objects, features and advantages of the invention will become more fully apparent from the following description. Figures 1(A) and 1(B) are a cross sectional view and an explanatory drawing, respectively, which show the basic structure of the press machine used according to the present invention. Figures 2(A), 2(B) and 2(C) are frontal elevation and cross sectional views showing the shapes of the blank with boss. Figures 3(A), 3(B) and 3(C) are cross sectional views which respectively show the structures needed for stamping different shaped blanks with bosses. Figures 4(A), 4(B) and 4(C) are schematic frontal elevation views showing, as other embodiments of the present invention, parts having tooth profiles produced by a stamping process using a round punch. Figures 5(A) and 5(B) are cross sectional views showing the structures wherein excess thickness recesses are provided in the dies used for the secondary stamping process. Figures 6(A)-6(D) are frontal elevation and cross sectional views showing the conditions under which the processes appropriate for the required degree of precision forming are selected. Figures 7(A)-7(C) are frontal elevation views showing the parts with tooth profile and boss. Embodiments of the present invention are hereinafter described with reference to the drawings. The basic structure of a press machine using the processes of the present invention is shown in Figs. 1(A) and 1(B). The press machine in the present embodiment comprises a punch 1, a female die 2 and a counter 4. As shown in Figs. 3(A), 3(B) and 3(C), punch 1 is formed in a shape conforming to the top configuration of blank-with-boss 3. The tooth profile inlet of female die 2 has a 20-150° angle taper provided thereto as shown in Figs. 1(A) and 1(B), as well as a mirrored surface provided to improve sliding characteristics. Counter 4 pushes the press-formed blank-with-boss 3 from a downward direction, extruding said blank-with-boss 3 toward the top of female die 2. A blank with a shape substantially that of the finished product is produced in a prior operation by machining, cold forging or warm forging as shown in Figs. 2(A), 2(B) and 2(C). As shown in Fig. 2(A), blank-with-boss 3 forms a dish-shaped cross section with a projecting section 31 comprising the boss and an annular body 32 having an exterior surface with a tooth profile stamped thereon. As shown in Fig. 2(B), blank-with-boss 3 forms an H-shaped cross section with a tabular section 33 comprising the boss and an annular section 34 having an exterior surface with a tooth profile stamped thereon. As shown in Fig. 2(C), blank-with-boss 3 forms a cruciform cross section with a central axial section 35 comprising the boss and a circular plate 36 having an exterior surface with a tooth profile stamped thereon. The configuration of punch 1 itself, which is not shown in Fig. 1(A), comprises a tooth profile on its exterior surface, said tooth profile configuration conforming to the minor diameter configuration of female die 2. The configuration of the bottom of punch 1 is formed so as to conform to the top configuration of the aforesaid blank-with-boss 3, and in the case where blank 3 forms a dish-shaped cross section as shown in Fig. 3(A), the bottom configuration of said punch 1 comprises an inverted convexity having a projection provided thereon for stamping the shaft hole. When blank 3 forms an H-shaped cross section as shown in Fig. 3(B), the bottom configuration of punch 1 comprises a projection, and when a shaft hole and mounting hole are stamped on circular plate 33, additional projections for stamping said shaft and mounting holes are provided, however, these projections are not shown in the drawing. In the case where blank 3 forms a cruciform cross section as shown in Fig. 3(C), the bottom configuration of punch 1 comprises an inverted concavity. The configuration of a toothed part-with-boss 3′ is shown Figs. 7(A), 7(B) and 7(C). [Operation] In the manufacture of a toothed part-with-boss 3′ by means of a press machine of the aforesaid construction, punch 1 and female die 2 have a blank-with-boss 3, which is produced in a prior operation, of the shape shown in Figs. 2(A), 2(B) and 2(C) provided therebetween, said punch 1 being forced in a downward direction. In the case where the clearance between punch 1 and female die 2 is minimal, debris from blank 3 at the bottom of punch 1 is ejected. The bottom configuration of punch 1 conforms to the top configuration of blank 3 and the form thickness of said blank 3 adequately flows in the tooth direction because no spacing is provided between punch 1 and blank 3. Blank 3 transits female die 2 with minimal frictional resistance and the surface of toothed part 3' is formed smoothly because the inlet to female die 2 has a 20-150° taper as well as a mirrored surface provided thereon. The angle of the taper provided at the inlet of female die 2 may vary according to the thickness of said blank 3, and an appropriate angle in the range of from 20-150° may be determined by experimentation. The present invention provides the advantage of further extending the useful life span of the die because minimal pressure is exerted by punch 1 on the surface in opposition. This condition occurs because the stamping process may be performed at reduced pressure between female die 2 and punch 1 since the press pressure of punch 1 is dispersed by the aforesaid taper. According to the basic structure as shown in Fig. 1, a trimming taper is produced on blank 3, by female die 2 on the bottom and by punch 1 at the top, because a taper is provided at the inlet to said female die 2, said blank 3 as a whole forming an inverted trapezoid. Toothed parts which do not require high precision formation can be completed in a single stamping operation comprising the single combined cycle of descending and ascending strokes of the press. However, in the manufacture of high precision toothed parts, the trimming taper, which reduces the precision of said parts, must be removed as appropriate for the required quality. To achieve this aim, the top-to-bottom orientation of blank 3 is reversed, and the trimming taper of said blank 3 is removed by means of counter 4 and punch 1 which conform to the configuration of said reversed blank 3. In such a case, the present invention effectively removes, by means of the stamping process, all trimming taper from interior minor and major diameters and the pitch circle formed by female die 2. [Further Embodiments] In a case where the tooth profile is modular or fine, a round punch having no tooth profile on its exterior surface is used as the punch 1 in order to extend the useful life span of said punch 1. When a round punch is used, excess thickness 37 or buildup 38 occurs on the punch side of toothed part 3' as shown in Figs. 4(A)-4(C) because the clearance between said punch 1 and female die 2 is increased. When excess thickness 37 is produced the major diameter of toothed part 3' remains unchanged, but when buildup 38 is produced the diameter of toothed part 3' is greater than normal. Excess thickness 37 or buildup 38 can be removed in a secondary process of machining or grinding. Also, when a higher degree of precision is required similar to that of trimming taper removal, it is desirable to perform a secondary pressing operation on the toothed part 3' which has excess thickness 37 or buildup 38 produced thereon in order to increase the precision of the tooth profile. A secondary pressing process can be performed on toothed part 3' having excess thickness 38 produced thereon, but buildup 38 is treated separately, because there are instances when buildup 38 is not suitable for a secondary pressing process. In the case of excess thickness 37, an excess thickness recess 11 can be provided on punch 1 prior to performing a primary pressing process so as not to increase the processing pressure as shown in Fig. 5(A), and an excess thickness recess 41 is also provided to counter 4 prior to each secondary pressing process, as shown in Fig. 5(B). In cases when a round punch is not used, there is a method whereby shear drop 39 or excess thickness 37 is removed by machining or grinding after toothed part 3', which has a shear drop 39 or excess thickness 37 produced thereon as shown in Figs. 6(A) and 6(C), is subjected to a primary pressing process, and a method whereby a primary pressing operation is performed so as to not result in the production of either shear drop or excess thickness as shown in Figs. 6(B) and 6(D). In a case where high precision is not required for toothed part 3', it is desirable that toothed part 3' having shear drop 39 and excess thickness 37 produced thereon undergo a primary pressing process in order to reduce the surface pressure of punch 1 and improve the performance of die 2. When high precision is required for toothed part 3', the configuration of the punch is made to conform to the shapes of the die and the blank without spacing so as to avoid producing shear drop and excess thickness, and the counter is constructed without an excess thickness recess as previously described.

Claims: A process for manufacturing a finished part (3') having a tooth profile and a boss from a blank (3) which is produced by a prior forging or machining operation to have a shape substantially equal to the shape of said finished part (3'), i.e. to have a boss with a top and/or bottom projection and/or recess, said process comprising the steps of arranging the blank (3) in front of a tapered inlet of a female die (2) having a tooth profile, and of pressing the blank (3) in its axial direction through the female die (2) by means of a punch (1) which, at its end engaging the blank (3), has a shape conforming to the respective configuration of the blank (3), characterized in that said process further comprises the steps of using a female die (2) with a mirrored inlet surface and having a taper also at its opposite inlet, both tapers being in the range of 20° to 150°, and of pressing said blank (3) a second time through said female die (2) in a direction opposite to the direction of said first pressing step by means of a counter (4) which, at its end engaging said blank (3), has a shape conforming to the respective configuration of said blank (3). A process as claimed in claim 1, wherein at the step of pressing said blank (3) a first time through said female die (2) a punch (1) is used which has a tooth profile. A process as claimed in claim 2, wherein said punch (1) and said counter (4) each have an excess thickness recess (11, 41) provided thereon. A process as claimed in claim 1, wherein at the step of pressing said blank (3) through said female die (2) a first time a round punch (1) is used having no tooth profile formed thereon. A process as claimed in any preceding claim, further characterized by the steps of removing a trimming taper after said first pressing step, and of inverting the orientation of said blank before performing said second pressing step. A process as claimed in any preceding claim, wherein said blank (3) is clamped between said punch (1) and said counter (4) during the first pressing stroke as well as during the second pressing stroke.

Inventors: YOKOYAMA, MICHIHIRO
Applicants: KABUSHIKI KAISHA YOKOYAMA SEISAKUSHO
Application year: 1987
Main classification: B21K1
IPC codes: F16H55, B21K1