COMPACTED-POWDER OPPOSED TWIN-HELICAL GEARS AND METHOD

Abstract: A multiple-acting powder metal press is disclosed for making green form double helical gear compacts. The press has inner and outer lower punches, and an upper, outer punch. The upper and lower outer punches have left hand and right hand external helical profiles as chosen to produce a desired helical gear. The punches co-operate with left hand and right hand helical dies carried by the press about the punches. The helical faces require that the dies rotate relative to the punches during operation. A cam and roller mechanism may drive this rotation. The compact forming process commences with an open position in which powder is introduced to a vacant lower die cavity. The upper portions of the press advance downward to close the cavity. All parts of the press except the lower inner, or transfer, punch then move downward at the same speed to transfer powder to the extremities of the cavity. When transfer is complete both lower punches may be stopped, while the upper punches continue to advance. The dies advance at half the speed of the upper punches, rotating partially as they do so. Once the powder reaches its compacted density the upper and lower punches cease motion, but the dies continue to turn, separating themselves and compressed part. Finally the part is ejected and the press returns to the initial condition.

Description: COMPACTED-POWDER OPPOSED TWIN-HELICAL GEARS AND METHOD Field of Invention 5 This invention relates to the field of compacting presses for powder materials, and in particular to such presses as are used to compact powder metal into the form of gears, helical gears, and most particularly to opposed double helical, or herringbone, gears. Background ofthe Invention Powder compacting presses have been known for many years. They typically involve 10 at least three interacting pans: a die, an upper punch and a lower punch. Initially the top punch is separated from the die and powder is introduced into a cavity formed within the die above the lower punch. Subsequent motion of the opposed punches reduces the internal cavity volume to compress the powdered metal to desired density. The resulting green formed pan is removed from the cavity and sintered. For a part having sections of differing thickness 15 additional movable top or bottom punches may be added to promote transfer of powder within the cavity. The manufacture of gear teeth is more difficult when a helical gear is desired. Unlike a simple spur gear, as the die for a helical gear is closed it must also rotate relative to the punch, and then must achieve relative rotation in the opposite direction to release the compacted pan. 2 o Where the helix angle is shallow, and the thickness of the gear is modest, an externally helically threaded punch is, or opposed punches are, brought into a mating, internally helically threaded die under the pressure of longitudinally acting rams. The die and one punch or both punches are carried in bearings and the force of the ram acting against the threads causes the tool elements (i.e. die and punch or both punches) to auto-rotate. Auto25 rotating helical tool elements (i.e. die and punch or both punches) are known, as for example in U.S. 3,694,127 to Takahashi et al., and U.S. 5,259,744 to Take. When the helix angle or the thickness of the gear increases, the frictional resistance in such dies may become large. To overcome this friction it is known to use motors to apply a torque to the tool elements, or to cause rotation of the tool elements at an appropriate speed, 3 o given the helix angle, as longitudinal rams force the tool elements together. It is also known that if one wishes to make parts having keyways or eccentric bores or internal splines there must be no relative rotation of the punch or core feature relative to the compacted powder, since such motion would shear off the keyway or bore. 1 BNSDOCID <WO 0112367 A2 I > Powder metal gears with offset, phased or undercut upper and lower portions have been produced. In these cases the finished pans can comprise at least two gear profiles formed in opposing dies which separate on a parting plane. In the case of helical gears it would be advantageous to be able to produce a gear having a helical profile to one side ofthe parting plane of the dies, and a different profile to the other side, whether an opposed helix, a helix of different pitch of the same hand, or out of phase helix, or a spur gear, whether of the same diameter or tooth height or not. A typical application of this kind of technology relates to the production of symmetrical opposed helical gears, most often referred to as herringbone gears. It is advantageous to make herringbone gears from compacted and sintered powder metal since it is difficult and expensive to machine herringbone gears in the conventional manner. Conventional powder metallurgy may instead require back to back placement and juncture of two opposite-handed helical gears. This limits the sire and delicacy of the metal herringbone gears that can be manufactured, and also their quality. If welded together such gears may not be true. If mechanically fastened such gears may be unnecessarily bulky. U.S. 3,694,127 to Takahashi et al. shows, at figures 11 and 12, a powder metal compact and tooling for opposite handed helical threads. This apparatus cannot be used to produce herringbone gears, or even opposite handed gears in which the diameter of the gears is close, since, as noted in U.S. 5,259,744 to Take, the outer lower punch wall becomes too thin. Experience suggests that the minimum die wall thickness required to make a reliable tool is about 2 mm., which with allowance for the dedendum of the larger gear and the addendum of the smaller gear, would limit the parts which can be produced. The Takahashi device also relies on auto-rotation to move the upper punch, die, and lower outer punch all at once. Take can be used to make two helical gears of the same hand, but once again cannot make herringbone gears and is limited to producing helical gears that vary in diameter by at least the height ofthe teeth to be produced. In PCT application WO 97/43067 there is described a method and apparatus for manufacturing a gear with a pair of helical gears. The gear forms are located on the radially outer surface and may be of different configurations. There is, however, a need to provide a gear with internal helical gear teeth in certain applications. According to the present application there is provided a method of forming an annular gear having a radially inwardly directed circumferential wall with a pair of sets of teeth formed thereon from a powdered metal charge said comprising the steps of a) defining a mold cavity containing said powdered metal charge between a die and a pair of punch sets each having a punch and a core rod interconnected by 5 a thread form corresponding to a respective one of said sets of teeth, b) positioning each of said core rods to project axially from the respective punch to expose a portion of each of said thread forms within said cavity, c) compressing said powdered metal charge between said outer punches by axially displacing said punches relative to one another to form a compact io having each of said thread forms molded thereon, d) withdrawing said core rods from said cavity whilst following respective ones of said thread forms on said compact and e) removing said compact from said die. According also to the present invention there is provided a further a tool set for use in is a press to form an internally toothed annular component, said tool set comprising a die having an inner wall corresponding to the periphery of said component a pair of punch sets, each engagable with said die to define an enclosed mold cavity, each of said punch sets comprising punch and core rod interconnected by a thread form corresponding to a respective one of said sets of teeth, said core rods being axially displaceable relative to said outer punch to expose a 2 o portion of said thread form in said mold cavity and said punches being axially displaceable relative to one another to compress a powder charge in said cavity. Brief Description of Drawings Embodiments ofthe present invention will now be described by way of example only 25 with reference to the accompanying drawings in which: Figure 1 is a perspective view ofa component formed from metallic powder. Figure 2 is a section through a tool set and associated press components showing the tool set in an open position. Figure 3 is a section similar to Figure 2 with the tool set in an initial closed position. 3 o Figure 4 is a view similar to Figure 2 with the tool set in a pre compression configuration. Figure 5 is a view similar to Figure 2 with the die set in a compressed position. BNSDOCID <WO 0112367A2 I > Figure 6 is a view similar to Figure 2 with the die set in an eject position. Figure 7 is a view similar to Figure 2 of an alternative embodiment of tool set. Figure 8 is a view similar to Figure 3 ofthe alternative configuration. Figure 9 is a view similar to Figure 4 ofthe alternative configuration. Figure 10 is a view similar to Figure 5 ofthe alternative configuration. Figure 11 is a view similar to Figure 6 with the alternative configuration tool set in an eject position. Referring therefore to Figure 1, an internal herringbone gear 1010 has a body 1012 with a peripheral outer surface 1014 and a toothed radial inner surface 1016. The inner surface 1016 is formed in two sets of dissimilar gear teeth 1018, 1020. In the example shown in Figure 1, the gear teeth 1018, 1020 are of equal but opposite helix angle and of similar diameter although it will be appreciated that other configurations of teeth sets 1018, 1020 can be utilized, including combinations of helical gears and straight gears, or two helical gears ofthe same hand but different helix angle. The component 1010 is formed from a powdered metal charge that is formed under pressure into the finished shape in the tool set 1022 shown in Figures 8 through 12. The nature ofthe metal charge and its subsequent processing into a finished component is well known in the art of powdered metallurgy and therefore need not to be described further at this time. The tool set 1022, shown in an open position in Figure 8, includes a die assembly 1024 and upper and lower punch sets 1026, 1028. The tool set 1022 is used in combination with a multi stage hydraulic press of known construction. The drive cylinders associated with the press are shown schematically as hydraulic actuators in the drawings, but it will be appreciated by those skilled in the art that the configuration and drives for such a press will vary according to the particular press utilized. The punch sets 1026, 1028 and die assembly 1024 are displaceable relative to one another along the longitudinal axis indicated A-A under the control ofthe press. The die assembly 1024 includes a support 1030 whose position is controlled by a press cylinder 1032. The support 1030 locates a die 1034 having an inner surface 1036 conforming to the shape ofthe outer surface 1014 ofthe component 1010. The die 1034 is located by a keeper plate 1038 in a well-known manner so as to be readily removable from the support 1030. The upper punch set 1026 includes an outer support 1040 whose position is controlled by a press cylinder 1042. An outer punch 1044 is retained by a clamping ring 1046 on the lower face ofthe support 1040. The outer punch 1044 has an outer surface 1048 conforming to the 5 radially inner surface 1036 ofthe die 1034 so as to be a snug sliding fit within the die, and a radially inner surface 1050 that has a thread form corresponding to the teeth 1018 on the component 1010. A core rod 1060 is received in the outer punch 1044 and has a threaded outer surface 1062 complementary to the inner surface 1050 ofthe outer punch 1044. The core rod 1060 io depends from a housing 1063 that is rotatably mounted by bearings 1064, 1066 on a mounting block 1068. The block 1068 is displaceable relative to the housing 1040 under the influence ofa press cylinder 1070. An insert 1072 is located within the core rod 1060 and is rotatably supported by a bearings 1074 so as to be freely rotatable relative to the core rod. The end face 1076 ofthe core rod 1060 is recessed from the end faces 1078, 1080 ofthe insert 1072 and is outer punch 1044 respectively. The lower punch set 1028 is similar in construction to the upper punch set 1026 and includes an outer punch 1082 and a core rod 1084. The outer punch 1082 has a radially outer surface 1086 that is a sliding fit within the die 1034 and a radially inner surface 1088 having a thread form corresponding to the teeth 1020 on the component 1010. The outer punch 1082 20 is secured a lower support 1090 whose axial position is controlled by a press cylinder 1092. The core rod 1084 has an outer surface 1094 complementary to the thread form 1088. The core rod 1084 is secured to a housing 1096 which is rotatably supported on bearings 1098, 1100 on a support column 1102. The axial position ofthe column 1102 is controlled by a press cylinder 1104. 25 The tool set 1022 is initially positioned as shown in Figure 2 with an end face 1106 of the lower core rod 1084 flush with the upper surface 1108 ofthe die 1034. The outer punch 1082 is withdrawn relative to the core rod 1082 so that end face 1110 is below the end face 1108 ofthe die 1034. A cavity 1112 is thus formed to receive a charge of metallic powder. The relative position ofthe inner and outer punches is carefully controlled to provide the 3 o requisite volume for the cavity 1112 with the flush surfaces 1106, 1108 facilitating filling of the cavity with the charge. BNSDOCID <WO 0112367 A2 I > After charging, the tool set 1022 is moved to the configuration shown in Figure 9. The die assembly 1024 is displaced slightly axially by the press cylinder 1032 so that the upper surface ofthe charge is recessed below the upper surface 1108 ofthe die 1034. The upper punch set 1026 is lowered by press cylinder 1042 so that the outer punch 1048 is received within the die 1034. In this position, the end face 1106 ofthe lower core rod 1084 abuts the end face 1078 ofthe insert 1072 and the end face 1080 ofthe upper outer punch 1044 is aligned with the end face 1106 ofthe core rod 1084. The cavity 1112 is thus closed with a slight clearance provided between the end faces 1076, 1106 ofthe core rods 1060,1084. The press cylinder 1070 is then extended and press cylinder 1042 retracted to displace the core rods 1060, 1084 axially relative to the die 1034. The axial displacement ofthe core rods 1060, 1084 induces rotation relative to respective ones ofthe outer punches 1044, 1082. At the same time there is relative rotation between the core rods themselves, depending upon the relative configurations ofthe tooth sets 1018, 1020, which is accommodated by the insert 1072 and the clearance between the end faces 1076, 1106. In the example shown, the gears 1018, 1020 are of similar diameter and equal but opposite helix angle so that the punches 1060, 1084 are of similar diameter. The punches thus contra rotate as they are displaced axially. The core rods are displaced axially until they are located within the cavity 1112 in the correct proportion so that thread forms corresponding to each ofthe tooth sets 1018, 1020 are presented to the charge in the cavity 1112. The charge in cavity 1112 is then compressed by relative axial displacement between the outer punches 1044,1082. Conceptually, the end faces 1080, 1110 are driven toward one another by the press cylinders 1042, 1092 and in practice a controlled axial displacement ofthe die assembly 1024, core rods 1060, 1084 and upper outer punch 1044 is provided by the respective press cylinders whilst the lower outer punch 1082 remains stationary. The relative displacement continues until the final dimensions ofthe component 1010 are attained in the cavity 1112 as shown in Figure 4. During this displacement, the core rods auto rotate relative to their respective outer punches as accommodated by the bearings, 1064, 1066 and 1098, 1100 with relative rotation between the core rods being accommodated by the insert 1072. Once compressed, the die assembly 1024 is retracted by the press cylinder 1032 and the upper punch set retracted by the cylinder 1042. The component 1010 is thus exposed and available for removal. To facilitate removal ofthe component the die 1034 is initially withdrawn axially by the cylinder 1032 whilst the compact is supported by the end faces 1080,1110 of the respective outer punches 1044, 1082. The core rods 1060, 1084 are then 5 withdrawn whilst the outer punches 1044, 1082 support the compact and the upper punch set 1026 then raised to expose the compact. The initial withdrawal ofthe die permits a limited radial spring back ofthe molded component to facilitate removal ofthe core rods 1060, 1084. The tool set 1022 offers careful control over the finished component and ensures that the threaded formations used to define tooth sets 1018, 1020 remain engaged during filling io and ejection of the component. A further embodiment of tool set is shown through Figures 7 through 11 in which like components will be indicated with like reference numerals with a suffix 'a' added for clarity. As many of the components are identical only those specifically referred to will be identified in the drawing. 15 As may be seen from Figure 7, the lower punch set 1028a includes a core rod 1084a that engages with a thread form on threaded outer punch 1082a. A supplementary outer punch 1120 is interposed between the outer punch 1082a and the radial wall 1036a ofthe die 1034a. The supplementary punch 1120 is supported on column 1122 whose axial position is controlled by press cylinder 1124. 20 In the fill position shown in Figure 7, the supplementary punch 1120 is retracted relative to the outer punch 1082a to provide an enlarged cavity 1112a. After filling, the cavity is closed by adjustment of the die assembly 1024a and upper punch set 1026a as shown in Figure 8 and the core rods then adjusted as shown in Figure 9 to present a portion of each thread form 1062a, 1094a to the cavity 1112a. During the adjustment, the axial position of 25 the supplementary punch 1120 is adjusted by the press cylinder 1124 to move flush with the end face 1110a of the outer punch 1082a. As this occurs the relative position ofthe core rod 1084a and outer punch 1082a remains fixed and the powder contained in the recess between a supplementary punch 1120 and the outer punch 1082a is displaced to fill the void created by the extension ofthe core rod 1060a ofthe upper punch set 1026a. Thereafter, the charge is 30 compressed as shown in Figure 10 and ejected as shown in Figure 11 as with the previous embodiment. BNSDOCID- <WO 0112367A2 I > Again it will be noted that the engagement and disengagement ofthe upper punch set to permit filling and ejection occurs without disengagement ofthe thread forms so that the accuracy of those thread forms is preserved. Similarly the core rods and die may be removed whilst the component is fully supported by the outer punches.

Claims: COMPACTED-POWDER OPPOSED TWIN-HELICAL GEARS AND METHOD Field of Invention This invention relates to the field of compacting presses for powder materials, and in particular to such presses as are used to compact powder metal into the form of gears, helical gears, and most particularly to opposed double helical, or herringbone, gears. Background of the Invention Powder compacting presses have been known for many years. They typically involve at least three interacting pans: a die, an upper punch and a lower punch. Initially the top punch is separated from the die and powder is introduced into a cavity formed within the die above the lower punch. Subsequent motion of the opposed punches reduces the internal cavity volume to compress the powdered metal to desired density. The resulting green formed pan is removed from the cavity and sintered. For a part having sections of differing thickness additional movable top or bottom punches may be added to promote transfer of powder within the cavity. The manufacture of gear teeth is more difficult when a helical gear is desired. Unlike a simple spur gear, as the die for a helical gear is closed it must also rotate relative to the punch, and then must achieve relative rotation in the opposite direction to release the compacted pan. Where the helix angle is shallow, and the thickness of the gear is modest, an externally helically threaded punch is, or opposed punches are, brought into a mating, internally helically threaded die under the pressure of longitudinally acting rams. The die and one punch or both punches are carried in bearings and the force of the ram acting against the threads causes the tool elements (i.e. die and punch or both punches) to auto-rotate. Auto- rotating helical tool elements (i.e. die and punch or both punches) are known, as for example in U.S. 3,694,127 to Takahashi et al., and U.S. 5,259,744 to Take. When the helix angle or the thickness of the gear increases, the frictional resistance in such dies may become large. To overcome this friction it is known to use motors to apply a torque to the tool elements, or to cause rotation of the tool elements at an appropriate speed, given the helix angle, as longitudinal rams force the tool elements together. It is also known that if one wishes to make parts having keyways or eccentric bores or internal splines there must be no relative rotation of the punch or core feature relative to the compacted powder, since such motion would shear off the keyway or bore. 1 Powder metal gears with offset, phased or undercut upper and lower portions have been produced. In these cases the finished pans can comprise at least two gear profiles formed in opposing dies which separate on a parting plane. In the case of helical gears it would be advantageous to be able to produce a gear having a helical profile to one side of the parting plane of the dies, and a different profile to the other side, whether an opposed helix, a helix of different pitch of the same hand, or out of phase helix, or a spur gear, whether of the same diameter or tooth height or not. A typical application of this kind of technology relates to the production of symmetrical opposed helical gears, most often referred to as herringbone gears. It is advantageous to make herringbone gears from compacted and sintered powder metal since it is difficult and expensive to machine herringbone gears in the conventional manner. Conventional powder metallurgy may instead require back to back placement and juncture of two opposite-handed helical gears. This limits the sire and delicacy of the metal herringbone gears that can be manufactured, and also their quality. If welded together such gears may not be true. If mechanically fastened such gears may be unnecessarily bulky. U.S. 3,694,127 to Takahashi et al. shows, at figures 11 and 12, a powder metal compact and tooling for opposite handed helical threads. This apparatus cannot be used to produce herringbone gears, or even opposite handed gears in which the diameter of the gears is close, since, as noted in U.S. 5,259,744 to Take, the outer lower punch wall becomes too thin. Experience suggests that the minimum die wall thickness required to make a reliable tool is about 2 mm., which with allowance for the dedendum of the larger gear and the addendum of the smaller gear, would limit the parts which can be produced. The Takahashi device also relies on auto-rotation to move the upper punch, die, and lower outer punch all at once. Take can be used to make two helical gears of the same hand, but once again cannot make herringbone gears and is limited to producing helical gears that vary in diameter by at least the height of the teeth to be produced. In PCT application WO 97/43067 there is described a method and apparatus for manufacturing a gear with a pair of helical gears. The gear forms are located on the radially outer surface and may be of different configurations. There is, however, a need to provide a gear with internal helical gear teeth in certain applications. According to the present application there is provided a method of forming an annular gear having a radially inwardly directed circumferential wall with a pair of sets of teeth formed thereon from a powdered metal charge said comprising the steps of a) defining a mold cavity containing said powdered metal charge between a die and a pair of punch sets each having a punch and a core rod interconnected by 5 a thread form corresponding to a respective one of said sets of teeth, b) positioning each of said core rods to project axially from the respective punch to expose a portion of each of said thread forms within said cavity, c) compressing said powdered metal charge between said outer punches by axially displacing said punches relative to one another to form a compact 0 having each of said thread forms molded thereon, d) withdrawing said core rods from said cavity whilst following respective ones of said thread forms on said compact and e) removing said compact from said die. According also to the present invention there is provided a further a tool set for use in s a press to form an internally toothed annular component, said tool set comprising a die having an inner wall corresponding to the periphery of said component a pair of punch sets, each engagable with said die to define an enclosed mold cavity, each of said punch sets comprising punch and core rod interconnected by a thread form corresponding to a respective one of said sets of teeth, said core rods being axially displaceable relative to said outer punch to expose a o portion of said thread form in said mold cavity and said punches being axially displaceable relative to one another to compress a powder charge in said cavity. Brief Description of Drawings Embodiments of the present invention will now be described by way of example only 5 with reference to the accompanying drawings in which: Figure 1 is a perspective view of a component formed from metallic powder. Figure 2 is a section through a tool set and associated press components showing the tool set in an open position. Figure 3 is a section similar to Figure 2 with the tool set in an initial closed position. o Figure 4 is a view similar to Figure 2 with the tool set in a pre compression configuration. Figure 5 is a view similar to Figure 2 with the die set in a compressed position. Figure 6 is a view similar to Figure 2 with the die set in an eject position. Figure 7 is a view similar to Figure 2 of an alternative embodiment of tool set. Figure 8 is a view similar to Figure 3 of the alternative configuration. Figure 9 is a view similar to Figure 4 of the alternative configuration. Figure 10 is a view similar to Figure 5 of the alternative configuration. Figure 11 is a view similar to Figure 6 with the alternative configuration tool set in an eject position. Referring therefore to Figure 1, an internal herringbone gear 1010 has a body 1012 with a peripheral outer surface 1014 and a toothed radial inner surface 1016. The inner surface 1016 is formed in two sets of dissimilar gear teeth 1018, 1020. In the example shown in Figure 1, the gear teeth 1018, 1020 are of equal but opposite helix angle and of similar diameter although it will be appreciated that other configurations of teeth sets 1018, 1020 can be utilized, including combinations of helical gears and straight gears, or two helical gears of the same hand but different helix angle. The component 1010 is formed from a powdered metal charge that is formed under pressure into the finished shape in the tool set 1022 shown in Figures 8 through 12. The nature of the metal charge and its subsequent processing into a finished component is well known in the art of powdered metallurgy and therefore need not to be described further at this time. The tool set 1022, shown in an open position in Figure 8, includes a die assembly 1024 and upper and lower punch sets 1026, 1028. The tool set 1022 is used in combination with a multi stage hydraulic press of known construction. The drive cylinders associated with the press are shown schematically as hydraulic actuators in the drawings, but it will be appreciated by those skilled in the art that the configuration and drives for such a press will vary according to the particular press utilized. The punch sets 1026, 1028 and die assembly 1024 are displaceable relative to one another along the longitudinal axis indicated A-A under the control of the press. The die assembly 1024 includes a support 1030 whose position is controlled by a press cylinder 1032. The support 1030 locates a die 1034 having an inner surface 1036 conforming to the shape of the outer surface 1014 of the component 1010. The die 1034 is located by a keeper plate 1038 in a well-known manner so as to be readily removable from the support 1030. The upper punch set 1026 includes an outer support 1040 whose position is controlled by a press cylinder 1042. An outer punch 1044 is retained by a clamping ring 1046 on the lower face of the support 1040. The outer punch 1044 has an outer surface 1048 conforming to the radially inner surface 1036 of the die 1034 so as to be a snug sliding fit within the die, and a radially inner surface 1050 that has a thread form corresponding to the teeth 1018 on the component 1010. A core rod 1060 is received in the outer punch 1044 and has a threaded outer surface 1062 complementary to the inner surface 1050 of the outer punch 1044. The core rod 1060 depends from a housing 1063 that is rotatably mounted by bearings 1064, 1066 on a mounting block 1068. The block 1068 is displaceable relative to the housing 1040 under the influence of a press cylinder 1070. An insert 1072 is located within the core rod 1060 and is rotatably supported by a bearings 1074 so as to be freely rotatable relative to the core rod. The end face 1076 of the core rod 1060 is recessed from the end faces 1078, 1080 of the insert 1072 and outer punch 1044 respectively. The lower punch set 1028 is similar in construction to the upper punch set 1026 and includes an outer punch 1082 and a core rod 1084. The outer punch 1082 has a radially outer surface 1086 that is a sliding fit within the die 1034 and a radially inner surface 1088 having a thread form corresponding to the teeth 1020 on the component 1010. The outer punch 1082 is secured a lower support 1090 whose axial position is controlled by a press cylinder 1092. The core rod 1084 has an outer surface 1094 complementary to the thread form 1088. The core rod 1084 is secured to a housing 1096 which is rotatably supported on bearings 1098, 1100 on a support column 1102. The axial position of the column 1102 is controlled by a press cylinder 1104. The tool set 1022 is initially positioned as shown in Figure 2 with an end face 1106 of the lower core rod 1084 flush with the upper surface 1108 of the die 1034. The outer punch 1082 is withdrawn relative to the core rod 1082 so that end face 1110 is below the end face 1108 of the die 1034. A cavity 1112 is thus formed to receive a charge of metallic powder. The relative position of the inner and outer punches is carefully controlled to provide the requisite volume for the cavity 1112 with the flush surfaces 1106, 1108 facilitating filling of the cavity with the charge. After charging, the tool set 1022 is moved to the configuration shown in Figure 9. The die assembly 1024 is displaced slightly axially by the press cylinder 1032 so that the upper surface of the charge is recessed below the upper surface 1108 of the die 1034. The upper punch set 1026 is lowered by press cylinder 1042 so that the outer punch 1048 is received within the die 1034. In this position, the end face 1106 of the lower core rod 1084 abuts the end face 1078 of the insert 1072 and the end face 1080 of the upper outer punch 1044 is aligned with the end face 1106 of the core rod 1084. The cavity 1112 is thus closed with a slight clearance provided between the end faces 1076, 1106 of the core rods 1060,1084. The press cylinder 1070 is then extended and press cylinder 1042 retracted to displace the core rods 1060, 1084 axially relative to the die 1034. The axial displacement of the core rods 1060, 1084 induces rotation relative to respective ones of the outer punches 1044, 1082. At the same time there is relative rotation between the core rods themselves, depending upon the relative configurations of the tooth sets 1018, 1020, which is accommodated by the insert 1072 and the clearance between the end faces 1076, 1106. In the example shown, the gears 1018, 1020 are of similar diameter and equal but opposite helix angle so that the punches 1060, 1084 are of similar diameter. The punches thus contra rotate as they are displaced axially. The core rods are displaced axially until they are located within the cavity 1112 in the correct proportion so that thread forms corresponding to each of the tooth sets 1018, 1020 are presented to the charge in the cavity 1112. The charge in cavity 1112 is then compressed by relative axial displacement between the outer punches 1044,1082. Conceptually, the end faces 1080, 1110 are driven toward one another by the press cylinders 1042, 1092 and in practice a controlled axial displacement of the die assembly 1024, core rods 1060, 1084 and upper outer punch 1044 is provided by the respective press cylinders whilst the lower outer punch 1082 remains stationary. The relative displacement continues until the final dimensions of the component 1010 are attained in the cavity 1112 as shown in Figure 4. During this displacement, the core rods auto rotate relative to their respective outer punches as accommodated by the bearings, 1064, 1066 and 1098, 1100 with relative rotation between the core rods being accommodated by the insert 1072. Once compressed, the die assembly 1024 is retracted by the press cylinder 1032 and the upper punch set retracted by the cylinder 1042. The component 1010 is thus exposed and available for removal. To facilitate removal of the component the die 1034 is initially withdrawn axially by the cylinder 1032 whilst the compact is supported by the end faces 1080,1110 of the respective outer punches 1044, 1082. The core rods 1060, 1084 are then withdrawn whilst the outer punches 1044, 1082 support the compact and the upper punch set 1026 then raised to expose the compact. The initial withdrawal of the die permits a limited radial spring back of the molded component to facilitate removal of the core rods 1060, 1084. The tool set 1022 offers careful control over the finished component and ensures that the threaded formations used to define tooth sets 1018, 1020 remain engaged during filling and ejection of the component. A further embodiment of tool set is shown through Figures 7 through 11 in which like components will be indicated with like reference numerals with a suffix 'a' added for clarity. As many of the components are identical only those specifically referred to will be identified in the drawing. As may be seen from Figure 7, the lower punch set 1028a includes a core rod 1084a that engages with a thread form on threaded outer punch 1082a. A supplementary outer punch 1120 is interposed between the outer punch 1082a and the radial wall 1036a of the die 1034a. The supplementary punch 1120 is supported on column 1122 whose axial position is controlled by press cylinder 1124. In the fill position shown in Figure 7, the supplementary punch 1120 is retracted relative to the outer punch 1082a to provide an enlarged cavity 11 12a. After filling, the cavity is closed by adjustment of the die assembly 1024a and upper punch set 1026a as shown in Figure 8 and the core rods then adjusted as shown in Figure 9 to present a portion of each thread form 1062a, 1094a to the cavity 1 112a. During the adjustment, the axial position of the supplementary punch 1120 is adjusted by the press cylinder 1124 to move flush with the end face 1110a of the outer punch 1082a. As this occurs the relative position of the core rod 1084a and outer punch 1082a remains fixed and the powder contained in the recess between a supplementary punch 1120 and the outer punch 1082a is displaced to fill the void created by the extension of the core rod 1060a of the upper punch set 1026a. Thereafter, the charge is compressed as shown in Figure 10 and ejected as shown in Figure 11 as with the previous embodiment. Again it will be noted that the engagement and disengagement of the upper punch set to permit filling and ejection occurs without disengagement of the thread forms so that the accuracy of those thread forms is preserved. Similarly the core rods and die may be removed whilst the component is fully supported by the outer punches. WE CLAIM 1. A method of forming an annular gear having a radially inwardly directed circumferential wall with a pair of sets of teeth formed thereon from a powdered metal 5 charge said comprising the steps of f) defining a mold cavity containing said powdered metal charge between a die and a pair of punch sets each having a punch and a core rod interconnected by a thread form corresponding to a respective one of said sets of teeth, g) positioning each of said core rods to project axially from the respective punch 0 to expose a portion of each of said thread forms within said cavity, h) compressing said powdered metal charge between said outer punches by axially displacing said punches relative to one another to form a compact having each of said thread forms molded thereon, i) withdrawing said core rods from said cavity whilst following respective ones s of said thread forms on said compact and j) removing said compact from said die. 2. A method according to Claim 1 wherein at least one of said core rods is withdrawn by displacing it axially relative to the respective punch. 3. A method according to Claim 2 wherein each of said core rods is withdrawn by 0 relative displacement between respective ones of said core rods and punches. 4. A method according to Claim 3 wherein each of said thread forms has a helix angle less than 90° and said punch and core rod rotate relative to one another upon withdrawal of said core rod. 5. A method according to Claim 1 wherein one of said punch sets is inserted in said die 5 to define an open cavity and said charge is placed in said cavity prior to the other of said punch sets being inserted into said die. 6. A method according to Claim 5 wherein said core rod of said one punch set axially projects from said punch prior to placing said charge. 7. A method according to Claim 6 wherein an end face of said core rod projects to the o upper surface of said charge in said die. 8. A method according to Claim 7 wherein said end face of said core rod and an end face of said die are level with said upper surface of said charge. 9. A method according to Claim 7 wherein an end face of said core rod of said other set abuts said end face of said core rod of said one set upon insertion of said other punch set into said die. 5 10. A method according to Claim 6 including the steps of aligning said end face of said core rod of said one set and said end face of said die and filling said cavity with said charge up to said end faces. 11. A method according to Claim 10 including the step of axially displacing said die relative to said one punch set to offset said end face of said die from the upper surface o of said charge and subsequently inserting said other punch set into said die. 12. A method according to Claim 11 wherein end faces of said core rods are brought into abutment upon insertion of said other punch set. 13. A method according to Claim 12 wherein each of said core rods are moved axially relative to respective ones of said punches to position a portion of each of said thread 5 forms in said cavity. 14. A method of forming from a powdered metal charge an annular gear having a radially inwardly directed circumferential wall with a pair of dissimilar sets of teeth formed thereon comprising the steps of:- a) providing a die and a first punch set within said die, said punch set including a o punch and a core rod relatively rotatable and interconnected by a thread form corresponding to one of said sets of teeth, b) positioning said first core rods relative to said die to define a chamber to contain said charge and radially delimited by said core rod of said first punch set, to present a thread form to said chamber, 5 c) inserting a second punch set into said chamber, said second set having a punch and a core rod to expose a portion of each of said threads forms in said chamber. d) Rotating said punches relative to respective core rods to move said core rods toward one another and to compress said charge in said chamber to form a o compact, e) Rotating said core rods relative to respective ones of said punches to move 10 said core rods away from one another to withdraw said core rods from said compact and permit removal thereof from said die. 15. A method according to Claim 14 wherein said step of positioning said core rods includes rotating each of said core rods relative to respective ones of said punches to 5 displace said core rods conjointly relative to said die. 16. A method according to claim 14 wherein said step of positioning said first punch set includes aligning an end face of said core rod with an end face of said die. 17. A method according to Claim 16 including the step of placing said powdered metal charge in said chamber prior to insertion of said second punch set. 0 18. A method according to Claim 14 wherein said die is removed from said compact prior to removal of said core rods. 19. A tool set for use in a press to form an internally toothed annular component, said tool set comprising a die having an inner wall corresponding to the periphery of said component. s a pair of punch sets, each engagable with said die to define an enclosed mold cavity, each of said punch sets comprising punch and core rod interconnected by a thread form corresponding to a respective one of said sets of teeth, said core rods being axially displaceable relative to said outer punch to expose a portion of said thread form in said mold cavity and said punches being axially o displaceable relative to one another to compress a powder charge in said cavity. 20. A tool set according to Claim 19 wherein one of said punch sets includes a support member engagable with said core rod of said other set, to maintain end faces of said core rods in spaced relationship, said support member being rotatable relative to said core rod of said one set to facilitate relative rotation between said core rods as said core rods are conjointly displaced relative to respective ones of said outer punches. 11

Inventors: HINZMANN GERD, HINZMANN, GERD
Applicants: HINZMANN GERD, STACKPOLE LTD, HINZMANN, GERD, STACKPOLE LIMITED
Application year: 2000
Main classification: B22F5
IPC codes: B22F5