Patent Application
20100083724
1. Field of the Invention
This invention relates generally to metal forming operations that apply vertical force to a workpiece, and more particularly to use of a mandrel or punch and die to extrude a metal workpiece without producing a void in the component teeth.
2. Description of the Prior Art
In any cold forming process in which a punch or mandrel is forced vertically through a cylindrical workpiece, the natural flow of the workpiece material is downward toward the bottom of the workpiece and away from end where the punch first enters the workpiece. The direction of the material flow is due to the vertical forces of the press and the momentum it produces. When the teeth are being extruded by the forming process, this material flow usually leaves a void at the open end of the region where incomplete teeth are produced.
Die design can produce a counter flow, called back extrusion, but filling the voided region near the open end of the cylinder is more difficult due to the material being folded forward toward the bottom of the cylinder.
When extruding gear teeth, it is critical to move the workpiece material deep into the root of the mandrel teeth. The back extrusion process is very effective near the bottom of the gear, but near the top there is no mechanism to move the material laterally toward the axis along which the mandrel moves.
A need exists for a technique to prevent extruding incomplete teeth in the workpiece by causing flow of the workpiece material toward the central axis.
An apparatus for extruding teeth in a cylinder includes a press that includes a lower die plate for supporting the blank thereon, and upper die plate that moves along an axis relative to the lower die plate. A mandrel, aligned with the axis, moves with the upper die plate along the axis, and includes die teeth. An impingement ring, located between the upper die plate and the cylinder blank, has an opening that allows the die teeth of the mandrel to contact the blank, and includes a stinger that forces material on top of the cylinder edge toward the axis as the upper die plate or mandrel forces the impingement ring against the blank.
The invention contemplates a method for extruding teeth in a workpiece using a press that includes an upper die plate that moves along an axis relative to a lower die plate. A mandrel is aligned with the axis, is movable by the press along the axis and includes a surface formed with die teeth. The workpiece is placed on the lower die plate. An impingement ring that includes a stinger contacting the workpiece is placed between the upper die plate and the workpiece. The press is used to force the stinger against the cylindrical workpiece, to force material of the workpiece toward the axis, and to extrude the die teeth into the workpiece as the upper die plate forces the impingement ring and mandrel against the workpiece.
The impingement ring and its stinger can be produced and used simply and at low cost and as part of the die tooling. The stinger causes material of the workpiece to flow toward a void region of the workpiece where incomplete teeth would otherwise be extruded. Use of the impingement ring and its stinger, however, cause complete filling teeth in the rollover zone at the end of the extrusion cycle, producing complete teeth.
Cycle time is shortened because a later trimming and deburring operation is unnecessary.
The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art.
The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:
Referring now to the drawings, a hydraulic press 14 includes a lower die plate 16, resting on a base portion 18 of the press 14, and an upper die plate 20. Die guide posts 24 extend between upper die plate 20 and lower die plate 16. One end of each die guide post 24 is fixed to the upper die plate 20; the opposite end of each die guide post 24 has a ball bearing cage 26 attached to it. Affixed to lower die plate 16 are guide bushings 28 aligned with a respective ball bearing cage 26. Ball bearing cages 26 telescopically slide into their respective guide bushings 28 to allow axial movement of upper die plate 20 relative to lower die plate 16, minimizing friction and maintaining the two die plates 16, 20 mutually parallel. The upper die plate 20 translates along a vertical axis 29 toward and away from the lower die plate 16.
A support plate 30 that includes guide posts 24 at its lower surface is secured to upper die plate 20 for vertical movement with the upper die plate 20. A mandrel 32 is supported on and secured to the upper die plate 20. Mandrel 32 is formed with external die teeth 46, a lead surface 47, and a transition 48 connecting the lead surface and the body of the mandrel. The helix angle of die teeth 46 is the same as that desired in the teeth to be formed in a workpiece blank 58, such as a gear blank.
The blank 58, supported on the lower die plate 16, includes an annular shell having an internal surface 53 with a precise internal diameter, in which surface the internal helical gear teeth are to be extruded.
In operation, the gear blank 58 is supported on lower die plate 16 with its open upper end facing mandrel 32. The hydraulic press 14 is activated and forces the upper die plate 20 downward toward lower die plate 16, guided by die the guide posts 24. This axial translation carries mandrel 32 toward gear blank 58 such that the lead surface 47 enters the central opening 53 in the workpiece 58. Then the die teeth 46 on the mandrel are extruded into the material at the inner surface 53 of the workpiece blank 58.
When the mandrel 32 is in its desired angular position, hydraulic press 14 is actuated to continue axial translation of the upper die plate 20.
Die teeth 46 on mandrel 32 engage the inner surface of gear blank 58 and move downward into the material of the workpiece with a helical motion as they are forced into the blank, thereby forming helical gear teeth. When the predetermined depth of finished teeth is reached, hydraulic press 14 stops pressing on upper die plate 20 and retracts the upper die plate and mandrel 32.
The finished ring gear is then removed from press 14 and another blank 58 is inserted in its place preparatory to repeating the forming process.
As
At, or near the end of the stroke of the hydraulic ram, the stinger, 92, actuates to push material in the partly formed gear blank 58 laterally, i.e., radially inward toward axis 29 as stinger 92 is forced by the upper die plate 20 into contact with the top of the partly formed blank 58. This displacement of the workpiece material allows the mandrel 32 to produce fully formed teeth along the full thickness of the blank 58 including the rollover zone 88 at the top of the blank.
Although the method is described with reference to forming internal helical teeth in the blank 58, the die teeth on the mandrel 32 may be spur teeth or spline teeth, which may be located on an external surface or an internal surface of the mandrel. The teeth extruded in the blank 58 may be internal or external helical gear teeth, internal or external spur gear teeth, or internal or external spline teeth.
In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.
