| 摘要 |
For manufacturing a crank arm for a welded crankshaft a flat blank is gripped along its contour in a ring-shaped holder and is subjected to pressing forces acting perpendicular to the plane of the blank to produce, by extrusion, a crank pin stub and a journal pin stub projecting from opposite sides of the blank, respectively. Each stub can be extruded in two stages, the first of which results in a by and large axial material flow while the second stage produces a combined axial and radial expansion of the first formed stub to circular cylindrical shape. Simultaneously with the first extrusion a fillet merging smoothly into the stub is pressed into that lateral surface of the blank from which the stub is extruded. The fillet may extend continuously around the stub or alternatively it may be indented only along that part of the stub surface which is oriented towards the other stub. A pressing equipment for carrying out the method comprises a stationary lower tool with a segmented ring which determines the contours of the stub formed by the extrusion and of the surrounding fillet. The equipment comprises two interchangeable upper tools each having a pressing mandrel arranged to produce, in cooperation with an anvil at the bottom of the ring a substantially axial and a combined axial and radial flow of material, respectively, within the extruded stub. |
