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This is the fourth in a six-part series on heading basics contributed by Carpenter Technology Corporation. This installment recommends practices when combining upsettings and extrusions and discusses warm and hot heading techniques.
COMBINING UPSETTINGS AND EXTRUSION
Multiple station machines often combine upsetting and extruding operations to form large-head, small-shank parts. The reason is that upsets can involve 6 to 10 diameters, rather than the 4-1/2 diameters maximum. Upsetting and extruding, however, are separate operations, so maximum deformation of a blank must be figured separately for upsetting and extruding limits even with multi-station headers.
By starting with wire stock larger in diameter than the required shank, then extruding the shank and finally upsetting the head, maximum deformations can be reached for both extruding and upsetting based on initial stock size. For instance, a 1/2'' blank trap extruded to a reduction in area of 80 percent, and then upset 6 diameters, results in an actual upset having 70 diameters of the extruded shank size.
Since single-die, double-stroke headers (one die, two punches, two blows) are the norm in heading machines, combining upsetting and extrusion is common practice. The first blow extrudes the shank and partially forms the head; the second blow finishes the head.
An important rule for combining these two operations is that parts being formed in solid dies cannot have a shank length that exceeds 8 diameters (Figure 1). Since solid dies include a knockout pin, the knockout pin must overcome the great friction between the shank and the...