An empirical formula for workability limits in cold upsetting and bolt heading

Previous experimental work has focused on determination of forming limits in terms of local strains. The present study extends this approach. Fracture loci and strain paths were determined experimentally from cold upset tests on cylindrical specimens. Several combinations of cylinder length, diameter, lubrication conditions, and die surfaces were used to determine the influence of these parameters on fracture. Strain paths have been shown to be process and geometry dependent but material independent. On the other hand, fracture loci depend upon material properties but not on process parameters. The point of intersection of the process strain path with the material fracture locus represents fracture. Using a series of curve-fitting techniques, expressions were developed for determining this point in terms of process and material parameters.