The laws of perfect and approximate similarities in metal forming indicate that perfect similarity in deforming two different materials is practically impossible to achieve. Approximate similarity, however, is easy to obtain and proves to be very useful in predicting forming loads in extrusion and forging processes. Analysis of friction in model experiments shows how interface friction can be taken into account in model studies. Backward and forward extrusion loads are predicted from plasticine model experiments, and the results are compared with data for various steels. Using published experimenal data, the load-displacement curve in a closed-die forging has been predicted by means of model theory. The agreement between predicted and actual loads is well within useful engineering accuracy.

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