The influence of strain rate and the effect of friction on the forging load in simple upsetting and closed die forging
Forging provides an elegant solution to the problem of producing complicated shapes from heated metal. This study attempts to relate some of the important parameters involved when considering, simple upsetting, closed die forging and extrusion forging. A literature survey showed some of the empirical graphical and statistical methods of load prediction together with analytical methods of estimating load and energy. Investigations of the effects of high strain rate and temperature on the stress-strain properties of materials are also evident. In the present study special equipment including an experimental drop hammer and various die-sets have been designed and manufactured. Instrumentation to measure load/time and displacement/time behaviour, of the deformed metal, has been incorporated and calibrated. A high speed camera was used to record the behaviour mode of test pieces used in the simple upsetting tests. Dynamic and quasi-static material properties for the test materials, lead and aluminium alloy, were measured using the drop hammer and a compression-test machine. Analytically two separate mathematical solutions have been developed: A numerical technique using a lumped-mass model for the analysis of simple upsetting and closed-die forging and, for extrusion forging, an analysis which equates the shear and compression energy requirements to the work done by the forging load. Cylindrical test pieces were used for all the experiments and both dry and lubricated test conditions were investigated. The static and dynamic tests provide data on Load, Energy and the Profile of the deformed billet. In addition for the Extrusion Forging, both single ended and double ended tests were conducted. Material dependency was also examined by a further series of tests on aluminium and copper. Comparison of the experimental and theoretical results was made which shows clearly the effects of friction and high strain rate on load and energy requirements and the deformation mode of the billet. For the axisymmetric shapes considered, it was found that the load, energy requirement and profile could be predicted with reasonable accuracy.