Determination of the Heat Transfer Coefficient in the Die-billet Zone for Nonisothermal Upset Forging Conditions

A number of tests were conducted to measure the heat transfer coefficient between billet and tool in non-isothermal upset forging conditions. Elastic deformation of cylindrical specimens between flat punches was used to verify the proposed procedure, whose applicability to large plastic deformation was verified in plane strain tests. This paper mainly insists on theoretical aspects and on presentation of axis ymmetrica Itests. A fixture consisting of two flat 304 stainless steel dies was instrumented with type-K thermocouples to elastically deform 1100 Al cylindrical specimens at forging temperature, also instrumented with thermocouples, A procedure was designed to measure heat transfer coefficient. Inverse analysis based on comparison between numerical and experimental data was applied. A fitting technique, based on adjustment of input data, was aimed at (i) reaching a satisfactory agreement between experimental and analytical results and (ii) determining a mean value for the heat transfer coefficient. Different operating conditions were tested.