Warm Sheet Metal Forming with Localized In-Tool Induction Heating

Abstract: The increasing use of light metals and high strength steel in the automobile industry, demands for new sheet metal forming processes that can be applied successfully. In this thesis the subject of warm sheet metal forming is studied. In warm sheet metal forming the temperature of the blank is elevated either globally to one temperature evenly over the blank or locally where the flange region of the blank is given a higher temperature. A survey of existing knowledge on the subject shows that the formability can be improved remarkably. This is especially true for the deep drawing of aluminium alloys and magnesium alloys. Other benefits can also be found like the elimination of stretcher-strain marks, which can be found on certain aluminium alloys, and reduction of springback. The temperature of the blank is usually elevated by using heated tools that warm the blank through conduction. The tools are usually heated by utilizing electrical resistance heaters inserted at different locations into the tool. If the flange region is to be given a higher temperature the use of a heated blank holder and die can be used in conjunction with a cooled punch. In the thesis a new heating process is described called Localized In-Tool Induction Heating. The process integrates induction heating into the forming tool in such a way that a locally heated blank can be obtained. A short pre-heating time can then be followed by continual heating during the stroke. Since the blank is warmed, without heating the different parts of the tool, a fast and efficient process can be expected. A case study has been conducted where the manufacturing performance of Warm Sheet Metal Forming with Localized In-Tool Induction Heating has been compared with traditional sheet metal forming of a car trunk lid in aluminium. In the thesis it is concluded that warm sheet metal forming has a great potential, but the processes used must be further developed to meet production demands. A new process has been introduced and future research will further develop the process.