Prediction of formability in drawing of PCM using tensile test and DMA creep test

Abstract

An automotive pre-coated metal system (PCM) has been investigated to avoid the wet coating process out of environmental concerns. However, automotive pre-coated metal sheets must have high formability to withstand the harsh conditions such as cutting, pressing and stamping processes. For this reason, the deep drawing test is commonly used to evaluate the formability of PCM. We have investigated and reported attempts to increase the flexibility and stiffness of polyester coatings for automotive PCM. However, it is difficult to predict whether or not the coating would form in the drawing test.For this reason, we investigated a new method to predict formability in the drawing of PCM using a tensile test and DMA creep test. The correlation between tensile test and creep test was examined and forming coefficients FU and Fɛ were proposed.Results show that if FU and Fɛ >1, the PCM sample would have sufficient formability under the drawing condition. However, the tensile strength of film, if below the compressive stress of the deep drawing punch or die, also determines the success of forming in the drawing test.