New tribo-systems for sheet metal forming of advanced high strength steels and stainless steels

The environmental issue, concerning the lubrication in sheet metal forming, has become considerably important in the past 10 years. Besides the fact that legislation is becoming more restrictive on the type of lubricant industry is allowed to use, many companies are embracing the path of social responsibility and sustainability, which implies a careful application of environmentally friendly technology. On the other hand the global market requires more and more complex products, which ignites a chain reaction that affects the whole life cycle of the product. Regarding sheet metal forming, this means that the performance of the workpiece materials have to improve in order to satisfy higher strength and lower weight requirements. This however leads to challenges in the forming operation, especially when high surface expansion and elevated strain are involved. The challenge is to achieve long production run and fulfilling the product specification. This means that galling is one of the first problems occurring in sheet metal forming. The remedy has been so far the application of hazardous lubricant such as chlorinated paraffin oils. The technology in environmentally friendly lubrication is advancing but it faces the reluctance of industry in the application of new solutions, due to the high trial costs. This project presents a new methodology for testing new environmentally friendly tribo-systems for sheet metal forming of advanced high strength steels and stainless steels. For the purpose, a new Universal Sheet Tribotester was developed. A production process was selected at Grundfos, which is currently running with chlorinated paraffin oil. The process includes a deep drawing and two subsequent re-drawings in a progressive tool. The process was numerically analyzed to investigate the tribological conditions. A suitable laboratory test (BUT test) was selected to simulate the production process. The BUT test was numerically analyzed to verify that the tribological conditions are close to the production process ones. A few interesting new tribo-systems were selected to be investigated in the BUT test. Some of them showed promising results and were further tested in production. Besides the analysis of the lubrication performance, thermal investigation of the limit of lubrication was performed by means of numerical simulation. The results showed that there is a correlation between laboratory and production tests, but also that improvements are needed to emulate tribological conditions in production. This may allow a better characterization of the tribological conditions by means of numerical methods, when testing new solutions in production, therefore reducing the related costs.