Investigation of friction in the sheet metal forming process

Abstract

The presented bachelor thesis deals with the investigation of different influence factors on the friction coefficient. Furthermore it serves to characterize the mechanical properties of advanced high strength steels (AHSS). In this document there is given an overview of the fundamentals of tribology with special regard to the subtopics lubrication, wear and friction. Afterwards the fundamentals of AHSS including the explanation as well as their coarse mechanical properties, their chemical composition and their metallurgical structure as well as their industrial application were explained. The investigation of the friction coefficient concentrates on three different influence factors, based on a comprehensive literature research. These influence factors are the contact pressure, the viscosity of the used lubricant and the sliding velocity of the workpiece. To enable the needed experiments it was necessary to take the self-developed Sheet Metal Forming Simulator (SMFS) in operation. This taking in operation included tasks like, setting up the power supply for the sensors, welding of the measurement cables, designing an interface to control the PCL as well as the calibration of the sensors. In addition three different kinds of experiments were carried out including a tensile test, a bending test and a test to determine the different influence factors as already mentioned. The first tests were carried out with aluminum specimen in order to test the correct function of the SMFS. The bending test shows trustfully results whereas it could notice inaccuracies based on the shape of hand cut specimen which were used. The investigation of the different influence factors was performed with two hand cut specimens under the same boundary conditions. The experiments showed a slight increase of the friction coefficient with higher contact pressures, this observation correspond with the prior expectations based on the literature research. The experiments were carried out with low contact pressures up to 7 N/mm² and without lubrication. For following experiments it is necessary to use stronger materials and/or thicker specimen in order to increase the contact pressure. The shaping of stronger and thicker specimen is not possible without an appropriate shaping tool. As the delivery of the shaping tool delayed for a period of time that couldn’t be expected, it was impossible to perform the necessary experiments in time.