Process optimization by oscillating tool movements in bulk metal forming
Forming longitudinal toothings with an oscillating ram movement is used to produce high precision toothings and thin walled profiles from tubes [Figure 1]. High forming forces in conventional forming of longitudinal toothings lead to buckling when forming thin walled work pieces. Due to the oscillating ram movement the forming force can be reduced by up to 40 % [Figure 2]. This leads, amongst others, to an extension of the forming limits and enables e.g. the forming of toothings with smaller wall thickness. The reason for the reduction of the forming force is not clarified yet. Two theories are encountered in literature: One is the “friction theory” which attributes the force reduction to the rebuilding of the lubricating film during the back stroke. On the other hand the “softening theory” attributes the force reduction to softening effects like the Bauschinger-Effect due to the alternating load when using oscillating ram motion.
The main focus of this research project is to identify the reason for the force reduction. Additionally, the implementation of the reason in commercial simulation systems increases the accuracy of the representation of the numerical model.
To identify the reason for the force reduction and to implement that reason in commercial FE-Systems the process is experimentally und numerically investigated. To separate the two theories experimentally a tool with a container was produced which enables the adjustment of the radial stress on the tooth forming die. As a result, the back stroke can be executed without any load. Hence, softening effects like the Bauschinger-Effect can be excluded. With the help of that tool and the numerical investigations the mechanisms of the softening theory could be identified as the reason for the force reduction.