Oscillating forming processes allow forming with reduced process forces when liquid lubricants are used. They are industrially applied as oscillating cold forging processes for the production of splines. Previous investigations revealed that the force reduction is provoked by relubrication of the workpiece—tool contact zone. So far, the effect of the oscillation on tool wear remains unknown. The results presented in this paper show that the wear critical region of the tool is the calibration zone. Tool wear is emulated on a test bench under loads of representative cold forging processes. The results disclose several relevant phenomena. Friction conditions can vary considerably in the course of the oscillations. Wear protection layers are effective measures to prolong tool life also under these conditions. Prediction of wear development based on established models fails due to neglecting the local state of lubrication. Graphical Abstract

Oscillating forming processes offer outstanding opportunities for lightweight applications and economic advantages. Gears, especially splines, are industrially produced by oscillating ram movements. The oscillations enable the precise manufacturing of the gearing on the tubes. At the same time, they also enlarge the sliding distance in each stroke. Therefore, tool wear has to be considered carefully. Observations of oscillating gear forming processes reveal a startling phenomenon: Calibration regions of tools show the first wear marks during the manufacturing process, although the maximum contact stress is located in the forming area. According to Archard’s equation, the maximum wear is expected to be located in the area of maximum contact normal stress. In this paper wear prediction based on numerical simulations and a modified Archard ́s equation is presented. The implemented wear factor is of particular influence. Adequate values for this factor are derived from gear forming processes with tools made out of the steel 1.2379. Splines made of case hardening steel (16MnCrS5) can be produced with these tools, but wear is already evolving when laboratory lots are produced. Wear behavior and wear volume are recorded and used to determine the wear factor. The resulting values for wear factors in Archard’s equation indicate that changing contact and lubrication conditions during the pre-and the backstroke of oscillating processes have to be taken into account in wear modelling. This is achieved by a decomposition of the wear index into material and lubrication related factors. The extended model allows for a local wear forecast in processes with oscillating ram movements for which Archard’s classic wear model does not give plausible results.

Turbulent motion in open air must be studied in a way differing from that followed in laboratory experiments. We cannot choose or arrange for the most suitable conditions; we have to make the best of what nature offers; it is nearly impossible to stain air masses sufficiently so that they show streamlines-we have to judge their possible form from complicated effects. The results arrived at will depend upon the means at one's disposal and the way pursued.

Friction is one of the variables that have a far-reaching influence on forming processes. In the past, less attention was paid to static friction than to sliding friction in forming processes. In this paper, a test stand for the determination of static friction under load in metal forming is presented. The results are discussed using the example of an oscillating cold forming process. It could be shown that the expected influence of static friction is low in this application. Graphical abstract

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