Experimental investigation on slip conditions during thread rolling with flat dies

The process design of flat die rolling operations can be a tedious and costly process due to the challenges posed by small process windows. Within this work, an effort is made to closely investigate and understand the process limits caused by excessive slippage of the workpiece. Optical measurements are carried out to capture the characteristics of excessive slippage and the influence of the stroke rate and the tribological system on this process limit. Large differences in slippage were observed, depending on the tribological system. While systems with polymer based lubricants showed excessive slippage at low stroke rates, systems using oil or no lubricant endured higher stroke rates before process limits were reached. The optical measurements revealed three major forms of slippage: successful rolling without slippage, failure due to excessive slippage at process start, and failure due to excessive slippage at around one workpiece rotation.