Dry friction under pressure variation of PACVD TiN surfaces on selected automotive sheet metals for the application in unlubricated metal forming
Forming without lubricants opens up ecologic and economic benefits for producing industries. In addition, dry friction allows better transmission of the process loads to the required forming force. Without any surface treatment, however, unlubricated contact leads to highly increased wear during forming. One way to describe friction in a way relevant for metal forming processes is the determination of Coulomb's friction coefficients over varying process parameters, which is usually measured on highly dedicated test facilities. Within the present study, kinetic and static friction coefficients have been examined by strip drawing on universal tensile testing machines. Contact pressure was varied from 1 to 100 MPa by deploying two different friction tools. Amongst the material specific coefficients and the resulting trends of friction vs. pressure, their comprehensive connectibility overarching the test assemblies was of key research interest. Plasma assisted chemical vapor deposition (PACVD) of titanium nitride (TiN) has been deployed to the friction jaws of the testing tools, after conventional surface treatments for sheet metal forming tools (i.e. Tenifer nitro-carburation, plasma nitration and PVD-AlTiN) have failed in preliminary dry friction experiments. With this coating technology, dry friction of different automotive-typical sheet metal materials was tested successfully even at elevated pressure. Proportionally increasing trends of kinetic and static friction over pressure were obtained, which are linked overarching the experimental setups by linear regression.