Investigation of friction between plastic parts

The goal for this master thesis is to improve and map the main factors behind friction and wear for a commercial product used by Kongsberg automotive. Components in a gear shifter are investigated and the target is to achieve high tribological quality of the force transmission. Finding a solution for low friction and wear which is independent of lubrication is the main issue for all involved components. Different material combinations, surface textures and load conditions are variables in this thesis. Results presented are based on a literature, simulations, program development and tests. The objective for the literature study is to get knowledge about important factors which effects friction and wear for polymeric materials. Simulations is used for mapping constitutive variables in the contact region and analyze dependence of plasticity. A program written in Matlab is developed for the Forceboard (test equipment), where signals from transducers are processed and converted to staticand dynamic coefficient of frictions during long timespans. Reason for the program development is to achieve higher control in the experiments. Tests are performed with different material combinations, involved components are test plates and plungers similar to the actual application. Influence of textures are investigated for the material produced in purpose for low friction and high resistance against wear. The plunger is made of either one polymer type or steel. Time span for tests varies in purpose to compare the friction at initial state with the influence of wear. The equipment for the friction tests is a commercial product named forceboard. All tests are performed in a test rig with repeatable movements at kongsberg automotives test laboratory. Results show clear relation between friction and wear of polymeric materials used in the tests. Similar materials with different additives indicates large deviations for some tests. Experimental tests is the only reliable method for evaluating friction and influence by wear after large number of cycles. Results from conducted tests and related literature proved that both friction and wear are dependent on many variables e.g. contact pressure, temperature and surface topography. Test have also show that a suitable combination of materials and texture decrease the coefficient of friction and wear. Finally recommendations for further work are discussed.