Transformation hardening with high power diode laser systems using single and multiple tracks

Abstract

In 2002 a research project was started to explore the possibilities of HPDL and to inform some interested industrial companies in Belgium about laser hardening. Initial tests were performed with a 3 and 4 kW HPDL mounted on a robot and compared with similar tests obtained by other type of lasers. It was shown that any part of steel with at least 0,4 % carbon or nodular cast iron with a pearlitic matrix can be hardened successfully with a HPDL. It is known that a laser can be used to harden small and difficult to reach areas. The actual research was more focussed on the hardening of large areas on flat surfaces and other geometries. Special optics and multiple tracks were used to obtain this goal. The tests were performed on 5 different steel: C45, 42CrMo4, X210CrW12, X40Cr13 and on one pearlitic nodular cast iron. Each material was machined in 3 different geometries: flat steel sheet, flat steel sheet with different type of grooves and cylinders with a transition radius between two diameters.On the flat samples, multiple and parallel tracks were used to harden the material with several degrees of overlapping. This method lead to the formation of overlap zones where a decrease in hardness was observed due to backtempering. The influence of overlapping was examined and it was found that a high overlapping degree gives the best results in terms of hardness variations.With the U- and V-shaped grooves complete contour hardening of the grooves seemed difficult even by using special optics and multiple tracks. The best transverse hardness profile was obtained after applying separate tracks without overlapping. This result is acceptable for those applications where only critical zones must be hardened against wear.Cylindrical surfaces were hardened by spiral shaped tracks whereas the transition radius was hardened by one closed track. Similar results as on flat sheet were found.In the final stage of the project several industrial parts were hardened with HPDL using the experience from the tests on the special geometries. Some practical examples of laser hardening of bending blocs, gears, shafts etc. will be discussed.In 2002 a research project was started to explore the possibilities of HPDL and to inform some interested industrial companies in Belgium about laser hardening. Initial tests were performed with a 3 and 4 kW HPDL mounted on a robot and compared with similar tests obtained by other type of lasers. It was shown that any part of steel with at least 0,4 % carbon or nodular cast iron with a pearlitic matrix can be hardened successfully with a HPDL. It is known that a laser can be used to harden small and difficult to reach areas. The actual research was more focussed on the hardening of large areas on flat surfaces and other geometries. Special optics and multiple tracks were used to obtain this goal. The tests were performed on 5 different steel: C45, 42CrMo4, X210CrW12, X40Cr13 and on one pearlitic nodular cast iron. Each material was machined in 3 different geometries: flat steel sheet, flat steel sheet with different type of grooves and cylinders with a transition radius between two diameters.On the flat s...