TRANSFORMATION HARDENING WITH HIGH POWER DIODE LASER SYSTEMS USING SINGLE AND MULTIPLE TRACKS

摘要

In 2002 a research project was started to explore thepossibilities of HPDL and to inform some interestedindustrial companies in Belgium about laser hardening.Initial tests were performed with a 3 and 4 kW HPDLmounted on a robot and compared with similar testsobtained by other type of lasers. It was shown that anypart of steel with at least 0,4 % carbon or nodular castiron with a pearlitic matrix can be hardenedsuccessfully with a HPDL. It is known that a laser canbe used to harden small and difficult to reach areas. Theactual research was more focussed on the hardening oflarge areas on flat surfaces and other geometries.Special optics and multiple tracks were used to obtainthis goal. The tests were performed on 5 different steel:C45, 42CrMo4, X210CrW12, X40Cr13 and on onepearlitic nodular cast iron. Each material was machinedin 3 different geometries: flat steel sheet, flat steel sheetwith different type of grooves and cylinders with atransition radius between two diameters.On the flat samples, multiple and parallel tracks wereused to harden the material with several degrees ofoverlapping. This method lead to the formation ofoverlap zones where a decrease in hardness wasobserved due to backtempering. The influence ofoverlapping was examined and it was found that a highoverlapping degree gives the best results in terms ofhardness variations.With the U- and V-shaped grooves complete contourhardening of the grooves seemed difficult even by usingspecial optics and multiple tracks. The best transversehardness profile was obtained after applying separatetracks without overlapping. This result is acceptable forthose applications where only critical zones must behardened against wear.Cylindrical surfaces were hardened by spiral shapedtracks whereas the transition radius was hardened byone closed track. Similar results as on flat sheet werefound.In the final stage of the project several industrial partswere hardened with HPDL using the experience fromthe tests on the special geometries. Some practicalexamples of laser hardening of bending blocs, gears,shafts etc. will be discussed.