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Product Code: ICAL07_P543

High Speed Rotation Hardening of Steel Shafts and Holes with High Power Diode Lasers
Authors:
Guy Claus, Wtcm-Crif; Gent Belgium
Marko Seifert, Fraunhofer Iws; Dresden Germany
Presented at ICALEO 2007

Steel shafts can be hardened by laser using one continuous spiral track. This method however leads to a hardening zone which is not homogeneous in surface hardness and case depth. This is primarily due to the hemispherical shape of the hardening track as well as to tempering effects between two neighboring tracks of the spiral. A new method was developed to solve this problem for cylindrical shafts. The laser hardening was performed by rotating the shafts at a very high speed and by heating the shaft with two high power diode lasers of 6kW each equipped with fiber optics. At the start the shaft was shortly heated to attain the required hardening temperature. After preheating the lasers moved along the axis to obtain a continuous hardening of the shaft. Initial hardening tests were performed with 30 mm shafts made of low alloyed steel 42CrMo4V and later the same method was applied to harden cylinders with larger diameters up to 60 mm without overlapping. A second application of high speed rotation hardening by diode laser was the inside hardening of small holes drilled in 20 mm steel plates. With other techniques like induction hardening and conventional laser hardening, only a part of the inside surface can be hardened with heterogeneous hardening zones because of overlapping and tempering. The diameters of the holes were 10 and 20 mm. Three steels were tested: 42CrMo4, X210CrW12 and X40Cr12. By using a fast rotating mirror and a 6 kW diode laser, the inside surface of the holes were hardened with high precision and without overlapping effects. The resulting hardening zones of both the cylinders and the holes are very homogeneous in hardness and depth. Therefore, the method looks very promising as a new and flexible hardening technique for shafts that can compete with other methods like induction hardening. For inside hardening of holes, the described method is even better than induction method especially for hardening small diameter holes.

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