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High speed rotation hardening of steel shafts and holes with high power diode lasers

: Claus, G.; Seifert, M.

Lu, Y. ; Laser Institute of America -LIA-:
ICALEO 2007, 26th International Congress on Applications of Lasers & Electro-Optics. Congress proceedings. CD-ROM : October 29 - November 1, 2007, Orlando, FL, USA
Orlando, Fla.: LIA, 2007 (LIA 100)
ISBN: 0-912035-88-9
ISBN: 978-0-912035-88-8
International Congress on Applications of Lasers and Electro-Optics (ICALEO) <26, 2007, Orlando/Fla.>
Conference Paper
Fraunhofer IWS ()
Bohren=Spanen; Chrom-Molybdän-Vanadium-Stahl; Diodenlaser; Halbkugel; Hochdrehzahl; Hochleistungslaser; kontinuierliches Verfahren; Laserstrahlhärten; Maschinenwelle; Neuentwicklung; Oberflächenhärten; Temperatureinfluß; Tiefenprofil; Vorwärmen; Werkzeugstahl; Zylinder

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 neighbouring 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 6 kW each equipped with fiber optics. At the start the shaft is shortly preheated to attain the required hardening temperature. After preheating, the lasers moved along the axis to obtain a continuous hardening zone. Initial hardening tests were performed with 30 mm shafts made of low alloyed steel 42CrMo4V and later the same method was applied for the hardening of shafts 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. Two steels were tested: 42CrMo4 and X42Cr13. 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 o f both shafts and holes are very homogeneous in hardness and depth. Therefore, the method looks very promising as a new and flexible hardening technique for the heat treatment of shafts, which 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.