Analysis on the laser quenching technology of gears
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Laser beam processing Laser beam processing is a thermal processing process that redistributes light intensity to obtain a beam of uniform intensity. The laser beam processing technology system includes: defocusing system, galvanometer system, rotating mirror system, integral mirror system, waveguide integral system, beam combining system, spectroscopic reverse combining system, spherical-conical lens system, and toric mirror system. The defocusing system is one of the simplest optical paths for surface treatment, that is, the surface to be processed is offset from the focal plane of the focusing optical system by a distance along the optical axis, and the area of ​​the spot can be changed by changing the amount of defocus. This test uses a defocusing system. Effect of laser quenching (phase transformation hardening) process parameters on hardening depth The laser quenching test of the test block was carried out with different process parameters.
Effect of process parameters on hardening depth No. Laser power P, kW scanning speed V, mm/s spot width B, mm hardening depth H, mm Remarks 013.42551.04 023.42051.43, M033.43050.75 043.43050.85, lap 053.44201 .43 , lap joint, M063.43550.82, lap 07332250.98, lap 083.43550.59-094.03560.68-104.03060.90, M114.03760.65-, lap 124.03060.78, M133.53060.68-143.53560.55-, Lap 153.53560.57-164.03060.88, M173.53060.72-183.53060.70-, lap 194.525101.04 (Note: indicates that the hardening depth is close to or reaches 0.8mm, - indicates that the hardening depth is below 0.8mm; M refers to the surface Slightly melted; the overlap of the two lasers with overlap is 0.51.0mm. The results show that under certain process conditions, the depth of the hardened zone can reach 0.8mm or more, but the surface sometimes shows condensation. The roughness of the surface of the hardened zone is deteriorated. In high power (>4kW) and wide spot (about 10mm), the hardening depth can be ensured and the surface roughness of the hardened zone is not affected.
Microstructure and Hardness of Laser Hardened Zone Laser-treated specimens were cut along the center of the scan to prepare metallographic specimens. The hardness test was carried out using a HX-500 microhardness tester, and the microhardness test result (load: 1.96 N, dampening time: 15 s). The hardened zone structure was observed with an OLYMPUSPMG3 microscope. After quenching, the hardened treatment zone is martensite cryptocrystalline martensite (a, bc) and the transition zone is pearlite martensite. The Vickers hardness Hv (load 1.96N) in the hardened zone is greater than 500Hv (equivalent to 48HRC), up to 950Hv (equivalent to 55HRC).
Abrasion test The sample after laser quenching was processed into a test piece of 4 mm 8 mm and 10 mm by a wire cutter to perform an abrasion test. The weights before and after the wear were weighed by optical analysis scales, and the weight loss after wear was calculated. Abrasion test results (average weight loss, unit: g) Material method Laser quenching Conventional quenching 40CrNiMo0.0440.232 test results show that the average weight loss of laser phase transformation hardening samples is 19.
Through the above tests, the following conclusions are drawn: the ring gear made of 40CrNiMo can be hardened by laser quenching, the highest hardness can reach above 950Hv, and the average hardness of the hardened zone is more than 600Hv, which is much higher than the conventional quenching (350400Hv) hardness. The surface roughness of the quenching zone is basically the same as that before quenching, and the deformation is extremely small, which can replace the high frequency quenching. After the laser surface strengthening treatment, the depth of the hardened layer can reach 0.81.0 mm. The average weight loss after abrasion of the sample by laser phase transformation hardening is 19 of the conventional quenched sample. It can be seen that the wear resistance of the sample is greatly improved after the laser surface strengthening treatment. When multi-pass scanning is quenched, there is inevitably a temper softening zone. The process test shows that the region is very narrow when quenched under certain parameters, and the hardness of the softened zone is still close to twice the hardness of the base metal. The tempering zone can be reduced or avoided when quenching with a broadband spot.