Laser Hardening Of Cylinder Inner Wall Of Diesel Engine

At present, laser hardening technique of diesel engine cylinder has been wildlyused in domestic industry. Cylinder liner process requires high machining accuracy, highproduction cost, and complex technology. Laser hardening of cylinder inner wall of dieselengine can save processing time, simplify working processes, improve work efficiency,and guarantee high economic benefit. It plays a very significant role in the productionmanufacturing process. It is also a tendency to making high performance diesel engine bythis method. In order to meet the requirements of the production line, this paper hasstudied laser hardening of cylinder inner wall of grey iron diesel engine entirely.Experiment design was based on “Simplex Lattice Point Design”. Fourier transforminfrared microscopy/Raman spectrometer was used for measuring the transmittance of10.6μm CO₂laser in the coating, which was made by the ZnO, Al₂O₃, SiO₂, and rare-earthpowder. The regression calculated results of hardening layer depth data shows that thecoating composition containing5.24wt.%ZnO,61.32wt.%Al₂O₃and32.44wt.%SiO₂,and1wt.%rare-earth powder, which can result in a theoretical maximum hardening layer.Single factor experiment method was used for studying the influence that spotdiameter, scanning speed and power exerted on the laser absorption of HT250. Spotdiameter were3mm,4.5mm and6mm; scanning speed were15mm/s,20mm/s and25mm/s. Power played the most important role in the absorption. On the condition that theother parameters were determined, the hardening layer got thicker as the power washigher.This study used XJL-03type optical microscope（OM） and JSM-5610LV typescanning electron microscope （SEM） to observe the microstructure and used Philips X’Pert PRO type X-Ray Diffractomer（XRD） to do phase analysis. After laser hardening,there were austenite+mastenite+Fe₃C on surface layer. High carbon and the austenitestable elements Cu and Mn caused the formation of retained austenite.After laser hardening the wear resistance of HT250was tested by MM200wear tester.This experiment was designed by using four factors and three level orthogonal test. Lessretained austenite can improve the wear resistance, but wear resistance shall decrease as the increase of retained austenite, so the amount of retained austenite can determine thewear resistance.The parameters of laser hardening of diesel engine cylinder linging were30°reticulate cross-angle,3mm spot diameter,20mm/s scanning speed and1100W power. Thehardening areas of three engines were33.63%,41.66%and50.17%after calculation.The cylinder size hardly changed after200hours full load at full speed reliability test.It indicated that the cylinder had a high wear resistance and the thickness of hardeninglayer met requirements of long time working.