Research On Process And Properties Of Laser Spot Welding Between Stainless Steel And Cu-Ni Coated Low Carbon Steel

The 300 series austenitic stainless steel has high corrosion resistance, strength and toughness, and is widely used to produce electronic instruments, fine components in microelectronics and other fields. A joint of low carbon steel coated with a copper-nickel coat outside to the 300 series stainless steel not only performs the excellent characteristics of stainless steel, but also can reduce cost. Pulse laser can meet the demand of high accuracy and precision in joining these two kinds of thin metal sheets in the production line of electronics.In this paper, lap joint between 0.4mm Stainless steel and 0.5mm low carbon steel with nickel-copper coat was obtained using a 300 W Nd:YAG laser. Each effect of the factors including laser power, pulse shape, defocusing distance, spot distance, and welding sequence on the spot size and the maximum load were investigated in details; By designing a Taguchi experiments and conducting relevant variance analysis on the results, the rank of significance for laser power, pulse width, and defocusing distance to the spot penetration, spot diameter, and maximum pull force were compared and analyzed; Crack within weld is observed by a scanning electron microscope and the composition of different area of weld were analyzed by an energy disperse spectroscopy. It was concluded that:Lap spot weld between copper-nickel coated SPCD and stainless steel of good loading performance, excellent surface quality and small deformation can be obtained by a Nd:YAG laser. With the rising of laser power, the penetration, the surface diameter and the pull force would rise; A sharp pulse would cause a deeper penetration and more severe collapse of the center part, while a rectangular pulse would produce a shallow penetration and more reasonable collapse. When the defocusing distance is-2mm, a deeper penetration was obtained compared with a shallow penetration under the defocusing distance of larger than-2mm.Within a certain range(When laser power is from 1.1KW to 1.5KW, pulse duration is from 3ms to 5ms, defocusing distance keeps from-2mm to zero and pulse frequency is 1Hz), mathematical models to predict the maximum load of a weld is obtained using analysis of variance, and optimization parameters were derived out.Crack in the weld spot was attributed to the copper within the coating of the SPCD. Consequently, it is suggested to remove the copper coating prior to the laser welding process in order to avoid the crack.