Analysis On The Connection Process And The Strength Of SPCC Cold Rolled Steel Weld-bonded Joint

1.5 mm thick SPCC cold rolled sheet steel is used as test material in the paper.Study of weld-bonded tests is conducted by intermediate frequency inverter spot welding machine and mechanical performance test machine.Forming process of weldbonded nugget is analysed by simulation.(1)Orthogonal experiments with three factors and three levels are made on resistance spot welding and weld-bonding,and three factors are welding time,welding current,electrode pressure.Tensile shear test is conducted.The results show that welding current has major influence on quality of resistance spot welding and weldbonded joints,and the minor influence is welding time and electrode pressure.When welding current gets increasing,weld-bonded process appears splash easily.When welding time is 70 ms,and electrode pressure is 0.3 MPa,RSW joints achieve the maximal tensile strength at welding current 15.5 kA,and weld-bonded joints achieve the maximal tensile strength at welding current 15.0 kA too.The maximal tensile strength of RSW joints is 10179.722 N,and the maximal tensile strength of weldbonded joints is 11071.119 N.(2)Ultrasonic C-scan images and ultrasonic A signals are achieved by ultrasonic scanning device.Gray distribution of ultrasonic C-scan images in nugget structure of the joints and feature of A signals are analysed.Zones of resistance spot welding joints are divided into three zones: nugget zone,heat-affected zone,base material zone.Because weld-bonded process exists burning of glue,zones of weld-bonded joints are divided into four zones: nugget zone,heat-affected zone,glue line zone,glue gasification zone.Nugget edges of C-scan images are detected.Nugget diameters are measured by binaryzation images.The range of nugget diameters of RSW is from 4.63 mm to 5.30 mm,and the range of nugget diameters of weld-bonding is from 4.69 mm to 5.60 mm.(3)Simulation models of resistance spot welding and weld-bonding are established.Thermal cycle curves of nugget are extracted.Temperature field analysis of nugget forming is compared between resistance spot welding and weld-bonding.The results show that radial temperature distribution is higher than axial temperature distribution in the two nuggets.The bigger diameter is acquired in weld-bonded nugget.Existence of glue increases contact resistance between base material,which causes that heating rate of weld-bonded nugget is faster than that of resistance spot welding nugget.When lower welding current is used in weld-bonding,standard ellipse-shaped cross section is acquired.When higher welding current is used in weld-bonding,appearance of nugget gets distorted.This indicates that the process and quality of welding get deteriorated.According to the result,lower welding current is propitious to weldbonding.The result of simulation explains the phenomenon of welding process and mechanical properties test.