Research On Control Mode And Dynamic Characteristics Test In Dissimilar Steel Spot Welding Process

At present, with the strength and performance requirements of engineering structurescontinues to increase, more and more dissimilar welded structure is applied. Theheterogeneous joint can not only meet the requirements of special material properties indifferent work environment, but also can reduce the using amount of costly materials, whichimprove the reasonable utilization rate of materials. Using heterogeneous joint can not onlyreduce production costs, but also make full use of the performance advantages of differentmaterials, so make its performance cost ration far more than the homogeneous joint. So far,many welding methods have been used in dissimilar material welding, such as fusionwelding, braze welding, pressure welding, friction welding, diffusion welding, explosivewelding and so on. However, due to the large difference in melting point, thermalconductivity, linear expansivity, a variety of welding defects will appear in welded joint ofdismiss materials.The dynamic characteristics of dissimilar steel(i.e. Q235and1Cr18Ni9Ti) spot weldingprocess and the adaptability of spot welding monitor is explored using three kinds of spotwelding monitor mode(i.e. simple timing method, constant current method and IDRCmethod) for dissimilar steel spot welding process in this paper. Moreover，through the testanalysis of the performance and organization structure comprehensively, the features ofdissimilar steel spot welding have been revealed. The main research results are as follows:(1) There is a difference in spot welding dynamic characteristics of low-carbon steeland stainless steel. The current lag angle curve of low-carbon steel spot welding process hasan obvious valley point(i.e. the starting point of nugget formation), but the curve of stainlesssteel does not have the valley point and is monotonically increasing.(2) The current lag angle of dissimilar steel spot welding process is similar tolow-carbon steel，there is a valley point in this curve and it steady climb after the valley point.This phenomenon indicates the spot welding process of dissimilar steel can be monitored bythe IDRC method. (3) Under the condition of the ideal process, the main parameters of dissimilar steelspot welding by IDRC method: electrode pressure is3.0kN, welding current is7.0kA, andgiven threshold is140μs. Under the premise of forming a high-quality nugget, the currentlag angle curve of dissimilar steel spot welding process is compared with low-carbon steel.The result indicates the valley point of both is coincident, but the curve slope after the valleypoint is relatively slower, the control threshold is relatively smaller.(4) The nugget of dissimilar steel spot welding is asymmetrical. The nugget offset tothe side of the stainless steel base material. It cause the weld diameter on the interface is lessthan the maximum diameter of the nugget, making carrying capacity of welded joint decline.In order to simplify the process, hard specification is used to weaken the nugget offset. Inregard to damage form of dissimilar steel spot welding joint, it always has a clear selectivity,i.e. a hole was leaved in the side of low-carbon steel, and a button is formed on the other sideof the stainless steel base material.