| Spot weld bonding is a new type of sheet material connection technology,and it combines the advantages of resistance spot welding and adhesive bonding.The molded joint has excellent dynamic load carnying capacity,static load carrying capacity and sealing property.In the paper,1.5mm thick SUS304 austenitic steel plate is used as the text material to study the spot weld bonding process and fatigue performance.1.Studying on the process of spot weld bonding.With the help of medium frequency inverter dc spot welding machine,through the orthogonal test,obtained a high tensile strength of the spot weld bonding joints.Parameters as follows:preload time 70ms,welding current 10.0kA,power time 80ms,electrode pressure 12723.5N(supply pressure 0.5MPa),maintenance time 20ms.2.The tensile and shear tests were carried out on the resistance spot welding,adhesive bonding and spot weld bonding.The static failure load,failure displacement and energy absorption capacity of the joints was compared.The results show that the average energy absorption of the spot weld bonding is 0.22 times of that of the resistance spot welding,which is about 20 times of that of the adhesive bonding.The addition of structural adhesive reduces the static strength of the spot welding joint.For the spot welding bonding joint,the addition of copper powder in the structural adhesive is helpful to enhance the conductivity of the adhesive layer during the weld bonding process.As a result,the static strength of the spot weld bonding joint is also improved.3.The fatigue performance of the joint was tested under different load levels for the spot welding and the spot weld bonding joint respectively.The reliability of the experimental data is verified by the two-parameter Weibull distribution,and the data are fitted.The load-life curve of the joint is obtained.The failure and fracture analysis of the fatigue joints are performed by scanning electron microscopy.The results show that the fatigue life of the spot weld bonding joint is higher than that of the spot welding under the same load level in the restricted life.Both the spot weld and the crack source of the solder joint appear near the heat affected zone near the inner edge of the upper plate,and the failure modes of the two joints are defective fracture.In the Medium-long period,the fatigue striations appeared in both joints;but characteristics of low fatigue fracture of spot weld joint mainly manifested as dimpled rupture.4.Ultrasonic C-scan imaging of spot welding,gluing and welded joints was carried out by ultrasonic flooding focusing method.Characteristics of C-scan images under different welding parameters were analyzed and the corresponding A-scan signals were extracted.The nugget diameter was measured and compared with the nugget metallographic phase based on C-scan images.The results indicate that the shape and size of typical welding defects such as splashing and burn-off are clearly reflected in the ultrasonic C-scan image.Based on the C-scan image grayscale distribution characteristics and combined with the characteristic point of the A-scan signal,spot welding and welding joint C-scan images can be divided into,heat affected zone,fusion zone,nugget area.At the same time,by analyzing the gray scale scan line of the center of the over-welding core in the C-scan image,the edge of the nugget is determined and the rapid detection of the welding nucleus is realized.Compared with the result of metallographic analysis,the accuracy of the method is verified. |
PDF Full Text Request