Influence Of Ultrasonic Welding Parameters On The Tensile Strength Of The Joints Between PP And ABS

In this paper, according to production needs, the ultrasonic welded joints ofnew Bora FL left front door panel （PP）and decoration trim （ABS） were chosenas the research object. Through the welding structure design, the tensile strength ofthe welded joints is used as evaluation index. And the important welding processingparameters were selected to carry out the orthogonal experiment. The mainexperiment results are as follows:According to the structure and the performance requirements of the inside autodoor panel and decoration trim, the technology design of ultrasonic riveting andwelding structure of the FL door panel and decoration trim was carried out. The sixfreedom degrees of the two parts were respectively controlled to the designedlocations. And welding processing schedule was formulated. The six PP-ABSultrasonic welded joints at the decoration trim area of the door panel assembly wereinspected and tested. First,33pieces of welded joints were at random selected fromthe products to do tensile strength test, and the statistics data were found that theirdistribution was wide. The sample mean value was about267N and the processindex of Cpk was only0.73. Therefore, it is necessary to carry out experimentalresearch on the main welding parameters which have an effect on the tensilestrength of welded joints. Thus the optimal processing parameter combination will befound out to improve the welding quality.Three factors of welding depth, welding pressure and holding time werechosen to do experimental design with orthogonal table L9(34) in which each factorhas three levels. According to the orthogonal experiment scheme nine pairs of doorpanels and decoration trims were tested and three welded joints in every pair weretaken to do tensile test. And then the special tensile fixture was designed for tensiletest and tensile strength data of the joints were obtained. On the basis of qualitativeanalysis, individual analysis and repeated test data were quantitatively analyzedrespectively by the extreme difference and variance analysis and the results showthat when welding depth is6.9mm and other factors are unchanged, the tensilestrength of welded joints is highest. While welding pressure is2.7bar with constant other factors, the tensile strength of welded joints is highest. Factor A×B (weldingdepth×welding pressure) in the interaction item both at their second level will lead tothe optimal tensile strength of welded joints. And when the holding time is2s withconstant other factors, the tensile strength of welded joint is highest. The verificationtest with optimal combination of processing parameter level showed that themaximum fracture force of the welded joints are about500N, which is significantlyhigher than that of the welded joints from the original production.The detection of welded joints shows that the height Sh and diameter size Sdof the locking cap changed a little with changes of welding processing parameters.But the indentation depth Yh changed obviously. While Yh is about0.2-0.3mm andABS locking cap has smooth surface and integrity appearence, the strength ofwelded joints is high and the welding quality is good. Thus the indentation depth ofwelded joints can be monitored to determine welding quality. In order to ensure thewelding quality of the door panel assembly, ABS injection quality at the location ofwelding column should be controlled as well to prevent gas from entering the ABSmelt forming small air bubbles and decreasing the effective loaded area of thewelding column section. Dense small bubbles can also make ABS material embrittledue to stress concentration and result in fracture in plane model.