The Joining,Inspection And Repair Of Bond Discrepancy For C_f/PA6 Composite Based On Ultrasonic Welding Technology

The application of 30 wt.%C_f/PA6 composite in automobile industry led to the ultrasonic welding and adhesive-bonding widely used to fabricate body-in-white.However,the welding of the workpieces may be constrained by part geometry and designs.It is difficult to use the traditional ultrasonic welding ultrasonic double-sided welding(UDSW)because the horn is difficult to access the backside of the lower workpieces.Furthermore,it is unavoidable to cause various discrepancies in bonding joints.However,only part of discrepancies in bonding joints can be inspected by the current nondestructive evaluation(NDE)technique.Another issue is how to repair the discrepancy joints.Aiming at the above problems,as a part of the united fund program of General Motors Corporation(GM)-Zhengzhou University,―Joint Quality Inspection and Repair in Adhesive-Bonding of Polymeric Composites‖,this study focuses on the development of ultrasonic single-sided welding(USSW)technology of 30 wt.%C_f/PA6 composite,quality inspection technology of bonded 30 wt.%C_f/PA6 composite based on the ultrasonic welding and the repair technology of bond discrepancies in bonded 30 wt.%C_f/PA6 composite,respectively.The weldability and welding mechanism of ultrasonic single-side welding of 30 wt.%C_f/PA6 composite,and the relation of horn final displacement and bond discrepancies in bonded 30 wt.%C_f/PA6 composite were analyzed.The possibility of self-piercing riveting(SPR)and ultrasonic welding of bonded 30 wt.%C_f/PA6 composite were investigated.The feasibility of SPR and ultrasonic welding for repairing of bond discrepancies in bonded 30 wt.%C_f/PA6 composite was explored.The following results are obtained:30wt.%C_f/PA6 composite had a good weldability of ultrasonic single-side welding.The strengths of USSW 30 wt.%C_f/PA6 workpieces were higher than that of the traditional ultrasonic welding(UDSW)for the same welding parameters.The reason is that the USSW workpieces could dissipate more ultrasonic energy,had higher welding temperature at the faying interface and formed larger weld.The welding mechanism of USSW is that the bending deformation of welded workpieces caused by the suspension distance beneath horn endured a cyclic bendingspringback-bending deformation of upper and lower workpieces,which resulted in a relative sliding movement of upper and lower workpieces in faying interface during ultrasonic oscillations.Hence,the combination of Coulomb friction heat from the relative movement of the workpieces and intermolecular friction heat melted the materials and formed the weld at the faying surface.Because heat generated in single-sided ultrasonic welding of polymeric composite was similar to that of ultrasonic welding of metallic workpieces,the USSW mechanism can be analyzed with an analytical mode by considering the difference in bending deformation between the direction of width and length(suspension displacement direction)and the change of weld pressure and amplitude of horn during ultrasonic welding.The results of model analyses were in agreement with the experimental results.A decrease in adhesive coverage led to a decrease in strength of bonded 30 wt.%C_f/PA6 workpieces.The 50% of adhesive coverage area decreased the strength of bonded workpieces by 30%~45%.The decrease in bonding strength caused by the discrepancies in the core of overlap displacement is less than that in the side of overlap displacement;the adhesive coverage area for the lacking adhesive discrepancies and the air thickness for the kissing discrepancies influenced the final displacement of horn during ultrasonic inspection.The larger the adhesive coverage area for the lacking adhesive discrepancies,or the thinner the air thickness for the kissing discrepancies decreased,the larger the horn displacement.Hence,it is feasible using ultrasonic welding machine to inspect the bond discrepancies of 30 wt.%C_f/PA6 composite.The optimal inspection parameters of ultrasonic welding machine were(37)10mm horn,0.075 MPa inspection pressure and 1.0s inspection time when used to inspect bond discrepancies of 30 wt.%C_f/PA6 composite.A threshold horn displacement of 0.38 mm for sound adhesive joined 30 wt.%C_f/PA6 composite was determined under the present process parameter.It can be identified as a discrepancy joint when the measured horn displacement of adhesive-bonding workpieces was larger than the threshold horn displacement.It is feasible to join the 30 wt.%C_f/PA6 composite using SPR technology or weld the uncured adhesive-bonded 30 wt.%C_f/PA6 composite using ultrasonic welding technology.The strength of 30 wt.%C_f/PA6 composite SPR joints fabricated with 11 mm length rivet after put a cushion ring between the rivet head and upper sheets was higher than that of their USSW joints.The strength of uncured bonded-ultrasonic welded 30 wt.%C_f/PA6 workpieces was higher than that of ultrasonic welded workpieces while the strength of cured bonded-ultrasonic welded 30 wt.%C_f/PA6 composite approached to about 90% of the strength of the cured-bonded workpieces.The SPR and ultrasonic welding technology can be used to repair the discrepancies bonded 30 wt.%C_f/PA6 workpieces.The strength of the discrepancies bonded 30 wt.%C_f/PA6 workpieces can be restored to above 80% of the strength of normal joints after repaired with SPR and ultrasonic welding technology using the same parameters of SPR and ultrasonic welding of 30 wt.%C_f/PA6 workpieces.