Path Influence On Qualityand Path Optimization Method In Multiple Deposition Of GMAW Remanufacturing

GMAW (Gas Metal Arc Welding) remanufacturing is an important approach torepair damages on large metal components and has become one of the researchfocuses in the remanufacturing field, which has complicated thermal process andnumerous influence factors. In this paper, in order to realize the multiple depositingpath optimization of GMAW remanufaturing, the thermal process with the multipleheating pattern was systematically investigated. Theoretical derivation of multipleheating temperature field was explored. The stress, deformation and effect ofdepositing paths under the special heating pattern were researched by adoptingnumerical simulation and experimental methods, and a fuzzy comprehensiveevaluation system of multiple depositing paths was developed to realize the pathoptimization with multiple indicators. The achievements of this research could lay astrong theoretical foundation for the application of efficient and high-qualityremanufacture of large components and provide a feasible technological approachfor remanufacturing path optimization.Firstly, the theoretical derivation of temperature field in GMAW multiple planedepositing was conducted. The dynamic temperature field equations of single-passdepositing, multi-pass depositing, inter-pass cooling and last cooling wereanalytically derived by using both the point heat source and double ellipsoid heatsource under the static and moving coordinate systems respectively. In Matlabenvironment, the temperature field, thermal cycles, the inter-pass idle time rangeand the cooling time were calculated. Furthermore, the pre-heating effects of forepasses on rear passes and the post-heating effects of rear passes on fore passes in themultiple depositions were researched. The thermal cycles in the depositions ofdifferent directions and different powers were compared and analyzed. It was shownthat the heat diffusion condition of the same direction deposition was better than thatof the alternating direction deposition. When the power was too large, heataccumulation made the component over-heating. The effect of inter-pass idle timeon thermal cycles was analyzed. The heat accumulation could be controlledeffectively by setting inter-pass waiting times. The research could provide guidancefor the preliminary estimation of process parameter range.According to the character of external constraint, the remanufacturingcomponents researched in the paper were approximately classified into twosituations of one-dimensional and two-dimensional constraints. The finite elementmodels of deposition on plate substrate with one-dimensional constraint and repairprocess on block substrate with two-dimensional constraint were developed respectively. The temperature field, stress field and deformation of depositions wereanalyzed. Research results show that in one layer there are pre-heating andpost-heating effects between fore and rear passes, and the stress release effects ofrear passes on fore passes. There also are pre-heating and post-heating effectsbetween fore and rear layers, and the stress release effect of rear layers on forelayers. The component experienced multiple heating processes with single heatingsource in the deposition, and the heat accumulation was serious, resulting in thegeneration of excess heat and the bad forming. And the generation of excess heatcould be avoided by altering inter-pass idle times. Under the process parametersadopted, the transversal inter-pass stress decreased in the deposition on platesubstrate with one-dimensional constraint, and increased in the repair process onblock substrate with two-dimensional constraint. The deformation on altitudinaldirection was the largest, and had the largest effect on the planeness of repairsurface.Furthermore, the effects of process parameters on multiple depositions wereresearched. Results show that the transition of residual stresses varies steeper withthe increase of depositing length. The inter-pass and inter-layer stresses increase andthe residual stress decreases with the increase of inter-pass idle time. It is seen that alonger inter-pass idle time would avoid the overheating of component, decrease theresidual stress, and acquire a better forming result. Moreover, in the two differentconstraint situations, the effects of depositing sequences and directions ontemperature field, stress and deformation were researched. The heat diffusioncondition in the deposition of the same direction is better than that in the depositionof alternating direction, and the residual stress of component deposited in thealternating direction are smaller than that of component deposited in the samedirection. The temperature field, stress and deformation could be improved byoptimizing depositing paths, as keeping other parameters constant.There are numerous depositing path possibility and evaluating indicators inmultiple depositions of remanufacture, and it is difficult to choose the optimaldepositing path. In this paper, the path optimization under multiple indicators wascarried out by simulating the thinking and reasoning pattern of human and adoptingthe fuzzy comprehensive evaluation, which was developed based on the effects ofdepositing path. The multiple indicators included heat conduction, formingcondition, residual stress, buckling deformation and efficiency. The fuzzycomprehensive evaluation model was developed, which included the evaluationindicator set, evaluation result vectors, fuzzy language set, universe of fuzzy sets,fuzzification process, fuzzy deduction and non-fuzzification process. Meanwhile, aninteractive interface of fuzzy comprehensive evaluation of multiple depositing pathswas developed in Visual C++environment. For the professional users, weights could be input directly according to the knowledge and experience, and for the commonusers, the analytic hierarchy process was adopted.Finally, the verification was conducted via coupler knuckle instance. Accordingthe obtained effects of depositing paths, four depositing paths were researched,including the paths from the outside to the inside in the same and alternatingdirections and the paths from the inside to the outside in the same and alternatingdirections. The depositing paths were sequenced under each indicator, and verifiedby numerical simulation and experiments of coupler knuckle repair. According tothe repair quality requirements of coupler knuckle, the orders of indicators wereresidual stress, forming condition, heat conduction, efficiency and bucklingdeformation. The optimal path was obtained through the fuzzy comprehensiveevaluation system developed, which was from outside to inside in alternatingdirection. Moreover, the worn coupler knuckle was repaired by adopting theremanufacturing repair equipment of coupler knuckle. And the mechanicalperformances of component were tested, satisfying the operating requirements.