The Experiment Research On Welding Quality Control Of Stainless Steel EGR Cooler

With the intensification of vehicle exhaust pollution and the increasingly strict emission standards, the applications of EGR (Exhaust Gas Recirculation) cooler draws attention. EGR coolers are always exposed to vibration fatigue load, high temperature and corrosive gases during working, which requires higher manufacturing quality consequently. Welding is the most critical part in the EGR cooler’s manufacturing. So it is significant to control the welding quality of EGR cooler. This paper works on the quality control of welding in stainless steel YL-12C EGR cooler. With the supervisory control of fusion welding and brazing, we successfully developed the product, and has achieved a small batch production.In the fusion welding part of the trial process, Robot MIG welding torch swing uphill solution is used to solve the unstable quality problem of welding in the shell expansion joint. By adjusting the process parameters, a satisfactory bellows welded joints obtained.In the research of brazing process, BNi-5filler metal was chose for vacuum brazing of the core of YL-12C EGR cooler after wettability and metallographic characteristics comparative experiments and comprehensive analysis. The quality of brazed joints was investigated and evaluated. Quasi-cleavage fracture happened at cooling pipe-turbulent fins brazed joints during overpressure burst test of the cooler core, the crack expand along the Ni-Cr-Si brittle phase. Analysis showed defect joints occurred because of the excessively large joint gap. Actually the product sample could still pass various tests despite low brazed rate and the enterprise standard which regarded50%brazed rate joint as acceptable ones formulated, but the excessively large joint gap which was generated by imprecise assembly should be paid attention to.The wetting and joint forming characteristics of amorphous nickel-based filler metal foil which was applied in EGR cooler brazing process were investigated. By simulating test, it has been found that there is always a layer of remnant filler metal and its thickness increased with the use amount of filler metal; the interface of remnant layer and base metal will turn out internal migration to the base material, the depth of migration has no relationship with the residual layer’s thickness. With the increasing amount of filler metal, the allocation ratio of layer of remnant filler metal on corner and seam increased. Brazing fillet at the equilibrium shape is determined by energy minimization. The dissolution of stainless steel changed the properties of liquid filler metal, the liquid flowed so slowly that the remnant layer retained after brazing. The fusion-wetting-joint forming physical model was founded and the performance of filler metal foil was described. The minimum amount of filler metal foil was calculated. With spot welding filler metal foil-fin, the amount of brazing foil can be reduced during assembly; Installation of fixtures, change the fin design, spot welding tube-brazing foil-fin can reduce the brazing gap, improve the quality of brazing.