Experimental Study On Application Of Cold Welding Technology In Engine Remanufacturing

Remanufacturing is a green manufacturing technology which can protect ecological environment and can bring a lot of economical and social benefits. Because remanufacturing focuses on repairing the original parts, its cost is50%of a new one, and at the same time, it can save60%of energy and more than70%of material. Remanufacturing has become an important national strategy of saving energy, remitting resource and environmental crisis and promoting circulation economy.Cold-welding is a key technology to repair surface defects of engine parts such as scratches, wear and knocks with advantages of economy, convenience, precision and small heat affected zone (HAZ), etc. How to reduce repair defects, keep good repair binding force, reduce heat affected zone and residual stress, and achieve good hardness are the bottleneck problems of industrial application. In order to solve those problems, the project has done a systematic research about the cold-welding repair mechanism, damage forms of engine, micro-hardness, microstructure, combination strength, residual stress and milling processing of repaired area.In this paper, the surface defects on HT250material used in diesel engine cylinder were repaired by inferior-laser instantaneous melting cold-welding technology, and then the microstructure, properties and milling processing of Ni-base repaired layers were comprehensively analyzed.①The cold-welding repair mechanism and applicability are revealed through studying microstructure of repaired layer and base and elements diffusion in fusion interface. The interface of base and repaired layer is well bonded. The flake graphite in base region distributes evenly and the structure of repaired layer is dense. Element diffusion phenomenon can be observed clearly in fusion interface, which illustrates repaired layer and base is indeed micro-area metallurgical combination and cold-welding technology can be used to repair surface damages of parts.②The measurement of hardness in cold-welding area shows that the hardness value of repaired layer is lower than that of the base, which is beneficial to subsequent processing. The width of HAZ is narrow and there are some hardness fluctuations in it, which coincides with characteristics of micro-area impulse welding.③The combination strength between repaired layer and base and the surface residual stress of base were tested. The impacts of different cold-welding parameters on combination strength and residual stress distribution were also studied. The results show that cold-welding repair technology can improve the tensile strength of repaired objects which is still lower than that of raw materials. The results also show that cold-welding surface residual stress distribution range is quite small and it is residual tensile stress near welding seam center while it is compressive stress away from welding seam and transverse residual stress is the main residual stress. The high combination strength and small residual stress peak can be obtained by changing the time and energy parameters of cold-welding.④Considering cold-welding repaired layer was rough and micro structure contained hard phases, the orthogonal milling experiment was conducted to study the influences of different milling parameters on milling force, surface roughness and cutting efficiency in the processing of cold-welding repaired layer to optimize the milling parameters. The research shows that feed per tooth has great influence on milling force while cutting speed has a great effect on surface roughness. Surface quality can be improved by reducing feed per tooth and increasing cutting speed and cutting efficiency can be higher through increasing cutting speed and improving feed per tooth.This research can provide application mechanism, quality assurance technique and application standard of cold-welding technology in engine remanufacturing for its extensive application.