Basic Research On The Surface Repair Of The Crankshaft

Chinese auto output and possession were increasing with the rapid development of economy,resulting in more retirement vehicles. So the refabrication of the auto parts became the inevitable choice of economic growth and was strongly supported by the state. It increased the service life of the service life of components, but also reduced the pressures on resource and environmental pollution.The refabrication of the auto parts eased the employment tension and had a huge economic value and broad market space.During operation, the crankshaft was easily ran out for the wear, corrosion and scratches on surface. As the crankshaft had high added value, consistent failure, so this paper researched on the crankshaft of BYD473QB engine, which was produced by BYD company limited. The main content and conclusions were as follows:1) The research mainly analyzed the stress state of main journal and connecting rod journal, based on the working environment of the engine crankshaft BYD473QB. And the whole crankshaft model and single-crank crankshaft were calculated. The paper also researched the failure mode, abrasionmechanism and wearing law of damaged parts. The results showed that:the axial and radial force distribution on the main journal and connecting rod journal was nonuniform and it easily leaded to Elliptic and Tapered wear on Shaft neck; There was stress concentration near the filleted corner and oil hole on the crankshaft surface, where was maximum stress value reached 113MPa, and the surface stress was much greater than the internal stress. The endurance crack was apt to be produced on the crankshaft surface under alternation stress and oil wedge force.2) In this paper,Surfaces of the journal and the cracks of Crankshaft,which was based the normalized state of 45 steel,was repaired through three tests:Self-fluxing nickel-based alloy powder by laser remelting and HVOF,fast Nickel by brush plating,stainless steel by cold welding. And analyze the repair process parameters during the test performance of the repaired layer. The results showed that: compared with the traditional thermal spraying and laser cladding, the remelted layer, which need to allow sufficient allowance, was uniform, low in bond strength, high in surface roughness;the layer by brush plating was uniform and compact, the roughness was low; the heat-affected zone of the layer by cold welding was small and leaved almost no trace of repair.3) The results showed that there were jagged metallurgicalbonding between the remelted layer and the substrate by observing the metallographic structure and testing the bond strength. The surface structure of the rapid nickel plate was uniform and dense. There wasn't obvious transition layer between the coating and the substrate. It can be seen that the transition layer was mainly bonded by mechanical force. The metallurgicalbonding was assistant. The crizzle existed duing to the internal stress. The size of the crizzle largened and the number was more with the thickness of the transition layer was thicker. The metallurgicalbonding status was obvious between the plate and the substrate.because of the role of the flash and high temperature.4) The results with wear test show that; the samples were the main of small-scale abrasive wear,which were repaired with self-fluxing nickel-based alloy powder by laser remelting and HVOF,and with Stainless Steel by cold welding.but the hard spot of the layer by cold welding played the role of a certain improvement in the wear resistance;the samples were the main of adhesive wear,which were repaired with fast Nickel by brush plating, and as the load increases, cracks become more obvious.According to result of the analysis with the organization and composition,and a variety of performance testing, the surface repairs could basically meet the requirements of crankshaft. so the laser remelting and HVOF and brush plating methods for the crankshaft journal surface were feasible , but the thickness of the remelted layer was not more than 1mm, and the thickness of the brush plating layer was not more than 0.5mm. cold welding methed for the cracks and local defects of the crankshaft was feasible.