Manufacturing Process Of Large Crankshaft Die With Welding Surfacing Technology

The crankshaft is an important part of the engine, whose role is to bear load and transmit power.With the rapid development of automotive industry, the market demand is increasing. However, thedie used to manufacture large crankshafts usually has a complex cavity and works in poor conditions,so the life of the die is very shorter, which leads to increase of the cost and reduction of the productionefficiency. Repairing or manufacturing the die with welding surfacing technology can not onlyprolong its lifespan, but also shorten the production cycle and reduce the production cost. However,the application of welding surfacing technology is limited because of the complex die structure andthe harsh usage conditions. Aiming at some large crankshaft dies’ low life expectancy, the paperanalyzed the reasons of failure, and surfacing repair tests on large crankshaft dies were carried out.The failure reasons of the large crankshaft die were analyzed by the methods of fieldinvestigation and test analysis.The results show that mechanical fatigue crack and thermal wear aremain reasons. In general, thermal fatigue and plastic deformation are not major factors of the faileddie, but they will aggravate the wear of the cavity and accelerate the process of die failure. The life ofthe die can be extended by improving some resistance indexes of the die material, such as hightemperature (600℃) strength, high temperature (600℃) impact toughness, and thermal stability.The surfacing materials of large crankshaft dies were selected by comparing the performances ofdifferent materials. RMD535was selected as the buffer layer surfacing material, in consideration ofits high strength and high toughness. RMD647was chosen as the working layer surfacing material onaccount of its outstanding performances in crack resistance, adhesion wear properties, temperingstability, tensile strength, impact toughness, etc. The above two materials were used to repair the largecrankshaft die.The surfacing repair process of the large crankshaft die was investigated on the basis of theabove surfacing materials. Surfacing method, welding parameters, preheating process, heat treatment,and other supporting process were determined. The influences of tempering temperature and time onthe microstructure and properties of the surfacing metal were studied. The post-weld heat treatmentprocess of large crankshaft die was550℃×10h. The preheated process was set to400℃×10h throughtheoretical analysis and experimental verification. The common welding defects (pores, cracks, slag,undercut) and its causes in the surfacing manufacturing were systematic analyzed, and the appropriateprevention countermeasures were formulated. Finally, a complete surfacing manufacturing process planning of large crankshaft die wasformulated, and the repair test on the failure crankshaft die was conducted. The engineeringapplication results showed that the lifespan of the large crankshaft die after repaired significantlyincreased.