| As the core component of marine engine,crankshaft is known as the"heart"of marine diesel engine and plays a vital role in ship safety.Large marine crankshaft has the characteristics of heavy weight,high processing accuracy,strict performance requirement and high manufacturing technology difficulty.Whether there is capacity to manufacture crankshafts represents the level of a country’s shipbuilding industry.Crankshafts of large marine low-speed diesel engines in China have always depended on imports.The bottleneck of production technology of large marine crankshafts has seriously restricted the development of China’s shipbuilding industry.This project was based on the forming technology of the crank throw of marine assembled crankshaft with shaft journal between 400mm and 600mm,aiming at the shortcomings of the existing forming technology of the crank throw of marine assembled crankshaft,starting from changing the shape of forging blank of crankshaft,taking the rolled round bar as forging blank of marine crankshaft,and the upset-extruding composite technology to form the crank throw of marine assembled crankshaft which is based on a round bar is proposed.This technology is one-fire forming by heating round bar with energy saving and high production efficiency,instead of free forging process of multi-fire plate forging or bending forging.The high temperature deformation behavior was researched by thermal simulation compression experiment for S34MnV alloy steel,which was used as the special steel of large marine crankshaft.And the true stress-true strain curves were measured at high temperature,the constitutive model of flow stress of S34MnV alloy steel was established at high temperature.In this paper,the upset-extruding composite process of the crank throw of marine assembled crankshaft based on a round bar was developed.This process was one-fire and divided into three steps,namely,pre-upsetting,upsetting-bending forming and final forging.The pre-upsetting step was composed of bending stage and upsetting stage.The characteristics of this process were horizontal upsetting and extrusion,vertical bending and it was mainly subjected to horizontal upsetting and extrusion.Through the research of upset-extruding composite process of the crank throw of marine assembled crankshaft based on a round bar,the specific technological parameters of three steps of this process were obtained.The matching relationship between the horizontal upset-extruding speed and the vertical bending speed in the upsetting-bending forming step was analyzed in detail,and the optimal matching scheme of the horizontal upset-extruding speed and the vertical bending speed is gained.The technological parameters of upset-extruding composite process were optimized by orthogonal test,and the optimum technological parameters were obtained.The formulas for calculating the forming force of each step of upset-extruding composite process of the crank throw of marine assembled crankshaft were established based on data regression.The influence of key dimension parameters（mould structure parameters）on the upset-extruding composite process of the crank throw of marine assembled crankshaft was researched in depth.The results showed that radius increment△R of the top of crank throw and crank throw offset e were two important factors,which interact with the upset-extruding composite process.The effect of radius increment△R of the top of crank throw and crank throw offset e on the upset-extruding composite process was analyzed.The upset-extruding composite process of marine assembled crankshaft was divided by three parameters:relative radius increment△R/R0,relative offset e/R0 and crank throw aspect ratio L0/B0.The upset-extruding composite process could extend the application scope of RR method,TR method and NRR method,which could be extended to manufacture from the integral crankshaft of high-speed diesel engine to the assembled crankshaft of medium and low-speed diesel engine.In order to validate the key technology of the upset-extruding composite process of the crank throw of marine assembled crankshaft based on a round bar,the technological experiment for the crank throw was carried out.The experimental results show that upset-extruding composite process based on a round bar is feasible to form the crank throw of assembled crankshaft with shaft journal less than 600mm,and can be used in practical production as a new manufacturing process for the crank throw of marine assembled crankshaft with shaft journal less than 600mm. |
