| In recent years,the medium-speed diesel engine has been widely used in locomotives,marines and generator units.The diesel engine power,energy consumption,stability and other performance levels have been significantly improved.Crankshaft as one of the five key parts of the diesel engine is an important component for sustaining loads and transferring power,and its quality directly affects the overall performance and the reliability of the diesel engine.As the connecting rod journal is in the position of eccentric crank,it has been subjected to complex cycle torque and alternating load during the operation,which makes the connecting rod journal especially prone to fail due to the surface damage.Therefore,it is of great interest to strengthen the neck surface and to improve its mechanical properties and wear resistance.Currently,the connecting rod journal is mainly machined by the conventional rotary cutter machine,which uses the rotary cutter to rotate around the crank pin.During the machining,the low cutting speed and the long auxiliary time result in a low processing efficiency.In order to improve production efficiency and processing quality,the eccentric connecting rod journal can be cut by the ordinary lathe,which requires the new design of the corresponding fixture for machining the eccentric connecting rod journal so that the axis of the crankshaft connecting rod neck coincides with the rotation axis of the ordinary lathe.In this work,process analysis,process test and data analysis have been conducted for manufacturing process design,reinforcement of the connecting rod journal surface,and design of eccentric fixture.The manufacturing process and eccentric fixture of connecting rod journal are designed based on the studies performed on the material,structure and precision of the forged steel crankshaft as well as the many years' practical experience gained from manufacturing the casting crankshaft.The method of process test is used to analyze the wear resistance and deformation control of the intermediate frequency induction quenching and nitriding treatment,and the optimal method is identified.Furthermore,the mechanical properties and microscopic metallographic structure of the 240 H type forged steel crankshaft have been confirmed to fulfill TB/T 2385-93 “Diesel locomotive engine forged steel crankshaft technology condition” through the performance dissection test of “double crank”.A reasonable plan of 240 H type forged steel crankshaft manufacturing process is established based on the results of above-mentioned studies.In the process design and eccentric fixture design,a decentralized crankshaft turning process is achieved through the adjustment of the process and the use of connecting rod neck eccentric fixture.Compared to conventional processing methods,the production efficiency increases by 25%.The roughness grade of the thickness of the rod is raised from Ra3.2?m to Ra1.6?m,which ensures the processing quality.The reinforcement scheme of the connecting rod neck are compared,and it is found out that the intermediate frequency induction quenching scheme of the 240 H type forged steel crankshaft of 50CrMo4 + Ni + V is about 15% higher than that of the nitriding treatment scheme.Moreover,induction reinforcement scheme is superior to nitriding in deformation control.Therefore,it is concluded that the intermediate frequency induction reinforcement scheme is the best scheme for the reinforcement of the connecting rod neck of 240 H type forged steel crankshaft.The research topic of this work is selected based on the experience of crankshaft manufacturing and the analysis of fault data,and it is focused on solving the difficulty of manufacturing process and avoiding operation faults.With the aid of the method of process analysis,process test and data analysis,a feasible program for the manufacturing process of the forged steel crankshaft is obtained,which can be used in engineering practice to enhance the medium-speed diesel engine forged steel crankshaft manufacturing capacity. |
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