| Crankshaft is the core component of the engine, with the vigorous development of the auto industry in recent years, the demand of the crankshaft and yield also increased accordingly. Those crankshafts which have stable mechanic performance, good wear-resisting, and little cost will be competitive in market. Ductile cast iron is different from forged steel and cast iron with its microstructure, manufacturing and performance advantages. Ductile iron crankshaft arises at this moment, and with the increasing ratio in the manufacture of crankshaft, high performance of ductile iron crankshaft preparation technology research and application is of great significance.In this paper, we explore the preparation technology of high performance ductile iron crankshaft by two aspects, one is based on the optimization by iron based coated sand numerical simulation of casting solidification process; The other one is the ultrasonic processing of ductile cast iron melt. Numerical simulation was carried out on the solidification process to visualize the flow field and temperature field of castings, which is easy to predict shrinkage porosity defect, and shorten the development cycle; Acoustic cavitation and acoustic streaming effect of ultrasonic can break the solidification dendrite and increase the rate of nucleation, thus improve the mechanical properties.Mold the iron, sand shell and casting, in which the thickness of sand shell is8mm, and the casting consisting of pouring system and four crankshafts. Calculate the flow field and temperature field of the casting under the pouring temperature of1420℃. Calculation results show that, under this condition, completely filling need13s, casting surface temperature cooling to600℃need800s. in the center of the bend angle and shaft parts cooling speed is the slowest, which is the hot section location, easy to generate porosity defect after solidification shrinkage. Then the effect of pouring temperature and sand shell thickness was studied. We found that the crankshaft overall cooling speed faster, the melt feeding effect is not obvious under1400℃pouring temperature; And when the sand shell thickness is4mm. casting cooling speed is too fast, that the whole crankshaft surface solidification time is only80s,less than the situation of thickness in6mm and8mm,so that the shell do not have the effect of technology of iron based coated sand.We studied the effect of different materials such as graphite, titanium alloy, stainless steel and the size of the probe by water simulation, in order to choose a suitable probe to output power while melt ultrasonic treatment for ductile cast iron melt. Also designed and made the equipment for spheroidizing and shell mould-tectorial sand casting in laboratory. We studied the effect on microstructure and mechanical properties of ultrasonic treatment during spheroidizing and solidification processing. Founded that if we applying ultrasonic treatment in spheroidizing process and then in solidification process for about18s, the ferrite ductile iron content is only about2%, while without applying ultrasonic processing is about13%; The mechanical properties of specimens of applying ultrasonic treatment are slightly higher than that of not applying ultrasonic treatment samples. On the basis of laboratory study, we puts forward the melt ultrasonic treatment method for practical production and had the field tests for several time. The results showed that the tensile strength of samples treated by ultrasonic, mainly within the scope of800-870Mpa, while the tensile strength of those without ultrasonic treatment is about793Mpa, also the ballistic work and break elongation of former are about10%higher than the latter, which has a good comprehensive mechanical properties. |
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