Process design and optimization of sand casting and investment casting

In the process of sand casting, the performance of sand mold is one of the key factors affecting the final quality of sand casting. The size and surface quality of the casting sand mold will be directly reflected in the size and surface quality of the final sand mold casting. The air emission and air permeability of casting sand mold also have an important impact on whether there are defects such as pores in sand mold castings. Therefore, three kinds of sand mold rapid prototyping manufacturing processes are studied in order to quickly manufacture high-quality sand mold and provide conditions for obtaining high-quality automobile engine parts. The following aspects are studied:

(1) The laser power, preheating temperature and scanning speed of laser selective sintering coated sand process are studied, and the secondary curing temperature and time of casting sand mold are studied to obtain the optimal manufacturing process parameters.

(2) Through the cutting comparison test, the original sand model of digital Moldless mold NC machining is selected, and two common defects are analyzed in order to obtain high-quality casting sand mold.

(3) The performance of the sand mold manufactured by 3D inkjet printing technology is tested and compared with the performance of the first two processes. It provides a reference basis for the selection of sand mold casting process in the subsequent rapid casting process.

In wax mold precision casting process, wax mold is the master mold to form the casting shell, so its dimensional accuracy directly affects the dimensional accuracy of the casting shell, and finally affects the dimensional accuracy of the casting. The preheating temperature, delamination thickness, laser power, scanning speed and other parameters of laser selective sintering PS powder process are studied. The temperature of wax infiltration process is tested to determine the optimal process parameters, so as to ensure the wax model with high dimensional accuracy.

A remarkable advantage of adopting rapid prototyping and other dieless casting processes is that the trial production cycle is short. If a more reasonable sand casting process is not obtained in the early design stage, it will need to carry out multiple rounds of commissioning to obtain qualified sand castings. This will lead to the waste of many sets of sand cores. More importantly, it will prolong the trial production cycle, and even lose the short cycle advantage compared with traditional casting.

Simulation technology is a very effective auxiliary means in the pouring process design of sand mold casting. Through the simulation of flow field, the state of molten iron flow, the degree of turbulence and the velocity of molten metal in each part of gating system and sand mold casting can be intuitively tested. According to the test, the scouring of molten metal on sand mold can be known, It can also analyze the entrainment and oxidation of liquid metal. Through the calculation of the temperature field, the temperature of the casting in the whole sand casting process can be predicted, and the tendency of shrinkage cavity and porosity casting defects can be predicted.

Firstly, the gating system is designed according to the empirical formula and previous production experience; Modeling the designed gating system to simulate pouring and solidification; The process is adjusted according to the simulation results, and the adjusted process is simulated again. After repeated for many times, the optimal sand casting process is obtained.

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