The net weight of machine tool body parts is 1762.75 kg, and the overall contour size of parts is 1985 mm x 1650 mm x 460 mm, which belongs to medium-sized parts.Due to the complex structure and large voids, it is not suitable to use mechanized production line, hand-shaped production mode and traditional gravity casting method to control the cost and quality of large and medium-sized castings produced in small batches.
Considering that large volume expansion will occur during solidification of grey cast iron, which will cause the size expansion of casting cavity and affect the dimensional accuracy of casting contour, internal quality and surface quality.High strength moulding sand and core sand should be selected. Besides cost, acid cured furan resin self-hardening sand is used in this process design to reduce cost as much as possible on the premise of making qualified products.
Castings are large in size and complex in structure, but with uniform thickness and concurrent solidification. Therefore, the pouring position should be set at the thin wall of the castings in a large quantity and arranged dispersedly, so that the liquid metal can fill the cavity quickly and uniformly, thus reducing the occurrence of shrinkage and shrinkage.Based on alloy solidification theory and practical experience, the relationship between structure and dimension of HT250 casting material is comprehensively analyzed. During pouring, the liquid metal is filled into the cavity quickly and smoothly. The center pouring system which combines the advantages of bottom pouring and top pouring is adopted and the horizontal pouring method is adopted.
1 Selection of gating system type
Grey cast iron has low melting point and good fluidity due to its high carbon content, close to eutectic composition. Casting temperature and carbon content have a great influence on fluidity.As this casting is a bed of grey cast iron with thin wall and complex structure, it is determined to be the mode of simultaneous solidification. Graphite expansion will occur in the process of crystallization and solidification of grey cast iron. Therefore, its expansion should be fully utilized to improve the shrinkage effect of the casting.
Therefore, its pouring system has two characteristics: large flow of molten iron and good slag retaining function.According to the design of parting surface and pouring position of this casting, the filling capacity and filling capacity as well as the convenience of moulding should be considered. Therefore, the medium pouring system is preferred.And since the semi-enclosed pouring system has smooth filling, small scouring force and certain slag retaining capacity, the semi-enclosed pouring system is adopted.
2 Gating System Structure
Through the above analysis, the schematic diagram of the structure and position of the casting system is shown in the figure.Casting technology plays a key role in casting quality. With the development of computer technology, the two key links of filling and solidification incan be simulated intuitively before the die test.Solidification simulation can accurately predict defects such as shrinkage holes, filling process can effectively and accurately predict defects such as underfilling, cold insulation and slag inclusion caused by liquid metal flow, and numerical simulation provides reliable technical and theoretical basis for optimizing casting process.
CREO software is used to carry out three-dimensional modeling of parts and casting system, ProCast is used to simulate the designed process, and casting defects are analyzed to optimize the original process.