Technological conditions of sand casting

The end cover of a certain type of motor is produced by sand casting, and the mold is made by traditional pattern modeling, sand 3D printing and sand NC milling. The basic outline of the casting is shown in Figure 1. The mass of the casting is 32.86kg and the material is gray cast iron HT200. The maximum size is 420mm × 420mm × 111mm, the maximum wall thickness reaches 36mm, and the thinnest part is about 6mm. It belongs to thin-walled gray iron castings. And each box is poured only one. At the same time, the mold is required to have sufficient hardness and strength, that is, there is no cracking or sand collapse in the process of transportation and pouring. The quality requirement is that the surface roughness of the casting RA ≤ 50 μ M and there shall be no shrinkage porosity and other defects. Because the three methods can achieve different casting accuracy, and according to the advantages of Moldless sand casting technology in mold forming, different process parameters are set in the aspects of mold draft angle and machining allowance of castings. The conventional mold structure is adopted, that is, the mold is divided into upper mold and lower mold according to the structure of the casting.

The casting has the characteristics of circular symmetry. In principle, the top injection and side injection gating systems meet the process requirements. However, in order to make it easier to distinguish the profile, the annular lap edge gating system in the side injection is adopted. The pouring riser and gating system are symmetrically arranged according to the middle hole of the end cover, and the open side riser and three trapezoidal inner sprues are used for joint horizontal feeding of the casting. The design of the gating system is shown in Figure 2. Different process parameters make the quality and size of blank castings different. Therefore, in order to eliminate the influence of gating system, the size of sprue and machining allowance are also adjusted. At the same time, the pouring time is set as 12s based on the traditional method, and the filling speed of the three methods is 3.904kg/sec.

The example results are based on the actual production situation of casting enterprises. In different batch production, the molten iron quality and production plan of each medium frequency furnace are different. In addition, different numbers of automation equipment and wood molds are set to match the needs of production scenarios. When the wood mold is affected by the surface wear of molding sand and air humidity, the structure will be irreversibly damaged, such as expansion, cracking and deformation. The upper limit of a set of wood molds is 50 times. When 3000 castings are produced in batch, the enterprise trial produces 10 sets of wood molds and puts them into molding production at the same time. Finally, 60 sets of wood molds need to be made. At the same time, the 3D printer of amsky-s800 is used, and the volume of forming bin is 800 × five hundred × 400mm, 1 machine can accommodate the printing of 2 upper molds of composite mold or 0.5 mold in a single casting method. The milling machine inputs 1 and 2 equipment respectively to participate in production. The simultaneous operation of multiple machines can greatly reduce the forming time per unit mold.

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