Views:76 Author:Site Editor Publish Time: 2020-09-02 Origin:Site
The design of sand molding castings must not only consider the requirements of work function and mechanical properties, but also the requirements of alloy casting performance and sand casting process for casting structure. Whether the structure design of dry sand castings is reasonable has a great impact on casting quality, productivity, and manufacturing costs. If the structure of the casting cannot satisfy the requirements of alloy casting performance, defects such as failure to pour, cold separation, shrinkage cavity, shrinkage porosity, pores, cracks, and deformation may occur.
The alloy with good fluidity has strong mold filling ability, and it is not easy to produce defects such as insufficient pouring and cold barrier during precision sand casting, and the minimum wall thickness of the casting that can be cast is also small. Different alloys have different minimum wall thicknesses under certain casting conditions.
When designing the wall thickness of the sand casting, it must be large: the "minimum allowable wall thickness" of the alloy to ensure the quality of the sand casting. The "minimum allowable wall thickness" of a casting mainly depends on the type of alloy, the casting method, and the size of the sand casting. However, the casting wall should not be too thick. Thick-walled castings have coarse grains, loose structure, easy to produce shrinkage cavity and shrinkage porosity, and the problem of reduced mechanical properties.
The sand casting capacity does not increase proportionally with the increase in the cross-sectional area. Designing a thick casting wall will cause metal waste. In order to improve the bearing capacity of the casting without increasing the wall thickness, the structural design of the sand casting should select a reasonable cross-sectional shape.
In addition, the ribs or walls inside the casting have worse heat dissipation conditions than the outer walls, and the cooling rate is slower. In order to prevent the grains of the inner wall from becoming thicker and generating internal stress, the thickness of the inner wall should generally be smaller than the outer wall. If the wall thickness of each part of the sand casting is too different, the metal will accumulate locally at the thick wall to form a hot joint, and it is easy to form shrinkage holes, shrinkage, and other defects at the hot joint during solidification and shrinkage.
The cooling rate of each part of sand casting is different, which is easy to form thermal stress, causing cracks at the junction of the thin wall and thick wall of the casting. Therefore, when designing sand castings, the wall thickness should be as uniform as possible to prevent the above defects.
When checking whether the sand casting wall thickness is uniform, the machining allowance of the casting should be taken into consideration. If the wall thickness is uniform everywhere on the part drawing, after adding the machining allowance, the casting thickness on the machining surface will increase, but the hot spot of the casting will be very large.
The above are the issues that need to be paid attention to when processing sand casting design. Do you understand? Hurry up and contact us to customize the sand casting design that suits your wishes! Yifei is a professional manufacturer and supplier for custom die casting, precision investment casting, sand mold casting and custom forging in China.