Precision Casting is Also Called Lost Wax Casting
Precision casting refers to the general term for the process of obtaining castings with precise dimensions. Compared with the traditional sand casting process, the castings obtained by precision casting have more precise dimensions and better surface finish.
Precision casting is also called lost wax casting. Its products are precise, complex and close to the final shape of the part. They can be used directly without or with little processing. It is an advanced process of near net shape forming.
Name: Precision Casting
Alias: lost wax casting
Definition: Casting process
Including: metal mold casting, pressure casting, investment casting, ceramic mold casting, lost foam casting.
The more commonly used one is investment casting, also known as lost wax casting: select appropriate investment materials (such as paraffin) to make an investment mold; repeat the process of dipping refractory paint and spreading refractory sand on the investment mold, hardening the shell and drying; Melt the internal investment mold to obtain the mold cavity; bake the mold shell to obtain sufficient strength and burn off the remaining investment material; pour the required metal materials; solidify and cool, and clean the sand after shelling to obtain high quality Finished product with precision. Heat treatment and cold processing and surface treatment are performed according to product needs.
The development of investment technology enables investment casting to produce not only small castings, but also larger castings. The outline size of the largest investment casting is nearly 2m, while the minimum wall thickness is less than 2mm. At the same time, investment castings are becoming more precise. In addition to linear tolerances, parts can also achieve higher geometric tolerances. The surface roughness of investment castings is also getting smaller and smaller, reaching Ra0.4μm.
Precision Casting Classification
Ceramic Mold Casting
A casting method that uses ceramic slurry to make casting molds to produce castings. Ceramic slurry is made of ethyl silicate hydrolyzate and fine refractory sand with relatively pure texture and high thermal stability, such as fused quartz, zircon, corundum, etc. In order to make the ceramic slurry gel in a short time, calcium hydroxide or magnesium oxide is often added as a catalyst. Since the refractory material composition and appearance used are similar to ceramics, it is called ceramic type. Ceramic mold casting is a new process developed on the basis of ordinary sand casting.
Among the total casting output, 60 to 70% of the castings are produced with sand molds, and about 70% of them are produced with clay sand molds. The main reason is that sand casting has lower cost, simpler production process and shorter production cycle than other casting methods. Therefore, castings such as automobile engine cylinder blocks, cylinder heads, crankshafts, etc. are all produced using the clay green sand process. When the wet type cannot meet the requirements, consider using clay sand surface dry sand type, dry sand type or other sand type. The weight of castings produced by clay green sand casting can range from a few kilograms to tens of kilograms, while the castings produced by clay dry mold can weigh tens of tons.
Generally speaking, for medium and large castings, iron castings can be produced with resin self-hardening sand molds, and steel castings can be produced with water glass sand molds. Castings with precise dimensions and smooth surfaces can be obtained, but the cost is higher.
Of course, sand casting often produces poor castings in terms of accuracy, surface finish, material density, metallographic structure, and mechanical properties. Therefore, when castings have higher requirements for these properties, other casting methods should be used, such as investment (loss of mold). Wax) casting, die casting, low pressure casting, etc.
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