What is investment casting ?

What is investment casting ?
Investment casting, also known as lost wax casting, includes processes such as pressing wax, wax repairing, tree forming, dipping, wax melting, molten metal casting and post-processing. Lost wax casting is to use wax to make a wax mold of the part to be cast, and then coat the wax mold with mud, which is a mud mold. After the clay mold is dry, put it in hot water to melt the inner wax mold. Take out the clay mold that has melted the wax casting mold and then bake it into a pottery mold. Once roasted. Generally, the pouring port is left when the mud mold is made, and then the molten metal is poured from the pouring port. After cooling, the required parts are made.

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Introduction to Investment Casting

When using wax to make patterns, investment casting is also called "lost wax casting". Investment casting usually refers to making a pattern in a fusible material, coating the surface of the pattern with several layers of refractory material to make a mold shell, and then melting the pattern out of the mold shell to obtain a mold without parting surface. A casting solution that can be filled with sand casting. Because the patterns are widely made of waxy materials, investment casting is often referred to as "lost wax casting".
The types of alloys that can be produced by investment casting include carbon steel, alloy steel, heat-resistant alloys, stainless steel, precision alloys, permanent magnet alloys, bearing alloys, copper alloys, aluminum alloys, titanium alloys, and ductile iron.
The shape of investment castings is generally more complex, the minimum diameter of the holes that can be cast on the castings can reach 0.5mm, and the minimum wall thickness of the castings is 0.3mm. In production, some parts that were originally composed of several parts can be designed into integral parts by changing the structure of the parts and directly cast by investment casting, so as to save processing time and consumption of metal materials, and make the part structure more accurate. to be reasonable.
The weight of investment castings Company is mostly zero to dozens of Newtons (from a few grams to more than ten kilograms, generally not more than 25 kilograms). It is more troublesome to use the investment casting method to produce too heavy castings.
The investment casting process is complicated and difficult to control, and the materials used and consumed are more expensive, so it is suitable for the production of small parts with complex shapes, high precision requirements, or difficult to perform other processing, such as turbine engine blades.

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advantage

The dimensional accuracy of investment castings is relatively high, generally reaching CT4-6 (CT10~13 for sand casting and CT5~7 for die casting). Of course, due to the complex process of investment casting, there are many factors that affect the dimensional accuracy of castings, such as mold casting. The shrinkage of the material, the deformation of the investment mold, the linear change of the shell during the heating and cooling process, the shrinkage rate of the alloy, and the deformation of the casting during the solidification process, etc., so the dimensional accuracy of ordinary investment castings is high, but its Consistency still needs to be improved (the dimensional consistency of castings using medium and high temperature waxes is much improved).
When pressing the investment mold, a mold with a high surface finish of the cavity is used, so the surface finish of the investment mold is also relatively high. In addition, the shell is made of high temperature-resistant special binder and refractory paint prepared from refractory materials, which is coated and hung on the investment mold, and the inner surface of the cavity that is in direct contact with the molten metal has a high smoothness. Therefore, the surface finish of investment castings is higher than that of general castings, generally reaching Ra.1.6~3.2μm.
The biggest advantage of investment casting is that investment castings have high dimensional accuracy and surface finish, so machining work can be reduced, just leave a little machining allowance on parts with higher requirements, and even some castings only Leave grinding, polishing allowance, can be used without machining. It can be seen that the use of investment casting method can save a lot of machine tool equipment and processing time, and greatly save metal raw materials.
Another advantage of the investment casting method is that it can cast complex castings of various alloys, especially superalloy castings. For example, the blade of a jet engine has a streamlined outline and an inner cavity for cooling, which can hardly be formed by machining. The investment casting process can not only achieve mass production and ensure the consistency of castings, but also avoid the stress concentration of residual knife lines after machining.

manufacture

The first process of investment casting production is to manufacture the investment mold. The investment mold is used to form the model of the cavity in the refractory shell. Therefore, in order to obtain castings with high dimensional accuracy and surface finish, the investment mold itself should have a high size. Precision and surface finish. In addition, the performance of the investment mold itself should also make the subsequent processes such as shell making as simple as possible. In order to obtain the investment mold with the above-mentioned high-quality requirements, in addition to having a good pressing shape (the mold for pressing the investment mold), it is also necessary to select the appropriate molding material (referred to as the mold material) and a reasonable molding process.

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