Investment casting, also known as lost wax casting, is a method of making a fusible model with fusible materials (such as wax or plastic), coating the model with several layers of special refractory coating, drying and hardening to form an integral shell, and then melting the model from the shell with steam or hot water, and then placing the shell in a sand box, filling it with dry sand molding, and finally placing the mold in a roasting furnace for high-temperature roasting (if a high-strength shell is used, the shell can be directly roasted after demolding without molding), and after the mold or shell is roasted, pouring molten metal into it to obtain a casting.
Investment casting process:
Manufacturing investment mold: The investment mold is a model used to form the cavity in the refractory shell. To obtain castings with high dimensional accuracy and surface finish, the investment mold itself should have high dimensional accuracy and surface finish. The mold material is generally prepared with wax, natural resin and plastic (synthetic resin). During the preparation, the various raw materials are melted and mixed into one by heating. Then, when cooled, the mold material is vigorously stirred to make the mold material into a paste state for pressing the mold. The mold pressing is generally carried out by pressing molding, which includes injection molding and extrusion molding.
Shell making: Shell making includes two processes: coating and sanding. Before coating, the mold needs to be degreased. When coating, the dip coating method is used. The surface of the mold should be evenly coated to avoid blanks and local accumulation. The welds, fillets, edges and grooves should be evenly coated with a brush or special tools to avoid bubbles. Before coating each layer of reinforcement layer, the floating sand on the previous layer should be cleaned. During the coating process, the paint should be stirred regularly to control and adjust the viscosity of the paint. Sanding is performed after coating. The most commonly used sanding methods are fluidized sanding and rain-type sanding. When sanding, the mold must be constantly rotated and inverted. Sanding too early can easily cause paint accumulation, and sanding too late can cause the sand particles to not adhere or not adhere firmly.
Melt-loss model: When the mold shell is dried and hardened to a certain extent, it is heated to melt the mold and flow out of the mold shell to form a casting cavity.
Mold shell baking: The dewaxed mold shell is placed in a baking furnace for high-temperature baking to further remove the residual mold material, moisture and other impurities in the mold shell, and improve the strength and refractoriness of the mold shell.
Pouring: The casting molten metal is injected into the mold cavity before the mold shell cools down, so that the molten metal has better fluidity in the mold cavity, thereby filling every detail in the mold cavity. Generally, injecting molten metal into the heated mold cavity will obtain a casting with higher precision, because the mold and the casting will eventually shrink at the same time during cooling, thereby reducing the impact of shrinkage on dimensional accuracy.
Post-processing: After the casting cools and solidifies, it undergoes post-processing steps such as sand removal, cleaning, cutting of pouring heads, heat treatment, and surface treatment to obtain parts that meet the requirements.
