Tolerance for investment casting

Investment Casting Tolerances means the dimension range that can be meet by investment casting. There are a variety of investment casting processes, such as lost wax casting, lost foam casting and solica sol casting. Each casting process has its own casting forming ways and is suitable for different types of products. Tolerances may be affected by a number of factors. Such as die temperature, wax or plastic temperature, injection pressure, mold or shell composition, back up sand, firing temperature, rate of cooling, position of the part on the “tree”, and heat treat temperature all bear directly on tolerances required in the investment casting industry. Althought there is a tolerance standard in investment casting industry, it may still vary from foundry to foundry, as some may be specialized in thin wall small parts, and others could be more professional in larger parts. Also the equipments may also has a certain effect on the casting tolerances.
Generally, we can divide investment casting tolerances into Linear Tolerances and Geometric Tolerances.
Linear tolerancing is normally applied to the following features of investment castings: Length, Concentricity, Fillet radii, Holes, Flatness, Straightness, Corner Radii, and Curved Holes. And the linear tolerances of each casting process are not the same. For example, water glass lost wax casting can control general linear tolerances between CT7-CT8, and lost foam casting can meet CT8-CT9, while the tolerances of silica sol casting is the most precise, it is CT5-CT6. Below is a list of tolerance standard for casting: