Casting Tolerances by Different Casting Processes

Casting processes play a pivotal role in manufacturing, offering versatile methods to shape molten metal into intricate designs. However, achieving precise dimensions and tolerances can vary significantly across different casting techniques.

Tolerances refer to the permissible limit of variation in a dimension or physical property of a part, impacting its functionality and assembly. In casting, achieving specific tolerances is influenced by factors like casting method, material properties, mold design, and post-processing techniques.

Casting tolerances are divided into Dimensional Casting Tolerances (DCT) and Geometrical Casting Tolerances (GCT). In ISO 8062 (corresponding to China's GB/T6414-1999) standard documents, the tolerance levels of casting dimensions are clearly specified. Here in the following you will see the general tolerances by different casting processes.

Sand Casting Tolerances

Sand casting, a traditional and widely used method, offers moderate tolerance capabilities. The nature of sand molds introduces some limitations due to mold erosion, sand expansion, and contraction. Typically, sand casting tolerances range from ±0.3 mm to ±3 mm per linear inch, making it suitable for larger parts where precision is not paramount.

Investment Casting Tolerances

Investment casting, also known as lost-wax casting, can be divided into water glass casting and silica sol casting. Both can provide superior accuracy compared to sand casting, but silica sol casting still have better DCT and GCT than water glass casting. The use of metal molds allows for tighter tolerances, typically within ±0.1 mm to ±0.3 mm per linear inch. This process suits intricate designs and smaller parts where precise dimensions are critical.

Die Casting Tolerances

Die casting, utilizing reusable metal molds, offers excellent dimensional accuracy. Tolerances in die casting commonly range from ±0.02 mm to ±0.1 mm per linear inch. Its ability to produce high volumes of intricate parts with minimal post-processing makes it ideal for applications requiring tight tolerances.

Gravity Casting Tolerances

Gravity casting, involving pouring molten metal into a permanent mold, falls between sand casting and die casting in terms of tolerances. Tolerances typically range from ±0.1 mm to ±0.5 mm per linear inch. While less precise than die casting, gravity casting is cost-effective for producing medium-sized parts.

Lost foam Casting Tolerances

Generally speaking, lost foam castings tolerances are not very tight because of the used simple foam mould. But usually, the DCT Grade by lost foam casting can reach CTG9~CTG13 and the GCT Grade by lost foam casting to be CTG5~CTG8.

Tolerance Factors Influencing Casting Processes

Several factors affect the achievable tolerances in casting processes. Material properties, mold design intricacy, cooling rates, and process controls significantly impact the final part's dimensions. Moreover, post-casting treatments such as machining or surface finishing can refine tolerances.

Conclusion

Different casting processes offer varying capabilities regarding tolerances, each catering to specific requirements of different industries and applications. Understanding these nuances aids manufacturers in selecting the most suitable casting method to achieve desired precision while balancing cost-effectiveness. Embracing advancements in casting technology continually improves tolerance capabilities, enhancing the quality and competitiveness of manufactured products.