INVESTMENT CASTING TOLERANCES

Investment casting, also known as precision casting or lost wax casting, is a manufacturing process used to create intricate and complex metal parts. Tolerances in investment casting refer to the acceptable variations or deviations from the specified dimensions or features of a cast part. Achieving tight tolerances is crucial in ensuring that the final product meets design requirements and performs as intended. The tolerance levels in investment casting depend on various factors, including the material used, part geometry, and the capabilities of the foundry. Here are some general considerations regarding investment casting tolerances:

1,Part Complexity: Parts with intricate features, thin walls, or complex geometries may have looser tolerances compared to simpler designs. Achieving tight tolerances becomes more challenging with increasing complexity.

2,Material Selection: The type of metal or alloy used in the casting process can influence achievable tolerances. Some materials may exhibit greater shrinkage during cooling, affecting the final dimensions of the cast part.

3,Size of the Part: Larger parts may have looser tolerances compared to smaller parts. Controlling dimensions becomes more challenging with increasing size.

4,Casting Method: Different investment casting methods may have varying tolerances. For example, the traditional lost wax process may have different tolerances compared to newer technologies or variations of the process.

5,Quality Control Measures: The implementation of stringent quality control measures and inspection processes can help ensure that the final cast parts meet the specified tolerances. This may include the use of advanced measuring tools and techniques.

6,Experience of the Foundry: The expertise and experience of the foundry in investment casting play a significant role in achieving tight tolerances. Established foundries with a history of precision casting are often better equipped to meet strict tolerance requirements.

7,Customer Requirements: Tolerance specifications are typically outlined in the customer’s design requirements or drawings. It’s essential for the foundry and the customer to communicate clearly about the acceptable tolerance levels for a given project.

8,Surface Finish: Tolerances may be influenced by the desired surface finish of the cast part. Parts requiring a high degree of surface smoothness or intricate details may have different tolerance considerations.

It’s important for designers and engineers to work closely with the foundry during the design phase to understand the limitations and capabilities of the investment casting process, ensuring that the specified tolerances are achievable. Additionally, communication between the customer and the foundry is crucial to establish clear expectations regarding tolerances and quality standards.

General Tolerances for Investment Casting:

1. Linear Dimensions:

   • Small parts (up to 25mm / 1 inch): ± 0.075 mm to ± 0.1 mm (± 0.003 to ± 0.004 inch).
   • Medium parts (25-100mm / 1-4 inches): ± 0.1 mm to ± 0.25 mm (± 0.004 to ± 0.010 inch).
   • Larger parts (> 100mm / 4 inches): ± 0.25 mm to ± 0.75 mm (± 0.010 to ± 0.030 inch).

2. Flatness: Typically, 0.05 mm per 25 mm of length (0.002 inches per inch) can be expected.

3. Surface Finish: Investment casting often provides a fine surface finish of around 63-125 Ra µin (1.6 to 3.2 Ra µm), although further machining may be needed for finer finishes.

4. Wall Thickness:

   • Minimum wall thicknesses can vary but are typically around 1.5 mm (0.060 inches) depending on the material and design.

5. Geometrical Tolerances:

   • For features such as concentricity or perpendicularity, tolerances are often within ±0.2 mm to ±0.5 mm (0.008 to 0.020 inch), though tighter tolerances can be achieved with secondary machining.

Investment casting is known for producing parts with close tolerances, making it suitable for applications requiring precision, such as aerospace, medical, and automotive components.

2. Tolerances

3. Carbon Steel