Investment Casting Tolerance
Discover Precisionvast’s detailed approach to ensuring exact dimensional accuracy in our casting processes, highlighting the specific tolerances for different casting methods
What is investment casting tolerance?
Linear Tolerances
Linear tolerances in investment casting typically apply to features like length, concentricity, fillet radii, holes, flatness, straightness, angular radii, and bent holes. Each casting process has distinct linear tolerances; for instance, water glass lost wax casting generally achieves tolerances between CT7 and CT8, while silica sol casting, known for its precision, reaches CT5 to CT6. Standard measurements use millimeters (mm) as the basic unit of dimension. At Precisionvast, we cater to your specific investment casting needs based on the actual requirements, adhering to these tolerance standards when dimensions are denoted in mm.
The following is a list of casting tolerance standards:
| ISO8062(GB/T6414) CT4-CT8 | |||||||||||
| Norminal dimension (mm) Linear dimension tolerance (ISO8062) | |||||||||||
| ＞ | ≤ | CT4 | CT5 | CT6 | CT7 | CT8 | |||||
| 0 | 10 | 0.26 | ±0.13 | 0.36 | ±0.18 | 0.52 | ±0.26 | 0.74 | ±0.37 | 1 | ±0.5 |
| 10 | 16 | 0.28 | ±0.14 | 0.38 | ±0.19 | 0.54 | ±0.27 | 0.78 | ±0.39 | 1.1 | ±0.55 |
| 16 | 25 | 0.3 | ±0.15 | 0.42 | ±0.21 | 0.58 | ±0.29 | 0.82 | ±0.41 | 1.2 | ±0.6 |
| 25 | 40 | 0.32 | ±0.16 | 0.46 | ±0.23 | 0.64 | ±0.32 | 0.9 | ±0.45 | 1.3 | ±0.65 |
| 40 | 63 | 0.36 | ±0.18 | 0.5 | ±0.25 | 0.7 | ±0.35 | 1 | ±0.5 | 1.4 | ±0.7 |
| 63 | 100 | 0.4 | ±0.2 | 0.56 | ±0.28 | 0.78 | ±0.39 | 1.1 | ±0.55 | 1.6 | ±0.8 |
| 100 | 160 | 0.44 | ±0.22 | 0.62 | ±0.31 | 0.88 | ±0.44 | 1.2 | ±0.6 | 1.8 | ±0.9 |
| 160 | 250 | 0.5 | ±0.25 | 0.7 | ±0.35 | 1 | ±0.5 | 1.4 | ±0.7 | 2 | ±1 |
| 250 | 400 | 0.56 | ±0.28 | 0.78 | ±0.39 | 1.1 | ±0.55 | 1.6 | ±0.8 | 2.2 | ±1.1 |
| 400 | 630 | 0.64 | ±0.32 | 0.9 | ±0.45 | 1.2 | ±0.6 | 1.8 | ±0.9 | 2.6 | ±1.3 |
Geometric Tolerances
Geometric tolerances include shape and positional tolerances. Geometrical tolerances include shape and positional tolerances. Geometrical tolerances are usually applied to the following features of investment casting: flatness, straightness, parallelism, roundness, hole tolerances, curved holes, internal radii and fillets.
Flatness：
The flatness tolerance is the total acceptable deviation from flatness. The surface of the investment cast part must lie between the flattest plane and the plane that affects the maximum permissible deviation.
The amount of volumetric shrinkage of the wax mold and metal during cooling always determines the flatness of the investment casting part. This shrinkage usually occurs in the center of the casting and is referred to as “stress deformation”. This “stress distortion” can be controlled by specialized techniques, but will always be present to some degree.
Straightness：
People are always confused about the difference between straightness and flatness because they seem so close. When it comes to straightness tolerances, the maximum tolerable diameter of a part that deviates from a perfectly straight line will determine straightness.
Straightness can be a real problem for some types of investment cast parts. This is because some relatively thin and short parts can bend easily. Based on our experience with Precsisiovast casting, we can check if the designed part will bend, but it is difficult to determine the degree of bending before production. As a rough estimate, axial bending at a constant cross section is approximately 0.024 inches per foot.
Arallelism：
When you see blueprints that include parallel prongs that are supported on only one end, it means that completing a precision investment casting will present special challenges. Once your part has parallelism requirements, our engineers at Precsisiovast Casting will discuss this with you prior to production.
It is difficult to maintain the parallelism of these prongs due to the volume shrinkage of the support structure. The yoke holes also deform considerably when ambient temperatures are reached. Careful design adjustments for volume shrinkage are critical to obtaining accurate workpieces. These workpieces require more tooling and finishing.
Roundness:
The radial difference between a true circle and a given circumference determines roundness. We can test roundness by reading the total indicated value.
Curved holes, inner radii and fillets
Curved holes can be made with preformed ceramic cores or soluble wax. Given the curvature, the normal hole tolerance will be doubled and the tolerance for all dimensions will be multiplied by 2. We cannot determine the size of these holes, so the diameter tolerance is +/- .005″. For internal radii and fillets, which are difficult to control and check, they should be designed as wide as possible.
Direction Tolerance:
1. Parallelism (∥) is used to control the requirement that the measured element (plane or line) on the part deviates 0° from the reference element (plane or line), i.e., the measured element must be equidistant from the reference.
2. Perpendicularity (⊥) is used to control the requirement that the measured element (plane or line) on the part deviates 90° from the reference element (plane or line), i.e., the measured element is required to be 90° from the reference.
3. Inclination (∠) is used to control the measured element (plane or line) on the part to deviate from a given angle (0° to 90°) with respect to a reference element (plane or line)
precisionvast foundry investment casting tolerances
The precisionvast foundry provides investment castings with excellent tolerances and confirms that every casting supplied is within the allowable tolerances. We always adhere to strict tolerance standards to ensure that all investment castings produced in our foundry are accurate and that further machining is avoided or minimized, resulting in cost savings for our customers. The core of our business is to provide high quality metal castings with the most accurate dimensions.
Even if we can’t achieve the tolerances you require after casting, our machining capabilities can help you achieve the required results. Contact our precisionvast investment casting facility and we will discuss the tolerances of your part in detail.
precisionvast foundry is the top customized investment casting manufacturer in China. We can provide a wide variety of investment casting parts in steel, titanium, high temperature alloys, aluminum, and other materials.
If you have any needs for investment casting solutions, please contact us!