Sand casting tolerances are sensitive to the materials used and the manufacturing process. International Organization for Standardization (ISO) Standard ISO 8062 for SG Iron castings made in machine-produced sand molds specifies general tolerances for metal alloy castings. Casting Tolerance (CT) 8–12 are the proper grades to use.
For the most part, sand casting cannot produce high-definition mirror finishes or parts with tight tolerances. Sand casting tolerance standards are typically discussed in the widely used industry, and these often fulfill the needs of the product design.
Table of Contents
Dimensional Sand Casting Tolerances
Below are the Sand Casting Tolerances for general industry standards.
Functional Dimensional
| Functional Dimensional Tolerance | |||
|---|---|---|---|
| Inches ( Each Additional Inch Add ± 0.01" ) | Millimeters ( Each Additional 25mm Add ± 0.025mm ) | ||
| 0~7 | ±0.021 | 0~175 | ±0.53 |
| 7~8 | ±0.023 | 175~200 | ±0.58 |
| 8~10 | ±0.25 | 200~250 | ±0.63 |
| 10~12 | ±0.27 | 250~300 | ±0.68 |
| 12~14 | ±0.029 | 300~350 | ±0.73 |
| 14~16 | ±0.031 | 350~400 | ±0.78 |
| 16~18 | ±0.033 | 400~450 | ±0.83 |
| 18~20 | ±0.035 | 450~500 | ±0.88 |
| 20~22 | ±0.037 | 500~550 | ±0.93 |
| 22~24 | ±0.039 | 550~600 | ±0.98 |
| 24~26 | ±0.041 | 600~650 | ±1.030 |
| Additional tolerance across mould and core joints. | |||
| ±0.0099" | ±0.25mm | ||
Non Functional Dimensions
| Non-Functional Dimensions | ||
|---|---|---|
| Wall Thickness Tolerance | ±0.008" | ±0.2mm |
| Straightness/Flatness Tolerance (excluding localised pattern depressions) | ±0.004" per inch | 0.1mm per 25.4mm |
| Angular Tolerance | ± _° UP to 3" | ± _° UP to 7.60mm |
| Typical Surface Finish | 80 MICROINCHES | 2.0 MICROMETRES |
| 50% Additional Tolerance up to | 5.000" | 127mm |
| 33% Additional Tolerance above | 5.000" | 127mm |
For the sand casting services from Leisheng Machinery, We can do better casting tolerances
Dimension Tolerances & the Factors that Affect Them
Tolerances in dimensions refer to the allowable range of final product variations from their nominal dimensions. The degree to which tolerances can be satisfied is affected by several variables, including but not limited to the following:
- Whether a single or a small number of castings are made from a pattern or a huge number of pieces are mass-produced
- The dimensions and casting's design
- Mold and core production machinery, including the pattern and core box
- Methods used to create molds and cores
- The density and length of the casting
- Is the final step in the process of finishing and inspecting the castings to be gaging and improving the dimensions?
Casting Cores and Design
Tolerances that are possible depending on several factors, including the complexity of the casting design (particularly the addition of cored passages). The capacity to create cores that resist bowing or sagging due to their own size or shape and the pressure of surrounding metal may limit the accuracy and precision of cored passage dimensioning.
Types of Dimension
Different sorts of dimensions exist depending on whether they are determined by the mold alone, the core alone, or a mix of the two, with and without the effect of the separation line.
Pattern and Core Box Equipment
The pattern used to make the casting significantly impacts the degree to which the casting’s dimensions match those of the design. Since the steel will contract as it cools in the mold, the pattern must be built with accurate proportions. And it’s not uncommon for foundries that use the same pattern to create castings with somewhat differing tolerances.
In order to make the most efficient use of the foundry’s experience with impeded contraction, it is advised that the foundry has chosen to perform a certain casting and also have control of pattern construction.
When deciding which materials to use for a pattern, it’s also essential to consider how long it will be used in manufacturing. Softwood patterns will have larger dimensional differences from casting to casting within a lot than metal patterns will.
Dimension Length and Casting Weight
Dimensional differences are highly sensitive to the casting’s weight. Process capability in terms of dimensional tolerances is nonlinearly affected by casting weight and dimension length.
Dimensional and Gaging Upgrading
Tolerances for as-cast surface dimensions are negotiated between the castings’ maker and the buyer. However, the tolerances chosen should be comparable to the process capabilities for the specific operating conditions being considered to reduce the rejection of castings due to dimensional reasons. When dimensional tolerances are tighter than what can be achieved during production, additional processing is needed to improve the casting’s quality.
Mold Processes
The manufacturer and purchaser of the castings agree upon the tolerances for the castings’ as-cast surface dimensions. To reduce casting rejection owing to dimensional reasons, the tolerances used should be comparable to the process capabilities for the particular operating conditions being evaluated. Additional processing is required to increase the casting quality when the dimensional tolerances are tighter than what can be achieved during production.
Significance of Sand Casting Tolerances
Standards vary depending on the type of material or manufacturing method being used. Therefore, positional and length (per inch) tolerances, material grades, customer needs and specs, and other factors are all considered and evaluated throughout each process. Additionally, each association has its own set of rules and regulations.
Quite a few outcomes are possible when tolerances aren’t met.
- More metal castings and mechanical discards
- Consumer complaints about the warranty
- An improperly operating product
- Modify the casting and/or manufacturing tools
- Additional machining
In the end, they all have an impact on expenses, and none of them are really pleasant. It might be minor if you’re lucky. But usually, it’s a big deal. Although there are many steps and factors to think about, the key to making the best choice is to work with a reliable collaborator who is familiar with the nuances involved.
