Table of Contents
How important are the linear dimensional tolerances? You would understand if you had ordered castings in an unfitted size. They can help you reduce costs in sourcing components for cars, machines, or consumer hardware. In the following sections, linear dimensional tolerances will be explained, including the grades and how to choose them .
1. What is the linear dimensional tolerance of a casting?
There will be shrinkage and mild displacement during the molten metal cooling process. Therefore, the product size will not be 100% accurate. Linear dimensional tolerance is the acceptable margin of error. (For example, if the dimensional tolerance of a 100mm component is ±0.5mm, then the actual measurement, which ranged from 99.5mm to 100.5mm, is acceptable.)
There is an international standard (ISO 8062-3) that provides a reference framework for both buyers and suppliers.
2. Linear dimensional tolerance grades of castings
16 linear dimensional casting tolerance grades are defined and designated as DCTG 1 to DCTG 16 in ISO 8062-3.
Grade range | Tolerance level | margin of error (for 100mm component) |
DCTG 1–4 | Very tight | <±0.3mm |
DCTG 5–9 | Medium | ±0.5–0.9mm |
DCTG 10–14 | Loose | ±1–4mm |
DCTG 15–16 | Very loose | >±4mm |
The tolerance level is tighter with a smaller numeric value.
3. How to select the appropriate grade for different casting processes?
The grade range of the product is different in different casting process.
High-pressure Die Casting |
DCTG 4–6 |
±0.3 – ±0.5 mm | High-volume, small-to-medium aluminium/zinc parts |
Investment Casting (Silica Sol) | DCTG 4–6 | ±0.3 – ±0.5 mm | Complex shapes, stainless steel, aerospace |
Investment Casting (Water Glass) | DCTG 7–8 | ±0.6 – ±0.9 mm | Carbon steel, cost-sensitive precision parts |
Green Sand Casting | DCTG 10–13 | ±1.0 – ±3.0 mm | Large, low-cost structural components |
Therefore, it is important to discuss with the factory before finalizing the design, as the required tolerance grade often determines which casting process is suitable.
4. The influence of linear dimensional tolerances on castings
Not only the number on the design, the linear dimensional tolerances can also affect:
l Cost: to tighten the grade from DCTG 10 to DCTG 6, the cost can be double or more
l Post-processing: the casting of loose tolerance required CNC machining post-processing
l Assemble fitness: the deviation in tolerance can affect assembly if the component is required to assemble with other parts
l Surface roughness: the looser the tolerance, the rougher the surface will be
l Scrap rate: the scrap rate will become higher if the required tolerance does not match the process capability
5. Are there any other casting parameters?
l Geometrical Casting Tolerances (GCT): flatness, roundness, perpendicularity, etc
l Machining allowance: spare extra materials for further cutting
l Draft angle: the angle that allows the casting to demold, usually ranging from 0.5°–3°
l Wall thickness: die casting can reach the thickness of 0.8mm, while sand casting requires 3mm or above
l Surface Roughness (Ra): the average deviation of the surface from a mean line
l Porosity: important to sealing or pressure-bearing parts and required to be verified by X-ray or CT scan
6. Here are 5 recommended factories that produce castings using international standard casting tolerances
Fuchun Casting(China) | Precision casting and produces 8,000 tons annually. CT5–CT8 |
EASIAHOME (China) | ISO 9001 certified, with one-stop service. CT5–CT6 |
Dawang Metals (China) | Consists of three factory sites with 120,000 square meters. ISO 9001 + 14001 |
Casting Quality Industrial (China) | Can reach CT4 and is suitable for stainless steel |
MetalTek International (USA) | Suitable for buyers who require an AS9100 (aerospace) certificate |
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