Machining in metal castings is defined as the process of mechanically eliminating unnecessary material, and this process is a vital cog in the wheel. As such, we at VR Foundries, allow a certain amount of additional material for machining allowance when required, particularly when the product or part cast comes with tight tolerance.

Tolerance is the total admissible variations of size. It is the difference between the limit of size. Solidification shrinkage, Mould expansion, and thermal contraction all play a role in the tolerance of the finished part in the process of green sand casting. As a result, there are some limits for tolerances when it comes to the as-cast part. We deploy subsequent machining with a tighter tolerance.

Unlike VR foundries, not all supplier foundries provide machining in-house and create a cast production that can be changed by machining to deliver its intended requirements for the part. In order to achieve this, there must be a good relationship between the customer’s engineering and purchasing officer and the casting manufacturer. Here are some of the points that must be given due consideration:

• The casting process, along with pros and limitations
• Machining stock allowance (quantity of material that is still available for finishing after rough cutting) to ensure clean-up on all machined surfaces
• Production design with respect to applying the clamping and fixture devices in order to secure the piece properly during machining
• Choosing material specifications and the right  heat treatment method
• How many parts to be produced?

You should check every casting design when first produced to confirm if all machining needs are achievable. We follow an effective method which is to make a complete layout of the sample casting, and find out if there is appreciable machining stock allowance on all casting surfaces requiring machining.

In the case of simpler designs, a fuller layout of the casting isn’t required. But in cases of complex machining dimensions, it is important that you check casting thoroughly. This can also be carried out by creating target points and making outlines indicating all machined surfaces; thereby, confirming that consistency is maintained at all phases of production.