In this section
Design guidelines
Practical design-for-manufacture rules for investment castings: wall thickness, transitions, fillets, holes, cores, undercuts, ribs, bosses, draft, machining allowance and part consolidation.
02Tolerances
Tolerancing of investment castings: ISO 8062-3 casting tolerance grades, VDG P 690, geometrical tolerances to ISO 1101, datum systems, machining allowance, shrinkage and distortion.
03Surface finish
Surface texture of investment castings: Ra and Rz, typical as-cast, blasted, ground and machined conditions, how to specify surface requirements and visual acceptance standards.
04Process comparison
Qualitative comparison of investment casting with sand, shell mould, die, centrifugal and lost foam casting, forging, CNC machining, MIM, sheet metal, welding and additive manufacturing.
How to use this guidance
The pages in this section separate three kinds of statement: requirements published in standards, general industry practice, and typical indicative values. Indicative values help in early design; they are not guaranteed manufacturing limits. The earlier a design is discussed with the foundry, the more of the advantages of the process can be used, because gate positions, datum targets and wall transitions can still be influenced.
A practical sequence for a new part
- Define function, loads, environment and the material family.
- Decide which surfaces are functional and will be machined, and which can remain as cast.
- Shape the remaining geometry for casting: uniform walls, generous radii, feeding paths.
- Choose the tolerance standard and grade for as-cast dimensions and tolerance the functional features individually.
- Define datum targets on as-cast surfaces for measurement and first machining operation.
- State material standard, heat treatment, surface, inspection and documentation requirements.
- Review the result with the foundry before tooling is ordered.