A part designed with casting in mind costs less, fills better and needs less rework. These guidelines cover the points that matter most when you design or convert a part for investment casting. Exact limits depend on alloy, part size and geometry, so review your drawing with the foundry early.
Keep Wall Thickness Even
Uniform walls solidify more evenly and distort less. Sudden changes from thin to thick sections create hot spots, where shrinkage porosity can form. Blend section changes gradually and remove mass that the part does not need.
Respect Minimum Wall Thickness
Very small castings can run close to 1 mm in some alloys, while medium and larger parts usually need about 1.5 to 2.5 mm. Longer, thinner walls are harder to fill. Aluminum, bronze, magnesium and steel also behave differently, so confirm the limit for your alloy.
Add Fillets and Radii
Sharp inside corners concentrate stress and can cause hot tears and shell damage. Generous fillets help metal flow and strengthen the part. Sharp outside corners are also hard to reproduce, so a small radius is usually better.
Plan for Feeding and Gating
Metal must feed the part as it solidifies, moving from thin sections toward the gate. If the heaviest section sits far from any possible gate, feeding becomes difficult. Show the foundry where gate marks are acceptable, and mark the surfaces that must stay clean.
Think About Holes and Internal Shapes
Investment casting can produce through holes, blind holes and internal passages, but long, narrow holes are limited because the ceramic must coat and dry inside them. Soluble wax or ceramic cores can create more complex shapes. Where a hole has a tight tolerance, cast it undersize and finish it after casting.
Set Tolerances Only Where They Matter
Apply general casting tolerances to most of the part, and use tighter values only on functional features. Tight values everywhere raise inspection and rejection costs. Our tolerance page and our guide to VDG P690 classes explain the options.
Define Datums and Machining Allowance
Clear datum points let the foundry and the machine shop measure a part the same way. Add machining allowance only to surfaces that truly need machining. A cast surface that meets the drawing saves cost.
Review the Design Before Tooling
Changing a wax injection die is costly, so the best moment for review is before tooling starts. Send your drawing or 3D model to BRK Metal, and our team will review castability, material and tolerances for your part.