Investment casting patterns from the 3D printer

Polymaker specifies 1,100–1,200 °C over 40–60 minutes for shell burnout – at that temperature the ceramic shell sinters while the pattern burns out. The ash residue below 0.003% is stated by the manufacturer without a measurement temperature or test standard. Important: this is a manufacturer statement, not a test certificate for your kiln. Ramp rate, hold time and result depend on your investment material, pattern wall thickness and kiln type – Polymaker explicitly notes that every foundry has to determine its own schedule. We therefore recommend dialling in the first run with a sample part. After cooling, the shell should be rinsed with water to flush out any remaining ash.

The printed pattern sits within normal FFF tolerances; we produce exactly to the dimensions in your CAD file. What matters, though, is the full shrinkage chain: print shrinkage, investment shrinkage and alloy shrinkage on solidification all add up – and only your foundry knows the last two, because they depend on the investment material and the metal. We therefore do not apply a shrinkage allowance on our own initiative. Either send us an already compensated model, or tell us the scaling factor you want – we apply it and document it in the order.

That is not a question of the pattern but of your foundry: the PolyCast pattern burns out with minimal residue and is no longer present in the finished casting. In principle, therefore, all alloys common in investment casting are possible – bronze, brass, silver, gold, stainless steel, aluminium. The limits are set by your foundry's investment material and kiln technology, not by the pattern material.

A pattern has to survive two loads the later casting never sees: handling and investing. Very delicate webs can float up or break during investing. As a guide value we work with roughly 0.8–1.0 mm minimum wall thickness on a 0.4 mm nozzle; finer structures are feasible, but we assess them upfront on your specific geometry. Since PolyCast reaches only about half its tensile strength in the Z direction (~26 instead of ~53 MPa), we deliberately avoid orienting thin webs vertically.

The gating system is a foundry decision – position, cross-section and feeder layout depend on alloy, casting process and tree layout. We print the sprue if it is part of your CAD file. Alternatively we bond gating channels afterwards: PolyCast can be softened with isopropyl alcohol and joined cohesively, without introducing any foreign material into the cavity.

Two points are critical. First moisture: PolyCast absorbs up to 2.09% water – we therefore print from dry-stored material and ship the patterns packaged. Second heat: at around 53 °C heat deflection temperature a pattern will already distort in a hot vehicle or a sunlit storeroom, and any distortion transfers one-to-one into the casting. Patterns should be kept cool and invested promptly.