Vacuum Casting for Prototypes and Small Series
When you need more than one part but not a production tool, vacuum casting copies a master pattern into a short run of polyurethane parts that look, feel and assemble like the intended engineering plastic.
How the process works
A master pattern is produced first, usually CNC machined from your CAD data or supplied as a printed part. A silicone mould is taken from it, and polyurethane resin is cast under vacuum so air is pulled out of the cavity before the part forms. After de-moulding the parts are cured, trimmed and finished. A silicone mould yields a limited series before it wears; further moulds are taken from the same master, so the run stays consistent.
When it is the right choice, and when it is not
Vacuum casting earns its place when you need a short run of a complex shape before tooling exists: design verification parts, fit and assembly checks, show models, and pre-series parts for early customers. It is the wrong choice for production volumes, where injection moulding wins on unit cost, and for parts that carry real load, run hot, or need tight fits, where a machined part in the production material is the honest answer. We will say so in the DFM review rather than quote something that will disappoint.
Resins and what they imitate
Polyurethane systems are selected to imitate the production plastic: ABS-like and PP- or PE-like grades for housings and general parts, PMMA-like grades where you need transparency, and flexible grades in the Shore A range for seals, gaskets and overmoulded grips. Colour, surface texture and inserts can be included. Cast resin is not the production polymer, and we treat it as a stand-in rather than a substitute.
Accuracy and what we flag up front
Cast parts are dimensionally looser than machined metal, and resin shrinks as it cures, so tolerances are agreed per drawing and confirmed during DFM review instead of being assumed from a table. Where a bore, sealing face or thread has to be exact, we machine that feature after casting rather than promising it out of the mould.
Finishing and how it fits with machining
Sanding, priming, painting and pad printing are not done in house; they are placed with qualified subcontractors selected for environmental compliance and located close to our plant, with quality and delivery responsibility staying with us. Because the master pattern is machined here, vacuum casting sits naturally next to CNC work: cast housings with machined sealing faces, or a cast prototype now and machined parts later from the same data.