What are the finishing options for vacuum cast parts?

What are the finishing options for vacuum cast parts?



Vacuum casting is the perfect complement to 3D printing (additive manufacturing) and CNC machining for producing prototypes, particularly when you need low volumes rather than one-offs. Depending on the intended use for the parts and, therefore, the functional and aesthetic requirements, we can apply a wide range of finishes.Get more news about Vacuum Casting Part,you can vist our website!

Vacuum casting is used for concept models, functional prototypes, jigs and fixtures, and end-use parts, so the finish(es) must be selected carefully to suit the application.

Material considerations
Parts are vacuum cast in polyurethane resin. However, resins are available in a choice of grades, meaning parts can have very different material properties – from hard grades simulating glass-filled nylon or ABS, through to soft elastomeric grades. Furthermore, resins can be water-clear or pigmented to match almost any colour or tint, and surfaces can be high-gloss, satin, matt or textured. Consequently, many parts need no secondary finishing operations thanks to the combination of pigmented resin and as-moulded surface finish.

Post-processing
All vacuum cast parts need to at least have gates and risers removed (required for the flow of resin through the tool), and mould tool part lines often need cleaning up. This is done by hand and the degree of work required varies.

Sometimes skilful use of a scalpel is sufficient, while other parts may need to be lightly sanded to remove witness marks, then polished back. It all depends on the grade of polyurethane, whether the surface is an ‘A’ surface or ‘B’ surface, if any subsequent finishing operations are required, and the part’s intended use.

By this point the part will have already been heat-cured but it may be necessary to place it on a curing fixture for up to seven days to prevent distortion and maintain tighter tolerances.

Aesthetic finishing options
If a better aesthetic is required than can be provided by pigmented resin, then the part can be primed and painted. Paints do not adhere well to low-modulus elastomers, so painting is really only suitable for harder grades of polyurethane resin. For parts that have been overmoulded with a softer grade to create tactile grips or functional seals, these areas can be masked prior to painting.

We can wet-spray virtually any colour onto vacuum cast parts and the finish can be specified as high-gloss, satin or matt. Clear lacquer is a further option for improving the appearance of as-cast parts, or a soft-feel rubberised coating can be applied over some or all of the part.

Another option, also applicable only to harder grades of resin, is vacuum metallisation. This is a popular option when prototyping, for example, consumer goods or automotive lights, but it can also enable vacuum cast parts to mimic metallic components in non-functional models.