Investment casting gives a wider freedom of design than most other metal forming techniques. The following guidelines will enable the optimum advantages to be gained from this process - but please call our experts in at the earliest possible design stage, so that we can work together and advise on how the design options may affect techniques and economics. For development purposes we can produce wax models for design discussions or cast metal prototypes using our own Rapid Prototyping machine.
TOLERANCES
Tolerances should only be specified on critical and functional dimensions. Unnecessary or over-close tolerances may make the castings less economic. Consistent process repeatability will be achieved, even on non-toleranced dimensions.
Refer to the following tables for linear and geometric tolerances, click here
MATERIALS
Parts can be cast in our very wide range of materials, including:
• Carbon & Low Alloy Steels
• Stainless & Heat Resisting Steels
• Nickel & Cobalt Alloys
• Magnetic Alloys & Tool Steels
• Aluminium & Zinc Alloys
• Copper based Alloys
WALL SECTIONS
Unlike die-castings and plastic mouldings, it is not necessary to have a uniformly thin section all over. In fact, it is often helpful to have some thicker sections to enable metal to be fed into the casting at those points. Good design will enable sound castings to be produced and may result in significant cost savings. Our design advice is at no obligation – we welcome the chance to assist you at the earliest stage.
The section thickness that can be cast depends on the alloy, the surface area and the complexity of the casting. For aluminium and zinc, the typical wall thickness is 2 to 3 mm, but 1.5 mm or less can be achieved on some features. Thicker walls are needed for steel or copper based alloys, usually 3 mm or more, but a thickness of 2 mm or less can be achieved over small areas.
DATUM PLANES
These are best chosen to satisfy the functional requirements of the component. Datum planes across the centre of the casting, rather than at one end, are usually preferable.
Datum points, showing where the casting will be picked up for machining will enable the same points to be used for dimensional checking. Please ask for our advice, in conjunction with the machinist.
HOLES
Holes should be kept as short as possible in relation to diameter. Square holes, 'D' and other odd-shaped holes are as easy to cast as round holes. Blind holes are more difficult than through holes - we will advise you on what can be cast at the enquiry stage.
INTERNAL CORNERS
These can be stress raisers - use the largest fillet radii possible. External corners will not have burrs or sharp edges like machined corners.
UNDERCUT FEATURES
Investment Castings are ideal for producing undercut detail. Where complex internal shapes are required, removable inserts in the tool are used. If this is not possible, then soluble wax cores or ceramic preformed cores can be used, but these will inevitably add to the casting and tooling costs.
FINISHED MACHINED AREAS
These can be kept to a minimum thanks to the casting accuracy and flexibility of design. The amount of machining allowance will depend on customers' requirements, but we are ready to advise on this at the design stage. We can also supply fully machined castings, including surface treatments and threaded inserts.
RAPID PROTOTYPING
We can produce Rapid Prototypes in a full range of cast metals using our in-house facilities. (Click for a comprehensive guide.)
P.I. Castings Ltd Davenport Lane, Altrincham, Cheshire, England WA14 5DS
Tel: +44 (0) 161 928 5811 Fax: +44 (0) 161 927 7023 Email: admin@pi-castings.co.uk |
