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Print Requirements


Print Requirements

Casting drawings will include information about the casting geometry (size, shape, draft, radii, etc..) The casting drawing will also contain the acceptable tolerance level, defect level, and surface finish. As well as any inspection requirements, radiography, magnetic particle inspection, destructive testing. Material will be defined on the print with possibly the mechanical properties of the material. Geometric dimensioning and tolerancing may also come into play on a casting design.

All of this, when included on a print, helps convey the expectation of the part to the foundry. Make sure to display what is critical to your part on the print. If you need to have good elongation in your material, this may require a specific heat treat to the part. You may need to maintain a consistent surface finish in an area and this may define, for the foundry, areas that gating and risering can and cannot be.

A casting can also have the part number, heat lot and foundry code cast into the part. Specification of the location and size of this lettering is required. If raised lettering causes interference, the lettering can be cast in a recessed pad.

A machined casting will have dimensions for the machined features as well as dimensions relating the machined features to the cast features. The machining print may include a note on corner breaks required, surface finish callouts for the machined surfaces, geometric tolerances, etc.

Foundries typically prefer two drawings, one for the casting and one for the finished machined part. The casting print will include the amount of finished stock required. 3mm or 0.125″ of machine stock is typical.

When geometric tolerancing is used on a casting print or machined casting print, it is always good practice to establish datum points at specific locations on a cast surface for the various datum planes. With the surface inconsistencies, this practice allows consistent inspection and layout at the foundry, machinist, outside inspection lab and customer. All tooling can be built to reference these datum points and it will go a long way to help with any dimensional issues that may come up with a machined casting.

datum-points

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