Die Casting Tolerance Specification Guide

As-cast tolerances apply to surfaces formed directly by the die. They depend on part size, alloy, wall design, tool condition and process control, so they should not be copied from a generic table without review.

Machined tolerances apply to features produced after casting. Because the feature is cut rather than formed, the achievable tolerance is usually tighter, but it depends on the datum and fixturing strategy.

• As-cast values reflect the casting process
• Machined values reflect the cutting process
• Both depend on the datum strategy
• Confirm against the drawing during DFM

As a planning reference for this factory, as-cast features are typically quoted around ±0.05 mm and machined features around ±0.01 mm, with the final value confirmed against the drawing and feature.

Large dimensions, multiple datum references and thin walls all reduce the achievable tolerance. Critical features should be identified on the drawing so they can be reviewed first.

• As-cast: typically around ±0.05 mm
• Machined: typically around ±0.01 mm
• Large dimensions need wider tolerance
• Mark critical features on the drawing

A datum strategy should connect the casting, the machining setup and the inspection method. If the casting datum and the machining datum are unrelated, bore position and flatness become difficult to control.

Where possible, use stable features such as a machined face or a defined boss pattern as the primary datum, and keep the critical features on the same chain.

• Use stable features as datums
• Keep a single datum chain
• Align casting, machining and inspection
• Document the datum plan

The drawing should state which dimensions are inspected, at what frequency and with which method. That information drives the inspection plan and the records supplied with production.

Typical documents can include dimensional reports, material records, first-article documents and project-specific PPAP files, as agreed in the quotation or quality agreement.

• State inspection scope on the drawing
• Agree sampling and methods
• Define the required records
• Keep records traceable to the lot