Die casting finish and allowances: In pressure die casting of non-ferrous alloys (e.g., aluminium, zinc), what level of machining allowance is typically provided on the casting?

Introduction / Context:
Die casting is a near-net-shape process that uses precision steel dies and high-pressure injection to produce components with excellent dimensional accuracy and surface finish. Correctly choosing machining allowance affects cost, cycle time, and tool life. This question probes understanding of process capability compared with sand or investment casting.

Given Data / Assumptions:

• High-pressure die casting (hot- or cold-chamber).
• Dimensional repeatability is high; surfaces are smooth.
• Only minor post-processing may be required (e.g., flash trimming, drilling).

Concept / Approach:
Because steel dies provide stable cavity dimensions and controlled cooling, die castings achieve tight tolerances and smooth surfaces. Therefore, only a small machining allowance is needed, typically for critical fits, sealing faces, or to remove minor die wear effects. Large allowances would negate the economic advantages and increase machining cost unnecessarily, while “no allowance” is risky for precision fits or after surface treatments that slightly alter dimensions.

Step-by-Step Solution:
Compare process capabilities: die casting vs. sand casting.Recognise that die casting yields near-net shape with good finish.Provide only minimal stock on critical features for finishing.Thus, machining allowance is small.

Verification / Alternative check:
Tolerancing guides show typical die casting dimensional tolerances tighter than sand-cast parts, confirming minimal finishing stock is adequate.

Why Other Options Are Wrong:
Large or very large allowances waste material and time.

“Not provided” can lead to undersize after finishing steps; some stock is prudent.

Sand casting needs larger allowances; equating the two ignores different accuracy levels.

Common Pitfalls:
Ignoring die thermal expansion and shrink factors; not accounting for surface treatments (anodising, plating) that can change dimensions slightly; assuming all faces need machining when as-cast surfaces often suffice.

Final Answer:
small