Casting accuracy — the typical dimensional tolerance achievable with the shell moulding casting process is:
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A+0.05 mm
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B±0.2 mm
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C+0.5 mm
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D±1 mm
Answer
Correct Answer: ±0.2 mm
Explanation
Introduction / Context:Different casting processes offer different levels of dimensional accuracy and surface finish. Shell moulding uses a thin resin-bonded sand shell formed on heated patterns, giving better precision than green sand and approaching permanent-mould processes for many parts.
Given Data / Assumptions:
- Small to medium-sized castings typical for shell moulding.
- Standard process capabilities without special secondary operations.
- Tolerances expressed as symmetric or unilateral values in millimetres.
Concept / Approach:
Published capability data for shell moulding generally indicate tolerances around ±0.3 mm down to ±0.1–0.2 mm depending on size, making ±0.2 mm a representative average for exam purposes. Options like +0.05 mm are unrealistically tight for typical shell castings, while ±1 mm is more characteristic of conventional sand casting.
Step-by-Step Solution:
1) Compare process capability ranges across casting methods.2) Select the value that aligns with standard shell moulding practice.3) Conclude that ±0.2 mm is the best representative tolerance from the given options.Verification / Alternative check:
Vendor datasheets and handbooks list shell moulding accuracy between green sand and investment casting, supporting ±0.2 mm as a reasonable benchmark.
Why Other Options Are Wrong:
+0.05 mm is too tight for typical shell; +0.5 mm and ±1 mm are looser than the known capability of shell moulding.
Common Pitfalls:
Confusing investment casting tolerances with shell moulding; overlooking that unilateral tolerances in options may be distractors.
Final Answer:
±0.2 mm