Press tool theory — identify the incorrect statement Which of the following statements is WRONG with respect to sheet-metal press operations and die geometry?
-
AThe angular clearance on dies typically varies from about 0.5° to 1°.
-
BIn a drawing operation, the metal flows plastically into the die cavity.
-
CIn press operations, the final size of a pierced hole is independent of the punch size.
-
Dnone of the above
-
EDie clearance affects cutting load and edge quality.
Answer
Correct Answer: In press operations, the final size of a pierced hole is independent of the punch size.
Explanation
Introduction / Context:Accurate pressworking requires correct die clearance, proper punch and die sizing, and understanding of material flow during operations such as blanking and deep drawing. This question probes common misconceptions that lead to dimensional errors or poor edge quality.
Given Data / Assumptions:
- Conventional cold press operations on sheet steel or non-ferrous alloys.
- Standard practice: punch size controls pierced hole size; die opening controls blank size.
- Typical die angular clearance is small to facilitate stripping and reduce friction.
Concept / Approach:In piercing, the punch shears through the sheet and the hole left in the work matches the punch dimension (with allowance for elastic recovery and edge break). Therefore, the hole size depends directly on the punch size. Drawing is a plastic flow process where the blank is pulled into the die by the punch while material thins or thickens slightly, so statement (b) is correct. Small angular clearance on die walls (0.5° to 1°) aids part ejection and reduces scuffing, so (a) is also correct.
Step-by-Step Solution:Recall sizing rule: pierced hole size ≈ punch size; blank size ≈ die opening.Evaluate statement (c): says “independent of punch size” which contradicts the rule.Conclude: (c) is the wrong statement.
Verification / Alternative check:Tolerance tables in die design handbooks specify punch undersize/oversize based on desired hole/blank size and material springback, reaffirming dependence on punch dimensions.
Why Other Options Are Wrong:
- (a) True: small angular relief is standard.
- (b) True: drawing relies on plastic flow controlled by blank-holder pressure and friction.
- (d) “none of the above” is false because (c) is wrong.
- (e) True statement about clearance influence.
Common Pitfalls:Mixing the rules for blanking and piercing; remember: punch controls hole, die controls blank.
Final Answer:In press operations, the final size of a pierced hole is independent of the punch size.