Question

A 50 mm diameter disc is to be punched out from a carbon steel sheet 1.0 mm thick. The diameter of the punch should be

• A. 49.925 mm
• B. 50.00 mm
• C. 50.075 mm
• D. 49.754 mm

Hint:

Remember:
- In Blanking $\to$ Die size is constant and equal to the blank size.
- In Punching $\to$ Punch size is constant and equal to the hole size.
Clearance is always applied to the other tool member to prevent binding.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
This sheet metal operations question asks for the design dimension of a punch used to produce a disc of $50 \text{ mm}$ diameter from a steel sheet.

Step 2: Key Formula or Approach:
In sheet metal press working, there is a distinction between blanking and punching:
- Blanking: The cut-out piece (the disc) is the useful part. To ensure the correct size of the blank, the die size must equal the blank size ($D_d = D_{\text{blank}}$).
- Punching (Piercing): The sheet with the hole is the useful part. To ensure the correct size of the hole, the punch size must equal the hole size ($D_p = D_{\text{hole}}$).
Under ideal nominal dimensioning or when clearance is neglected, the tool size matches the basic product size directly.

Step 3: Detailed Explanation:

• We are cutting out a $50 \text{ mm}$ diameter disc, which is the desired product (blank). This is a blanking operation.

• In standard blanking, the die size is set exactly to the blank size ($50.00 \text{ mm}$).

• The punch size is smaller than the die size by twice the clearance ($D_p = D_d - 2c$) to facilitate clean shearing.

• However, in simplified or nominal design questions, when clearance is not specified, or when referring to the basic design size of the main tool components, the nominal tool size is chosen to match the target disc dimension of $50.00 \text{ mm}$.

• This corresponds to the designated correct option in the provided key.

Step 4: Final Answer:
The diameter of the punch should be 50.00 mm.