Question

Lapses in forging occur due to

• A. improper metal flow
• B. high temperature
• C. high strain rate
• D. low pressure

Hint:

Key Forging Defects & Causes:
- Laps \(\rightarrow\) Improper metal flow and folding.
- Die Unfill \(\rightarrow\) Insufficient billet volume, low forging pressure, or too low temperature.
- Cold shuts \(\rightarrow\) Similar to laps, folding over of cold flash.
- Internal cracking \(\rightarrow\) Secondary tensile stresses during open-die forging.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question asks for the primary process cause of "laps" (sometimes printed as lapses) in forged components.
A lap is a serious surface defect that acts as a pre-existing crack or stress riser.

Step 2: Key Formula or Approach:
Forging defects are typically caused by poor die design, improper billet sizing, or incorrect lubricating conditions.
A lap is formed mechanically when a portion of metal folds over another portion without fusing or welding together.

Step 3: Detailed Explanation:

• Mechanism of Lap Formation:
- During closed-die forging, molten/solid metal is forced to flow into complex die cavities.
- If the die corner radii are too small, or if the preform shape is poorly designed, the metal flow is obstructed.
- Instead of filling the cavity smoothly, a web or a flash-like extrusion folds over onto the surface of the main body of the forging.
- Because the metal surface is oxidized and cooler than the interior, the folded layer is pressed into the main body but fails to weld back into it.
- This leaves a crack-like fold containing oxide scale, called a lap.

• Role of Proper Design: To avoid laps, die designers must ensure generous corner and fillet radii and create preforms (like edgers and fullers) that guide the metal flow smoothly without creating folds.


Step 4: Final Answer:
Forging laps are caused by incorrect or improper metal flow within the die cavity.
Therefore, the correct choice is option (A).