B. Improper design of die

- Cold shut is a forging defect that occurs when two portions of metal fail to fuse together properly during the forging process.
- The defect is characterized by a visible line or seam on the surface of the forged part, indicating a lack of proper bonding between the two sections.
- The primary reason for cold shut is the improper design of the die used in the forging process.

Reasons for Cold Shut:
1. Insufficient material flow:
- The die design plays a crucial role in ensuring proper material flow during forging.
- If the die is not designed properly, it may result in restricted material flow, leading to incomplete fusion between the metal sections.
- Insufficient material flow can occur due to improper die cavity design, inadequate draft angles, or incorrect die dimensions.

2. Improper die temperature:
- Another factor contributing to cold shut is the improper cooling of the die during the forging process.
- If the die temperature is too low, it can cause premature solidification of the metal, preventing proper fusion.
- On the other hand, if the die temperature is too high, it can result in excessive material flow and distortion, also leading to cold shut.

3. Inadequate die lubrication:
- Proper lubrication is essential to facilitate smooth material flow and prevent sticking or dragging of the metal on the die surface.
- Insufficient or improper die lubrication can result in uneven material flow, promoting the formation of cold shut defects.

4. Misalignment of the two die halves:
- Cold shut can also occur if there is a misalignment between the two die halves during the forging process.
- Misalignment can create gaps or misfits between the metal sections, preventing proper bonding.

Conclusion:
- While all the mentioned reasons can contribute to cold shut defects, the primary reason is the improper design of the die used in the forging process.
- It is crucial to ensure that the die is designed correctly, taking into account factors such as material flow, die temperature, lubrication, and alignment, to prevent the occurrence of cold shut defects.