Forging Defects

FORGING DEFECTS

The different types of defects that may occur during the forging operations are as follows:

1. Cold shuts: These are the short cracks at corner of the forging. It is caused by the improper die design. Cold shut occurs where the corner and the fillet radii are small as a result of which metal does not flow properly into the corner.

2. Forging laps and folds: A lap appears as a seam in the surface of a forging that can extend into the interior of the forging. It is caused by the improper die design.

3. Incomplete filling of dies: This defect occurs when some sections of the die are not completely filled by the flowing metal. This defect is caused due to wrong amount of bar stock or improper forging die design.

4. Flakes: These are basically internal ruptures caused by the rapid cooling of large forgings from forging temperature. Rapid cooling causes the exterior to cool quickly causing internal cracks.

5. Scale Pitting: It is primarily due to improper cleaning of the stock used for forging. The oxide scales occurring at high temperature stick on the dies and gets embedded into the finish forging surface.

6. Surface cracking: It is due to the temperature difference between surface and center or excessive working of the surface at too low temperature.

7. Flash line crack after trimming: It occurs more often in thin workpieces. Therefore, should increase the thickness of the flash.

8. Web buckling: It occurs in upsetting forging due to high compressive stress and insufficient material.

9. Internal cracks: It is due to the secondary tensile stress produced during drastic change in shape of the raw stock.

10. Die shift: It is caused by misalignment of dies.

11. Burnt and overheated metal: It is caused by improper heating conditions.

12. Fins and rags: These defects occur when loose metal is driven into the surface.

13. Ruptured fibre structure: It is due to inadequate stock size.

14. Hair cracks or micro cracks: It is due to metal ingot or too rapid cooling of forging.