What Is A Forging Defect?
Forging shapes metal by hammering, striking, or pressing it against an anvil or die. It’s a top manufacturing process that makes strong, durable parts.Even though forging is a great process, it’s not perfect. Defects can happen, often due to preventable mistakes or poor processes.
To avoid these, careful planning is needed, like using the right amount of material and designing the die and process properly. Skilled smiths must handle the operation with care, as each type of defect has its own fix to keep it from happening.
What Are The Main Types Of Forging Defects?
Following are the main types of forging defects:
- Unfilled section
- Incomplete filling of dies
- Incomplete forging penetration
- Scale pits
- Cold shut
- Die shift
- Improper grain growth
- Flakes
- Surface cracking
- Cracking at the flash
- Internal cracks
- Residual stress in forging
Let us discuss about the causes and remedies of each in detail.
#1 Unfilled Section
This forging defect happens when parts of the product aren’t fully filled. It’s usually caused by bad die design, low-quality materials, or poor forging methods.
This defect can also result from poor die layout, insufficient material, or inadequate heating. To prevent it, ensure the die is well-designed, the material is heated properly, and there’s enough raw material.
#2 Incomplete filling of dies
This defect happens when there’s a loss of metal content. It’s often caused by not enough metal, too few hammer blows, a poorly designed die, or low stock temperature.
To avoid this defect, ensure the ingot size is sufficient. Other key steps include proper hammering, well-designed dies, and maintaining the right stock temperature.
#3 Incomplete forging penetration
This defect happens when forging is incomplete, usually due to light or uneven hammer blows. To prevent it, the forging press should be properly controlled and used correctly.
#4 Scale pits
Scale pits are common forging defects caused by not cleaning the forged surface properly. This leads to small cracks or holes in the metal. They often occur when forging in an open environment. This defect causes irregular positioning on the forging surfaces. It can be avoided by properly cleaning the forge surface to remove any debris.
#5 Cold shut
Cold shut defects appear as small cracks at the corners of the workpiece. They can occur due to an improperly designed forging die, sharp corners on the object, or excessive cooling after forging. Cold shut defects can be avoided by increasing the fillet radius of the die to prevent cracks at the corners.
#6 Die shift
Die shift happens when the upper and lower dies aren’t properly aligned. It occurs due to incorrect dimensions of the workpiece. To avoid die shift, ensure the dies are properly aligned. Before pressing, place one-half of the workpiece on the upper die. Then the other half on the lower die. This helps to achieve proper alignment.
#7 Improper grain growth
Improper grain growth is a forging defect caused by poor metal flow during casting, which disrupts the product’s grain structure. This can be fixed by improving the die design.
#8 Flakes
Flakes are internal cracks in forged parts. They are caused by rapid cooling. This weakens the material. Ensure the forged product cools properly. This will prevent the defect.
#9 Surface cracking
Surface cracks are temperature-related defects. They occur when forging is done at low temperatures. Maintain the proper forging temperature, to prevent this.
#10 Cracking at the flash
Cracking at the flash occurs when thin flash develops cracks during trimming, with some cracks penetrating the interior. This is typically caused by an overly thin flash.To prevent cracking at the flash, you can increase the flash thickness, move the flash to a less critical area, trim while hot, and reduce stress on the forging.
#11 Internal cracks
Internal cracks are forging defects caused by secondary tensile stresses during the process. This can be avoided by ensuring proper die design during manufacturing.
#12 Residual stress in forging
Residual stress occurs when forged parts cool unevenly during the process. This stress causes plastic deformation. It leads to distortion of the object.
This defect is mainly caused by excessive rapid cooling of the forged piece. The risk can be reduced by cooling the piece slowly.
Prevention Techniques For Forging Defects
Here are additional ways to prevent forging defects:
- Shallow cracks and cavities can be removed by hammering them out during cold forging using pneumatic chisels.
- Surface cracks and decarburized areas can be removed by grinding on special machines. Ensure the workpiece isn’t underheated, decarburized, overheated, or burnt.
- Design the die properly, considering all factors to minimize defects.
- Keep the parting line of the forging on one plane to avoid mismatches.
- Damaged forgings from the press can be straightened to save material.
- Forging can correct fiber lines and improve mechanical properties, while annealing and normalizing remove internal stresses from heating and cooling.
Conclusion
I hope this article covers everything you need to know. If I missed anything or you have questions, feel free to ask in the comments. If you found it helpful, please share it with your friends!
