Common forging defects | What to look out for
What are forging defects?
Forging defects are imperfections in manufacturing processes. While no forging process is perfect, an imperfection becomes a defect when its effect on the mechanical properties of a metal piece means it no longer fits the client’s specifications. Forging defects have a few typical causes, including improper cooling and poor die design. Here are nine typical defects.
One of the most common defects is an unfilled section: when a produced object has some portions missing. Unfilled sections occur for several reasons. For example, poor heating, faulty forging techniques, or bad-quality dies can create an unfilled section. You can avoid this defect by ensuring enough raw materials are available, using proper dies, and correctly applying heat to the raw material.
Cold shuts occur when poor die designs are used in low-temperature forging processes. Small cracks at the edges of forged pieces are evidence of a cold shut. Cold shut is particularly common when forging metal pieces with sharp corners. This defect is relatively easy to address: by increasing the die’s fillet radius, you can avoid cold shuts.
Scale pits are relatively common defects typical in open-air forging techniques. They occur because of improper cleaning and create irregular deputations on forging surfaces. If you properly clean surfaces throughout open environment forging processes, scale pits are relatively easy to avoid.
Die shift / Mismatch
Die shift occurs when the upper and lower die is misaligned. When you use misaligned dies, the final product will not have the intended dimensions, potentially leaving it useless. Thankfully, you can resolve this defect by re-aligning the dies and placing the piece between them, furnishing the correct dimensions, and allowing work to continue.
Also, for greater precision and consistency, you can introduce self-sets into the die design process. This removes any existing inaccuracies in the forging machine and provides consistently matched top and bottom cavities.
Flakes are one of the most common forging defects. Flakes are internal cracks that appear after improper cooling. In particular, internal cracks form when metal is mistakenly cooled too quickly. This mistake weakens the metal piece and is avoided by slowing the cooling rate.
Improper grain growth
Improper grain growth is a product of unexpected metal flow during casting operations. When improper grain growth occurs, forging creates an undesired grain structure, meaning the piece has sub-optimal mechanical properties. For example, the metal might be too brittle or weaker at higher temperatures. Using proper die designs addresses this fault.
Grain refinement can be aided by an increased level of reductions (hot working), and it may also be possible to refine the grain size by subsequent heat treatment, such as normalising. Of course, such grain refinement may only be possible in certain alloys that contain grain-refining elements such as Titanium, Aluminium, and Vanadium.
Incomplete forging penetration
Incomplete forging penetration is a simple forging defect. It occurs when hammer blows hit the metal piece excessively lightly or rapidly. As the name suggests, this issue leaves the piece incompletely forged, often meaning you can’t use it for its intended purpose. You can avoid this defect by ensuring proper press control throughout your operations.
Surface cracking is the result of working on cold surfaces. Surface cracking is easy to spot: cracks appear across the forged surface. Surface cracking can be very detrimental to the durability of metal pieces, which leaves forged products with surface cracking unsuitable for many manufacturing processes. Maintaining temperature control while working is the best way to stop this issue from slowing you down. This includes proper heating of the workpiece, as well as pre-heating of the forging, dies.
Residual stress in forging
Like other forging defects, improper cooling during the forging process is the cause of residual stress. Residual stress can deform the metal, potentially causing major issues with your equipment. Pieces should be subjected to slower cooling to ensure they evade this defect. Residual stress can be very problematic, reducing the piece’s strength and potentially causing it to break when placed under high pressure. Uniform cooling of the forged items will help and subsequent normalising of the forgings.
How we can help?
At Greg Sewell Forgings, we know how frustrating it can be to have the success of your work threatened by forging defects. As one of Australia’s largest forging operations, we have a wealth of experience identifying, addressing, and replacing faulty metal parts. Are you worried about potential defects with your metalwork? Get in touch today! We offer a comprehensive forging testing service that can help inspect your equipment and address any potential issues. For more information check out our blog on Best Forging Inspection Methods.
We also provide forged custom metal fabrication services, covering various materials from high-grade stainless steel to low-grade carbon. If you’ve found an issue, we can replace defective equipment and get you back up and running as quickly as possible. Whatever your forging needs, Greg Sewell Forgings is the partner you can trust.