Forging Defects
Forging is a metallurgical process used extensively in the manufacture of parts for vehicles, industrial machines and consumer goods. During the process, a metal is heated and then compressed using complex dies in order to form a desired shape. While forging is often a reliable and cost effective method of producing parts, it is subject to a variety of defects that can reduce product quality and result in costly delays.
Oxide Film. The use of high temperatures to heat the metal during forging will cause a thin layer of oxide to form on the surface of the part. Over time, this oxide film can cause surface corrosion and weaken bonds, reducing the parts durability.
Porosity. This defect is caused when air or gas pockets become trapped inside the forged part. These pockets can weaken the strength of the part, or lead to cracks that can allow contaminants to enter and cause further damage.
Lamination. During the forging process, the metal is subject to extreme temperature gradients and rapid cooling, which can cause small areas of the metal to remain in their softer condition for a longer period. These areas may quench at a different rate than the surrounding metal, resulting in lamination.
Scaling. This common defect is caused when the surface of the metal oxidizes, separating and forming a layer of scale. This layer of scale can reduce the parts strength and result in rusting.
Unfilled Cavities. When forging a complex shape, the intense pressure and heat of the dies can cause the metal to fill the larger cavities in the part, while smaller areas remain empty. This can lead to parts with weakened structural integrity.
Inclusions. Inclusions are small pieces of foreign material, such as slag, dirt or rust, that become trapped in the metal during the forging process. These inclusions can interfere with the parts performance, and can even lead to failure or breakdown under stressful conditions.
Cold Shuts. These defects occur when two different molten streams of metal meet, forming a weak bond and creating a localized area of weakness in the part.
Improper Grain Flow. Forging is a process of compressing the metal, and will produce a long grain that follows the form of the part. If the pressure is not applied evenly, the grain will form in an irregular pattern, which can reduce the strength of the part.
Bridging. Bridging is a defect that occurs when the metal stretches too far between two adjacent dies, forming an uneven joint. This can lead to cracks and weak spots in the part, reducing its performance.
In order to reduce the risk of these forging defects, manufacturers must have a thorough understanding of the requirements of each application and design dies to accommodate these needs. Furthermore, they should pay special attention to maintaining accurate temperatures and pressures throughout the process, and constantly monitor the parts to identify and eliminate defects early on in the production process. Working with the right forging partner, these defects can be avoided and the parts can be produced with high quality and reliability, ensuring that the customer receives the best possible product.
