In some industries, castings have historically been "known" as the way to design and produce a part. At the time, purchasing a casting made sense due to the geometry or configuration of the part. However, today there are many reasons to look at converting castings to forgings. To start, you first need to understand the difference between these two metalworking processes. In the simplest terms,
• Casting is the process of heating metal until molten. While it's in the molten (liquid) state, it is poured into a mold or vessel to create the desired shape.
• Forging requires heating the metal to its point of plasticity, then hammering, pressing, or rolling to shape the part. When forging a part, better uniformity of composition and structure is achieved. During the forging process, recrystallization and grain-refinement occur, resulting in increased strength.
The most common complaint about castings is porosity – voids in the finished component during solidification. Based on the location of porosity, the component may need to be welded or scrapped. Most castings failures are due to porosity, lower tensile or fatigue strength, and defects. You may not know whether or not a casting can maintain its integrity until it fails because castings do not have consistent grain structures. Properties in cast metals are inconsistent due to how the metal settles in the mold and the rate at which each casting cools.
Forging, on the other hand, is more dependable by nature because the forging process strengthens metal while forming it by directing grain flow. The forging process eliminates porosity through the compression of the material, achieving a 3:1 minimum reduction. Forging also lessens the need for expensive alloys to achieve desired metallurgical properties.
Today, there are more options to achieve a unique-shaped part. Forging technology has made significant strides in the past decade and now can offer complex shapes, which traditionally were thought to be casting-only pieces. This type of near-net-shape forging allows you to explore options beyond castings. The casting to forging conversion process can be very straightforward if you have design authority and are open to design change.
Considering all the costs in a product's development through the lifecycle, the long-term benefits of forgings outweigh the short-term cost-savings that castings might seem to offer. So, where is the best place to begin when looking to convert a casting to a forging.
First, you must understand that not all parts can or should be made as forgings; castings work well for a variety of applications. It's best, to begin with evaluating the piece in question.