Open Die Forging
Open die forging can also be known as smith forging and involves the use of dies that are simple in shape and do not encompass the material. It differs from closed-die forging, which involves fully enclosing the workpiece within two dies joined together. Rather, the metal workpiece is hammered or pressed into the desired shape.
Quick links to Open Die Forging Information
Applications of Open Die Forging
Open die forging can be used to make larger products (up to 80 feet long and 150 tons) and allows for larger products to be made than any other type of forging. Open die forging is used for high-strength metal pieces and smaller scale production runs. Industries in which the open die forging process is widely used include home appliances, electronics, cement, military, marine, material handling, automotive, aerospace, and medical.
Materials Used in Open Die Forging
Metals that are popular for the open die forging process includes titanium, aluminum, nickel, copper, stainless steel, and carbon steel.
Process of Open Die Forging
In the process of open die forging, a metal workpiece, also called a billet, is heated above the recrystallization temperature, roughly several thousand degrees Fahrenheit. The billet is rested on a fixed anvil and is pounded with a press or a hammer. The force applied by the hammer causes the billet to conform to the anvil and hammer’s shape (or die). This die can be a variety of shapes, including flat, convex, or concave. It may also include a tool to form holes in the workpiece.
The billet typically takes multiple strikes until it takes the shape of the die, requiring the operator to constantly readjust and reposition the workpiece so that the shape is correct. A final product can be made with multiple forged parts. There are some cases where open die forgings can also be used as a pre-forming measure for other machining operations. In order for a product’s performance to be ideal, certain aspects of the open die forging process can be readjusted to achieve a desired grain structure.
Open die forging can be performed hot or cold, and there are three open die forging processes that are commonly used. Each of these procedures fabricates the metal billet into a different configuration, and thus, each process is appropriate for various applications. The first, cogging, or drawing out, involves using a flat or slightly contoured die to compress a billet, causing it to increase in length and decrease its thickness. After a section of the material is compressed, the die is advanced along the length of the billet and compression is performed all over again. This length of advancement is known as a “bite” and is typically 40 to 75 percent of the die’s width. In order to decrease the billet’s width even further, the length of the bite is reduced. One product that is forged using this process is metal fences.
The second technique that is used is fullering. This procedure is often used during manufacturing processes that require several forging operations. Therefore, fullering is implemented to evenly distribute the billet. The fullering process involves an open die with convex surfaces that compresses onto both sides of the billet, deforming it. As a result, the metal flows outward around the sides of the die. There are several benefits of the fullering process, which include giving the product a clean surface finish, lessening the risk of damaging the billet.
The third technique, edging, is also used as a preemptive step to prepare a billet for additional metal forgings procedures. In contrast to the convex dies used in fullering, dies used in edging have a concave shape. The edging dies deform the metal billet by causing the metal to flow inward and conform to the hollow created by both sides of the die, as opposed to fullering, where the metal being forced outward around the die’s edges. This process gets its name due to the procedure being performed on the edges of the billet.
Open Die Forging Customization
Tooling allows for easy customization and the forging of a variety of shapes, such as those which are round, hexagonal, square, and rectangular.
The basic shapes that can be made with open die forging include:
- Pierced Blanks
- Pancake Forgings
- Metal Shells
- Step Shafts
Benefits of Using Open Die Forging
Open die forging is more appropriate for creating uniquely shaped products and lower volume production runs due to the required tooling being simpler and lower in cost. Compared to the cast metal method, the pressure applied in open die forging fortifies products and grants them a longer service life. It also improves a product’s grain structure, decreased porosity, and higher density.