The processes of Open Die Forging and Die Stamping involve the working of metal parts in a wide range of temperaments and temperatures. Open Die Forging involves the shaping of hot metal parts over a mandrel, with the metal lying across the mandrel while a die is placed inside a die mold. The metal part is working at its appropriate temperatures, ranging between 500 F to 2400 F, and slowly formed into the desired shape via the instrumented precision of the tool being used.
There are two main types of Open Die Forging: closed die forging and open die casting. In closed die forging, the metal pieces are positioned on a mandrel, while the die is in a pre-heated position, and are struck by a tool. When the piece cools quickly, the metal changes shape, and is once again molded to the new mold. With closed die forging, the tool and the die remain in constant contact during the casting process, which allows the mold to be more stable and accurate.
Open Die Forging and closed die casting both utilize the same tooling for the tooling to be placed over the mandrel. The difference between the two is that in forging, the tool is not allowed to move during the shaping process; however, in casting, it must remain in constant contact with the mold until the metal is formed into the end product. The difference in the two is simple in principle, but can be a great challenge in practice. Casting requires the use of a mandrel with multiple dies to be positioned over the metal being shaped. Once the metal is shaped, it is then hammered to remove any excess material from the tooling and the additional metal is placed over the mold.
Open die forgers typically allow for a higher level of precision than traditional die forgers. The reason for this is that the mold is not held in constant contact with the surface of the die, and therefore the mechanical properties that govern conductivity, tensile strength, etc., are maintained throughout the casting process. Because there is no need to have the material remain in constant contact with the mold, the product will be made with a finer grain. This means that the final product will be more difficult to cast because there will be more surface area without any need to move the mold around on the die.
One of the advantages to using Open Die Forging techniques is that the time required to create the specific size of the cavity for the part is less. Since the tool can be removed from the molten metal and inspected before the part is crafted, the design is precise and repeatable. The speed in which the parts can be crafted is also important because parts made this way have a faster cooling rate than traditional dies. This allows for a higher degree of part completion rate due to faster cooling times and a high tolerance of higher stress levels. While this type of forging requires less manual work, it also requires more manual effort to complete the process.
There are many advantages and disadvantages associated with the use of Open Die Forging processes and the specific method should be selected based on the type of material being cast. Most tool parts produced in this process incorporate a carbon steel core and steel shaft and fitting. The advantage to using this process for high stress parts, such as those used for casting necklines and lacing, is that the carbon steel used in the core provides a more dense, harder feel and better compressive strength.