Closed-Die Aluminum Forging
Closed-die forging is a process of forging hot metal into a specific shape by pressing two shaped metal plates against a workpiece with great force. The part will bend and deform into the shape of the faces on each plate, filling the available space. The dies will fully enclose the workpiece, forcing the metal to fill the entire available cavity, and release as a negative image of the plates.
It is called closed “die” forging because the plates used to shape a workpiece are together called a die. Specifically, it is closed-die precisely because it is completely closed around a workpiece. This is opposed to an open-die that does not completely enclose a workpiece and allows the material to expand outward into the space between the die plates.
When is Closed-Die Forging Used?
Closed-die forging can also be called impression die forging. It is most commonly used on small or medium-sized components and is primarily utilized to make complex shapes that require little to no after forging work. The process is considered a form of plastic (REMO NOTE: Is “plastic” the correct word?) deformation, meaning that parts are expected to keep the shape that they are forced to take after the die is opened. Closed-die forging is performed at medium-high temperature, below the material’s melting temperature at a range of temperatures that make the material soft and workable.
Often, closed-die forging is performed in steps. Especially if a part is a highly complex shape, the piece will be passed through multiple dies. Each die will deform a part further from its original billet form into the final shape. Forcing a piece to change shape too radically may break the part, though this is less of a concern with forging aluminum rather than steel.
Strengths of Closed-Die Aluminum Forging
Aluminum is an affordable and popular material used in closed-die forging due to its ductility, relatively high strength-to-weight ratios, good adaptability with alloying elements, and low melting temperature. Aluminum can be heated and cooled relatively quickly in a heating oven and can undergo greater deformation in a single die than steel.
Closed-die forging has a number of advantages when compared to other forms of forging and metal forming processes:
- Closed-Die Forging vs. Open-Die Forging: When comparing closed die and open-die forging, one must understand that these processes are for different purposes. Open-die forging cannot form pieces to a specific shape in the way that closed-die forging can. Open-die forging can often accommodate very large pieces, but its lack of precision and complex shaping limits its uses.
- Closed-Die Forging vs. Casting: Casting is the process by which molten metal is poured into a mold cavity; the molten metal flows into the available space and cools into the internal shape of the mold. Casting has the benefit of producing very complex shapes, even those shapes that closed-die forging may struggle to produce. However, casting does not benefit from the strength gains of the plastic deformation process. Completely melting the metal dislodges the grain structure and allows it to reset into a chaotic and easily breakable state. Even heat-treating casting cannot achieve the strength gains of a forged part.
- Closed-Die Forging vs. Hammer Forging: Hammer forging, also called drop forging, uses a powerful hammer to pound pieces into shape. Hammer forging has the same problems as open-die forging but has the benefit of requiring less overall force. Drop forging can be performed at lower temperatures, but like open-die forging, it cannot form complex shapes as a closed-die forge can.
- Closed-Die Forging vs. Machining: Sometimes, a complex part can be made directly through a machining process, which uses cutting tools to remove material from cold metal stock to a finished piece. This process can be relatively fast for simpler shapes but can take a long time for more complex shapes. Machining also breaks apart the grain structure and leaves the overall part weaker than a closed-die forged part. Machining can achieve a degree of precision that no forge is able to accomplish, but not all parts require the extreme precision of machine tools. A forged part can achieve the desired dimensions at a lower cost and with greater part performance.
How Does Anchor Harvey Do It Better?
Anchor Harvey has a few key advantages that make their forging process better than the competition:
- Forge Engineering: Anchor Harvey has a team of professional forge engineers that design the part, the die, and the manufacturing process before the production run even begins.
- In-house Tool and Die Shop: The machine shop at the Anchor Harvey facility can custom make all forge dies to ensure the quality of the die. In addition, the tool and die shop can rework dies at any time during a production run.
- Heat Treatment: Anchor Harvey’s in-house heat treatment facilities can also perform heat treatments without components ever leaving the facility. This reduces lead times and allows engineers to track and adjust the process at any time.
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