Forging, as a metal forming process, defines itself by forcing a ductile metal component into a specific shape as needed for its purpose. Forging provides several definite advantages over other metal forming processes such as casting, but that’s not a complete capture of the intricacies of metal forging.
There are 4 primary forging methods that all come under the definition of “forging”:
Open- and Closed-Die Forging refers to the use of a Die (a pre-shaped forming tool), Drop-Forging refers to the use of a power hammer, and Roll Forging refers to the use of heavy roller wheels that the part is forced through. For the purposes of this article, drop-forging and roll forging will not be covered; this will be a survey of the differences in closed vs open die forging.
What is Die Forging?
Before one can understand the differences between the types of die forging, one must understand the principles of die forging and its purpose. Die Forging uses a “die”, which (simply) is a piece of metal that is formed to contain the negative image of specific shape. A die is often referred to as the “tool”, because it is being used as a tool in the forming process.
When a piece of metal is forced into the die – under great pressure – the part will form itself into the shape of the die impression. The metal that is being formed, often referred to as the “workpiece”, is often heated before being forced into the tool which makes it more easily deform.
Forging is an ancient technique; blacksmiths have been forging metals including copper, bronze, iron, and steel as far back as 4500 BCE. Modern die forging, however, is a relatively recent invention. The forces required to form metal using open and closed die forges were far beyond what humanity was capable of before the industrial revolution.
Open die forging defines itself by the use of an open die, or what might sometimes appear to be half of a die. Sometimes, the use of a power hammer is employed; most commonly open die forging will refer to a heavy press applying consistent pressure onto a part to form it. Most important to the open die process is that the part is never completely enclosed in a die. Instead, the part is formed mostly unconstrained on simple shaped dies or flat plates.
It is not impossible for the open die forging process to produce smaller or precision shaped pieces, but the nature of unconstrained forming makes this much less ideal than a close die forging process. In the conversation of open vs closed die forging, open die forging is ideal for simpler parts such as pins, bars, blanks, and spindles; while the close die forging process can be used for the more precision and smaller forging needs.
The closed die forging process uses a tool that forms a complete (or mostly complete) seal around the workpiece. The workpiece is thus forced to take the shape of the die. Closed die forging can sometimes also be referred to as impression die forging.
To elaborate, open die forging uses flat plates or simple shapes that may or may not match the desired shape of the piece. In closed die forging, two or more tools that each must contain the shape desired on the outside of the workpiece are brought together.
In open vs closed die forging, closed die forging has a few advantages:
Closed die forging can be used to form any number of materials including aluminum, titanium, steel, and alloys.
Closed die forging can be used to form smaller pieces.
Closed die forging can create complex shapes impossible on an open die press.
Closed die forging can create parts with precision, which will reduce time spent on precision machining.
Closed die forging often requires less human interaction in the forging process, which reduces the chance of error and injury.
Open vs Closed Die Forging in Aerospace
Aerospace applications often require precision parts in complex shapes. Thus, when considering open vs closed die forging, aerospace manufacturers will naturally lead toward closed die forging to make the complex precise parts necessary. Anchor Harvey is a premier closed die forging shop that provides the engineering prowess, manufacturing knowledge, and quality tooling necessary for forging all types of precision aerospace parts. If you need quality forged aerospace parts, there is no better producer than Anchor Harvey.