When specifying aluminum, how to process the material into the desired part reliably and cost-effectively is an important consideration. Cold forming is one of the methods manufacturers employ to achieve this goal. While there are a few options when it comes to cold forming, one of the fastest growing techniques is known as impact extrusion.
Cold forming, also known as cold working, describes many metalworking processes in which the metal is shaped at or close to room temperature. In contrast to hot working, the crystalline properties of the metal are altered due to the process, which often results in an increase in mechanical properties.
What is extrusion?
Extrusion is a metal forming process generally performed to make lineal products that have a fixed cross-sectional profile. This is accomplished by forcing the metal (or other material) through a die that has the desired solid or hollow cross-section.
There are several benefits associated with extrusion. One, there is basically an infinite number of shapes that can be made via extrusion, often of very complex design. It can also be used with metals that are otherwise quite brittle because the only stresses involved are compressive and shear. The finished parts also tend to have an excellent surface finish
While impact extrusion is one method, there is a range of various extrusion options that manufacturers have at their disposal. These include the standard hot extrusion and cold extrusion processes as well as friction extrusion. Another similar process is drawing, the only difference being that the metal is pulled rather than pushed through the die.
What is the impact extrusion process?
What distinguishes impact extrusion from other processes is that the workpiece is forced through the aperture at a much higher velocity than with other methods. The first step in the impact extrusion process is to take a metal slug and place it in the press. The press might be mechanical or hydraulic in nature and capable of cycling up to sixty times per minute.
The slug will then be pushed into the die at extreme velocity by a punch, forcing the metal of the slug to reform itself around the punch while conforming to the die on the outside. This action controls the finished form of both the interior and exterior of the workpiece. Lubricants can be added as necessary to facilitate the process.
One impact is enough for the slug to take on its new shape and a counter punch is used to eject the metal from the die. There are three types of impact extrusion operations. Forward impacting is when the slug is pushed into the die. Reverse impacting forces the slug around the punch. Combined impacting is when the slug is forced both into the die and around the punch at the same time.
It should be noted that the thickness of the work piece can be directly correlated to the clearance between the punch and the die. This means that the thinner the work piece is, the tighter the tolerances will be. Also, as preciously mentioned, the finished product will have a better surface finish than the starting piece. The grain structure of the aluminum is refined during this work-hardening process which strengthens the metal in its new form.
What are the advantages of impact extrusion?
Impact extrusion is growing in popularity, especially when it comes to working with aluminum alloys. As already pointed out, because it is a cold-working technique, there’s no need to heat the workpiece beforehand, saving time and money while gaining the benefits of cold-working.
It also is faster because only one impact is necessary. The power of the punching mechanism only requires one strike. The tooling costs tend to be lower, while the tools themselves have a longer life than in other techniques. In terms of efficiency, the impact extrusion process has a high output, with minimal waste material.
Other benefits offered by impact extrusion include increased corrosion resistance, a uniform grain alignment and lighter finished products compared to other methods. In addition, there is little if no machining needed on the finished products after the process.
Which aluminum alloys are associated with impact extrusion?
All aluminum alloys are well suited to impact extrusion. Some advantages offered by aluminum alloys that make impact extrusion an excellent choice include a much lower density compared to steel, copper, nickel and other metals. Aluminum is also non-toxic when it comes to food storage, and extrusion is widely used to produce food containers such as beverage and food cans. Moreover, the recyclability of aluminum alloys makes it a great choice when sustainability is a consideration.
Most of the aluminum alloys used in the process are in the 1000 series and 6000 series.
What are common impact extrusion applications?
It’s important to know that impact extrusions are somewhat limited in their geometry. The finished dimension needs to have a symmetrical cross section be it round, square or oval; part bases must also be thicker than the side walls due to the nature of material flow in the process.
Impact extrusion can be used for a wide array of applications. Common uses include pump components, pressure vessels, drive components, air conditioning parts, gas tank connectors, food and beverage cans, cartridges and tubes of all varieties.
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