In general, forging describes a type of metal forming process in which a workpiece is shaped using compressive forces, such as from the blows of a hammer. Upset forging involves compressing the length of the metal to increase its diameter, width or thickness.
Of particular note in this process is it’s suitability for long parts. The metal bar is heated, and forging pressure is applied in the direction of the axis. Upset forging makes it easy to produce long parts with a forged end, best for parts that require a complex geometry that would otherwise be difficult to obtain.
The workpiece typically starts out as wire, bar or rod, though there are machines that can take bars as wide as 10 inches in diameter. Normally, these machines use split dies with many cavities within them, allowing the workpiece to slide easily from one cavity to the next. When the die is closed, the forging die applies force to the workpiece, forming and ‘upsetting’ it into the space.
Another method of upset forging is utilized to increase the diameter or width/length of an aluminum workpiece to fit a larger dimensional requirement. If a round or block size isn’t large enough for a particular application, it’s axis can be forged at the ends to increase the lateral dimensions.
All forms of forging help to improve material integrity by improving and refining grain structure, reducing voids, inclusions and alloy segregation, increasing mechanical properties and improving response to heat treatment processing.
What do manufacturers need to know about upset forging?
When designing parts for upset forging, certain rules must be kept in mind. For instance, the length of the metal workpiece to be upset should be no more than three times the diameter. If a greater length is needed, the diameter of the upset should be no greater than 1.5 times that of the stock.
Upset forging provides a number of advantages that are beneficial for manufacturers. For instance, because of the nature of the process, there is very little risk of the work piece cracking. Furthermore, the mechanical stresses are aligned in such a way that the parts have excellent fatigue resistance.
The process is also efficient, as there is only partial heating required, helping to reduce the consumption of energy and lower CO2 emissions. Likewise, very little material is wasted during the forging process. There is also little need for machining after the part has been shaped.
What makes aluminum well suited for forging applications?
In general, aluminum is well suited for forging applications. Combined with its other properties, including its light weight and high strength to weight ratio, forged aluminum makes a great option for applications in the automotive and aerospace industries.
Because aluminum has a low melting point, it gets forged at lower temperatures than many other metals. Furthermore, because its low density means it does not retain heat as well, hot tooling is necessary to prevent the workpiece from cooling too rapidly during the forging process. The common forging temperatures range between 775 and 875°F.
Aluminum is also known for its low flow stress and excellent ductility. This means that extremely complex shapes can be forged using aluminum alloys, especially when compared to other metals, such as steel. Aluminum also lacks the scale or grain growth that other metals exhibit during upset forging.
What aluminum alloys work best with upset forging?
Many aluminum alloys are well suited for forging applications, but 6061 is among the most popular.
What applications rely on upset forging?
Parts that are frequently made via the upset forging process include screws, shafts, bolts, couplings, piston rods, engine valves, cluster gear banks and more. As stated previously, it is also an excellent method for increasing the cross section of larger workpieces in billet or block form.
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