Forging is an important metal manufacturing process. It uses force and temperature in shaping metals. It is one of the oldest ways of working with metals. This is how metalsmiths made implements and tools like kitchenware, weapons and hand tools. Forging, like many other ancient manufacturing processes, underwent a fillip during the industrial revolution when innovators brought in new techniques and enterprising entrepreneurs enthusiastically adopted them for cheaper production and higher output volumes.
There are many different types of forging processes: swaging, cogging, roll forging, press forging, automatic hot forging, upsetting, open-die forging, and closed die forging. Of these, closed-die forging is one of the most popular methods. Also known as an impression-die casting, it is preferred for producing high-quality material at moderate costs.
The process is very simple where we use force from two sides to imprint the die on the manufacturing part. The dies move towards each other, eventually covering the part. It may cover it whole or in part. The process does not significantly change the shape and size of the material. Hence, the raw material is kept close to the final part in terms of shape and size. The top or bottom die carries the forged shape as a negative image.
The metal is heated and then placed on the bottom die. The top die or the ram falls on the workpiece. The ram falls repeatedly over the piece, forcing it to fill the contours of the die block. This process is repeated as many time as needed to ensure that the contours are completely covered. The workpiece is under tremendous pressure and may flow into crevasses between the dies, in places where we don’t want it to. These pieces are called flash. These pieces are usually small and hence, cool quickly. They are later trimmed off easily.
In the closed die forging process, the action of the ram is very quick and its contact with the work-piece is also extremely momentary, on the scale of milliseconds. In commercial forging, the entire process may be repeated on the same workpiece for different outcomes. The raw material will go through a series of cavities where the dies will shape it so that we get the desired results. In the first cavity, the dies will act to give the metal its rough shape. The ram will force the metal to fill the space. Later cavities will work to further shape the metal, giving it new dimensions and shape.
This process allows us to give the metal many different contours and bends. The last cavity is used to give the part a final finish. However, we also often use machining to finish the product.
Improvements in closed-die forging like all manufacturing processes closed die forging process has improved with technological advancements. One of the most important steps is automation. The raw material is fed and then processes like mechanical positioning, turning and manipulation move the piece throughout the die cavities. The heat is also controlled. There are fewer human errors and the closed die forging process takes very little time.
Another interesting development is the flashless forging. In this type of forging, the die casts are completely closed, so that when the dies are brought together they form a closed cavity and the metal does not flow out. As a result, there is no flash. This removes the necessity of flash removal and makes the production process more efficient. It also reduces metal wastage. Flash can account for as much as 45% wastage of the original material! However, the die has to be very precisely designed. We also need optimal lubrication and placement. This can increase production costs.
Why you should go for closed die forging process?
Closed-die forging is a popular forging method because we can get complicated shapes. One of its disadvantages is the higher cost of production. The more precise the die design, the higher the cost. However, this is only the initial cost. In closed die forging, the cost comes down with recurring batches. It is a fast and efficient forging method and hence, the overall costs are actually far lower. This method also gives us a higher strength-to-weight ratio.