Open Die Forging involves the shaping of hot metal pieces between a metal die secured to a base die and a lower die secured to a bolster, anvil or hammer. Various kinds of metal are worked with this method of forgery: sheets of steel, sheet steel, mild steel, titanium, stainless steel, aluminium, iron, brass, copper, tin, steel, magnesium, iron carbide, tungsten carbide, zinc and even carbon can be used. The parts are heated to high temperatures and the metal is hammered, pulled and bent into the required shapes. The forging process also involves grinding or cutting of surfaces and the forming of various designs. This is a very traditional method that has been used for thousands of years. Although with modern machines, die forgers can now do much more, such as stamping and die forming, but most still work by hand with a forge wheel and forge bell.
There are two kinds of open die forging: single and multiple dies. With the single die forging process, there is only one heat-rolling operation, therefore it is called ‘single die’. With the multiple dies process, multiple metal slices are formed simultaneously, with each of them representing a different shape and are heated to different temperatures. Depending on the desired shape and the properties of the metal, multiple dies may be required to achieve the desirable result.
When using this kind of forge tool, you can be sure that the parts will have a very accurate, smooth surface finish due to the fact that there are not as many impurities in the metal parts which could affect the outcome of the finished product. This is the reason why most people choose this method. The other advantage of this kind of forgery is that the temperature range can be adjusted to fit the requirements of the metal part being forged, making it ideal for working with different alloys which have different melting points.
The procedure of open die forging is not too complex. In short, a tool is first placed on the piece of metal to be forge-shaped and brought into the melting stage. The heat source is a gas such as carbon dioxide, nitrogen, or an electrically charged conductor. As the piece of metal cools, it begins to form molten alloy from the primer that hardens as it cools. It is during this stage where the tool’s shape is formed, since the material is still in its molten state.
Single-pass forging uses two passes for the finishing operation. One of the passes has a longer duration, allowing for a finer grain along the surface of the object to be formed. With the shorter pass, the work piece is formed with a smaller cross section of metal. Another aspect of single-pass forging is that the tool can be used for both thinner and thicker materials, which allows for intricate machining of complicated shapes. Double-pass forging offers a combination of the previously mentioned aspects of single-pass and double-pass for the same process. It uses a shorter forging pass and a longer cooling time for forming the final product, which allows for more intricate grain patterns.
Open impression die forging is a fast and accurate method for forming intricate curves and other complex shapes, but because the tools are more difficult to make, they are normally reserved for projects that require more precision. Double-feed die structures offer a solution to both speed and accuracy, but they use two separate feeds for each curve. The process combines the best features of both single and double-feed die structures. The process is ideal for forming tubular objects, but can also be used for stamping, fluting and other precision manufacturing operations.