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Forging

Forging Definition and Development


Forging is a metal processing process that uses forging pressure machines to put pressure on metal billets, which will produce plastic deformation in order to obtain certain mechanical properties, a certain shape and dimensions.  So we usually call metal forging.

blacksmith forgingAs one of the oldest metalworking process, there is a long histoty of forging technique. At the beginning of forging process, it was performed by a smith using hammer and anvil, through introducing water power to the production and working of iro. In the 12th century, allowed the use of large trip hammers or power hammers that exponentially increased the amount and size of iron that could be produced and forged easily. The smithy or forge has evolved over centuries to become a facility with engineered processes, production equipment, tooling, raw materials and products to meet the demands of modern industry.

Nowadays, modern metal forging is operated either with presses or with hammers powered by compressed air, electricity, hydraulics or steam. These hammers may have reciprocating weights in the thousands of pounds. Smaller power hammers, 500 lb (230 kg) or less reciprocating weight, and hydraulic presses are common in art smithies as well. Some steam hammers remain in use, but they became obsolete with the availability of the other, more convenient, power sources.

Why Forging (Forging vs Casting) ? 



Compared with cast or machined part, metal forging can produce a piece with higher strength. During the metal shaping process, its internal grain deforms to follow the final shape of the part. As a result, the grain is continuous throughout the part, giving rise to a piece with improved strength characteristics. Besides, unlike pouring, high pressure to forge parts will make compact inner structure, and it will not easy to produce inner defects.

Secondly, when compared to casting or fabrication, forging can offer a lower total cost in a more cost-effective way. When you take all the costs that occured from procurement to lead time to rework into consideration, then factor in the costs of scrap, downtime and further quality issues, forging can win the long-term benefits that can outweigh castings or fabrications that might offer short-term cost-savings.

Thirdly, forging can offer a short production cycle. When forging, if the shape is not quite complex, it can be just one-time forged, in just few seconds, and then trimmed to get finished part. So in general, we can finish production in a short production cycle within 20 days.

Next, compared with casting, metals after forging can improve its organizational structure and mechanical properties. Casting organization after forging method, due to metal deformation and recrystallization, make original bulky dendrite and columnar grain to fine grain and uniform axial recrystallization organization, make original segregation, porosity, slag compaction in the steel ingot rammed and welded, thus to make its organization become more closely, and improve the plasticity and mechanical properties of the metal.

Metal Forging materials



Steel Forging: Main materials of forging are forged steel, such steel could be carbon steel, alloy steel and stainless steel. Stainless steel is the most expensive material in forging for its special material characteristics. Normally such steels are all improted from domestic material factories in round bar shape. And each material specification can have different diameters to better suit the shape of forgings. Common steel specifications are 20#, 35#, 45#, 20Cr, 40Cr, 20CrMnTi, 20CrMo, 30CrMo, 35CrMo, 42CrMo, Q235, Q345, A105, ect. 

Aluminum Foging: Aluminum is used in metal forging for its lightweight. High-strength aluminium alloys have the tensile strength of medium strong steel alloys while providing significant weight advantages. Therefore, aluminium forged parts are mainly used in aerospace, automotive industry and many other fields of engineering especially in those fields, where highest safety standards against failure by abuse, by shock or vibratory stresses are needed. Such parts are for example chassis parts, steering components and brake parts. Commonly used alloys are AlSi1MgMn (EN AW-6082) and AlZnMgCu1,5 (EN AW-7075). About 80% of all aluminium forged parts are made of AlSi1MgMn. The high-strength alloy AlZnMgCu1,5 is mainly used for aerospace applications.

To meet large demands of forgings and ensure our production capacities, we have a special material warehouse to stock different steel bars. And to distinguish different material specifications, they are marked with different colours. 

Metal Forging Process and Types



Different forging methods have a different process, we generally divide metal forging processes into open die forging and closed die forging.

Open Die Forging: Also known as smith forging. In open-die forging, a hammer strikes and deforms the workpiece, which is placed on a stationary anvil. Open die forging gets its name from the fact that the dies (the surfaces that are in contact with the workpiece) do not enclose the workpiece, allowing it to flow except where contacted by the dies. The operator therefore needs to orient and position the workpiece to get the desired shape. The dies are usually flat in shape, but some have a specially shaped surface for specialized operations. For example, a die may have a round, concave, or convex surface or be a tool to form holes or be a cut-off tool. Open-die forgings can be worked into shapes which include discs, hubs, blocks, shafts (including step shafts or with flanges), sleeves, cylinders, flats, hexes, rounds, plate, and some custom shapes. Open-die forging lends itself to short runs and is appropriate for art smithing and custom work. In some cases, open-die forging may be employed to rough-shape ingots to prepare them for subsequent operations. Open-die forging may also orient the grain to increase strength in the required direction. 

Closed Die Forging: Also called impression die forging. In closed die forging, the metal is placed between upper and lower dies, which are attached to an anvil. The hammer is then dropped on the workpiece, causing the metal to flow and fill the die cavities. The hammer is generally in contact with the workpiece at the speed of milliseconds. Depending on the size and complexity of the part, the hammer may be dropped multiple times in quick succession. Excess metal is squeezed out of the die cavities, forming what is referred to as "flash". The flash cools more rapidly than the rest of the material, and is stronger than the metal in the die, so it helps prevent more flash from forming. This also forces the metal to completely fill the die cavity. After forging, the flash is removed. In commercial closed die forging, the workpiece is usually moved through a series of cavities in a die to get from an ingot to the final shape. The first forging is used to distribute the metal into the rough shape in accordance to the needs of later cavities; this impression is called an "edging", "fullering", or "bending" impression. The following cavities are called "blocking" cavities, in which the piece is working into a shape that more closely resembles the final product. These stages usually impart the workpiece with generous bends and large fillets. The final shape is forged in a "final" or "finisher" impression cavity. If there is only a short run of parts to be done, then it may be more economical for the die to lack a final impression cavity and instead machine the final features. Closed die forging has been improved in recent years through increased automation which includes induction heating, mechanical feeding, positioning and manipulation, and the direct heat treatment of parts after forging. One variation of closed die forging is called "flashless forging", or "precision forging". In this type of forging, the die cavities are completely closed, which keeps the workpiece from forming flash. The major advantage to this process is that less metal is lost to flash. Flash can account for 20 to 45% of the starting material. The disadvantages of this process include additional cost due to a more complex die design and the need for better lubrication and workpiece placement. Closed-die forging has a high initial cost due to the creation of dies and required design work to make working die cavities. However, it has low recurring costs for each part, thus forgings become more economical with more volume. This is one of the major reasons closed-die forgings are often used in the automotive and tool industries. Another reason forgings are common in these industrial sectors is that forgings generally have about a 20 percent higher strength-to-weight ratio compared to cast or machined parts of the same material.

Generally speaking, open die forging is designed for large metal components, and closed die forging is mainly for small precision parts, see more about differences between closed die forging and open die forging......

Application of Metal Forgings



As one of the main metal processing process,applications of forgings are so wide. Such forgings are mostly used by people when safety factor is considered and good mechanical properties are needed. So forgings can be used in mining machinery(mining drill bits), agricultural machinery (agricultural wear parts), forestry machinery (mulcher hammer/teeth), automotive industry,trailer parts, ect. Click our photo gallery page can help you to learn more about forging applications.

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