Metal Forging: All About Different Forging Methods And Their Uses

Forging is a manufacturing process in which the metal is pounded, pressed or squeezed under heavy pressure into high powered strength parts known as Forging. The process is typically performed by preheating the metal into its desired temperature before it is given the shape. But it is crucial to remember that this process is entirely different from that of Casting Process, as the metal used is never poured or melted, which is being done in the casting process.

Why Use Forgings And Where Are They Used?

Forging process creates stronger parts than those, which are manufactured by any other metal process. This is the reason Forging process is more preferred as reliability and human safety are utmost important. You will rarely find forgings in daily day to day life as they are the component inside parts of assembled items such as automobiles, airplanes, ships, oil drilling equipment, engines, tractors, missiles, all other kinds of capital equipment to name a few.

Who Purchase These Forgings?

These customized parts vary in various shape, size and finesse - from the wrench and hammer in your toolbox to accommodate tolerance precision parts in the Boeing 747 and NASA space shuttle. In fact, a 747 Boeing contains nearly 18,000 forgings. Some of the purchasers and consumer markets include national defence, aerospace, agriculture, automotive, mining, construction, material handling and general industrial equipment.

What Metals Are Forged?

Any metallic substance can be forged. However, the common metals which are used are alloy and stainless steels, carbon, brass, copper, aluminium, titanium, hard tool steels, and high-temperature alloys containing cobalt, molybdenum or nickel. Each of these metals has its own distinct weight or strength characteristics which provide maximum utilization if best applied to any specific parts by the customer.

How Are Forgings Produced?

Gear Forging, or Forging copper, or be it forged steel rings, are all done by customized shaping of the metal by deformation that includes a myriad of techniques and equipment. The key to understanding forging designs, one needs to know the forging characteristics and operations of how the metal flow and what each produces. Forging is one process which takes into the metal's natural flow of grain into its advantage to confirm the unique contours of each part.

Hammer and Press Forging

The forging copper and other metals are carved into shape either by a press or a hammer. Forging done by the hammer is conducted out by repetitive blows. But the hammer forging and its productivity all depend on the techniques and skill of the operator. With the rise of technology and the arrival of automated hammers, it has resulted in the lesser time taken, enhanced flexibility and lesser worker dependency. During the process of the press, the stock is hit usually once in each blow.

The Open Forging or Hammer process

Open die forging is nothing but a modern day extension of the hammer and press process that a metal smith practised in anvil the pre-industrial period.

In the open die forging process, the workpiece is not entirely held in the die to give the desired shape. Usually, the open die forging technique is connected with large parts such as metal shafts, sleeves and disks. Most of the open die forging products is built on flat forging dies. Sometimes the round swaging dies and V-shaped dies are utilised in along with the flat dies.

Methods implemented on open die presses include:

• Outstretch and reduce the cross-section of the ingot or billet and expand it
• Upset forging to decrease the length of the ingot or billet where only one side of the metal requires forging
• Upset, outstretch, and piercing processes coupled with forging over a mandrel for unevenly shaped forged steel rings

As the open die forging includes hammered or pressed workpiece, it is frequently manipulated within the dies till it gets its final forged shapes. Because the process depends more on the workers' skill, this process is ambiguous and substantial workpiece stock quantities are preserved to provide forging abnormalities.

The forged parts of the workpiece are roughly shaped and finished to final dimensions. But with the increasing demand and use of the open die forging method and all other forging processes of this type are being automated.

On the other hand, the features of roll-forged elements are very satisfying. In most cases, roll-forged components have no flash, and the metal grain structure is convenient and constant in all parts. The forged steel rings and rolls offer a certain amount of descaling, making the product exterior smooth and free of scale pockets.

Impression Die Forging

In the impression die forging process, two dies are taken together and the workpiece goes through plastic deformation until its developed sides reach the side walls of the die.

 

During the process of impression die forging, some material starts to slip outside the die impression, forming some flashes.

 

Once the flashes cool down, they form intensified resistance to deformation. These cooled flashes build pressure inside the bulk of the workpiece and help material flowing into the vacant impressions.

 

Closed die forging, another type of impression die forging, is performed within a narrow cavity that restricts excess material from flashing out. This process is not dependant on the flash formation. Thus this is the most popular type of impression die forging.

 

The forging dies become more influential than the workers' skill in case of impression die forging methods. Impression forging program usually shapes materials and finish the piece with the preform, pierce, or cut method.

 

Precision Forging

Precision Forging means close-tolerance or close to final type forging. This forging technique is not a special technology but an advancement of the existing forging methods to a point where the forged part can be fitted with little or without any subsequent machining.

 

These advancements include not only the forging method but also preheating, descaling, lubricating, and temperature control works. But the application of Precision Forging method depends on the relevant financial condition of the business. Due to expensive tooling and development costs, precision forging is usually limited within the exceptionally high-quality apparatus.

 

Steel Ring Rolling

Ring rolling has grown from an art to a stringently managed engineering method. Faultless forged steel rings and other metal rings are constructed on a wide range of equipment.

 

Ring rolling gives a product a consistent, smooth exterior with peripheral grain orientation. These rings generally have diverging strength and elasticity, and often are less costly to manufacture than closed die forgings.

 

In whole, the ring rolling process gives uniform grain flow, ease of production, and adaptability in material, volume, size and geometry.

 

Cutting-edge ring rolling apparatus can roll different shapes in both inner and outer breadth of the forged ring, allowing them for unique weight reductions, and reduced material and machining expense.

 

Extrusion

In the Extrusion method, the forging workpiece is put in a container and pressed till it reaches the flow-stress level. The workpiece then thoroughly fills the container, and further pressure causes it to move through the cracks, and create the extruded metal piece.

 

There are different variants of the extrusion process, and many of them are patented. In all states, the degree of heating, the competence of scale elimination or restriction, and the effectiveness of lubrication are matters of obvious concern. The variety of shapes produced through hot extrusion is various. Dimensional precision, surface property, and productivity are high, and a higher range of deformation can be accomplished in a single procedure than in any other metal forging technique.

 

Extrusion can be Direct as well as Reverse, depending on the direction of motion between the ram and the extruded product. An extruded product can be both hollow and solid. Tube extrusion is ideal of forwarding extrusion of hollow shapes, and reverse extrusion is best for mass manufacturing of containers.

 

Piercing

Piercing method is closely connected to reverse extrusion process. However, it is recognised by the higher flow of the punch that is related to the velocity of the workpiece material.

 

Secondary Processes

Along with the primary forging methods, secondary methods are also employed often.

 

• Deformation - The deformation method is such a secondary forging process where divergent compression is applied. The width of the drawing ring may be reasonably smaller than the external width of the pre-forged crust to manage or reduce wall density and raise the height of the shell in a drawing or ironing procedure.

 

• Bending - Even after the completion of copper forging, forged gear, or any other metal forging process, bending can be performed. Furthermore, bending can be applied at any stage of the forging process. It is nearly impossible to build complicated shapes in only one die impression. Thus performing forging stock by bending or rolling the forged metal, or by following a fundamental die may be more profitable.

 

• Preform Forging - The preform design in metal forging performs an essential role in advancing the forging product characteristic, such as defect-free quality and proper metal movement. Preforming also helps in improved productivity, extended die life, and reduced worker expenses. Copper Forging, steel forging or any other metal forging in single die impression is usually effective for much smaller parts.

 

Special Techniques

After deformation of metal, the forged parts often undergo added metalworking. In case of open die forging the flash is removed. The punched holes may be required, and polished surface finish, as well as closer dimensional accuracy, may be needed. To meet the requirements, additional forging techniques are implemented.

 

• Trimming - Flash is trimmed before the forged metal is ready to use. Seldom, mainly with crack-sensitive alloy metals, trimming is done by grinding, sawing, milling, or flame cutting.

 

• Coining - It is typically the sizing works with stress applied to sharp surfaces to increase tolerance, smoothen surface, and reduce draft. Coining is usually performed on exteriors parallel to the parting line, while ironing is meant to be forced by a cup-shaped element through a ring to measure on the outward diameter. Minor metal flow is included in either direction and flash is not grown.

 

• Swaging- This is related to the open die forging method how the stock is drawn out within the flat, narrow dies. However, instead of stock, the hammer is wheeled to deliver increased blows to give the forged metal the desired finishing. Swaging can be paused at any stage in the length of stock and is usually used for pointing tube and bar ends and for manufacturing advanced columns and shafts of decreasing width.

 

Different Types of Forging

There are three major types of forging – Cold Forging, Warm Forging and Hot Forging.

 

• Cold Forging

Cold forging involves either closed die forging or the impression die forging with lubrication and circular dies at or near room temperature. Cold forging usually processes carbon and standard alloy steels like forged steel rings. These cold forged workpieces are generally proportional and rarely exceed 25 lb. The main benefit of cold forging is the material savings due to its exact shapes that need little or no finishing. Fully enclosed impressions and extrusion metal flow allow draftless, close-tolerance elements. Thus, production rates are very high with outstanding die life. While cold forging usually enhances the mechanical qualities, the change is not useful in common operations and economic advantages are principal interest here.

 

• Warm Forging

Warm forging has plenty of economic benefits that mark its rising use as a production technique. In the warm forging, the temperature range of forging steel runs above room temperature to below the recrystallization temperature. However, the temperature ranging between 1,000 and 1,330°F is most preferred for the highest commercial potential for warm forging. Compared to cold forging, warm forging has the potential benefits of minimised tooling charges, decreased press loads, improved steel ductility, removal of the need to tempering preceding forging, and desirable forged properties that lead to eliminating further heat treatment.

 

• Hot Forging

In Hot forging method recrystallization occurs concurrently with deformation, thus circumventing strain crystallisation. For this to occur, high workpiece temperature, resembling the metal's recrystallization temperature, must be achieved during the entire process. The kind of hot forging is isothermal forging, where materials and dies are heated to equal temperature. In nearly all instances, isothermal forging is carried on super-alloys in a vacuum or extremely repressed atmosphere to stop oxidation.