Introduction to Forging


Forging is a manufacturing process in which metal is pressed, pounded, or squeezed under great pressure into high-strength parts. This is usually done by heating the metal, but some forgings are produced without heat.

Generally, forged components are shaped by either a hammer or a press. Forging by hammer is carried out in a succession of die impressions using repeated blows. In a press, the component is usually hit only once in each die impression.


The three basic types of alloy forgings are: open-die forgings, closed-die forgings, and rolled rings.

2. CLOSED/IMPRESSION-DIE FORGING

Impression-die / closed-die forging accounts for the majority of forging production. In impression-die forging, two dies are brought together and the work piece undergoes plastic deformation until its enlarged sides touch the die side walls.

Some material flows outside the die impression, forming flash. The flash cools rapidly and presents increased resistance to deformation, effectively becoming part of the tool. This builds pressure inside the bulk of the work piece, aiding material flow into unfilled impressions.


Process Operations - Impression Die Forging

In the simplest example of impression die forging, two dies are brought together and the workpiece undergoes plastic deformation until its enlarged sides touch the side walls of the die. Then, a small amount of material begins to flow outside the die impression forming flash that is gradually thinned. The flash cools rapidly and presents increased resistance to deformation and helps build up pressure inside the bulk of the workpiece that aids material flow into unfilled impressions.


Upsetting

Fundamentally, impression die forgings produced on horizontal forging machines (upsetters) are similar to those produced by hammers or presses. Each is the result of forcing metal into cavities in dies which separate at parting lines.

The impression in the ram-operated "heading tool" is the equivalent of a hammer or press top die. The "grip dies" contain the impressions corresponding to the hammer or press bottom die. Grip dies consist of a stationary die and a moving die which, when closed, act to grip the stock and hold it in position for forging. After each workstroke of the machine, these dies permit the transfer of stock from one cavity to another in the multiple-impression dies.



ALUMINIUM FORGING

Of all structural metals and alloys, the aluminium alloys are the most readily forged to precise intricate shapes. There are a number of reasons for this: aluminium alloys are ductile; they can be forged with dies heated essentially to the same temperatures as the work-piece; they do not develop scale during heating; and they require lower forging pressures.

Most aluminium -alloy bars are supplied as rounds or rectangular shapes suitable for forging. Most bars are extruded from billet or ingot, though at least three producers offer continuously cast, fine-grain bar suitable for direct heating and subsequent forging.

Forging temperatures are very low, being below incandescent temperatures. Thus, temperature controls and furnace construction for aluminium are different from those used with ferrous materials. Radiation type (infra-red) sensors are increasingly used for measuring billet surface temperatures. Most indirect-fired, re-circulating air furnaces are controlled by internal thermocouples.

Forging Temperatures for aluminium Alloys (°F)
Alloy Solidus Temperature Solution Temperature Hammer Mechanical Press Hydraulic Press
5083 1090 Not HT 700-850 750-900 750-950
2014 945 850 700-800 750-850 750-875
2025 970 890 800-875 800-900 800-900
6061 1080 920 700-875 700-900 700-925
7075* 890 800 675-775 700-800 700-850
7050* 900 830   700-800 700-820
7079* 900 850 700-800 700-825 700-850
*These alloys are not usually forged in hammers due to internal temprature increases with a lower melting temprature


Die temperature ranges for the forging of aluminium alloys

Forging process/equipment

Die temperature

C

F

Open-die forging

Ring rolling

95-205

200-400

Mandrel forging

95-205

200-400

Closed-die forging

Hammers

95-150

200-300

Upsetters

150-260

300-500

Mechanical presses

150-260

300-500

Screw presses

150-260

300-500

Orbital (rotary) forging

150-260

300-500

Roll forging

95-205

200-400

Hydraulic presses

315-430

600-800

 


Alloy Designation

Temper


Mechanical Properties(Min. Values)

Numerical

Conventional

R Mpa

Rp 0,2[Mpa]

A5[%]

HB

EN AW 2011

EN AW-AlCu6BiPb

T6

340

230

10

100

EN AW 2014

EN AW-AlCu4SiMg

T6/T651

440

380

6

120

EN AW 6061

EN AW-AlMg1SiCu

T6

280

240

7

85

EN AW 6082

EN AW-AlSi1MgMn

T6

310

260

6

90

EN AW 7075

EN AW-AlZn5,5mgCu

T6/T73

500/445

425/375

7.0/6.0

135/120




COLD FORGING

Most forging is done as hot work, at temperatures up to 2300 degrees F, however, a variation of impression die forging is cold forging. Cold forging encompasses many processes - bending, cold drawing, cold heading, coining, extrusions and more, to yield a diverse range of part shapes. The temperature of metals being cold forged may range from room temperature to several hundred degrees.

Process Capabilities

Cold forging encompasses many processes bending, cold drawing, cold heading, coining, extrusion, punching, thread rolling and more to yield a diverse range of part shapes. These include various shaft-like components, cup-shaped geometry's, hollow parts with stems and shafts, all kinds of upset (headed) and bent configurations, as well as combinations.

Most recently, parts with radial flow like round configurations with center flanges, rectangular parts, and non-axisymmetric parts with 3- and 6-fold symmetry have been produced by warm extrusion. With cold forging of steel rod, wire, or bar, shaft-like parts with 3-plane bends and headed design features are not uncommon.

Typical parts are most cost-effective in the range of 10 lbs. or less; symmetrical parts up to 7 lbs. readily lend themselves to automated processing. Material options range form lower-alloy and carbon steels to 300 and 400 series stainless, selected aluminium alloys, brass and bronze.

There are times when warm forging practices are selected over cold forging especially for higher carbon grades of steel or where in-process anneals can be eliminated.

Often chosen for integral design features such as built-in flanges and bosses, cold forgings are frequently used in automotive steering and suspension parts, antilock-braking systems, hardware, defense components, and other applications where high strength, close tolerances and volume production make them an economical choice.

In the process, a chemically lubricated bar slug is forced into a closed die under extreme pressure. The unheated metal thus flows into the desired shape. As shown, forward extrusion involves steel flow in the direction of the ram force. It is used when the diameter of the bar is to be decreased and the length increased. Backward extrusion, where the metal flows opposite to the ram force, generates hollow parts. In upsetting, the metal flows at right angles to the ram force, increasing diameter and reducing length.

Process Operations – Cold Forging

MACHINING

Conventional machining, one of the most important material removal methods, is a collection of material-working processes in which power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to mechanically cut the material to achieve the desired geometry. Machining is a part of the manufacture of almost all metal products, and it is common for other materials, such as wood and plastic, to be machined.

A room, building, or company where machining is done is called a machine shop. Much of modern day machining is controlled by computers usingcomputer numerical control (CNC) machining.

The three principal machining processes are classified as turning, drilling and milling. Other operations falling into miscellaneous categories include shaping, planing, boring, broaching and sawing.

  • Turning operations are operations that rotate the workpiece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning.
  • Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the workpiece. Milling machines are the principal machine tool used in milling.
  • Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the workpiece. Drilling operations are done primarily in drill presses but sometimes on lathes or mills.
  • Miscellaneous operations are operations that strictly speaking may not be machining operations in that they may not be swarf producing operations but these operations are performed at a typical machine tool. Burnishing is an example of a miscellaneous operation. Burnishing produces no swarf but can be performed at a lathe, mill, or drill press.


DIE SHOP

Die cutting is the process of using a die to shear webs of low strength materials, such as rubber, fiber, cloth, paper, corrugated fiberboard, paperboard, plastics,pressure sensitive adhesive tapes, foam and sheet metal. In the metalworking andleather industries, the process is known as clicking and the machine may be referred to as a clicking machine.

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