11 Things You Should Know About Forging Process.

Forging

What is forging?

In forging, the deformation of metal and alloys are done in the specified shapes by application of repeated blows from a hammer.
Forging may be carried out at room temperature (cold forging) or at elevated temperatures (warm or hot forging) depending on the homologous temperature. Cold forging requires higher forces (because of the higher strength of the workpiece material), and the workpiece material must possess sufficient ductility at room temperature to undergo the necessary deformation without cracking.
Cold-forged parts have a good surface finish and dimensional accuracy.
Hot forging requires lower forces, but the dimensional accuracy and surface finish of the parts are not as good as in cold forging.
Forgings generally are subjected to additional finishing operations, such as heat treating to modify properties and machining to obtain accurate final dimensions and a good surface finish.

Which type of raw material is used in Forging?

The raw material is usually a billet of round or square cross-section.
The volume of raw material is larger than the finished component.
Depending on the end use of the component, the forged part may be used as such or (more frequently) it has to be machined to correct size to close tolerances.
The initial volume of material must be decided based on the machining allowance.

How is the forging process classified?

Forging process is done by hand or with the help of power hammers.
Sometimes hydraulic presses are also used for forging.

What is Hand forging?

The material spreads laterally under the action of the compressive forces due to hammer blows.
Cracks would be developed on brittle material like cast iron from the blows of hammer and hence cannot be forged.
An ordinary blacksmith uses an open-hearth using coke (or sometimes steam coal) as fuel for heating the metal and when it has become red-hot, blacksmith’s assistant (called striker on hammer man) uses a hand held hammer to deliver blows on the metal piece while the blacksmith holds it on an anvil and manipulates the metal piece with a pair of tongs.
Small forgings and small quantity production is possible through this process.
This process is also known as hand forging.

What are the various forging operations?

Upsetting: It is the process of enlarging the cross-section at expense of the length of the work piece.
Drawing down: The reversal of upsetting process is known as drawing down. In this process the cross-sectional area is reduced while the length in increased.
Cutting: Extra metal from the job is removed by means of hot chisels in this operation.
Bending: Bending of bars, flats and other such material is often done by a blacksmith. First the portion at the bend location is heated for making a bend.
Extra material is provided so that after bending, the cross-section at the bend does not reduce due to elongation.
Punching and drifting: Punching is an operation in which a force is applied through the work piece with the help of a punch to produce a rough hole.


The job is heated, kept on the anvil and a punch of suitable size is forced to about half the depth of the job by hammering. The job is then turned upside down and punch is forced in from the other side, this time through and through. Punching is usually followed by drifting i.e, forcing a drift in the punched hole through and through. This produces at better hole as regards its size and finish.
Setting down and finishing: Setting down is the operation by which the rounding of a corner is removed to make it a square. It is done with the help of a set hammer. Finishing is the operation where the uneven surface of the forging is smoothened out with the use of a flatter or set hammer and round stems are finished to size with the use of swages after the job has been roughly brought to desired shape and size.
Forge welding: Sometimes, it may become necessary to join two pieces of metal. Forge welding of steel is quite common and consists of heating the two ends to be joined to white heat (1050°C – 1150°C).
Then the two ends of steel are brought together having previously been given a slight convex shape to the surfaces under joining. The surfaces are cleaned of scale. They are then hammered together using borax as flux. The hammering is started from centre of the convex surface and it progresses to the ends. This results in the slag being squeezed out of the joint.

What is Open die forging?

Open-die forging is one of the simplest forging operation.

Although most open-die forgings typically weigh 15 to 500 kg (30 to 1000 lb), forgings of 300 tons have also been made.

Part sizes may range from very little (the size of nails, pins, and bolts) to enormous (up to 23 m (75 ft), long shafts for transport propellers).

Open-die forging can be depicted by a solid workpiece put between two flat dies and decrease in height by compacting it so this process is also called as upsetting or flat-die forging.

The die surfaces also may have shallow cavities or incorporate features to create similarly simple forgings.

What is barreling?

Barreling is caused essentially by frictional forces that oppose the outward flow of the workpiece at the die interfaces and in this manner it can be minimized by utilizing an effective lubricant.

Barreling also can develop in upsetting hot workpieces between cold dies.

The material close to the die surface cools quickly, while the remainder of workpiece remains moderately hot.

Thus the material at the top and bottom of the workpiece has higher barrier to deformation than the material at the center.

Because of this the central portion of the workpiece grows laterally to a more extent than at the ends.

Barreling from thermal impact can be decreased or removed by making use of heated dies.

Thermal barriers, for eg. glass cloth, at the die workpiece interfaces also can be used for this reason.

What is cogging?

Cogging (also called drawing out) is fundamentally an open-die forging operation in which the thickness of a bar is diminished by successive forging steps (bites) at specific intervals.

The thickness of bars and rings can be decreased by comparable open-die forging techniques.

cogging

Steps in cogging operation

Because the contact region between the die and the workpiece is little , a long section of a bar can be decreased in thickness without need of enormous forces or heavy machinery.

Black smiths perform such operations with a hammer and an anvil, using hot pieces of metal.

Average items are iron fences of different designs.

Note that cogging can be a harsh substitute for moving operations.

Cogging of bigger workpieces typically is finished by utilizing mechanized equipment and computer controls in which lateral and vertical movements are facilitated to create the ideal part.

What is impression die forging?

In impression-die forging, the workpiece takes the shape of the die cavity when it is forged between two shaped dies.

Impression die forging

Steps in impression die forging

This cycle generally is done at raised temperatures to lower the needed forces and to attain improved ductility in the workpiece.

What is closed die forging?

In closed-die forging, flash can’t form (so the term flashless forging), and the workpiece completely fills the die cavity.

Because of this the forging pressure is exceptionally high, and exact control of
the blank volume and proper die design are important to create a forging with the ideal dimensional tolerances.

Undersized blanks save the complete filling of the die cavity; conversely, oversized blanks generate too much pressures and may cause dies to fail prematurely or the machine to jam.

What are the steps of forging process?

  1. Set up slug, billet, or preform by processes such as shearing (cropping), sawing, or cutting off. If necessity, then clean the surfaces by means such as shot blasting.
  2. For hot forging, heat the workpiece in an appropriate furnace and then, if necessary descale it with a wire brush, water jet, steam, or by scraping.

There may be some descaling also from the starting stages of forging, when the scale (which is brittle) falls off during deformation.

  1. For hot forging, preheat and lubricate the dies; for cold forging, lubricate the blank.
  2. Forge the billet in suitable dies and in the appropriate arrangement. If necessities eliminate any excess material (such as flash) with the help of trimming, machining, or grinding.
  3. Clean the forging, check its dimensions, and (if necessary) machine it to final dimensions and specified tolerances.
  4. Perform extra operation, for eg. straightening and heat treating (for improved mechanical properties). Also, perform any finishing operations that may be need, like as machining and grinding.
  5. Inspect the forging for any outside and inside defects.

Forging Handbook pdf:

Frequently Asked Questions:

What is the process of forging?

In forging, the deformation of metal and alloys are done in the specified shapes by application of repeated blows from a hammer.

What are the types of forging?

The types of forging are as follows:

Hand Forging.

Open Die Forging.

Impression Die Forging.

Closed Die Forging.

What is hand forging?

The material spreads laterally under the action of the compressive forces due to hammer blows.
Cracks would be developed on brittle material like cast iron from the blows of hammer and hence cannot be forged.
An ordinary blacksmith uses an open-hearth using coke (or sometimes steam coal) as fuel for heating the metal and when it has become red-hot, blacksmith’s assistant (called striker on hammer man) uses a hand held hammer to deliver blows on the metal piece while the blacksmith holds it on an anvil and manipulates the metal piece with a pair of tongs.
Small forgings and small quantity production is possible through this process.
This process is also known as hand forging.

What is open and closed forging?

Open Forging:

Open-die forging is one of the simplest forging operation.

Although most open-die forgings typically weigh 15 to 500 kg (30 to 1000 lb), forgings of 300 tons have also been made.

Part sizes may range from very little (the size of nails, pins, and bolts) to enormous (up to 23 m (75 ft), long shafts for transport propellers).

Open-die forging can be depicted by a solid workpiece put between two flat dies and decrease in height by compacting it so this process is also called as upsetting or flat-die forging.

Closed Forging:

In closed-die forging, flash can’t form (so the term flashless forging), and the workpiece completely fills the die cavity.

Because of this the forging pressure is exceptionally high, and exact control of
the blank volume and proper die design are important to create a forging with the ideal dimensional tolerances.

Undersized blanks save the complete filling of the die cavity; conversely, oversized blanks generate too much pressures and may cause dies to fail prematurely or the machine to jam.

What is hot forging?

Hot forging requires lower forces, but the dimensional accuracy and surface finish of the parts are not as good as in cold forging.

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