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Forging Processes

Introduction

Forging dates back to ancient times and was associated with the village blacksmith.  Virtually all ductile metals may be forged by first preheating the work piece to a forging temperature.  The work piece can be a billet, a wrought bar, a cast or sintered ingot etc.  The forging process can then be completed by hammering the work piece to the desired shape.

Forging has a marked beneficial effect on the metals being shaped.   Their toughness and strength are improved because the process results in a beneficial orientation of the metal grain structure.  The repeated hot working causes the metal to become more dense and the grain "flow lines" to follow the contour of the final component.

There are a number of variations of the forging process a number are listed below.

1) Open Die/hammer or smith forging
2) Drop forging.(closed die)
3) Press forging
4) Upset forging
5) Swaging
6)Roll forging.

Open Die Forging

Open die (smith forgings) are made by using steam or air hammers or presses in conjunction with blacksmith tools or flat type dies.  There is little lateral confinement of the work piece.  The desired shape is obtained by manipulating the workpiece between blows.

This process employs low cost tooling, is relatively simple, but has less control in determining grain flow, mechanical properties and dimensions than other forging methods.  This process can only be carried out by skilled operators.

With this process only parts of simple shape can be made.  However depending on the size of he hammer used forgings of up to 90 te can be made.

Closed Die Forging

This process is based on hammering the work pieces into into the desired shape by means of closing dies. The hammering or pressing is performed, respectively, by a mechanical or hydraulic press.  Small and medium sized forgings are generally made in presses ranging in capacity from 500 to 10000 te.

Closed die forgings have good dimensional accuracy, with improved mechanical properties compared to open die forgings.   The process has good reproducibility and rapid production rates are possible.  The initial cost of tooling is very high.

Closed die forging can be used to produce parts from a few grammes to 100 kg.

Press Forging

In this process a slow squeezing action is used to form the metal.   The slow squeezing action penetrates the entire workpiece allowing the process to be used for the forging of large objects.  Press forges are made in sizes of up to 50,000 te.   Upt to 15000 te the presses may be mechanical or hydraulic.  The larger presses are always hydraulically powered.

Press forgings may use either open dies or closed dies.   the latter are used for smaller components which may be fully formed in one forging stroke.

This process may is used for the production of large objects train wheels and aircraft landing gear parts.

Upset Forging

This process uses barstock which is heated at the end which is being forged.   The bar is gripped in the fixed half of a die so that the length of material being forged projects.  The forging blow is delivered by a moving die. Simple shapes are produced in a single stage but more complicated shapes require multiple stages.

The process, if carried out cold is called cold heading

Swaging

Swaging is the forging method used for sizing, pointing, tapering, and otherwise shaping of the ends of rods or tubing.


Rolling

Rolling is the most important metal working process and can be performed on either hot or cold metal.  Material is passed between cast of forged steel rolls which compress it and move it forward.  Rolling is a economical method of deformation if metal is required in long lengths of uniform cross section.  Normal rolling achieves thickness reduction of about 2:1.

Slabs and blooms.

Ingots are first rolled into either rectangular slabs or square blooms which are produced as intermediate stages.  In this rolling process the ingots are passed through the plain rolls repeatedly in one direction and then in the reverse direction at each stage the rolls are brought closer together.  If square blooms are required the material is rotated through 90o between rolling operations.

Plates Strips and Sections.

The rolling process can be used to produce plates, strips and rolled sections including channels, Universal Columns angles sections etc.  The plates and strips are generally formed using plain rolls.   The rolls can bow which results in the plate being thicker at the middle.  The rolls can be backed up in four high roll arrangements. with additional rolls to reduce this tendency..

Planetary rolling mills

Small diameter rollers are more effective than large ones in conveying rolling forces to deforming metal. Planetary mills take advantage of this principle.   This process can achieve thickness reductions of up to 25:1



Links Providing information on forging
  1. Process Encyclopaedia..U.of Cambridge website- Useful information
  2. Metals about forging..Lots of Links
  3. Casting or Forgings SFSA: Article - Looking at the two options
  4. What are the types of forgings Forging Industry Association - Useful basic notes
  5. Library of Manufacturing;.. A complete document providing detailed info on all primary forming processes


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Last Updated 17/01/2008