Metal Forming Process:Rolling, Forging, Extrusion, Principle, Applications

Metal Forming Process-Principle:It is a process in which the forces are applied on the material such that the stresses induced in the material are greater than the yield stress and less than the ultimate stress so that the plastic deformation produced in the material will be used for changing the shape of the component is called as Metal Forming Process.

Metal Forming Process-Rolling,Forging,Extrusion,Principle,Applications
Metal Forming Process-Rolling, Forging, Extrusion, Principle, Applications
               Table of Contents:

1.Metal Forming Process

1.1 Advantages of Metal Forming Process

2.Metal Rolling Process

2.1 Principle

2.2 How to Avoid Bending during Rolling?

2.3 Types of Rolling Mills

2.4  Rolling Applications

3.Forging Process

3.1  Classification of Forging Process

3.2  Applications of Forging Process

3.3  Hand Forging Process

3.4  Machine Forging

3.5  Hand Forging Operations

4.Extrusion Process

4.1  Principle

4.2  Types of Extrusion Process

4.3  Applications of Extrusion Process

Metal Forming Process undergoes two types of processes.

1.Cold working

Deforming the material at a temperature,  less than recrystallization temperature is called as cold working Process.

2.Hot  working

Deforming the Material at a temperature greater than or equal to recrystallization temperature is called as hot working Process.

Recrystallization temperature is the minimum temperature at which the grains start changing their behavior.

1.1 Advantages of Metal Forming Process:

  1. Wastage Of material will be minimum or sometimes zero.
  2. The grain orientation is possible.
  3. The material is converted from isotropic to anisotropic properties.
  4. In some material forming processes, increase in strength and hardness of the material will be taking place.
  5. The production rate is high.

This is the detailed explanation of Metal forming Process along with its advantages.

2.Metal Rolling (Metal Forming Process):

2.1 Principle: In Rolling operation, the material(metal strip) is compressed in between the two rotating rollers such that the stress responsible for changing of the shapes is only by compressive stress. This process reduces the actual thickness to the desired thickness.

Presence of friction between rollers and the strip is making it pull the strip into the rollers without applying any pulling and pushing.

Rolling is classified according to the temperature of the metal being rolled. If the temperature of the metal is above the recrystallization temperature, then the process is known as hot rolling. If the temperature of the metal is below the recrystallization temperature during rolling, then the process is known as cold rolling.

2.2 How to avoid bending during rolling?

To avoid the bending of the strip during rolling, the surface velocity of both the rollers must be equal.

I.e. Vtop roller = Vbottom roller

–>(πDN)top roller  = (πDN)bottom roller

–>(DN)top roller  = (DN)bottom roller

If Dt = Db =>Nt = Nb               {Here Dt=Dia of Top Roller & Db = Dia of bottom Roller}

To ensure that the contact area between the rollers and the strip at both the sides, the dia of both the sides must be same. hence RPM of both the rollers also will become the same.

2.3 Types of Rolling:

Metal Rolling is classified into 5 Types and they are as follows.

  1. Two High Rolling mill
  2. Three High Rolling mill
  3. Four High Rolling mill
  4. Cluster Rolling mill
  5. Tandem Rolling mill
Metal Rolling-Types of Rolling Mills
Metal Rolling-Types of Rolling Mills

The explanation of above metal rolling types was as follows.

1.Two High Rolling mill:

  • It consists of two rolling mills which are rotated in opposite directions to each other.
  • The material is to be passed in between these two rolling mills such that the compressive forces can changes its thickness from the original.

2.Three High Rolling mill:

  • Three Rolling mills are arranged one on the other in the vertical direction such that two metal strips can pass in between the rollers at a time and shape change(reduce their thickness)  takes place.
  • By this, productivity increases.

3.Four High Rolling mill:

  • Four Rolling mills are arranged one on the other in the vertical direction such that only one metal strip can pass in between the rollers and shape change(reduce their thickness)  takes place.
  • The Upper and lower rollers are just for support(Backup Rollers) whose diameter is bigger than the other two rollers are held in Vertical direction, one on the other and the material is to be passed in between the two small rollers and shape change takes place.
  • This type of rolling is applicable to the high thickness materials where high compressive forces are needed to reduce the thickness of the material.

4.Cluster Rolling Mill:

  • The material is to be passed through the two small rollers which are in support by Four backup rollers.
  • This type of rolling is applicable to the high thickness materials where high compressive forces are needed.

5.Tandem Rolling Mill:

  • In this type of rolling mill, the material is to be continuously passed through the pair of rollers so that we can obtain the desired shape and thickness.
  • Applicable to High thickness materials.


2.4 Rolling Applications/Products:

  • Rolling is used for making rods, hollow seamless tubes, etc.
  • By rolling process, Large length cross sections are produced
  • Bearings, Rings of turbines  and other machines are the products of rolling
  • It is used for mass production of threaded parts like bolts, screw etc.
  • Steel sheets and plates are made by the rolling process.
  • Cement Kilns are produced from rolling process only.
  • It is used in automotive industries for manufacturing various parts.

3.FORGING (Metal Forming) Process:

Forging is a Metal Forming Process in which the workpiece is heated to higher temperatures and is placed on the die(work region). Now, a large amount of compressive force is applied on to the workpiece with either similar die or hammers in a vertical direction so that the shape change(deformation) takes place.

In the forging process, the forces applied are either continuous or intermittent impact loads.

metal forming-metal forging Process
metal forming-metal forging Process

3.1 Forging is classified into various types.

1. According to the Temperature:

  1. Hot Forging
  2. Cold Forging

2.According to the arrangement of Die

  1. Open Die Forging
  2. Close Die Forging

3.According to the Forging equipment

  1. Smith forging
  2. Drop Forging
  3. Press Forging
  4. Machine Forging

3.2 Applications Of Forging Process:

  • Agriculture tools, Cutting tools, nails, machine parts spring, hook, screw, pin etc.
  • Furniture manufacturing.
  • Aircraft and missile product.
  • Building materials like a handle, bolt, hinge, etc.
  • Home appliance and military products.

3.3 HAND FORGING (Metal Forming Process):

Hand Forging is also called as Smithing or Blacksmithing. It is the simplest form of forging in which the metal to be heated to high temperatures in the fire of a forge, and then it is beaten into shape on a metal anvil with sledges or hammers in order to get the required shape.

hand forging Process
hand forging Process

Hand forging always uses drop hammer type because the continuous force due to the human hand is not sufficient to produce the deformation in the workpiece.

  • The workpiece is compressed between two flat or simple shaped dies.
  • It is Similar to compression test when the work part has a cylindrical cross-section and is compressed along its axis or its sides.
  • This Deformation operation reduces height and increases the diameter of the work or Cross section.

3.4 Machine forging Process:

In machine forging, because the force required is obtained from a machine, it is possible to use either continuous force application or intermittent impact load application known as drop hammer type.

4.Extrusion Process(Metal Forming Process):

4.1 Extrusion Principle:

  • Extrusion is a compression process in which the work metal is forced to flow through a die opening to produce a desired cross-sectional shape called as an Extrusion process.

In the extrusion process, the forces are applied on the raw material by using a RAM in a closed container such that stresses induced in the material is greater than the flow stress of the material.

As the behavior of the material is like a fluid, the material can flow through the small opening available in the container, taking the shape and size remains the same as that of opening.

Ex: Squeezing toothpaste out of a toothpaste tube.

4.2 Types of Extrusion Process:

1.Forward Extrusion

2.Backward Extrusion

1.Forward Extrusion:

In forward extrusion, the direction of movement of Ram and extruded component are in the same direction.

In the case of Forward extrusion, every point of raw material has to travel against the container wall friction for the extrusion to be taken place.

Hence, the force required for Forward Extrusion is higher than the Backward Extrusion.

Forward Extrusion Process
Forward Extrusion Process

2.Backward Extrusion:

In Backward extrusion, the direction of movement of Ram and extruded component are in the opposite direction.

In the case of Backward extrusion, the raw material can deform directly and the flow takes place through a die opening to change the shape of the component.

Hence, the force required for backward Extrusion is very much lower than Forward Extrusion.

backward extrusion process
backward extrusion process

4.3 Applications of Extrusion Process:

  • Extrusion is widely used in the production of hollow pipes and tubes.
  • Aluminum extrusion is used in structural work in many industries.
  • The extrusion process is used to produce frames, windows, doors, etc. in automotive industries.
  • Plastic objects can be produced widely by an Extrusion process.

This is the explanation of the Metal Forming Process in a detailed way. If you have any doubts, you can feel free to ask from the comments section.


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