Forging processes – open, impression, and closed die forging – forging operations – hot and cold working of metals Metal rolling – types of rolling – flat strip rolling – shape rolling activities – rolled part defects Rod and wire drawing principles – tube drawing principles – extrusion principles – types – hot and cold extrusion

Metal Forming in Bulk

  • Rolling – a compression procedure that uses two rolls to reduce the thickness of a slab.
  • Forging is a compression process that takes place between two opposing dies.
  • Extrusion is a compression technique in which metal is forced through a die aperture.
  • Pulling a wire or bar through a die aperture is known as drawing.

Metal forming is classed as a bulk deformation process, which is characterised by substantial deformations and large shape changes, as well as a short surface area-to-volume ratio.

  • Forging
  • Extrusion
  • Rolling
    Metal forming process: Hot working and Cold working

Wire and bar drawing

sheet metalworking processes. Because the initial metal’s surface area-to-volume ratio is high, this ratio can be used to identify bulk deformation from sheet metal operations.

  • Bending operations
  • Deep or cup drawing
  • Shearing processes
  • Miscellaneous

Hot Working (0.5 – 0.75Tm)

  • Hot working is the plastic deformation of metal at a temperature higher than the recrystallization temperature.
  • When the atoms of metal reach a specific higher energy level under the influence of heat and force, new crystals begin to form. Recrystallization is the term for this process.
  • When this happens, the original grain structure established by previously performed mechanical work is no longer there, and new strain-free crystals are created instead.
  • The temperature at which hot working is accomplished is crucial, because any residual heat in the material after working promotes grain growth, resulting in poor mechanical characteristics.


  1. Power requirement: Deformation requires less forces and, as a result, less power.
  2. Materials to be made: All ductile and brittle materials can be produced.
  3. Material properties: The material has no strain hardening and no residual stresses.
  4. Distortion amount: Greater ductility of the material is available, allowing for more deformation. Bulky jobs can be completed.
  5. Product quality: A favourable grain size is obtained, resulting in improved material mechanical characteristics.


  1. Energy requirement: Heat energy is required and so is pricey.
  2. Limited materials: Hot working is not possible with materials that become brittle at higher temperatures.
  3. Loss of property: Material is lost as a result of scale creation. Surface finish: Due to scale formation, the material’s surface finish is poor.
  4. Surface finish: Due to scale formation, the material’s surface finish is poor.
  5. Surface decarburization: The surface of ferrous metals is decarburized, and the surface hardness may be poor.
  6. Quality of the product: Parts have low precision and dimensional control.
  7. Reproducibility: Parts’ interchangeability and repeatability are poor.
  8. Tools and equipment: Tooling and equipment have a shorter lifespan.

Cold working(less than 0.3T m)

  • Cold working is the process of plastically deforming metals at room temperature (i.e., below the recrystallization temperature).
  • Slightly high temperatures can be used to promote ductility while reducing strength in some circumstances.
  • Because cold working has a number of specific advantages, numerous cold-working procedures have become increasingly significant.
  • They’ve been more popular in recent years as a result of significant advancements, and this trend appears to be set to continue.


  1. Cost: Because no heating is necessary, chilly work is less expensive.
  2. Surface quality: The metal has no scale formation. The product does not need to be cleaned after processing, and the surface finish is improved.
  3. Product quality: Because of the improved dimensional control, no secondary machining operation is usually required.
  4. Product reproducibility: The parts are more interchangeable and reproducible.
  5. Product characteristics: Although deformation requires a lot of energy, some of that energy is used to improve the strength, fatigue, and wear qualities of items.
  6. Material characteristics: It is possible to impart directional qualities to a material.
  7. Material quality: The surface is not decarburized. There is no material loss and only minor contamination issues.
  8. Handling issues: Cold metal has almost no handling issues.


  1. Limited resources: Cold working is not possible with brittle materials.
  2. Limited-edition items: Parts that are large and bulky are difficult to shape. Hardening of the strain occurs (may require intermediate annealing)
  3. Limited deformation: At room temperature, metals are less ductile, allowing for less distortion.
  4. Power requirement: Deformation necessitates higher forces.
  5. Capacity of equipment: More powerful and heavier equipment is necessary.
  6. Surface quality: Metal surfaces must be clean and scale-free prior to deformation.
  7. Product quality: The component may contain undesired residual stresses.


In general, cold forming procedures are better suited to tiny and medium-sized items that will be produced in high quantities:

To recoup the increased cost of the requisite equipment and tooling, a large volume of manufacturing is required.

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