PROCESSES FOR FORMING METAL

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
  

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.

Advantages

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.

Disadvantages

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.

Advantages

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.

Disadvantages

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.

Applications

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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