Lecture notes on metal forming for first year undergraduate students

In the first year of manufacturing processes students study about the metal forming process.

1. Manufacturing Processes Metal forming Dr. Roshan Kumar Hota Email: [email protected] Phone: [phone] Website: roshanrobotics.com 1

2. Bulk deformation

3. Sheet metalworking

4. Material behaviour in metal forming Flow curve Flow stress is defined as the instantaneous value of stress required to continue deforming the material– to keep the material “flowing”. It is the yield strength of the metal as a function of strain, which can be expressed as: In the plastic region the metal’s behaviour is expressed by the flow-curve:

5. Material behaviour in metal forming Average flow-stress is the average value of stress over the stress-strain curve from the beginning of the strain to the final value that occurs during deformation.

6. Temperature in metal forming Cold working/ cold forming : metal forming performed at room temperature or slightly above. Greater accuracy, better surface finish, higher strength, grain flow, savings on fuel. Higher forces and power required, care must be taken to ensure that the surface of the starting material is free from scale and dirt, ductility and strain hardening limit the amount of forming that can be done to the part. Warm working : Forming operations performed above the room temperature and below the recrystallization temperature. Plastic deformation properties are enhanced by increasing the workpiece temperature. Dividing line between cold working and warm working.

7. Temperature in metal forming Hot working/ hot forming : deformations at temperatures above the recrystallization temperature. Recrystallization temperature is about one half of its melting point on the absolute scale. Deformation itself generates heat. 0.5Tm to 0.75Tm. Capability to produce substantial plastic deformation. Significantly smaller flow coefficient. Shape of the workpart can be significantly altered, lower forces and power required to deform the material, metals that usually fracture in cold working can be hot formed, strength properties are usually isotropic, absence of oriented grain structure, no strengthening of part from work hardening. Isothermal forming : forming operations carried out in such a way as to eliminate surface cooling and the resulting thermal gradients in the workpart . It is accomplished by pre-heating the tools to the same temperature as the workpart . Hot hardness: highly alloyed steels, many titanium alloys, and high-temperature nickel alloys.

8. Strain rate sensitivity Perfectly plastic material. Strain rate is defined as:

9. Strain rate sensitivity

10. Typical values

11. Rolling Flat rolling: Shape rolling: work is deformed into a contoured cross-section. I-beams, L-beams, and U-channels, rails. The process is accomplished by passing the work through rolls that have the reverse of the desired shape.

12. Rolling mills