Fundamentals of metal working

Fundamentals of metal or mechanical working.
Reference- Mechanical Metallurgy by George Dieter

1. A presentation on FUNDAMENTALS OF METAL WORKING Submitted by: Raghav Saxena 2014PMT5403 Submitted to: Dr. V K Sharma Associate Professor MNIT,Jaipur Department of Metallurgical & Materials Engineering

2. What is Metal Working ? Metalworking  is the process of  working  with  metals  to create individual parts, assemblies, or large-scale structures.

3. Useful shapes in metal can be generated in two basic ways: By plastic deformation process i.e. Metal Forming Process (Example- Forging, Rolling, Extrusion, etc.) By metal removal or machining process (Example- Shaping, milling, etc.)

4. Classification of Metal working processes on the basis of the type of forces applied: Direct compression type processes Indirect compression processes Tension type processes Bending processes Shearing processes

5. Direct compression type processes: Force is applied to the surface of the work piece, and the metal flows at right angle to the direction of the compression. Examples: Forging, Rolling, etc.

6. Indirect compression processes: The primarily applied forces are tensile, but the indirect compressive forces developed by the reaction of the work piece with the die reach high values. Examples: Wire Drawing, Tube Drawing, Extrusion, Deep Drawing, etc.

7. Tension type processes: The primary force for this type of process is Tension force. Example: Stretch Forming, etc.

8. Bending processes: This process involves the application of bending moments to the sheet. Example: Bending, etc.

9. Shearing processes: This process involves the application of shearing forces of sufficient magnitude to rupture the metal in the plane of shear. Example: Sheet metal operations like Blanking, Piercing, etc.

10. Factors affecting metal working: Flow stress Temperature Strain Rate Metallurgical Structure Friction Lubrication Composition

11. Flow stress: Flow stress is the true stress acting inside the material. It differs from engineering stress as it takes into account the changes in the dimensions of the work piece. To accurately predict the forming loads, we need accurate values of stresses i.e. flow stress. Flow curve is desirable to be drawn for actual working conditions as the operations involve large plastic strains.

12. Temperature: On the basis of temperature, forming processes are classified into Hot-working, Cold-working, & Warm-working operations. Hot working of metals is defined as deformation of metal above recrystallization temperature, so that recovery processes takes place simultaneously.

13. Cold Working of metals is defined as working of metals below recrystallization temperature, so that no recovery process is possible. Warm Working of metals is plastic deformation of metal at temperature above room temperature but below recrystallization temperature.

14. If a metal is cold worked, its strength increases & ductility decreases with increase in percentage cold worked. If a metal is hot worked, its strength decreases but ductility increases with increase in annealing temperature.

15. Strain Rate Effects: Flow stress of metal increases with strain rate. Temperature of the work piece is increased because of adiabatic heating. Improved lubrication at tool-metal interface.

16. Metallurgical Structure: The presence of preferred orientation causes anisotropy of mechanical properties. If the work piece is an alloy, the structure of other phases present inside the alloy may cause softening or hardening. Precipitation occurs with time & it changes the mechanical properties depending upon their nature. These alterations in mechanical properties ultimately changes flow stress.

17. Friction Friction  is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other . It changes the normal pressure distribution over a work piece & sometimes perform cold welding. In hot working, sticking friction (where there is no relative motion between work piece & tool) is a usual case.

18. Lubrication Extra forces can be avoided if we use proper lubrication. Cold welding & heating is controlled when there exists a lubrication film between the tool-job interface. It improves surface finish of the product & thus saving extra cost for finishing. Boundary lubricants with extreme pressure (EP) must be added to the fluid to form a boundary film at the interface.

19. Composition: The dependency of required load & mechanical properties undoubtedly depends of the composition of the job. Metal with different alloying elements shows an entirely different range of properties. To attain desired characteristics, proper composition of work piece must be selected with minimum amount of impurities.

20. Thank You