1. Principle of the process Design For Manufacturing (DFM)
Metal forming
Principle of the process
Structure
Process modeling
Defects, Pros and Cons
Design For Manufacturing (DFM)
Process variation
Module 8 d

2. Cold, warm, hot
Module 8

3. Cold Working Performed at room temperature or slightly above
Many cold forming processes are used in mass production operations
Minimum or no machining usually required
These operations are near net shape or net shape processes

4. Advantages of Cold Forming
Better accuracy, closer tolerances
Better surface finish
Strain hardening increases strength and hardness
Grain flow during deformation can cause desirable directional properties in product
No heating of work required

5. Disadvantages of Cold Forming
Higher forces and power required for deformation
Surfaces of starting work must be free of scale and dirt
Decreased ductility and increased strain hardening limit the amount of forming that can be done
In some cases, metal must be annealed before further deformation can be accomplished
In other cases, metal is simply not ductile enough to be cold worked

6. Warm Working
Performed at temperatures above room temperature, but below recrystallization temperature
Occurs in the range from 0.3Tm to 0.5Tm, where Tm = melting point (absolute temperature) for metal

7. Advantages & Disadvantages of Warm Working
Lower forces and power than in cold working
More intricate work geometries possible
Need for annealing may be reduced or eliminated
Disadvantage
Work piece must be heated

8. Hot Working
Deformation at temperatures above the recrystallization temperature
Occurs in the range from 0.5Tm to 0.75Tm
Capability for substantial plastic deformation - far more than is possible with cold working or warm working. This is because
Strength coefficient (K) is substantially less than at room temperature
Strain hardening exponent (n) is zero (theoretically)
Ductility is significantly increased

9. Advantages of Hot Working
Work part shape can be significantly altered
Lower forces and power required
Metals that usually fracture in cold working can be hot formed
No strengthening of part occurs from work hardening
Advantageous in cases when part is to be subsequently processed by cold forming

10. Disadvantages of Hot Working
Lower dimensional accuracy
Higher thermal energy needed to heat the work piece
Work surface oxidation (formation of scale)
Thus, poorer surface finish
Higher temperature decreases tool life of dies and rolls

11. Principle of the process Design For Manufacturing (DFM)
Metal forming:
Rolling
Principle of the process
Structure
Process modeling
Defects, Pros and Cons
Design For Manufacturing (DFM)
Process variation
Module 8 d

12. Rolling Mill Configurations
(a) Two-high, (b) three-high, (c) four-high

13. Rolling Mill Configurations
(d) Cluster mill, (e) tandem rolling mill

14. Thread Rolling
Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies
Important process for mass producing bolts and screws
Performed by cold working in thread rolling machines
Advantages over thread cutting (machining):
Higher production rates
Better material utilization
Stronger threads and better fatigue resistance

15. Thread Rolling
(1) Start of cycle, (2) end of cycle