1. FUNDAMENTALS OF METAL FORMING
SME Video - Forming Processes
Forging (vts_14)
Overview of Metal Forming
Material Behavior in Metal Forming
Flow Stress
Average Flow Stress
In-class Assignment
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

2. Metal Forming Plastic deformation
Tool (die) applies stresses that exceed the yield strength of the metal
Metal takes a shape determined by the geometry of the die
Cold working
Warm working
Hot working
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

3. Classification of Metal Forming Processes
Compressive stresses
Tensile stresses
Shear stresses
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

4. Material Properties in Metal Forming
Desirable material properties:
Low yield strength
High ductility
Properties are affected by temperature:
Ductility increases and yield strength decreases when work temperature is raised
Other factors:
Strain rate and friction
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

5. Basic Types of Deformation Processes
Bulk deformation
Rolling
Forging
Extrusion
Wire and bar drawing
Sheet metalworking
Bending
Deep drawing
Cutting
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

6. Bulk Deformation Processes - Rolling
Significant deformations and massive shape changes
"Bulk" refers to workparts with relatively low surface area‑to‑volume ratios
Starting work shapes
Cylindrical billets
Rectangular bars
rolling
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

7. Forging
forging
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

8. Extrusion
extrusion
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

9. Wire and Bar Drawing drawing
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

10. Sheet Metalworking Operations performed on metal sheets
High surface area‑to‑volume ratio
Often called pressworking
Presses perform these operations
Parts are called stampings
punch and die tooling
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

11. Sheet Metal Bending bending
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

12. Deep Drawing
drawing
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

13. Shearing of Sheet Metal
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

14. Material Behavior in Metal Forming
Plastic region of stress-strain curve
Material is plastically deformed
In plastic region, metal's behavior is expressed by the flow curve:
K = strength coefficient
n = strain hardening exponent
Flow curve based on true stress and true strain
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

15. Flow Stress Metals at room temperature
Strength increases when deforming
strain hardening
Flow stress = instantaneous value of stress required to continue deforming the material
Yield strength as a function of strain
Yf = flow stress
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

16. Average Flow Stress where = average flow stress
 = maximum strain during deformation process
Stress-strain curve
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

17. In-class Example
A metal has a flow curve with parameters: strength coefficient = 850 MPa and strain-hardening exponent = A tensile specimen of the metal with gage length = 100 mm is stretched to a length = 157 mm.
Determine the flow stress at the new length and the average flow stress that the metal has been subjected to during the deformation.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

18. SME Video
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

19. In-class Assignment
A particular metal has a flow curve with parameters: strength coefficient = 35,000 lb/in2 and strain-hardening exponent = A tensile specimen of the metal with gage length = 2.0 in is stretched to a length = 3.3 in.
Determine the flow stress at this new length and the average flow stress that the metal has been subjected to during deformation.
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

20. Production Scheduling Machine-Machine Diagrams
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

21. Time Permitting Content
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

22. Temperature in Metal Forming
K and n in the flow curve depend on temperature
Strength (K) and strain hardening (n) are reduced at higher temperatures
Ductility is increased at higher temperatures
Deformation operation can be accomplished with lower forces at elevated temperature
Three temperature ranges in metal forming:
Cold working
Warm working
Hot working
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

23. Cold Working Performed at room temperature Mass production operations
Near net shape or net shape processes
Advantages of Cold Forming
Better accuracy, closer tolerances
Better surface finish
Strain hardening and directional properties
Disadvantages of Cold Forming
High forces
Ductility and strain hardening limit process
Annealing for further deformation
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

24. Warm Working
Above room temperature but below recrystallization temperature
0.3Tm, where Tm = melting point (absolute temperature) for metal
Advantages of Warm Working
Lower forces than in cold working
More intricate work geometries possible
Need for annealing may be reduced
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

25. Hot Working
Deformation at temperatures above the recrystallization temperature
Recrystallization temperature = about one‑half of melting point on absolute scale (0.5Tm)
Capability for substantial plastic deformation
Why?
Strength coefficient (K) is substantially less
Strain hardening exponent (n) is zero (theoretically)
Ductility is significantly increased
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

26. Hot Working Advantages of Hot Working
Workpart shape can be significantly altered
Lower forces and power required
Use for metals that fracture in cold working
Strength properties are generally isotropic
No strengthening due to work hardening
Disadvantages of Hot Working
Lower dimensional accuracy
Higher energy (due to the thermal energy)
Work surface oxidation (scale)
Shorter tool life
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

27. Strain Rate Sensitivity
Theoretically, metal in hot working behaves like a perfectly plastic material
Strain hardening exponent n = 0
Additional phenomenon “Strain rate sensitivity” occurs at elevated temperatures
= true strain rate
v = velocity of the ram
h = instantaneous height of workpiece
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

28. Strain Rate Sensitivity
linear scale
log-log scale
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

29. Observations about Strain Rate Sensitivity
Increasing temperature decreases C and increases m
At room temperature, effect of strain rate is almost negligible
Flow curve is a good representation of material behavior
As temperature increases, strain rate becomes increasingly important in determining flow stress
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

30. Friction in Metal Forming
In most metal forming processes, friction is undesirable:
Metal flow is retarded
Forces and power are increased
Tooling wears faster
Friction and tool wear are more severe in hot working
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

31. Lubrication in Metal Forming
Metalworking lubricants are applied to tool‑work interface in many forming operations to reduce harmful effects of friction
Benefits:
Reduced sticking, forces, power, tool wear
Better surface finish
Removes heat from the tooling
©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e