IUBAT- International University of Business Agriculture and Technology
Founded 1991 by Md. Alimullah Miyan
COLLEGE OF ENGINEERING AND TECHNOLOGY(CEAT)
Metal Forming
Course Title: Manufacturing Process
Course Code : MEC 237
Course Instructor: Dr. Md Rakibuzzaman
Fundamentals of Metal
Forming
Chapter 17
(Book: Fundamentals of Modern
Manufacturing by Mikell. P. Groover)
2
❖ Goals and Outcomes
▪ Overview of Metal Forming
▪ Material Behavior in Metal Forming
▪ Temperature in Metal Forming
3
Metal forming processes
✔ Metal forming: Large set of manufacturing processes in
which the material is deformed plastically to take the
shape of the die geometry.
✔ The tools used for such deformation are called die,
punch etc. depending on the type of the process.
✔ Deformation results from the use of a tool, usually called
a die in metal forming, which applies stresses that
exceed the yield strength of the metal. The metal
therefore deforms to take a shape determined by the
geometry of the die.
✔ Plastic deformation: Stresses beyond yield strength of
the workpiece material is required.
Metal forming processes
✔ Stresses applied to plastically deform the metal are usually
compressive.
✔ However, some forming processes stretch the metal, while
others bend the metal and still others apply shear stresses
to the metal.
✔ To be successfully formed, a metal must possess certain
properties. Desirable properties include low yield strength
and high ductility.
✔ These properties are affected by temperature.
✔ Ductility is increased and yield strength is reduced when
work temperature is raised.
✔ The effect of temperature gives rise to distinctions
between cold working, warm working and hot working.
✔ Strain rate and friction are additional factors that affect
performance in metal forming.
Bulk deformation processes
▪ Bulk forming: It is a severe deformation process resulting
in massive shape change. The surface area-to-volume of
the work is relatively small. Mostly done in hot working
conditions.
▪ Starting work shapes for these processes include
cylindrical billets and rectangular bars.
Rolling Forging Extrusion Wire drawing
Rolling
▪ In this process, the workpiece in the form of slab or plate
is plate is compressed between rotating rolls in the
thickness direction, so that the thickness is reduced.
▪ The rotating rolls draw the slab into the gap and
compresses it. The final product is the form of sheet.
Forging
▪ The workpiece is compressed between two opposing
dies containing shape contours.
▪ The die shapes are imparted into the final part.
▪ Forging is traditionally a hot working process, but many
types of forging are performed cold.
Extrusion
▪ The workpiece is compressed or pushed into the die
opening to take the shape of the die hole as its cross
section.
Wire or rod drawing
▪ Similar to extrusion, except that the workpiece is pulled
through the die opening to take the cross section.
Sheet forming processes
▪ Sheet metal forming involves forming and cutting
operations performed on metal sheets, strips, and coils.
▪ The surface area–to–volume ratio of the starting metal is
high. Tools include punch, die that are used to deform
the sheets.
Bending Deep drawing Shearing
Cold working
▪ Cold working is metal forming performed at room
temperature or slightly above.
✔ Advantages:
1) No heating is required
2) Greater accuracy, meaning closer tolerances can be achieved
3) Better surface finish is obtained
4) Higher strength and hardness of the part due to strain
hardening
5) Directional properties can be imparted
6) Products process better reproducibility and interchangeability.
7) Contamination problems are almost negligible.
Cold working
✔ Disadvantages:
1) Higher forces and power are required to perform the
operation
2) Care must be taken to ensure that the surfaces of the
starting workpiece are free of scale and dirt
3) Less ductility is available
4) Strain hardening occurs
5) Undesirable residual stresses may be produced
Warm working
▪ Plastic deformation properties are normally enhanced
by increasing workpiece temperature, forming
operations are sometimes performed at temperatures
somewhat above room temperature but below the
recrystallization temperature
✔ Advantages: (compare to cold forming)
1) Lower forces and power
2) More intricate work geometries possible
3) Need for annealing may be reduced
Warm working
✔ Advantages: (Compared to hot forming)
1) Lesser amount of heat energy requirement
2) Better precision of components
3) Lesser scaling on parts
4) Lesser decarburization of parts
5) Better dimensional control
6) Better surface finish
7) Lesser thermal shock on tooling.
8) Lesser thermal fatigue to tooling, and so greater life of
tooling.
Hot working
▪ Hot working involves deformation at temperatures
above the recrystallization temperature.
✔ Advantages: (compare to cold forming)
1) The shape of the work part can be significantly altered
2) Lower forces and power are required to deform the metal
3) Metals that usually fracture in cold working can be hot
formed
4) No strengthening of the part occurs from work hardening
5) No residual strength in the material.
Hot working
✔ Disadvantages:
1) Lower dimensional accuracy
2) Higher total energy required
3) Work surface oxidation
4) Poorer surface finish
5) Shorter tool life
