19.1.
Bulk deformation processes are important because they can produce strong, high-
quality parts, improve mechanical properties, reduce waste, and are cost-effective for
making large quantities of metal products.
19.2.
The four basic bulk deformation processes are:
1. Rolling
2. Forging
3. Extrusion
4. Wire (or bar) drawing
19.3.
Rolling is a process where metal is passed through rollers to reduce its thickness or to
give it a desired shape.
19.4.
• Bloom: A large, square-shaped piece of metal (more than 150 mm or 6 in
square).
• Slab: A flat, rectangular metal piece made from a bloom.
• Billet: A smaller, square or round piece of metal (less than 150 mm or 6 in
square) made from a bloom.
19.5.
Some products made by rolling mills include:
• Plates
• Sheets
• Beams
• Rails
• Bars
• Rods
19.6.
Draft is the difference between the starting thickness and the final thickness of the
metal after rolling.
19.7.
Sticking happens in hot rolling when the hot metal sticks to the rolls, causing defects
and operational issues.
19.8.
Ways to reduce force in flat rolling:
• Use hot rolling
• Apply lubricants
• Use smaller diameter rolls
• Make multiple passes with small reductions
19.9.
A two-high rolling mill has two rolls, one on top and one at the bottom.
19.10.
A reversing mill allows the rolls to rotate in both directions so the metal can be passed
back and forth through the rolls.
19.11.
Other bulk forming processes using rolls:
• Ring rolling
• Thread rolling
• Roll forging
19.12.
Forging is a process where metal is shaped by compressive forces using a hammer or
press.
19.13.
Three types of forging by how much the work is constrained:
1. Open-die forging
2. Impression-die forging
3. Flashless forging
19.14.
Flash is desirable in impression-die forging because it helps fill the die cavity
completely and removes extra material easily.
19.15.
Trimming is the process of cutting off the excess flash from a forged part after it has
cooled.
19.16.
Two basic types of forging equipment:
1. Hammers
2. Presses
19.17.
Isothermal forging is done by keeping both the workpiece and the die at the same high
temperature to improve metal flow and reduce stresses.
19.18.
Extrusion is a process where metal is forced through a die to create objects with a fixed
cross-sectional shape.
19.19.
• Direct extrusion: Metal is pushed in the same direction as the ram movement.
• Indirect extrusion: The die moves toward the stationary metal billet.
19.20.
Products made by extrusion:
• Aluminum window frames
• Pipes
• Tubes
• Rods
• Bars
19.21.
In direct extrusion, friction occurs between the billet and the container walls, increasing
the ram force. In indirect extrusion, the billet doesn't move against the walls, so there's
less friction.
19.22.
Centerburst defects in extrusion and roll piercing both involve cracks forming inside
the material due to high tensile stresses at the center.
19.23.
• Wire drawing: Reducing the diameter of a wire by pulling it through a die.
• Bar drawing: Similar process, but for thicker bars.
19.24.
Although the metal is pulled (tensile stress), the die squeezes it from the sides
(compressive stress), improving shape control.
19.25.
The drawing stress must be lower than the metal’s yield strength to avoid breaking the
workpiece.
19.26. (Video)
Forged parts perform better than cast parts because forging aligns the grain structure
along the shape of the part, increasing strength and toughness.
19.27. (Video)
Accessory tools used in open-die forging:
• Mandrels
• Swages
• Fuller tools
• Tongs
• Hammers
19.28. (Video)
Performing operations discussed:
• Upsetting
• Drawing out
• Punching
• Bending
• Flattening
