1. DEFECTS IN
FORMED COMPONENTS
FREDY JAMES J.
13MY03
JABIN MATHEW BENJAMIN
13MY04
DEPT. OF METALLURGICAL ENGINEERING
PSG College of Technology
2. Forming or Metal forming
•Metalworking process
•Principle of plastic deformation
•Without adding or removing material
Processes:
a)Rolling
b)Forging
c)Extrusion
d)Drawing
a
b
c d
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3. ROLLING DEFECTS
Wavy edges
Result from concave roll bending and
Thinner along its edges than at its center
Cracks
Result from poor material ductility
Convex roll bending
Severe conditions cause centre split
Alligatoring
Defects in the original cast material
Only surface of work is deformed
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4. FORGING DEFECTS
Surface crack
Excessive working at low temperatures
High sulphur concentration
Crack at flash
More prevalent for thinner flash
Penetrates to work
Internal cracks
Secondary tensile stresses
Cold shuts
Lubricant residue
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5. DRAWING DEFECTS
Wrinkling in the flange
Occurs due to compressive buckling in the circumferential direction
(blank holding force should be sufficient to prevent buckling.
Wrinkling in the wall
Takes place when a wrinkled flange is drawn into the cup or if the
clearance is very large, resulting in a large suspended (unsupported)
region.
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6. Tearing
High tensile stresses that cause thinning and failure of the metal in the cup wall.
If the die has a sharp corner radius.
Earring
When the material is anisotropic
Varying properties in different directions.
Surface scratches
If the punch and die are not smooth
If the lubrication of the process is poor.
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7. Defects in Extrusions
Surface Cracking / Fir-tree cracking
High friction or speed.
Sticking of billet material on die land.
Material sticks, pressure increases, product stops and starts to move again.
produces circumferential cracks on surface, similar to a bamboo stem.(bambooing).
Internal Cracking/ Chevron cracking
Center of extrusion tends to develop cracks of various shapes.
Center-burst, and arrowhead
Center cracking:
Increases with increasing die angle.
Increases with impurities.
Decreases with increasing R and friction. 7
8. REFERENCE
George E. Dieter, Mechanical Metallurgy, SI Metric
Edition, 1988
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