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8/10/2019 Lecture12 Sheet Metalworking
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Sheet Metalworking Processes
Cutting Bending
Stretch Forming
Deep Drawing
Stretch Drawing (Stamping)
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Sheet Metalworking Materials
Steels
Low carbon steels (
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Automotive Steels
Types Yield(MPa) Tensile(MPa)El. (%) Examples
Mild Steels
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Composition and Strengthening Mechanism
Steel
Type
HSS Grade
Family
Alloying
Additions
Major
Constituents
Minor
Phases
Strength
Mechanisms
C-Mn CHSS Mn, P, Si + Fe3C N/A SS+GR
HSLA CHSS Ti, Nb, P,
Mn, Si, B
+ Fe3C TiN, TiC,
NbC
SS+GR+
Precipitation
hard.
Dual
Phase
AHSS Mn, Si, Nb,
V
+
martensite
N/A SS+GR+
Transformation
strengthening
TRIP AHSS Mn, Si, Al,
Cr, Mo, Ni
+ bainite +
austenite
N/A SS+GR+
Transformation
strengthening
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Relevant Material Properties
Discontinuous Yielding and Lders Lines YS, TS, el., K, n, and r
r value is used to express the anisotropy of materials
Planar anisotropy
Normal anisotropy
t
wr
4
2 45900 rrrrm
4
2 45900 rrrr
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Relevant Material Properties
Strain hardening exponent nindicates the ductility of the material,because u= n.
Tensile strength can be calculated as
n
e
n
KTS
where e is the base of the natural logrithm, e = 2.7183.
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Shearing
Shearing force
hle
nKChlTSCP
n
s
11 )(
where C1= 0.7 on average
hPCE ss 2
where C2= 0.5 for soft material,
0.35 for hard material.
Shearing energy
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Many Types of Operations
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Bending
Neutral line depends onRb/hratio:Rb/h>2 neutral line at 1/2 h,
Rb/h
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Springback
Elastic recovery of part after
bending is complete
Factors that make it worse:
Thinner sheet Higher Strength material
3
2.02.0 431
Eh
R
Eh
R
R
R bb
f
b
h
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Compensating for Springback
Overbend the part
Use a smaller radius
die
Elevate temperature
Stretch Bending
Repeat Bending
Forge Bend
Use a thicker sheet to
start with
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Stretch Forming
a. Single die required, low production rate
b. Male and female dies needed, high production rate
c. embossing
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Deep Drawing
Blank is allowed to draw into
the die, and thickness is
normally unchanged.
Limiting Drawing Ratio (LDR)
LDR=d0max/ Dp Constraint of blank-holder
gives improved process control
and quality
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Forming Limit Diagram (FLD)
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Experimental Strain Analysis
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Experimental Strain Analysis
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Stamping of Auto Body Parts
(Auto/Steel Partnership Publication, 1998)
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Stamping Press
Main Shaft Main Bushing
Linkage
Slide
Thermistor
StrainGage
Accelerometer
Binder Ring
Blank
Main Shaft Main Bushing
Linkage
Slide
Thermocouple
StrainGage
Accelerometer
Binder Ring
Blank
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Stamping Failure Diagnosis using Grid Marks
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Hydroforming
Before Pressure
Die OpenDieClosing
1stPressure
Stage
Die Closing
2ndPressure
StageDie Closed
(a)(b)
(c)
(d)
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Automotive Structural Part
Hydroformed Dodge Dakota
Radiator EnclosureStamped Dodge Dakota
Radiator Enclosure
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Stamped Radiator Closure Hydroformed Radiator Closure
17 components
36.4 Ibs/16.5 kg
8 components ( -9 )
25.4 lbs/11.5 kg (-11 Ibs, -30%)
Part Consolidation and Weight Reduction
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Forming of Tailor Welded Blanks
6ton-6ton 9.6ton-2.4ton
0.70mm0.66mm
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TWB Applications
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Material Type
HSLA & Ultra HS Steel
Lower E Materials
Aluminum
Mild Steel
Galvanized Steel
Stainless Steel