lecture12 sheet metalworking

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

lecture12 sheet metalworking

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