Lecture 5 Sheet Metal Forming

8/14/2019 Lecture 5 Sheet Metal Forming

1/55

Sheet Metal Forming

2.810 Fall 2008

Professor Tim Gutowski

Minoan gold pendant of bees encircling the Sun, showing theuse of granulation, from a tomb at Mallia, 17th century BC. In

the Archaeological Museum, Irklion, Crete.


2/55

Readings1. Sheet Metal Forming Ch. 16 Kalpakjian

2. Design for Sheetmetal Working, Ch. 9Boothroyd, Dewhurst and Knight


3/55

Historical Note;

Sheet metal stamping was developed as a mass

production technology for the production of bicyclesaround the 1890s. This technology played animportant role in making the system of interchangeableparts economical (perhaps for the first time).


4/55

Steps in making Hub Steps in Sprocket making

Ref Hounshell


5/55

Stress Strain diagram materialsselection

E

y

Y


6/55

Basic Sheet Forming Processes(from http://www.menet.umn.edu/~klamecki/Forming/mainforming.html)

Shearing

Bending

Drawing


7/55

Shear and corner press


8/55

Brake press


9/55

Finger press

LMP Shop Video


10/55

Shearing Operation ForceRequirement

Die

SheetPunch TD

Part or slug

F = 0.7 T L (UTS)

T = Sheet ThicknessL = Total length ShearedUTS = Ultimate Tensile Strength of material


11/55

Yield Criteria

Y

Y/2

Tresca Mises

max = (2/3)1/2Y = 0.82Y max = (1/2) Y


12/55

Schematic of a Blanked Edge


13/55

bending strain


14/55

Stress distribution through thethickness of the part

yY

Y

-Y

Y

Elastic Elastic-plastic

Resulting Moment, M = 2Y (b h/2) h/4 = Ybh2/4

h

-Y

Fully plastic


15/55

Balance external and internal moments

h

-Y

Fully plastic

F

F/2 F/2

Ybh2/4 = FL/4

F = bh2Y/L

L


16/55

Bending Force Requirement

PunchWorkpiece T

Die

W

Force

T = Sheet ThicknessW = Width of Die OpeningL = Total length of bend

(into the page)UTS = Ultimate TensileStrength of material

)(2

UTSW

LTF=

Show Bending Video


17/55

Bending Moment Curvature

M

1/

EI

1/Y

MY

Loading

EI Unloading

1/R01/R1


18/55

Springback


19/55

Elastic Springback Analysis

L

x

y

h

b

1. Assume plane sections remain plane:y = - y/ (1)

2. Assume elastic-plastic behavior for material

M

= 1/K

My

E

y

Y = E


20/55

M

1/

EI

1/Y

MY

Loading

EI Unloading

1/R01/R1

3. We want to construct the followingBending Moment M vs. curvature 1/ curve

Springback is measured as 1/R0 1/R1 (2)Permanent set is

1/R1


21/55

4. Stress distribution through the thickness of the beam

yY

Y

-Y

h

-Y

Y

Elastic Elastic-plastic Fully plastic


22/55

5. M = A y dA

Elastic region

At the onset of plastic behavior= - y/E = - h/2E = -Y (4)

Y

This occurs at1/= 2Y / hE = 1/Y (5)

d

y

dAb

hdy

Substitution into eqn (3) gives us the moment at on-set of

yield, MYMY= - EI/Y= EI 2Y / hE = 2IY/h (6)

After this point, the M vs 1/r curve starts to bend over.

Note from M=0 to M=MY the curve is linear.

EIdAyEydAM ===

2

(3)


23/55

In the elastic plastic region yY

Y

Ybyyh

Yb

yb

y

YyYb

Ybydy

y

yYbydyybdyM

YY

y

Y

h

y

h

y

y

Y

Y

Y

Y

Y

222

0

32/

2

2/

0

3

2)

4(

32

22

22

+=

+=

+==

=

22

2/3

1

14 h

y

Y

bh

MY

Note atyY=h/2, you get on-set at yield, M = MYAnd atyY=0, you get fully plastic moment, M = 3/2 MY

(7)


24/55

To write this in terms ofMvs 1/ rather than M vsyY, notethat the yield curvature (1/)

Y

can be written as (see eqn (1))

2/

1

h

Y

Y

= (8)

Where Y is the strain at yield. Also since the strain atyYis -Y, we can write

Y

Y

y

=1

(9)

Combining (8) and (9) gives

1

)1(

2/

YY

h

y= (10)


25/55

Substitution into (7) gives the result we seek:

=

2

1)1(

311

23

Y

YMM (11)

M

1/

EI

1/Y

MY

Loading

EI Unloading

1/R01/R1

Eqn(11)

Elastic unloading curve

= 1

11

)1( R

M

M Y

Y

(12)


26/55

Now, eqns (12) and (13) intersect at 1/= 1/R0

Hence,

=

2

010 1

)1(

3

11

2

311

)1( RM

RR

M YY

Y

Y

Rewriting and using 1/= 2Y / hE, we get

3

2

0

1043

11

=

hEY

RhE

Y

RR (13)


27/55


28/55

tension

compression

Pure Bending

Bending & Stretching


29/55

Stretch Forming

Loading Pre-stretching

Wrapping Release

* source: http://www.cyrilbath.com/sheet_process.html


30/55

Stretch forming

F = (YS + UTS)/2 * AF = stretch forming force (lbs)YS = material yield strength (psi)UTS = ultimate tensile strength of the material (psi)

A = Cross-sectional area of the workpiece (in2)


31/55

Auto body panels

10 - 11 panels3 to 5 dies each

~$0.5M each ~$20M investment


32/55

Tooling for Automotive Stamping


33/55

Forming Limit Diagram


34/55

Material SelectionMaterial selection is critical in both product and process design.Formability is the central material property.

This property must be balanced with other product and processconsiderations such as strength, weight, cost, and corrosionresistance.

Auto vs. Aerospace Example

Auto Body Panel Airplane Body Panel

Progressive stamping stretch forming1010 Steel, cold-rolled 2024 Aluminum, T3 temper.04 sheet, custom order .08 sheet, oversize

Double-sided Zinc clad mechanically polishedCost ~ $.35-.45/lb Cost ~ $4.0/lbUTS ~ 300 MPa UTS ~ 470 MPa

YS ~ 185 MPa YS ~ 325 MPaElongation ~ 42% Elongation ~ 20%

n = .26 n = .16


35/55

Comparison of representative

Parts: Aero and AutoAuto Aero

Part Description Body Panel Body Panel

54"X54" 54"X54"

Forming Process Progressive Stamping Stretch FormingMATERIAL

Material

1010 Steel, cold-rolled,

.04" sheet, custom orderdouble-sided Zinc clad

2024 Aluminum, T3

temper, .08" sheet,

oversize mechanicallypolished

Scrap 40% 20%

Material Cost $0.45/lb $4.00/lb

Per part $15.75 $105.00

LABOR

Set-up Time 1.5hr 1.0hr

Parts/Run 2,000 30Cycle Time 0.25 min 2.5 min

Total Labor 0.30 min 4.5 minLabor Rate** $20.00/hr $20.00/hr

Stretch-Form Labor Cost $0.10 $1.50

FIXED

Equipment $5,000,000 $1,000,000

Tools/Dies $900,000 $45,000

(200 manhours labor)TOTAL TRANSFER COST $25 $265


36/55


37/55


38/55

Steel can production at Toyo Seikan

See Appendix D; http://itri.loyola.edu/ebm/


39/55

DWI Comparison TULC steel can w/ tin

limits recycling ironing process

requires lubricants &

coolant waste water painting process

requires coating and

baking VOCs andCO2

tin free steel

dry forming with 20umpolyester sheet

printing processreduces VOCs and

CO2


40/55

reduced waste water & CO2


41/55

Recycling Aluminum Cans ~50% of aluminum

cans are recycled 40% recycled contentin new cans

secondary aluminumrequires 95% lessenergy than primaryaluminum

Can recycling limitedby Mg alloy

Al/Mg alloy


42/55

AluminumP

roduction

Process

Mining

4 MJ/kg Al

Bayer Process

30.4 MJ/kg

Rolling20.3 MJ/kg

Hall-Heroult

Process

245.3MJ/kg

Illustration from;IAI web pageData from; Alcoa; Martchek, Fisher & KlockoSAE paper 982177, 1998


43/55

Recycling Aluminum Cans

50% of aluminumcans are recycled

40% recycled contentin new cans

95% less energy than

primary aluminum

Shredded

Screen

De-

lacquer

Melt

&

Blend

RollPour


44/55

Recycling Aluminum Cans

50% of aluminumcans are recycled

40% recycled contentin new cans

95% less energy than

primary aluminum

Shredded

Screen

De-

lacquer

Melt

&

Blend

RollPour

Separate

for

Lead

Separate

for Mg


45/55

New developments Tailored blanks

Binder force control Segmented dies

Alternative materials; cost issues


46/55

-

SHAPEMEASUREMENT

SHAPECONTROLLER

WORKPIECE

desiredshape +

shapeerror

finishedpart

DISCRETE DIESURFACE

DISCRETE DIE

FORMING PRESS

CONTROLLER

TRACING CMM

Part Error

Die Shape

Change

New

Part

Shape

The Shape Control Concept


47/55

Conventional Tooling

Tool

Pallet

Parking Lot

60 Ton Matched Discrete Die


48/55

60 Ton Matched Discrete Die

Press(Robinson et al, 1987)

Tool Setup

Actuators

Programmable

Tool

Passive

Tool

Press Motion

Cylindrical Part Error


49/55

Cylindrical Part Error

Reduction

0

10

20

30

40

50

60

P1 P2 P3 P4

PART CYCLE

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

RMSE

rror[x0.0

01in.]

MAX

RMS

SSYYSSTTEEMM EERRRROORR TTHHRREESSHHOOLLDD

MAXIM

ALSHAPEERR

OR

[x0.0

01in.]


50/55

Large Scale Tool

6 feet

Stretch Forming with Reconfigurable


51/55

Stretch Forming with Reconfigurable

Tool @ Northrop Grumman

Alternative materials for auto


52/55

Alternative materials for auto

body panels

Comparison


53/55

Comparison

Steel Vs SMC $0.35/lb

0.03 thick

7.6 lb 40% scrap

$4.25 matl cost

400/hr

5 workers

$18.90/hr (Union) $0.24 labor cost

$5,000,000 equipment

$900,000 tools

$7.71 unit cost at 100,000 units

$0.65/lb

.0.12 thick

7.0 lb 6% scrap

$4.84 matl cost

40/hr

$12.50/hr (non-Union)

$0.63 labor cost $1,200,000 eqipment

$250,000 tools

$7.75 unit cost at 100,000 units

Ref John Busch

Cost comparison between sheet


54/55

Cost comparison between sheet

steel and plastics and composites forautomotive panels ref John Busch


55/55

See websiteSteps to Building a Sheet Metal Chassis for your 2.810 Car Using

Solidworks, by Eddy Reif

Lecture 5 Sheet Metal Forming

Documents

Transcript of Lecture 5 Sheet Metal Forming