l05 blanking and fine blanking

8/16/2019 l05 Blanking and Fine Blanking

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© WZL/Fraunhofer IPT

Blanking and FineblankingSimulation Techniques in Manufacturing Technology

Lecture 5

Laboratory for Machine Tools and Production Engineering

Chair of Manufacturing Technology

Prof. Dr.-Ing. Dr.-Ing. E.h. Dr. h.c. Dr. h.c. F. Klocke


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Seite 2 © WZL/Fraunhofer IPT

Calculation of blanking parts5

Fineblanking4

Shearing3

Requirements on blanking parts2

Introduction1

Outline


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Deep Drawing

Ironing

Spinning

Hydroforming Wire Drawing Pipe Drawing

Collar Forming

Casting Forming Cutting Joining Coating Changing ofMaterial Properties

CompressiveForming

Tenso-

Compressive

Forming

TensileForming

Bend FormingShear

FormingSevering

Translate Twist

Intersperse

Manufacturing Processes

according to DIN 8580ff

Open DieForging

Closed Die

Forging Cold Extrusion Rod Extrusion

Rolling Upsetting

Hobbing

Thread Rolling

Stretch Forming

Extending

Expanding

Embossing

With linearToolMovement

Withrotating ToolMovement

Shearing

Fine Blanking

Cutting with a

single Blade Cutting with

two approaching

Blades Splitting

Tearing

Introduction

Sheet Metal Forming Processes


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Introduction

What is blanking?

Definition:

Mechanical separation of workpieces by a shearing process without formation of chips – if necessary, including additional forming-operations.


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Fineblanking4

Shearing3


Introduction1

Outline


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Requirements on blanking parts

Required quality of blanking parts

surface evenness

smooth sheared zone

cutting burr

rupture zone

draw-in

achievableroughness

angular deviation


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Fineblanking4

Shearing3


Introduction1

Outline


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Shearing - Introduction

Shearing – Introduction

application IT-classification costs output

Shearing

high

rough (IT 11) low high

lowfine (IT 7)

shearedsurface


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Shearing - Characterisation of the process

Open and closed cut in shearing

open cut closed cut

tool flankopen flank


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Differentiation of blanking and piercing

blanking piercing

waste

waste


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Tool design of shearing

punch

sheet metal

blanking die

u – die clearenceapp. 0,05 x sheet thickness

with:

u = ½·(a – a1)

a – dimension of cutting die

a1 – punch dimension

α – relief angleof cutting die

U

blank holder


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Process sequences of shearing

1 2

3 4

charging ofthe punch

elastic& plasticdeformation

shearing& cracking

break through


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Shearing – Achievable accuracy

Errors on sheared workpieces

burr height hG

draw-in height hE

draw-in

shearing zone

rupture zone

tR

hG

hE

crack depth tR


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Influence of die clearance on the sheared surfaces

smallclearance

bigclearance

By a small die clearance, distortion wedges are generated by squeezing of the materialbetween two cracks

no formation of distortion wedge

formation of distortion wedge


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Quality of sheared surface depending on specific die clearance

s

p e c i f i c d i e

c l e a

r a n c e :

d i e

c l e a

r a n c e

u S

/ s h e e t t h i c k n e s s s


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Influence of specific die clearance on crack depth

blanking

specific die clearance us / %

C r a c

k d e p t h

t R

s h e e

t t h i c k n e s s s

Part diameter

da = 30 mm


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Relation between burr height and number of cuts

ductilesheet

brittlesheet

burr height


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Shearing - Forces in shearing

Reduction of cutting force by modification of tools

Contact between punch and sheet

slopedcut

planecut

s h

total punch stroke

f o r c e F

0 s 2s 3s

0,3 Fmax

0,6 Fmax

0,9 Fmax

Fmax h = 0 (plane cut)

h = 1/3 s (sloped cut)

h = s (sloped cut)

h = 2s(sloped cut)

=

work s(h=0) = work s(h=2s)

Due to workpiece-bending, sloped cut is only suited for piercing.


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Reduction of cutting force by modification of tools

conical punchgrooved punchplane cut sloped cut

conical die grooved die punch offset


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Dependence of quality on shearing strength of carbon steel

carbon concentration tensile strength breaking elongation sheet thickness

die clearance part diameter aspect ratio Die / punch radius

Cutting resistance kS is defined as the cutting force (Fs) referring to the cutting surfacekS = FSmax / AS (with As= ls*s)


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Shearing – Wear

Wear on the punch

wear on shaft area

wear on front facefatigue wear on front face

fatigue wear and wear on frontface especially appear for lowersheet thickness (s < 2 mm)

wear on shaft area

– is caused by friction betweenpunch and sheet in direction ofpunch movement

– appears during cutting of thickersheets (s ≥ 2 mm)


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open cut

Workpiece

Shearing – wear

Influences on wear

Source: reiner, Müller Weingarten, Feintool

Tool Machine

Type of process

tool wear

materialhardnesssurfaceguidancedie clearance

stiffness

kinematics

alloystiffnesshardnessdimensionshape

open cutclosed cut

closed cut


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Shearing – Tool design

Multi-stage blanking tool

4 stageMulti-stage blanking toolfor shearing of rotor- andstator-sheets

stator rotor


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Fineblanking4

Shearing3


Introduction1

Outline


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Fineblanking - Introduction

Fineblanking - Introduction

application IT-classification costs output

shearing

fineblanking

high

rough (IT 11) low high

lowfine (IT 7)

shearedsurface


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Fineblanking – Characterisation of the process

Animation of fineblanking

clamping

plastic deformation

cutting


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fineblankingshearing

1 – cutting die(2 – guiding plate)3 – punch

FS – punch force

1 – cutting die2 – vee ring and

blank holder

3 – punch4 – counter punch

FS – punch forceFR – vee ring and blank

holder forceFG – counter punch

force

Fineblanking – Characterisation of the process

Differences between shearing and fineblanking

die clearance5% 0,5%


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Fineblanking – Details

Geometry of vee rings

thin sheets

thick sheets

sheet thickness s5 – 15 mm

sheet thickness s3 – 5 mm

blank holderwith vee ring

cutting die

• create compression stresses

• prevent horizontal movement of thesheet / material flow

vee ring

cutting line

toothed

inward notch

outward notch

vee ring cutting line

intention:


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Fineblanking - Details

Dependence of workpiece quality on influencing quantities

counter punch force draw-in width draw-in height

smooth shearingzone

deflexion

Process parameters affect workpiece quality:

example:

draw-in height die clearance sheet thickness

blank holder forcecounter punchforce

Workpiece quality can be influenced by process parameters:example:


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Fineblanking – obtainable precision

Definition of degree of difficulty in fineblanking

s

l o t a , s t i c k b / m m

sheet thickness s / mm

e d g e r a d i u s r

i , r a / m m

sheet thickness s / mm

degree of difficulty

S1 – easy

S2 – medium

S3 – difficultedge angle a

Fi bl ki i f t h i


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Fineblanking – comparison of techniques

Comparison of sheared surface in shearing and fineblanking

shearing

fineblanking

In fineblanking, the smooth sheared zone can take a share of 100%

Fi bl ki li ti


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Fineblanking – application

Application examples

fineblanking

shearing

In fineblanking, the sheared surface can be used as a functional surface

Fineblanking Field of application


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Fineblanking – Field of application

Application examples in automotive industry

valve plate

gear shifting gate door lock window lift

synchronising disc

belt pretensioner

ABS-pulse generator

cooling systemseat belt componentsseat adjustment

brakes

gear


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Fineblanking4

Shearing3


Introduction1

Outline


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Calculation of blanking process

• Analytical calculation method

• FEA of (fine)blanking processes

Principals and drawbacks

Advantage over analytical calculation by means of examples


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Calculation of blanking process - cutting force

S S S k lsF ⋅⋅=max

mS Rk 8,0=

maximum cutting force

s :sheet thicknesslS :length of cutting linekS :cutting resistance

approximate calculation withtensile strength


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Calculation of blanking process - cutting energy

( )∫=g x

S S dx xF W 0

maxS gS F xcW ⋅⋅=

cutting energy

x :cutting distanceFS :current cutting force

c :correction factorincluding variables likematerial properties,effective cutting distance,size of die clearance andfriction


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Calculation of fine blanking process - vee ring force

m R R R RhlF ⋅⋅⋅=

4approximation value for the vee ring force

lR :length of vee ringhR :overall height of vee ring

Rm :material tensile strength


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Calculation of fine blanking process - counter punch force

GqG q AF ⋅=

220

mm

N qG =

270

mm

N qG =

Approximation for the counter punch force

Aq :cutting piece surface

qG :specific counter punch force

Value of the specific counter punch force for

small sized, thin workpieces

Value of the specific counter punch force forlarge, thick workpieces


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Calculation of fine blanking process - cutting force

GSt S F F F −=

sl

F

A

F k

S

S

S

S S

⋅

== maxmax

m

S

R

k C =

1

mgS gS RslC slF ⋅⋅⋅=⋅⋅= 1τ

9,06,01


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Simulation fine blanking

Simulation of fine blanking offers the opportunity to include:

This leads to the following results:

• force over punch travel• stress field

• strain rate field• draw-ins• prediction of fracture

• flow stress data• friction properties• thermomechanical coupling

More exact input data can be enclosed:

instead of mgS RslC F ⋅⋅⋅= 1

.const Rm =

l05 blanking and fine blanking

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