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© WZL/Fraunhofer IPT

Blanking and Fineblanking

Simulation Techniques in Manufacturing Technology

Lecture 5

Laboratory for Machine Tools and Production Enginee ring

Chair of Manufacturing Technology

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

Seite 2© WZL/Fraunhofer IPT

Calculation of blanking parts5

Fineblanking4

Shearing3

Requirements on blanking parts2

Introduction1

Outline


� Deep Drawing� Ironing� Spinning� Hydroforming� Wire Drawing� Pipe Drawing� Collar Forming

Casting Forming Cutting Joining Coating Changing of Material Properties

Compressive Forming

Tenso-Compressive

Forming

Tensile Forming

Bend FormingShear

FormingSevering

� Translate� Twist� Intersperse

Manufacturing Processesaccording to DIN 8580ff

� Open DieForging

� Closed Die Forging

� Cold Extrusion � Rod Extrusion� Rolling� Upsetting� Hobbing� Thread Rolling

� Stretch Forming� Extending� Expanding� Embossing

� With linear Tool Movement

� With rotating Tool Movement

� Shearing� Fine Blanking� Cutting with a

single Blade� Cutting with

two approaching Blades

� Splitting� Tearing

Introduction

Sheet Metal Forming Processes


Introduction

What is blanking?

� Definition :

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



Fineblanking4

Shearing3


Introduction1

Outline


Requirements on blanking parts

Required quality of blanking parts

surface evenness

smooth sheared zone

cutting burr

rupture zone

draw-in

achievableroughness

angular deviation



Fineblanking4

Shearing3


Introduction1

Outline


Shearing - Introduction

Shearing – Introduction

application IT-classification costs output

Shearing

high

rough (IT 11) low high

lowfine (IT 7)

sheared surface


Shearing - Characterisation of the process

Open and closed cut in shearing

open cut closed cut

tool flank open flank



Differentiation of blanking and piercing

blanking piercing

waste

waste



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 angle of cutting die

U

blank holder



Process sequences of shearing

1 2

3 4

charging of the punch

elastic & plastic deformation

shearing & cracking

break through


Shearing – Achievable accuracy

Errors on sheared workpieces

burr height h G

draw-in height h E

draw-in

shearing zone

rupture zone

tR

hG

hE

crack depth t R



Influence of die clearance on the sheared surfaces

small clearance

big clearance

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

no formation of distortion wedge

formation of distortion wedge



Quality of sheared surface depending on specific di e clearancesp

ecifi

c di

e cl

eara

nce:

di

e cl

eara

nce

u S/ s

heet

thic

knes

s s



Influence of specific die clearance on crack depth

blanking

specific die clearance u s / %

Cra

ck d

epth

tR

shee

t thi

ckne

ss s

Part diameter da = 30 mm



Relation between burr height and number of cuts

ductilesheet

brittlesheet

burr height


Shearing - Forces in shearing

Reduction of cutting force by modification of tools

Contact between punch and sheet

slopedcut

planecut

s h

total punch strokefo

rce

F

0 s 2s 3s

0,3 Fmax

0,6 Fmax

0,9 Fmax

Fmaxh = 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.



Reduction of cutting force by modification of tools

conical punchgrooved punchplane cut sloped cut

conical die grooved diepunch offset



Dependence of quality on shearing strength of carbo n 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 surface kS = FSmax / AS (with As= ls*s)


Shearing – Wear

Wear on the punch

wear on shaft area

wear on front facefatigue wear on front face

� fatigue wear and wear on front face especially appear for lower sheet thickness (s < 2 mm)

� wear on shaft area – is caused by friction between

punch and sheet in direction of punch movement

– appears during cutting of thicker sheets (s ≥ 2 mm)


open cut

Workpiece

Shearing – wear

Influences on wear

Source: reiner, Müller Weingarten, Feintool

Tool Machine

Type of process

tool wear

materialhardnesssurfaceguidancedie clearance

stiffnesskinematics

alloystiffnesshardnessdimensionshape

open cutclosed cut

closed cut


Shearing – Tool design

Multi-stage blanking tool

4 stage Multi-stage blanking tool for shearing of rotor- and stator-sheets

stator rotor



Fineblanking4

Shearing3


Introduction1

Outline


Fineblanking - Introduction

Fineblanking - Introduction

application IT-classification costs output

shearing

fineblanking

high

rough (IT 11) low high

lowfine (IT 7)

sheared surface


Fineblanking – Characterisation of the process

Animation of fineblanking

clamping

plastic deformation

cutting


fineblankingshearing

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

FS – punch force

1 – cutting die2 – vee ring and

blank holder3 – 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%


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 the

sheet / material flow

vee ring

cutting line

toothed

inward notch

outward notch

vee ring cutting line

intention :


Fineblanking - Details

Dependence of workpiece quality on influencing quan tities

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 punch force

Workpiece quality can be influenced by process para meters:example:


Fineblanking – obtainable precision

Definition of degree of difficulty in fineblankingsl

ot a

, stic

k b

/ mm

sheet thickness s / mm

edge

rad

ius

ri ,

ra

/ mm

sheet thickness s / mm

degree of difficulty

S1 – easy

S2 – mediumS3 – difficultedge angle a


Fineblanking – comparison of techniques

Comparison of sheared surface in shearing and fineb lanking

shearing

fineblanking

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


Fineblanking – application

Application examples

fineblanking

shearing

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


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



Fineblanking4

Shearing3


Introduction1

Outline


Calculation of blanking process

• Analytical calculation method

• FEA of (fine)blanking processes

Principals and drawbacks

Advantage over analytical calculation by means of examples


Calculation of blanking process - cutting force

SSS klsF ⋅⋅=max

mS Rk 8,0=

maximum cutting force

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

approximate calculation with tensile strength


Calculation of blanking process - cutting energy

( )∫=gx

SS dxxFW0

maxSgS FxcW ⋅⋅=

cutting energy

x :cutting distanceFS :current cutting force

c :correction factorincluding variables like material properties, effective cutting distance, size of die clearance and friction


Calculation of fine blanking process - vee ring forc e

mRRR RhlF ⋅⋅⋅= 4 approximation value for the vee ring force

lR :length of vee ringhR :overall height of vee ringRm :material tensile strength


Calculation of fine blanking process - counter punch force

GqG qAF ⋅=

220

mm

NqG =

270

mm

NqG =

Approximation for the counter punch force

Aq :cutting piece surfaceqG :specific counter punch force

Value of the specific counter punch force for small sized, thin workpieces

Value of the specific counter punch force for large, thick workpieces


Calculation of fine blanking process - cutting force

GStS FFF −=

sl

F

A

Fk

S

S

S

SS ⋅

== maxmax

m

S

R

kC =1

mgSgS RslCslF ⋅⋅⋅=⋅⋅= 1τ

9,06,0 1 << C

cutting force

FSt :punch forceFG :counter punch force

Fsmax :maximum cutting forceAS :shearing surface

factor of shearing strength

kS :shearing resistanceRm :tensile strength

calculation according to VDI-standard 3345

lg :total length of cutting liness :material thicknessτS :shear strengthC1 :factor of shearing strength due to

yield stress ratioRm :material tensile stress

shearing resistance

advised value is C1= 0,9 (safety)


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 RslCF ⋅⋅⋅= 1

.constRm =

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