Chapter 3 STUDTool Wear and Tool Life

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Chapter3

TOOL WEAR AND TOOL LIFE

2/6/2013 ProfDrAdelM.Abdelmaboud Manuf.Technology Chapter3 ToolwearandToolLife 1


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. , . , . ., ,

ManufacturingProcesses

for

Engineering

, , ,

NJ.

. ,

Manufacturing 3/e2007JohnWiley&Sons,

.

2/6/2013Prof

Dr

Adel

M.

Abdelmaboud

Manuf.

Technology

Chapter

3

Toolwear

and

Tool

Life

2


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TOOL WEAR AND TOOL LIFE

Introduction

Thelife

of

acutting

tool

can

be

terminated

by

.

Twomain

categories

of

tool

life:

1. Gradualwearingofcertainregionsofthe

,

2. Abrupt toolfailure.

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Life3


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Whenthetoolwearreachesaninitiallyaccepted

amount,

t ere

are

wo

op ons,1. toresharpenthetoolonatoolgrinder,or2. toreplacethetoolwithanewone.This(i) whentheresourcefortoolresharpeningis

.

(ii) (ii)thetooldoesnotallowforresharpening

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Life5


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Gradualwearoccursatthreeprincipallocation

onacutt ngtoo .

Accordingly,threemaintypesoftoolwearcan

bedistinguished,

1. craterwear2. flankwear

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2/6/2013 7Prof

Dr

Adel

M.

Abdelmaboud

Manuf.

Technology

Chapter

3

Toolwear

and

ToolLife


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Crater wear: consists of a concave section on the

too ace orme y t e act on o t e c p s ng

on the surface. Crater wear affects the

rake angle of the cutting tool and consequently,

makin cuttin easier.At the same time, the crater wear weakens the

tool wedge and increases the possibility for tool

breakage. In general, crater wear is of arelatively small concern.

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Flank

wearFlankwear:

occurs on the tool lank as a result o riction between the

machined surface of the workpiece and the tool flank.Flank wear appears in the form of socalled wear land

and is measured by the width of this wear land, VB OR

(FW), flank wear affects to the great extend themechanics of cutting. Cutting forces increase significantly

with flank wear.

I t e amount o an wear excee s some cr t ca va ue(VB > 0.5~0.6 mm), the excessive cutting force may cause


.


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Cornerwear:

occurs on the tool corner. Can be considered as a part of the wear land

between the corner wear and flank wear land. We consider corner wearas a separate wear type because of its importance for the precision of

Corner wear actually shortens the cutting tool thus increasing gradually

the dimension of machined surface and introducing a significant

dimensional error in machining, which can reach values of about

0.03~0.05 mm.



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1-Flank wear

Rapid flank wearcausing poor surface finish or out of tolerance.ause: Cutting speed too high or insufficient wear resistance.

Solution

1. Reduce the cutting speed..

2. Select an Al2O3 coated grade.3. For work-hardening materials, select a smaller entering angle

or a more wear resistant grade.



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2-Notch wear

.

Cause

a) Oxidationb) Attrition

S o u t o na) Select a cermet gradeb) Reduce the cutting speed. (When machining heat resistant materialwith ceramics, increase cutting speed)



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3-Crater wear

Excessive crater wear causing a weakened edge. Cutting edge

breakthrough on the trailing edge causes poor surface finish..

Cause

Diffusion wear due to cutting temperatures that are too high on therake face.

SolutionSelect an Al2O3 coated grade.Select positive insert geometry.


, ,the feed


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4-Plastic deformation

Plastic deformation. Edge depression or flank impression.

Leads to poor chip control and poor surface finish.Risk of excessive flank wear leading to insert breakage.

Cause

, .

Solution

Select a harder grade with better resistance to plastic deformation.Ed e de ression reduce feed.


Flank impression reduce speed.


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5-Built-up edge (B.U.E.)

Built-up edge causing poor surface finish and cutting edge frittering when the built-upedge is torn away.

Cause

Workpiece material is welded to the insert due to:a u ng a s oo ow.

b) Negative cutting geometry.c) Adhesive workpiece material.

Solution


b) Select a positive geometry. Reduce feed at the beginning of the cut.c) Select a thin coated PVD grade and a positive geometry.


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7-Frittering

ma cutt ng e ge ractures r tter ng caus ng poor sur ace n sand excessive flank wear.

Cause

a) Grade is too brittleb) Insert geometry is too weakc) Built-up edge

Solution

a Select tou her rade.

b) Select an insert with a stronger geometry (bigger chamfer for ceramicinserts).

c) Increase the cutting speed or select a positive geometry.Decrease the cuttin s eed and coolant.


Reduce feed at the beginning of the cut.


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8-Thermal cracks

Small cracks perpendicular to the cutting edge causing

frittering.

Cause

Thermal cracks due to temperature variations caused by:a Intermittent machinin

b) Varying coolant supplySolution

a) Select a tougher grade with better resistance to crack

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Life

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propaga onb) Coolant should be applied copiously, or not at all


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9-Insert breakage

Insert breakage that damages not only the insert but also the shimand workpiece.

Causea ra e s oo r e

b) Excessive load on the insertc) Insert geometry is too weakd) Insert size is too small

o u o n

a) Select a tougher grade.

b) Reduce the feed and/or the depth of cut.-


, .d) Select a thicker/larger insert


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10-Slice fracture - ceramics

CauseExcessive tool pressure

Solution

Reduce the feed

Select an insert with a smaller chamfer, or use anothergeometryto change cutting force direction

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1. Cuttin forceisexcessiveand or

dynamic,leadingtoBrittleFracture.

2. Cuttingtemperature

is

too

high

for

the

toolmaterialleadingThermalFailure.3. GradualWearingofthecuttingtool



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ProfDrAdelM.Abdelmaboud Manuf.

Technology Chapter3 ToolwearandTool

Life

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GradualWearMode

Gradualwearoccursattwolocationsonatool:

1. Craterwearoccursontopra e ace

2. Flankwear

occurs

on

flank

(side

of

tool)

Craterwear

flankwear

on

acemented

carbidetool,


o wo u oo , ow o o y o

wearthatoccur


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1. Adhesion wear: Fra ments o the work iece et

welded to the tool surface at high temperatures;eventually, they break off, tearing small parts of the tool

with them.

2. Abrasion: Hard particles, microscopic variations onu u

surface and break away a fraction of tool with them.

. ,

tool diffuse across to the chip; the rate of diffusion

increases exponentially with temperature; this reduces


the fracture strength of the crystals


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ToolLife

.

cuttingproceeds,

the

amount

of

tool

wear

.

Toolwearmustnotbeallowedtogobeyonda

.Toollifeisdefinedasthetimeintervalforwhich

grindingorresharpeningofthetool.

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ToolLife 25


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TaylorToolLifeEquation

where:

v =cuttingspeed,m/min; nVT C=

T =toollife,min;and

n andC are

parameters

that

depend

on

feed,depthofcut,workmaterial,and

toolingmaterial,butmostlyonmaterial

(workand

tool).



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Effect

of

cuttin

s eed

on

tool

flank

wear

Effectofcuttingspeedontoolflankwear(FW)forthreecutting

speeds,usingatoollifecriterionof0.50mmflankwear

2/6/2013 ProfDr

Adel

M.

Abdelmaboud

Manuf.

Technology

Chapter

3

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Tool

Life29


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Effect of cuttin s eed on tool flank wear

2/6/2013 Prof

Dr

Adel

M.

Abdelmaboud

Manuf.

Technology

Chapter

3

Tool

wear

and

ToolLife 30


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Changes

in

sound

emitted

from

operation

Chipsbecomeribbonlike,stringy,anddifficultto

disposeof

Degradationofsurfacefinish

magnifyingoptics

can

determine

if

tool

should

be

replaced.

2/6/2013 ProfDr

Adel

M.

Abdelmaboud

Manuf.

Technology

Chapter

3

Toolwear

and

Tool

Life 31

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Chapter 3 STUDTool Wear and Tool Life