Cutting Tool Technology

8/10/2019 Cutting Tool Technology

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Cutting Tool Technology


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Cutting Tool Technology

It has two principal aspects:

1. Tool material

Developing materials that can withstand the forces,temperatures and wearing in machining process.

2. Tool geometryOptimizing the geometry of the cutting tool for the

tool material and for a given operation.


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The cutting tool materials must possess a number of important

properties to avoid excessive wear, fracture failure and hightemperatures in cutting.

The following characteristics are essential for cutting materials to

withstand the heavy conditions of the cutting process and to produce

high uality and economical parts:

Tool failure modes identify the important properties that a tool

material should possess:

Toughness to avoid fracture failure.

!ot hardness ability to retain hardness at high temperatures.

"ear resistance hardness is the most important property to

resist abrasive wear.

CUTTING TOOL MATERIALS


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CUTTING TOOL MATERIALS harne!! at ele"ate tem#erature! #so$called hot hardness% so

that hardness and strength of the tool edge are maintained in highcutting temperatures.

Toughne!!$ ability of the material to absorb energy without

failing. &utting is often accompanied by impact forces especially

if cutting is interrupted, and cutting tool may fail very soon if it isnot strong enough.

%ear re!i!tance$ although there is a strong correlation between

hot hardness and wear resistance, latter depends on more than

'ust hot hardness. Other important characteristics include surfacefinish on the tool, chemical inertness of the tool material with

respect to the wor( material, and thermal conductivity of the tool

material, which affects the maximum value of the cutting

temperature at tool$chip interface.


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)ig: Typical hot hardness relationships for selected tool materials.

&lain car'on !teel !ho%! a ra#i lo!! o( harne!! a! tem#eratureincrea!e!.

)igh !#ee !teel i! !u'!tantially 'etter* %hile cemente car'ie!

an ceramic! are !igni(icantly harer at ele"ate tem#erature!.


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Car'on Steel! It is the oldest of tool material. It is inexpensive, easily

shaped, sharpened. The carbon content is *.+-./ with small uantities of

silicon, chromium, manganese, and vanadium to refine

grain size.

This material has low wear resistance and low hot hardness.

0aximum hardness is about !1& +2.

3sed for drills taps, broaches, reamers.

4imited to hand tools and low cutting speed operation. #1ed

hardness temp.: 2**5 &%

The use of these materials now is very limited.


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)igh S#ee Steel +)SS,

)irst produced in -6**s. They are highly alloyed withvanadium, cobalt, molybdenum, tungsten and chromium

added to increase hot hardness and wear resistance.

&an be hardened to various depths by appropriate heat

treating up to cold hardness in the range of !1& +7$+.

The cobalt component give the material a hot hardness

value much greater than carbon steels.#1ed hardness temp.:

+**&%

The high toughness and good wear resistance ma(e !88

suitable for all type of cutting tools with complex shapes for

relatively low to medium cutting speeds.


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)igh S#ee Steel +)SS, !ighly alloyed tool steel capable of maintaining hardness

at elevated temperatures better than high carbon and lowalloy steels.

One of the most important cutting tool materials

9specially suited to applications involving complicatedtool geometries, such as The most widely used toolmaterial today for taps, drills, reamers, gear tools, endcutters, slitting, broaches, etc.

Two basic types1. Tung!ten ty#e* designatedT grae!

2. Moly'enum ty#e* designatedM grae!


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)igh S#ee Steel Com#o!itionTwo basic types of !88

M-!erie! +--/-2,$

&ontains +/ molybdenum, +/ tungsten, / chromium,

2/ vanadium ; cobalt

!igher, abrasion resistance!.8.8. are ma'orly made of 0$series

T-!erie! +10-/-1,$

&ontains -< / tungsten, / chromium, -/ vanadium

; cobalt

undergoes less distortion during heat treating


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Cemente Car'ie!

Introduced in the -67*s. These are the most important

tool materials today because of their high hot hardness

and wear resistance.

There may be other carbides in the mixture, such astitanium carbide #Ti&% and=or tantalum carbide #Ta&% in

addition to "&.

The main disadvantage of cemented carbides is their low

toughness.


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Cemente Car'ie! General

&ro#ertie! !igh compressive strength, but low to moderate tensile

strength

!igh hardness #6* to 6 !1>%

?ood hot hardness

?ood wear resistance

!igh thermal conductivity

!igh elastic modulus +** x -* 70@a #6* x -*+lb=in2%

Toughness lower than high speed steel


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This hard tool material is produced by a powder

metallurgy techniue, sintering grains of tungsten carbide

#"&% in a cobalt #&o% matrix #as the binder, it provides

toughness%. @articles -$ Am in size are pressed ; sintered to desired

shape in a !2atmosphere furnace at -** &.

>mount of cobalt present affects properties of carbidetools. >s cobalt content increases B strength, hardness ;

wear resistance increases.

Cemente Car'ie!


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Cemente Car'ie!


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In!ert AttachmentIn !#ite o( more traitional tool material!* cemente car'ie! are a"aila'le a!

in!ert! #rouce 'y #o%er metallurgy #roce!!.

In!ert! are a"aila'le in "ariou! !ha#e!* an are u!ually mechanically attache'y mean! o( clam#! to the tool holer* or 'rae to the tool holer.

The clam#ing i! #re(erre 'ecau!e a(ter an cutting ege get! %orn* the in!ert

i! ine3e +rotate in the holer, (or another cutting ege.

4hen all cutting ege! are %orn* the in!ert i! thro%n a%ay. The ine3a'le

car'ie in!ert! are ne"er regroun.I( the car'ie in!ert i! 'rae to the tool holer* ine3ing i! not a"aila'le* an

a(ter reaching the %ear criterion* the car'ie in!ert i! re-!har#ene on a tool

griner.


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Ty#e! o( Cemente Car'ie!

Two basic types:

1. Non !teel cutting grae! - only 4C Co

2. Steel cutting grae! - TiC 5 TaC ae to 4C Co


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Non Steel Cutting Car'ie Grae!

3sed for nonferrous metals and gray cast iron

@roperties determined by grain size and cobalt content

>s grain size increases, hardness and hot hardness

decrease, but toughness increases.

>s cobalt content increases, toughness improves at the

expense of hardness and wear resistance.


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Steel Cutting Car'ie Grae!

3sed for low carbon, stainless, and other alloy steels

)or these grades, Ti& and=or Ta& are substituted for

some of the "&.

This composition increases crater wear resistance for

steel cutting, but adversely affects flan( wear resistance

for non steel cutting applications.


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Coate 4C

One advance in cutting tool materials involves the applicationof a very thin coating # -* Am% to a C$grade substrate, which

is the toughest of all carbide grades.

&oating may consists of one or more

thin layers of wear$resistantmaterial, such as titanium carbide

#Ti&%, titanium nitride #Ti%,

aluminum oxide #>l2O7%, and=or

other, more advanced materials.

&oating allows to increase

significantly the cutting speed for the

same tool life.

8tructure of a multi$layer

coated carbide insert


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Coate Car'ie!

&emented carbide insert coated with one or more thin layersof wear resistant materials, such as Ti&, Ti, and=or>l2O7

&oating is applied by chemical vapor deposition or physical

vapor deposition.

&oating thic(ness E 2. -7 m #*.***- to *.*** in%

>pplications: cast irons and steels in turning and millingoperations.

Fest applied at high speeds where dynamic force and thermal

shoc( are minimal.


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Ceramic!

@rimarily fine grained >l

2O7, pressed and sintered at highpressures and temperatures into insert form with no binder.

A##lication!: high speed turning of cast iron and steel

ot recommended for heavy interrupted cuts #e.g. rough

milling% due to low toughness

There is no occurrence of built$up edge, and coolants

are not reuired.

>l2O7also widely used as an abrasive in grinding.


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Ceramic!

Two types are available: "hite or cold$pressed ceramics, which consists of only

>l2O7 cold pressed into inserts and sintered at high

temperature.

Flac( or hot$pressed ceramics, commonly (nown as

cermet #from ceramics ; metal%. This material consists of

G*/ >l2O7and 7*/ Ti&.

Foth materials have very high wear resistance but lowtoughness, therefore they are suitable only for continuous

operations such as finishing turning of cast iron and steel at

very high speeds.


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Cermet!&ombinations of Ti&, Ti, and titanium carbonitride #Ti&%,

with nic(el and=or molybdenum as binders.

8ome chemistries are more complex.

A##lication!$

high speed finishing and semi$finishing of steels, stainless

steels and cast irons.

!igher speeds and lower feeds than steel cutting carbide

grades Fetter finish achieved, often eliminating need for grinding.


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6iamon

Diamond is the hardest substance ever (nown of allmaterials.

4ow friction, high wear resistance.

>bility to maintain sharp cutting edge.

3se is limited because it gets converted into graphite at

high temperature #G** 5&%. ?raphite diffuses into iron

and ma(e it unsuitable for machining steels.

It is used as a coating material in its polycrystalline form,or as a single$ crystal diamond tool for special

applications, such as mirror finishing of non$ferrous

materials.


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Synthetic 6iamon!8intered polycrystalline diamond #8@D% $ fabricated by

sintering very fine grained diamond crystals under high

temperatures and pressures into desired shape with little or

no binder.

3sually applied as coating #*. mm thic(% on "&$&o insert

>pplications: high speed machining of nonferrous metals

and abrasive nonmetals such as fiberglass, graphite, andwood.

$ ot for steel cutting


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Cu'ic 7oron Nitrie ext to diamond, cubic boron nitride #&F% is hardest

material (nown. 1etain hardness up to -***5&.

Fy bonding *. mm thic( polycrystalline &F onto a

carbide substrate through sintering under pressure.

&F is used mainly as coating material because it is verybrittle.

In spite of diamond, &F is suitable for cutting ferrous

materials.

A##lication!$ machining steel and nic(el based alloys.


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8@D and &F tools are expensive.

0ade by bonding #*.$-.* mm% 4ayer of poly crystalline

cubic boron nitride to a carbide substrate by sintering

under @ressure. "hile carbide provides shoc( resistance &F layer

provides high resistance and cutting edge strength.

&ubic boron nitride tools are made in small sizes withoutsubstrate.

Cu'ic 7oron Nitrie

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Cutting Tool Technology