First Year,

Mechanical Engineering Dept.,

Faculty of Engineering,

Fayoum University

Dr. Ahmed Salah Abou Taleb

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Manufacturing Processes 1(MDP 114)

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Cutting-Tool Materials and

Cutting Fluids

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Modes of Tool Failure • Fracture failure

– Cutting force becomes excessive and/or dynamic, leading to brittle fracture

• Temperature failure

– Cutting temperature is too high for the tool material

• Gradual wear

– Gradual wearing of the cutting tool

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Modes of Tool Failure • Fracture and temperature failures are premature

failures

• Gradual wear is preferred because it leads to the longest possible use of the tool

• Gradual wear occurs at two locations on a tool:

– Crater wear –

occurs on top rake face

– Flank wear –

occurs on flank (side of tool)

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Modes of Tool Failure

(a) Crater wear, and

(b) flank wear on a cemented carbide tool, as seen through a toolmaker's microscope

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Modes of Tool Failure

Tool wear as a function of cutting time Flank wear (FW) is used here as the measure of tool wear Crater wear follows a similar growth curve

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Modes of Tool Failure

Effect of cutting speed on tool flank wear (FW) for three cutting speeds, using a tool life criterion of 0.50 mm flank wear

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Taylor Tool Life Equation

where

v = cutting speed;

T = tool life; and

n and C are parameters that depend on feed,

depth of cut, work material, tooling material, and

the tool life criterion used

• n is the slope of the plot

• C is the intercept on the speed axis

CvT n

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Cutting Tool Materials

Typical Values of n and C in Taylor Tool Life Equation

Tool material n C (m/min) C (ft/min)

High speed steel:

Non-steel work 0.125 120 350

Steel work 0.125 70 200

Cemented carbide

Non-steel work 0.25 900 2700

Steel work 0.25 500 1500

CeramicSteel work 0.6 3000 10,000

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Cutting tool is subjected to:

1. High temperatures,

2. High contact stresses

3. Rubbing along the tool–chip interface and along the

machined surface

Cutting-tool material must possess:

1. Hot hardness (see right)

2. Toughness and impact strength

3. Thermal shock resistance

4. Wear resistance

5. Chemical stability and inertness

Cutting Tool Materials

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• Tool materials may not have all of the desired properties for

a particular machining operation

Cutting Tool Materials

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Cutting Tool Materials

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Cutting Tool Materials

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Cutting Tool MaterialsTool Materials (also used for dies and moulds in casting, forming, and shaping metallic and non-metallic materials):

1.High-speed steels

2.Cast-cobalt alloys

3.Carbides

4.Coated tools

5.Alumina-based ceramics

6.Cubic boron nitride

7.Silicon-nitride-based ceramics

8.Diamond

9.Whisker-reinforced materials and nanomaterials

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Cutting Tool MaterialsHigh Speed Steel (HSS):

• High-speed steel (HSS) tools were developed to machine at

higher speeds than was previously possible

• They can be hardened to various depths, have good wear

resistance and are inexpensive

• There are two basic types of high-speed steels:

molybdenum (M-series) and tungsten (T-series)

• High-speed steel tools are available in wrought, cast and

powder-metallurgy (sintered) forms

• They can be coated for improved performance

• The major alloying elements in HSS are chromium,

vanadium, tungsten, cobalt, and molybdenum

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Cutting Tool MaterialsCast Cobalt:

• Cast-cobalt alloys have high hardness, good wear

resistance and can maintain their hardness at elevated

temperatures

• They are not as tough as high-speed steels and are

sensitive to impact forces

• Less suitable than high-speed steels for interrupted cutting

operations

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Cutting Tool MaterialsCarbides – Cemented – Sintered Carbide :

They have the following characteristics:

1. High hardness over a wide range of temperatures

2. High elastic modulus

3. High thermal conductivity

4. Thermal expansion

5. Versatile

6. Cost-effective tool and die materials for a wide range of

applications

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Cutting Tool MaterialsCarbides – Cemented – Sintered Carbide (Tungsten):

• Tungsten carbide (WC) consists of tungsten-carbide

particles bonded together in a cobalt matrix

• As the cobalt content increases, the strength, hardness,

and wear resistance of WC decrease

• Toughness increases because of cobalt high toughness

Carbides – Cemented – Sintered Carbide (Titanium):

• Consists of a nickel–molybdenum matrix

• Has higher wear resistance than tungsten carbide but is not as tough

• Suitable for machining hard materials and for cutting at speeds higher than tungsten carbide

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Cutting Tool MaterialsCarbides – Cemented – Sintered Carbide (Insert):

• High-speed steel tools are shaped for applications such as

drill bits and milling and gear cutters

• Inserts are individual cutting tools with several cutting points

• Clamping is the preferred method of securing an insert and

insert has indexed (rotated in its holder) to make another

cutting point available

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Cutting Tool MaterialsCarbides – Cemented – Sintered Carbide (Insert):

• Available in a variety of shapes: square, triangle, diamond

and round

• The smaller the included angle, the lower the strength of the

edge

Chip-breaker features on inserts for the purposes of:

1. Controlling chip flow during machining

2. Eliminating long chips

3. Reducing vibration and heat generated

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Cutting Tool MaterialsCoated Tools

New alloys and engineered materials are being developed to

have high strength and toughness, abrasive and chemically

reactive with tool materials

• Coatings have unique properties:

1. Lower friction

2. Higher adhesion

3. Higher resistance to wear and cracking

4. Acting as a diffusion barrier

5. Higher hot hardness and impact resistance

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Cutting Tool MaterialsCoated Tools

Common coating materials are:

1. Titanium nitride

2. Titanium carbide

3. Titanium carbonitride

4. Aluminum oxide

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Cutting Tool MaterialsCoated Tools

Titanium-nitride Coatings

• Have low friction coefficients, high hardness, resistance to

high temperature and good adhesion to the substrate

• Improve the life of high-speed steel tools and improve the

lives of carbide tools, drill bits, and cutters

• Perform well at higher cutting speeds and feeds

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Cutting Tool MaterialsCoated Tools

Titanium-carbide Coatings

• Coatings have high flank-wear resistance in machining

abrasive materials

Ceramic Coatings

• Coatings have low thermal conductivity, resistance to high

temperature, flank and crater wear

Multiphase Coatings

• Desirable properties of the coatings can be combined and optimized with the use of multiphase coatings

• Coatings also available in alternating multiphase layers