Tech 3113Manufacturing Tooling

Nageswara Rao Posinasetti

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3B Cutting Tool Design

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Cutting Tool Materials Required properties

Higher hardness Hot hardness Wear resistance Toughness Low friction Better thermal characteristics

May 3, 2023(c) TMH New Delhi, Manufacturing Technology Vol 2,Metal Cutting and

Machine Tools by P N Rao3

Carbon Tool Steels These are essentially plain carbon

steels with carbon percentages between 0.6 to 1.5% and some very small alloy additions such as Manganese, Silicon, Tungsten, Molybdenum, Chromium and Vanadium.

Beyond 200C (392F ) they loose their hardness and cease to cut.

May 3, 20234

High Speed Steel This class of tool materials have significant

quantities of tungsten, molybdenum, chromium and vanadium.

The complex carbides of tungsten, molybdenum and chromium distributed through out the metal matrix provide very good hot hardness and abrasion resistance.

For the same hardness, less amount of molybdenum (compared to Tungsten) needs to be added, however more care need to be exercised in hardening as decarburizing takes place in molybdenum steels.

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High Speed Steel The main advantages of high speed

steels is in their high hardness, hot hardness, good wear resistance, high toughness and reasonable cost.

Toughness of high speed steels is highest among all the cutting tool materials.

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Cemented Carbides Cemented carbides are produced by

the cold compaction of the tungsten carbide powder in a binder such as cobalt, followed by liquid-phase sintering.

High hot hardness. Higher Young's modulus. Carbides are more brittle and

expensiveMay 3, 20237

Cemented Carbides The usual composition of the straight

grade carbides is 6 wt% Co and 94 wt% WC with the cobalt composition ranging from 5 to 12 wt%.

Addition of titanium carbide (TiC) increases the hot hardness, wear resistance, and resistance to thermal deformation, but decreases the strength. The usual composition is about 5–25 wt%. May 3, 20238

Cemented Carbides Choose a grade with the lowest cobalt content

and the finest grain size consistent with adequate strength to eliminate chipping.

Use straight WC grades if cratering, seizure or galling are not experienced in case of work materials other than steels.

To reduce cratering and abrasive wear when machining steel, use grades containing TiC.

For heavy cuts in steel where high temperature and high pressure use a multi-carbide grade containing W-Ti-Ta and/or lower binder content.

May 3, 20239

Cemented Carbides Cemented carbides being expensive are

available in insert form in different shapes such as triangle, square, diamond, and round.

Each of the edge would act as a cutting edge. As seen from the Fig 2.26, the tool bit is

made of tungsten carbide, while the tool holder shank is made from alloy steel to provide the necessary strength and reduce the total cost.

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Coated Carbides Several coatings and coating methods have

been developed for cutting tools. Since late 60's thin (about 5 m) coating of TiN

has been used on cemented carbide tools. Ceramic coatings used are hard materials and

therefore provide a good abrasion resistance. They also have excellent high temperature

properties such as high resistance to diffusion wear, superior oxidation wear resistance, and high hot hardness.

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Cemented Carbides Choose a grade with the lowest cobalt content

and the finest grain size consistent with adequate strength to eliminate chipping.

Use straight WC grades if cratering, seizure or galling are not experienced in case of work materials other than steels.

To reduce cratering and abrasive wear when machining steel, use grades containing TiC.

For heavy cuts in steel where high temperature and high pressure deform the cutting edge plastically, use a multi carbide grade containing W-Ti-Ta and/or lower binder content.

Ceramics Ceramics are essentially alumina (Al2O3) based

high refractory materials introduced specifically for high speed machining of difficult to machine materials and cast iron.

These can withstand very high temperatures, chemically more stable and have higher wear resistance than the other cutting tool materials.

The main problems of ceramic tools are their low strength, poor thermal characteristics and the tendency to chipping.

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Ceramics Use the highest cutting speed recommended and

preferably select square or round inserts with large nose radius.

Use rigid machine with high spindle speeds and safe clamping angle.

Machine rigid workpieces. Ensure adequate and uninterrupted power supply. Use negative rake angles so that less force is

applied directly to the ceramic tip. The overhang of the tool holder should be kept to

a minimum; not more than 1.5 times the shank thickness.

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Ceramics Large nose radius and side cutting edge angle on

the ceramic insert to reduce the tendency of chipping.

Always take a deeper cut with a light feed rather than a light cut with heavy feed; ceramic tips are capable of cuts as deep as one-half the width of the cutting surface on the insert.

Avoid coolants with aluminium oxide based ceramics.

Review machining sequence while converting to ceramics and if possible introduce chamfer or reduce feed rate at entry.

Diamond Diamond is the hardest known (Knoop hardness ~

8000 kg/mm2) material that can be used as a cutting tool material.

It has most of the desirable properties of a cutting tool material such as high hardness, good thermal conductivity, low friction, non-adherence to most materials, and good wear resistance.

Artificial diamonds which are basically polycrystalline (PCD) in nature. These are extensively used in industrial application because they can be formed for any given shape with a substrate of cemented carbide.

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May 3, 2023Rao P N18

Cutting Tool MaterialsCarbon steels

Low strength, softer materials, non ferrous alloys, plastics

Low cutting speeds, low strength materials

May 3, 2023Rao P N19

Cutting Tool MaterialsCarbon steels

Low strength, softer materials, non ferrous alloys, plastics

Low cutting speeds, low strength materials

HSS All materials of low and medium strength and hardness

Low to medium cutting speeds, low to medium strength materials

May 3, 2023Rao P N20

Cutting Tool MaterialsCarbon steels

Low strength, softer materials, non ferrous alloys, plastics

Low cutting speeds, low strength materials

HSS All materials of low and medium strength and hardness

Low to medium cutting speeds, low to medium strength materials

Cemented carbides

All materials upto medium strength and hardness

Not suitable for low speed application

May 3, 2023Rao P N21

Cutting Tool MaterialsCarbon steels

Low strength, softer materials, non ferrous alloys, plastics

Low cutting speeds, low strength materials

HSS All materials of low and medium strength and hardness

Low to medium cutting speeds, low to medium strength materials

Cemented carbides

All materials upto medium strength and hardness

Not suitable for low speed application

Ceramics Cast iron, Ni-base super alloys, non ferrous alloys, plastics

Not for low speed operation or interrupted cutting. Not for machining Al, Ti alloys.

Rigidity Strength Weak links Force limitations Speed, feed and size Related force components Chip disposal Uneven motions Chatter

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Guidelines for Cutting tool Design

Back rake angle Side rake angle End relief angle Side relief angle End cutting edge angle Side cutting edge angle Nose radius

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Basic tool angles (Tool Signature)

Establish the operating conditions Select the

Cemented carbide grade Nose radius Insert shape Insert size Insert thickness Tool style Rake angle Shank size Chip breaker

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Selecting carbide Tools

Feed, speed and depth of cut greatly influence the machining performance.

Also lead angle affects the performance

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Establish the operating conditions

Increase the speed Decrease the feed and/or depth of

cut Change to a tougher grade carbide

insert Use a negative rake Hone the cutting edge before use Check the rigidity and tool overhang

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To reduce cutting edge chipping

Select the cemented carbide gradeStraight carbides - Tungsten carbide (WC) and cobalt binder

Cast iron, nonferrous and nonmetallic materials

Resistance to edge wear

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Select the cemented carbide gradeStraight carbides - Tungsten carbide (WC) and cobalt binder

Cast iron, nonferrous and nonmetallic materials

Resistance to edge wear

WC + Titanium carbide + Tantalum carbide with cobalt binder

Steels Resistance to cratering

Coated carbides

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Based on surface finish

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Select the nose radius

Round – strong and large radius, good for higher feed rates

Square – medium stronger Traingular – least stronger, less

number of cutting edges, but more versatile in use

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Select the insert shape

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Smallest size based on the depth of cut used

Cutting edge should be 1.5 times that of the length of cutting edge engagement.

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Select the insert size

Gives the strength of the tool

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Select the insert thickness

Based on the geometry of the operation to be performed.

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Select the tool style

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Select the Rake Angle

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Select the Shank Size

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Select the Chip Breaker

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Tool Holder Identification

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Carbide Insert Identification

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Drilling Reaming Milling Gear cutting

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Multiple-Point Cutting Tools

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d = drill diameter, in f = feed in/rev This is valid for alloy steel 200

BHN

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Power requirement for Drilling8.18.0200,25, dfMTorque

28.08.0 625500,57, ddfTThrust

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Power requirement for Reaming

2.01

21

8.18.0

1

1300,23

dddd

dfkM

2.01

1

8.08.0

1

1600,42

dddd

dfkT

d1 = reamer diameter, in.

f = feed in/rev

k = constant based on number of flutes, See Table 3-11.

Power in HP

M = tool torque, in-lb N = speed, rpm Power in Watts = Hp * 746

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Power

025,63NMPc

Depends on the material removal rate

Uses empirical equations developed based on experiments

See Machinery’s Handbook pp 1052 – 1062 (28th Edition)

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Machining Power

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Pc = KpCQW

Pc = power at the cutting tool

Pm = power at the motor

Kp = power constant (see tab 24, 25 and 30)

Q = metal removal rate (tab 29)

EWQCK

EPP pc

m

DRILLING

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For Inch units only:

T = 2 kd Ff Ft B W + kd d2 J W

M = Kd Ff FM A W

Pc = MN/63,025

T = Thrust; lb or N

M = Torque; in-lb or N.m

N = Spindle rpm

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