Cutting tools technology

TOOLS CLASSIFICATION

&

DESIGN OF TOOLS

S. Venkatesh Kumar, Lecturer.

METTU UNIVERSITY

FACULTY OF ENGINEERING & TECHNOLOGY

DEPARTMENT OF MECHANICAL ENGINEERING

Chapter – 5

DESIGN OF MANUFACTURING TOOLS & DIES

S. Venkatesh Kumar, Lect. / Mechanical Engg., Mettu University

Material Removal Processes

A family of shaping operations, the common

feature of which is removal of material from a

work piece so the remaining part has the desired

geometry

Machining – material removal by a sharp

cutting tool, e.g., turning, milling, drilling

Abrasive processes – material removal by

hard, abrasive particles, e.g., grinding

Non-Traditional processes - various energy

forms other than sharp cutting tool to remove

material

2


Machining Operations

Most important machining

operations:

Turning

Milling

Drilling

Other machining operations:

Shaping and planing

Broaching

Sawing

3


Machining Operations

4


Cutting Tool Classification

1. Single-Point Tools

One dominant cutting edge

Point is usually rounded to form a nose

radius

Turning uses single point tools

2. Multiple Cutting Edge Tools

More than one cutting edge

Motion relative to work achieved by

rotating

Drilling and milling use rotating multiple

cutting edge tools

5


Cutting action involves shear deformation of work

material to form a chip

As chip is removed, new surface is exposed

Machining


Speed and Feed

Speed is rotational motion of spindle which

allows the tools to produce cut into blank

OR

the relative movement between tool and w/p,

which produces a cut

Feed is linear motion of tool which spreads

cut on the blank

OR

the relative movement between tool and w/p,

which spreads the cut

7


Single point cutting tool removes material

from a rotating workpiece to form a

cylindrical shape

Turning


Used to create a round hole, usually by means of a

rotating tool (drill bit) with two cutting edges

Drilling

9


Rotating multiple-cutting-edge tool is moved across

work to cut a plane or straight surface

Two forms: peripheral milling and face milling

(c) peripheral milling (d) face milling.

Milling

10


Cutting Parameters in Machining

Three dimensions of a machining

process:

Cutting speed (v) – primary motion

Feed (f) – secondary motion

Depth of cut (d) – penetration of tool

into work piece

For certain operations, material removal

rate can be computed as

RMR = v f d

11


Cutting Conditions for Turning

Speed, feed, and depth of cut in turning.

12


More realistic view of chip formation, showing shear zone

rather than shear plane. Also shown is the secondary shear

zone resulting from tool-chip friction.

Chip Formation

13


Chip Thickness Ratio

Where,

r = chip thickness

ratio;

to = thickness of the

chip prior to chip

formation; and

tc = chip thickness

after separation

Chip thickness after cut

is always greater than

before.

So chip ratio always

less than 1.0

14

c

o

t

tr


Types of Chip in Machining

1. Discontinuous chip

2. Continuous chip

3. Continuous chip with Built-up Edge (BUE)

4. Serrated chip

Type of chip depends on material type and

cutting conditions

15


Brittle work materials

Low cutting speeds

Large feed and depth of cut

High tool-chip friction

Discontinuous Chip

16


Ductile work materials

High cutting speeds

Small feeds and depths

Sharp cutting edge

Low tool-chip friction

Continuous Chip

17


Ductile materials

Low - to - medium cutting

speeds

Tool-chip friction causes

portions of chip to adhere

to rake face

BUE forms, then breaks off,

cyclically

Continuous With BUE

18


Semi continuous - saw-

tooth appearance

Cyclical chip forms with

alternating high shear strain

then low shear strain

Associated with difficult-to-

machine metals at high

cutting speeds

Serrated Chip

19

S. Venkatesh Kumar, Lect. / Mechanical Engg., Mettu University 20

Types of Metal Cutting Process

Orthogonal cutting is also known as two dimensional metal

cutting in which the cutting edge is normal to the work piece.

(angle = 90o)

Oblique cutting is also known as three dimensional cutting in

which the cutting action is inclined with the job by a certain angle

called the inclination angle. (angle ≠ 90o)


Orthogonal & Oblique Cutting

21


CUTTING TOOL TECHNOLOGY

Tool Geometry

Tool Life

Tool Materials

Cutting Fluids


TOOL GEOMETRY

23


Tool Geometry

24


Tool Geometry – Single Point Cutting Tool

S. Venkatesh Kumar, Lect. / Mechanical Engg., Mettu University26

Back rake angle (αb)

It is the angle between the face of the tool and a line

parallel with base of the tool measured in a

perpendicular plane through the side cutting edge.

This angle helps in removing the chips away from the

work piece.

Side rake angle (αs)

It is the angle by which the face of tool is inclined side

ways.

This angle of tool determines the thickness of the tool

behind the cutting edge.

It is provided on tool to provide clearance between

work piece and tool so as to prevent the rubbing of

workpiece with end flank of tool.


End Relief Angle (ERA)

It is defined as the angle between the portion of the end

flank immediately below

the cutting edge and a line perpendicular to the base of

the tool, measured at right angles to the flank.

It is the angle that allows the tool to cut without rubbing

on the workpiece.

Side Relief Angle (SRA)

It is the angle that prevents the interference as the tool

enters the material.

It is the angle between the portion of the side flank

immediately below the side edge and a line

perpendicular to the base of the tool measured at right

angles to the side.


End Cutting Edge Angle (ECEA)

It is the angle between the end cutting edge and a

line perpendicular to the shank of the tool.

It provides clearance between tool cutting edge

and work piece.

Side Cutting Edge Angle (SCEA)

It is the angle between straight cutting edge on the side

of tool and the side of the shank.

It is also known as lead angle.

It is responsible for turning the chip away from the

finished surface.


Tool Signature

Convenient way to specify tool angles by use of a standardized

abbreviated system is known as tool signature or tool

nomenclature.

The seven elements that comprise the signature of a single point

cutting tool can be stated in the following order:

Tool signature 0-7-6-8-15-16-0.8

1. Back rake angle (0°)

2. Side rake angle (7°)

3. End relief angle (6°)

4. Side relief angle (8°)

5. End cutting edge angle (15°)

6. Side cutting edge angle (16°)

7. Nose radius (0.8 mm)


Tool Geometry - Multi-Point Cutting Tool


Power and Energy Relationships

A machining operation requires power

The power to perform machining can be

computed from:

Pc = Fc vWhere,

Pc = cutting power;

Fc = cutting force; and

v = cutting speed

31


TOOL FAILURE

32


Three Modes of Tool Failure

1. Fracture failure

Cutting force becomes excessive at the tool

point, leading to brittle fracture

2. Temperature failure

Cutting temperature is too high for the tool

material causing softening of tool point. This

leads to plastic deformation and loss of sharp

edge.

3. Gradual wear

Gradual wearing of the cutting edge causes

loss of tool shape, reduction in cutting

efficiency. Finally tool fails in a manner similar

to temp failure


Preferred Mode: Gradual Wear

Fracture & 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)


Tool Wear

• Crater wear occurs

because of tool chip

flow on top rake face.

High friction, temp

and stresses at the

face/chip interface are

responsible.

Measured as area or

depth of dip

• Flank wear results

from rubbing of flank

(& or relief) face to the

newly generated

surface. Measured by

width of wear band

called wear land.

• Notch wear occurs because

of tool rubbing against

original work surface,

which is harder than

machined one


Crater wear

Flank wear


Tool Wear Vs Time


Effect of Cutting Speed on Wear


Tool Life vs. Cutting Speed


Taylor Tool Life Equation

nvT Cwhere

• v = cutting speed;

• T = tool life;

• n is the slope of the

plot;

• C is the intercept on the

speed axis at one

minute tool life

n

C

n and C are parameters that depend on feed,

depth of cut, work material, tooling material,

and the tool life criterion used


TOOL

MATERIALS

41


Tool Materials

Tool failure modes identify the

important properties that a tool

material should possess:

Toughness - to avoid fracture

failure

Hot hardness - ability to retain

hardness at high temperatures

Wear resistance - hardness is the

most important property to resist

abrasion


High Speed Steel (HSS)

Highly alloyed tool steel capable of maintaining

hardness at elevated temperatures better than

high carbon and low alloy steels

One of the most important cutting tool materials

Especially suited to applications involving

complicated tool geometries, such as drills, taps,

milling cutters, and broaches

Two basic types (AISI)

1. Tungsten-type, designated T- grades

2. Molybdenum-type, designated M-grades


High Speed Steel Composition

Typical alloying ingredients:

Tungsten and/or Molybdenum

Chromium and Vanadium

Carbon, of course

Cobalt in some grades

Typical composition (Grade T1):

18% W, 4% Cr, 1% V, and 0.9% C


Cemented Carbides

Class of hard tool material based on

Tungsten Carbide (WC) using powder

metallurgy techniques with Cobalt (Co) as

the binder

Two basic types:

1. Non-steel cutting grades - only WC-Co

2. Steel cutting grades - TiC and TaC

added to WC-Co


Cemented Carbides – General

Properties

High compressive strength but

low - to - moderate tensile strength

High hardness (90 to 95 HRc)

Good hot hardness

Good wear resistance

High thermal conductivity

High elastic modulus - 600 x 103 MPa

Toughness lower than high speed steel


Cermets

Ceramic - Metal Composite

Cemented carbide is a kind of cermet

Combinations of TiC, TiN, and titanium carbonitride

(TiCN), with nickel and/or molybdenum as binders.

Some chemistries are more complex

Applications:

High speed finishing and semi finishing of steels,

stainless steels, and cast irons

Higher speeds and lower feeds than steel-cutting

carbide grades

Better finish achieved, often eliminating need for

grinding


Coated Carbides

Cemented carbide insert coated with one or

more thin layers of wear resistant materials,

such as TiC, TiN, and/or Al2O3

Coating applied by chemical vapor deposition

or physical vapor deposition

Coating thickness = 2.5 - 13 m (0.0001 to

0.0005 in)

Applications: cast irons and steels in turning

and milling operations

Best applied at high speeds where dynamic

force and thermal shock are minimal


Ceramics

Primarily fine-grained Al2O3, pressed and

sintered at high pressures and

temperatures into insert form with no

binder

Applications: high speed turning of cast

iron and steel

Not recommended for heavy interrupted

cuts (e.g. rough milling) due to low

toughness

Al2O3 also widely used as an abrasive in

grinding


Synthetic Diamonds

Sintered Polycrystalline Diamond (SPD) -

fabricated by sintering very fine-grained

diamond crystals under high

temperatures and pressures into desired

shape with little or no binder

Usually applied as coating (0.5 mm thick)

on WC-Co insert

Applications

High speed machining of nonferrous

metals and abrasive nonmetals such as

fiberglass, graphite, and wood.


Cubic Boron Nitride (cBN)

Next to diamond, cubic boron nitride

(cBN) is hardest material known

Fabrication into cutting tool inserts same

as SPD: coatings on WC-Co inserts

Applications: machining steel and

nickel-based alloys

SPD and cBN tools are expensive


TOOL CUTTING

TEMPERATURES

52


Cutting Temperature

Approximately 98% of the energy in

machining is converted into heat

This can cause temperatures to be very

high at the tool-chip interface

The remaining energy (about 2%) is

retained as elastic energy in the chip

53


Cutting Temperatures are Important

High cutting temperatures

Reduce tool life

Produce hot chips that pose safety

hazards to the machine operator

Can cause inaccuracies in part

dimensions due to thermal

expansion of work material

54


CUTTING FLUIDS

55


Cutting fluid is a type of coolant and lubricant

designed specifically for metalworking and machining

processes.

There are various kinds of cutting fluids, which include

oils, oil-water emulsions, pastes, gels and other gases.

They may be made from petroleum distillates, animal

fats, plant oils, water and other raw ingredients.

Depending on context, type of cutting fluid is being

considered, it may be referred to as cutting fluid,

cutting oil, cutting compound, coolant, or lubricant.

Cutting Fluids

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Economic Advantages to Using Cutting Fluids

Reduction of tool costs

Reduce tool wear, tools life longer

Increased speed of production

Reduce heat and friction so higher cutting speeds

Reduction of labor costs

Tools life longer and require less regrinding, less

downtime, reducing cost per part

Reduction of power costs

Friction reduced so less power required by

machining


Characteristics of a Good Cutting Fluid

Good cooling capacity

Good lubricating qualities

Relatively low viscosity

Stability (long life)

Rust resistance

Nontoxic

Transparent

Nonflammable


Types of Cutting Fluids

Most commonly used cutting fluids

• Either aqueous based solutions or

cutting oils

Three categories

• Cutting oils

• Emulsifiable oils

• Chemical (synthetic) cutting fluids


QUERRIES

60


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Date post:	23-Jan-2018
Category:	Engineering
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Cutting tools technology

Engineering