Lecture 3 (MP-1)

Manufacturing Processes-2SUBJECT CODE :4ME04

DEPARTMENT OF MECHANICAL ENGINEERING

SEM 4

BY MR.K.P.PAWAR

LECTURER ANURADHA

COLLEGE OF ENGINEERING

* Unit-1( Theory of Metal Cutting)

Objectives of Lecture

To understand basic single point tool geometry

To learn tool signature system

To study cutting tool materials

LECTURE -3

A tool bit is a non-rotary cutting tool used in metal lathe ,shapers and planers

Such cutters are also often referred to by the set-phrase name of single-point cutting tool, as distinguished from other cutting tools such as a saw or water jet cutter

The cutting edge is ground to suit a particular machining operation and may be re-sharpened or reshaped as needed.

The ground tool bit is held rigidly by a tool holder while it is cutting.

Introduction : Single point cutting tool

Basic single point tool geometry

1.Back Rake

Help to control the direction of the chip, which naturally curves into the work due to the difference in length from the outer and inner parts of the cut.

Helps counteract the pressure against the tool from the work by pulling the tool into the work.

2.Side Rake

Along with back rake controls the chip flow and partly counteracts the resistance of the work to the movement of the cutter

Can be optimized to suit the particular material being cut.

Ex. Brass requires a back and side rake of while aluminum uses a back rake of and a side rake of

.3.Nose Radius

Makes the finish of the cut smoother as it can overlap the previous cut and eliminate the peaks and valleys that a pointed tool produces.

Having a radius also strengthens the tip, a sharp point being quite fragile.

4.Clearance Angle

All the other angles are for clearance in order that no part of the tool besides the actual cutting edge can touch the work.

The front clearance angle is usually while the side clearance angle is and partly depends on the rate of feed expected.

Tool Signature

Indicates the angles that a tool utilizes during the cut

Specifies the active angles of the tool normal to the cutting edge

Some of the common systems are:

1. American System

2. British System

3. Continental System

4. International System

American System

Defines the principle angles like side rack, back rake, nose ,etc. with regarding to the cutting edge and without any reference to their locations.

This system of nomenclature does give any indication of the tool behavior with regards to the flow of chip during the cutting operation.

Three reference planes adopted for designated different tool angles are similar to conventional machine drawing.

American System

For example a tool may designated in the following sequence:8-14-6-6-6-15-1

1. Back rack angle :8

2. Side rack angle : 14

3. End relief angle : 6

4. Side relief angle :6

5. End cutting edge angle: 6

6. Side cutting edge angle :15

7. Nose radius :1mm

British SystemThis system defines the maximum rake

The variation of tool parameters in this system are indicated in the order of :

1. Back rake

2. Side rake

3. End relief angle

4. Side relief angle

5. Side cutting edge angle

6. Nose radius

Continental System: German System Various tool parameters are specified with reference to the tool

reference planes.

International System: Internationally adopted system, developed recently. Incorporates the salient features of tool nomenclature of

different systems in it.

Cutting Tool Materials

Properties of cutting tool material:1. Hot hardness2. Wear & abrasion resistance3. Impact toughness4. Increased thermal conductivity5. Lower co-efficient of thermal expansion6. Lower chemical & mechanical affinity for the work material7. Easy to grind & sharpening8. High specific heat9. Low coefficient of friction between work & the tool10. Easy to fix to the tool holder

Selection of tool material depends up on following factors:

1. Type of cutting operation

2. Material of work piece

3. Machine tool to be used & surface finish required

Cutting Tool Materials

Over the years, a wide variety of cutting tool materials have been developed to meet the ever increasing demand of machining herder & harder materials.The various cutting tool materials can be grouped as follows:1. Plain carbon steel2. Medium Alloy Steel3. High Speed Steel4. Non-ferrous Cast Alloy5. Cemented Carbides6. Ceramics or Oxides7. Cermets8. Diamond9. Cubic Boron Nitride(CBN)10. UCON11. Sialon12. Coronite

Carbon tool steels

1.Unstable

2.Very inexpensive

3.Extremely sensitive to heat

4.Mostly obsolete in today's commercial machining

5.It is still commonly found in non-intensive

6.Applications such as hobbyist or MRO machining, where economy-grade drill bits, taps and dies, hacksaw blades and reamers are still usually made of it (because of its affordability)

7.Hardness up to about HRC 65

8.Sharp cutting edges possible

1.Unstable

2.Inexpensive

3.Retains hardness at moderate temperatures

4.The most common cutting tool material used today

5.Used extensively on drill bits and taps



High speed steel

1.Unstable

2. Moderately expensive

3.The high cobalt versions of high speed steel are very resistant to heat and thus excellent for machining abrasive and/or work hardening materials such as titanium and stainless steel.

4.Used extensively on milling cutters and drill bits


6.Sharp cutting edges possible.

HSS cobalt

Cast cobalt alloys

1.Stable

2.Expensive

3.Somewhat fragile

4.Despite its stability it doesn't allow for high machining

speed due to low hardness. Not used much.



1.Stable

2.Moderately expensive

3.It is offered in several "grades" containing different proportions of tungsten carbide and binder (usually cobalt)

4.High resistance to abrasion

5.High solubility in iron requires the additions of tantalum carbide and niobium carbide for steel usage

Cemented carbide

6.Its main use is in turning tool bits although it is very common in milling cutters and saw blades.

7.Hardness up to about HRC 90.

8.Sharp edges generally not recommended.

Ceramics

1.Stable

2.Moderately inexpensive

3.Chemically inert and extremely resistant to heat, ceramics are usually desirable in high speed applications, the only drawback being their high fragility

4. Ceramics are considered unpredictable under unfavorable conditions

5. The most common ceramic materials are based on alumina (Aluminium oxide), silicon nitride and silicon carbide

6.Used almost exclusively on turning tool bits


8.Sharp cutting edges and positive rake angles are to be avoided

Cermets1.Stable

2.Moderately expensive

3.Another cemented material based on titanium carbide (TiC)

4.Binder is usually nickel

5.It provides higher abrasion resistance compared to tungsten carbide at the expense of some toughness

6. More chemically inert

7. Extremely high resistance to abrasion

7.Used primarily on turning tool bits although research is being carried on producing other cutting tools


9.Sharp edges generally not recommended.

1.Stable

2.Very Expensive

3.The hardest substance known to date

4.Superior resistance to abrasion but also high chemical affinity to iron which results in being unsuitable for steel machining.

6.Extremely fragile

7.Used almost exclusively on turning tool bits although it can be used as a coating on many kinds of tools

8.Sharp edges generally not recommended

Diamond

Diamond tools

Question & Answer Session

Q1. What are different angles involved in single point tool geometry?

Q2. What are different tool signature system ?

Q4. What are different cutting tool materials ?

Lecture 3 (MP-1)

Engineering