Introduction to machine tool / Single point cutting tool

The tool is wedge shape object of hard material. It is usually made from H.S.S. Beside H.S.S. machine tool is also made from High Carbon Steel, Satellite, Ceramics, Diamond, Abrasive, etc. The main requirement of tool material is hardness. It must be hard enough to resist cutting forces applied on work piece. Hot hardness, wear resistance, Toughness, Thermal conductivity, & specific heat, coefficient of friction, are other requirement of tool material. All these properties should be high.
We discuss about tool material in another thread very soon.

• Classification of cutting tools

A] According to number of cutting edge.

1. Single point cutting tool

It is simplest from of cutting tool & it have only one cutting edge.
Examples – shear tools, lathe tools, planer tools, boring tolls etc.

1. Multi point cutting tool

In this two or more single point cutting tools arranged together as a unit. The rate of machining is more & surface finish is also better in this case.
Example- milling cutter, drills, brooches, grinding wheels, abrasive sticks etc.

B] According to motion

1. Linear motion tools – lathe tools, brooches
2. Rotary motion tools – milling cutters, grinding wheels
3. Linear & rotary motion tools – drills, taps, etc.

• Single point cutting tool geometry

The single point cutting tool mainly consist of tool shank & cutting part called point. The point of cutting tool is bounded by cutting face, end flank, side/ main flank, & base. The chip slide along the face.
The side / main cutting edge ‘ab’ is formed by intersecting of face & side / main flank
The end cutting edge ‘ac’ is formed by the intersection of end flank & base.
The point ‘a’ which the intersection of end cutting edge & side cutting edge is called nose
Mainly the chip cuts by side cutting edge.

• Terminology of single point cutting tool

1. Shank – It is main body of tool. The shank used to grippesd in tool holder.
2. Flank – The surface or surface below the adjacent of the cutting edge is called flank of the tool.
3. Face – It is top surface of the tool along which the chips slides.
4. Base – It is actually a bearing surface of the tool when it is held in tool holder or clamped directly in a tool post.
5. Heel – It is the intersection of the flank & base of the tool. It is curved portion at the bottom of the tool.
6. Nose – It is the point where side cutting edge & base cutting edge intersect.
7. Cutting edge – It is the edge on face of the tool which removes the material from workpiece. The cutting edges are side cutting edge (major cutting edge) & end cutting edge ( minor cutting edge)
8. Tool angles-Tool angles have great importance. The tool with proper angle, reduce breaking of tool, cut metal more efficiently, generate less heat.
9. Noise radius –It provide long life & good surface finish sharp point on nose is highly stressed, & leaves grooves in the path of cut.Longer nose radius produce chatter.

1. Side cutting edge angle (C[SUB]s[/SUB]) (lead angle ) –

It is the angle between side cutting edge & side of tool flank.
The complementary angle of the side cutting edge is called “Approach angle”.
With lager side cutting edge angle the chips produced will be thinner & wider which will distribute the cutting forces & heat produced more over cutting edge.
On other hand greater the component for force tending to separate the work & tool. This causes chatter.

1. End cutting edge angle (C[SUB]e[/SUB]) –

This is the angle between end cutting edge & line normal to tool shank.
It satisfactory value is 80 to 150.
This is denoted by “C[SUB]e[/SUB]”
Function – Provide clearance or relief to trailing end of cutting edge.
It prevent rubbing or drag between machined surface & the trailing port of cutting edge.

1. Back rack/ Front rake / Top rake angle (α[SUB]b[/SUB]) –

It is the angle between face of tool & plane parallel to base.
It is denoted by “α[SUB]b[/SUB]”

1. Side rake angle (α[SUB]s[/SUB]) –

It is angle between face of tool & the shank of the tool.
It is denoted by “α[SUB]s[/SUB]”

1. Front clearance angle / End relief angles –

The angle between front surface of the tool & line normal to base of the tool is known as a front clearance angle
It avoid rubbing of workpiece against tool.

1. Side clearance /relief angle –

This formed by the side surface of the tool with a plane normal to the base of the tool.
It avoid rubbing between flank & workpiece when tool is fed longitudinally.

1. Lip angle / cutting angle –

It is the angle between face & flank. Longer lip angle stronger will be cutting edge. This angle is maximum when clearance & rake angle are minimum. Lager lip angle allows high depth of cut, high cutting speed, work on hard material. It increase tool life & transfer heat fastly.

• Designation of cutting tool / Tool signature –

Tool signature is the description of the cutting part of the tool. There are two system for tool signature.

1. Machine reference system (or American Standard Association system) (ASA)
2. Tool reference system (or Orthogonal rake system) (ORS)

We discuss only reference system as it is widely used.

1. Machine reference system (or American Standard Association system) (ASA)—

In this system angles of the tool face are defined in two orthogonal planes, parallel to the axis of the cutting tool & perpendicular to the axis of cutting tool, both planes being perpendicular to the base of the tool.
So tool signature or tool designation under machine reference system is given by [SUB]b[/SUB]-[SUB]s[/SUB]-Q[SUB]e[/SUB]-Q[SUB]s[/SUB]-C[SUB]e[/SUB]-C[SUB]s[/SUB]-R
where
α[SUB]b[/SUB]=Back rake angle
α[SUB]s[/SUB]=side rake angle
Q[SUB]e[/SUB]= end cleance angle
Q[SUB]s[/SUB]= side clearance angle
C[SUB]e[/SUB]= end cutting edge angle
C[SUB]s[/SUB]= side cutting edge angle
R= nose radius.

• Tool wear / Tool failure –

After use of some time tool is subjected to wear.
Cause of tool wear—

1. Interaction between tool & chip.
2. Cutting forces.
3. Temperature increase during cutting.

*Effect of tool wear—
Tool wear changes tool shape, decrease efficacy. Tool wear induce loss of dimensional accuracy, loss of surface finish. It increases power consumption.
*Classification of tool wear –

1. Flank wear
2. Crater wear on tool face
3. Chipping
4. Breakage
5. Loss of hardness at high temperature

1. Flank wear.

It occurs on flank. It is due to friction between newly machined wokpiece surface & contact area of flank. The worn region at flank is called ’wear land’.
The width of wear land (hf) is account as a measure of wear & it is determined by means of tool maker microscope.
Causes—

1. Feed of brittle material is less than 0.15 mm/rev.
2. Abrasion by hard particles & inclusions in workpiece.
3. Abrasion by fragment of built up edge.
4. Shearing of micro welds between tool & work.

1. Crater wear –

The small cavity is crated on the face of the tool. This small cavity is called ‘crater’ which develops at some distance from cutting edge.
Causes—

1. Pressure of chips when it is slide over face of tool.
2. High temp at tool- chip interface. Some times it reaches to the melting temperature.
3. Crater wear is more in case of continuous chips of ductile material.
4. Lack of lubrication.
5. Feed is less than 0.15 mm/rev.
6. Low cutting speed.

A quantitative term setting the limit of the permissible valve of wear is known as ‘criterion wear’.