Introduction

Generally metal components are made into different shapes and dimensions by using various metal working processes.

Metal working processes are classified:

• Chips less or Metal forming process - forging,rolling and pressing

• Metal cutting or Chip forming process - turning: drilling and milling

• Machining is an essential process of finishing by which work pieces are produced to the desired dimensions and surface finish by gradually removing the excess material from the preformed blank in the form of chips with the help of cutting tool.

• Cutting action involves shear deformation of work material to form a chip.

• As chip is removed, new surface is exposed.

Chip Thickness Ratio Chip

• Thickness ratio is defined as the thickness of metal before cutting to the thickness of metal after cutting.

r=t₁/t₂

where r = chip thickness ratio;

t₁ = thickness of the chip prior to chip formation

t₂ = chip thickness after separation

• Chip thickness after cut always greater than before.

Chip formation

• The type of chip produced during metal cutting depends upon the machining conditions and material being cut.

1) Properties of material (Brittle or Ductile)

2)Depth of cut / Cutting Speed

3) Effective rake angle of tool

4)Cutting fluid.

Types of Chip

1. Continuous chip

2. Discontinuous chip

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

Continuous Chip

• Continuous chips are formed by the continuous plastic deformation of metal without fracture in front of the cutting edge of the tool.

• Ductile material like aluminium and copper are considered to be best for continuous type chips.

Continuous chips tend to be formed.

• Material should be ductile in nature

• Rake angle and cutting speed should be high

• Friction should be minimum

• Depth of cut should be small

Discontinuous Chip

• According to name this chips are breakup in to small segment and these chips are convenient to collect handle and dispose off.

• These type of chips are forms while machining the brittle material.

• This chips are formed when friction between tool and work piece is high and cutting speed is low with small rake angle.

Discontinuous chips tend to be formed

• Brittle material

• Low cutting speed

• Small rake angle

Continuous chip with Built-up Edge (BUE)

• This type of chip is similar to continuous chip, only difference is that it has a build up edge at 4 the face of tool and also it not so smooth.

• At high temperature chips material get stick to the cutting edge and tool face near the nose it is called BUE.

• As the cutting goes continuous built up edge increases and change the geometry of tool.

• This chip is obtain by machining on ductile material under high temperature. chips tend to be formed.

  • Ductile Material
  • Inadequate cutting fluid

Purpose of machining

• Most of the engineering components need dimensional accuracy and good surface finish for serving their purposes.

• Performing like casting, forging etc., generally cannot provide the desired accuracy and finish.

• Need semi-finishing / finishing and it is done Pakalpo machining.

Machining to high accuracy and finish essentially enables a product :

• Fulfill its functional requirements.

• Improve its performance.

• Prolong its service.

Requirements of machining

• The lank and the cutting tool are properly mounted (in fixtures) and moved in a powerful device called machine tool.

• Enabling gradual removal of layer of material from the work surface resulting in its desired dimensions and surface finish.

• Additionally some environment called cutting fluid is generally used to ease machining by cooling and lubrication.

• Provide power to the tool-work pair for the machining action.

• Control of the machining parameters (speed, feed and depth of cut)

Specification of machine tools Centre lathe

• Maximum diameter and length of the jobs that can be accommodated.

• Power of the main drive (motor).

• Range of spindle speeds and range of feeds.

  Types of cutting tools

• Cutting tools may be classified according to the number of major cutting edges (points) involved

• Single point - turning tools, shaping, planning and slotting tools

• Multipoint - milling cutters and broaching tools

• Space occupied by the machine.

Types of metal cutting processes

Orthogonal cutting process

• The cutting edge of the tool remains normal to the direction of tool feed.

• The chip coils in a tight flat spiral

• The force which shears the metal acts on a smaller area so the tool life is less.

• Produces sharp corners

Oblique cutting process

• The cutting edge of the tool is inclined at an angle to the direction of tool feed.

• The chip flows side ways in a long curl.

• Tool life is more because the cutting force acts on larger area.

• Produces a chamfer at the end of cut.