introduction to machine tools and metal cutting

introduction to machine tools and metal cutting

Introduction:-

Metals are shaped into usable forms through various processes. Of these, some are called non cutting shaping processes, i.e., those in which no chip formation takes place, and the metal is shaped under the action of heat, pressure or both. This category includes operations like forging, drawing, spinning, rolling, extruding, etc. Against this, there are other processes in which the components are brought to the desired shape and size by removing the unwanted material from the parent metal in the form of chips through machining. This is termed as cutting shaping. A few of the important machining processes falling in this category are turning, boring, milling, drilling, shaping, planning, etc.

Machining of metal involves forging cutting tool through the excess material of the work piece in the form of small chips. This excess material progressively separated from the work piece desired shape and size. In this theory
1.Machine tools do not require, elaborate tooling.
2.The process of machining can be employed to all engineering materials.
3.The wear of tool is not costly.
Elements of cutting process or Mechanics of metal cutting :-
1.work piece
2.Tools
3.Chip
4.Cutting fluids.

The figure shows the position of cutting tool in relation to work in order to cut metal with less effect. In this there are 3 basic angles are important.

1. Back angle(α)
2. Clearance angle(𝜃)
3. shear angle(∅)
METHODS OF METAL CUTTING:-

In cutting process are (1) orthogonal cutting (2) oblique cutting.

(1) Orthogonal cutting:- In orthogonal cutting the cutting edge of tool remains at right angles to the direction of cutting velocity or work feed. This type of cutting also know as two- dimensional cutting.
The main features of two- dimensional cutting are

(i) The cutting edge of the tool remains normal to the direction of tool feed or work feed.

(ii) The direction of the chip flow velocity is normal to the cutting edge of the tool.

(iii) The cutting edge is longer then the width of the cut.

(2) Oblique cutting :- In Oblique cutting the cutting edge of tool is inclined and not perpendicular to motion of work piece is known as oblique cutting. This type of cutting also know as three - dimensional cutting

The main features of three - dimensional cutting are
(i) The cutting edge of the tool always remains inclined at an acute angle to the direction of tool feed or work feed.
(ii) The direction of the chip flow velocity is at an angle ‘𝛽’ with the normal to the cutting edge of the tool. The angle is known as chip flow angle.

(iii) The cutting edge may or may not be longer than the width of cut.

In any cutting operation the following observations are can be made.

1. Metal is cut by removal of chips. Which may be in the form of continuous ribbon or discontinuous chips. In this the chip is thicker than the depth of cut.
2. a lot of heat is generated in the process of cutting due to friction between the chip and tool.
3. There is no flow of metal at right angles to the direction of chip flow.

CLASSIFICATION OF CUTTING TOOLS :-

All the cutting tools used in metal cutting can be broadly classified as

1. Single point tools:- Those having only one cutting edges ; such as lathe tools, shaper tools, planer tools, boring tools, etc.
2. Multi-point tools:- Those having more than one cutting edges; such as milling cutters, drills, broaches, grinding wheels, etc.