This document discusses the theory of metal cutting. It covers topics such as tool geometry, chip formation, types of chips, tool wear, cutting fluids, and tool material selection. It describes the two main types of metal cutting processes as orthogonal and oblique cutting. Orthogonal cutting involves two forces while oblique cutting involves three forces. Chip formation occurs through shear deformation of the work material. The main types of chips are continuous, discontinuous, continuous with BUE, and serrated. Continuous chips form under conditions like small chip thickness and high cutting speed, while discontinuous chips occur when machining brittle materials.

1. UNIT-II THEORY OF METAL
CUTTING
Mr. S. V. Deshmukh
Asst. Prof.

2. THEORY OF METAL CUTTING
 Tool Geometry,
 Tool Signature,
 Chip Formation,
 Types of Chip,
 Tool Wear,
 Surface Finish,
 Cutting Fluids and Machinability,
 Selection of Tool Materials.

3. TOOL GEOMETRY
 Basic Elements of machining
 Workpiece
 Tool
 Chip

4. TYPES OF METAL CUTTING
PROCESSES
 The metal cutting process is mainly classified into two types
1. Orthogonal cutting process
2. Oblique cutting process
Orthogonal cutting process (Two - dimensional cutting)
 The cutting edge or face of the tool is 90 deg. to the line of
action or path of the tool or to the cutting velocity. This
cutting involves only two forces and this makes the analysis
simple.
 The cutting edge of the tool remains normal to the direction
of tool feed or work feed.
 The direction of the chip flow velocity is normal to the
cutting edge of the tool.
 The angle of inclination of the cutting edge of the tool with
the normal to the velocity is zero.

5. ORTHOGONAL CUTTING PROCESS (TWO -
DIMENSIONAL CUTTING)
 The chip flow angle between the direction of chip flow
and the normal to the cutting edge of the tool, measured
in the plane of the tool face is zero.
 The longer edge is longer than the width of the cut.

6. OBLIQUE CUTTING PROCESS (3-
DIMENSIONAL CUTTING)
 The cutting edge or face of the tool is inclined at an
angle less than 90 deg. to the line of action or path of the
tool or to the cutting velocity. Its analysis is more
difficult of its three dimensions.
 The direction of the chip flow velocity is at an angle with
the normal to the cutting edge of the tool. The angle is
known as chip flow angle.
 The cutting edge of the tool is inclined at an angle with
the normal to the direction of work feed or tool feed i.e.
the velocity.
 Three mutually perpendicular components of cutting
forces act at the cutting edge of the tool.

7. Oblique cutting

8. CLASSIFICATION OF CUTTING TOOLS
 Single Point Tools :- Those having only one cutting edge,
such as lathe tool, shaper tool, planer tool, boring tool,
etc..
 Multi-point Tool :- Those having more than one cutting
edge such as milling cutter, drills, broaches, grinding
wheel, etc.
 The cutting tools can be also classified according to the
motion as;
 Linear motion tools
 Rotary motion tools
 Linear and Rotary tools

9. IMPORTANT TERMS IN CUTTING
TOOL
 Shank: The portion of the tool bit which is not ground to
form cutting edges and is rectangular in cross section.
 Face: The surface against which the chip slides upward.
 Flank: The surface which face the work piece. There are
two flank surfaces in a single point cutting tool. One is
principal flank and the other is auxiliary flank
 Heel: The lowest portion of the side cutting edges.
 Nose radius: The conjunction of the side cutting edge
and end cutting edge. It provides strengthening of the
tool nose and better surface finish.
 Base: The underside of the shank.

11. PRINCIPAL ANGLES OF SINGLE POINT
TOOLS
 Rake angle : It is the angle formed between the face of
the tool and plane parallel to its base.
 If this inclination is towards the shank, it is known as
back rake or top rake.
 When it is measured towards the side of tool it is called
the side rake.
 Positive rake - helps reduce cutting force and thus
cutting power requirement.
 Zero rake - to simplify design and manufacture of the
form tools.
 Negative rake - to increase edge-strength and life of the
tool.

12.  Clearance angle (α): Angle of inclination of clearance or
flank surface from the finished surface.
 Clearance angle is essentially provided to avoid rubbing of the
tool (flank) with the machined surface which causes loss of
energy and damages of both the tool and the job surface.
Hence, clearance angle is a must and must be positive (30 ~
15 deg) depending upon tool-work materials and type of the
machining operations like turning, drilling, boring etc.
 Clearance angles: αx = Side clearance angle (Side relief
angle): angle of inclination of the principal flank from the
machined surface (or CV) and measured on Horizontal plane.
 αy = Back clearance angle (End relief angle): same as αx but
measured on perpendicular plane.

13.  Relief Angle : It is the angle formed between the flank of
the tool and a perpendicular line drawn from the cutting
point to the base of the tool.
 Cutting Angle : the total cutting angle of the tool is the
angle formed between the tool face and a line through
the point, which is a tangent to the machined surface of
the work at that point.

15. TOOL SIGNATURE
 The term tool signature or tool designation is used to
denote a standardized system of specifying the principle
tools and angles of single point cutting tool.
1. American (or ASA) system : its defines the principal
angles like side rake, back rake, nose etc. without to
their locations with regard to the cutting edge.
2. British system : this system according to B-S 1886-
1952, defines the maximum rake.
In the order of rake angle, side rake, end relief angle,
side relief angle, end cutting angle, side cutting edge
angle and nose radius.
3. International system
4. Continental system : German or DIN system, russian
system.

16. REFERENCE PLANES
 The coordinate system
 It is assumed that the tool, although held in position in
space with reference to the workpiece, is not operating
on the workpiece.
 It consists of three principal reference planes.
 Horizontal plane which contains the base of the shank of
the cutting tool.
 Vertical plane is normal to the base plane and parallel to
the direction of feed of the cutting too (XX’).
 Transverse plane (YY’) is perpendicular to both the
above reference plane and is parallel to the transverse
motion of the tool, i.e. depth of cut.

18. THE ORTHOGONAL SYSTEM
 In this system of reference planes it is assumed that the
cutting tool is operating against the workpiece.
 The horizontal plane contains the base of the cutting tool
and is known as the base plane.
 Which is perpendicular to the base plane, contains the
principal cutting edge and is called the cutting plane,
 The third plane, which is perpendicular to both the above
plane is known as orthogonal plane.

20. TOOL GEOMETRY IN COORDINATE
SYSTEM
 This system having been adopted by American standard
association is also known as A.S.A system of tool
signature.
 The nomenclature of reference planes as X, Y and Z,
some authors describe it as X-Y-Z plane system.
 This system of reference planes, together with the
principal angles of a single point cutting tool.
 Different parameters are mentioned in the order- back
rake, side rake, end relief angle, side relief angle, end
cutting edge angle, side cutting edge angle and nose
radius.
 The value of nose angle Ɵ will depend upon the values
of ɸe and ɸc.

21. Ex. Describe a tool with 8, 10, 6, 6, 6, 10, 2 signature in A.S.A
system.

22. TOOL GEOMETRY IN ORTHOGONAL
SYSTEM
 This system is also known as orthogonal rake system
(O.R.S.) or international system.
 The main parameters of a single point cutting tool are
designated in the following order.
 Inclination angle (λ)
 Orthogonal angle (α)
 Side relief angle (γ)
 End relief angle (γ1)
 Auxiliary cutting angle (ɸ1)
 Approach angle (ɸ0)
 Nose radius (R)

24. INTER-RELATIONSHIP BETWEEN ASA
AND ORS SYSTEM
 To convert some tool parameters in ASA system to ORS
system and vice versa.
 The following relationship will help in such conversion
tan α = tan αy cos ɸ0 + tan αx sin ɸ0
tan λ = tan αy sin ɸ0 −tan αx tan ɸ0
tan αx = sin ɸ0 tan α − cos ɸ0 tan λ
tan αy =cos ɸ0 tan α + sin ɸ0 tan λ

25. CHIP FORMATION
 Cutting action involves shear deformation of work
material to form a chip.
 As chip is removed, new surface is exposed.

26. MECHANISM OF CHIP FORMATION
 The form of the chips is an important index of machining
because it directly or indirectly indicates :
 Nature and behavior of the work material under
machining condition
 Specific energy requirement (amount of energy required
to remove unit volume of work material) in machining
work
 Nature and degree of interaction at the chip-tool
interfaces.

27. The form of machined chips depend mainly upon
• Work material
• Material and geometry of the cutting tool
• Levels of cutting velocity and feed and also to some extent on
depth of cut
• Machining environment or cutting fluid that affects temperature
and friction at the chip-tool and work-tool interfaces.
Knowledge of basic mechanisms of chip formation helps to
understand the characteristics of chips and to attain favorable
chip forms.

28. FOUR BASIC TYPES OF CHIP IN
MACHINING
1. Discontinuous chip
2. Continuous chip
3. Continuous chip with Built-up Edge (BUE)
4. Serrated chip

29. 1.CONTINUOUS CHIPS
 Continuous chips are usually formed with ductile
materials at high rake angles and/or high cutting
speeds.
 A good surface finish is generally produced.
 continuous chips are not always desirable,
particularly in automated machine tools, it tends to
get tangled around the tool and operation has to be
stopped to clear away the chips.

30.  Continuous chips usually form under the following
conditions:
 Small chip thickness (fine feed)
 Small cutting edge
 Large rake angle
 High cutting speed
 Ductile work materials
 Less friction between chip tool interface through efficient
lubrication
 Deformation of the material takes place along a narrow shear
zone, primary shear zone.
 CCs may, because of friction, develop a secondary shear zone
at tool–chip interface. The secondary zone becomes thicker as
tool–chip friction increases.
 In CCs, deformation may also take place along a wide primary
shear zone with curved boundaries.

31. 2. DISCONTINUOUS CHIPS
 Discontinuous chips consist of segments that may be
firmly or loosely attached to each other.
 These chips occur when machining hard brittle
materials such as cast iron.
 Brittle failure takes place along the shear plane before
any tangible plastic flow occurs.
 Discontinuous chips will form in brittle materials at
low rake angles (large depths of cut).

32. DCs usually form under the following conditions:
1.Brittle work piece materials
2.Work piece materials that contain hard inclusions and
impurities, or have structures such as the graphite flakes in
gray cast iron.
3. Very low or very high cutting speeds.
4. Large depths of cut.
5. Low rake angles.
6. Lack of an effective cutting fluid.
7. Low stiffness of the machine tool.
Because of the discontinuous nature of chip formation,
forces continually vary during cutting.
Hence, the stiffness or rigidity of the cutting-tool holder,
the Work holding devices, and the machine tool are important
in cutting with both DC and serrated-chip formation.

33. 3.BUILT-UP EDGES CHIPS
 BUE, consisting of layers of material from the work piece
that are gradually deposited on the tool, may form at the tip
of the tool during cutting.
 As it becomes larger, BUE becomes unstable and eventually
breaks up.
 Part of BUE material is carried away by the tool side of the
chip; the rest is deposited randomly on the work piece
surface.
 The process of BUE formation and destruction is repeated
continuously during the cutting operation, unless measures
are taken to eliminate it.

34. EFFECTS OF BUE FORMATION
 It unfavorably changes the rake angle at the tool tip
causing increase in cutting forces and power consumption
 Repeated formation and dislodgement of the BUE causes
fluctuation in cutting forces and thus induces vibration
which is harmful for the tool, job and the machine tool.
 Surface finish gets deteriorated
 May reduce tool life by accelerating tool-wear at its rake
surface by adhesion and flaking
 Occasionally, formation of thin flat type stable BUE may
reduce tool wear at the rake face.