This document discusses chip formation and cutting tool geometry in metal cutting operations. It describes the mechanics of chip formation, where a wedge-shaped tool exerts pressure on the workpiece, inducing shear deformation and removing material in the form of chips. The types of chips formed depend on whether the material is ductile or brittle. Continuous, discontinuous, and continuous chips with built-up edges are discussed. The document also outlines the geometry of single point cutting tools, designation systems, types of rakes, orthogonal and oblique cutting methods, forces on tools, and the purpose and types of chip breakers used.

1. CHIP FORMATION & CUTTING
TOOL GEOMETRY
Md. Tarek Ur Rahman Erin
Sr. lecturer, Dept. of MTE, WUB

2. CONTENTS
■ 1. Introduction
■ 2. Mechanics of chip formation
■ 3. Single point cutting tool and its designation
■ 4. Methods of machining
■ 5. Types of chips
■ 6. Forces on single point cutting tool
■ 7. Chip Breakers
■ 8. Specific cutting pressure

3. INTRODUCTION
Metal cutting or machining is the process of producing
workpiece by removing unwanted material from a block of
metal, in the form of chips.
This process is most important because almost all
products get their final shape and size directly or indirectly
by machining.
Its major drawback is that in this process there is a lot of
material lost in the form of chips.

4. MECHANICS OF CHIP FORMATION
A wedge shaped tool is made to move relative to the workpiece.
As the tool makes contact with the workpiece it exerts pressure
on it resulting in compression of the metal near the tool tip.
This induces shear – type deformation within the metal and it
starts moving upward along the face of the tool.
As the tool advances this process of shearing goes on increasing
and material is removed.

5. MECHANICS OF CHIP FORMATION

6. CHIP FORMATION IN DUCTILE
MATERIALS
As the tool makes contact with the
workpiece it results in exerting pressure on
the material in front of it.
This causes the shear deformation in
the workpiece and the metal starts moving
up in laminar form along the face of the
tool.
This is also known as Pispannen’s
model of chip formation.
Figure : Chip formation in ductile
materials

7. CHIP FORMATION IN BRITTLE
MATERIALS
Cracks develop in the workpiece near
the tool tip.
This crack results in stress
concentration.
Hence, crack propagation intensity
increases and the chip detaches itself from
the base material.
This results in a discontinuous, irregular
shape and sized chip.
Figure : Chip formation in brittle
materials

8. SINGLE POINT CUTTING TOOL
• It consists of a sharpened cutting edge called its point .
• The point is bounded by the face, the side flank, the end flank and
the base.
• The side cutting edge is formed by intersection of face and side
flank.
• The end cutting edge is formed by intersection of face and end
flank.
• The point where end and side cutting edge meets is called the
nose of the tool.

9. SINGLE POINT CUTTING TOOL
Figure: Single point cutting tool

10. TOOL DESIGNATION
By designation or nomenclature of the tool we mean the
designation of the shape of the tool.
There are two systems widely used for tool designation :
• ASA System ( American standards association system ) or
ANSI System ( American National standards Institute system ).
• ORS ( Orthogonal Rake system)
In this discussion, we will know about ASA system.

11. TOOL DESIGNATION BY ASA SYSTEM
In this system the angles of
the tool face i.e. its slope,
are defined in two
orthogonal plane, one
parallel to and another
perpendicular to the axis of
cutting tool.
Figure :Tool designation by ASA system

12. TYPES OF RAKES
Figure :Types of rakes angle

13. TYPES OF RAKES
The use of positive rake is recommended in following conditions :
• While machining low strength ferrous and non ferrous materials.
• When low power machines.
• When machining long shafts of low diameters.
• When the set up lacks strength and rigidity.
• When cutting is done at low speeds.

14. TYPES OF RAKES
The use of negative rake is recommended in following conditions :
• While machining high strength alloys.
• When there are high impact loads.
• When there are highly rigid setups.
• When cutting is done at high speeds.

15. TYPES OF RAKES

16. METHODS OF MACHINING
In the cutting operation the tool is wedge shaped and has a
straight cutting edge.
Basically, there are two methods of metal cutting, depending
upon the arrangement of the cutting edge w.r.t. the direction of
relative tool work motion :
1. Orthogonal cutting
2. Oblique cutting

17. ORTHOGONAL CUTTING
Orthogonal cutting is a type of metal cutting in which the cutting
edge of wedge shape cutting tool is perpendicular to the direction of
tool motion.
In this cutting the cutting edge is wider than width of cut.
In this case the chip slides directly up the tool face.
Figure: Orthogonal cutting

18. OBLIQUE CUTTING
In oblique cutting, the cutting edge of the tool is set at an angle
other than 90˚ with respect to the direction of the velocity vector of
the tool.
In this case lateral direction of chip movement is obtained.
Figure: Oblique cutting

19. DIFFERENCE BETWEEN ORTHOGONAL AND
OBLIQUE CUTTING

20. CONTENTS
■ 1. Types of chips
■ 2. Forces on single point cutting tool
■ 3. Chip Breakers
■ 4. Specific cutting pressure

21. CHIPS AND ITS TYPES
The waste/dust material produced while machining any surface is
termed as chip. Depending on the workpiece material and the
cutting conditions, the following types of chip formation can be
distinguished.
Continuous chips
Discontinuous chips
Continuous chips with built up edges (BUE)

22. CONTINUOUS CHIPS
If the metal chips formed during machining is without segments
i.e. without breakage, than it is called as continuous types of chips.
Continuous chips are formed when the ductile material is
machined with high cutting speed and minimum friction between
the chip and tool face.
Figure: Continuous chips

23. CONTINUOUS CHIPS
If the metal chips formed during machining is without segments
i.e. without breakage, than it is called as continuous types of chips.
Continuous chips are formed when the ductile material is
machined with high cutting speed and minimum friction between
the chip and tool face.
Figure: Continuous chips

24. CONTINUOUS CHIPS
The conditions which are responsible for the formation of
continuous types of chips are :
I. Ductile material like mild steel is used.
II. Bigger rake angle of the tool.
III. High cutting speed.
IV. Minimum friction between the chip and tool interface.
V. Small depth of cut.

25. CONTINUOUS CHIPS
• Advantages of Continuous Chips:
I. Better surface finish to the ductile material.
II. Less heat generation due to minimum friction between the tool
face and chip.
III. Low power consumption.
IV. Long tool life due to less wear and tear.

26. DISCONTINUOUS CHIPS
If the chips formed during machining process is not continuous
i.e. formed with breakage is called discontinuous chips.
Discontinuous types of chips are formed when hard and brittle
metals like brass, bronze and cast iron is machined.

27. DISCONTINUOUS CHIPS
Conditions which are responsible for the formation of discontinuous
chips are : Low feed rate.
I. Small rake angle of the tool.
II. High cutting speed.
III. High friction forces at the chip tool interface.
IV. Too much depth of cut.

28. DISCONTINUOUS CHIPS
Advantages :
The formation of discontinuous types of chips in brittle materials
provides good surface finish, increases the tool life and reduces the
consumption of power.
Disadvantages :
When discontinuous chips are formed in the ductile materials, the
workpiece result in poor surface finish and excessive wear and tear
of the tool takes place.

29. CONTINUOUS CHIP WITH BUILT UP EDGE
Continuous chips with built up edge is formed by machining
ductile material with high friction at the chip-tool interface.
It is similar to the continuous types of chips but it is of less
smoothness due to the built up edge.
Figure: Continuous chip with built up edge

30. FORMATION OF BUILT UP EDGE
• When the chip flows in upward direction there exist high friction in
between the interface of the chip and tool.
• Due to the high friction between the chip and tool a very intense
heat is generated at the nose of the tool.
• The compressed metal adjacent to the tool nose gets welded to it.
This compressed metal welded to the nose is called built up edge.
• Due to formation of the built up edge the rake angle of the tool
gets changed and so is the cutting force.

31. CONTINUOUS CHIP WITH BUILT UP EDGE
The factors which are responsible for promoting the
formation of the BUE chips are:
Excessive feed rate.
Small rake angle of the tool.
Low cutting speed.
Lack of coolant and this increase the friction between the chip
tool interfaces.

32. CONTINUOUS CHIP WITH BUILT UP EDGE
Advantages :
The making of the BUE has one advantage i.e. it protects the tool
from getting damaged from high friction and temperature
generated during machining process and hence the tool life
increases.
Disadvantages :
The formation of these types of chips results in rough surface finish,
change in the rake angle and cutting forces.

33. COMPARISON BETWEEN ALL CHIP TYPES

34. FORCE ON A SINGLE POINT TOOL
The work material offers resistance to the cutting tool, during
metal cutting.
This resistance is overcome by the cutting force applied to the
tool face.
The work done by this force in cutting is expended in shearing the
chip from the work, deforming the chip and overcoming the friction
of the chip on the tool face and tool flank on the cutting surface.

35. FORCE ON A SINGLE POINT TOOL
Magnitude of this force depends upon :
- material being machined - tool angles
- rate of feed - cutting speed
- depth of cut - coolant used

36. FORCE ON A SINGLE POINT TOOL
Magnitude of this force depends
upon :
- material being machined - tool
angles
- rate of feed - cutting speed
- depth of cut - coolant used
Figure: Force on a single point tool

37. CHIP BREAKERS
Continuous chips produced while machining ductile materials
often causes difficulties of handling because they occupy
considerable space and have sharp edges.
They may also be hot.
They also get entangled and start rotating with the job.
Hence, it is desirable to break these chips into short convenient
length for their proper disposal. This operation of chip breaking is
done by chip breakers.

38. CHIP BREAKERS
Chip breakers are classified as :
I. Groove type
II. Obstruction type
Figure: Groove type chip breakers Figure: Obstruction type chip breakers

39. CHIP BREAKERS
Advantages :
Ensure safety for operator.
Increase tool life.
Facilitate the removal of chips from cutting zone.
Reduce the cutting resistance and vibration, hence increase
machine performance.
Machined surface do not get spoiled by continuous chips.
Increase productivity (decrease time loss) – small chips take less
volume than continuous chip, so it does not need chip disposal as
frequent as continuous chip.

40. CHIP BREAKERS
Disadvantages of chip breaker :
Frequent chip braking and hitting at flank of tool may causes
harmful vibration.
Some cases the use of chip breaker causes the spoilage of
surface finish quality.
Heat and stress concentrated at sharp cutting edge, results the
rapid failure of cutting edge.

41. BIBLIOGRAPHY
A Text book of manufacturing technology by R.K. Rajput – Laxmi
publications.
A Text book of production engineering by P.C. Sharma – Chapter
no. 14 – S. Chand and company Limited, 2006 Edition, ISBN 81-
219-0421-8.
Manufacturing process II – Lecture by Dr. V.K. Jain Indian Institute
of technology, Kanpur.
Images from www.google.com
www.mecholic.com
www.mechanicalbooster.com

42. Thank You