Manufacturing Tech. II
Manufacturing Tech. II
Manufacturing Tech. II
UNIT -1
The angle between the tool face and the line parallel to the base of the tool is
2. What is tool?
It is the joining of side and end cutting edges by means of small radius in
order to increase the tool life and better surface finish on the work piece.
• Cutting speed
• Feed
• Depth of cut.
Oblique cutting: - The cutting edge is inclined at an acute angle with normal to
The sheared material begins to flow along the cutting tool face in the form of
small pieces . The compressive force applied to form the chip is called cutting
force
efficient. K=1/r
The chip breakers are used to break the chips into small pieces for removal,
machined
Tool life is defined as the time elapsed between two consecutive tool
resharpening. During this period the tool serves effectively and efficiently
C= Constant
Cutting speed
Tool material
Cutting fluid
Work material
14.What are the four important characteristics of materials used for cutting
tools?
Hot hardness
Wear resistance
Cemented
carbides Ceramics
Diamonds
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16. What are the functions of cutting fluids?
It lubricates the cutting tool and thus reduces the co-efficient of friction
It washes away the chips from the tool. It prevents the tool from
17. What are the factors responsible for built-up edge in cutting tools?
During cutting process, the interface temperature and pressure are quite high
and also high friction between tool chip interfaces causes the chip material to
weld itself to the tool face near the nose. This is called built up edge
It should have a high specific heat, high heat conductivity and high film co-
efficient.
It should be odorless
PART-B
1. Explain orthogonal cutting and oblique cutting with its neat sketches and compare?
Tool life
Tool wear is a time dependent process. As cutting proceeds, the amount of tool wear
increases gradually. But tool wear must not be allowed to go beyond a certain limit in
order to avoid tool failure. The most important wear type from the process point of
view is the flank wear, therefore the parameter which has to be controlled is the width
of flank wear land, VB. This parameter must not exceed an initially set safe limit,
which is about 0.4 mm for carbide cutting tools. The safe limit is referred to as
allowable wear land (wear criterion),
. The cutting time required for the cutting tool to develop a flank wear land of width
is called tool life, T, a fundamental parameter in machining. The general relationship
of VB versus cutting time is shown in the figure (so-called wear curve). Although the
wear curve shown is for flank wear, a similar relationship occurs for other wear
types. The figure shows also how to define the tool life T for a given wear criterion
VBk
Machinability
Machinability is a term indicating how the work material responds to the cutting
process. In the most general case good machinability means that material is cut with
good surface finish, long tool life, low force and power requirements, and low cost.
Steels Leaded steels: lead acts as a solid lubricant in cutting to improve considerably
machinability.
Resulphurized steels: sulphur forms inclusions that act as stress raisers in the chip
formation zone thus increasing machinability.
Other metals
Aluminum: easy-to-cut material except for some cast aluminum alloys with silicon
content that may be abrasive.
Cast iron: gray cast iron is generally easy-to-cut material, but some modifications and
alloys are abrasive or very hard and may cause various problems in cutting.
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Cooper-based alloys: easy to machine metals. Bronzes are more difficult to machine
than brass.
For each machining operation, a proper set of cutting conditions must be selected
during the process planning. Decision must be made about all three elements of
cutting conditions,
Depth of cut
Feed
Cutting speed
Carbon Steels
It is the oldest of tool material. The carbon content is 0.6~1.5% with small quantities of silicon,
Chromium, manganese, and vanadium to refine grain size. Maximum hardness is about HRC 62. This
material has low wear resistance and low hot hardness. The use of these materials now is very limited.
First produced in 1900s. They are highly alloyed with vanadium, cobalt, molybdenum, tungsten and
Chromium added to increase hot hardness and wear resistance. Can be hardened to various depths by
appropriate heat treating up to cold hardness in the range of HRC 63-65. The cobalt component give
the material a hot hardness value much greater than carbon steels. The high toughness and good wear
resistance make HSS suitable for all type of cutting tools with complex shapes for relatively low to
medium cutting speeds. The most widely used tool material today for taps, drills, reamers, gear tools,
end cutters, slitting, broaches, etc.
Cemented Carbides
Introduced in the 1930s. These are the most important tool materials today because of their high hot
hardness and wear resistance. The main disadvantage of cemented carbides is their low toughness.
These materials are produced by powder metallurgy methods, sintering grains of tungsten carbide
(WC) in a cobalt (Co) matrix (it provides toughness). There may be other carbides in the mixture, such
as titanium carbide (TiC) and/or tantalum carbide (TaC) in addition to WC.
Ceramics
Ceramic materials are composed primarily of fine-grained, high-purity aluminum oxide (Al2O3),
pressed and sintered with no binder. Two types are available:
White, or cold-pressed ceramics, which consists of only Al2O3 cold pressed into inserts and sintered
at high temperature.
Surface finish
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The machining processes generate a wide variety of surface textures. Surface texture consists
of the repetitive and/or random deviations from the ideal smooth surface. These deviations are
Three main factors make the surface roughness the most important of these parameters:
Fatigue life: the service life of a component under cyclic stress (fatigue life) is much shorter if
the surface roughness is high
Bearing properties: a perfectly smooth surface is not a good bearing because it cannot maintain
a lubricating film.
6. What are the different types of cutting fluids used in machining process?
Cutting fluids
Cutting fluid (coolant) is any liquid or gas that is applied to the chip and/or cutting tool to
improve cutting performance. A very few cutting operations are performed dry, i.e., without
the application of cutting fluids. Generally, it is essential that cutting fluids be applied to all
machining operations.
To remove heat in cutting: the effective cooling action of the cutting fluid depends on the
method of application, type of the cutting fluid, the fluid flow rate and pressure. The most
effective cooling is provided by mist application combined with flooding. Application of fluids
to the tool flank, especially under pressure, ensures better cooling that typical application to the
chip but is less convenient.
Tool wear
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The life of a cutting tool can be terminated by a number of means, although they fall broadly into
two main categories:
Gradual wearing of certain regions of the face and flank of the cutting tool, and abrupt tool
failure. Considering the more desirable case the life of a cutting tool is therefore determined
by the amount of wear that has occurred on the tool profile and which reduces the efficiency of
cutting to an unacceptable level, or eventually causes tool failure.
Gradual wear occurs at three principal locations on a cutting tool. Accordingly, three main
types of tool wear can be distinguished,
1. Crater wear
2. Flank wear
3. Corner wear
Crater wear: consists of a concave section on the tool face formed by the action of the chip sliding on
the surface. Crater wear affects the mechanics of the process increasing the actual rake angle of the
cutting tool and consequently, making cutting easier. At the same time, the crater wear weakens the
tool wedge and increases the possibility for tool breakage. In general, crater wear is of a relatively
small concern.
Flank wear: occurs on the tool flank as a result of friction between the machined surface of the
workpiece and the tool flank. Flank wear appears in the form of so-called wear land and is measured
by the width of this wear land, VB, Flank wear affects to the great extend the mechanics of cutting.
Cutting forces increase significantly with flank wear. If the amount of flank wear exceeds some
critical value (VB > 0.5~0.6 mm), the excessive cutting force may cause tool failure.
Corner wear: occurs on the tool corner. Can be considered as a part of the wear land and respectively
flank wear since there is no distinguished boundary between the corner wear and flank wear land. We
consider corner wear as a separate wear type because of its importance for the precision of machining.
Corner wear actually shortens the cutting tool thus increasing gradually the dimension of machined
surface and introducing a significant dimensional error in machining, which can reach values of about
0.03~0.05 mm.
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