The document discusses manufacturing processes, specifically material removal processes like machining. It defines manufacturing as the process of converting raw materials into products through physical or chemical processes. Machining involves removing unwanted material from a workpiece in the form of chips using cutting tools. The key aspects covered are: - Types of chips produced and factors affecting chip formation - Mechanics of chip formation including shear plane angle relationships - Orthogonal cutting model for analyzing forces during machining - Advantages and disadvantages of machining processes

1. MANUFACTURING PROCESSES-II
Engr. Umair

2. What is Manufacturing?
 The word manufacturing is derived from two latin words, manus (hand) and factus (make), the
combination means made by hand.
 Manufacturing, in its broadest sense, is the process of converting raw materials into products.
 Manufacturing can be defined in two ways, one technologic and other economic.
- Technologically, manufacturing is the application of physical and chemical processes to alter the
geometry, properties and appearance of a given starting material to make parts or products;
manufacturing also includes assembly of multiple parts to make products.
- Economically, manufacturing is the transformation of materials into items of greater value by
means of one or more processing and/or assembly operations.
Production vs Manufacturing
 Production engineering is a complete cycle as it involves procurement of raw material, storing
that raw material as inventory, conversion of raw into semi finished or finished goods,
dispatching, sales forecasting etc. but manufacturing is a part of production engineering which
just involves in the value addition of raw materials (conversion of raw into semi finished or
finished goods).

3. Chapter No. 01

4. Material Removal (Cutting)
Topics:
 Mechanics of Chip Formation
 Types of Chips produced
 Forces and Pressures involved
 Surface Finishing and Integrity
 Machinability
 Calculation of Material Removal Rate(MRR)

7. Material Removal / Metal Cutting (Machining)
Introduction:
• Metal cutting or machining is the process of producing a work piece by removing unwanted
material from a block of metal in the form of chips.
• This process is most important since almost all the products get their final shape and size by
material removal either directly or indirectly.
• The major draw back of the process is the loss of the material in the form of chips.
• Machining is the general term used to describe material removal, it covers several processes,
which are usually divided into the following broad categories.
 Cutting, which generally involves single-point or multipoint cutting tools and processes,
such as turining, boring, tapping, milling, sawing, and broaching.
 Abrasive processes, such as grinding, honing, lapping, and ultrasonic machining.
 Advanced machining processes, which use electrical, chemical, thermal, hydrodynamic,
and optical sources of energy, as well as combination of these energy sources, to remove
material from the work piece surface.

8. Advantages Of Machining
• Variety of work materials
Machining can be applied to a wide variety of work materials. Virtually all solid metals can be
machined. Plastics and plastic composites can also be cut by machining. Ceramics pose difficulties
because of their high hardness and brittleness; however, most ceramics can be successfully cut by the
abrasive machining processes.
• Variety of part shapes and geometric features.
Machining can be used to create any regular geometries, such as flat planes, round holes, and
cylinders. By introducing variations in tool shapes and tool paths, irregular geometries can be created,
such as screw threads and T-slots. By combining several machining operations in sequence, shapes of
almost unlimited complexity and variety can be produced.
• Dimensional accuracy.
Machining can produce dimensions to very close tolerances. Some machining processes can achieve
tolerances of 0.025 mm (0.001 in), much more accurate than most other processes.
• Good surface finishes.
Machining is capable of creating very smooth surface finishes. Roughness values less than 0.4 microns
(16m-in.) can be achieved in conventional machining operations. Some abrasive processes can
achieve even better finishes.

9. Disadvantages
• Wasteful of material.
Machining is inherently wasteful of material. The chips generated in a machining operation are wasted
material. Although these chips can usually be recycled, they represent waste in terms of the unit
operation.
• Time consuming
A machining operation generally takes more time to shape a given part than alternative shaping
processes such as casting or forging.

10. Chip formation
• As the tool moves against the work piece a layer of metal is separated
from the work piece,
• Which comes out sliding over the tool face in the form of chips.
• The separation of material from the parent body (i.e. from the work
piece) could be due to
1. Fracture process
2. Peeling process
3. Crack formation and propagation, ahead of the cutting edge
4. Shearing and plastic flow process.
• To ascertain the exact process involved in cutting many scientists all over
world did much investigations.
• And the chips were subsequently examined with the microscope.

11. Mechanism of chip formation
 Machining is a semi-finishing or finishing process essentially done to impart
required or stipulated dimensional and form accuracy and surface finish to enable
the product to,
 fulfill its basic functional requirements
 provide better or improved performance
 render long service life.
 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.

12.  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.
Mechanism of chip formation in machining ductile materials

13. Machining Terminology

14. Mechanism of chip formation in machining brittle materials
 The basic two mechanisms involved in chip formation are ,
 Yielding – generally for ductile materials
 Brittle fracture – generally for brittle materials
 Machining of brittle material produces discontinuous chips and mostly of irregular
size and shape. The process of forming such chips is schematically shown in Fig.

15. Geometry and characteristics of chip forms
 The geometry of the chips being formed at the cutting zone follow a particular
pattern especially in machining ductile materials.
 The major section of the engineering materials being machined are ductile in
nature, even some semi-ductile or semi-brittle materials behave ductile under the
compression.
 Different types of chips of various shape, size, colour etc. are produced by
machining depending upon
 Different types of chips of various shape, size, colour etc. are produced by
machining depending upon
– type of cut, i.e., continuous (turning, boring etc.) or intermittent cut (milling)
– work material (brittle or ductile etc.)
– cutting tool geometry (rake, cutting angles etc.)
– levels of the cutting velocity and feed (low, medium or high)
– cutting fluid (type of fluid and method of application)
Types of chips and conditions for formation of those chips

16.  The basic major types of chips and the conditions generally under which such types
of chips form are given below:
Discontinuous type
• of irregular size and shape : - work material – brittle like grey cast iron
• of regular size and shape : - work material ductile but hard
• feed – large
• tool rake – negative
• cutting fluid – absent or inadequate
Continuous type
• Without BUE : work material – ductile
• Cutting velocity – high
• Feed – low
• Rake angle – positive and large
• Cutting fluid – both cooling and lubricating

17. With BUE : -
• work material – ductile
• cutting velocity – medium - feed – medium or large
• cutting fluid – inadequate or absent.
Jointed or segmented type
• work material – semi-ductile
• cutting velocity – low to medium
• feed – medium to large
• tool rake – negative
 Often in machining ductile metals at high speed, the chips are
deliberately broken into small segments of regular size and shape by
using chip breakers mainly for convenience and reduction of chip-tool
contact length

18. Mechanics Of Chip Formation
The geometry of most practical machining operations is somewhat complex. A
simplified model of machining is available that neglects many of the geometric
complexities, yet describes the mechanics of the process quite well. It is called the
orthogonal cutting model.
THE ORTHOGONAL CUTTING MODEL
By definition, orthogonal cutting uses a wedge-shaped tool in which the cutting
edge is perpendicular to the direction of cutting speed. As the tool is forced into
the material, the chip is formed by shear deformation along a plane called the
shear plane, which is oriented at an angle f with the surface of the work. Only at
the sharp cutting edge of the tool does failure of the material occur, resulting in
separation of the chip from the parent material.

19. The tool in orthogonal cutting has only two elements of geometry: (1) rake angle
and (2) clearance angle. As indicated previously, the rake angle determines the
direction that the chip flows as it is formed from the work part; and the clearance
angle provides a small clearance between the tool flank and the newly generated
work surface. During cutting, the cutting edge of the tool is positioned a certain
distance below the original work surface. This corresponds to the thickness of the
chip prior to chip formation, to. As the chip is formed along the shear plane, its
thickness increases to tc.
The ratio of to to tc is called the chip thickness ratio(or simply the chip ratio)r:
The geometry of the orthogonal cutting model allows us to establish an important
relationship between the chip thickness ratio, the rake angle, and the shear plane
angle. Let ls be the length of the shear plane. We can make the substitutions: to =
ls SinØ, and tc = ls cos (Ø - α). Thus,

20. This can be rearranged to determine as follows
The shear strain that occurs along the shear plane can be estimated by examining
Figure. Part (a) shows shear deformation approximated by a series of parallel plates
sliding against one another to form the chip. Consistent with our definition of shear
strain each plate experiences the shear strain shown in Figure 21.7(b).

21. Referring to part (c), this can be expressed as
which can be reduced to the following definition of shear strain in metal cutting:
Problem (01):
In a machining operation that approximates orthogonal cutting, the cutting tool has
a rake angle = 10o . The chip thickness before the cut to = 0.50 mm and the chip
thickness after the cut tc = 2.8 cm. Calculate the shear plane angle and the shear
strain in the operation.
(9.7o, 5.877)

22. Chip control
Discontinuous chips are generally desired because they
 are less dangerous for the operator.
 do not cause damage to work piece surface and machine tool.
 can be easily removed from the work zone.
 can be easily handled and disposed after machining.
 There are three principle methods to produce the favorable discontinuous chip.
 proper selection of cutting conditions.
 use of chip breakers.
 change in the work material properties.

23. Assignment (01)
1) In an orthogonal cutting operation, the tool has a rake angle =
15o. The chip thickness before the cut = 0.30 mm and the cut
yields a deformed chip thickness = 0.65 mm. Calculate (a) the
shear plane angle and (b) the shear strain for the operation.
2) In an orthogonal cutting operation, the 0.25-in wide tool has a
rake angle of 5o. The lathe is set so the chip thickness before the
cut is 0.010 in. After the cut, the deformed chip thickness is
measured to be 0.027 in. Calculate (a) the shear plane angle and
(b) the shear strain for the operation.

24. FORCE RELATIONSHIPS AND THE MERCHANT EQUATION
Introduction
Knowledge of the cutting forces is essential for the following reasons:
 proper design of the cutting tools
 proper design of the fixtures used to hold the work piece and cutting tool
 calculation of the machine tool power
 selection of the cutting conditions to avoid an excessive distortion of the work
piece.
 Cutting is a process of extensive stresses and plastic deformations. The high
compressive and frictional contact stresses on the tool face result in a substantial
cutting force F.

25. Cutting force components
In orthogonal cutting, the total cutting force F is conveniently resolved into two
components in the horizontal and vertical direction, which can be directly
measured using a force measuring device called a dynamometer.
The two force components act against the tool:
ΠCutting force FC: This force is in the direction of primary motion. The cutting
force constitutes about 70~80 % of the total force F and is used to calculate the
power P required to perform the machining operation.
P = VFC
• Thrust force FT: This force is in direction of feed motion in orthogonal
cutting. The thrust force is used to calculate the power of feed motion

26. Force determination
Cutting forces are measured by means of special device called tool force
dynamometer mounted on the machine tool.
Cutting force control
The cutting force value is primarily affected by:
 cutting conditions(cutting speed V, feed f, depth of cut d)
 cutting tool geometry(tool orthogonal rake angle)
 properties of work material

28. INTRODUCTION

29. Terminology

35. POWER AND ENERGY RELATIONSHIPS IN MACHINING
A machining operation requires power. The product of cutting force and speed
gives the power (energy per unit time) required to perform a machining
operation:
Where Pc = cutting power, N-m/s or W (ft-lb/min); Fc = cutting force, N (lb);
and v = cutting speed, m/s (ft/min). In U.S. customary units, power is
traditionally expressed as horsepower by dividing ft-lb/min by 33,000. Hence,
Where HPc = cutting horsepower, hp. The gross power required to operate the
machine tool is greater than the power delivered to the cutting process because
of mechanical losses in the motor and drive train in the machine. These losses
can be accounted for by the mechanical efficiency of the machine tool:
Where Pg = gross power of the machine tool motor, W; HPg = gross
horsepower; and E = mechanical efficiency of the machine tool. Typical values
of E for machine tools are around 90%.

36. It is often useful to convert power into power per unit volume rate of metal cut.
This is called the unit power, Pu (or unit horsepower, HPu), defined:
where RMR = material removal rate, mm3/s (in3/min). The material removal
rate can be calculated as the product of tow. Power is also known as the specific
energy U.

40. Problem (01)
In a turning operation on stainless steel with hardness = 200 HB, the cutting
speed = 200 m/min, feed = 0.25 mm/rev, and depth of cut = 7.5 mm. How much
power will the lathe draw in performing this operation if its mechanical
efficiency = 90%.Use Table (above) to obtain the appropriate specific energy
value.
(Pg=19.44 kW)
Problem (02)
Determine cutting power and specific energy in the machining operation if the
cutting speed = 100 m/min. Summarizing the data and results from previous
examples, to = 0.50 mm, w = 3.0 mm, Fc = 1557 N.
( 1.038 N-m/min3 )

41. CUTTING TEMPERATURE
Of the total energy consumed in machining, nearly all of it (98%) is converted
into heat. This heat can cause temperatures to be very high at the tool–chip
interface—over 600C (1100F) is not unusual. The remaining energy (2%) is
retained as elastic energy in the chip. Cutting temperatures are important
because high temperatures (1) reduce tool life,(2) produce hot chips that pose
safety hazards to the machine operator, and (3) can cause inaccuracies in work
part dimensions due to thermal expansion of the work material. Here we discuss
the methods of calculating and measuring temperatures in machining
operations.
The equation can be used to predict the increase in temperature at the tool–chip
interface during machining:
------------------ Cook’s equation
where ΔT = mean temperature rise at the tool–chip interface, Co( Fo ); U =
specific energy in the operation, N-m/mm3or J/mm3(in-lb/in3); v = cutting
speed, m/s (in/sec); to = chip thickness before the cut, m (in);ρC = volumetric
specific heat of the work material, J/mm3-C (in-lb/in3-F);K = thermal diffusivity
of the work material, m2/s (in2/sec).

42. Problem (03)
For the specific energy U = 1.038 N-m/min3, calculate the increase in
temperature above ambient temperature of 20 o C. Use the given data , v = 100
m/min, to = 0.50 mm. In addition, the volumetric specific heat for the work
material = 3.0 (10-3) J/mm3-C, and thermal diffusivity = 50 (10-6)m2/s (or 50
mm2/s). (ΔT=353oC)
Problem (04)
Orthogonal cutting is performed on a metal whose mass specific heat = 1.0 J/g-
C, density = 2.9 g/cm3, and thermal diffusivity = 0.8 cm2/s. The cutting speed is
4.5 m/s, uncut chip thickness is 0.25 mm, and width of cut is 2.2 mm. The
cutting force is measured at 1170 N. Using Cook’s equation, determine the
cutting temperature if the ambient temperature = 22oC.
(T=729oC)

43. Surface Finish
• 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
 roughness: small, finely spaced surface irregularities (micro irregularities)
 waviness: surface irregularities of grater spacing (macro irregularities)
 lay: predominant direction of surface texture

44. Surface Finish
• Three main factors make the surface roughness the most important of these
parameters:
1. Fatigue life: the service life of a component under cyclic stress (fatigue
life) is much shorter if the surface roughness is high
2. Bearing properties: a perfectly smooth surface is not a good bearing
because it cannot maintain a lubricating film.
3. Wear: high surface roughness will result in more intensive surface wear in
friction.
• Surface finish is evaluated quantitatively by the average roughness height, Ra

45. Surface Finish
• Roughness Control:
Factors, influencing surface roughness in machining are
 tool geometry(major cutting edge angle and tool corner radius),
 cutting conditions(cutting velocity, depth of cut and feed), and
 work material properties(hardness).
• Feed marks:
During cutting with a single point cutting tool (e.g. turning), the tool leaves a
spiral profile on the machined surface as it moves across the work piece, so
called feed marks. The height of the feed marks is nothing but the surface
roughness height and can be assumed equal to Ra.
The influence of the other process parameters is outlined below:
 Increasing the tool rake angle generally improves surface finish
 Higher work material hardness results in better surface finish
 Tool material has minor effect on surface finish.
 Cutting fluids affect the surface finish changing cutting temperature and as
a result the built-up edge formation

46. Machinability
Introduction:
Machinability is a term indicating how the work material responds to the cutting process.
There are various criteria used to evaluate machinability, the most important of which
are: (1) tool life, (2) forces and power, (3) surface finish,(4) ease of chip disposal. and
(05) low cost. The type of machining operation, tooling, and cutting conditions are also
important factors. A closer definition of machinability requires that some quantitative
judgments be made. Several possibilities are available, but in practice so called
machinability index is often quoted. The machinability index KM is defined by
KM = V60
/V60R
where V60
is the cutting speed for the target material that ensures tool life of 60 min,
V60R
is the same for the reference material. Reference materials are selected for each
group of work materials (ferrous and non-ferrous) among the most popular and widely
used brands.

47. Machinability
If KM > 1, the machinability of the target material is better than that of the reference
material, and vice versa. Note that this system can be misleading because the index is
different for different machining processes.
Machinability of different materials:
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.
 Difficult-to-cut steels: a group of steels of low machinability, such as stainless
steels, high manganese steels,
 Precipitation-hardening steels. Other metals

48. 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.
 Copper-based alloys: easy to machine metals. Bronzes are more difficult to machine
than brass.

49. Machinability
Methods for improvement of machinability:
Adding some elements
• Adding lead and sulphur to obtain so-called free-machining steels.
• Thermally assisted machining
To relieve machining of difficult-to-cut materials, some heat can be added to the cutting
zone to lower shear strength of work material. The heat source is a oxy fuel torch, laser
beam or plasma arc, focused on an area just ahead of the cutting tool:
• Although effective, thermally-assisted machining has a limited practical application
because of the high cost and difficult process control.

50. • Problem (04)
A series of tool life tests are conducted on two work materials under
identical cutting conditions, varying only speed in the test procedure. The
first material, defined as the base material, yields a Taylor tool life
equation (vT)0.28 = 350, and the other material (test material) yields a
Taylor equation (vT)0.27 = 440, where speed is in m/min and tool life is in
min. Determine the machinability rating of the test material using the
cutting speed that provides a 60-min tool life as the basis of comparison.
(131%)