Singh R. Introduction to Basic Manufacturing Processes and Workshop Technology
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468 Introduction to Basic Manufacturing Processes and Workshop Technology
Zero line
Upper
deviation
Lower
deviation
Tolerance
Basic size
Min. Limit
of size
Max. Limit
of size
Fig. 26.1 Basic size deviation and tolerances for both shaft and hole
26.3.3 Zero Line and Deviation
In graphical representation of limits, straight line to which the deviations are of zero
deviation and the represented of zero deviation are referred. The zero line is also known as
line of zero deviation is generally drawn as horizontal line and the positive deviations are
shown above this line and the negative deviations below it.
The algebraic difference between the actual or maximum size and the corresponding
the basic size is called deviation. The deviations from the basic dimensions at the
boundaries of the tolerance zone are called upper and lower deviations as depicted in
Fig. 26.2.
Tolerance
Lower deviation
Upper deviation
Tolerance
Lower deviation
Upper deviation
Max. Dia
Min. Dia
Max. Dia
Min. Dia
Shaft
Hole
Zero line &
line of zero
deviation
Basic
size
Fig. 26.2 Upper and lower deviations for both shaft and hole
26.3.4 Upper Deviation
It is the algebraic difference between the two maximum limit of any size of the part and
the corresponding basic size.
26.3.5 Lower Deviation
It is the algebraic difference between the minimum limit of any size of the part and the
corresponding basic size.
26.3.6 Mean Deviation
It is the arithmetical mean between the upper and lower deviations of any size of the
part.
Inspection and Quality Control 469
26.3.7 Fundamental Deviation
It is the one of the deviations, which is conventionally chosen to define the position of
tolerance zone in relation to the zero line. The deviation of the tolerance band on shaft or
hole away from the basic size is called the fundamental deviation. It is shown in Fig. 26.3.
The zero line shown is the line of zero deviation and represents the basic size. A zero line
is a straight line to which the deviations are referred. For conventions, the zero line is drawn
horizontally. The positive deviations are shown above and the negative deviations are shown
below it.
Fundamental deviation
Tolerance zone
Tolerance
Zero line
Fig. 26.3 Fundamental deviation
26.4 FITS
26.4.1 Allowance
In a specific type of fit, the difference between hole size and shaft size is called allowance.
Allowance is used to explain the difference between clearance fit and interference fit. Positive
allowance specifies the clearance fit whereas negative allowance in a fit specifies the interference
or force fit.
The relationship existing between two parts, shaft and hole, which are to be assembled,
with respect to the difference in their sizes before assembly is called a fit. When the parts
are assembled into sub-assembly units and sub assembly units are assembled into full assembly,
the mating surfaces of different components are joined together for proper functional
requirement. One of them may fit into the other in form of joint or fit. The fit may be with
suitable degree of tightness and freedom for required relative movement between mating
parts for specific functional requirements of the fit. The classification of fits is given in
Fig.26.4.
Clearance fit
Transition fit
Interference fit
Slidin
g
fit
Runnin
g
fit
Push
fit
Li
g
ht ke
y
in
g
fit
Press fit
or
Drivin
g
fit
force fit
or
Shrink fit
Fits
Fig. 26.4 General tree classification of fits
Components are assembled to perform a specific function. The characteristic of the
assembly is determined by the fit. Fit is the general term used to signify the relative degree
of tightness or looseness of assembled parts, which decides the relative movement between
mating parts. Particular type of fit results from the difference in the sizes of mating parts.
Fig. 26.5 shows the various types of fits. Two parts can fit each other in three ways, viz.
470 Introduction to Basic Manufacturing Processes and Workshop Technology
1. Clearance fit
2. Interference fit
3. Transition fit.
Basic
size
Hole
Shaft
Hi
g
h limit
Shaft
Shaft
Interference fit
Clearance fit
Low limit
Transition fit
Fig. 26.5 Graphical representation of types of fits
26.4.2 Clearance Fit
Clearance fit is one in which two assembled parts are always free to move relative to
each other in the assembly. In the clearance fit, the largest permitted shaft diameter is
smaller than the diameter of the smallest hole. The difference between the size of hole and
the size of shaft is defined as clearance. Clearance fits have limits of size prescribed so that
a clearance always results in a positive allowance, or air space is left between mating parts.
The parts can be assembled by hand. Clearance fit is of two kinds namely sliding and running
fits. Examples of clearance fit are door hinges, wheel and axle, shaft and bearing, etc. used
in the assembly of parts.
26.4.3 Interference Fit
In the interference fit, mating parts in sub assembly or main assembly are joined tightly
together and no relative motion is possible. The minimum permitted diameter of the shaft
is larger than the maximum allowable diameter of the hole. In this case, the shaft and the
hole member in any sub assembly or main assembly is to be attached permanently and used
as a solid component but according to the application of this combination, this type of fit can
be varied. Interference fit is used for permanent or semi-permanent assembly of parts, which
require rigidity and alignment and no relative motion, such as dowel pins and bearings in
casting. The difference between the size of shaft and the size of hole in anysub assembly or
main assembly is called interference or negative clearance or negative allowance. Interference
fit has limits of size so prescribed that interference always results when mating parts are
assembled. Transition fits is of two kinds namely driving or press fit and shrink or force fit.
To assemble, parts are usually pressed together using an arbor press.
26.4.4 Transition Fit
In this type of fit, the diameter of the largest allowable hole is greater than that of the
smallest shaft, but the smallest hole is smaller than the largest shaft, so that small positive
or negative clearance between the shaft and hole member is employable. Thus, transition fit
has limits of size of hole and shaft such that either a clearance or an interference fit may
result when two specific parts from the lot are assembled. Here the tolerance zones of the
hole and shaft overlap. Transition fits are a compromise between clearance and interference
Inspection and Quality Control 471
fit where a small amount of either clearance or interference is permissible. Transition fit is
of two kinds namely push fit and light keying fits. That is, sometimes shaft is slightly larger
than the hole and sometimes slightly smaller than the hole. Spigot in mating holes, coupling
rings and recesses are the examples of transition fit.
26.5 HOLE BASIS SYSTEM
When hole is kept as constant member and different fits are obtained by varying the
shafts sizes in a particular fit shown in Fig. 26.6, then the limit system is known as hole basis
system.
26.6 SHAFT BASIS SYSTEM
When shaft is kept as constant member and different fits are obtained by varying the
hole sizes as shown in Fig. 26.6, then the limit system is termed as shaft basis system of
making sub-assembly or assembly.
Hole
Shaft
Basic size
Zero line
Hole
Shaft
Shaft
Shaft
Hole
Hole
Hole
Hole
Hole
Shaft
Shaft
Shaft
Shaft
Fig. 26.6 Hole basis system and shaft bases system
26.7 SURFACE FINISH
Good surface finish on part has become an essential requirement of a product quality
and for its better life. By imparting a surface finishing process on the part, its dimension does
not change functionally and significantly. Either a very negligible amount of material is
removed or certain material is added to the surface of the job. Surface finishing processes
should not be misunderstood as metal removing processes in any case as they are primarily
intended to provide a good surface finish or decorative or protective coating on to the metal
surface for its better life and excellent appearance. Surface cleaning process is also accepted
as a surface finishing process. Some of the such surface finishing processes are lapping,
honing, super finishing, belt grinding, polishing, sanding, tumbling, organic finishes, deburring,
electroplating, buffing, metal spraying, painting, inorganic coating, anodizing, parkerizing,
galvanizing, plastic coating, metallic coating and anodizing. The characteristics of good finish
or roughness of surfaces can be understood by following components, which are described as
under.
26.7.1 Roughness (Primary texture)
It refers to relatively finely spaced surface irregularities of small wavelength on the part
which results from the inherent action of the manufacturing process. It may involve transverse
feed marks and the irregularities on the machined surface.
472 Introduction to Basic Manufacturing Processes and Workshop Technology
26.7.2 Waviness (Secondary texture)
It consists of those surface irregularities on the part, which are of considerable wavelength
of a periodic character. It may be caused by vibrations, machine or work deflection, chatter,
wrapping, etc. It appears in machining operations such as turning, milling, planning shaping,
broaching and grinding.
26.7.3 Profile
It is defined as the contour of any section through a surface on the part.
26.7.4 Lay
It is defined as the direction of the predominant surface pattern on the part. It is
ordinarily determined by the method used in the production of the article.
26.7.5 Flaws
These are surface imperfections such as minute cavities, holes, porosities, cracks, etc.
which appear at frequent intervals and at random locations. The flaws should not be available
on the surface.
Some of the well recognized methods for evaluating the roughness of a surface on the
parts are centre line average (CLA) method, envelope method and root mean square (RMS)
method.
26.8 QUALITY CONTROL
The term quality of product in production processes implies the best for the money
invested and does not necessarily mean the best. Therefore quality of the product is the
relative term and generally explained with reference to the end use of a product. A product
can be referred to be of good quality if it works very well and perform good function in a
particular situation for which it is meant or designed while in other situation it may not work
well and it is said to be of bad quality. The word control means regulation, which further
implies observations and manipulation. It suggests when to inspect, how often to inspect and
how much to inspect. The basic philosophy of quality control is both preventive and remedial.
Quality control strategy sometime identifies the important check measures and implements
them to check so that the defective items are not produced at all. When rejection of products
is increasing, some immediate corrective action should be evolved and taken suitably to
prevent further recurrence of product rejection of parts. Therefore well-planned inspection
will act to be an important tool of controlling quality of products. It checks the products at
specified stages while quality control attempts to bring the variable factors of manufacturing
under control for achieving the total product specification for meeting customary demands to
the maximum possible extent.
26.8.1 Stastical Quality Control
Full inspection of the finished product by usual inspection devices is time consuming and
costly. Also in a continuous production process 100% inspection may not be found practicable.
Certain statistical techniques have been formulated to evaluate materials, processes and
products by observing capabilities and trends in variations so that continual analysis predictions
may be made to control the desired quality level of the part. These statistical techniques are
called statistical quality control techniques. These techniques are
Inspection and Quality Control 473
1. Control charts for measurable quality characteristics. These are described as
charts for variables, or as charts for X and R (average and range) and charts for
average and standard deviation.
2. Control chart for fraction defective. This is described as the p chart.
3. Control chart for number of defects per unit. This is described as p chart.
26.8.2 Control Charts
Control charts are commonly used in quality control in industries to maintain a continuous
evaluation of the manufacturing process. Control chart is simply a frequency distribution of
the observed values plotted as points in order of occurrence so that each value has its own
identity relative to the time of observation. Points on the control charts may or may not be
connected. The chart is provided with limit lines, called control limits, having, in general, one
upper control limit and one lower control limit. A process is said to be in control if the
observed values are influenced only by chance causes fall within the limits and out of control
when assignable causes seem to be operating in the system and the observed value fall
outside the limits. It is important that the control limits of the control charts do not represent
the performance limit or limits of the manufacturing process nor do these represent the
specification limits of the manufacturing drawing of the part. The performance limits of the
manufacturing process of the part are the limiting dimensions within which practically all
parts fall. If the distribution is normal or near normal, there are three sigma limits of the
total distribution in both side and three sigma limits forms the basis of quality control.
However, points which fall outside of the control limits do not represent rejected item only
signal that some corrective action is essential to check the manufacturing function and hence
may lead to control the whole processing process for avoiding wastage involved in rejection
of the items.
26.9 ISO 9000
ISO is the International Organization for Standardization based in Geneva, Switzerland.
It was founded in 1947 for the purpose of advancing standardization around the world and
setting up standards for achieving and maintaining quality. This non-governmental organization
now comprises over 130 member countries. Each country is represented by its respective
national standards body (for India, it is Bureau of Indian Standards) and participates in
developing standards to facilitate trade of goods and services in the global marketplace. The
standards developed apply not only to the economic related activities but also cover the
related technology and science involved in these pursuits.
ISO 9000 series of internationally recognized quality management standards represents
the essential requirements that every enterprise needs to address to ensure the consistent
production and timely delivery of its goods and services to the marketplace. Their generic
nature allows for their application to any type of organization. Consistency in production and
reliability in delivery are as important as what an organization is selling in today’s marketplace.
It is essential to meet consistently all of the customer’s expectations all the time and every
time, to keep them satisfied and loyal.
The ISO 9000 series is able to provide these quality management benefits to organizations
of any size, public or private, without dictating how the organization is to be run. Certification
to an internationally recognized quality management standard like one from the ISO 9000
series is becoming an important part of distinguishing an organization from its competitors.
474 Introduction to Basic Manufacturing Processes and Workshop Technology
ISO 9000 is becoming popular because it controls quality and saves money too. A company
may decide to use ISO 9000 for many reasons. To develop the system one has to start with
gap analysis. A gap analysis will help the enterprise to identify the gaps that exist between
the ISO 9000 standard and current processes and will tell exactly what one needs to do to
meet the ISO 9000 quality management standard. An enterprise may chose to follow this path
because it needs to control or improves the quality of products and services or to reduce the
costs associated with quality or to become more competitive. Alternatively, an enterprise may
choose this simply because its customers expect it to do so or because a governmental body
has made it mandatory.
26.10 QUESTIONS
1. What is the importance of interchangeability in fitting of mating parts?
2. Define the terms: tolerance, allowance, interference and clearance in fits.
3. Illustrate the unilateral tolerance with figures. How is the tolerance specified?
4. Which points you will keep in mind in selecting the tolerance between the piston and cylinder
of an engine?
5. Write short notes on the following:
(i) Nominal size (ii) Basic size (iii) Tolerance (iv) Allowance, (v) Hole Basis System and
(vi) Shaft basis system.
6. Write short note on unilateral system of tolerances covering the points-definition, application
and advantages over die bilateral system.
7. Describe any system of setting limits and fits.
8. State the importance of limits and fits in production of articles.
9. Give the classifications of fits between the mating parts. What type of fit you will require
between the piston rod and stuffing box.
10. Describes the various types of fits.
INDEX
475
A
A feeler gauge 381
Abrasives 41
Accidents 26-38, 44, 45, 47, 49, 50
Accidents in industries 30
Acid pickling 298
Additions in polymer 98
Additives 208-212, 214, 220, 223, 228, 230,
236, 238
Adhesives 159, 160
Adjustable frame hacksaw 392
Adjustable gap gauge 381
Admiralty brass 81
Admiralty gun metal 90, 91
Advantages of continuous casting 251, 295
Advantages of die casting over sand casting
247
Advantages of forging 261, 267, 268
Advantages of powder metallurgy 462
Advantages of resistance welding 333
Age hardening 151
Air furnace 102, 112, 113
Air seasoning 156
Allotropy of iron 131
Allowance 469, 470, 474
Alloy cast iron 53, 54, 58
Alloy steel 52, 53, 64, 66, 68, 73, 75
Alloying elements in steel 65
Alpha iron 132, 136
Aluminium 76-80, 85, 89, 92, 93, 99, 100, 101
Aluminium alloy 77, 101, 187
Aluminium bronze 85
Annealing 130, 138, 139, 140, 142, 150
Annealing and normalizing 139
Antioch process 237
Anvil 269, 270, 272, 273, 274, 275, 280, 281
Application of heat and solder 344
Applications of continuous casting 252
Applications of cupola 108
Applications of cyaniding 147
Applications of different plain carbon steels
75
Applications of forging 260, 261
Applications of powder metallurgy 464, 465
Applications of rolling 288
Applications of spot welding 330
Arbor 447, 449, 452, 453, 455
Arc welding equipment 318, 327
Arc welding equipment, setup and related tools
318
Arc welding equipments 327
Arc welding machines 325, 327, 328
476 Introduction to Basic Manufacturing Processes and Workshop Technology
Arc welding processes 310, 317
Atomic hydrogen welding 311, 317, 346
Atomization 459, 465
Auger 165, 172, 173
Aus-tempering 144, 145, 151
Austenite 132-136, 138, 140-143, 147
Austenitic stainless steel 70, 71
Automatic guards 36, 37
Automation 2, 3, 7, 8, 9, 15, 16
Availability of steel in market 72
Axe 165, 172
B
Bainite 142, 143, 144, 145
Bakelite 96, 97
Band saw 176, 177, 178
Basic principle of arc welding 317
Batch production 3, 12
Batch furnaces 131
Bauxite 76, 77
Bearing or antifriction alloys 76, 90
Bed of high precision lathe 101
Bell metal 85
Bellows 202
Bench drilling machine 388
Bench lathe 406, 407
Bending 267, 272, 273, 296, 300, 301, 305
Beryllium bronze 84
Bessemer’s matte 86
Bevel gauge 162, 163, 377
Beveled edge firmer chisel 170
Bever protractor 368
Bick iron 352
Binder 208, 209, 210, 213, 220, 221, 223, 228,
229, 230, 231, 234, 236, 238, 240
Black heart malleable iron casting 58
Blanking 296, 299, 300, 348, 359, 363
Blast furnace 102, 103, 104, 114
Blending 458, 461, 465
Blending of metallic powders 461
Boring 406, 415, 422, 430, 431, 433
Boring tool 165, 172, 178, 430, 433
Box or batch type furnaces 264
Brass and bronze pattern 182
Brasses 80, 83, 101
Braze welding 311, 321, 342, 347
Brazing 310, 311, 312, 321, 341, 342, 347
Brittleness 119, 120, 129
Broaching machine 445
Bronzes 80, 83, 84, 101
Built-up edge 402, 404
Bulk modulus 120, 125
Butt weld joint 308
C
CAD 8, 9, 12, 13, 15, 16
CAD/CAM 8, 13, 15
Calipers 365, 375
CAM 8, 9, 12, 13, 14, 15, 16
Capstan and turret lathe 408
Carbides 92, 93
Carbon arc welding 310, 317, 321, 346
Carbon tool steel 64, 71, 75
Carbon-dioxide gas molding 234
Carburizing welding flame 313
Carning or C process 248
Carpenter vice 164, 165
Carpentry 152, 153, 154, 159, 162, 163, 164,
165, 167, 171, 173, 174, 176, 177, 178
Carpentry machines 176
Carpentry shop 152, 153, 159, 162, 163, 165,
171, 173, 174, 177, 178
Carpentry tools 178
Carriage 407-411, 413, 418, 419, 421
Index 477
Cartridge brass 81
Case hardening 137, 145, 147, 149, 151
Case hardening processes 151
Cast iron 52-59, 62, 63, 75
Cast iron castings 57
Cast iron patterns 181
Ccasting 179-184, 186-195, 241-259
Casting defects 241, 243, 252, 253, 258, 259
Casting techniques 241, 248
Causes of accidents 32, 33, 34, 45
Cemented carbides 92
Cementite 131-133, 135, 136, 138, 139, 142,
143
Central lathe 407-410, 421
Centre punch 365, 368
Centrifugal casting 249, 250, 251, 258
Centrifugal casting processes 249
Centrifuging casting 251, 252, 258
Centrifuging casting setup 251, 252
Ceramics materials 93
Ceramics tool 92
Cermets 464, 465
Chaplets 192, 196, 225, 239
Characteristic of metal powders 460
Characteristics of a good timber 158, 178
Characteristics of cold working 293
Characteristics of forged parts 269
Charging of cupola furnace 108
Charpy test 126, 127
Checkers 110
Chemical composition of white cast iron 56
Chemical properties 116, 117, 129
Chief alloying elements 65
Chills 196, 226, 239
Chip breaker 402, 405
Chipping hammer 321
Chisel 165, 166, 169, 170, 366, 388, 394, 396
Choice of materials 128
Chucks 411, 412
CIM 2, 9, 11, 13, 15, 16
CIM technologies 13
Circular saw 176, 177, 178
Clamp 160, 165
Clamping divices 384
Clamping tools 193
Clapper box 435, 437, 439, 442, 443
Classification of files 384, 386, 387
Flassification of fits 469
Classification of hot working processes 285
Classification of molding processes 232
Classification of moulding machines 205
Classification of welding and allied processes
310
Claw hammer 174
Clay content test 215
Clearance fit 469, 470
Closed molding boxes 203
Cluster mill 287
CNC 2, 4, 9, 14
Coatings 395
Coining process 304
Cold chamber casting machine 246
Cold chamber die casting 244, 246, 257
Cold drawing 301, 302, 304
Cold extrusion 297, 304
Cold pressure welding 311, 333, 338
Cold working 293-296, 299, 304, 305
Cold working process 294-297, 305
Collapsibility 211, 214, 229, 234
Column 450-453, 457
Column and knee type milling machine 450,
451, 452, 453, 457
Combination layout 23
Combination set 162, 163, 365, 378, 379