1. CH 2: MANUFACTURING ASPECT
Specification
• “Details and specific descriptions of the
requirement of making or fabricating a product.
Can be a written document describing in detail
the scope of work, type of materials to be used,
special construction techniques, dimensions,
colors, or a list of the qualities and characteristics
of a product”
• Example of “specification” in a manufacturing
drawing.

3. Standardisation
• Standardization (or standardisation) is the process of agreeing on
standards, which are (usually voluntary, written) agreements on
technical specifications that define parameters and properties of
products (goods and services).
• In the context of technologies and industries, standardization is the
process of establishing a technical specification, called a standard
(eg: size, quality, dimension, testing, assembling, etc) among
• The goals of standardisation
– standardization can be to help with or ensure independence of single
suppliers
– Help to make easy in fabrication, compatibility, safety, repeatability,
quality, interoperability of products, components or services in global.
• Standardisation bodies eg: ISO, BS, ANSI, SIRIM etc

5. Tolerance
• In order to ensure that assemblies function properly their
component parts must FIT TOGETHER in a particular way.
• This is defined as the permissible or acceptable variation in
the dimensions (height, width, depth, diameter, and angles)
of a part.
• The root of the word “tolerance” is the Latin tolerare,
meaning “to endure” or “put up with.”
• No component can be manufactured to an exact size (called
the nominal or basic size), so the designer has to decide on
appropriate upper and lower limits for each dimension Refer
Fig 2.2)
• Accurately toleranced dimensioned features usually take
much more time to manufacture correctly and therefore can
increase production costs significantly.

6. Tolerance
Importance of tolerance control
• Dimensional tolerances become important only
when a part is to be assembled or mated with
another part.
• Surfaces that are free and not functional do not need
close tolerance control.
• Fig below shows the basic size, deviation, and
tolerance on a shaft, according to the ISO system.
• Fig below shows the various methods of assigning
tolerances on a shaft: (a) bilateral tolerance, (b)
unilateral tolerance, and (c) limit dimensions.

9. Limits and fits
• Limits and fits are essential in specifying
dimensions for holes and shafts.
• When parts are assembled together, engineers
have to decide how they will fit together and the
economics associated with it.
• How they will fit together?
– Clearance fit
– Transition fit
– Interference fit
• Economics?
– Interchangability

10. Limits and fits
• There are two standards on limits and fits, as
described by the American National Standards
Institute (see ANSI B4.1, B4.2, and B4.3). One
standard is based on the traditional inch unit.
• The other is based on the metric unit and has
been developed in greater detail. In these
standards, capital letters always refer to the
hole and lowercase letters to the shaft.

11. Limits and fits - definition
• Tolerance is the difference between the
maximum limit of size and the minimum limit of
size.
• Fit expresses the relationship between a mating
parts with respect to the amount of clearance or
interference which exists when they are
assembled together.
• Hole - designate all INTERNAL features of a part,
including parts which are not cylindrical.
• Shaft - designate all EXTFRNAL features of a part,
including parts which are not cylindrical.

12. • Upper deviation - difference between the maximum
limit of size and the corresponding basic size. This is
designated ‘ES' for a hole and 'es' for a shaft.
• Lower deviation- difference between the minimum
limit of size and the corresponding basic size. This is
designated ‘EI' for a hole and 'ei' for a shaft.
• Grade of Tolerance - Group of tolerances with the
same level of accuracy for all basic sizes.
• Clearance - difference between the size of the hole and
shaft (positive)
• Clearance - difference between the size of the hole and
shaft (negative)

15. Product Quality
• Product quality always has been one of the
most important aspects of manufacturing
operations.
• In view of a global competitive market,
continuous improvement in quality is now a
major priority, particularly for large
corporations in industrialized countries.
• In Japan, the single term kaizen is used to
signify never-ending improvement.

16. Product Quality
• Quality may be defined as a product’s fitness
for use.
• Several dimensions of quality generally are
identified; these include characteristics such
as performance, durability, reliability,
robustness, and serviceability, as well as
aesthetics and perceived quality.

17. Product Quality
• Contrary to general public perception, high
quality products do not necessarily cost
more, especially when considering the fact
that poor-quality products:
– Present difficulties in assembling and
maintaining components.
– Result in the need for in-field repairs.
– Have the significant built-in cost of customer
dissatisfaction.

18. Quality Assurance
• Quality assurance is the total effort made by a
manufacturer to ensure that its products conform to
a detailed set of specifications and standards.
• It can be defined as all actions necessary to ensure
that quality requirements will be satisfied; whereas,
quality control is the set of operational techniques
used to fulfill quality requirements.
• An important aspect of quality assurance is the
capability to (a) analyze defects as they occur on the
production line and (b) promptly eliminate them or
reduce them to acceptable levels.