CIM 15ME62 Module-2: CAD and Computer Graphics Software; Module 3: Line Balancing

Chapter 3
CAD and Computer Graphics Software

The Design and Design Process
• Design: An act of devising an original solution to a problem by a
combination of principles and resources.
• Design process is the pattern of activities that is followed by a
person, called designer, in arriving at the solution of a
technological problem.
• The design process is an iterative procedure which checks the
suitability of the design again and again.
• A preliminary design is made based on the available information
and is improved upon as more and more information is generated
/ available.
• The design (solution to a problem) progresses in a step-by-step
manner from some statement of need through identification of
problem, a search for solutions and development of the chosen
solution to trial production and use.
• The description of design steps is known as model of the design
process.

The Computer Aided Design
• Any type of design activity which makes use of the
computer to develop, analyze, or modify an engineering
design.
• CAD systems are based on ICG – a user oriented system in
which the computer is employed to create, transform, and
display data in the form of pictures or symbols.
• The ICG system is a combination of hardware and software.
• The hardware consists of a CPU, one or more graphics
display terminals (monitors), and peripheral devices such
as mouse, keyboard, printers and plotters.
• The software consists of
– The computer programs needed to implement graphics processing
on the system,
– Additional specialized application programs to accomplish
particular engineering functions required by the company.

• In a CAD system, the ICG (interactive computer graphics)
system is one component and the other major component
is the human designer.
• ICG is a tool used by the designer to solve a design
problem. ICG magnifies the power of the designer
(synergistic effect).
• In the computer aided design process,
– The designer uses his/her intellectual skills (.. conceptualization,
independent thinking);
– The computer performs the task best suited to its capabilities
(speed of calculations, visual display, storage of large amount of
data).

• The user (..designer) communicates data and commands to
the computer through any of several input devices.
• The computer communicates with the user via a monitor /
screen.
• The designer creates an image (.. of the object being
design) by entering commands to call the desired software
subroutines stored in the computer.
• The image is constructed using basic geometric elements –
points, lines, planes and solids.
• The image can be modified by suitable commands by the
designer – scale, move, rotate, or other transformations.
• The desired details of the image are thus formulated by
above manipulations.

The Shigley’s Design Process
• The design process is an iterative process which checks the
suitability of the design again and again.

The Design Process
• Recognition of need involves the realization by someone
that a problem exists for which some feasible solution is to
be found. This might be the identification of some defect in
a current machine design activity by an engineer or the
perception of a new product marketing opportunity by a
salesman.
• Definition of problem involves a thorough specification of
the item to be designed. This specification will generally
include functional and physical characteristics, cost,
quality, performance, etc.
• During the synthesis phase of the design process various
preliminary ideas are developed through research of
similar product or design in use.

The Design Process
• The resulting preliminary design is then subjected to appropriate
analysis to determine their suitability for the specified design
constraint. If this design fails to satisfy the constraints, they are
redesigned or modified on the basis of the feedback from the analysis.
This iterative process is repeated until the proposed design meets the
specification or until the designer is convinced that the design is not
feasible.
• Evaluation: The assessment or evaluation of the design against the
specification established during the problem definition phase is then
carried out. This often requires the fabrication and testing of a
prototype model to evaluate operating performance quality, reliability,
etc.
• Presentation: The final phase of design process is the presentation of
the design. This include the documentation of the design through
drawing, material specification, assembly lists and so on.

The CAD Process
• In CAD process , the last four phases
of traditional design process are
replaced by the following phases:
• Geometric modeling
• Engineering analysis
• Design review and evaluation
• Automated drafting
• Geometrical modeling is concerned
with the computer compatible
mathematical description of the
geometry of an object.
• The geometry of the object is
displayed in the form of an image on
the screen and can be manipulated
through signals from CPU.

The CAD Process
• A Geometric Model is constructed by inputting three types
of commands to the computer, viz.
– Generating basic geometric elements such as points, lines, planes
and solids
– Carry out transformation such as scaling, rotation, moving, etc. of
these elements.
– Join the above elements to get the desired shape of the object being
created.
• The created model is stored in the database of the computer
in the form of a mathematical model.
• Modification and analysis can be done on this model as and
when required.

The CAD Process
• Forms of Geometric Model (how an object is represented?)
• Wire frame models
• Surface models
• Solid models
• Wireframe models represent (display) an object by a frame of
interconnecting lines (or wires) or edges.
• Wire-frame modelling uses points and curves (i.e. lines, circles,
arcs) to define objects.
• Wire frame models of complex parts can be confusing.
• Do not represent an actual solid (no surface and volume).
• Cannot model complex curved surfaces.
• Orthographic views like plan, elevation, end view, etc. are the
examples with hidden lines removed.

The CAD Process
• Wireframe models
• What does the object looks like?
• Some ambiguous views….

The CAD Process
• The Wireframe Models

The CAD Process
• The Surface Models • An enhancement to the
wireframe representation of
objects.
• The object appear solid to
the viewer, but is still stored
in the computer as a wire-
frame model.
• Used to generate smoothly
varying or faired surfaces
(ship building, automotive,
aircraft, etc.)
• Surface models eliminate
ambiguities inherent in
wireframe models.
• Computationally more
tedious & require more skill.

The CAD Process
• The Surface Models - Advantages
• Renders the model for better visualization and presentation,
objects appear more realistic.
• Provides the surface geometry for CNC machining.
• Provides the geometry needed for mold and die design.
• Complex free-formed surfaces (car & aircraft bodies) can be
modeled.
• Surface properties such as roughness, color and reflectivity
can be assigned and demonstrated.

The CAD Process
• The Surface Models - Limitations
• Cannot be used to calculate dynamic properties.
• Surface models provide no information about the inside of
an object.

The CAD Process
• The Surface Models - Entities
Analytic entities
• Plane surface
• Ruled surface
• Surface of revolution
• Tabulated surface
Synthetic entities
• Hermite Cubic spline surface,
• B-spline surface,
• Bezier surface, and
• Coons patches.

Ruled (lofted) surface
This is a linear surface. It interpolates linearly between two
boundary curves that define the surface.

Surface of Revolution
An axi-symmetric surface that can be generated by rotating a
planar wireframe entity in space about the axis of symmetry a
certain angle.

Tabulated Surface
A surface generated by translating a planar curve a certain
distance along a specified direction.

The CAD Process
• The Solid Models In solid modeling, the solid
definitions include vertices (nodes),
edges, surfaces, weight, and volume.
The model is a complete and
unambiguous representation of a
precisely enclosed and filled
volume.
Can be created using CSG (C-rep,
set-theoretic, Boolean)) or using
building blocks (B-rep, graph
based) approaches.

The CAD Process
• The Solid Modelling Techniques (approaches) - CSG
• The models are built out of solid graphic primitives, such as
rectangular blocks, cubes, spheres, cylinders, and pyramids.
• Primitives are those regular solids stored in the program in
advance and are used to create a solid of the same shape
but of the size specified by the user.
• CSG defines a model in terms of combining basic and
generated (using extrusion and sweeping operation) solid
shapes.
• Boolean operations are used to construct a model.

The CAD Process
• The solid primitives

The CAD Process
• The Boolean Operations
• Union (Unite, join) - the
operation combines two
volumes included in the
different solids into a single
solid.
• Subtract (cut) - the
operation subtracts the
volume of one solid from
the other solid object.
• Intersection - the
operation keeps only the
volume common to both
solids
A U B
B - A
A - B
A intersected with B

The CAD Process
• The Boolean Operations

The CAD Process
The Solid Modelling Techniques – B-rep
•Solid model is defined by the enclosing surfaces or
boundaries.
• The database consists of the geometric information about
the vertices, faces, and edges of an object with the
topological data on how these are connected.
• B-rep data structure is a graphical representation of the
sequence of points (nodes or vertices), edges and faces to
represent a solid.

The CAD Process
The B-rep data structure

The CAD Process
The B-rep Solid Model Operations
• Extrude
• Revolve
• Sweep (Lin., Rot.)
• Loft
• Fillet
• Chamfer

The CAD Process
The B-rep Solid Model Operations – Applied Features
• Fillet & Chamfer are the applied features – used on created
model to modify it.

The CAD Process
The B-rep Solid Models – Creating Features from
Sketches

The C-Rep and B-Rep Differences

The CAD Process
• Engineering Analysis (2nd step in CAD
process)
• In optimizing any engineering design, some type of
analysis is required such as:
– Surface area, weight, volume, CG, MI, etc. (Mass
properties)
– Computation of stresses, strains and deformations in
structural members.
– Heat transfer, temperature changes in boilers, engine
blocks, etc.
– Aerodynamic analysis on automobile bodies, airplanes,
turbine blades, etc.
– Computations of pressure, velocity, turbulence of fluids
in specific applications.
F
E
A

The CAD Process
• Design Review & Evaluation (3rd step in CAD
process)
• Process of checking the accuracy of the design.
– Layering
– The geometric image of the final part to be produced is
overlaid on the image of the rough casting to ensure the
availability of sufficient material on the raw part.
– The procedure can be performed in stages.
– Interference checking
– Involves analyzing an assembled structure for…its
components may occupy the same space. This risk occurs in
designing large chemical plants and other complicated piping
structures.
– Kinematics

The CAD Process
• Automated Drafting (4th step in CAD process)
• Creation of hardcopy engineering drawings directly from
the CAD database.
• Productivity is mutli-times more than the manual drafting.
• Some features are:
– Automatic dimensioning
– Generation of crosshatched areas
– Scaling & other transformations of the drawing
– Developing sectional views
– Generating more than three views
– Adherence to company’s standards by custom programming

Computer Graphics Software
• The set (collection) of programs that help the user to
operate the computer graphics system.
• The programs include – generation of the image on the
monitor (screen); manipulate the image; accomplish
various types of interaction between the user and the
system.
• Additionally, specialized programs may also be used for
functions related to CAD/CAM (modeling, analysis and
manufacturing).

• *Ground rules for designing a graphics software:
• Simplicity – the graphics software should be easy to use.
• Consistency – should operate in a consistent and
predictable way to the operator.
• Completeness – should be no inconvenient omissions in the
set of graphics functions.
• Robustness – the graphics system should be tolerant of
minor instances of misuse by the operator.
• Performance – graphics programs should be efficient and
speed of response should be fast and consistent.
• Economy – graphics should not be too expensive as to make
their use prohibitive.
*Newmann and Sproull, 1979, Principles of Interactive Computer Graphics, McGraw-Hill

• The Software Configuration of a graphics system
(model):
• A conceptual model by Foley & Van Dam suggests three
modules in a graphics system.

• The central module, the application program, controls the
storage of data into and retrieves data out of the application
database.
• It is implemented by the user to construct the model of a physical
entity whose image is to be viewed on the monitor.
• Application programs are written for particular problem areas:
mechanical, civil, electrical, chemical, aerospace, etc.
• The graphics package is the software support between the user
and the graphics terminal (manages graphical interaction
between user and the system).
• Consists of input and output subroutines.
• Input subroutines accept input commands and data from the
user and forward them to the application program.
• Output subroutines control the image on the terminal (2D or 3D
graphical pictures.

• The application database contains:
• Mathematical, numerical and logical definitions of the
application models – mechanical components, automobile
bodies, electronic circuits, etc.
• Alphanumeric information associated with the models – bill
of materials, mass properties, analysis results, etc.
• System commands, function menus, plotter output routines,
etc.
• The database resides in computer memory (primary
storage) and secondary storage also.

• Functions of a graphics package:
• Generation of graphic elements
• Transformations
• Display control and windowing functions
• Segmenting functions
• User input functions
• A graphic element is a basic image entity such as a dot
(point), line segment, circle, plane and solid. Alphanumeric
characters and special symbols may also be part of a
geometric element.
• The term ‘primitive’ is used to refer graphic elements such as
a cube, cylinder, sphere, etc.

• Transformations are used to change the image on
the screen and to reposition the object in the
database.
• A complete application model can be constructed by
using transformations – scaling, translation, rotation,
mirroring, etc.

• Display control and windowing enables the viewer (or user)
to view the image from the desired orientation and the
desired magnification.
• Accomplished by using various transformations.
• Referred to as windowing because the graphics screen is like a
window through which the graphics model is observed by
placing the window in different orientation.
• Hidden line removal is another aspect of display control ( a
feature where the entire model is divided into its visible and
invisible edges (or lines)).

• Segmenting functions provide users with the capability to
selectively replace, delete, or otherwise modify portions of the
image.
• The segment may define a single element or logical grouping
of elements that can be modified as a unit.
• User input functions are a critical set of functions in the
graphics package that permit the user to enter commands or
data into the system.

• Constructing the Geometry:
• The use of graphic elements
• Defining the graphic elements (points, lines, arcs, circles, etc.)
• Editing the geometry

Transformations
• Most editing features in a graphics system are built based on
transformations.
• Major transformations are – translation, scaling and rotation.
• Using the rules of matrix algebra, a point or line (or other
geometric element represented in matrix form) can be
operated on by a transformation matrix to yield the new
element.
• Transformations can be carried out either in 2-dimensions or
in 3-dimensions.

Transformations - Translation
• Moving or repositioning the image of the object or model
across the screen.
• Accomplished by adding the distance through which the
drawing is to be moved to the co-ordinates of each corner
point.
• Let, (x, y) be the coordinates of a corner point. Let (x1, y1) be
the coordinates of translated point. Let Tx and Ty be the
distances by which the point is moved in x and y directions.
• Coordinates of translated point are:
• x1 = x + Tx and y1 = y + Ty

• Example of translating a line
• A line is defined by the matrix shown. It is to be translated in
space by 2 units in x-direction and 3 units in y-direction.
Obtain the new matrix of the translated line. Show also on the
graph, the original and translated lines.
L’ =

• Example of translating a rectangle

Transformations - Scaling
• Reducing or enlarging the size of the image.
• Can be accomplished by multiplying original
coordinates with scale factors in x- and y-directions.
• Scaling is usually relative to the origin.
• Scaling need not necessarily be done equally in the x
and y directions.
• Let, (x, y) be the coordinates of a point. Let (x1, y1)
be the coordinates of scaled point. Let Sx and Sy be
the scaling factors in x and y directions.
• Coordinates of scaled point are:
• x1 = x .Tx and y1 = y . Ty

• Example of scaling a line
• A line is defined by the matrix shown. It is to be
scaled in space by 2 units in x-direction and 2 units in
y-direction. Obtain the new matrix of the scaled line.
Show also on the graph, the original and scaled lines.
L’ =
=
=x

Transformations - Rotation
• The points of an object are
rotated about the origin by
the given angle.
• The rotation is accomplished
by multiplying original
coordinates of a point with
the rotation matrix.
• For a positive angle, the
rotation is in the
counterclockwise direction.
• The rotated coordinates of a
point are:

• Example of rotating a line
• A line is defined by the matrix shown. It is to be
rotated w.r.t origin by 30 degrees. Obtain the new
matrix of the rotated line. Show also on the graph,
the original and rotated lines.
=
The rotation matrix is given by,

• Concatenation
• Carrying out different transformations in sequence
can be termed as concatenation.
• Used under circumstances such as:
• Rotation of the element about an arbitrary point in
the element-
– translation to the origin, then rotation about the origin,
then translation back to the original location.
• Magnifying the element but maintaining the location
of one of its points in the same location-
– scaling (magnified) followed by a translation to locate the
desired point as needed.
=

• Example of concatenation
• A point defined by coordinates (3, 1) is to be scaled
by a factor of 2 and then rotated by 45 degrees.
x
=

Chapter - 4
Computerized Manufacture
Planning and Control System
Computer Aided Process Planning – A linkage between the CAD and CAM

Process Planning
• Other names used:
• Manufacturing planning, material processing, process engineering,
and machine routing.
• Meaning
• The act of preparing detailed work instructions to produce a part.
• How to realize a given product design.
• Which machining processes and parameters are to be used (as well
as those machines capable of performing these processes) to
convert (machine) a piece part from its initial form to a final form
predetermined (usually by a design engineer) from an engineering
drawing.
• The most appropriate manufacturing and assembly processes and
the sequence in which they should be accomplished to produce a
given part or product according to specifications set forth in the
product design documentation.

Product Realization
Design Machine
Tool
Scheduling and Production Control
Process
Planning
http://www.businessmanagementideas.com/production-management/process-planning/procedure-of-process-
planning-7-steps-industries/9424

Process Planning – Who?
• Usually accomplished by manufacturing engineers (…….
industrial engineers, production engineers, and process
engineers).
• A manufacturing engineer must be familiar with the particular
manufacturing processes available in the factory and be able
to interpret engineering drawings.
• The most logical sequence to make each part / product
depends on the planner’s planner’s knowledge, skill and
experience.

Process Planning - Details
• Interpretation of design drawings.
• Choice of processes and sequence.
• Choice of equipment
• Choice of tools, dies, molds, fixtures, and
gages.
• Analysis of methods.
• Setting of work standards.

Product Realization
Product design
Process planning
Operation programming
Verification
Scheduling
Execution
Process,
machine
knowledge
Scheduling
knowledge

Process Plan for Parts
• For individual parts, the processing sequence is
documented on a form called a route sheet (operation
sheet).
• Processing sequence defines the route that the part must
follow in the factory.
• Typical information in a route sheet:
– All operations to be performed on the work part, listed in the
order in which they should be performed.
– A brief description of each operation indicating the
processing to be accomplished, with references to dimensions
and tolerances on the part drawing.
– The specific machines on which the work is to be done.
– Any special tooling, such as dies, molds, cutting tools, jigs or
fixtures, and gages.

Process Plan for Parts – Typical Route Sheet

Process Plan for Parts – Typical Sequence
Typical sequence of processes required in part fabrication

• A basic process determines the starting geometry of the work
part.
• Metal casting, plastic molding, and rolling of sheet metal are
examples of basic processes.
• The starting geometry must often be refined by secondary
processes, operations that transform the starting geometry
into the final geometry (or close to the final geometry).
• When sand casting is the basic process, machining operations are
generally the secondary processes.
• When a rolling mill produces sheet metal, stamping operations
such as punching and bending are the secondary processes.
• Plastic molding and other operations that require no
subsequent secondary processing are called net shape
processes.

• Property-enhancing operations do not alter the geometry of
the part, only the physical properties;
• Heat-treating operations on metal parts are the most common
type.
• Finishing operations usually provide a coating on the work
part (or assembly) surface; examples include electroplating,
thin film deposition processes, and painting.
• The purpose of the coating is to enhance appearance, change
color, or protect the surface from corrosion, abrasion, and other
damage.
• Finishing operations are not required on many parts; for
example, plastic moldings rarely require finishing. When
finishing is required, it is usually the final step in the processing
sequence.

Process Plan for Assemblies
• Factors considered are:
– The anticipated production quantities.
– Complexity (type) of the assembled product, for
example, the number of distinct components.
– Assembly processes used, for example, mechanical
assembly versus welding.

Computer Aided Process Planning (CAPP)
• Limitations in manual process planning
• Automating the task of process planning using computer
overcomes the limitations and the benefits are:
• Process rationalization and standardization.
• Automated process planning leads to more logical and consistent
process plans than manual process planning. Standard plans tend
to result in lower manufacturing costs and higher product quality.
• Increased productivity of process planners.
• The systematic approach and the availability of standard process
plans in the data files permit more work to be accomplished by
the process planners.
• Reduced lead time for process planning.
• Process planners working with a CAPP system can provide route
sheets in a shorter lead time compared to manual preparation.

• Improved legibility.
• Computer-prepared route sheets are neater and easier to
read than manually prepared route sheets.
• Incorporation of other application programs.
• The CAPP program can be interfaced with other application
programs, such as cost estimation and work standards.

• Other Benefits.
• 58% reduction in process planning effort
• 10% saving in direct labor
• 4% saving in material
• 10% saving in scrap
• 12% saving in tooling
• 6% reduction in work-in-process

Computer Aided Process Planning - Approaches
• Retrieval (Variant) CAPP systems
• Generative CAPP systems.
• Semi-generative CAPP systems
• Retrieval (Variant) CAPP systems
• Various parts to be manufactured are classified, given codes
and grouped within certain families.
• A standard process plan (route sheet) is stored in computer
database for each part (code) number.
• The standard route sheets are based on current part routings
that are being used in the factory or on an ideal process plan
that has been prepared for each family.

Retrieval CAPP System - Procedure
Continuous as new parts
are designed and added to
the company’s database.

• Retrieval CAPP systems
• This process plan is also used for the new parts that come
under the same family.
• The system developed is such that it is easier to retrieve the
process plans for the new work parts.
• The whole process plan documents the operations as well as
the sequence of operations on different machines.
• The retrieval CAPP system offers lots of flexibility as one can
do lots of editing and changes as per the requirements.

Generative CAPP systems
The process plan is created based on the logical procedures similar
to those used by a human planner (instead of retrieving and editing
an existing plan contained in a computer database).

• Generative CAPP systems
• The process sequence is planned without human assistance
and without a set of predefined standard plans.
• Designing a generative CAPP system is usually considered
part of the field of expert systems, a branch of artificial
intelligence.
• The ingredients are –
– the knowledge and logic of the human process planners.
– computer-compatible description of the part to be
produced.
– capability to apply the process knowledge and planning
logic contained in the knowledge base to a given part
description.

• Generative CAPP systems – the ingredients
• The technical knowledge of manufacturing and the logic
used by successful process planners must be captured and
coded into a computer program.
• This knowledge and logic of the human process planners is
incorporated into a so-called knowledge base.
• The generative CAPP system then uses that knowledge base
to solve process planning problems (i.e., create route sheets).

• Computer-compatible description of the part to be produced
contains all of the pertinent data and information needed to
plan the process sequence.
• Two possible ways of providing this description are:
– The geometric model of the part that is developed on a CAD
system during product design
– A GT code number of the part that defines the part features in
significant detail.

• The capability to apply the process knowledge and planning
logic contained in the knowledge base to a given part
description.
• The CAPP system uses its knowledge base to solve a specific
problem—planning the process for a new part.
• This problem-solving procedure is referred to as the
inference engine in the terminology of expert systems.
• The CAPP system synthesizes a new process plan from
scratch for each new part it is presented to by using its
knowledge base and inference engine.

Production Planning and Control (PPC) Systems
• What product are to be produced?
• What quantity is to be produced?
• When they are to be produced?
• What are the resources required? (human, material and
machines & equipment)
• Producing in-house or to buy?
In general, PPC consists of
• Deciding which products to make, in what quantities, and
when they should be completed
• Scheduling the delivery and/or production of the parts and
products.
• Planning the manpower and equipment resources needed to
accomplish the production plan.

Production Planning & Control Activities
• Aggregate production planning (Operations Planning)
• Aggregate planning determines the resource capacity a firm
will need to meet its demand over an intermediate time
horizon - 6 to 12 months in the future.
• AP helps developing an economic strategy for meeting
demand.
• Strategies for meeting the demand are:
• Producing at a constant rate and using inventory to absorb
fluctuations in demand (level production)

• Strategies for meeting the
demand are:
• Hiring and firing workers to
match demand (chase demand)
• Maintaining resources for high-
demand levels.
• Increasing or decreasing working
hours (overtime and undertime).
• Subcontracting work to other
firms.
• Using part-time workers
• Providing the service or product
at a later time period
(backordering)

• Master production (schedule) planning
• The master production schedule (MPS), also called the
master schedule, specifies which end items or finished
products a firm is to produce, how many are needed, and
when they are needed.
• The master production schedule produces a more specific
schedule by individual products.
• An MPS is usually expressed in days or weeks and may
extend over several months.

• Material requirements planning (MRP)
• A technique for determining the quantity and timing for
acquiring dependent demand items needed to satisfy
master schedule requirements.
• One objective of MRP is to maintain the lowest possible
level of inventory. MRP does this by determining when
component items are needed and scheduling them to be
ready at that time, no earlier and no later.
• MRP is useful for dependent and discrete demand items,
complex products, job shop production, and assemble-to-
order environments.
• Inputs of MRP are: Master Schedule, Product Structure File
(Bill of Materials), Item Master or Inventory Status File

• Inputs & Outputs of MRP

• Product Structure File (Bill of Materials)
• The product structure file contains a bill of material
(BOM) for every item produced.
• BOM is a list of all the materials, parts, and sub-assemblies
that make up a product, including quantities, parent–
component relationships, and order of assembly.
• The timing and order of assembly can best be described by
a product structure diagram or tree.
• An assembled item is sometimes referred to as a parent,
and a component as a child.

A Sample Product Structure Tree
The Product The components

A Sample Product Structure Tree

Referring to the product structure diagram for product A, determine:
a. how many K’s are needed for each A.
b. how many E’s are needed for each A.
c. the low-level code for item E.
An Example on Product Structure Tree

• A BOM is desired for a bracket (Z100) that is made up of a
base (A10), two springs (B11), and four clamps (C20). The
base is assembled from on clamp (C20) and two housings
(D21). Each clamp has one handle (E30) and each housing
has two bearings (F31) and one shaft (G32).
• Design a product structure tree that includes the level
coding information.
• Show the data in the form of an indented BOM.

• Item Master File
• The item master file, or inventory file, contains an
extensive amount of information on every item that is
produced, ordered, or inventoried in the system.
• Includes such data as on-hand quantities, on-order quantities,
lot sizes, safety stock, lead time, and past usage figures.
• Provides a detailed description of the item, specifies the
inventory policy, updates the physical inventory count,
summarizes the item’s year-to-date or month-to-date usage,
and provides internal codes to link this file with other related
information in the MRP database.
• The item master file is updated whenever items are
withdrawn from or added to inventory or whenever an order
is released, revised, or completed.

Some Important Terms in MRP
Gross requirements
(GR)
The total expected demand for an item or raw material during each
time period without regard to the amount on hand. (For end items
it is MPS; for components, the quantity is derived from the
planned-order releases of their immediate “parents.”
Scheduled receipts
(SR)
Open orders that have been placed and are scheduled to arrive
from vendors or elsewhere in the pipeline by the beginning of a
period.
Projected on hand
(POH)
Expected inventory available on hand at the beginning of each time
period
Net requirements
(NR)
The actual amount needed in each time period.
Planned-order receipts
(PORT)
The quantity expected to be received by the beginning of the
period in which it is shown.
Planned-order releases
(PORL)
Equals planned-order receipts offset by lead time. This amount
generates gross requirements at the next level in the assembly or
production chain. When an order is executed, it is removed from
“planned-order releases” and entered under “scheduled receipts."

GR Planned-order releases of immediate “parents” x No. required per unit
SR Given
POH POH of previous period + SR + PORT – GR
NR GR – (POH + SR) if positive, otherwise zero
PORT NR, in the case of Lot for Lot
PORL PORT offset by lead time
Some Important Terms in MRP
Sample MRP
Item LT =
Week: 1 2 3 4 5 6
Gross requirement
Scheduled receipts
Projected on-
hand
Net Requirement
Planned receipts
Planned order releases

• A certain product X has the demand for which MPS is shown
below. The lead time is 1 week, the scheduled receipt in the first
week is 20 units, on-hand inventory in the beginning of first
week is 100 units and LOL is used. Prepare the MRP.
MRP Example
Week: 1 2 3 4 5 6
MPS for X, units 80 120 100 120 120 100
Item : X
LT = 1
week
Week: 1 2 3 4 5 6
Gross requirement 80 120 100 120 120 100
Scheduled receipts 20
Projected on-
hand
100 40 0 0 0 0 0
Net Requirement -- 80 100 120 120 100
Planned order receipts - 80 100 120 120 100
Planned order releases 80 100 120 120 100

• Complete the MRP shown below.
MRP Example
LT = 4 weeks;
Order Qty. = 70
units;
Safety Stock = 40
units
Week: 1 2 3 4 5 6 7 8 9 10 11 12
Gross
requirement
20 20 25 20 20 25 20 20 30 25 25 25
Scheduled
receipts
70
Projected
on-hand
65
Net Requirement
Planned order
receipts
Planned order
releases

• Complete the MRP shown below.
MRP Example
LT = 4 weeks;
Order Qty. = 70
units;
Safety Stock = 40
units
Week: 1 2 3 4 5 6 7 8 9 10 11 12
Gross
requirement
20 20 25 20 20 25 20 20 30 25 25 25
Scheduled
receipts
70
Projected
on-hand
65 45 95 70 50
100
30
75 55
105
35
75 50 95 70
Net Requirement
Planned order
receipts
70 70 70
Planned order
releases
70 70 70

• A technique for determining what personnel and equipment
capacities are needed to meet the production objectives
embodied in the MPS and MRP.
• Focuses on short-range time horizon
• Helps to plan the capacity of a system and identifies
underloads and overloads.
• The important inputs to CRP are:
– The planned order releases from the MRP process
– A routing file: which machines or workers are required to
complete an order from the MRP plan, in what order the
operations are to be conducted, and the length of time each
operation should take.
– An open orders file: contains information on the status of jobs
that have already been released but have not yet been
completed.
Capacity Requirement Planning

Inputs and Outputs of CRP
•Load is the standard hours of work (or equivalent units of production) assigned to
a production facility.
•Load profiles are a graphical comparison of load versus capacity.

• The normal capacity of a department is 40 hours per week.
We can see that the machine is underloaded in periods 1, 5,
and 6, and overloaded in periods 2, 3, and 4.

Example of Load Profile of a Facility

• Underloaded conditions can be leveled by:
– Acquiring more work - transferring similar work from other
machines in the same shop that are near or over capacity;
making components in-house that are normally purchased
from outside suppliers; seeking work from outside sources.
– Pulling work ahead that is scheduled for later periods -
quick and easy alternative to alleviate both underloads and
overloads.
– Reducing normal capacity

• Overloaded conditions can be leveled by:
• Eliminating unnecessary requirements;
• Rerouting jobs to alternative machines, workers, or work
centers;
• Splitting lots between two or more machines;
• Increasing normal capacity;
• Subcontracting;
• Increasing the efficiency of the operation;
• Pushing work back to later time periods; or
• Revising the master schedule.

• The process of balancing underloads and overloads by
different strategies.
Load Levelling

Shop Floor Control (SFC)
OR
Production Activity Control
(PAC)

• Shop floor control (SFC)
• A set of activities in production control that are concerned
with:
– releasing production orders to the factory,
– monitoring and controlling the progress of the
orders through the various work centers, and
– acquiring current information on the status of the orders.

Shop Floor Control (SFC) - Phases

• The order release provides the documentation needed to
process a production order through the factory.
• The collection of documents is sometimes called the shop
packet which includes the route sheet, material
requisitions, job cards, move tickets and the parts list, if
required for assembly jobs.
• The two inputs to order release are:
• Authorization to produce that derives from the master
schedule. The authorization proceeds through MRP.
• The engineering and manufacturing database that provides
the product structure and process plans needed to prepare
the various documents.

• The order scheduling phase assigns the production orders
to the various work centers in the plant (dispatching).
• A dispatch list is prepared indicating which production
orders should be accomplished at the various work centers.
• It also provides information about relative priorities of the
different jobs (the order of processing based on due dates).
• Machine loading (allocating orders to work centers) and Job
sequencing are the two problems addressed by order
scheduling.

• The order progress phase monitors the status of the
various orders in the plant, work-in-process, and other
measures that indicate the progress of production.
• It provides such information in the form of reports as:
• Work order status reports indicate the status of
production orders:
– the current work center where each order is located,
– processing hours remaining before completion of each order,
– whether each job is on time or behind schedule, and
– the priority level of each order.
• Progress reports indicate performance of the shop during
a certain period – how many orders completed vs. planned.
• Exception reports identify deviations from the production
schedule (e.g., overdue jobs) and similar nonconformities.

Computer Aided Quality
Control (CAQC)

Computer Aided Quality Control (CAQC)
• Quality Control Basics
• A set of activities followed to ensure that a part or product is
produced according to the specifications.
• Inspection is a predominant process used for quality control
(examining a part or product in relation to the design
standards specified for it).
• Inspection may be for – incoming raw materials, WIP,
finished goods and shipping stage
• May be 100% or sampling.
• Testing is associated with the functional aspects of the item
– often directed at the final product rather than part.
• Testing may be destructive or non-destructive.

• The use of the computers for quality control of the product
is called as the computer aided quality control.
• The two major parts of computer aided quality control are
computer aided inspection (CAI) and computer aided
testing (CAT).
• CAI and CAT are performed by using the latest computer
automation and sensor technology.
• The main objectives of the CAQC are to improve the quality of
the product, increase the productivity in the inspection
process and reduce the lead times in manufacturing.

• With CAI and CAT, 100% percent inspection and testing can be
accomplished without much difficulty.
• With 100% inspection, the company does not have to depend
on statistical quality control method.
• With computer controlled inspection, it is not necessary for the
quality control department to settle for less than perfection.
• In CAQC, the inspection process is integrated with the
manufacturing process and it is located along the production
line.
• As soon as the product is manufactured, it is tested
immediately by the computerized process without moving it to
some other location.

• Non-contact sensors are used for the inspection purpose and
they inspect the product without coming in contact with the
product.
• In the advanced technology production lines, the robots would
be used to carry-out the inspection process thus further
speeding the process.
• The data collected by the non-contact sensors is sent as the
feedback to the computerized control system.
• The system would carry out the analysis of the data including
statistical trend analysis.
• Based on the analysis of the data, the system will be able to
adjust the process variables.

Coordinate Measuring Machine (CMM)
• At its most basic, a coordinate is a point, a fixed singular
location in three-dimensional space. A series of points can be
used to define the parameters of a complex shape.
• Therefore, a coordinate measuring machine (CMM) is any
device that is able to collect this set of points for a given object
and to do so with an acceptable degree of accuracy and
repeatability.
• A CMM consists of a heavy base plate or table which serves as
the foundation for an object placed on it to be measured.
• It is a massive slab of granite or some other dense material
that is stable, rigid, immune to fluctuations caused by the
environment, and ground with a very flat top face.

• To this table, a moveable bridge
or gantry is mounted.
• Vertical posts support a
horizontal beam, and on this
beam will be suspended
another vertical column that
holds the measuring probe.
• The bridge or gantry is able to
move along the X-axis.
• The vertical spindle can move
along the bridge thus defining
the Y axis.
• The probe on the vertical
column can move up and down
which defines the Z-axis over
the table.

• There are different technologies
available that can be used as a probe,
partly depending on the objects to be
measured and the degree of accuracy
required.
• A precise sphere of ruby mounted on
the tip of the stylus is the most
common.
• The tip of the probe communicates
its information to a computer which
interprets the data with specialized
software to create a 3D map of the
part in question from the cumulative
set of points.

CIM 15ME62 Module-2: CAD and Computer Graphics Software; Module 3: Line Balancing

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