LECTURE NOTES ON

Rapid Prototyping

PREPARED BY

Dr PRAMOD KUMAR PARIDA

ASSISTANT PROFESSOR

DEPARTMENT OF MECHANICAL ENGINEERING

COLLEGE OF ENGINEERING & TECHNOLOGY (BPUT)

BHUBANRSWAR
 Syllabus

PEME5303 RAPID PROTOTYPING (3-0-0)

Module – I (12 hours)
Product Development: Classification of manufacturing processes, Different manufacturing
systems, Introduction to rapid Prototyping (RP), Need of RP in context to batch
production, FMS and CIM and its application. Product prototyping – solid modeling and
prototype representation, reverse engineering, prototyping and manufacturing using
CNC machining.

Basic principles of RP steps in RP, Process chain in RP in integrated CAD-CAM

environment, Advantages of RP
Module - II (12 hours)
Rapid Manufacturing Process Optimization: factors influencing accuracy. Data preparation
errors, Part building errors, Error in finishing, influence of build orientation.
Classification of different RP techniques based on raw materials, layering technique (2D or
3D) and energy sources.
Process technology and comparative study of stereo lithography (SL) with
photopolymerisation, SL with liquid thermal polymerization, solid foil polymerization,
selective laser sintering, selective powder binding, Ballastic particle manufacturing –
both 2D and 3D, Fused deposition modeling, Shape melting

Module – III (12 hours)

Laminated object manufacturing solid ground curing, Repetitive masking and deposition.
Beam interference solidification, Holographic interference solidification special topic on RP
using metallic alloys, Programming in RP modeling, Slicing, Internal Hatching, Surface skin
films, support structure.
Software for RP: STL files, Overview of Solid view, magics, imics, magic communicator, etc.
Internet based software, Collaboration tools.
Text Book :
1. Rapid Prototyping and Engineering Applications, Frank W. Liou, CRC Press
2. Introduction to Rapid Prototyping, Amitav Ghosh, North West Publication, New Delhi
Reference Books :
1. Rapid Manufacturing, Flham D.T &Dinjoy S.S Verlog London 2001.
2. Rapid Prototyping Materials, Gurumurthi, IISc Bangalore.
3. Rapid Automated, Lament wood. Indus press New York
4. Stereo Lithography and other RP & M Technologies, Paul F. Jacobs: SME, NY 1996.
5. Rapid Prototyping, Terry Wohlers Wohler's Report 2000" Wohler's Association 2000.
 Module – I
Manufacturing
The English word manufacture is several centuries old. The term
manufacture comes from two
Latin words, manus (hand) and factus (make). As per oxford English
dictionary manufacture refers “to make or produce goods in large
quantities, using machinery”.
Working definition of manufacturing
There are two types of working definitions available for manufacturing: as a
technical process and as an economic process.
Technologically: Manufacturing is the application of physical and chemical
processes to alter the geometry, properties and or appearance of a given
starting material to make parts or product as shown in Figure

Definition of manufacturing in terms of technology

Economically: Manufacturing is the transformation of materials into items
of greater value by means of one or more process and or assembly
operation as shown in Figures.

Definition of manufacturing in terms of economic value

Diagrammatic representation of Manufacturing

Factors Contributing to Production Growth

Activities involved in Manufacturing

 Development and Progress of Manufacturing
Classification of the Manufacturing Process:
 The manufacturing process used in engineering industries basically
perform one or more of the following functions:
 Change the physical properties of the work material
 Change the shape and size of the work piece.
 Produce desired dimensional accuracy and surface finish.
 Based on the nature of work involved these processes may be divided
into following seven categories:
1. Processes for changing physical properties of the materials –
Hardening, Tempering, Annealing, Surface Hardening.
2. Casting Processes – Sand Casting, Permanent mold casting, die
casting, Centrifugal casting
3. Primary metal working processes – Rolling, forging, extrusion,
wire drawing
4. Shearing and Forming processes – Punching, blanking, drawing,
bending, forming
5. Joining processes – Welding, brazing, soldering, joining
6. Machining Processes – Turning, drilling, milling, grinding
7. Surface finishing processes – Lapping, honing, superfinishing
 Spectrum of Manufacturing Process

MANUFACTURING SYSTEM
The term manufacturing system refers to a collection or arrangement of
operations and processes used to make a desired product or component. It
includes the actual equipment for composing the processes and the
arrangement of those processes. In a manufacturing system, if there is a
change or disturbance in the system, the systems would accommodate or
adjust itself and continue to function efficiently. Normally the effect of
disturbance must be counteracted by controllable inputs or the system
itself. Figure below gives the general definition for any manufacturing
system.

General representation of Manufacturing system

TYPES OF MANUFACTURING SYSTEMS

The manufacturing systems differ in structure or physical arrangement.

According to the physical arrangement, there are four kinds of classical
manufacturing systems and two modern manufacturing systems that is
rapidly gaining acceptance in industries.

The classical systems are

1. Job shop
2. Flow shop
3. Project shop
4. Continuous process

The modern manufacturing systems are

1. Linked cell system (Cellular manufacturing system)
2. Flexible manufacturing system (FMS)

Job shops
In a Job shop, varieties of products are manufactured in small lot sizes to a
specific customer order. To perform a wide variety of manufacturing
processes, general purpose production equipment is required. Workers
must have relatively high skill levels to perform a range of different work
arrangements.

The production machines are grouped according to the general type of

manufacturing processes as shown in Figure below. The lathes are in one
department, drill presses in another and so on. Each different part requiring
its own sequence of operations can be routed through the various
departments in the proper order. For this ‘ROUTE SHEETS’ are used. The
layout made for this purpose is called as functional or process layout.

Functional or process layout

Advantages of process layouts

 Can handle a variety of processing requirements
 Not particularly vulnerable to equipment failures
 Equipment used is less costly
 Possible to use individual incentive plans

Disadvantages of process layouts

 In-process inventory costs can be high
 Challenging routing and scheduling
 Equipment utilization rates are low
 Material handling is slow and inefficient
 Complexities often reduce span of supervision
 Special attention for each product or customer
 Accounting and purchasing are more involved

Examples: Machine shops, foundries, press working shops, plastic,

industries.
Flow shops

The flow shops have a “product oriented layout” composed mainly of flow
lines. This system can have high production rates. The plant may be
designed to produce the particular product or family, using “Special
purpose machines” rather than general purpose equipment. The skill level
of the laborer tends to be lower than in production job shop. When the
volume of production becomes large, it is called “mass production”. The
material flow is through a sequence of operations by material handling
devices. The time the item spends in each station or location is fixed and
equal. The workstations are arranged in line according to the processing
sequence needed as shown in Figure below

Product layout

Advantages of product layout

 High rate of output
 Low unit cost
 Labor specialization
 Low material handling cost
 High utilization of labor and equipment
 Established routing and scheduling
 Routing accounting and purchasing
Disadvantages of product layout
 Creates dull, repetitive jobs
 Poorly skilled workers may not maintain equipment or quality of
output
 Fairly inflexible to changes in volume
 Highly susceptible to shutdowns
 Needs preventive maintenance
 Individual incentive plans are impractical

Example: Automated assembly line and Television manufacturing factory.

Project shop
In this type, a product must remain in a fixed position or location because of
its size and weight. The materials, machines and people in fabrication are
brought to site. The layout is also called as fixed position layout. Figure
below shows the project shop layout.
Example: Locomotive manufacturing, large aircraft assembly and
shipbuilding

Project shop layout

Advantages of project layout

 Minimum capital investment
 Continuity of operation
  Less total production cost.
 Offers greater flexibility
 Allows the change in production design.
 Permits a plant to elevate the skill of its operators

Disadvantages of project layout

 Machines, tools and workers take more time to reach the fixed
position.
 Highly skilled workers are required.
 Complicated jigs and fixtures (work holding device) may be required.

Continuous process
In this continuous process, the product seems to flow physically. This
system is sometimes called as flow production when referring to the
manufacture of either complex single parts, such as scanning operation, or
assembled products such as TVs. However, this is not a continuous
process, but high volume flow lines. In continuous process, the products
really do flow because they are liquids, gases, or powers. Figure 1.5 shows
the continuous process layout. It is the most efficient but least flexible kind
of manufacturing system. It usually has the leanest and simplest production
system because this manufacturing system is the easiest to control
because it has the least work- in progress(WIP).
Examples: Oil refineries, chemical process plants and food processing
industries

Continuous process layout

Linked cell manufacturing system

Cellular manufacturing (CM) is a hybrid system for linking the advantages

of both job shops (flexibility in producing a wide variety of products) and
flow lines (efficient flow and high production rate). A cellular manufacturing
system (CMS) is composed of “linked cells”. Figure below shows the main
structure of cellular manufacturing system. In cells, the workstations are
arranged like a flow shop. The machines can be modified, retooled and
regrouped for different product lines within the same “family” of parts. This
system has some degree of automatic control for loading and unloading of
raw materials and work pieces, changing of tools, transferring of work
pieces and tools between workstations. Cells are classified as manned and
unmanned cells. In manned cells multifunctional operators can move from
machine to machine and the materials can be moved by the operator. In
the unmanned cells, an industrial robot is located centrally in the cell for
material handling. Automated inspection and testing equipment can also be
a part of this cell.

Main structure of cellular manufacturing System

Advantages of CMS

The advantages derived from CMS in comparison with traditional

manufacturing systems in terms of system performance have been
discussed in Farrington (1998), Kannan (1999), Suresh (2000),Hug (2001)
and Assad (2003). These benefits have been established through
simulation studies, analytical studies, surveys, and actual implementations.

They can be summarized as follows:

Setup time is reduced: A manufacturing cell is designed to handle parts

having similar shapes and relatively similar sizes. For this reason, many of
the parts can employ the same or similar holding devices (fixtures). Generic
fixtures for a part family can be developed so that time required for
changing fixtures and tools is decreased.

Lot sizes are reduced: Once setup times are greatly reduced in CM, small
lots are possible and economical. Small lots also provide smooth
production flow.

Work-in-process (WIP) and finished goods inventories are reduced:

With smaller lot sizes and reduced setup times, the amount of WIP can be
reduced. The WIP can be reduced by 50%when the setup time is cut to
half. In addition to the reduced setup times and WIP inventory, finished
goods inventory is reduced. Instead of make-to-stock systems with parts
either being run at long, fixed intervals or random intervals, the parts can
be produced either JIT in small lots or at fixed, short intervals.

Material handling costs and time are reduced:

In CM, each part is processed completely within a single cell (wherever
possible). Thus, part travel time and distance between cells is minimal.
A reduction in flow time is obtained:
Reduced materials handling time and reduced setup time greatly reduce
flow time.
Tool requirements are reduced:
Parts produced in a cell are of similar shape, size, and composition. Thus,
they often have similar tooling requirements.

A reduction in space required:

Reductions in WIP, finished goods inventories, and lot sizes lead to less
space required.
Throughput times are reduced:
In a job shop, parts are transferred between machines in batches.
However, in CM each part is transferred immediately to the next machine
after it has been processed. Thus, the waiting time is reduced substantially.

Product quality is improved:

Since parts travel from one station to another as single unit, they are
completely processed in a small area. The feedback is immediate and the
process can be stopped when things go wrong.

Better overall control of operations:

In a job shop, parts may have to travel through the entire shop. Scheduling
and material control are complicated. In CM, the manufacturing facility is
broken down into manufacturing cells and each part travels with a single
cell, resulting in easier scheduling and control.

Flexible manufacturing system

A FMS integrates all major elements of manufacturing into a highly
automated system. The flexibility of FMS is such that it can handle a variety
of part configurations and produce them in any order. Figure 1.7 shows
flexible manufacturing system. The basic elements of FMS are a) works
station b) automated material handling and automated storage and retrieval
systems c) control systems. Because of major capital investment; efficient
machine utilization is essential. Consequently, proper scheduling and
process planning are crucial, that are complex in nature. Because of the
flexibility in FMS, no setup time is wasted in switching between
manufacturing operations; the system is capable of different operations in
different orders and on different machines.
 Flexible manufacturing system

Advantages:
 Parts can be produced randomly in batch sizes, as small as one, and
at lower cost.
 The lead times required for product changes are shorter
 Reduced WIP
 Labour and inventories are reduced
 Production is more reliable, because the system is self-correcting and
so product quality is uniform.
 Increased machine utilization
 Fewer machines required
 Reduced factory floor space
 Greater responsiveness to change
Automation:

With the advent of mass manufacturing concept, the fruits of technology

have reached the common man. Without mass production, cost of the
products would have kept several items, which are now common, far
beyond the reach of most people. To increase the productivity hence lower
the production cost as much as possible automation was introduced in the
engineering manufacturing industries. At the onset such automation was
primarily named as Automatic Mechanization. These specially designed
manufacturing units could be cost effective only when huge quantity of a
particular item was needed to be manufactured. The variations in products
were few and the demand for individual items was large. Thus this type of
automation now- a-days called ‘Hard Automation’.

In the 1940’s the concept of computer emerged and that led to the
development of ‘numerical control’ for machine tools. Changing a set-up for
switching over from one job to another involved changing a substantial
amount of the hardware i. e. cams, fixtures, tooling etc. it was time
consuming and was expensive also. Once the concept of computer
developed it becomes possible to store and feed information with the help
of numbers. Numerical control (NC) implies that the necessary information
for producing a particular component in a machine can be provided with the
help of numbers. Thus switching over from one job to another involved
feeding new data and no major modification of the hardware is necessary.
Consequently, such units are very flexible in the sense that switching over
from one job to another can be done without major time delay and
expense. Use of such flexible machines is termed as ‘Flexible
Automation’. With the tremendous development in computer science and
micro-electronics, flexible automation has become very inexpensive to
achieve. The machines are also now directly controlled by computers and
such a control is called ‘Computer Numerical Control (CNC)’

It is easy to visualize that with the help of such flexible automation, the
requirement of specialized hardware for automatic production of a
particular item is eliminated. Cost effective automatic manufacturing has
hence become feasible even for small and medium size batches. Figure
below indicates the cost effectiveness of different types of manufacturing
automation for different ranges of production.
 Cost effectiveness of different types of manufacturing automation

Along with the progress in computers, microelectronics and sensor

technology gradually appeared in the technological world i.e. ‘Industrial
Robotics’. With the development of industrial robots, manufacturing
industry entered another era where it became possible to realize the dream
of true automation. The human work force for tending machines and
inspection stations and more important assembly stations could now be
replaced by industrial robots. Figure below shows the various stages of
mechanization and automation in the engineering manufacturing industry.
 Stages of Mechanization in Manufacturing

The use of computers in assisting manufacturing started before CAD

developed as useful tool. In the early days the use of computers in
extending the applications of NC technology, specially to part
programming, was termed as computer aided manufacturing (CAM) and it
was delinked from the design activities. Initially CAD and CAM evolved as
separate activities, but gradually it became evident that certain tasks were
common to both. Use of CAD/CAM in an effective manner helps to improve
the design as manufacturing considerations can be incorporated into the
design. A substantial amount of improvement in productivity and quality has
been found to be possible through the use of CAD.CAM technology.
Figure below shows the scheme for CAD/CAM in a modern industry.

Basic scheme of a manufacturing industry using CAD/CAM

Though the application of computers in manufacturing became quite

extensive, the various associated activities still remained
compartmentalized and distinct. Once the technology of flexible automation
matured integration of the different activities became feasible.
Computer Integrated Manufacturing (CIM)
In a very competitive and open global market survival is possible only if a
good product variety is offered, quality and reliability are assured, cost is
made attractive and the time gap between the conceptualization of a
product and delivery is reduced. To satisfy so many requirements it is
essential to strive for optimal use of man. Machine and material. This is
possible only if all the activities associated with design and manufacturing
are integrated. As mentioned earlier the required electromechanical and
computer technologies for such an integration was ready in 80’s. such a
system is termed as ‘computer integrated manufacturing system’(CIMS)
and the technology has been given the name ‘computer integrated
manufacturing (CIM)’. CIM not only implies the use of computer in
designing a product, planning inventory and production, controlling the
operations and accomplishing many other designs, manufacturing,
management and business related issues but suggest a marriage of the
diverse functions under the control of one central supervisory computer.
The figure below indicates the information flow, material flow and functions
involved in CIM.

Structure of CIM
In concurrent engineering (CE) product is developed by a team involving
engineers from both the design section and the production shop. The
advantages of concurrent engineering are based on the economic leverage
of addressing all aspects of design of a product as early as possible. Hence
using concurrent engineering most of the design modification is
incorporated as early as possible. It is also true that the importance of early
modification is very significant and the ability of the early change to
influence the product cost is much larger as indicated. Hence using
concurrent engineering most of the design modifications are incorporated
as early as possible.

The duration of prototype development is an important factor and it is found

that more than 25% of the total product development time goes in
fabricating the prototype. The figure below shows the typical duration of
product development and prototype fabrication.

(a) Typical duration of product development, (b) typical duration of

prototype development
Figure below indicates the product development cycle and the prototype for
different stages.

Types of prototypes at different stages of product development

 In the early stage of product development a ‘design model’ and a

‘geometric prototype’ are prepared. The design model is made
primarily to decide the overall appearance and it is used for
ergonomics analysis. Since there is no functional requirement these
models are easy to process, non metallic materials can be used for
making these models.
 In geometric prototypes the dimensional features of the product,
accuracy and tolerances are of primary importance. These prototypes
are also made of model making materials as functional aspects are of
secondary importance. These prototypes are used primarily for
process planning. Appearance and many geometric features are not
considered at this stage.
  In the next step technical prototypes are made using the same
material and the same manufacturing processes as the intended final
product. The technical prototypes are useful in assessing various
product qualities like reliability, product life etc.
 After the necessary modifications the first series of the product is
manufactured and marketed.

Rapid Prototyping (RP)

Though the principle of concurrent engineering (CE) is quite clear and the
advantages of the concept for improved quality and reduced cost are
implicit, it is not possible to incorporate CE effectively in the absence of
some technique for quick development of prototype. To reduce the
development time and adopt concurrent engineering in its true spirit, quick
and inexpensive fabrication of prototype parts is essential and rapid
prototyping technology has made that possible.

A family of unique fabrication processes developed to make engineering

prototypes in minimum lead time based on a CAD model of the item
•The traditional method is machining
−Machining can require significant lead-times –several weeks, depending
on part complexity and difficulty in ordering materials
•RP allows a part to be made in hours or days given that a computer model
of the part has been generated on a CAD system

WYSIWYG-What You See Is What You Get

Why Rapid Prototyping?

•Because product designers would like to have a physical model of a new

part or product design rather than just a computer model or line drawing
−Creating a prototype is an integral step in design
−A virtual prototype (a computer model of the part design on a CAD
system) may not be sufficient for the designer to visualize the part
adequately
−Using RP to make the prototype, the designer can visually examine and
physically feel the part and assess its merits and shortcomings
Reverse Engineering:
In today’s intensely competitive global market, product enterprises are
constantly seeking new ways to shorten lead times for new product
developments that meet all customer expectations. In general, product
enterprise has invested in CADCAM, rapid prototyping, and a range of new
technologies that provide business benefits. Reverse engineering (RE) is
now considered one of the technologies that provide business benefits in
shortening the product development cycle. Figure below depicts how RE
allows the possibilities of closing the loop between what is “as designed”
and what is “actually manufactured”.

Product development cycle

What Is Reverse Engineering?

Engineering is the process of designing, manufacturing, assembling, and
maintaining products and systems. There are two types of engineering,
forward engineering and reverse engineering. Forward engineering is the
traditional process of moving from high-level abstractions and logical
designs to the physical implementation of a system. In some situations,
there may be a physical part/product without any technical details, such as
drawings, bills-of-material, or without engineering data. The process of
duplicating an existing part, subassembly, or product, without drawings,
documentation, or a computer model is known as reverse engineering.
Reverse engineering is also defined as the process of obtaining a
geometric CAD model from 3-D points acquired by scanning/digitizing
existing parts/products. The process of digitally capturing the physical
entities of a component, referred to as reverse engineering (RE), is often
defined by researchers with respect to their specific task.
Reverse engineering is now widely used in numerous applications, such as
Manufacturing, industrial design, and jewelry design and reproduction For
example, when a new car is launched on the market, competing
manufacturers may buy one and disassemble it to learn how it was built
and how it works. In software engineering, good source code is often a
variation of other good source code. In some situations, such as
automotive styling, designers give shape to their ideas by using clay,
plaster, wood, or foam rubber, but a CAD model is needed to manufacture
the part. As products become more organic in shape, designing in CAD
becomes more challenging and there is no guarantee that the CAD
representation will replicate the sculpted model exactly.
Reverse engineering provides a solution to this problem because the
physical model is the source of information for the CAD model. This is also
referred to as the physical-to-digital process depicted in Figure 1.2. Another
reason for reverse engineering is to compress product development cycle
times. In the intensely competitive global market, manufacturers are
constantly seeking new ways to shorten lead times to market a new
product.
Rapid product development (RPD) refers to recently developed
technologies and techniques that assist manufacturers and designers in
meeting the demands of shortened product development time. For
example, injection-molding companies need to shorten tool and die
development time drastically. By using reverse engineering, a three-
dimensional physical product or clay mock-up can be quickly captured in
the digital form, remodeled, and exported for rapid prototyping/tooling or
rapid manufacturing using multi-axis CNC machining techniques.
Why Use Reverse Engineering?
Following are some of the reasons for using reverse engineering:
• The original manufacturer no longer exists, but a customer needs the
product,
e.g., aircraft spares required typically after an aircraft has been in service
for several years.
• The original manufacturer of a product no longer produces the product,
e.g., the original product has become obsolete.
• The original product design documentation has been lost or never existed.
• Creating data to refurbish or manufacture a part for which there are no
CAD data, or for which the data have become obsolete or lost.
• Inspection and/or Quality Control–Comparing a fabricated part to its CAD
description or to a standard item.
• Some bad features of a product need to be eliminated e.g., excessive
wear might indicate where a product should be improved.
• Strengthening the good features of a product based on long-term usage.
• Analyzing the good and bad features of competitors’ products.
• Exploring new avenues to improve product performance and features.
• Creating 3-D data from a model or sculpture for animation in games and
movies.
• Creating 3-D data from an individual, model or sculpture to create, scale,
or reproduce artwork.
• Architectural and construction documentation and measurement.
• Fitting clothing or footwear to individuals and determining the
anthropometry of a population.