MODULE-V

COMPUTERIZED
MANUFACTURING PLANNING
SYSTEM
• Computer aided process planning
• Group technology
 MANUFACTURING PLANNING/ PROCESS
PLANNING
• Process planning is that function within a manufacturing facility that establishes which machining process and process
parameters are to be used to convert a work material (blank) from its initial form (raw material) to a final form defined by
an engineering drawing. Process planning is a common task in small batch, discrete parts metal working industries.
• The process planning activity can be divided into the following steps:
• Selection of processes and tools
• Selection of machine tools/Manufacturing equipment
• Sequencing the operations
• Grouping of operations
• Selection of work piece holding devices and datum surfaces (set ups)
• Selection of inspection instruments
• Determination of production tolerances
• Determination of the proper cutting conditions
• Determination of the cutting times and non-machining times (setting time, inspection time) for each operation
• Editing the process sheets
 Computer aided process planning (CAPP)
• Process planning involves the preparation and documentation of
plans for manufacturing the products.
• CAPP is the implementation of this planning with the help of
computers.
• The other major functions in the production planning involve
activities such as Material Requirements planning (MRP) and
Capacity Requirements Planning (CRP)
 Computer aided process planning (CAPP)
Retrieval CAPP systems
• Retrieval type CAPP, also termed
Variant CAPP systems, are
designed using the principles of
group technology, part
Classification and coding.
• In this system, a standard
process plan is prepared for each
part code number and stored in
a computer. Preparation of this
data base is a major task and can
be based on the existing routings
or an ideal plan.
 Computer aided process planning (CAPP)
Retrieval CAPP systems
• As per flow diagram of Retrieval CAPP systems, it begins with deriving the GT code for
the part for which the process plan has to be prepared.
• Using this code in the part family file in the computer, it’s standard route card is
searched.
• The engineer then studies the plan and checks if any modification are required. If
required the engineer edit the standard plan as per the requirements. Because of this
ability to modify the existing process plan this system is given the name variant CAPP
systems.
• The engineer can either use existing process plan or write a new process plan for part,
which then becomes the standard process plan for the new part code number.
• The process planning function ends with the process plan formatter. It prints route sheet
in a proper format. The formatter may call other application programs into use, like to
determine the machining conditions for various machine tool operations, to calculate
standard times for operations, cost estimations.
• this printed process plan is taken as the basis for further operations.
 Computer aided process planning (CAPP)
Generative CAPP systems
• Generative CAPP systems are more advanced systems involving experts systems.
• There are three main components required for the development of fully generative CAPP
systems.
1. Creation of knowledge base :- In this system, the complete technical knowledge of
manufacturing and the logic developed by expert planners is coded and loaded into
computer. This forms the knowledge base for the generative CAPP systems.
2. Computer compatible part description- CAD model :- For the CAPP system to apply its
knowledge base to the point for which the route sheet can be developed, it’s needs a
compatible description information of the part. This is generally done by creating a
CAD model of the part, which completely describes the part geometry and
dimensional and other process details required.
3. Inference engine:- the next requirement of the system is to apply the coded
knowledge base to the supplied part description by CAD model. That means it should
solve the process planning problem for the given part and generate the output. This
problem solving procedure is termed as inference engine.
 Materials requirements planning (MRP)
• MRP is a system of planning and scheduling materials requirements
for various production activities. It helps in working out a detailed
production plan for production systems having different products, sub
assemblies, components and materials.
• MRP systems starts with master schedule for the end products and
work backwards to determine the time schedule and quality of each
component required.
• The production schedule of the end product is used to determine the
requirements for sub assemblies, components and raw materials.
Materials requirements planning (MRP)
Flow chart of MRP
 Materials requirements planning (MRP)
Flow chart of MRP
1. Forecast data:- this is the market research data used to estimate the production
requirements for a particular period.
2. Orders :- this indicates the firm orders by customers for a product to be produced and
delivered within a given period.
3. Master production schedule (MPS) :- it specifies the complete requirements of an end
product, its quality and time of requirement. It’s a production plan developed on the
basis of inputs like firm customer orders and demand forecast.
4. Inventory status:- the inventory status is an essential information of the raw materials,
assemblies and sub assemblies. It indicates on hand quantities, gross requirements,
schedule receipts and planned order releases for the item.
5. Bill of materials :- it consists of details of materials, parts and sub assemblies that
make an end product. The BOM file represents each and every part by a unique
identification number and helps processing by a process which translate end items
requirements into components.
 Capacity requirements planning
• Capacity refers to the output from a production system. Many times
terms like designed capacity, installed capacity…etc are commonly
used to express the possible output.
• Capacity can be defined as the limiting capability of a production
system to produce the required output, within a given period and
expressed as output in units per unit time.
• Capacity planning is the process deciding the quantity of goods to be
produced. It’s basic step required for an organization decide on the
production quantity.
• Capacity planning forms the basis for facility location, process
technology, material requirements and fund management.
 Capacity requirements planning
• If the Capacity existing is more than the demand, then the
management had to explore the possibilities of reducing Capacity by
temporarily closing the facility, reducing the shifts, working hours.
• If a higher Capacity requirement in able existing facility can be met
with available plant, then it can work overtime increase shifts and
working days.
• Capacity planning time horizons
1. Long range decision
2. Medium range decisions
3. Short range decisions
 Group technology
• Group technology is an operations based on the recognition that
similarities occur in the design and manufacture of discrete parts.
Similar parts can then be arranged into part families.
• To implement such a system, some form of classification of parts and
coding is required.
• Part classification and coding is concerned with identifying the
similarities and using these similarities to evolve a classification code.
Similarities are of two types: design attributes (such as geometric
shape and size), and manufacturing attributes (the sequence of
processing steps required to make the part).
 PART FAMILIES

• A part family is a collection of parts which are similar either because of geometry and size or
because similar processing steps are required in their manufacture.
• The parts within a family are different, but their similarities are close enough to merit their
identification as members of the part family.
• The major obstacle in changing over to group technology from a traditional production shop is the
problem of grouping parts into families.
• There are three general methods for solving this problem.
• i. Visual inspection
• ii. Production flow analysis
• iii. Parts classification and coding system
• What is desirable in a computer integrated manufacturing environment is a software which will
analyze the geometric model of the part and come out with a set of alphabetic/ numeric
characters which can broadly embed similarities.
PARTS CLASSIFICATION and CODING SYSTEMS
• Parts classification and coding systems can be grouped into three
general types:
i. Systems based on design attributes
ii. Systems based on part manufacturing attributes
iii. Systems based on both design and manufacturing attributes
 PARTS CLASSIFICATION
i) Part Design Attributes ii) Part Manufacturing Attributes
• Basic (External/Internal) shape • Major process of manufacture
• Axisymmetric/Prismatic/sheet • Surface treatments/coatings
metal • Machine tool/processing
• Length/diameter ratio equipment
• Material • Cutting tools
• Major dimensions • Operation sequence
• Minor dimensions • Production time
• Tolerances • Batch quantity
• Surface finish • Production rate
• Fixtures needed
 Coding systems
• A part coding scheme consists of symbols that identify the part’s design and/or
manufacturing attributes. The symbols in the code can be all numeric, all
alphabetic, or a combination of both types.
• There are three basic code structures used in group technology applications:
• i. Hierarchical structure
• ii. Chain type structure
• iii. Hybrid structure which is a combination of the above two
• With the hierarchical structure, the interpretation of each succeeding symbol
depends on the value of the preceding symbols. In the chain type structure, the
interpretation of each symbol in the sequence is fixed and does not depend on
the value of preceding digits. Most of the commercial parts coding systems are
used in industry are a combination of the two pure structures.
 Coding systems
• When selecting a coding system for a component’s representation,
there are several factors to be considered. They include:
• i. The geometry of components (i.e., rotational, prismatic, deep
drawn, sheet metal etc.)
• ii. The code structure
• iii. The digital representation (i.e., binary, octal, hexadecimal etc.)
• iv. Material of manufacture - ferrous, non ferrous, plastics,
composites etc.