Computer Aided Process Planing. Process Planning Approaches Report . 1. Variant(Retrieval) CAPP Approach. 2.Generative CAPP Approach.

1. A
SEMINAR REPORT
ON
Process Planning Approaches
Submitted By
Chethan kumar
MSRIT

2. PROCESS PLANNING
The product design is a plan for the product and its components and
subassemblies. To convert the product design into a physical entity, a
manufacturing plan is needed. The activity of developing such a plan is
called process planning.
It is a link between product design and manufacturing. Process
planning involves determining the sequence of processing and assembly
steps that must be accomplished to make the product. It is concerned with
the engineering and technological issues of how to make the product and
its parts. What types of equipment and tooling are required to fabricate the
part and assemble the product.
It involves determining the most appropriate manufacturing and
assembly process and sequence in which they should be accomplished to
produce a given part or product according to the specifications set forth in
the product design documentation.
All the related information is documented on a Rout Sheet. The
planning begins with engineering drawings, specifications, parts or
material lists and a forecast of demand. The scope and variety of process
that can be planned are generally limited by the available processing
equipment and technological capabilities of the company or the plant.
Process planning is usually accomplished by manufacturing
engineers. Based on process planner’s skill, knowledge, and experience,
the processing steps are developed in the most logical sequence, to make
each part.

3. The following are the list of many decisions and details usually
included within scope of process planning.
 Interpretation of design drawings
The part or product design must be analyzed (materials, dimensions,
tolerances, surface finishes etc) at the start of the process planning
procedure.
 Process and sequences
The process planner must select which processes are required and
their sequence. A brief description of all processing steps must be
prepared.
 Equipment selection.
In general, process planers’ must develop plans that utilize existing
equipment in the plant. Otherwise, the component must be purchased or an
investment must be made in new equipment.
 Tools, Dies, Moulds, fixtures and gauges.
The process planner must decide what tooling is required for each
processing step. The actual design and fabrication of these tools is usually
delegated to a tool design department and tool room or an outside vendor
specializing in that type of tool is contracted.
 Method analysis.
Workplace layout, small tools, hoists for lifting heavy parts even in
some cases hand and body motions must be specified for manual
operations. The industrial engineering department is usually responsible for
this area.

4.  Work standards.
Work measurement techniques are used to set time standards for each
operation.
 Cutting tools and cutting condition.
These must be specified for machining operations often with
reference to standard handbook recommendation.
The results of planning are:
 Routings which specify operations, operation sequences, work centers,
standards, tooling and fixtures. This routing becomes a major input to the
manufacturing resource planning system to define operations for
production activity control purposes and define required resources for
capacity requirements planning purposes.
 Process plans which typically provide more detailed, step by step work
instructions including dimensions related to individual operations,
machining parameters, set-up instructions, and quality assurance check
points.
 Fabrication and assembly drawings to support manufacture.
Manual process planning as mentioned earlier is based on a
manufacturing engineer’s experience and knowledge of production
facilities, equipment, their capabilities, processes and tooling. Process
planning is a time-consuming process and the results vary based on the
person doing the planning.

5. COMPUTER - AIDED PROCESS PLANNING (CAPP)
Process planning translates design information into the process steps
and instructions to efficiently and effectively manufacture products. As the
design process is supported by many computer aided tools, computer aided
process planning has evolved to simplify and improve process planning
and achieve more effective use of manufacturing resources.
3.1 CAD/CAM INTEGRATION AND CAPP FEATURES
A frequently overlooked step in the integration of CAD/CAM is the
process planning that must occur. CAD systems generate graphically
oriented data and may go so far as graphically identifying metal etc to be
removed during processing. In order to produce such things as NC
instructions for CAM equipment, basic decisions regarding equipment to
be used, tooling and operating sequence need to be made.
This is the function of Computer Aided Process Planning. Without
some elements of CAPP there would be no such thing as CAD/CAM
integration. The CAD/CAM systems that generate tool paths and NC
programs include limited CAPP capabilities or imply a certain approach to
processing.
CAD systems also provide graphically oriented data to CAPP
systems to use to produce assembly drawings etc. further, this graphically
oriented data can then be provided to manufacturing in the form of
hardcopy drawings or work instruction displays. This type of system uses
work instruction displays at factory workstations to display process plans
graphically and guide employees through assembly step by step.
The assembly is shown on the screen and as a employee steps
through the assembly process with footswitch, the components to be
inserted or assembled are shown on the CRT graphically along with text
instructions and warnings at each step.

6. If NC machining processes are involved, CAPP software exists which will
select tools, feeds, and speeds and prepare NC programs.
3.2 COMPUTER-AIDED PROCESS PLANNING : TYPES
Computer aided process planning systems are around two
approaches. These approaches are called:
1. Retrieval CAPP system or Variant Approach
2. Generative CAPP systems or Generative Approach
Some Computer aided process planning systems are combine the two
approaches in what is known as Semi Generative Approach.
1. Retrieval CAPP System or Variant Approach
The retrieval type is suitable for a family of parts. This system draws a
standard process plan and stores it in the database. Whenever a different
part from the family is to be processed, the standard process plan is
retrieved and appropriately modified hence the retrieval to this system. The
retrieval systems relies on the concept of group technology for part coding
and classification.
It is also compatible with the concept of cellular manufacturing in which
cells are designed and laid out for family-of-parts production. In this type,
as mentioned earlier a standard process is stored in computer files for each
part code number called the Route Sheet.
The retrieval CAPP system operates as given in figure 2. Before the
system can be used for process planning, a significant amount of
information must be compiled and entered into the CAPP data files. This is
referred to as the “preparatory step”.

7. It consists of the following steps:
i. Selecting an appropriate classification and coding scheme for the
company.
ii. Formatting part families for the parts produced by the company.
iii. Preparing standard process plans for the part families.
Steps (ii) and (iii) continue as new parts are designed and added to the
company’s design database.

8. GENERAL PROCEDURE FOR RETRIEVAL CAPP SYSTEMS
After the preparatory phase has been computed, the system is
ready for use. For a new component for which the process plan is to be
determined, the first step is to determine the GT code number for the part.
With this code number a search is made for the part family file to
determine if a standard rout sheet exists for the given part code.
If the file contains a process plan for the part, it is retrieved (hence the
word “retrieval” for this CAPP system) and displayed for the user. The
standard process plan is examined to determined whether any
modifications are necessary.
It might be that although the new part has the same code number, there
are minor differences in the process required to manufacture it. The user
edits the standard plan accordingly. This capacity to alter an existing
standard process plan is what gives the retrieval system its alternative
name: “variant” CAPP system.
If the file does not contain a standard process plan for the given
code number, the user may search the computer file for a similar or related
code number from which a standard route sheet does exists. Either by
editing an existing process plan or by starting from scratch the user
prepares the rout sheet for the new part. This rout sheet becomes the
standard process plan for the new part code.
The process planning session concludes with the process plan
formatter, which prints out the route sheet in the proper format. The
formatter may call other application programs into use. For eg:- to
determine machining conditions for the various machine tool operations in
the sequence, to calculate standard time for the operations or to compute
cost estimates for the operations.

9. One of the commercially available Retrieval CAPP systems is
Multi Capp, from OIR, the Organization for Industrial research. It is an
online computer system that permits the user to create new plans, or
retrieve and edit existing process plans as explained earlier.
2. Generative CAPP System or Generative Approach
The generative method of developing process plans involves
starting from scratch every time a different part is to be processed; no plans
are available as the baseline. The basic requirement for a generative
process planning system is that the given component model/drawing is to
be interpreted in terms of manufacturability. Here instead of retrieving and
editing an existing plan contained in the computer database, generative
system creates the process plan based on logical procedures. In a fully
generative CAPP system the process sequence is planned without human
assistance and without a step of predefined plans.
A generative CAPP system is usually considered part of the field
of expert systems, a branch of artificial intelligence. An expert system is a
computer program that is capable of solving complex problems that
normally require a human with years of education and experience. Process
planning fits within the scope of this definition.
There are several ingredients required in a fully generative process
planning system:
i. First the technical knowledge of manufacturing and the logic used by
successful process planners’ must be captured and coded into a computer
program. In expert systems applied to process planning, the knowledge and
logic of 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 (ie create route sheets

10. ii. Second ingredient in process planning is a computer compatible
description of the part to be produced. This description contains all the
pertinent data and information needed to plan the process sequence. Two
possible means of providing this description are:
a. The geometric model of the part that is developed on a CAD
system during product design and
b. a GT code number of the part that defines the part features in
significant details.
iii. The third ingredient in a generative CAPP system is the capability to
apply the process knowledge and planning logic contained in the
knowledge base to a given part description.
In other words, 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.
By using its knowledge base and inference engine, the CAPP system
synthesizes a new process plan from scratch for each new part it is
presented.

12. Advantages of Generative Process Plan
 They rely less on group technology code numbers since the
process, usually uses decision tree to categorize parts into
families.
 Maintenance and updating of stored process plans are largely
unnecessary.
 New Components can planned as easy as existing components
Advantages and Disadvantages CAPP over manual process
planning
 It can systematically produce accurate and consistent process
plans.
 It leads to the reduction of cost and lead times of process plan.
 Skill requirement of process planer are reduced to develop
feasible process plan.
 Interfacing of software for cost, manufacturing lead time
estimation, and work standards can easily be done.
 Leads to the increased productivity of process planar