Variant (retrieval) , Generative, integration of CAD/CAM, Route sheet/ operations sheet

1. Computer aided process planning

2. Processplanning
Process planning is concerned with determining the sequence of individual
manufacturing operations needed to produce a given part or product.
The resulting operation sequence is documented on a form typically referred to as
operation sheet/route sheet. The operation sheet is a listing of the production
operations and associated machine tools for a work part or assembly.
Process planning is an important stage of product development since production
tooling like jigs, fixtures, special tools etc. can be designed only after the process is
finalized.

3. Definition
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.

4. The process planning activity can be divided into to following steps
• Selection of processes and tools
• Selection of machine tools
• 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

5. Route sheet

6. Role of Process Planning in CAD/CAM Integration

7. Computer Aided Process Planning
• Process rationalization and standardisation
• Productivity improvement
• Product cost reduction
• Elimination of human error
• Reduction in time
• Reduced paper work
• Faster response
• Improved legibility

8. Approaches to CAPP
Types of Approaches
• Variant Approach - Computer search for existing or similar process
plans of similar part families using codes, retrieves and then edit
according to new process sequence.
• Generative Approach - Computer generates new process plan every
time when a new plan is needed.
• Hybrid Approach

9. Data Input to CAPP
• Generally the geometric model of the part is the input for the process planning
system.
• The input to the process planning system may be engineering drawing or CAD
model.
The other prerequisites for process planning are given below:
- Parts list
- Annual demand/batch size
- Accuracy and surface finish requirement (CAD Database)
- Equipment details (Work centre Database)
- Data on cutting fluids, tools, jigs & fixtures, gauges
- Standard stock sizes
- Machining data, data on handling and setup

10. Variant or Retrieval Approaches to CAPP
Part
Description GT Code Process Plan
Retrieve/Edit
New
Process Plan
Master Plans
Database

11. Variant or Retrieval CAPP system

12. Variant or Retrieval CAPP system
A variant process planning system uses the similarity among Components to retrieve the existing process plans.
A process plan that can be used by a family of components is called a Standard plan. A standard plan is stored
permanently with a family number as its key. A family is represented by a family matrix, which includes all
possible members. The variant process planning system has two operational stages: 1. preparatory stage 2.
Production stage. During the preparatory stage, existing components are coded, classified, and subsequently
grouped into families. The process begins by summarizing process plans already prepared for components in
the family. Standard plans are then stored in a database and indexed by family matrices. The production stage
occurs when the system is ready for production. An incoming part is first coded. The code is then input to a
part family search routine to find the family to which the component belongs. The family number is then used
to retrieve a standard plan. Some other functions, such as parameter selection and standard time calculations,
can also be added to make the system more complete. This system is used in a machine shop that produces a
variety of small components

13. Advantages of Variant type CAPP
• Once a standard plan has been written, a variety of components can be
planned.
• Comparatively simple programming and installation (compared with
generative systems) is required to implement a planning system.
• The system is understandable, and the planner has control of the final
plan.
• It is easy to learn, and easy to use.

14. Disadvantages of Variant type CAPP
• The components to be planned are limited to similar components
previously planned.
• Experienced process planners are still required to modify the
standard plan for the specific component.
• Variant planning cannot be used in an entirely automated
manufacturing system, without additional process planning.

15. Generative Approaches to CAPP
Part
Descriptive
System
New
Process Plan
Process Plan
Logic
Machine
Tool
Cutting
Tool
Jigs &
Fixtures Material
Manufacturing Database

16. Generative process planning is a system that synthesizes process Information in order to create a process plan
for a new Component automatically. In a generative planning system, process plans are created from
information available in manufacturing database without human intervention. Upon receiving the design
model, the system can generate the required operations and operation sequences for the component.
Knowledge of manufacturing must be captured and encoded into efficient software. By applying decision logic,
a process Planner’s decision making can be imitated. Other planning functions, such as machine selection, tool
selection, process optimization, and so on, can also be automated using generative planning techniques.
The generative planning has the following advantages:
1. It can generate consistent process plans rapidly.
2. New components can- be planned as easily as existing Components.
3. It can be interfaced with an automated manufacturing

17. Forward planning (Generative)
In generative process planning, when process plans are generated, the
system must define an initial state in order to reach the final state
(goal). The path taken represents the sequence of processes. For
example, the initial state is the raw material and the final state is the
component design. Then a planner works in modifying the raw work
piece until it takes on the final design qualities. This is called forward
planning.

18. Backward planning (Generative)
Backward planning uses a reverse procedure. Assuming that we have a
finished component, the goal is to go back to the unmachined work
piece. Each machining process is considered a filling process.

19. For forward planning, we must know the successor surface before
we select a process.
Backward planning eliminates this conditioning Problem since it
begins with the final surfaces and processes are selected to satisfy
the initial requirements.

20. A-3
Q1. With a neat sketch explain the methodology to be followed in for
developing a retrieval type CAPP system.
Q2.Briefly explain the need for computer aided process planning. Write
any five differences between variant and generative type of computer
aided process planning.