Computer Aided Processs Planning (CAPP)

questions.

1.Write short notes on  CAPP      5Marks.
2.Make a brief note on computer Aided Process Planning (CAPP).  4 Marks
3.CAPP                  2 marks
4.Variant approach to CAPP
5.What is CAPP? How IT helps in integration of design and manufacturing?   6 marks
6.What are the capabilities that an effective Computer Aided Processs Planning (CAPP) system should have? Discuss in brief.        6 marks
7.What do you mean by Computer Aided Process planning (CAPP) and  state some of its     advantages. Under what situation, CAPP is preferred as compared to manual process planning   10 marks

8.What is computer aided process planning (CAPP)? What are the types of data required for developing a CAPP system? Differentiate between variant and generative systems of process planning                                                        8 marks

9. What is computer Aided process planning (CAPP)? How is it superior to manual process  planning?               5 Marks

10.Explain the available better features in ‘computer aided Process planning (CAPP)’over the   ‘conventional process planning approach.’ How does CAPP help in selection of machine tools?   (6+2)         
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Computer Aided Processs Planning (CAPP)

The primary purpose of process planning is to translate the design requirements into manufacturing process details. This suggests a system in which design information is processed by the process planning system to generate manufacturing process details. CAPP integrates and optimizes system performance into the inter-organizational flow. For example, when one changes the design, it must be able to fall back on CAPP module to generate manufacturing process and cost estimates for these design changes. Similarly, in case of machine breakdown on the shop floor, CAPP must generate the alternative actions so that most economical solution can be adopted in the given situation. 

When comapred with manual experience-based process planning, CAPP offers following advantages;

1. Systematic developemnt of accurate and consistent process plans
2. Reduction of cost and lead time of process planning
3. Reduced skill requirements of process planners
4. Increased productivity of process planners

Higher level application programs such as cost and manufacturing lead time estimation and work standards can be interfaced

Two major methods are used in computer aided process planning;
                            The variant CAPP method and
                            The generative CAPP method

 4 The variant CAPP method

In variant CAPP approach, a process plan for a new part is created by recalling, identifying and retrieving an existing plan for a similar part and making necessary modifications for the new part. Sometimes, the process plans are developed for parts representing a family of parts called 'master parts'. The similarities in design attributes and manufacturing methods are exploited for the purpose of formation of part families. A number of methods have been developed for part family formation using coding and classification schemes of group technology (GT), similiarity-coefficient based algorithms and mathematical programming models. 

The variant process planning approach can be realized as a four step process; 

1. Definition of coding scheme

2. Grouping parts into part families

3. Development of a standard process plan

4. Retrieval and modification of standard process plan

A number of variant process planning schemes have been developed and are in use. One of the most widely used CAPP system is CAM-I developed by McDonnell-Douglas Automation Company. This system can be used to generate process plan for rotational, prismatic and sheet-metal parts.

The generative CAPP method

The next stage of evolution is towards generative CAPP. In the generative CAPP, process plans are generated by means of decision logic, formulas, technology algorithms and geometry based data to perform uniquely many processing decisions for converting part from raw material to finished state. There are two major components of generative CAPP; a geometry based coding scheme and process knowledge in form of decision logic data. The geometry based coding scheme defines all geometric features for process related surfaces together with feature dimensions, locations, tolerances and the surface finish desired on the features. The level of detail is much greater in a generative system than a variant system. For example, details such as rough and finished states of the parts and process capability of machine tools to transform these parts to the desired states are provided. Process knowledge in form of in the form of decision logic and data matches the part geometry requirements with the manufacturing capabilities using knowledge base. It includes selection of processes, machine tools, jigs or fixtures, tools, inspection equipment and sequencing operations. Development of manufacturing knowledge base is backbone of generative CAPP. The tools that are widely used in development of this database are flow-charts, decision tables, decision trees, iterative algorithms, concept of unit machined surfaces, pattern recognition techniques and artificial intelligence techniques such as expert system shells.

   6 Capabilities that an effective Computer Aided Process Planning (CAPP) system 

1. It has capability to retrieve and modify existing plans or to create a new plan.   
2. It has capability to integrate design and manufacturing for better quality and higher production rates.
3. It reduces lead times for process planning.
4. It improves legibility
5. It  provides rationalization and standardization.
6. it has ability to incorporate other application programs
7. It reduces various costs 
8.  CAPP is able to prepare routing sheets more quickly compared to traditional methods
9. CAPP has ability to modify process plans to suit specific needs.    

Explain the available better features in ‘computer aided Process planning (CAPP)’over the   ‘conventional process planning approach.’

1. By comparison with    conventional process planning approach the use of computers in process planning helps to achieve the following:
2. It can systematically produces accurate consistent process plans.
3. It can reduce the cost and lead time in process planning
4. The skill required to process planners are reduced.
5. It results increased productivity of process planners.
6. The application programs such as cost and manufacturing lead time estimation and work standards can easily be interfaced.    

 Advantages of CAPP and future trends

CAPP has some important advantages over manual process planning which includes;

1. Reduced process planning and production lead-times
2. Faster response to engineering changes in the product
3. Greater process plan accuracy and consistency
4. Inclusion of up-to-date information in a central database
5. Improved cost estimating procedures and fewer calculation errors
6. More complete and detailed process plans 
7. Improved production scheduling and capacity utilization

Improved ability to introduce new manufacturing technology and rapidly update process plans to utilize the improved technology

There are number of difficulties in achieving the goal of complete integration between various functional areas such as design, manufacturing, process planning and inspection. For example, each functional area has its own stand-alone relational database and associated database management system. The software and hardware capabilities among these systems pose difficulties in full integration. There is a need to develop single database technology to address these difficulties. Other challenges include automated translation of design dimensions and tolerances into manufacturing dimensions and tolerances considering process capabilities and dimensional chains, automatic recognition of features and making CAPP systems affordable to the small and medium scale manufacturing companies.