COMPUTER AIDED PROCESS PLANNING

What is process planning .Difficulties in traditional process planning,CAPP Model,Types of CAPP ,1.Retrieval type CAPP (variant) systems.
2.Generative CAPP systems.
3.Hybrid CAPP systems.
Process planning system , Machinability data systems , Benefits of CAPP

1. Computer – Aided process planning (CAPP)

2. What is process planning 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 referred to as route sheet . The route sheet is a listing of the production operations and associated machine tools for a work part or assembly.

3. Difficulties in traditional process planning There are variations in the level of details found in route sheet among different companies and industries . In one extreme case , process planning is accomplished by releasing the part print to production shop with the instructions ( make to drawing ) Most firm provide a more detailed list of steps describing each operation and identifying each work centre. Traditionally the task for manufacturing engineers in an firm to write these process planning for new part designs to be produced by the shop . Process planning procedure is highly dependent on the experience and judgement of the planner. Manufacturing engineer responsibility to determine an optimal routing for each new part design

4. CAPP Model

5. Computer-Aided process planning (CAPP) In the view of the problems encountered with process planning , attempts have been made to capture the logic , judgements and experience required for this important function and to incorporate them into computer programs . The program automatically generates the manufacturing operation sequence . CAPP reducing the routine clerical work of manufacturing engineers. The following alternative approaches to CAPP have been developed: 1.Retrieval type CAPP (variant) systems. 2.Generative CAPP systems. 3.Hybrid CAPP systems.

6. 1.Retrieval type CAPP (variant) systems. The variant process planning approach can be realized as a four step process Definition of coding scheme Grouping parts into part families (Group Technology) Development of a standard process plan Retrieval and modification of standard process plan

7. 1.Retrieval Type CAPP (variant) systems In this approach the parts produced in the plant are grouped into part families and distinguished according to their manufacturing characteristics. For each part families, a std process plan is established. The std process plan is stored in computer files and then retrieved for new work parts, which belongs to that part family. The CAPP program then searches the part family matrix file to determine if a match exists If the file contains an identical code number , the std machine rooting and the operation sequence are Retrieval from the computer file for display for user The std process plan is examine and edited the part design and prepare part document in proper form. If an exact match cannot found the between the code numbers in the computer file and the code number for new part, the user search the machine root file and the operation sequence file for similar part that can used to develop the plan for the new part.

8. 2.Generative process planning It is the system which creates plan by means of decision logic, formulas, geometry based data and other logical procedures . In this method process plans are prepared without the assistance of human and predefined plans The computer would employed a set of algorithms to progress through the various technical and logical decisions towards the finial plan for mfging After retrieving this information, the system can generate the required processes and process sequences for the work part. A pure generative system can produce a complete process plan from GT codes with part classification and design data,

9. Two major components of generative Geometry description and coding component: This 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. Process knowledge database & decision making logic: The knowledge will be in the form of decision logic . It is required to match the part geometry requirement with manufacturing capability using decision logic and data. It includes selection of processes, mfg. equipment's, work holding devices, jigs & fixtures, inspection instruments, etc.

10. Geometric definition From CAD Part interrogation Feature extraction Feature recognition Selection of process Selection of M/C tool Operations and Time calculations Interference system M/C specification & capability Knowledge Acquisition K n o w l e d g e Base Final P r o c e ss Plan Diagram of Generative process Plan

11. 3.Hybrid CAPP System

12. Process planning system

13. Machinability data systems The machinability data systems are based on two types Mathematical modeling based on the empirically derived equations that fit a range of experimential data. Database systems that enable machinability data occurred from a large database

14. Mathematical modeling represents machinability variables in terms of machining parameters. In general a machinability parameters variable y (metal removal rate , tool wear rate , part surface finish) can be expressed as: y=f(x1,x2,x3,x4) where x1,x2,x3,x4 are metal cutting parameters. The most important mathematical model for the metal cutting processes is taylor s tool life. vt n =c v is cutting speed T is tool life in minutes n is empirically derived tool life exponent c is const of material

15. 2.Database systems

16. Benefits of CAPP Productivity Consistency of plans Accuracy Of plans Capacity utilization Ability to Introduce New technology Lead time of Process plan Routine clerical work Mfg. and process Planning cost Work in progress Skill requirement Of planner Increases Reduces

17. Computer- aided Manufacturing Resource Planning