24-11-2012, 06:18 PM
computer automated process planning (CAPP)
Computer-Aided-Process-Planning-CAPP.doc (Size: 143.5 KB / Downloads: 27)
INTRODUCTION
Technological advances are reshaping the face of manufacturing, creating paperless manufacturing environments in which computer automated process planning (CAPP) will play a preeminent role. The two reasons for this effect are: Costs are declining, which encourages partnerships between CAD and CAPP developers and access to manufacturing data is becoming easier to accomplish in multivendor environments. This is primarily due to increasing use of LANs; IGES and the like are facilitating transfer of data from one point to another on the network; and relational databases (RDBs) and associated structured query language (SQL) allow distributed data processing and data access.
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With the introduction of computers in design and manufacturing, the process planning part needed to be automated. The shop trained people who were familiar with the details of machining and other processes were gradually retiring and these people would be unavailable in the future to do process planning. An alternative way of accomplishing this function was needed and Computer Aided Process Planning (CAPP) was the alternative. Computer aided process planning was usually considered to be a part of computer aided manufacturing. However computer aided manufacturing was a stand alone system. Infact a synergy results when CAM is combined with CAD to create a CAD/CAM. In such a system CAPP becomes the direct connection between design and manufacturing.
Moreover, the reliable knowledge based computer-aided process planning applicationMetCAPP software looks for the least costly plan capable of producing the design and continuously generates and evaluates the plans until it is evident that non of the remaining plans will be any better than the best one seen so far. The goal is to find a useful reliable solution to a real manufacturing problem in a safer environment. If alternate plans exist, rating including safer conditions is used to select the best plans
1.1 COMPUTER AIDED DESIGN (CAD)
A product must be defined before it can be manufactured. Computer Aided Design involves any type of design activity that makes use of the computer to develop, analyze or modify an engineering design. There are a number of fundamental reasons for implementing a computer aided design system.
a. Increase the productivity of the designer: This is accomplished by helping the designer to visualize the product and its component subassemblies and parts; and by reducing the time required in synthesizing, analyzing, and documenting the design. This productivity improvement translates not only into lower design cost but also into shorter project completion times.
b. To improve the quality of the design: A CAD system permits a more thorough engineering analysis and a larger number of design alternatives can be investigated. Design errors are also reduced through the greater accuracy provided by the system. These factors lead to a better design.
c. To improve communications: Use of a CAD system provides better engineering drawings, more standardization in the drawings, better documentation of the design, fewer drawing error, and greater legibility.
d. To create a database for manufacturing: In the process of creating a the documentation for the product design (geometries and dimensions of the product and its components, material specification for components, bill of materials etc), much of the required data base to manufacture the product is also created.
Design usually involves both creative and repetitive tasks. The repetitive tasks within design are very appropriate for computerization.
1.2 COMPUTER AIDED MANUFACTURING (CAM)
By the time computer use in design began, numerical control technology (NC technology) had matured to become cost effective for applications in machining. An important in numerical control is part-programming. A part-program is simply a set of statements comprehensible to the machine control unit (MCU) , that oversees slide and tool movements and other auxiliary functions. In the case of components with complex geometries, part-programs had to carry out lengthy calculations for which it was logical to use computers. This gave rise to machine control units (MCU’s) with built in microprocessors- the building blocks of computers. The use of computers in extending the applications of NC technology, especially to part-programming was earlier termed Computer Aided Machining (CAM) and the associated technology was called Computer Numerical Control (CNC). Later Computer Aided Machining became an acronym for Computer Aided Manufacturing (CAM). Earlier Computer Aided Manufacturing used to denote computer use in part-programming only. Today it means any non design function of manufacturing that is computer aided.
1.3 CAD/CAM
As the use of computers in design and manufacturing broadened under CAD and CAM, it became evident that certain tasks were common to both, eg:-both design and manufacturing require data on tolerances. Part geometries created during CAD can readily be saved in the database for latter use. The forward slash (/) between CAD and CAM was meant to reinforce the shared functions of design and manufacturing.
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 Route Sheet .The planning begins with engineering drawings, specifications, parts or material lists and a forecast of demand. The scope and variety of processes that can be planned are generally limited by the available processing equipment and technological capabilities of the company or the plant.