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Automation (21-541) Sharif University of Technology Session # 13
Advanced Manufacturing Laboratory Department of Industrial Engineering Sharif University of Technology Session # 13
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Automation (21541), Session # 13
Session Schedule Computer-Aided Process Planning (CAPP) CAPP integration with CAD Computer-Aided Process Planning based on CAD software solutions Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 2
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Computer-Aided Process planning (CAPP)
Process planning primitives 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. 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 plan is finalized. 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. 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. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 3
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Computer-Aided Process planning (CAPP)
Process planning primitives The current approaches for computer aided process planning can be classified into two groups: Variant Generative The current approaches for computer aided process planning can be classified into two groups: i. Variant ii. Generative Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 4
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Computer-Aided Process planning (CAPP)
Variant Process planning- Group Technology A part family is a collection of parts which are similar either because of geometry and size or because similar processing steps are required in their manufacture. The parts within a family are different, but their similarities are close enough to merit their identification as members of the part family. There are three general methods for solving this problem. Visual inspection Production flow analysis Parts classification and coding system A part family is a collection of parts which are similar either because of geometry and size or because similar processing steps are required in their manufacture. The parts within a family are different, but their similarities are close enough to merit their identification as members of the part family. The major obstacle in changing over to group technology from a traditional production shop is the problem of grouping parts into families. There are three general methods for solving this problem. i. Visual inspection ii. Production flow analysis iii. Parts classification and coding system What is desirable in a computer integrated manufacturing environment is a software which will analyze the geometric model of the part and come out with a set of alphabetic/ numeric characters which can broadly embed similarities. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 5
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Computer-Aided Process planning (CAPP)
Variant Process planning- Group Technology Part Design Attributes Basic (External/Internal) shape Axisymmetric/Prismatic/sheet metal Length/diameter ratio Material Major dimensions Minor dimensions Tolerances Surface finish Part Manufacturing Attributes Major process of manufacture Surface treatments/coatings Machine tool/processing equipment Cutting tools Operation sequence Production time Batch quantity Production rate Fixtures needed Part Design Attributes Basic (External/Internal) shape Axisymmetric/Prismatic/sheet metal Length/diameter ratio Material Major dimensions Minor dimensions Tolerances Surface finish Part Manufacturing Attributes Major process of manufacture Surface treatments/coatings Machine tool/processing equipment Cutting tools Operation sequence Production time Batch quantity Production rate Fixtures needed Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 6
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Computer-Aided Process planning (CAPP)
Variant Process planning- Coding structures A part coding scheme consists of symbols that identify the part’s design and/or manufacturing attributes. The symbols in the code can be all numeric, all alphabetic, or a combination of both types. There are three basic code structures used in group technology applications: Hierarchical structure Chain type structure Hybrid structure which is a combination of the above two A part coding scheme consists of symbols that identify the part’s design and/or manufacturing attributes. The symbols in the code can be all numeric, all alphabetic, or a combination of both types. There are three basic code structures used in group technology applications: i. Hierarchical structure ii. Chain type structure iii. Hybrid structure which is a combination of the above two With the hierarchical structure, the interpretation of each succeeding symbol depends on the value of the preceding symbols. In the chain type structure, the interpretation of each symbol in the sequence is fixed and does not depend on the value of preceding digits. Most of the commercial parts coding systems are used in industry are a combination of the two pure structures. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 7
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Computer-Aided Process planning (CAPP)
Variant Process planning- Coding structures Coding systems that have been successfully implemented in process planning: OPITZ system The CODE system The KK-3 system The MICLASS system DCLASS system COFORM (coding for machining) Some of the coding systems that have been successfully implemented in process planning are given below: i. OPITZ system ii. The CODE system iii. The KK-3 system iv. The MICLASS system v. DCLASS system vi. COFORM (coding for machining) Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 8
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Computer-Aided Process planning (CAPP)
Variant Process planning- Coding structures OPITZ classification system: The OPITZ coding system digit sequence: ABCD The first nine digits are intended to convey both design and manufacturing data. The first five digits, 12345, are called the “form code” and describe the primary design attributes of the part. The next four digits, 6789, constitute the “supplementary code”. It indicates some of the attributes that would be of use to manufacturing (work material, raw work piece shape, and accuracy). The extra four digits, “ABCD”, are referred to as the “secondary code” and are intended to identify the production operation type and sequence. The Opitz coding system uses the following digit sequence: ABCD The basic code consists of nine digits, which can be extended by adding four more digits. The first nine digits are intended to convey both design and manufacturing data. The general interpretation of the nine digits is indicated in Fig 9.5. The first five digits, 12345, are called the “form code” and describe the primary design attributes of the part. The next four digits, 6789, constitute the “supplementary code”. It indicates some of the attributes that would be of use to manufacturing (work material, raw work piece shape, and accuracy). The extra four digits, “ABCD”, are referred to as the “secondary code” and are intended to identify the production operation type and sequence. The secondary code can be designed by the firm to serve its own particular needs. In the form code, the first digit identifies whether the part is a rotational or a nonrotational part. It also describes the general shape and proportions of the part. Fig 9.5 shows the specification scheme. For the rotational work pieces, the coding of the first five digits is given in Fig. 9.6. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 9
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Computer-Aided Process planning (CAPP)
Variant Process planning- Coding structures OPTIZ classification system: The OPTIZ coding system digit sequence: ABCD The Opitz coding system uses the following digit sequence: ABCD The basic code consists of nine digits, which can be extended by adding four more digits. The first nine digits are intended to convey both design and manufacturing data. The general interpretation of the nine digits is indicated in Fig 9.5. The first five digits, 12345, are called the “form code” and describe the primary design attributes of the part. The next four digits, 6789, constitute the “supplementary code”. It indicates some of the attributes that would be of use to manufacturing (work material, raw work piece shape, and accuracy). The extra four digits, “ABCD”, are referred to as the “secondary code” and are intended to identify the production operation type and sequence. The secondary code can be designed by the firm to serve its own particular needs. In the form code, the first digit identifies whether the part is a rotational or a nonrotational part. It also describes the general shape and proportions of the part. Fig 9.5 shows the specification scheme. For the rotational work pieces, the coding of the first five digits is given in Fig. 9.6. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 10
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Computer-Aided Process planning (CAPP)
Variant Process planning- Coding structures OPTIZ classification system: The OPTIZ coding system digit sequence: ABCD The Opitz coding system uses the following digit sequence: ABCD The basic code consists of nine digits, which can be extended by adding four more digits. The first nine digits are intended to convey both design and manufacturing data. The general interpretation of the nine digits is indicated in Fig 9.5. The first five digits, 12345, are called the “form code” and describe the primary design attributes of the part. The next four digits, 6789, constitute the “supplementary code”. It indicates some of the attributes that would be of use to manufacturing (work material, raw work piece shape, and accuracy). The extra four digits, “ABCD”, are referred to as the “secondary code” and are intended to identify the production operation type and sequence. The secondary code can be designed by the firm to serve its own particular needs. In the form code, the first digit identifies whether the part is a rotational or a nonrotational part. It also describes the general shape and proportions of the part. Fig 9.5 shows the specification scheme. For the rotational work pieces, the coding of the first five digits is given in Fig. 9.6. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 11
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Computer-Aided Process planning (CAPP)
Variant Process planning- Coding structures OPITZ classification system: The OPITZ coding system digit sequence: ABCD The overall length/diameter ratio, L/D = 1.6, so the first code = 1. The part is stepped on both ends with a screw thread on one end, so the second digit code would be 5 The third digit code is 1 because of the through hole. The fourth and fifth digits are both 0, since no surface machining is required and there are no auxiliary holes or gear teeth on the part. The complete form code in the OPITZ system is “15100”. To add the supplementary code, we would have to properly code the sixth through ninth digits with data on dimensions, material, starting work piece shape, and accuracy The Opitz coding system uses the following digit sequence: ABCD The basic code consists of nine digits, which can be extended by adding four more digits. The first nine digits are intended to convey both design and manufacturing data. The general interpretation of the nine digits is indicated in Fig 9.5. The first five digits, 12345, are called the “form code” and describe the primary design attributes of the part. The next four digits, 6789, constitute the “supplementary code”. It indicates some of the attributes that would be of use to manufacturing (work material, raw work piece shape, and accuracy). The extra four digits, “ABCD”, are referred to as the “secondary code” and are intended to identify the production operation type and sequence. The secondary code can be designed by the firm to serve its own particular needs. In the form code, the first digit identifies whether the part is a rotational or a nonrotational part. It also describes the general shape and proportions of the part. Fig 9.5 shows the specification scheme. For the rotational work pieces, the coding of the first five digits is given in Fig. 9.6. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 12
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Computer-Aided Process planning (CAPP)
Variant Process planning The following are the sequences in the design of a variant process planning system: Family formation Data base structure design Search algorithm development and implementation Plan editing Process parameter selection/updating The following are the sequences in the design of a variant process planning system: i. Family formation ii. Data base structure design iii. Search algorithm development and implementation iv. Plan editing v. Process parameter selection/updating Family Formation Part family classification and coding were discussed earlier. This is based on the manufacturing features of a part. Components requiring similar processes are grouped into the same family. A general rule for part family formation is that all parts must be related. Then, a standard process plan can be shared by the entire family. Minimum modification on the standard plan will be required for such family members. DATA BASE STRUCTURE DESIGN The data base contains all the necessary information for an application, and can be accessed by several programs for specific application. There are three approaches to construct a data base: hierarchical, network, and relational. SEARCH PROCEDURE The principle of a variant system is to retrieve process plans for similar components. The search for a process plan is based on the search of a part family to which the component belongs. When, the part family is found, the associated standard plan can then be retrieved. A family matrix search can be seen as the matching of the family with a given code. Family matrices can be considered as masks. Whenever, a code can pass through a mask successfully, the family is identified. PLAN EDITING AND PARAMETER SELECTION Before a process plan can be issued to the shop, some modification of the standard plan may be necessary, and process parameters must be added to the plan. There are two types of plan editing: One is the editing of the standard plan itself in the data base, and the other is editing of the plan for the component. For editing a standard plan, the structure of the data base must be flexible enough for expansion, additions, and deletions of the data records. A complete process plan includes not only operations but also process parameters. The data in the process parameter files are linked so that we can go through the tree to find the speed and feed for an operation. The parameter file can be integrated into variant planning to select process parameters automatically. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 13
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Computer-Aided Process planning (CAPP)
Generative Process planning Generative process planning is a system that synthesizes process information in order to create a process plan for a new component automatically. Knowledge of manufacturing must be captured and encoded into efficient software. By applying decision logic, a process planner’s decision making can be imitated. The generative planning has the following advantages: It can generate consistent process plans rapidly. New process plans can be created as easily as retrieving the plans of existing components. It can be interfaced with an automated manufacturing facility to provide detailed and up-to-date control information. 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 data base 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: i. It can generate consistent process plans rapidly. ii. New process plans can be created as easily as retrieving the plans of existing components. iii. It can be interfaced with an automated manufacturing facility to provide detailed and up-to-date control information. Fig shows the modular structure of a generative CAPP system. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 14
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Computer-Aided Process planning (CAPP)
Generative Process planning In generative process planning, when process plans are generated, the system must define an initial state in order to reach the final state (goal). In forward planning, the initial state is the raw material and the final state is the component design. A planner works in modifying the raw work piece until it takes on the final design qualities. Backward planning uses a reverse procedure. Assuming that we have a finished component, the goal is to go back to the un-machined Work piece. Each machining process is considered a filling process 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 workpiece until it takes on the final design qualities. This is called forward planning. Backward planning uses a reverse procedure. Assuming that we have a finished component, the goal is to go back to the un-machined workpiece. Each machining process is considered a filling process. Forward and backward planning may seem similar. However they influence the programming of the system significantly. Planning each process can be characterized by a precondition of the surface to be machined and a post condition of the machining (the end result). For forward planning, we must know the successor surface before we select a process, because the post condition of the first process becomes the precondition for second process. Backward planning eliminates this problem since it begins with the final surfaces from and processes are selected to satisfy the initial requirements. In forward planning, the steps to obtain the final surface with the desirable attributes must be carefully planned to guarantee the result. On the other hand, backward planning starts with the final requirements and searches for the initial condition. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 15
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Computer-Aided Process planning (CAPP)
Generative Process planning Decision logic The decision logic determines how a process or processes are selected. The major function of the decision logic is to match the process capabilities with the design specification. The different techniques in decision logic are: Decision trees; Decision tables Artificial Intelligence (AI) There are two types of knowledge involved in process planning systems: Component knowledge, and process knowledge. The component knowledge defines the current state of the problem to be solved (declarative knowledge). On the other hand, the knowledge of processes defines how the component can be changed by processes (procedural knowledge). CAPP BASED ON DECISION LOGIC The decision logic determines how a process or processes are selected. The major function of the decision logic is to match the process capabilities with the design specification. The different techniques in decision logic are: i. Decision trees ii. Decision tables These two techniques are methods of describing or specifying the various actions associated with the combination of input conditions. CAPP BASED ON ARTIFICIAL INTELLIGENCE (AI) AI can be defined as the ability of a device to perform functions that are normally associated with the human intelligence. These functions include reasoning, planning, and problem solving. Applications for AI have been in natural language processing, intelligent data base retrieval, expert consulting systems, theorem proving, robotics, scheduling, and perception problems. Process planning applications have been considered as part of an expert consulting system. There are two types of knowledge involved in process planning systems: Component knowledge, and process knowledge. The component knowledge defines the current state of the problem to be solved (declarative knowledge). On the other hand, the knowledge of processes defines how the component can be changed by processes (procedural knowledge). There are several methods to represent declarative knowledge: i. First order predicate calculus ii. Frames and semantic networks Procedural knowledge can be represented by IF (condition), THEN (action) statements which are similar to decision trees or decision tables. In AI such rules can be called production rules. Even after the descriptive and procedural knowledge have been represented, conclusions cannot be deduced, because we do not have mechanism to apply the appropriate rules to the problem. Control knowledge is similar to human knowledge in reasoning, which deduces certain facts from the knowledge base concerning problem. This can be a difficult task to program on a computer. Computer Aided Process Planning has been an active area of research work in AI for many years. Feature recognition, feature process correlation, process sequencing, blank selection, cutting parameter selection, tool selection etc. are the segments of CAPP where AI can contribute to improve the quality of process plans.s Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 16
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Computer-Aided Process planning (CAPP)
Implementation consideration The process planning function is manufacturing system dependent. This implies that no one single process planning system can satisfy all of the different manufacturing systems needs. There are several factors that must be considered when one attempts to implement a process planning system. These include: i. Manufacturing system components ii. Production volume/batch size iii. Number of different production families For a moderate number of component families and many similar components in each family, a variant process planning system is usually the most economic automated planning alternative. Fig Illustrates the economic regions for the different planning alternatives. Advanced Manufacturing Laboratory, Department of Industrial Engineering, Sharif University of Technology Automation (21541), Session # 13 17
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