Research on CAPP in the process from CAD to cam

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Research on CAPP in the process from CAD to cam this paper discusses the important role played by computer aided process planning (CAPP) in the process of product transition from CAD to cam, expounds the composition, content, classification and basic technology of CAPP system, predicts the future development trend of CAPP, and shows that CAPP is very suitable for the increasingly automated manufacturing process

1. Overview

process design is an important part of the technical preparation for the production process of mechanical manufacturing. It is the link between product design and the actual production of the workshop. It is a decision-making process with strong experience and changing with the environment. At present, the market of mechanical products is dominated by multi variety and small batch production. The traditional process design method is far from meeting the requirements of the development of the current mechanical manufacturing industry

with the development of mechanical manufacturing technology and the requirements of multi variety and small batch production, especially the development of cad/cam system towards integration and intelligence, the traditional process design method has been far from meeting the requirements, and computer aided process design (CAPP) has emerged

capp is a process in which the geometric information (graphics) and processing process information (materials, heat treatment, batch, etc.) of the machined parts are input to the computer, and the computer automatically outputs the process documents such as the process route and process content of the parts. CAPP belongs to the category of engineering analysis and design, and is one of the important production preparations. Due to the emergence of manufacturing system [1], CAPP is connected with computer aided design (CAD) upward and computer aided manufacturing (CAM) downward. It is a bridge between design and manufacturing. Design information can only be generated from process design, and design can only be integrated with manufacturing through process design

2. The basic composition of CAPP system


varies greatly depending on the working principle, product object and scale of CAPP system. The basic components of CAPP system are shown in Figure 1, including:

1) control module

the main task of the control module is to coordinate the operation of each module, which is the window of human-computer interaction, realize the information exchange between human and computer, and control the acquisition mode of part information

2) part information input module

when the part information cannot be obtained directly from the CAD system, this module is used to input the part information

3) process design module

the process design module makes decisions on the processing process flow and generates a process card for use by the processing and production management departments

4) process decision module

the main task of the process decision module is to generate the process card, calculate the size between processes, and generate the process diagram

5) step decision module

the work step decision module designs the work step contents, determines the cutting parameters, and provides the tool position files required to form the NC machining control instructions

6) NC machining instruction generation module

nc machining instruction generation module calls the NC instruction code system to generate NC machining control instructions according to the tool position file provided by the step decision module

7) output module

the output module can output process flow cards, process cards, step cards, process diagrams and other documents. It can also output various process documents from the existing process document library, and use tools to modify the existing process documents to obtain the required process documents

8) dynamic simulation of machining process

dynamic simulation of machining process simulates the generated machining process and checks the correctness of the process

Figure 1 basic block diagram of CAPP system

2.2 contents

capp mainly includes: blank selection and blank drawing generation; Selection of positioning datum and clamping scheme; Selection of processing

methods; Arrangement of processing sequence; Selection of general machine tools, cutting tools, fixtures, measuring tools and other process equipment; Calculation of process parameters; Put forward the design scheme of special machine tools, cutting tools, fixtures, measuring tools and other process equipment; Output of process documents

2.3 steps

the plastic box on the booth of Dongguan jishuo Industry Co., Ltd. is also very important. The CAPP steps are shown in Figure 2, which are divided into five steps: 1) input the product drawing information; 2) Prepare the process route and process content; 3) Determine processing equipment and process equipment; 4) Calculate process parameters; 5) Output process documents

Figure 2 CAPP flow chart

2.4 classification

according to its working principle, the system can be divided into retrieval type, derivation type and creation type [2]

the retrieval process design system is aimed at the standard process. The designed standard process of parts is numbered and stored in the computer. When formulating the process of parts, you can search according to the input part information to find the appropriate standard process

derived process design is a process of deriving a new part by retrieving the process of similar typical parts and adding, deleting or using the principle that parts have similarity and similar parts have similar process

the generative process design system is different from the derivative system. It automatically generates the process of parts based on the input part information and the engineering data and decision-making methods in the system

2.5 basic technology of CAPP

basic technology of CAPP includes:

1) group technology

group process is to form parts with similar size, shape and process into one part family [3]. As shown in Figure 3, the process is formulated according to the part family for production and manufacturing, so as to expand the batch, reduce the variety, facilitate the adoption of high-efficiency production methods, improve labor productivity, and open up a way for multi variety and small batch production to improve economic benefits

Figure 3 group technology example figure

the similarity of parts in geometry, size, functional elements, accuracy, materials, etc. is basic similarity. Based on the basic similarity, the similarity derived from the production, operation and management of manufacturing and assembly is called secondary similarity or derived similarity. Therefore, secondary similarity is the development of basic similarity, which has important theoretical significance and practical value

The basic principle of group process shows that the similarity of parts is the basic condition to realize group process. Group technology is to reveal and make use of basic similarity and secondary similarity. It enables industrial enterprises to obtain unified data and information, obtain economic benefits, and lay a foundation for the establishment of integrated information systems

2) description and acquisition of part information

inputting part information is the first step of computer-aided process design. Part information description is the key of CAPP. It is difficult in technology and heavy in workload, and it is an important factor affecting the efficiency of the whole process design

the accuracy, scientificity and completeness of part information description will directly affect the quality, reliability and efficiency of the designed process. Therefore, the information description of parts shall meet the following requirements:

⑴ the information description shall be accurate and complete. The so-called integrity means to meet the needs of computer-aided process planning, rather than to describe all the information

⑵ the information description shall be easy to be accepted and processed by the computer, with friendly interface, convenient use and high work efficiency

⑶ the information description shall be easy to be understood and mastered by engineering technicians and used by operators

⑷ since it is computer-aided process design, the information description system (module or software) shall consider the requirements of computer-aided design, computer-aided manufacturing, computer-aided detection and other aspects, so as to share information

3) process design decision-making mechanism

4) acquisition and expression of process knowledge

5) automatic generation of process diagram and other documents

6) automatic generation of NC machining instructions and dynamic simulation of machining process; This also shows that the development of valves is very rapid

7) the establishment of process database

3. The role of CAPP in cad/cam integrated system

in the middle and late 1980s, the unit technology of CAD and cam became more and more mature. With the development of machinery manufacturing towards cims[4] (Computer Integrated Manufacturing System) and ims[4] (Intelligent Manufacturing System), the integration requirements of cad/cam are urgent problems to be solved. Cad/cam integrated system is actually a cad/capp/cam integrated system. CAPP obtains the geometric topology information and process information of the parts from the CAD system, and obtains the production conditions, resources, technical level and other information of the enterprise workers from the engineering database. It carries out process design and forms the process flow card, operation card, step card and NC machining control instructions, which plays a link role in CAD and cam. In order to achieve this goal, the following problems must be solved in the integrated system:

1) CAPP module can directly obtain the geometric information, material information and process information of parts from CAD module to replace the input of part information description

2) the geometric modeling system of CAD module must provide not only geometric shape and topology information, but also process information, detection information, organization information and structure analysis information of parts

3) it must adapt to the NC machining control of various NC systems 11. Stress control rate range: 0.005 ~ 5% fs/s command generation

4. The development trend of CAPP in the future

with the increasing maturity of CAD, CAPP and cam unit technology, and the proposal and development of CIMS and IMS, CAPP is developing towards intelligence, integration and practicality. At present, the hot issues in the research and development of CAPP system are:

1) generation and acquisition of product information model

2) research on CAPP architecture and development of CAPP Tool System

3) CAPP system under concurrent engineering mode

4) distributed CAPP system based on distributed artificial intelligence technology

5) comprehensive application of artificial neural network technology and expert system in CAPP

6) practical CAPP system for enterprises

7) integration of CAPP and automatic production scheduling system

5. Conclusion

the significance of computer-aided process planning is that it can liberate process designers from a large number of heavy and repetitive manual work, so that they can devote their main energy to the creative work such as the development of new products, the improvement of process equipment and the research of new processes; It can greatly shorten the cycle of process design, ensure the quality of process design, and improve the competitiveness of products in the market; It can improve the standardization of enterprise process design and is conducive to the optimization of process design; It can adapt to the needs of modern manufacturing links that are becoming more and more automated, and create the necessary technical foundation for the realization of computer integrated manufacturing system


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[3] shiminghua, Xiao Fang, wenshuhong, etc Implementation of CAPP and process management system in assembly enterprises [j] Modular machine tools and automatic machining technology, 2004.01 (end)

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