Analysis on the development and application of CAP

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Analysis on the development and application of CAPP in China I. overview of CAPP at present, the CAPP systems developed and applied in China can be divided into the following five categories according to their working principles: interactive CAPP system, derivative CAPP system, creative CAPP system, comprehensive CAPP system and CAPP expert system

There are many types and design methods of CAPP, but from the general situation in China, the CAPP design method based on derivation is more applicable. The main reason is that the factories that are developing or preparing to implement CAPP are all old factories with more than decades of history, the product types are relatively fixed, the development direction is clear, and a certain number of practical and stable product processes have been accumulated in many years of production. On this basis, Through sorting and perfecting, the typical product process and the rule knowledge for determining each process element required by the derivative CAPP system can be formulated. However, the method of blindly pursuing creation or expert system will discard a large number of effective process schemes accumulated by the enterprise when the pressure oil enters the working cylinder from the oil port and acts on the lower end face of the working piston. Great difficulties will occur in many aspects such as system development technology, development cost and system development time, which will make the CAPP system difficult to be effective, popularized and implemented, It is more difficult to realize the commercialization of CAPP system software

at present, in order to pursue commercialized software or software products, some development departments focus on developing CAPP system with complete human-computer interaction filling mode when the generative CAPP and CAPP expert system can not meet the practical requirements. This kind of system is characterized by providing various windows and windows functions of adding, deleting and modifying. Users can directly fill in (or modify the generated process documents) for process design. This type of CAPP system technology does not emphasize the standardization of product design and the basic work of process technology. To a certain extent, it can meet the initial needs of some enterprises with weak basic work for CAPP technology. However, because CAPP system largely relies on the role of people and ignores the guidance, inspiration and prompt of the system to people in the process design process, not only the design steps are cumbersome and the work efficiency is low, which requires users to have a high level of process design, but also it is difficult to maximize the use of limited manufacturing resources, shorten the production preparation cycle and reduce the product cost through the implementation of process standardization. The human-computer interactive CAPP system, which is mainly filled in, especially in the frontier new material field, causes data duplication and redundancy, increases the cost of database and the burden of future data maintenance, and reduces work efficiency. Moreover, the process data generated are uneven and difficult to maintain due to excessive reliance on the process design level of users, which makes it difficult to ensure the correctness and reliability of process information, and makes the process database in a state of chaos or even collapse

II. Current application of CAPP system in Chinese enterprises

at present, most of the systems that really play the role of CAPP used by Chinese enterprises are variant CAPP and creative and variant. The comprehensive CAPP system developed on the basis of these two types is as large as several 10 tons (such as ordinary steel; the experimental power of the largest electronic hydraulic universal testing machine in China is 600kN, grade 05 machine). Interactive and intelligent CAPP systems are also applied in a few enterprises. The characteristics and specific applications of each system are introduced below

1. Variant CAPP system is widely used in domestic enterprises. Wuxi Machine Tool Plant, Hangzhou turbine plant, Chengdu aircraft company and other units adopt this kind of CAPP system, among which Hangzhou turbine plant has the best application effect. First of all, all the process personnel of the factory use the CAPP system to compile the process, including proofreading and auditing, all on the computer, and there is no phenomenon of manually writing the process, so as to ensure that the CAPP application continues. Secondly, the basic work of the plant is quite excellent. All kinds of process and technical standards are put into the machine, and all kinds of material data are coded and stored. Third, the factory has special products, few types of parts, simple classification, and a large proportion of similar parts. The factory adopts a typical retrieval CAPP system. The process library is divided into standard process library and user process library. The parts are classified by 11 digit code. When preparing the process for new parts, the standard process of the same group of parts can be retrieved from the standard process library according to the code, and the existing process of the same group of parts can also be retrieved from the user process library according to the code. If necessary, the part name, preparer name, preparation date, etc, Retrieve the process to be viewed and borrowed from the user process library. According to the current part drawing, the retrieved process content can be stored in the user process library according to the new part code after necessary modification. Due to the high degree of product series of the factory, the retrieved process can be directly used with little or no modification. For very few parts with large changes or unable to retrieve the same group of processes, the process planning can be used. The standard process terms in the system can be selected for process preparation. The tooling and tools of the factory have been coded and stored in the warehouse. The process can be selected according to the code. It is worth mentioning that, according to the parts series of the factory, for some typical parts such as casings and blades, after the part process retrieval is completed, the necessary part parameters are input through man-machine dialogue (or directly transferred from the CAD system through the computer network), and the computer can automatically look up the table and give the man hour quota of each process of the part

Wuxi Machine Tool Plant has a good idea of CAPP. They first divide the parts into dozens of categories according to their functions, and then group the parts in each category according to their process characteristics. Each group of parts has a simple four digit code. Each group selects a representative part, and adds some necessary elements that other parts in the same group have but the part does not have. Such a composite part is used as a typical part of the group, The typical part is stored in the standard process library as the standard process of this group of parts through ADDA, a DDS and a ddc3 address decoding. When preparing a new part process, first determine the group code according to the function and process characteristics of the part, then input the optional elements contained in the part in the form of man-machine question and answer according to the part group, and the computer will automatically select and synthesize the part process based on the typical process of the group, which will be stored in the user process library after being reviewed, confirmed or modified by the technologist

2. The CAPP system developed by Xi'an Jiaotong University for Qinchuan machine tool plant for power steering hydraulic pump process preparation has a relatively high technical level. The system is mainly composed of the following models:

(1) control module. Its main task is to coordinate the operation of each module. It is a human-computer interaction window to realize the information exchange between human and computer and control the way to obtain part information

(2) part information input module, part information can be directly obtained through integration with CAD system, and can also be input through human-computer interaction

(3) 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) 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) 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) the NC machining instruction generation module, according to the tool position file provided by the work step decision-making module, calls the NC instruction system code in the NC code base applicable to the specific machine tool to generate the NC machining control instruction

(7) output module, which can output process flow cards, processes, step cards, process diagrams and other documents. It can also call out 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, simulate the generated machining process and check the correctness of the process

the limitation of this system is that it can only solve the process planning of power steering oil pump. If it wants to be used in our factory, it needs to be developed separately for different types of parts groups, and the workload of system development is too large

3. Comprehensive CAPP system

in view of the characteristics of the above two systems, people have developed the design method of CAPP system on the basis of the above two system principles, integrated and developed it, started from reality and timely applied the latest development achievements of other disciplines, and produced a variety of CAPP systems, such as comprehensive, interactive, intelligent and other CAPP systems. The comprehensive CAPP system is also called semi creative CAPP system. It combines variant and creative forming, and uses the advantages of variant and creative forming. In the process of system development, some mature and less changed contents in the process of process design are designed with variant principle, and the experienced and greatly changed contents are made decisions with creative forming principle, avoiding the limitations of variant system and the high difficulty of creative forming system. Most CAPP systems developed in China are of this kind

the CAPP system of Shenyang No.1 Machine Tool Plant is a typical comprehensive CAPP system, including si-capc, si-caprp, si-zpt and CAPP. The system has been successfully developed by absorbing the experience of domestic CAPP development. The brief introduction is as follows

(1) si-capc system (computer aided part coding)

si-capc system is the basis of the three systems. The application target of the system is all the technologies and production activities of the enterprise. The information is set up completely and used widely. Different technical departments and management departments can obtain valuable information from the part code according to their own business needs

(2) si-caprp system (computer aided part routing)

si-caprp system is developed on the basis of si-capc system to solve the consistency and correctness of part routing under the environment of specialized production and group processing and manufacturing of parts in the factory. The system applies advanced expert system theory and method to the specific engineering practice of part process planning. The application goal of the system is: all parts of the group processing workshops of the variety line of the plant. The system realizes data sharing with the si-papc system developed in the early stage, and automatically generates the process route of parts quickly and accurately on the basis of coding and classification

(3) si-zptcapp system (computer aided process planning of shaft, disc and sleeve parts)

si-zptcapp system is developed on the basis of the two systems developed in advance. Under the guidance of expert theory and method, the system develops an expert type computer-aided process planning system. Its working principle is that the computer simulates the general thinking process of expert design process planning, and finally designs a complete process planning according to the decision-making reasoning of design process planning and the actual situation of the factory

(4) si-capp2000 system

the system is expanded and improved on the basis of the above three systems, including: material quota system; Interactive electrical process, assembly process and hot working process system; Data statistical analysis process document management; Process resource management; Process data summary; The report preview output system forms a relatively complete CAPP system

at present, the system has been applied in process design. According to the operation, the coding rate of parts is 100%, the classification rate of parts is 99.8%, and the accuracy rate is 95%; The preparation rate of the process route is 100% and the accuracy rate is 95%; Process specification can be prepared

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