Research on the key technologies of generalization

Research on the key technologies of generalization and practicality in CAPP system

Introduction

CAPP is an important part of manufacturing informatization. It converts product data into manufacturing oriented mandatory data, and is a bridge between CAD and cam. Due to the inconsistent level of CAD application in enterprises, enterprises do not pay attention to the process, the generative CAPP system has not entered the practical stage, the limitations of the function of the process design system, and the dependence of process design on product objects, manufacturing environment and production types, etc., the popularization and Application of CAPP are limited to a certain extent

this paper discusses and gives the structure and key technologies of the generalized CAPP system, and focuses on solving the problem that the degree of generalization of the CAPP system is incompatible with the practicality of the system. On the basis of summarizing the experience of process design in enterprises and standardizing the part structure, process knowledge and manufacturing resources, the feature process information model based on seven categories of geometric basic features and ten categories of geometric additional features is established by adopting the geometric feature classification method consistent with the traditional process knowledge. The process design template based on geometric basic features is established, and the process parametric matching method is adopted in the template. The main process route of the part is determined by the process design template of geometric basic features, and the geometric additional feature processes are superimposed into the main process route of the part according to the feature process superposition rules and auxiliary rules. In order to adapt to the changes of manufacturing environment in different enterprises, a process environment resource adapter is established to match the equipment and process equipment in the generated process specification with the actual resources in the enterprise. The breakthrough progress of these technologies is conducive to the development of a universal and practical CAPP system. At the same time, it conforms to the thinking habits of process personnel, and promotes the popularization and application of CAPP to a big step towards generalization and practicality

1 Structure of general CAPP system

this paper studies the universality of CAPP system from the mode. The structure of general CAPP system is shown in Figure 1. The process generation of the system adopts the technology of process design template based on geometric basic features, and is built on the management platform of process knowledge base/manufacturing resource base. It can meet the requirements of system initialization, process knowledge update and system expansion, and can cover shaft class, box class The preparation of process procedures for support, disc sleeve, gear and other parts conforms to the thinking habits of technologists

2 feature description and extraction of part information

2.1 part feature process model

the description and input of part information is one of the key technologies of CAPP system to drive the axis change system of photoelectric encoder. The input information of CAPP system is the geometric and manufacturing feature information of the parts to be machined. It is the initial basis for CAPP system to make process decisions and generate parts processing process

according to the characteristics of process planning average value process design and the formation relationship of parts in the processing process, the geometric features are divided from the perspective of process independence, and the geometric features of parts are divided into basic features and geometric additional features. Among them, the basic features describe the main external surface of the basic geometry of the part, and the additional features describe the secondary geometry of the part and the features with combination requirements in terms of function, structure and process characteristics, which are attached to the basic features. The basic features determine the process procedure framework of the part and the main process route of the part processing. The additional features are the description of the specific structure of the part. On the basis of the processing of the basic geometric features, it generally needs to increase the process or at least increase the work steps to form. According to this definition, a part can be regarded as a combination of one basic feature and several additional features

from the perspective of manufacturing, the feature information of parts can be divided into overall features, geometric features and process features. The force measuring piston rotates with great friction or does not rotate, in which the geometric feature is the carrier of the process feature, and the process feature can be obtained by mapping and transforming the geometric feature

1) the overall feature refers to the management information of parts, and the parameters described include product model, part name, part drawing number, material name, blank type, overall size, production batch, etc. 2) Geometric features refer to the geometry and size of parts, which can be divided into seven basic geometric features and ten additional geometric features. 3) Process characteristics refer to process attributes attached to geometric characteristics. Including precision features, material features, technical features and resource features. The characteristic process model of the part is shown in Figure 2

2.2 input of part feature information

2.2.1 establishment of part feature process parameter library

build part feature process parameter library to store part feature process information. The information in the characteristic process parameter library is divided into two types of information, one is logic judgment information, which gives a series of parameters provided by the system according to national standards or specifications, such as accuracy grade, heat treatment status, material brand, etc. One is quantitative parameter information, which requires the input of process designers, such as structural dimensions, measurement parameters, etc

each geometric feature (including geometric basic features and geometric additional features) is used as the carrier of feature information, given a unique identification, and stored in the way of database. The content required by the feature is the parameters of the field, and different features are the records of the database. Each record is the sum of feature information

in order to facilitate process decision-making and the storage and management of part information, part information is composed according to part features. Part feature information storage adopts object-oriented class structure to form part feature class library. The parameters in the feature class library play a decisive role in the formulation of process route, the selection of process equipment and cutting parameters

2.2.2 input of feature information

input of part feature information includes input of overall feature information and input of feature process information. The general feature information of parts is generated in the product design stage, and has been stored in the system database, which can be automatically imported from the product database. Feature process information is mainly the information marked on the part drawing. Due to the inconsistency of CAD models and the limitations of automatic recognition technology, it is necessary to use human-computer interaction on the system input interface for selective input or direct input

the input of part feature process information is carried out in two steps. The first step is to identify the basic geometric feature parameters and corresponding process parameters of the parts according to the drawing information of the parts. The recognition of basic geometric features is mainly based on the outer contour of the part. The contour and structure irrelevant to the process design can be appropriately simplified to facilitate the processing of features, including the drawing and generation of process diagrams. The second step is to identify the geometric additional feature parameters and corresponding process parameters of the parts according to the drawing information of the parts. When identifying the geometric additional features, we mainly consider the datum relationship of various structural elements that need to be processed, the measured dimensions, the connection parameters with the contour, etc

3 process generation based on feature process design template

3.1 process design template based on geometric basic features

process design template based on geometric basic features is divided according to the geometric characteristics of parts. Its purpose is to make the template structure smaller, reduce the ambiguity of the template, and improve the accuracy of template adaptation. Features are the basic elements of parts. Different parts are composed of the same several geometric features. The process of geometric features and the superposition method of various geometric feature processes are solved, and this kind of template can be used to generate various part processes

the design of process template based on geometric basic features divides the process information set of geometric basic features into two parts: conditions and conclusions. The condition part is composed of feature number, feature name, blank state, material heat treatment, maximum accuracy, etc. The conclusion part is divided into rough machining, semi finishing machining, finishing machining, grinding machining, precision machining and other stages according to the machining process. The sequence of the process content of each stage is: process number - process name - process content - Workshop - Equipment - tools - fixtures - benchmark - working hours, etc. The process content includes several work steps, process accuracy and geometric dimensions. The process content is expressed with different parameters and standardized. In this way, the processes of the geometric basic features of the parts are orderly arranged and combined according to the processing stage to form the feature process design template

3.2 process generation method based on feature template

the structure of process design template of geometric basic features is shown in Figure 3. Process generation uses the geometric basic feature process design template to determine the main process route of the part. At the same time, considering the additional feature process of the part, according to certain superposition rules, the additional feature process is added to the main process route to realize the generation of the part process specification, so that the process modification is small and the process generation is simple

(1) matching of geometric basic feature technology

according to the material of the part and the accuracy level with the highest machining surface accuracy requirements in the geometric basic features, divide the machining stages of the part, match the geometric basic feature process design module, generate the basic feature technology of the part, and form the main process route of the part

(2) matching of geometric additional feature process

according to the processing sequence of geometric additional features of parts, match the additional feature process module according to the name, feature number and maximum accuracy of geometric additional features of parts, and generate the additional feature process of parts in turn

(3) superposition of basic feature process and additional feature process

according to the feature process superposition rule, the additional feature process is successively inserted into the process trunk route of the part to generate the initial process file of the part

3.3 establishment of feature process superposition rule base and auxiliary rule base

in order to realize the geometric basic feature process and additional feature process to generate part process according to certain rules, it is necessary to establish feature process superposition rule base and store it in the form of table in the database. The abscissa field of the table has 17 kinds of basic features and additional features, and the ordinate field of the table has 10 kinds of additional features, and each geometric feature is divided into five precision sections, such as rough machining, semi finishing machining, finishing machining, grinding machining, precision machining, etc., thus forming the feature process superposition rule matrix. This feature process superposition rule table not only reflects the superposition rules of different accuracy sections, geometric basic feature processes and geometric additional feature processes, geometric additional feature processes and geometric additional feature processes, but also reflects that the sequencing of each process in the same accuracy section should meet the corresponding logical relationship, such as the plane is before the hole processing, the thread is after the hole processing, and the geometric basic features and geometric additional feature processing have a master-slave relationship, Such as circumferential groove, thread and keyway after shaft machining

however, the feature process superposition rules still cannot fully meet the requirements of feature process superposition, and some auxiliary rules are needed to generate the initial process file of parts. For example, the machining section of the geometric basic feature process is determined according to the highest accuracy. For the cylindrical with different accuracy of the step axis, the low-precision cylindrical machining process is automatically generated in the calling geometric basic feature process template according to the accuracy auxiliary rules, and it does not need to call out all, and then delete the redundant part, etc

4 establishment of enterprise resource adapter

the difficulties in popularizing and applying CAPP system mainly include different manufacturing resource environments and