Characteristics and key technologies of integrated numerical control system

Characteristics and key technologies of integrated numerical control system

1 introduction

In modern manufacturing system, due to the appearance of Internet and distributed computing technology, the design and manufacture of products are increasingly dispersed, and collaborative manufacturing is increasingly becoming an effective mode to produce high-quality products faster and more economically. At present, the numerical control system is developing in the direction of integration, and its purpose is to provide an effective collaborative working environment for each independent department in the product production process. The traditional CIMS technology is huge and comprehensive, which is difficult to implement in ordinary small and medium-sized enterprises, so the company came into being.

2. The concept and key technologies of the company.

2. The concept of1inc

Integrated numerical control (INC) abstracts the function realization in CIMS (such as CADPCAMPCAPPPNCP) into a series of independent functional modules, and then integrates these functional modules to form a concrete numerical control system.

Take the whole workflow of INC system used in water jet machine tool as an example (see figure 1). The whole system is based on engineering database, including graphic database, cutting parameter database, fixture database, nozzle database, process database, NC code database and so on. They are integrated through Intranet/Internet to form an engineering database. INC system can be divided into six sub-modules: module aided design (CAD), aided process (CAPP), optimization decision-making, numerical control machining (CNC), system monitoring and overall planning.

Figure 1 system work flow chart of water jet company

2.2 the difference between Inc and ONC and DNC

Compared with traditional CNC system, the core of open CNC system lies in its openness, and it must provide different applications with the ability to run on the system platform. Provide function-oriented dynamic reorganization tools; Provide a unified and standardized application user interface. Many countries in the world have started the research plan of open CNC system, among which the OMAC plan of the United States has a great influence. Osaca (Automatic Control Open System Architecture) in Europe and OSEC (Controller Open System Environment) in Japan [3]. The main goal of direct numerical control (DNC) and distributed numerical control (DNC) systems is to control the production of a group of CNC machine tools or the whole factory more effectively, which is actually a kind of distributed manufacturing.

Different from ONC and DNC, INC takes numerical control as its core, all its modules are oriented to numerical control, and all its work is for numerical control processing. For example, the general CAM system pays attention to feature recognition, the establishment of geometric modeling of parts and the definition of machining tracks of parts, while the CAM module of INC pays attention to the simulation of parts machining process and the generation of NC machining codes, in order to verify the correctness of manual programming or automatic programming NC machining programs of parts. Compared with distributed manufacturing, INC is closer to collaborative manufacturing.

2.3 Key technologies of the company

INC has three key technologies: CAD technology for numerical control; CAPP technology oriented to numerical control and numerical control technology based on CAD/CAPP information integration.

CNC-oriented CAD technology includes image preprocessing, intelligent recognition, image vectorization and CAD/CAPP integration technology. The CNC-oriented CAPP technology includes path optimization, process optimization, CAPP/CAM integration, process database establishment and management technology.

The numerical control technology based on CAD/CAPP information integration mainly includes the interface and interaction technology with CAD/CAPP integrated system (based on STEP standard extension), embedded equipment development technology and real-time technology.

This paper will discuss and study the interface and interaction technology based on CAD/CAPP information integration.

3. Interface and interactive technology between CNC system and CAD/CAPP.

At present, the NC programming mode used in industrial applications is still based on ISO 6983(GPM code) standard. With the rapid development and wide application of CAX technology and system integration technology, the standard can no longer meet the requirements of modern CNC system, and has become a bottleneck problem restricting the development of CNC technology and even automated manufacturing.

In 1997, Europe * * * put forward the optimal scheme, which extended the STEP technology to the bottom equipment of automatic manufacturing, developed an object-oriented data model (called STEP2NC) conforming to the STEP standard, extended the data conversion standard of product model to the CNC field, and re-established the interface between CAD/CAPP and CNC, so as to realize the seamless connection between CAD/CAPP/CNC and realize the complete opening in the true sense.

The data exchange between the traditional CNC system and CAD/CAPP is unidirectional, and any modification of the CNC program in the field can not be directly fed back to the CAD/CAPP system, and the information recording the initial machining requirements when generating the CNC program has been lost. The use of STEP-NC can reduce the problem that machining information is easy to be lost, realize two-way data flow, save the changes made, and make the part program and optimized machining description feedback to the design department (CAD) in time, so that the design department can update the data in time and obtain a complete and coherent machining process data file.

Fig. 2 shows the data model based on STEP-NC standard, which contains all tasks of machining workpieces. Its basic principle is programming based on manufacturing features (such as holes, cavities, threads, chamfers, etc.). ), rather than directly programming the relative motion between the tool and the workpiece. In this way, the CNC system can directly read the STEP data file from the CAD system, thus eliminating the problem of precision reduction that may be caused by data type conversion.

Figure 2. Data model based on STEP-NC

Fig. 3 shows the structural model of the CNC system adopting the STEP-NC standard, including three modes of combining STEP-NC with the CNC system at present. 1 mode is a transitional form. The upper-level CAD/CAPP system conforming to STEP standard and STEP-NC interface realize two-way data flow, and the lower level converts STEP-NC data code into GPM code by adding a code conversion interface conforming to STEP-NC standard, thus realizing the current numerical control system. Mode 2 is a relatively simple and elementary mode, which is different from mode 1 in that the lower layer adopts a new STEP-NC controller to directly read the processing files in STEP data format. Mode 3 is the development and perfection of mode 2, which makes the system more integrated, re-divides the functions between design layer and workshop layer, and realizes the integration of macro planning of CAPP system and CAD system, micro function and workshop layer. In view of the wide application of ISO6983 standard in the field of numerical control, it is unrealistic to completely replace it with ISO 14649 standard in a short time, so 1 mode will exist in the system for a long time before the STEP-NC controller is widely used [5].

Fig. 3 Structure model of CNC system based on STEP standard

The seamless connection between CAD/CAPP/CNC based on STEP-NC standard will be realized. The bidirectional data flow between CAD/CAPP and CNC will enable the design department to clearly understand the machining reality and adjust the production plan in time and quickly according to the information returned by field programming, which will greatly improve the production efficiency. In addition, the functions among CAD, CAPP and CNC will be re-divided into macro planning of CAPP system and integration of CAD system, as well as micro functions and integration of CNC.

4. Application example

AWJ water jet machine tool (national patent product) forms high-pressure water jet or abrasive jet through high-pressure pipeline to realize cutting and polishing of workpiece. The initial condition is the digital image of the workpiece, which is processed by the CAD/CAPP integrated system of Inc. The data is directly transmitted to the CNC sub-module, and the CNC sub-module generates the machining simulation. INC system is based on Windows platform, which is suitable for integrated NC machining of water jet cutting machine.

Fig. 4 shows the image preprocessing module of INC system. The initial digital image is in the upper left corner, and the outline of the lower right corner is obtained after a series of processing.

Fig. 4 Image preprocessing module

Fig. 5 shows that the processed contour is input into CAD software for slight modification, and then the CAPP software integrated into CAD software is used to design the appropriate processing technology. Finally, the generated NC code is input into the simulation software, as shown in Figure 6, and the simulation cutting can be performed. In this way, a series of work from digital image to finished product processing in INC system has been completed.

Figure 5 CAD/CAPP module

Figure 6 CNC machining module running interface

5. Conclusion

Modern manufacturing system requires dynamic data transmission between design, technology and manufacturing departments in time and coordinated operation in an environment. The numerical control technology based on STEP-NC can effectively integrate CAD/CAPP/CNC, and the production efficiency will be greatly improved. During the whole machining process, the machining data stream can be quickly accessed and shared in various departments, enterprises and even internationally, and the bottleneck effect between CAD/CAPP and CNC will no longer exist, and the production cycle of products will be greatly shortened. According to the research data of STEP Tools, the application of STEP-NC will reduce the data preparation time before processing by 75%, the process planning time by 35% and the processing time by 50%.

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