Automated programming of nc-machines: evolution of shopfloor programming.

Ficko, Mirko ; Pahole, Ivo ; Balic, Joze 等

Abstract: Since the beginning of use of numerically controlled machines (CNC) there has been a tendency towards increasing the productivity in creation of CNC programs (G-code) and, in the same time, reducing the exactingness of programming. Striving for these two targets has led to two separate manners of programming which are, today, most widely used: computer--aided programming and programming on the machine. Due to the variety of properties the area of use differs completely. Both manners of programming do no more satisfy the requirements of modern use of CNC machines. In last years systems for automated programming are appearing, promising that they will replace programming on the machine in the future.

Key words: computer aided manufacturing, automated programming.

1. INTRODUCTION

In general, modern CNC machines are used for specific tasks, but they are increasingly used also as the replacement of conventional machines. In this case, often geometrically simple cases are machined able to be simply programmed. For such cases, frequently, manual programming or programming on the machine are still always used.

There are many products not requiring computer-aided programming. Considering, for example, the tool for forming of sheet steel, which is very complex, it can be established that only some elements have an exacting 3D shape, whereas, the other parts are mainly built out of basic geometrical features.

In the first part the paper presents the evolution of CNC programming since the beginning till today, in second part it defines the trends in the development of shop-floor programming.

2. EVOLUTION OF PROGRAMMING

Soon after John T. Parsons had developed the CNC machine in early fifties (Parsons, 1958), the need for efficient programming of these machines appeared. During the development of the technology of CNC control of machine tools several modes of programming appeared; the following of them are most widely used and present still today:

--Manual programming.

--Shop-floor programming.

--CAM programming.

In the sixties and seventies of the preceding century in most cases manual programming sufficed in industrial practice. However, due to limitations of the human intelligence it is not possible in this manner to utilize fully the CNC machines. Programming of CNC machines requires the capabilities at which the computer is more apt than the human. Therefore, the use of computer for creation of G-code started soon. Though, at the beginning computers had insufficient capabilities and restricted possibilities of input compared to today's conditions. That posed problems, particularly, when describing the product geometry. Thus, higher program languages were developed, out of which APT was most widely used (IIT Research Institute, 1967), assuring more advanced input of the product geometry and also more advanced programming. Thus, much repeating manual programming work was spared. The use of such aids for manual programming can be considered to be the superstructure of manual programming and an intermediate stage of development up to computer-aided programming. By the use of higher programming languages the programming of the tool path mainly for simple shapes of products, consisting, particularly, of straight lines and circular arcs, was simplified and its time shortened. However, in such programming the human was still busy solving geometrical problems.

While the describing, textual input of geometry is usually rather simple for 2D or 2.5D form, it is practically inapplicable for the input of 3D geometry. Therefore, manual programming is not appropriate for programming geometrically exacting shapes and today it is often too exacting and too slow even for simple shapes (Ficko, 2006). It must be borne in mind that computer aided programming originates in manual programming and uses the approaches based on manual programming. Familiarization with manual programming is, thus, a key to good exploitation of the CAM application (Smid, 2004).

Since the beginning of commercial use of CNC machines the programming has been possible also on the machine itself by the use of the incorporated keyboard. The controls assure manual operating of the machine on the coordinates and a more advanced programming in the higher-level programming language inherent in the controls. However, special attention must be paid to programming on the machine, since it has developed and survived until today, whereas manual programming is disappearing. Programming on the machine and/or shop-floor programming, just like the manual programming, gradually started to acquire more complex commands and functions supported in the machine controls in distinction from manual programming supported by the use of the computer (like in case of APT). Those functions comprise, particularly, the machining cycles, repeating operations, operations executed according to pattern and logical operations (Smid, 2004). However, these advanced capabilities of controls are not very much applicable due to difficulties in communication and interaction between the machine and the human.

Also the required level of knowledge for better exploitation of capabilities of the controls is too high for machine operators. Thus, the machine operators, usually, cannot take full advantage of the capabilities of the controls. Further, the productivity of such programming is bad, since it does not exceed much the productivity of manual programming. The human is still always the main performer of the computation operations and, simultaneously, the restricting factor.

Such manner of programming of CNC machines is widely used for machining simpler parts in customized production. Programming on the machine does away with the need for the programmer and computer supported technologies, which results in the reduction of cost and facilitation of organization. Of course, with the use of programming on the machine the advantages of modern technologies available are renounced. If the advantages of modern CNC machines are renounced, also the important competitive advantages are lost and productivity decreased.

The beginnings of the CAM reach back to seventies to the time of the programming language APT, but in the eighties of the previous century the development became outstanding. The computer technology made progress and graphic interfaces, ensuring intuitive and interactive input of geometry, were presented. 3D CAD models became the principal carriers of information. Surface and solid models and accelerated shaded computer graphics with high definition were introduced. The development of CAD models was followed by the development of CAM software taking full advantage of more and more precise and extensive geometry information from the CAD model. Because of increasing applicability of CAM software and accessibility of platforms for running those applications the CAM software became popular among the users of CNC machines.

Creation of CNC programs by CAM software became irreplaceable, particularly, for complex workpieces and/or sculptured shapes. By expansion of the area of use of the CNC machines also to customized production also the need for productivity and simplicity of the CAM software increased.

3. AUTOMATED PROGRAMMING BETWEEN SHOPFLOOR PROGRAMMING AND CAM

Today, practically all G-code is created in two ways differing in the area of use and advantages/disadvantages:

--CAM supported programming; applicable for programming of the most complex CNC machines and the most exacting machining. Programming is exacting and requires highly qualified programmers--technologists having technological knowledge and experience in addition to programming skills. The CAD model of the product and blank is needed for programming.

--Programming on the machine (controls); for programming of simple shapes, in particular, in customized or small-lot production. It is widely employed in workshop use of CNC machines. Programming can be affected by the machine operator with relatively little knowledge, having technological knowledge and experience. There is no need for CAD models. The disadvantages are the low productivity; the machine is occupied during programming, much defects resulting from human factor.

Although the CAM programming is superior in almost all technical properties, it has some disadvantages, particularly, of organizational and technical character. Because of those deficiencies the users need a system which is simple for use, such as programming on the machine, and exploits the advantages of CAM programming. It can be seen that the purpose and properties of these two types of programming complement themselves as shown in Fig.1. For simple, particularly, 2D and 2,5D products, above all in customized workshop production the programming on the machine is often used, whereas for more exacting shapes the CAM programming is used.

However, the programming on the machine is less and less competitive and is losing users. The programming on the machine does not belong to the CAx-chain of technologies. With the exit from the CAx-chain in the manufacture the possibilities, assured by modern technologies in this area, such as simulation of cutting, simulation of machine and optimization are renounced.

[FIGURE 1 OMITTED]

Due to modern CAx support of the manufacture the opportunity appeared to satisfy the need for a new manner of programming which would combine the advantages of the manual and CAM programming. Highly automated programming simple for use and appropriate, particularly, for simple and also more complex problems is needed (Balic). In this case, simple problems are meant to be technologically nonexacting machining, particularly, of products built from geometrical features (Balic & Korosec 2002). Automated programming will assure high productivity in creation of programs and will do away with the need for highly qualified personnel for programming of CNC machine tools. This new manner of creation of programs will require little interfering and deciding of the human.

4. CONCLUSIONS

Today, in fact, all G-code except the simplest ones are created by CAM applications. However, there is an area of use, where manual programming and shop-floor programming are still always used, particularly, because of cost-effectiveness and organizational nonexactingness. Due to incontestable disadvantages of those manners of programming the need for highly automated CAM programming capable of being executed directly beside or even on the machine appears. Such automated programming will reduce the area of use of CAM programming and will eliminate the manual programming almost completely.

5. REFERENCES

Parsons, J.T. Motor Controlled Apparatus For Positioning Machine Tool, U.S. Patent 2820187, filed May 5, 1952, and issued Jan 14, 1958

IIT Research Institute. (1967). APT part programming, McGraw-Hill, New York

Ficko, M.; Pahole, I. & Balic J. (2006). Avtomatizacija programiranja NC-strojev s programskim paketom EdgeCAM / Automatisation of programming of NC machines by EdgeCAM. in Proc. Orodjarstvo 2006, Polajnar, A. (Ed.), Poje, J. (Ed.) & Junkar, M. (Ed.), pp. 181-182, ISBN 961-6226-89-4 Portoroz, 10.-12. Oct, 2006, Fakulteta za strojnistvo, Maribor

Smid, P. (2003). CNC programming handbook: A comprehensive guide to practical CNC programming, Industrial Press, cop., ISBN 0-8311-3158-6, New York

Balic, J. & Korosec M. (2002). Intelligent tool path generation for milling of free surfaces using neural networks. International Journal of Machine Tools & Manufacture, Vol. 42, No. 10 (August 2002), pp. 1171-1179, ISSN 0890-6955