Aspects regarding a complex concept of multifunctional CNC machine-tool with large number of axis.

Grejdanescu, Roxana ; Strajescu, Eugen ; Avramescu, Valeriu 等

1. INTRODUCTION

The economic medium, which each day is more complex, with a continuous increasing of the its hardness and uncertainty, requires industrial reactivity, flexibility, competitiveness and tenacity. In the current context, the performance criteria are fundamental, and system flexibility is a gained internal attribute when there are created the conditions for the company to be able to adjust production without great efforts, producing the products in the required quantities, the required time, the cost imposed by market, at the level of quality set by the rules and contract conditions. Machines--tools is central to all these technical, economic and managerial approaches (Botez, 1966).

During the time these knew an important evolution, today, the machine-tools being considered as a complex system consisting of mechanical elements, fixed or mobile, with analogue, digital, satellite or voice command, data acquisition and handling, automatic loading and unloading of parts and tools, auto--adapting to external or internal variables, defects diagnosis and automatic troubleshooting and predicted maintenance, etc.

There is necessary the usage of new performing machines-tools, which are capable to accomplish the types of the parts' surfaces and which can reduce the duration of the processing cycle. So there is imposed the achievement of machines-tools which are characterized by high productivity, multifunctionality, equipped with modularised, universal and specialized elements, which have to allow the rapid adapting to various processing necessities.

2. FLEXIBLE AUTOMATION AND CNC MACHINES

Flexibility represents the ability of a machine/ technological system to adapt quickly (in minimum time) to different production tasks. It can be appreciated that the large series products' manufacture is characterized by a reduced flexibility. Switching to the manufacture of a product to another one, takes long time and high training costs. Manufacturing productivity is however very high.

The manufacture of the small series products on classic machine-tool are characterized by reduced flexibility. Switching to the manufacture of a product to another one is achieved with big consumption of time and money. The manufacturing productivity is reduced.

In order to reduce the disadvantages of the classic small manufacture, there was introduced the flexible automation. Flexible Automation refers to machines-tools with numerical commands, equipped with high capacity tools' stores, grouped into cell lines and flexible systems in which robots and industrial manipulators are indispensable elements.

The automation of a machine tool, after a numeric program, means its command based on numbers (Lungu, 1997). These suppose that all the information (geometric and technological information), which have to be sent to the machine, at a part processing, are numerically expressed and the machine tool have to understand the meaning of these numbers and on their base to make the part's processing, automatically, without the human operator intervention.

As it can be noticed in figure 1, the numeric command equipment (NCE) is attached to the conventional machine tool (CMT). This make possible that the same machine (turning machine, milling machine, boring machine) be attached to different numeric command equipments, which are made by different producers, but which accomplish that machine's functions (Kief, 1999).

The numeric command equipment has as components an electronic board and traductors to measure the real displacement of the mobile elements of the machine (sliding elements, tables, supports) after different coordinate axes.

The information introduced by the NC program are transmitted and processed by the electronic board and then are provided to the electric or electro-hydraulic equipment of the conventional machine which accomplish the suitable commands towards the work circuits and the auxiliary ones of the machine tool. On the other side, the information regarding the real displacement of the machine's elements are provided by the traductors, for displacement measure, by the inverse connection, which compares the real displacement with the programmed one, the movement stopping when the two values are the same.

The achievement of a CNC machine tool doesn't suppose only the attachment at a conventional machine tool of the numeric command equipment, but also there is necessary to comes up with constructive solutions towards it, and those should lead to the equality between the precision and productivity performances of the machine and the performances given by the numeric command equipment.

At the mechanical processing of a part, on a machine tool, there is necessary to provide to the machine some work information:

* Information about the shape of the part, which are those data which determine the trajectory of action point, line, or surface, between the tool and part which is to be processed. These information are named geometric data;

* Information towards the processing technology, which lead to the wanted shape: the cutting regime's parameters (the cutting speed or the main shaft speed, the advance speed, the depth of cutting), the tool number, its type, the individual work steps succession. These data are named technological data.

The surface generation of a part on a machine tool is achieved by the relative movement between the part and tool (Sandu, 2008). Function of the shape of the generator and directory curves, this relative movement suppose the accomplishment of two or more movements of the machine's elements (sliding elements, tables, supports) after different directions.

Any machine tool accomplishes some movements function to some specific axes. The correct determination of axes is very important because the program takes account these axes. In the numeric command there was introduced the axis notion as being a linear or rotational movement. These movements are done by the mobile elements of the CNC machine.

[FIGURE 1 OMITTED]

3. NEW CONCEPT OF MULTIFUNCTIONAL MACHINE WITH LARGE NUMBER OF AXES

This paper is based on the development of a new concept of CNC multifunctional machine-tool, for processing as turning, milling, boring, mortising, toothing, plane, exterior and interior cylindrical and helicoidally rectification (SC ICTCM, 2007)'

The configuration methodology of the new concept of multifunctional machine starts with the representative parts' study, respectively of their specific surfaces, and the assurance of the possibilities for these surfaces' generation.

The machine, (Figure 2.) (SC ICTCM, 2007), allows the processing of cylindrical parts, which have the length/ diameter rapport ~ 5 and small diameters, diameters smaller than 200 mm for turning operations, and process the parts with dimensions less than 600x600mm, with h=500mm for milling, drilling, boring, mortising, toothing, plane, exterior and interior cylindrical and helicoidally rectification.

From technological point of view, the multifunctional machine will be made in such of way so that, on the machine's frame, on the same guides oriented on the X axis, there will be displaced two longitudinal sliding elements, which are CNC commanded and which can individually or/and concomitantly move, but keeping a certain preset force between them.

Each of these longitudinal sliding elements are equipped with a transversal sliding element, which is Y axis oriented, CNC commanded, and these sliding elements can individually or/and concomitantly move, but keeping a certain preset force between them. Z axis will be perpendicular on XY plane and will intersect the X axis at the middle of the distance between the extreme limits of the longitudinal sliding elements, and the origin point of the machine's reference system, O, will be found at the intersection of Z axis with XY plane.

On Z axis, there will be displaced two sliding elements: a superior one above the XY plane and an inferior one, below this plane, each element being equipped with a machine-tool shaft, preferential is a milling shaft. The two vertical sliding elements, CNC commanded, can individually or/and concomitantly move, but keeping a preset force between them. Also, the axes of the two shafts are coaxial and the angular speeds are independent. At this base structure, there can be also added other accessories which are necessary for the normal and optimal development of the wanted technological operations (supports for the turning knifes, for the mortising-toothing knifes, for the rolling device, for the milling-toothing-rectification device, angular speed demultiplier, angular speed multiplier, device for shaping and acute the rectification stone, turning universal and fixe and rotational tops sets). The actuation of the sliding elements from the base structure and from the supplementary structure and also at least the rotation of the inferior or superior shafts is accomplished in CNC, resulting more motion axes simultaneously actuated, to which there are added the command of each process, made by the computer. The machine is equipped with a CNC system with large number of axis, which allows: the achievement of a various types of cutting processing, the generation of a very large diversity of surfaces, practically unlimited, the determination of the main optimal axis for the processing type which is need to be accomplished at that moment. The structure with 6 sliding elements and 2 main axes, impose the achievement of an unusual frame, which has to allow the intersection of the movements of these sliding elements and also the facile access of the human operator in order to assembly and to set the tools and the parts which are to be processed.

[FIGURE 2 OMITTED]

In order to obtain a multifunctional machine with a minimum necessary complexity, its main structure contains only the movements which are common to the operations which are mentioned above. Other movements specific only to certain operations, are accomplished by equipping the machine with other specific devices. The synchronization of all these movements, in order to obtain the wanted surfaces, is achieved by the CNC command in correlation with proper software programs.

4. CONCLUSIONS

The CNC multifunctional machine tool for cutting processing has a pronounced character of originality, being a new and innovative product.

The processing axes combination, the possibility to use various types of tools, the usage of some intelligent catching and fixing systems, the sensors' integration, CNC command and active control, seen in adaptive and modular way, allow to the new concept of multifunctional machine to generate complex geometrical surface, surface which is required by the part's functionality. The virtual model of this concept confirms the generation possibilities of many complex surface types.

5. REFERENCES

Botez, I. (1966). Bases of surfaces generation on machines-tools, Technical Publishing Office, Bucharest

Kief, H.B. (1999). NC/CNC Handbook, Carl Hasen Verlag, Munchen Wien

Lungu, I. (1997). Machine-tools with numerical comand and flexible processing system, Ed. Modus, Resita

Sandu, I.G. (2008). Surfaces generation, Romanian Academy Publishing Office, Bucharest

SC ICTCM SA. (2007). CNC multifunctional machine for the following processing: turning, milling, drilling, boring, mortising, toothing and plane, exterior and interior cylindrical and helicoidally rectification, INNOVATION National Project, Bucharest