Performance analysis of machine tools.

Bleicher, Friedrich ; Dorn, Christoph ; Stark, Matthias 等

1. INTRODUCTION

Saving energy will be the number one issue for the next few decades. Savings in this area not only bring economic advantages in times of a global restructuring, but are also an issue of environmental policy. Meanwhile, there are already many projects that deal with this issue. For example, the "Energy Innovation Center Dresden" was opened at the end of February 2009 (Schall, 2009). Another example is the advisory program of the Hessian Ministry of Economic Affairs, which promotes integrated pollution control for small and medium-sized enterprises (Schall, 2009).

At the Institute for Production Engineering and Laser Technology at the Technical University of Vienna the first measurements of machine tools are currently being carried out. It is analyzed how efficiently a machine tool uses its power. The findings of these studies are intended for both planning a testing machine hall, as well as for further research in the field of machine tools. This project provides the basic data for another project entitled "Interdisciplinary Research on Energy Optimization in Manufacturing Plants".

Professors, academic staff, students, machine tool manufacturers and all companies involved in developing parts for machine tools now face an enormous task. From now on it is about saving energy in areas where so far only a few people have dared to try: in the field of complicated process flows.

2. INFORMATION

The first machine tool to be investigated with respect to its energy consumption is the model VF-3SSHE from the machine tool manufacturer HAAS. The machine was equipped with current transformers, current sensors, flow sensors and a load cell. The study tested the individual processes, total processes, combinations as well as processes under load and idle. All the processes described in this report have been carried out with a tool made from coated solid carbide (D = 16mm) from the tool manufacturer Garant. The experiments were conducted under load using a test piece (Figure 1), which was specially designed for this purpose. The test piece was designed to be machined on three axis or five axis machine tools, therefore all degrees of freedom can be examined. It is processed by drilling and milling. The concept was developed for energetic comparisons (Section 7) between different machine tools.

[FIGURE 1 OMITTED]

3. TYPICAL PROCESS AND CURRENT PEAKS

Significant current spikes at the machine tool are caused by the following processes:

* Turning on the machine tool

* Turning on the pumps for the cooling lubricant

* Acceleration of the spindle

* Acceleration of the X-, Y-, Z- axes

* Changing the tool (Section 6)

Figure 2 illustrates the occurrence of these current peaks. The diagram shows an idle process.

1. Retooling

2. Ramping-up of spindle

3. Fast movement of axes

[FIGURE 2 OMITTED]

A typical process (Figure 3) is explained more specifically below:

1. Ramping-up of spindle (current peak up to 90A)

2. Feeding in X direction

3. Tool entering material

4. Tool fully engaged

5. Tool exiting material

6. Feeding in XY direction

7. Feeding in Z direction (current peak up to 17A)

8. Stoping spindle and axes

[FIGURE 3 OMITTED]

4. DETERMINATION OF ENGINE POWER UNDER LOAD AND IDLE

Due to the measurement range below idle having too low of a current consumption, the idle power has been obtained by measuring four points under load and applying a linear fit (Figure 4 and Equation 2). To calculate the different power ratings of the machine tool under load, PLoad (Equation 1), the results of the power and power factor measurement were used.

[P.sub.Load] [W]=U[V] * I[A] * [square root of 3] * cos [phi][1] (1)

[P.sub.Idle] (diagram) = 1,789 [kW] (2)

[FIGURE 4 OMITTED]

5. RETOOLING

The tool change at rapid traverse 100% is discussed in more detail because of its distinctive characteristics. Typical characteristics for this process (Figure 5) are current peaks, accompanied by compressed air increases.

The following sequence describes the storing of a tool in to the tool magazine:

1. Quarter turn gripper (grab tool)

2. Downward movement (withdraw tool from spindle)

3. Half turn gripper

4. Upward movement (put tool into magazine pouch)

5. Quarter turn gripper (starting position)

6. Unfold magazine pouch (empty pouch)

7. Tool removal from spindle (open spindle)

8. Collapse magazine pouch (loaded pouch)

[FIGURE 5 OMITTED]

6. CONCLUSION

In contrast to the high starting current of the electric motors and the high consumption of compressed air during the tool change, the energy used during the main process (Figure 3, step 3-6) is low. Reducing the energy consumption at the auxiliary processes is the key to energy efficient production. Researchers want to compare machine tools from various manufacturers on power consumption, efficiency and accuracy. The results will provide information about which machine tool is producing most efficiently and most accurately at the same time. At the end of these evaluations the goals of the projects, mentioned in section 1, are reached. Further goals are to increase the efficiency of machine tools by means of innovations based on the previous results. Challenges for the future include, for example, precalculating and compensating for current peaks, lowering consumption of compressed air, developing economical controls and reducing the idle power. With all these developments, the machine accuracy must not decrease. Through the cooperation of university and machine tool manufacturers, research and development in this direction can be intensified. A decrease of the power requirement at the auxiliary processes would mean a more efficient use of the available energy. The motto of the continuing investigations should read thus: "Maximum gain from minimum resources" (Frauenhofer study on energy efficiency in production, 2009).

7. REFERENCES

Bleicher, F. (2008). HPM- High Performance Manufacturing, Bleicher F., Kopac J., Meyer L.W. & Stich V., 978-3-20001355-1, Vienna

Schall, E. P. (2009). To conserve resources--lower costs. b, Innovation Centre Energy Efficiency founded. VDI- Z, 5/2009, pp 8-8

Weck, M. (2002). Construction and calculation of machine tools, Springer, 978-3540225027, Berlin

*** Frauenhofer study on energy efficiency in production (2009) http://www.bmbf.de/de/12596.php--Federal Ministry for education and research, Accessed on: 2009-1002

*** Frauenhofer & Verbund Produktion (2009). Congress resource-efficient production, Gentle on resources production, Prof. Klocke, F; DI Lung, D. & DI Schlosser, R. (2009), pp 14-14, Congress Centre Leipzig, 02.2009, Frauenhofer Institute, Chemnitz