ICCAS2004 August 25-27, The Shangri-La Hotel, Bangkok, THAILAND
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1. INTRODUCTION
Recently, the tool-setup monitoring system of the high speed precision machining tool is required to produce the high precision part of the complicated shape in manufacturing process of the semiconductor, display and precision machine industry. As the shape of cutting part is gradually complicated and high precise, the reduction of time of tool-setup in high speed precision machine is very important to improve the productivity and machining precision and to prevent the falling-off in quality of the product by breakage and wear of cutting tool. In high speed precision machining tool, the run-out is occurred in 2૫30 times of the thickness of normal cutting chip that the combination of errors is such as the geometrical fixing error of the cutting tool fixed in spindle axis, asynchronous motion error and clamping fixture error.
And also the run-out is caused by the spindle bearing and misalignment of axis between tool, shank and spindle.
Generally, the high speed cutting is said in the case of higher than 8,000 rpm of spindle rotation. At this time the tool life is decreased to about 50% and the surface roughness of cutting part is radically degraded when the run-out is increased in 10 micron.
In high speed machining tool the exactness of tool-setup could extend the tool life and this means less than tool wear.
Therefore, it reduces the production cost and also it improves the productivity by reducing the time of tool-setup. In this study, the monitoring of tool-setup is accomplished by developing the measuring method of the run-out when the spindle is stopped and rotated in more than 30,000 rpm. And also the cutting error and dynamic phenomena in tool-setup error are analyzed by implementing the non-contact measuring system of highly fine dynamic displacement of cutting tool and the dynamic phenomena of high speed spindle.
2. TOOL SETUP MONITORING SYSTEM
2.1 Monitoring of high speed precision cutting tool
In general, the tool dynamometer is used as in-process monitoring tool when the cutting force is monitored in cutting process. But it is very difficult to monitor the state change of fine tool in real time because of the constraint of attaching position of sensor according to the shape and size of workpiece. The many researches of monitoring of tool and cutting state by signal of cutting force are accomplished by using the tool dynamometer but they have the problem to apply to the real manufacturing line. It is possible to monitor the state of cutting tool by using AE(Acoustic Emission) sensor because the signal change to load change in cutting process is confirmed as the tool dynamometer[1,2,3]. But there is no method to directly measure the cutting force from air-spindle used in this study. And also it has many problems in measuring the wear and breakage of tool by using conventional measuring tools. Therefore, in this study, the monitoring system is developed to perform easy and precise tool setup without giving any load to workpiece after or before establishing cutting tool and workpiece.
2.2 TOOL SETUP MONITORING 2.1.1 TOOL IDENTIFICATION
In NC machine, in order to perform the job in NC program NC operator confirms whether the tool is exactly installed or not. Before progressing of the cutting job, the tool setup monitoring is required to prevent several errors occurred in cutting by inexact tool setup, to realize intelligence of the high speed precision cutting tool and to extend the tool life. And also, in high speed precision cutting tool, the tool setup monitoring system is required to confirm whether the exact tool is installed in chuck or NC program is proper to the cutting job. By the algorithm analyzing it, it is confirmed whether the tool is exactly installed. The measuring data of tool setup are diameter of shank, length of shank and shape of cutting edge in tool.
Tool-Setup Monitoring of High Speed Precision Machining Tool
Kyoung Taik Park*, Young Jae Shin* Byung Soo Kang** Research Department of Intelligent Precision Machine, KIMM, Daejeon, Korea (Tel : +82-42-868-7131; E-mail: ktpark@kimm.re.kr)
Abstract: Recently the monitoring system of tool setting in high speed precision machining center is required for manufacturing products that have highly complex and small shape, high precision and high function. It is very important to reduce time to setup tool in order to improve the machining precision and the productivity and to protect the breakage of cutting tool as the shape of product is smaller and more complex. Generally, the combination of errors that geometrical clamping error of fixing tool at the spindle of machining tool and the asynchronized error of driving mechanism causes that the run-out of tool reaches to 3ൄ20 times of the thickness of cutting chip. And also the run-out is occurred by the misalignment between axis of tool shank and axis of spindle and spindle bearing in high speed rotation. Generally, high speed machining is considered when the rotating speed is more than 8,000 rpm. At that time, the life time of tool is reduced to about 50% and the roughness of machining surface is worse as the run-out is increased to 10 micron. The life time of tool could be increased by making monitoring of tool-setup easy, quick and precise in high speed machining tool. This means the consumption of tool is much more reduced. And also it reduces the manufacturing cost and increases the productivity by reducing the tool-setup time of operator. In this study, in order to establish the concept of tool-setup monitoring the measuring method of the geometrical error of tool system is studied when the spindle is stopped. And also the measuring method of run-out, dynamic error of tool system, is studied when the spindle is rotated in 8,000 ૫ 60,000 rpm. The dynamic phenomena of tool-setup are analyzed by implementing the monitoring system of rotating tool system and the non-contact measuring system of micro displacement in high speed.
Keywords: : Run-out, Tool-Setup, Tool Monitoring, High Speed Precision Machining
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Fig. 1 Tool identification
2.1.2 Tool Wear & Breakage
Even though it is proved that the installed tool is proper to the cutting job, the errors occurred in real cutting process should be prevented by monitoring of wear and breakage of the installed tool. And, in real cutting process, calibration of error, prediction of tool life, exchanging time of tool are decided by data base of the cutting conditions obtained by experiment.
Fig. 2 Tool Wear & Breakage
2.1.3 Tool Misalignment
The exact tool setup is required to reduce the cutting error and to prevent run-out by the inexact installment of tool in cutting process. The eccentric displacement and angle of inclination between axis of tool and axis of spindle are measured by tool setup monitoring. In the base of these measured data, the obtained eccentric displacement and inclination angle are used for data base. And the effective working eccentric displacement and inclination angle are decided in comparison with the experimental or experienced data. In cutting process, the run-out should be minimized and the cutting error and reduction of tool life occurred by run-out should be prevented. The monitoring of geometrical tool installment is required to install the tool in chuck exactly and geometrically.
Fig. 3 Tool misalignment
3. EXPERIMENTS OF TOOL SETUP MONITORING
3.1 Experimental system of monitoring
First, the experiment is to monitor the initial tool setup before starting of the cutting process. The tool setup monitoring is performed when the spindle is stopped or maintained in minimum speed of rotation.
Fig. 4 Block diagram of tool setup monitoring
Fig.4 shows the block diagram of experimental system of the tool setup monitoring. The laser displacement sensor is used for reference trigger to detect the position of rotation of the air spindle that has maximum 60,000 rpm in rotation speed.
The measuring range of laser sensor is ധ60 micron and its output is analog ധ10 VDC. Its working distance is 18 mm and its output is digital + 10 V. When the laser sensor is used for reference trigger in high or low speed rotation of spindle, the exact number and reference position of spindle rotation are detected.
By using the measured data obtained when air spindle is stopped or rotated, the diameter and install length, eccentric displacement, inclination angle and shape of the cutting tool are computed by the developed algorithm. As the cutting tool has its feature shape, the shape information is obtained by measuring the number of cutting edge that generates the peak signal. The output of digital micrometer has two ᇹ10 VDC analog signal and this signal is converted by digital converter(14bit) and also digital oscilloscope is used for confirming the output of laser sensor and micrometer.
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Fig. 5 Experimental setup of tool setup monitoring 3.2 Experimental method of monitoring
3.2.1 Tool misalignment
In order to measure the tool misalignment, the edge shape signal except trigger signal and tool diameter in measuring range of digital micrometer is measured after the spindle of Z axis is moved in minus direction. When air spindle is rotated in minimum speed, the micrometer signal with the trigger signal in one rotation is measured. The micrometer signal in one rotation is analyzed and then the eccentric diameter is computed. By using these data, the eccentric displacement and inclination angle is obtained in comparison with the reference data of spindle. If, as shown in Fig. 6, the distance from the first measuring position to the cutting tool is x1 and the distance from the second measuring position to the cutting tool is x2, the inclination angle ଠഘ is computed.
Fig. 6 Measurement of eccentricity and inclination angle
The data base is constructed in the base of the cutting error that occurred by the eccentric displacement and inclination angle in real cutting process. The effective eccentric displacement and inclination angle obtained by experiments are used for the construction of data base. This data base is used for decision making of reinstalling of cutting tool setup.
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Fig. 7 Measured data of tool shank and tool edge part
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Fig. 8 Measured data of tool shank and tool edge part
3.2.2 Tool Identification
To define tool identification, the Z axis that the air spindle is attached on is used. If the stage of Z axis is moved in minus direction, the installed tool is moved into the measuring range of digital micrometer and the signal of micrometer is started to be detected. At this time, the stage is stopped and the moving distance of the stage is measured and then the length of tool is computed.
In the measuring range of micrometer, the diameter of the rotating spindle is measured and the shape of tool is computed from the detected edge signal. Therefore, the installed tool is confirmed and then the cutting process is decided. The program to interface with NC program is developed.
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Fig. 9 Measured diameter of upper and lower part of tool
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Fig. 10 Measured diameter of upper and lower part of tool
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3.2.3 Tool Wear & Breakage
To detect the state of the wear and breakage of cutting tool, the data of the first state of tool is required. The information of the wear and breakage is obtained by measuring the diameter of cutting edge to be contacted with workpiece in cutting process. The measured cutting error data in cutting process are used for data base and also the state of the wear and breakage of the cutting tool is used. By using this data base, the effective cutting error is predicted and the cutting process is decided.
4. CONCLUSION
Recently, the importance of the cutting tool setup is realized in the high speed precision cutting tool. The monitoring system of cutting tool setup is studied. The eccentric displacement and inclination of tool are the major causes in cutting error. And also the monitoring of tool identification and wear and breakage is very important to the high speed precision cutting process. In future, the tools of several shapes are used for the experiments of tool setup and also the data base is constructed in base of the experimental and experienced data. This information is used for knowledge base system to be operated in Web base.
ACKNOWLEDGEMENTS
This study is supported by the development project of Next Generation Production System.
REFERENCE
[1] H. S. Lee, S. M. Son, S. R. Kim, J. H. Ahn, "State Monitoring System of Micro-Grooving Using AE Signal,"
KSPE, Spring Conference 2001, pp. 322-335, 2001.
[2] S. H. Kim, D. J. Lee, J. H. Ahn, "Tool Monitoring of High Speed Tapping Machine Using AE Sensor," KSPE, Fall Conference 2001, pp. 315-318, 2001.
[3] A. E. Bayoumi, G. Yucesan and L.A. Kendall, "An Analytic Mechanistic Cutting Force Model for Milling Operations", Trans. ASME, 116, 8, p324, 1994.
