Recent Developement and Trends in Tool Condition Monitoring
The trend in manufacturing is towards the intelligent machining systems. The productivity and quality of the output of such a system, as well as the machining cost, depend on many factors. One of the most significant factors for tool condition monitoring
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1 INTRODUCTION The effectiveness of new machining systems has been lower than expected. The weakest part of the machining system is the tool, i.e. the cutting edge. Sometimes we do not realize that the cutting edge is working probably in the most severe conditions within the whole technical field. The specific cutting force in turning hardened steel could be more than SOOON and the temperature is around 1000°C, when two surfaces are sliding one over the other without any lubricant. Namely, the coolant vaporizes before entering between the tool and the chip or between contact surfaces of the tool and the workpiece. The problern is how long the tool will be able to cut, i.e. what the tool wear rate or the tool life will be. The productivity, the machining cost, the quality, the integrity of the machined surface, and the profit strongly depend on tool wear or toollife. Not only the tool breakage is very important for the effectiveness ofthe machining system but the detection of tool wear as well. When the tool is wom the machining process has to be stopped and the tool must be changed. The rnachining system is not producing when the tool or the tool tip is changed. Since the operator is not available on a new machining system to determine when the tool is wom, there is a need for reliable and simple tool wear sensor systems. The chip form can change with the increase of tool wear, which could be very important in turning, since the long chip can stop the turning process in long-cut cases. The chip control system has to be used in such conditions. In milling, the chip is usually short and does not stop the milling process. From the author's experience a long chip can be obtained in face milling stainless steel with carbide cutter, even if the width of the workpiece is only 50 mm and the cutter diameter is 1OOmm. The chip could be more than 500 mm long due to the welding of stainless steel chips. Published in: E.Kuljanic (Ed.) Advanced Manufacturing Systemsand Technology, CISM Coursesand Lectures No. 437, Springer Wien New York, 2002.
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E. Kulianic, M. Sortino
Tool wear sensor system and, for tuming in some cases, the chip control system are the ·minimum requirements for a successful functioning of a machining system. Advanced sensor design, coupled with signal processing technologies, provides improved information about the process condition thus enabling process optimization and control. lt is not adequate to have information relating solely to tool wear or to tool condition. Additionally, capabilities such as in-process quality control and machine tool diagnostics are the requirements of the future, i.e. there is a shift from monitoring the tool condition to monitoring the process conditions and the resulting part quality. Many different sensors are available for monitoring the machining systems, Figure l [1]. However, the most common sensors used in industrial conditions are force, power and acoustic emission sensors. The most important sensor is the one which ensures a successful and reliable machining process
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