CNC machine tool monitoring by AE sensors: Difference between revisions

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=== Techniques of Machine tool Monitoring ===

Machine Tool monitoring is done either with or without additional sensors. Machine Tool monitoring, using sensors is mainly based on the cutting force measurement components using a multi-channel table dynamometer or rotating dynamometer, vibration amplitude using multi-channel accelerometers, audible sound from the machining process, and high-frequency sound or acoustic emission, AE. A Sensor less machine tool monitoring are mainly based on measuring of internal drive signals, such as the feed motor current, spindle motor current and spindle power. Combined measuring of multiple quantities is also possible.<ref>{{cite book|last1=REPO|first1=JARI|title=Thesis on Condition Monitoring of Machine Tools and Machining Processes using Internal Sensor Signals|date=2010|___location=Stockholm,Sweden}}</ref>

== ACOUSTIC EMISSION (AE) SENSOR ==

In this article, machine tool monitoring is explained with Acoustic Emission (AE) Sensors.AE Sensor is commonly defined as the sound emitted as an elastic wave by a solid when it is deformed or struck, caused by the rapid release of localized stress energy. Therefore, it is an occurence phenomenon which releases elastic energy into the material, which then propagates as an elastic wave. The detection frequency range of acoustic emission is from 1 KHz to 1 &nbsp;MHz. Rapid stress-releasing events generate a spectrum of stress waves starting at 0 &nbsp;Hz, and typically falling off at several MHz. AE can be related to an irreversible release of energy. It can also be generated from sources not involving material failure including friction, cavitation and impact.<ref>{{cite web|website=http://www.tms.org.}}</ref> The three major applications of AE sensors phenomena are: a) Source ___location - determine the locations of occurrence of an event b) Material mechanical performance - evaluate and characterize materials/structures; and c Health monitoring – monitors the safety operation.<ref>{{cite web|website=http://www.tms.org.}}</ref>

=== How an AE Sensor Monitors Machine Tool===

An acoustic emission (AE) sensor works on principle of measuring the high-frequency energy signals produced during cutting process. It also measures the AE energy resulting from the fracture when a tool breaks. It is best suited to applications where the level of background AE signal is low compared to the sound of tool breakage. This makes the AE sensor ideal for breakage detection of small drills and taps. It is easy to install on both new and existing machines. AE sensor detects force proportional monitoring signals even in machining operations, which generate very small cutting forces. In combination with true power, it increases the reliability of breakage monitoring.<ref>{{cite book|last1=arbor|first1=ann|title=MTC tool and process monitoring|date=1997|publisher=Artiscompany|___location=USA}}</ref> It is used especially with solid carbide tools, or very small tools on large machines and multi spindles. Most of the sensors have to be attached to the machine tool surface.<ref>{{cite book|last1=hur|first1=Winter|title=Piezo-instrumentation|date=1997|publisher=Kistler company|___location=Switzerland}}</ref> However, there are alternative methods of AE wave transmitting. A rotating, wireless AE sensor consists of a rotating sensor and a fixed receiver.<ref>{{cite book|last1=Aachen|title=Wireless AE sensor AEL 200|publisher=Prometec company|___location=Germany}}</ref> An AE sensor can also receive the acoustic waves via a jet of cooling lubricant, which can be connected directly to the tool or workpiece.<ref>{{cite book|first1=nordmann|title=Nordmann sensor technology|date=1997|publisher=Nordmann company|___location=Germany}}</ref><ref>{{cite book|title=Fluid sound sensor WAE 100|publisher=Prometec company|___location=Aachen, Germany|edition=Aachen, Germany: Prometec company}}</ref>

The Machine tool monitoring systems commonly use sensors for measuring cutting force components or quantities related to cutting force (power, torque, distance/displacement and strain). AE sensors are relatively easy to install in existing or new machines, and do not influence machine integrity and stiffness. All systems suppliers also use acoustic emission sensors, especially for monitoring small tools and for grinding.All sensors used in Machine tool monitoring systems are well adjusted to harsh machine tool environments. The difficulties in designing reliable Machine tool monitoring can be related to the complexity of the machining process itself, which may have one or more of the following characteristics, apart from the changes of the machine tool itself.<ref>{{cite journal|last1=Dimla|first1=Dimla E|title=Sensor signals for tool-wear monitoring in metal cutting operations–a review of methods|journal=International Journal of Machine Tools and Manufacture|date=2000|volume=8|issue=40|page=1073|url=40 (8): 1073}}</ref>

==References==

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