CNC machine tool monitoring by AE sensors: Difference between revisions

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{{multiple issues|{{technical|date=May 2015}}

A [[machine tool]] monitoring system is a flow of [[InformationData processing|information]] and system processing in which the information selection, obtaining data, processing of information and [[Decision-making|decision making]] on the refined information are integrated. The aim of tool condition monitoring is to detect early the disturbances in the [[machining]] process and wear of machine tool components.<ref>{{Cite book|url=https://books.google.com/books?id=uAi8NH6XH2MC&q=CNC+machine|title=Preparing and Proving CNC Machine Tool Programs|publisher=Benchmark Media Limited|language=en}}</ref>

{{Orphan|date=September 2015}}}}

This article is about '''CNC machine tool monitoring by AE sensors.'''

A [[machine tool]] monitoring system is a flow of [[Information processing|information]] and system processing in which the information selection, obtaining data, processing of information and [[Decision-making|decision making]] on the refined information are integrated. The aim of tool condition monitoring is to detect early the disturbances in the [[machining]] process and wear of machine tool components.<ref>{{Cite book|url=https://books.google.com/books?id=uAi8NH6XH2MC&q=CNC+machine|title=Preparing and Proving CNC Machine Tool Programs|publisher=Benchmark Media Limited|language=en}}</ref>

The condition of tool has been researched extensively in the past and have focused on detection of [[tool wear]], tool breakage and the estimation of remaining tool life. It is very important for on-line identification of tool condition in machining process for enhanced productivity, better quality of parts and lower costs for unmanned, automated manufacturing systems.<ref>{{cite web|url=http://www.eng.nus.edu.sg/EResnews/0310/rd/rd_7.html|website=www.eng.nus.edu.sg}}</ref>

== Techniques of machine tool monitoring ==

Machine tool monitoring can be done with or without additional [[Sensor|sensorssensor]]s. Using additional sensors, monitoring can be done by measuring:

* the cutting force (with a multi-channel table [[dynamometer]] or rotating dynamometer)<ref>{{Cite journal|lastlast1=Jemielniak|firstfirst1=K.|last2=Arrazola|first2=P.J.|date=January 2008|title=Application of AE and cutting force signals in tool condition monitoring in micro-milling|url=https://linkinghub.elsevier.com/retrieve/pii/S1755581708000400|journal=CIRP Journal of Manufacturing Science and Technology|language=en|volume=1|issue=2|pages=97–102|doi=10.1016/j.cirpj.2008.09.007}}</ref>

* [[vibration]] amplitude using multi-channel [[Accelerometer|accelerometersaccelerometer]]s<ref>{{Cite journal|lastlast1=Haber|firstfirst1=R.E.|last2=Jiménez|first2=J. E.|last3=Peres|first3=C.Ronei|last4=Alique|first4=J. R.|date=2004|title=An investigation of tool-wear monitoring in a high-speed machining process|url=https://linkinghub.elsevier.com/retrieve/pii/S0924424704003553|journal=Sensors and Actuators A: Physical|language=en|volume=116|issue=3|pages=539–545|doi=10.1016/j.sna.2004.05.017|bibcode=2004SeAcA.116..539H }}</ref>

* audible sound from the machining process

* [[High frequency|high-frequency]] sound or [[acoustic emission]]<ref>{{Cite journal|last=Li|first=Xiaoli|date=January 2002|title=A brief review: acoustic emission method for tool wear monitoring during turning|url=https://linkinghub.elsevier.com/retrieve/pii/S0890695501001080|journal=International Journal of Machine Tools and Manufacture|language=en|volume=42|issue=2|pages=157–165|doi=10.1016/S0890-6955(01)00108-0}}</ref>

Sensor-less machine tool monitoring is done by measuring internal drive signals such as:

* feed motor [[Electric current|current]]

* spindle motor current

* 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 sensor ==

Machine tool monitoring is explained with [[Acoustic emission|Acoustic Emission]] (AE) sensors.<ref>{{Cite journal|lastlast1=Liang|firstfirst1=S. Y.|last2=Dornfeld|first2=D. A.|date=1989-08-01|title=Tool Wear Detection Using Time Series Analysis of Acoustic Emission|url=https://asmedigitalcollection.asme.org/manufacturingscience/article/111/3/199/392992/Tool-Wear-Detection-Using-Time-Series-Analysis-of|journal=Journal of Engineering for Industry|language=en|volume=111|issue=3|pages=199–205|doi=10.1115/1.3188750|issn=0022-0817|url-access=subscription}}</ref>. An AE sensor is commonly defined as the sound emitted as an [[Elastic Wave|elastic wave]] by a solid when it is [[Deformation (mechanics)|deformed]] or struck, caused by the rapid release of localized [[Stress–energy tensor|stress energy]]. Therefore, it is an occurrence 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&nbsp;kHz to 1&nbsp;MHz.

Rapid stress-releasing events generate a spectrum of [[Stressstress wave|stress waves]]s 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 name="auto">{{cite web|url=http://www.tms.org|title=The Minerals, Metals & Materials Society (TMS) }}</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 name="auto" />

=== How an AE sensor monitors machine tool===

An AE sensor works on the principle of measuring the [[High frequency|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 [[Drill|drillsdrill]]s and taps. It is easy to install on both new and existing machines.

An 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=|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 (geometry)|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<ref>{{Cite journal|lastlast1=Beruvides|firstfirst1=G.|last2=Quiza|first2=R.|last3=del Toro|first3=R.|last4=Haber-Guerra|first4=R.E.|date=2013|title=Sensoring systems and signal analysis to monitor tool wear in microdrilling operations on a sintered tungsten–copper composite material|url=https://linkinghub.elsevier.com/retrieve/pii/S0924424713002768|journal=Sensors and Actuators A: Physical|language=en|volume=199|pages=165–175|doi=10.1016/j.sna.2013.05.021|bibcode=2013SeAcA.199..165B }}</ref> 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|doi=10.1016/S0890-6955(99)00122-4}}</ref>