title: Dynamic ultrasonic contact detection using acoustic emissions.
abstract: For a non-contact ultrasonic material removal process, the control of the standoff position can be crucial to process performance; particularly where the requirement is for a standoff of the order of <20 μm. The standoff distance relative to the surface to be machined can be set by first contacting the ultrasonic tool tip with the surface and then withdrawing the tool to the required position. Determination of this contact point in a dynamic system at ultrasonic frequencies (>20 kHz) is achieved by force measurement or by detection of acoustic emissions (AE). However, where detection of distance from a surface must be determined without contact taking place, an alternative method must be sought. In this paper, the effect of distance from contact of an ultrasonic tool is measured by detection of AE through the workpiece. At the point of contact, the amplitude of the signal at the fundamental frequency increases significantly, but the strength of the 2nd and 3rd harmonic signals increases more markedly. Closer examination of these harmonics shows that an increase in their intensities can be observed in the 10 μm prior to contact, providing a mechanism to detect near contact (<10 μm) without the need to first contact the surface in order to set a standoff.
authors.affiliation: Machining and Condition Monitoring Group, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK; Zeeko Ltd., 4 Vulcan Court, Coalville, Leicestershire LE67 3FW, UK.
authors.forename: S L
authors.initials: SL
authors.lastname: Turner
authors.affiliation: Machining and Condition Monitoring Group, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
authors.forename: A
authors.initials: A
authors.lastname: Rabani
authors.affiliation: Machining and Condition Monitoring Group, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK. Electronic address: dragos.axinte@nottingham.ac.uk.
authors.forename: D A
authors.initials: DA
authors.lastname: Axinte
authors.affiliation: Zeeko Ltd., 4 Vulcan Court, Coalville, Leicestershire LE67 3FW, UK.
authors.forename: C W
authors.initials: CW
authors.lastname: King
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D008422:Materials Testing / Q000295:instrumentation*; D008669:Metallurgy / Q000295:instrumentation*; D013010:Sonication / Q000295:instrumentation*; D013016:Sound; D014463:Ultrasonography / Q000295:instrumentation*
keywords: Acoustic emission; Dynamic standoff detection; Non-contact ultrasonic machining