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Challenges to the interpretation of the electromagnetic feedback from laser welding
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.ORCID-id: 0000-0002-7706-6994
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
GE Healthcare, Oxford.
Visa övriga samt affilieringar
2011 (Engelska)Ingår i: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 49, nr 2, s. 188-194Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This paper considers the point that it is not possible to interpret individual weld perturbations from the raw electromagnetic feedback collected from laser weld zones. The presentation of electromagnetic data as a 3D cloud is presented as a new, useful tool in the analysis of this feedback. It is shown that there is a very low correlation between the plasma or thermal signals and the reflected light signal from the weld zone, and that a strong correlation exists between the plasma and thermal signals. It is also demonstrated that data points from a weld perturbation form a different 3D cluster to those from the stable welding process. A strategy for future real time data analysis is presented utilising a suitably shaped data cloud envelope. The rates of data fit to the various segments of such an envelope could be correlated with specific weld anomalies.

Ort, förlag, år, upplaga, sidor
2011. Vol. 49, nr 2, s. 188-194
Nyckelord [en]
Materials science - Other material science
Nyckelord [sv]
Teknisk materialvetenskap - Övrig teknisk materialvetenskap
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
URN: urn:nbn:se:ltu:diva-8299DOI: 10.1016/j.optlaseng.2010.08.018ISI: 000285169500002Scopus ID: 2-s2.0-78449248930Lokalt ID: 6cb4a7c0-d60a-11df-8b36-000ea68e967bOAI: oai:DiVA.org:ltu-8299DiVA, id: diva2:981191
Anmärkning

Validerad; 2011; 20101012 (ricols)

Tillgänglig från: 2016-09-29 Skapad: 2016-09-29 Senast uppdaterad: 2019-06-03Bibliografiskt granskad
Ingår i avhandling
1. Analysis and Monitoring of Laser Welding and Surface Texturing
Öppna denna publikation i ny flik eller fönster >>Analysis and Monitoring of Laser Welding and Surface Texturing
2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Analys och övervakning av lasersvetsning samt ytstrukturering
Abstract [en]

This thesis can be conveniently divided into three sections as follows;

Part I. Monitoring of laser welding 

In laser materials processing there has always been a need for suitable methods to supervise and monitor the processes on-line, to ensure correct production quality or to trigger alarms when failures are detected. Numerous investigations have been made in this field, including experimental and theoretical work. It is common practice in this field to monitor surface temperature, plasma radiation and back-reflected laser light, coaxially with the laser beam.  Traditionally, the monitoring systems involved carry out no statistical analysis of the signals received – they merely involve thresholds.

The first two papers in this thesis look at the feedback collected during laser welding using a co-axial setup from a Digital Signal Processing point of view and also uses high speed video photography to correlate signal perturbations with process anomalies. Digital signal processing techniques such as Kalman filtering, Principal Component Analysis and Cluster Analysis have been applied to on-line measurement data and have generated new ways to describe laser welding behaviour using parameters such as reflected pulse shape. The limitations of commercially available welding supervision systems have been studied and design suggestions for the next generation of on-line weld monitoring equipment have been formulated.

Having progressed from thin section welding with continuous wave lasers to pulsed laser welding, the thesis then moves on to pulsed laser surface melting.

Part II Analysis of surface texturing of titanium.

The second part of the thesis concentrates on laser structuring of titanium surfaces for medical implants. The two papers in this section present an analysis of the laser-material interactions which create surfaces suitable for osseointegration (bone attachment). The work concentrates on a commercially available surface used for screw implants in dentistry; BioHelix™. This surface is generated by an intense bombardment of laser pulses and the surface is thus disrupted during solidification. The formation of various levels and types of roughness are analysed and it is noted that laser generated rough surfaces are fundamentally different from those with a mechanically produced roughness. One key point is that laser generated rough surfaces can include overhanging features. This finding lead to the research carried out in part III of the thesis.

Part III. Analysis and classification of laser generated surfaces.

The final section of the thesis presents research which uses statistical techniques to identify whether or not a roughened surface includes overhanging features. The presence or otherwise of such features is important because they can affect the wettability of surfaces and thus their suitability for implant surfaces, adhesive bonding and lubrication etc. Micro Computer Tomography was used to generate a typical cross section of the surface under investigation. At equally spaced positions the profile of this cross section is then allocated vectors which are normal to the profile at each point. The angles of the vectors can then be analyzed to reveal the presence or otherwise of overhanging features. The presence of overhangs on the material surface is indicated by the existence of normal vectors with angles that exceed 180°. The papers in this section also investigate possibilities and limitations of using statistical methods in conjunction with Micro Computer Tomography.

The papers have in common processing of data for laser materials processing, by advanced methods to identify and extract essential information from the processes and the resulting material properties.

Ort, förlag, år, upplaga, sidor
Luleå: Luleå tekniska universitet, 2019
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nyckelord
Laser welding, monitoring, Signal processing, laser texturing, texture analysis
Nationell ämneskategori
Bearbetnings-, yt- och fogningsteknik
Forskningsämne
Produktionsutveckling
Identifikatorer
urn:nbn:se:ltu:diva-74145 (URN)978-91-7790-404-5 (ISBN)978-91-7790-405-2 (ISBN)
Disputation
2019-10-15, E632 - Studion, Luleå tekniska universitet, Luleå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2019-06-04 Skapad: 2019-06-03 Senast uppdaterad: 2019-09-18Bibliografiskt granskad

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Olsson, RickardEriksson, IngemarPowell, JohnKaplan, Alexander

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