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Increased stability in laser metal wire deposition through feedback from optical measurements
University West, Department of Engineering Science, Division of Electrical and Automation Engineering. (PTW)
University West, Department of Engineering Science, Division of Electrical and Automation Engineering. (PTW)
University West, Department of Engineering Science, Division of Electrical and Automation Engineering. (PTW)
Chalmers Tekniska Högskola.
2010 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 48, no 4, 478-485 p.Article in journal (Refereed) Published
Abstract [en]

Robotized laser metal-wire deposition is a fairly new technique being developed at University West in cooperation with Swedish industry for solid freeform fabrication of fully densed metal structures. It is developed around a standard welding cell and uses robotized fiber laser welding and wire filler material together with a layered manufacturing method to create metal structures. In this work a monitoring system, comprising two cameras and a projected laser line, is developed for on-line control of the deposition process. The controller is a combination of a PI-controller for the bead width and a feed-forward compensator for the bead height. It is evaluated through deposition of single-bead walls, and the results show that the process stability is improved when the proposed controller is used.

Place, publisher, year, edition, pages
2010. Vol. 48, no 4, 478-485 p.
Keyword [en]
Laser deposition, metal wire, machine vision, process control, robotic welding equipment
National Category
Control Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-2082DOI: 10.1016/j.optlaseng.2009.08.012ISI: 000275074900011OAI: oai:DiVA.org:hv-2082DiVA: diva2:283485
Projects
RMS
Available from: 2009-12-28 Created: 2009-12-28 Last updated: 2016-02-09Bibliographically approved
In thesis
1. Towards full Automation of Robotized Laser Metal-wire Deposition
Open this publication in new window or tab >>Towards full Automation of Robotized Laser Metal-wire Deposition
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Metal wire deposition by means of robotized laser welding offers great saving potentials, i.e. reduced costs and reduced lead times, in many different applications, such as fabrication of complex components, repair or modification of high-value components, rapid prototyping and low volume production, especially if the process can be automated. Metal deposition is a layered manufacturing technique that builds metal structures by melting metal wire into beads which are deposited side by side and layer upon layer. This thesis presents a system for on-line monitoring and control of robotized laser metal wire deposition (RLMwD). The task is to ensure a stable deposition process with correct geometrical profile of the resulting geometry and sound metallurgical properties. Issues regarding sensor calibration, system identification and control design are discussed. The suggested controller maintains a constant bead height and width throughout the deposition process. It is evaluated through real experiments, however, limited to straight line deposition experiments. Solutions towards a more general controller, i.e. one that can handle different deposition paths, are suggested.

A method is also proposed on how an operator can use different sensor information for process understanding, process development and for manual on-line control. The strategies are evaluated through different deposition tasks and considered materials are tool steel and Ti-6Al-4V. The developed monitoring system enables an operator to control the process at a safe distance from the hazardous laser beam.

The results obtained in this work indicate promising steps towards full automation of the RLMwD process, i.e. without human intervention and for arbitrary deposition paths.

Publisher
82 p.
Series
Technical Report, ISSN 1403-266X ; R002/2009
Keyword
Laser metal wire deposition, process control, process development, optical sensors, robotic weld equipment
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-2148 (URN)
Presentation
2009-03-13, C120, Högskolan Väst, Trollhättan, 10:15 (English)
Opponent
Supervisors
Projects
RMS
Available from: 2010-03-03 Created: 2010-01-19 Last updated: 2010-04-22Bibliographically approved
2. Monitoring and Control of Robotized Laser Metal-Wire Deposition
Open this publication in new window or tab >>Monitoring and Control of Robotized Laser Metal-Wire Deposition
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thesis gives a number of solutions towards full automation of the promising manufacturing technology Robotized Laser Metal-wire Deposition (RLMwD). RLMwD offers great cost and weight saving potentials in the manufacturing industry. By metal deposition is here meant a layered manufacturing technique that builds fully-dense structures by melting metal wire into solidifying beads, which are deposited side by side and layer upon layer. A major challenge for this technique to be industrially implemented is to ensure process stability and repeatability. The deposition process has shown to be extremely sensitive to the wire position and orientation relative to the melt pool and the deposition direction. Careful tuning of the deposition tool and process parameters are therefore important in order to obtain a stable process and defect-free deposits. Due to its recent development, the technique is still manually controlled in industry, and hence the quality of the produced parts relies mainly on the skills of the operator. The scientific challenge is therefore to develop the wire based deposition process to a level where material integrity and good geometrical fit can be guaranteed in an automated and repeatable fashion. This thesis presents the development of a system for on-line monitoring and control of the deposition process. A complete deposition cell consisting of an industrial robot arm, a novel deposition tool, a data acquisition system, and an operator interface has been developed within the scope of this work. A system for visual feedback from the melt pool allows an operator to control the process from outside the welding room. A novel approach for automatic deposition of the process based on Iterative Learning Control is implemented. The controller has been evaluated through deposition experiments, resembling real industrial applications. The results show that the automatic controller increases the stability of the deposition process and also outperforms a manual operator. The results obtained in this work give novel solutions to the important puzzle towards full automation of the RLMwD process, and full exploitation of its potentials.

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology, 2012. 186 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola, ISSN 0346-718X ; 3336
Keyword
Laser Metal Wire Deposition, Additive Layer Manufacturing, Robotic Weld Equipment, Optical Sensors, Process Control, Process Development, Process Stability, Iterative Learning Control
National Category
Robotics Control Engineering
Identifiers
urn:nbn:se:hv:diva-4206 (URN)978-91-7385-655-3 (ISBN)
Public defence
2012-03-23, F123, Högskolan Väst, Trollhättan, 10:00 (English)
Opponent
Available from: 2012-03-26 Created: 2012-03-14 Last updated: 2015-10-02Bibliographically approved

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