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Non-intrusive instrumentation and estimation: Applications for control of an additive manufacturing process
University West, Department of Engineering Science, Division of Automation Systems. Department of Signals and Systems Automatic control, Automation and Mechatronics, Chalmers University of Technology. (PTW)ORCID iD: 0000-0002-2824-0271
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For integration of additive manufacturing into industrial production, there is a need for capable yet robust automation solutions. Such solutions are to ensure consistent process outputs, both with regard to deposit geometry and material properties. In this thesis, instrumentation and control solutions have been investigated for the laser metal wire deposition additive manufacturing process. This particular process is promising with regard to e.g. high deposition rates and negligible material waste. However, due to its inherent dynamics, it requires automatic control in order to prove competitive. A large number of process parameters affect the resulting quality of the deposit. Successful control of these parameters is crucial for turning laser metal wire deposition into an industrially tractable process. This requires relevant and reliable process information such as the temperature of the deposit and the positioning of the tool relative to the workpiece. Due to the particular requirements of instrumenting the process, only non-intrusive measurement methods are viable. In this thesis, such measurement solutions are presented that advance automatic control of the laser metal wire deposition. In response to the need for accurate temperature measurements for the process, a new temperature measurement method has been developed. By adopting the novel concept of temporal, rather than spectral, constraints for solving the multispectral pyrometry problem, it opens up for temperature measurements which compensates for e.g. an oxidising deposit. For maintaining a good deposition process in laser metal wire deposition, control of tool position and wire feed rate is required. Based on measurements of resistance through the weld pool, a simple yet well performing control system is presented in this thesis. The control system obtains geometrical input information from resistance measurements made in-situ, and feeds this information to an iterative learning controller. This results in a robust, cheap and practical control solution for laser metal wire deposition, which is suitable for industrial use and that can easily be retrofitted to existing equipment.

Place, publisher, year, edition, pages
Göteborg: Chalmers University of Technology, , 2015. , 98 p.
Series
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie, ISSN 0346-718X ; 3829
Keyword [en]
Additive Manufacturing, Automation, Emissivity, Emissivity Compensated Spectral Pyrometry, Laser Metal Wire Deposition, Metal Deposition, Pyrometry, Resistance Feedback Control, Thermometry
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-7428ISBN: 9789175971483 (print)OAI: oai:DiVA.org:hv-7428DiVA: diva2:793078
Opponent
Supervisors
Available from: 2015-03-06 Created: 2015-03-06 Last updated: 2016-02-08Bibliographically approved
List of papers
1. Emissivity compensated spectral pyrometry for varying emissivity metallic measurands
Open this publication in new window or tab >>Emissivity compensated spectral pyrometry for varying emissivity metallic measurands
2014 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, no 2, 025010- p.Article in journal (Refereed) Published
Abstract [en]

A novel method for converting electromagnetic spectral radiance information into emperature measurements is presented. It allows for varying spectral emissivity of the metallic measurand during the course of the measurement. Such variations are due to e.g. thermal oxidation or temperature dependent emissivity. Based on the assumption that emissivity changes with time and temperature in a continuous manner, it is further assumed that an emissivity estimate at one sample instance can be derived from the estimated emissivity found at the previous samples together with updated spectral information. This leads to successive recalculations of spectral emissivity together with corresponding temperature values. The proposed algorithm has been proven to give accurate temperature estimates from a measurement based on data captured by a standard UV-Vis spectrophotometer even for an oxidizing Ti-6Al-4V specimen in a temperature range between 900K and 1400K. The method however, is not limited to these wavelength- or temperature-ranges.

Place, publisher, year, edition, pages
Bristol: IOP Publ.,, 2014
Keyword
Emissivity Compensated Spectral Pyrometry
National Category
Robotics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5607 (URN)10.1088/0957-0233/25/2/025010 (DOI)000332697800010 ()2-s2.0-84892898937 (Scopus ID)
Note

Del av lic.  

Available from: 2013-09-18 Created: 2013-09-18 Last updated: 2016-02-08Bibliographically approved
2. Emissivity compensated spectral pyrometry: algorithm and sensitivity analysis
Open this publication in new window or tab >>Emissivity compensated spectral pyrometry: algorithm and sensitivity analysis
2014 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, no 2, 025011- p.Article in journal (Refereed) Published
Abstract [en]

In order to solve the problem of non-contact temperature measurements on an object with varying emissivity, a new method is herein described and evaluated. The method uses spectral radiance measurements and converts them to temperature readings. It proves to be resilient towards changes in spectral emissivity and tolerates noisy spectral measurements. It is based on an assumption of continuous changes in emissivity and uses historical values of spectral emissivity and temperature for estimating current spectral emissivity.

The algorithm, its constituent steps and accompanying parameters are described and discussed. A thorough sensitivity analysis of the method is carried out through simulations. No rigorous instrument calibration is needed for the presented method and is therefore industrially tractable.

Place, publisher, year, edition, pages
Bristol: IOP, 2014
Keyword
Spectral pyrometry
National Category
Robotics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5608 (URN)10.1088/0957-0233/25/2/025011 (DOI)000332697800010 ()2-s2.0-84892836708 (Scopus ID)
Available from: 2013-09-18 Created: 2013-09-18 Last updated: 2016-02-08Bibliographically approved
3. Emissivity estimation for high temperature radiation pyrometry on Ti–6Al–4V
Open this publication in new window or tab >>Emissivity estimation for high temperature radiation pyrometry on Ti–6Al–4V
2013 (English)In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 46, no 2, 871-880 p.Article in journal (Refereed) Published
Abstract [en]

The paper demonstrates a versatile procedure suitable for industrial implementation of temperature measurement on a hot titanium alloy. The driving force has been the need for an accurate temperature measurement during additive manufacturing using laser welding technology where Ti–6Al–4V-wire is melted. The challenges consider both industrial constraints and the varying emissivity of the surface. Measurements makes use of a narrow bandwidth spot radiation pyrometer and a calibration procedure for estimation of the surface temperature through spectral emissivity estimation. The theoretical results are validated through experiments. A number of difficulties in radiation temperature measurements for metals with varying surface properties are discussed; especially the case of surface oxidation. The uncertainty in temperature reading due to the uncertainty in the emissivity estimate is established along with a model that qualitatively describes surface oxidation. The procedure is expected to be useful for several manufacturing applications where it is important to control high temperatures.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Ti-6Al-4V; Temperature; Emissivity; Radiation pyrometer; Laser metal deposition; Calibration, WIL, Work-integrated Learning
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
ENGINEERING, Physics; Work Integrated Learning
Identifiers
urn:nbn:se:hv:diva-4856 (URN)10.1016/j.measurement.2012.10.019 (DOI)000314428600004 ()2-s2.0-84870711131 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 266271
Available from: 2012-12-06 Created: 2012-12-06 Last updated: 2016-02-08Bibliographically approved
4. Resistance measurements for control of laser metal wire deposition
Open this publication in new window or tab >>Resistance measurements for control of laser metal wire deposition
2014 (English)In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 54, no March, 62-67 p.Article in journal (Refereed) Published
Abstract [en]

A method for controlling robotized laser metal wire deposition online by electrical resistance metering is proposed. The concept of measuring the combined resistance of the wire and the weld pool is introduced and evaluated for automatic control purposes. Droplet formation, detachment of the wire from the weld pool and stubbing can be hard to avoid during processing due to the sensitive process and short reaction times needed for making on-line adjustments. The implemented system shows a possible route for automatic control of the process wherein such problems can be avoided automatically. The method proves to successfully adjust the distance between the tool and the workpiece through controlling the robot height position, thus increasing stability of the laser metal wire deposition process.

Place, publisher, year, edition, pages
London: Elsevier, 2014
Keyword
Laser metal wire deposition;Automatic control ;Resistance ; Additive manufacturing
National Category
Robotics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5610 (URN)10.1016/j.optlaseng.2013.10.010 (DOI)000328720700010 ()2-s2.0-84887089320 (Scopus ID)
Funder
EU, FP7, Seventh Framework Programme, 266271
Available from: 2013-09-18 Created: 2013-09-18 Last updated: 2016-02-08Bibliographically approved
5. Automatic detection of material phase transitions from spectroscopic data
Open this publication in new window or tab >>Automatic detection of material phase transitions from spectroscopic data
2013 (English)In: Proceedings of the IECON 2013: 39th Annual Conference of the IEEE Industrial Electronics Society, 2013, 2384-2389 p.Conference paper, (Refereed)
Abstract [en]

When using a temperaturemeasurementmethod which utilizes spectral information for measuring the temperature of varying emissivity measurands, there is a need for a temperature reference at some point in time. In this work, such a reference is created from the spectral radiance data already used by the temperature measurement method. A method of using knowledge of the measurand material's phase transitions and spectral radiance data as a temperature reference is presented. Through automatical identification of phase transitions from radiance spectra employing signal processing, the temperature is known at a certain instance in time, just like required by the temperature measurement method. Three methods for automatic identification of material phase transitions from spectroscopic data are examined and evaluated. The methods are, based on derivatives, steady-state identification and cross correlation respectively. They are introduced and evaluated using experimental data collected from a solidifying copper sample. All methods proved to identify the phase transitions correctly. The addition of automatic phase transition identification supplements the existing temperature measurement method such that it becomes a stand alone, reference free method for measuring the true absolute temperature of a measurand with varying emissivity.

Series
Proceedings of the Annual Conference of the IEEE Industrial Electronics Society, ISSN 1553-572X
Keyword
materialphase transitions, spectroscopic data, WIL, Work-integrated Learning, AIL
National Category
Robotics
Research subject
ENGINEERING, Manufacturing and materials engineering; Work Integrated Learning
Identifiers
urn:nbn:se:hv:diva-5609 (URN)10.1109/IECON.2013.6699504 (DOI)2-s2.0-84893523136 (Scopus ID)978-1-4799-0223-1 (ISBN)
Conference
IECON 2013. 39th Annual Conference of the IEEE Induistrial Electronics Society. In conjunction with ICELIE 2013, IWIES 2013. Vienna, Austria 10-13 November 2013
Note

 Article number 6699504

Available from: 2013-09-18 Created: 2013-09-18 Last updated: 2016-02-08Bibliographically approved
6. Resistance based iterative learning control of additive manufacturing with wire
Open this publication in new window or tab >>Resistance based iterative learning control of additive manufacturing with wire
2015 (English)In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 31, 116-123 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents successful feed forward control of additive manufacturing of fully dense metallic components. The study is a refinement of former control solutions of the process, providing more robust and industrially acceptable measurement techniques. The system uses a solid state laser that melts metal wire, which in turn is deposited and solidified to build the desired solid feature on a substrate. The process is inherently subjected to disturbances that might hinder consecutive layers to be deposited appropriately. The control action is a modified wire feed rate depending on the surface of the deposited former layer, in this case measured as a resistance. The resistance of the wire stick-out and the weld pool has shown to give an accurate measure of the process stability, and a solution is proposed on how to measure it. By controlling the wire feed rate based on the resistance measure, the next layer surface can be made more even. A second order iterative learning control algorithm is used for determining the wire feed rate, and the solution is implemented and validated in an industrial setting for building a single bead wall in titanium alloy. A comparison is made between a controlled and an uncontrolled situation when a relevant disturbance is introduced throughout all layers. The controller proves to successfully mitigate these disturbances and maintain stable deposition while the uncontrolled deposition fails.

Keyword
Additive manufacturing, Metal deposition, Automatic control, Resistance, Process measurement, Iterative learning control
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-7429 (URN)10.1016/j.mechatronics.2015.03.008 (DOI)000367772000013 ()
Note

Available online 10 April 2015. Ingår i avhandling

Available from: 2015-03-06 Created: 2015-03-06 Last updated: 2016-02-08Bibliographically approved

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