Fredrik Sikstrom | University West, Sweden (original) (raw)
Papers by Fredrik Sikstrom
Sensors, May 20, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Procedia Manufacturing, 2018
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
The use of automated laser welding is a key enabler for resource efficient manufacturing in sever... more The use of automated laser welding is a key enabler for resource efficient manufacturing in several industrial sectors. One disadvantage with laser welding is the narrow tolerance requirements in t ...
The International Journal of Advanced Manufacturing Technology, Jan 5, 2017
The research conducted sheds a light on the question why robust in-process monitoring and adaptiv... more The research conducted sheds a light on the question why robust in-process monitoring and adaptive control are not fully implemented in the welding industry. In the research project FaRoMonitA, the possibilities to monitor the weld quality during welding have been investigated. Research conducted in this area has merely focused on technical issues investigated in a laboratory environment. To advance the research front and release some barriers related to industrial acceptance, the studies conducted in this paper have been both quantitative and qualitative in form of experiments combined with an interview study. The quality property weld penetration depth was chosen for in-process monitoring to evaluate the industrial relevance and applicability. A guaranteed weld penetration depth is critical for companies producing parts influenced by fatigue. The parts studied were fillet welds produced by gas metal arc welding. The experiments show that there is a relationship between final penetration depth and monitored arc voltage signals and images captured by CMOS vision and infrared cameras during welding. There are still technical issues to be solved to reach a robust solution. The interview study indicates that soft issues, like competence and financial aspects, are just as critical.
Optics and Laser Technology, 2019
Narrow laser welded butt joints are monitored by a photodiode system. • The photodiode signal is ... more Narrow laser welded butt joints are monitored by a photodiode system. • The photodiode signal is analyzed using continuous wavelet transform. • The system is evaluated by both continuous wave and pulsed mode laser beam welding. • The wavelet transform signal detects fast beam deviations from the joint.
Optics and Laser Technology, Nov 1, 2017
The automated laser beam butt welding process is sensitive to positioning the laser beam with res... more The automated laser beam butt welding process is sensitive to positioning the laser beam with respect to the joint because a small offset may result in detrimental lack of sidewall fusion. This problem is even more pronounced in case of narrow gap butt welding, where most of the commercial automatic joint tracing systems fail to detect the exact position and size of the gap. In this work, a dual vision and spectroscopic sensing approach is proposed to trace narrow gap butt joints during laser welding. The system consists of a camera with suitable illumination and matched optical filters and a fast miniature spectrometer. An image processing algorithm of the camera recordings has been developed in order to estimate the laser spot position relative to the joint position. The spectral emissions from the laser induced plasma plume have been acquired by the spectrometer, and based on the measurements of the intensities of selected lines of the spectrum, the electron temperature signal has been calculated and correlated to variations of process conditions. The individual performances of these two systems have been experimentally investigated and evaluated offline by data from several welding experiments, where artificial abrupt as well as gradual deviations of the laser beam out of the joint were produced. Results indicate that a combination of the information provided by the vision and spectroscopic systems is beneficial for development of a hybrid sensing system for joint tracing.
International Journal of Heat and Mass Transfer, May 1, 2023
Procedia Manufacturing, 2018
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
The International Journal of Advanced Manufacturing Technology, Nov 27, 2018
Robotized laser beam welding of closed-square-butt joints is sensitive to how the focused laser b... more Robotized laser beam welding of closed-square-butt joints is sensitive to how the focused laser beam is positioned in relation to the joint, and existing joint tracking systems tend to fail in detecting the joint when the gap and misalignment between the work pieces are close to zero. A camera-based system is presented based on a high dynamic range camera operating with LED illumination at a specific wavelength and a matching optical filter. An image processing algorithm based on the Hough transform extracts the joint position from the camera images, and the joint position is then estimated using a Kalman filter. The filter handles situations, when the joint is not detectable in the image, e.g., when tack welds cover the joint. Surface scratches, which can be misinterpreted as being the joint, are handled by a joint curve prediction model based on known information about the nominal path defined by the robot program. The performance of the proposed system has been evaluated off line with image data obtained during several welding experiments.
Optics and Lasers in Engineering, Oct 1, 2023
Monitoring and control of automated laser beam welding is necessary in order to increase weld qua... more Monitoring and control of automated laser beam welding is necessary in order to increase weld quality and to optimise the process. This paper presents an evaluation of an optic monitoring system using photodiodes, integrated coaxial into the laser welding tool to monitor the optical electromagnetic emissions from the process. Three photodiodes are used, one for the visual spectra, one for the reflected laser light and one for the infrared spectra.A survey of previous research regarding monitoring of welding using photodiodes have been conducted, it indicated the need for development of a high bandwidth monitoring system able to capture the fast dynamic events of the welding process. Based on this a monitoring system was developed and the frequency components of the monitored signals was analysed. Welding experiments, using a 1 μm YAG laser on nickel-based alloy sheet metal of different thicknesses, has also been conducted in order to evaluate the correlation between monitored signals and change of parameters effecting the weld quality. Laser power and laser focus was changed during the experiments.I was shown that a bandwidth of 30 kHz for the monitoring system would be sufficient to capture the interesting components of the signals from the photodiodes. A clear correlation between signal level from the sensor monitoring the infrared spectra and weld penetration was found and also a correlation between reflected laser light and laser beam focus. High intensity peaks was found in the signal from the sensor monitoring the visual spectra. It is assumed, but not confirmed, that they show the formation plasma in the key hole.
The paper describes a robust vision sensor system that can find very narrow gaps between metal sh... more The paper describes a robust vision sensor system that can find very narrow gaps between metal sheets to be butt welded together. The use of automated laser beam welding is seen as a key enabler fo ...
Frontiers in Space Technologies
Additive manufacturing of parts on-site in space requires investigating the feasibility of adapti... more Additive manufacturing of parts on-site in space requires investigating the feasibility of adapting to zero-gravity and near-vacuum conditions, a technology applied today on Earth at standard conditions. While a few studies have been conducted for powder bed fusion, a feasibility study remains to be explored for direct energy deposition using a laser beam and a metal wire. This is the purpose of this study, which is conducted using a modeling approach based on computational fluid dynamics. The simulation model developed includes melting, re-solidification, vaporization, prediction of beam energy absorption as a function of the local surface temperature and curvature, ray tracing, tracking of free surface deformation and metal transfer, and wire-resistive heating. The study is carried out by starting from process parameters suited for stable on-Earth metal deposition. These conditions were also studied experimentally to validate the simulation model, leading to satisfactorily results...
International Journal of Heat and Mass Transfer
Optics & Laser Technology, 2022
This paper addresses the issue of evaluating an optical vision system to be integrated with a 1μm... more This paper addresses the issue of evaluating an optical vision system to be integrated with a 1μm laser beam welding tool for process monitoring. The boundary conditions for the system performance and system nature imposed by the needs in industrial production is highlighted. Initial welding experiments have been executed in order to understand the applicability of the vision system. The evaluation includes considerations on the required sensor bandwidth. The need for time synchronized data is emphasized and the use of numerical algorithms for enhancing the estimation and detection performanceof the system is discussed. The results shows a good potential for the system to give robust process information to be used in monitoring and control.
International Journal of Thermal Sciences, 2021
A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusio... more A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusion welding on melt thermal flow. Three beam shapes are studied at several welding travel speeds: a reference Gaussian profile and its elliptic elongations along and transverse to the welding travel direction. It is found that these beam shapes change not only the intensity and direction of the melt thermocapillary flow but also the flow pattern. For instance, and contrary to the other profiles, the beam shape elongated along the welding travel direction generates melt front vortices that assist metal pre-heating. It can result in deeper penetration, larger melt volume, and lower amount of thermal energy diffused into the heat affected zone. The simple elongation of a beam profile has thus a non-linear effect on the melt flow and in turn on the seam geometry as well as the temperature gradients in the heat affected zone.
Journal of Physics D: Applied Physics, 2021
Fluid dynamics models for laser material processing with metal fusion in conduction mode generall... more Fluid dynamics models for laser material processing with metal fusion in conduction mode generally assume a constant absorptivity. This parameter is known to govern the process. However, it used to be pre-set by extrapolating absorptance measurements made at different conditions or adjusted to reproduce experimental bead shapes. In this study a new approach is developed. It consists in predicting the absorptance as a function of local surface conditions, including the surface temperature. The proposed absorptance model is applied to the metal alloy Ti-6Al-4V. It is found that the absorptance of this alloy changes with surface temperature over a wide range of beam incidence angles. Thermo-fluid simulations with tracking of the free-surface deformation are performed for conduction mode beam welding test cases with a Yb fibre laser and different travel speeds. It is found that the absorptivity coefficient commonly used for this process clearly underestimates the absorptance and the melt pool geometry predicted for the process conditions of this study. The computational results are also compared against experimental results and good quantitative agreement of the melt pool depth, width, length, free surface contour geometry, and the curvature of the end depression left after re-solidification at the laser switch-off location is obtained. The results show that the absorptance field predicted depends on the melt pool development stage, on the spatial location within the beam spot, and on the process conditions.
Materials & Design, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Sensors, May 20, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Procedia Manufacturing, 2018
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
The use of automated laser welding is a key enabler for resource efficient manufacturing in sever... more The use of automated laser welding is a key enabler for resource efficient manufacturing in several industrial sectors. One disadvantage with laser welding is the narrow tolerance requirements in t ...
The International Journal of Advanced Manufacturing Technology, Jan 5, 2017
The research conducted sheds a light on the question why robust in-process monitoring and adaptiv... more The research conducted sheds a light on the question why robust in-process monitoring and adaptive control are not fully implemented in the welding industry. In the research project FaRoMonitA, the possibilities to monitor the weld quality during welding have been investigated. Research conducted in this area has merely focused on technical issues investigated in a laboratory environment. To advance the research front and release some barriers related to industrial acceptance, the studies conducted in this paper have been both quantitative and qualitative in form of experiments combined with an interview study. The quality property weld penetration depth was chosen for in-process monitoring to evaluate the industrial relevance and applicability. A guaranteed weld penetration depth is critical for companies producing parts influenced by fatigue. The parts studied were fillet welds produced by gas metal arc welding. The experiments show that there is a relationship between final penetration depth and monitored arc voltage signals and images captured by CMOS vision and infrared cameras during welding. There are still technical issues to be solved to reach a robust solution. The interview study indicates that soft issues, like competence and financial aspects, are just as critical.
Optics and Laser Technology, 2019
Narrow laser welded butt joints are monitored by a photodiode system. • The photodiode signal is ... more Narrow laser welded butt joints are monitored by a photodiode system. • The photodiode signal is analyzed using continuous wavelet transform. • The system is evaluated by both continuous wave and pulsed mode laser beam welding. • The wavelet transform signal detects fast beam deviations from the joint.
Optics and Laser Technology, Nov 1, 2017
The automated laser beam butt welding process is sensitive to positioning the laser beam with res... more The automated laser beam butt welding process is sensitive to positioning the laser beam with respect to the joint because a small offset may result in detrimental lack of sidewall fusion. This problem is even more pronounced in case of narrow gap butt welding, where most of the commercial automatic joint tracing systems fail to detect the exact position and size of the gap. In this work, a dual vision and spectroscopic sensing approach is proposed to trace narrow gap butt joints during laser welding. The system consists of a camera with suitable illumination and matched optical filters and a fast miniature spectrometer. An image processing algorithm of the camera recordings has been developed in order to estimate the laser spot position relative to the joint position. The spectral emissions from the laser induced plasma plume have been acquired by the spectrometer, and based on the measurements of the intensities of selected lines of the spectrum, the electron temperature signal has been calculated and correlated to variations of process conditions. The individual performances of these two systems have been experimentally investigated and evaluated offline by data from several welding experiments, where artificial abrupt as well as gradual deviations of the laser beam out of the joint were produced. Results indicate that a combination of the information provided by the vision and spectroscopic systems is beneficial for development of a hybrid sensing system for joint tracing.
International Journal of Heat and Mass Transfer, May 1, 2023
Procedia Manufacturing, 2018
Under the concept of "Industry 4.0", production processes will be pushed to be increasingly inter... more Under the concept of "Industry 4.0", production processes will be pushed to be increasingly interconnected, information based on a real time basis and, necessarily, much more efficient. In this context, capacity optimization goes beyond the traditional aim of capacity maximization, contributing also for organization's profitability and value. Indeed, lean management and continuous improvement approaches suggest capacity optimization instead of maximization. The study of capacity optimization and costing models is an important research topic that deserves contributions from both the practical and theoretical perspectives. This paper presents and discusses a mathematical model for capacity management based on different costing models (ABC and TDABC). A generic model has been developed and it was used to analyze idle capacity and to design strategies towards the maximization of organization's value. The trade-off capacity maximization vs operational efficiency is highlighted and it is shown that capacity optimization might hide operational inefficiency.
The International Journal of Advanced Manufacturing Technology, Nov 27, 2018
Robotized laser beam welding of closed-square-butt joints is sensitive to how the focused laser b... more Robotized laser beam welding of closed-square-butt joints is sensitive to how the focused laser beam is positioned in relation to the joint, and existing joint tracking systems tend to fail in detecting the joint when the gap and misalignment between the work pieces are close to zero. A camera-based system is presented based on a high dynamic range camera operating with LED illumination at a specific wavelength and a matching optical filter. An image processing algorithm based on the Hough transform extracts the joint position from the camera images, and the joint position is then estimated using a Kalman filter. The filter handles situations, when the joint is not detectable in the image, e.g., when tack welds cover the joint. Surface scratches, which can be misinterpreted as being the joint, are handled by a joint curve prediction model based on known information about the nominal path defined by the robot program. The performance of the proposed system has been evaluated off line with image data obtained during several welding experiments.
Optics and Lasers in Engineering, Oct 1, 2023
Monitoring and control of automated laser beam welding is necessary in order to increase weld qua... more Monitoring and control of automated laser beam welding is necessary in order to increase weld quality and to optimise the process. This paper presents an evaluation of an optic monitoring system using photodiodes, integrated coaxial into the laser welding tool to monitor the optical electromagnetic emissions from the process. Three photodiodes are used, one for the visual spectra, one for the reflected laser light and one for the infrared spectra.A survey of previous research regarding monitoring of welding using photodiodes have been conducted, it indicated the need for development of a high bandwidth monitoring system able to capture the fast dynamic events of the welding process. Based on this a monitoring system was developed and the frequency components of the monitored signals was analysed. Welding experiments, using a 1 μm YAG laser on nickel-based alloy sheet metal of different thicknesses, has also been conducted in order to evaluate the correlation between monitored signals and change of parameters effecting the weld quality. Laser power and laser focus was changed during the experiments.I was shown that a bandwidth of 30 kHz for the monitoring system would be sufficient to capture the interesting components of the signals from the photodiodes. A clear correlation between signal level from the sensor monitoring the infrared spectra and weld penetration was found and also a correlation between reflected laser light and laser beam focus. High intensity peaks was found in the signal from the sensor monitoring the visual spectra. It is assumed, but not confirmed, that they show the formation plasma in the key hole.
The paper describes a robust vision sensor system that can find very narrow gaps between metal sh... more The paper describes a robust vision sensor system that can find very narrow gaps between metal sheets to be butt welded together. The use of automated laser beam welding is seen as a key enabler fo ...
Frontiers in Space Technologies
Additive manufacturing of parts on-site in space requires investigating the feasibility of adapti... more Additive manufacturing of parts on-site in space requires investigating the feasibility of adapting to zero-gravity and near-vacuum conditions, a technology applied today on Earth at standard conditions. While a few studies have been conducted for powder bed fusion, a feasibility study remains to be explored for direct energy deposition using a laser beam and a metal wire. This is the purpose of this study, which is conducted using a modeling approach based on computational fluid dynamics. The simulation model developed includes melting, re-solidification, vaporization, prediction of beam energy absorption as a function of the local surface temperature and curvature, ray tracing, tracking of free surface deformation and metal transfer, and wire-resistive heating. The study is carried out by starting from process parameters suited for stable on-Earth metal deposition. These conditions were also studied experimentally to validate the simulation model, leading to satisfactorily results...
International Journal of Heat and Mass Transfer
Optics & Laser Technology, 2022
This paper addresses the issue of evaluating an optical vision system to be integrated with a 1μm... more This paper addresses the issue of evaluating an optical vision system to be integrated with a 1μm laser beam welding tool for process monitoring. The boundary conditions for the system performance and system nature imposed by the needs in industrial production is highlighted. Initial welding experiments have been executed in order to understand the applicability of the vision system. The evaluation includes considerations on the required sensor bandwidth. The need for time synchronized data is emphasized and the use of numerical algorithms for enhancing the estimation and detection performanceof the system is discussed. The results shows a good potential for the system to give robust process information to be used in monitoring and control.
International Journal of Thermal Sciences, 2021
A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusio... more A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusion welding on melt thermal flow. Three beam shapes are studied at several welding travel speeds: a reference Gaussian profile and its elliptic elongations along and transverse to the welding travel direction. It is found that these beam shapes change not only the intensity and direction of the melt thermocapillary flow but also the flow pattern. For instance, and contrary to the other profiles, the beam shape elongated along the welding travel direction generates melt front vortices that assist metal pre-heating. It can result in deeper penetration, larger melt volume, and lower amount of thermal energy diffused into the heat affected zone. The simple elongation of a beam profile has thus a non-linear effect on the melt flow and in turn on the seam geometry as well as the temperature gradients in the heat affected zone.
Journal of Physics D: Applied Physics, 2021
Fluid dynamics models for laser material processing with metal fusion in conduction mode generall... more Fluid dynamics models for laser material processing with metal fusion in conduction mode generally assume a constant absorptivity. This parameter is known to govern the process. However, it used to be pre-set by extrapolating absorptance measurements made at different conditions or adjusted to reproduce experimental bead shapes. In this study a new approach is developed. It consists in predicting the absorptance as a function of local surface conditions, including the surface temperature. The proposed absorptance model is applied to the metal alloy Ti-6Al-4V. It is found that the absorptance of this alloy changes with surface temperature over a wide range of beam incidence angles. Thermo-fluid simulations with tracking of the free-surface deformation are performed for conduction mode beam welding test cases with a Yb fibre laser and different travel speeds. It is found that the absorptivity coefficient commonly used for this process clearly underestimates the absorptance and the melt pool geometry predicted for the process conditions of this study. The computational results are also compared against experimental results and good quantitative agreement of the melt pool depth, width, length, free surface contour geometry, and the curvature of the end depression left after re-solidification at the laser switch-off location is obtained. The results show that the absorptance field predicted depends on the melt pool development stage, on the spatial location within the beam spot, and on the process conditions.
Materials & Design, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.