| 1. |
- Sundqvist, Jesper
(författare)
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Aspects of Heat Flow in Laser Processing of Metals
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the laser was invented in 1960, its use in manufacturing industry has been growing rapidly. Laser processing of metals is based on the flow of heat that is generated by the absorbed laser beam. One outstanding aspect of laser beams is high precision along with high controllability of energy transfer, which includes creative techniques of shaping the beam and in turn the process. The thesis presents six Papers A-F on different metal processing techniques, namely welding, hardening and cutting, the latter combined with additive manufacturing. For each respective technique it was studied how desired properties can be optimized by controlled use of the laser beam and in turn of the temperature field. Addressing their different complexity of the heat transfer, various theoretical and experimental analysis methods were applied.Laser beam welding is usually conducted with standard beam shapes, i.e. Gaussian or top-hat like, which is not always optimal for the process. Identification of an optimised weld pool shape or temperature cycle could increase the quality of welded products or even enable new applications. Papers A and B aim to increase the knowledge for non-standard beam shapes, particularly for single-pulse conduction mode welding. Paper A presents an investigation on an industrial application where a C-shaped weld joint is desired. The sensitivity to and optimization of different C-shaped beam irradiation profiles is discussed. The analysis is mainly carried out by applying Finite Element Analysis, FEA, to calculate the heat conduction contributions, showing unexpected sensitivity in certain regimes. Paper B presents a semi-analytical model for fast calculation of the temperature field from different beam profiles. Examples include multi-spots or the misalignment sensitivity of Diffractive Optical Elements.In Paper C, for laser hardening of 11% Cr ferritic stainless steel the temperature field was studied to enable hardening. It was shown that single-track hardening without sensitisation could be achieved but overlapping tracks had a continuous network of ditched grain boundaries and is thereby at risk for sensitisation. The sensitised area is caused by a reheating cycle.The same mechanism for the same material was studied in Paper D when applying a recently developed drop deposition technique, where additive manufacturing is fed by laser cutting. The same reheating isotherm becomes critical, but here sensitisation tests show a discontinuous network of ditched grain boundaries in the added material. The solid heat-affected zone on the other hand has a continuous network of ditched grain boundaries, which implies a sensitisation risk. The continuous network is however not in contact with the surface. The tested parameters is thus not at risk for intergranular corrosion through sensitisation.For friction stir welding of dissimilar metals, Ti-6Al-4V with AISI 304L stainless steel, Paper E, the influence of a laser-induced preheating temperature field on the tool forces was investigated through numerical simulation. By suitable application of laser preheating, the forces acting on the tool can be substantially lowered, in a robust manner.The temperature field from seam welding induces a residual stress field. In Paper F, for continuous wave laser keyhole welding of high strength steel butt joints, a method is presented to identify the residual stress behaviour of laser welded sheets by measurement of the fatigue crack growth rate during testing, by deriving the crack acceleration. The analysis was confirmed by hole drilling tests and by FEA.The knowledge and methods of the above different experimental and theoretical studies complement each other. They contribute to further optimize certain aspects through laser-induced temperature fields, for different manufacturing techniques.
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| 2. |
- Blackburn, Landen D., et al.
(författare)
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Dynamic machine learning-based optimization algorithm to improve boiler efficiency
- 2022
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Ingår i: Journal of Process Control. - : Elsevier BV. - 0959-1524. ; 120, s. 129-149
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Forskningsöversikt (refereegranskat)abstract
- With decreasing computational costs, improvement in algorithms, and the aggregation of large industrial and commercial datasets, machine learning is becoming a ubiquitous tool for process and business innovations. Machine learning is still lacking applications in the field of dynamic optimization for real-time control. This work presents a novel framework for performing constrained dynamic optimization using a recurrent neural network model combined with a metaheuristic optimizer. The framework is designed to augment an existing control system and is purely data-driven, like most industrial Model Predictive Control applications. Several recurrent neural network models are compared as well as several metaheuristic optimizers. Hyperparameters and optimizer parameters are tuned with parameter sweeps, and the resulting values are reported. The best parameters for each optimizer and model combination are demonstrated in closed-loop control of a dynamic simulation, and several recommendations are made for generalizing this framework to other systems. Up to 0.953% improvement is realized over the non-optimized case for a simulated coal-fired boiler. While this is not a large improvement in percentage, the total economic impact is $991,000 per year, and this study builds a foundation for future machine learning with dynamic optimization.
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| 3. |
- Kaplan, Alexander F. H., et al.
(författare)
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Laser induced reduction of iron ore by silicon
- 2023
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Ingår i: Journal of Alloys and Metallurgical Systems. - : Elsevier. - 2949-9178. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Iron ore powder accompanied by Si-powder as a reducing agent, was melted using a high-power laser beam. During laser melting of the two different powder beds placed next to each other, silicon merged and diffused into the iron ore, forming a ternary melt phase Fe-O-Si of around 30–60–10 at%. High speed imaging of the laser melting process as well as subsequent SEM-analysis of the generated nuggets showed the formation of droplets that merge with the surrounding Si- or ore-powder and form distinct domains. Under certain circumstances, the solidifying nuggets, of the order of 0.5–5 mm in size, generated numerous small domains, up to 25 µm, of high purity iron, 90 + at%, surrounded by a matrix of the above mentioned slag. Many of these Fe-domains were created in the vicinity of regions of high Si-content.
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| 4. |
- Abel, Olubunmi, et al.
(författare)
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Development of a Smartphone App for a Genetics Website : The Amyotrophic Lateral Sclerosis Online Genetics Database (ALSoD)
- 2013
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Ingår i: JMIR mhealth and uhealth. - : JMIR Publications, Inc.. - 2291-5222. ; 1:2
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Tidskriftsartikel (refereegranskat)abstract
- Background: The ALS Online Genetics Database (ALSoD) website holds mutation, geographical, and phenotype data on genes implicated in amyotrophic lateral sclerosis (ALS) and links to bioinformatics resources, publications, and tools for analysis. On average, there are 300 unique visits per day, suggesting a high demand from the research community. To enable wider access, we developed a mobile-friendly version of the website and a smartphone app. Objective: We sought to compare data traffic before and after implementation of a mobile version of the website to assess utility. Methods: We identified the most frequently viewed pages using Google Analytics and our in-house analytic monitoring. For these, we optimized the content layout of the screen, reduced image sizes, and summarized available information. We used the Microsoft. NET framework mobile detection property (HttpRequest. IsMobileDevice in the Request. Browser object in conjunction with HttpRequest. UserAgent), which returns a true value if the browser is a recognized mobile device. For app development, we used the Eclipse integrated development environment with Android plug-ins. We wrapped the mobile website version with the WebView object in Android. Simulators were downloaded to test and debug the applications. Results: The website automatically detects access from a mobile phone and redirects pages to fit the smaller screen. Because the amount of data stored on ALSoD is very large, the available information for display using smartphone access is deliberately restricted to improve usability. Visits to the website increased from 2231 to 2820, yielding a 26% increase from the pre-mobile to post-mobile period and an increase from 103 to 340 visits (230%) using mobile devices (including tablets). The smartphone app is currently available on BlackBerry and Android devices and will be available shortly on iOS as well. Conclusions: Further development of the ALSoD website has allowed access through smartphones and tablets, either through the website or directly through a mobile app, making genetic data stored on the database readily accessible to researchers and patients across multiple devices.
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| 5. |
- Eriksson, Ingemar, et al.
(författare)
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Melt behavior on the keyhole front during high speed laser welding
- 2013
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Ingår i: Optics and lasers in engineering. - : Elsevier BV. - 0143-8166 .- 1873-0302. ; 51:6, s. 735-740
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Tidskriftsartikel (refereegranskat)abstract
- The flow of molten metal on the front wall of a laser generated welding keyhole has been observed by high speed photography, optically measured by mapping the flow of ripples on the liquid surface and theoretically calculated. A clear downward flow can be observed and measured by a Particle Image Velocimetry algorithm. A theoretical calculation of the melt thickness on the keyhole front is also presented. Results indicate that the thickness of the liquid on the keyhole front is similar to that of the resolidified layer found in micrographs of the front if the laser is suddenly turned off. The measured surface ripple flow speeds are between two and four times as high as the theoretical average fluid flow rate.
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| 6. |
- Eriksson, Ingemar, et al.
(författare)
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Ultra high speed camera investigations of laser beam welding
- 2010
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Ingår i: Congress proceedings ICALEO. - Anaheim, CA : Laser institute of America. - 9780912035611 ; , s. 172-178
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- With the help of high speed camera equipment, researchers can now directly observe melt flow phenomena which only could be imagined or simulated in the past. In this paper the motion of the molten metal inside the keyhole has been observed at frame rates as high as 180000 fps to provide useful information about the laser beam welding process. This paper describes two different cases where high speed imaging has given new insights into the laser beam welding process: A. In pulsed welding the melt pool oscillations can create ripples on the solidified weld surface. With the help of a high speed camera this phenomenon was analyzed, and the pulse shape was adjusted to reduce the ripple amplitude to a minimum. B. In Zn-coated steel edge welding it could be seen that blowouts were sometimes created in the melt pool at some distance behind the keyhole. Direct slowmotion observation has led to the formulation of a phenomenological model of this effect.
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| 7. |
- Fedina, Tatiana, et al.
(författare)
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A comparative study of water and gas atomized low alloy steel powders for additive manufacturing
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- This work reports a study of the differences between laser processing of water and gas atomized low alloy steel powders with a focus on powder behavior and performance in additive manufacturing. Material packing densities were measured to establish a relationship between powder packing and track formation. The results showed that the track height when using water atomized powder was 15% lower than the value achieved for the gas atomized powder. High-speed imaging was utilized to observe the material behavior and analyze the powder particle movement under laser irradiation. It was found that water atomized powder has less particle entrainment due to its tendency towards mechanical interlocking. The occurrence of powder spattering and melt pool instabilities was also studied. More frequent spatter ejection is believed to be due to the higher amount of oxygen in the water atomized powder.
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| 8. |
- Forsman, Tomas, et al.
(författare)
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Nd:YAG laser welding of aluminium : factors affecting absorptivity
- 1999
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Ingår i: Lasers in engineering (Print). - 0898-1507 .- 1029-029X. ; 8:4, s. 295-309
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the factors affecting the absorptivity during Nd:YAG laser keyhole welding of a 6xxx aluminum alloy. The influence of surface condition on absorption is shown to be negligible. Experimental absorption measurements by calorimetry are compared to analytical absorption values using a simple model based on Fresnel absorption during multiple reflections in the keyhole.
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| 9. |
- Frostevarg, Jan, et al.
(författare)
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Improving weld quality by laser re-melting
- 2014
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Ingår i: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 26:4
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Tidskriftsartikel (refereegranskat)abstract
- Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and varying penetration. In some cases, it is technically and commercially viable to reduce undercut at the weld cap and smooth out the weld root profile by defocussing the welding laser and using it to remelt the welded surfaces.
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| 10. |
- Frostevarg, Jan, 1982-, et al.
(författare)
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The formation of osseointegrating surfaceson titanium by laser irradiation
- 2018
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Ingår i: 71st IIW General Assembly, C-IV.
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Konferensbidrag (refereegranskat)abstract
- Pulsed lasers can be used to modify the surface of medical implants in order to accelerate bone growth(osseointegration). Here, it is used to create a surface that is beneficial for rapid osseointegration, also calledBioHelix™, having ridges and covered in attached droplets of diameters between 1 and 20 μm. This paper presentsthe results of an experimental program in which a range of laser parameters were used to create different surfacetextures on titanium substrates. The resulting surfaces were analyzed by scanning electron microscope and MicroComputer Tomography. The paper explains how different types of surface are created by the laser-materialinteraction under different conditions. It is shown that optimization of the laser parameters results in a robustprocess which produces a surface that is fundamentally different from those created by other methods
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