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- Brandau, Benedikt
(författare)
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Spectral analysis in laser powder bed fusion
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about the investigation of the spectral interaction of electromagnetic radiation with metal powders. For this purpose, spectral data of powders for laser powder bed fusion processes are investigated in three papers using different techniques. In paper A the spectral radiation behavior of the laser interaction zone is considered, in paper B and C the absorbance behavior of different metal powders depending on their state and measurement method. Paper A investigates the spectral signal of the process light generated by laser material interaction in laser powder bed fusion. The detection is performed by a coaxially guided measuring beam and a quasi-coaxial measuring beam simultaneously guided by another scanning optics. The signal characteristics depend on the angle of incidence of the measuring beam to the laser material interaction zone. Using high-speed recordings and optical simulations, a model for describing the signal behavior could be determined. The measured spectral intensity distribution representing the degree for energy coupling can be corrected with a correction factor over the whole field for solid materials. This correction includes a function describing the numerical aperture of the measuring channel and the laser intensity on the working field. For the investigated powder, the measurement signal fluctuated strongly and no transferable model could be formed. The reason for this was the different absorbance behavior of the powders investigated. Paper B therefore deals in detail with the spectral absorbance behavior of metal powders for additive manufacturing. Using a high-precision spectrometer, 39 powders were measured reflectively over a wide spectral range and the absorbance determined. By varying the degree of use, aging, grain size and impurities, various influence parameters are determined experimentally and discussed theoretically. Based on 20 derived laser wavelengths, technically usable wavelengths with better process efficiency and stability are proposed. From the obtained absorbance, the efficiency of energy coupling can be estimated and form a broad data base for the optimization of laser parameters. In order to perform the absorbance determinations also in situ in a laser powder bed fusion system paper C describes a possibility of an inline absorbance determination by high resolution coaxial imaging. A method is discussed for geometrically correct and gapless imaging of the processing plane, recorded through the laser optics. By imaging at six different wavelengths, metal powders can be distinguished by their absorbance spectrum and impurities can be detected. In an experimental implementation the functionality of the method is proven. The results are validated by optical simulations, ray tracing and comparative measurements with a high-precision spectrometer.
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| 2. |
- Gabrielson, Per
(författare)
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High Performance Manufacturing of Advanced Thin Plates ─ Forming of Titanium and Stainless Steel Materials
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The manufacturing industry represents a highly important sector of the Swedish economy. The increasing demands placed on the quality and performance of products that are manufactured places increasing demands on the manufacturing processes involved. The aim of the dissertation has been to study how a particular forming process used in the production of thin sheet-metal parts of advanced character can best be analyzed, optimized, controlled and monitored, and how the processing results can best be predicted and be expressed in economic terms. The sheet-metal parts in question are composed of either stainless steel or pure titanium, formed into complex and intensive patterns, high demands being placed upon their precision of manufacture. An overarching goal was to be able to continuously and adaptively optimize the manufacturing process in terms of quality, process stability, production speed and sustainable resource utilization. To facilitate achievement of this ultimate goal, a laboratory platform was developed providing the testing methodology needed for process studies of different aspects of forming of critical importance. Use of this platform made it possible to focus on specific problems encountered industrially in the forming of the geometric patterns called for. Under the laboratory conditions created, knowledge and experience concerning relationships between important processing factors and the processing results obtained could be studied. In many cases, the results of the studies carried out could be combined with those obtained through use of more traditional testing methods, either to simplify or to verify results obtained. The laboratory platform and the studies carried out enabled the formability of the different materials involved to be rank-ordered and each of them to be assigned a formability index. The effects of different factors that affect the friction that occurred were also studied with the aim of being determining what forming conditions were optimal. It was found to be possible, with use of the methodology developed and of the increased knowledge and understanding it provided of the sheet-metal surfaces involved, of the lubrication employed, and of the formability of the sheet-metal material in question, to improve the performance of the process that was studied. Tool wear was assessed in a laboratory platform by means of appropriate measurement techniques. In order to keep the tool cost in an industrial setting as low as possible per part produced, it is important that the tool material and the coating of it employed be selected with adequate attention to both cost and performance. Various tool solutions for low-, medium- and high-volume production were studied. Taking account of the relationship between the costs associated with a reference tool and the wear index that applies can help to optimize the relationship between price and performance. The use of FE-analysis was seen as an important step in efforts for improvement aimed at creating a high-performance production system. Virtual aids can be useful in this context, contributing to time effectiveness in optimization of both the product in question and the manufacturing process involved. The laboratory platform made it possible to verify the results of the FE-analyses performed, enabling improvements both of the product and of the forming process employed to be implemented. A new control system that was developed based on use of AE (Acoustic Emission), able during the forming process to ensure virtually in real time the quality of the products being manufactured, was studied, as were various methods for describing the production system as a whole from the standpoint of cost. A method for analyzing production performance in terms of downtimes, in particular their character, effects and the costs per unit produced, was presented. A cost model likewise developed enabled both the downtimes and their causes to be expressed in economic terms. The dynamic downtime behavior of a production system was also studied from a cost perspective. There was found to be considerable potential for improvement of the production process as a whole. It was also shown that selection of the appropriate level of automation is important for achieving a production system having both a high level of performance and long-term sustainability. In connection with this, an economic model was presented for determining the optimal automation level under a given set of conditions.
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| 3. |
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| 4. |
- Larsson Heidenblad, David
(författare)
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Environmental History in the 1960s? : An Unsuccessful Research Application and the Circulation of Environmental Knowledge
- 2021
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Ingår i: History of Humanities. - : University of Chicago Press. - 2379-3163 .- 2379-3171. ; 6:2, s. 635-647
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Tidskriftsartikel (refereegranskat)abstract
- This article explores how the Swedish historian Birgitta Odén (1921–2016) sought to launch an interdisciplinary environmental research program in the late 1960s. Odén’s objective was to make history useful for political decision making, yet the research program never received any substantial funding. This article argues that the analytical concept of circulation of knowledge offers a fruitful way to revisit and contextualize this kind of failed or abandoned knowledge. Based on Birgitta Odén’s bequeathed papers and interviews with her former students, the study covers the years 1967 to 1969, and demonstrates how Oden conceived of environmental history in a period were no such field existed internationally. Moreover, the study illustrates how the humanities was connected to the social sciences, the sciences, the military research complex, and leading politicians in Sweden during the late 1960s.
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| 6. |
- Sjöström, Jesper
(författare)
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Didaktisk modellering
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ämnesdidaktik är ett kunskapsområde där utbildningsvetenskap möter ämnesinnehåll och skolpraktik. Det kan sägas vara (ämnes)lärares professionsvetenskap och syftar till att hjälpa lärarna att göra informerade didaktiska val i relation till undervisning av ämnesinnehållet. Under presentationen kommer ett ramverk, som består av tio aspekter av ämnesdidaktik, att presenteras (Sjöström, 2018). En av aspekterna handlar om undervisningsutvecklande ämnesdidaktisk forskning baserad på så kallad ”didaktisk modellering” (Ingerman & Wickman, 2015). Det innebär att ny ämnesdidaktisk kunskap utvecklas av (ämnes)didaktikforskare i samverkan med lärare. Man kan även kalla lärares systematiska utveckling av sin undervisning baserat på didaktiska modeller för didaktisk modellering. Utgångspunkten är en eller flera (ämnes)didaktiska modeller som prövas och förfinas i skolpraktiken. Två helt grundläggande didaktiska modeller är de didaktiska frågorna (Vem? Varför? Vad? Hur? etc.) respektive den klassiska didaktiska triangeln (lärare-ämnesinnehåll-elev), men det finns många fler, både stora och små, abstrakta och konkreta, och allmänna och ämnesspecifika. Fokus under presentationen kommer att vara på några didaktiska modeller och didaktisk modellering av betydelse för NT-lärares forskningsbaserade undervisning.
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