| 1. |
- Bejjani, Roland, et al.
(författare)
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Variations in the Surface Integrity of Ti-6Al-4V by Combinations of Additive and Subtractive Manufacturing Processes
- 2020
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Ingår i: Materials. - : MDPI. - 1996-1944. ; 13:8, s. 1-24
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) has recently been accorded considerable interest by manufacturers. Many manufacturing industries, amongst others in the aerospace sector, are already using AM parts or are investing in such manufacturing methods. Important material properties, such as microstructures, residual stress, and surface topography, can be affected by AM processes. In addition, a subtractive manufacturing (SM) process, such as machining, is required for finishing certain parts when accurate tolerances are required. This finish machining will subsequently affect the surface integrity and topography of the material. In this research work, we focused on the surface integrity of Ti-6Al-4V parts manufactured using three different types of AM and finished using an SM step. The aim of this study was to gain an understanding on how each process affects the resulting surface integrity of the material. It was found that each AM process affects the materials’ properties differently and that clear differences exist compared to a reference material manufactured using conventional methods. The newly generated surface was investigated after the SM step and each combination of AM/SM resulted in differences in surface integrity. It was found that different AM processes result in different microstructures which in turn affect surface integrity after the SM process.
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| 2. |
- Cedergren, Stefan, et al.
(författare)
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Machinability of cast titanium alloy Ti-6Al-4V with addition of boron
- 2020
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Ingår i: MATEC Web of Conferences. - : EDP Sciences. - 2261-236X. ; 321
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Tidskriftsartikel (refereegranskat)abstract
- Cast titanium products generally have coarser microstructures compared to wrought, which explains their limited mechanical properties. However, instead of additional thermo-mechanical processing steps, as in the case of wrought components, the microstructure of castings can be refined by additions of boron. This enhances yield strength, tensile strength and ductility. In order to investigate the influence on machining of this microstructural refinement, cutting tests were performed in three different Ti-6Al-4V castings, having 0, 0.06 and 0.11 wt.% boron. Five machinability criteria were studied; cutting force, chip breakability, burr formation, surface roughness and tool wear. The results show anisotropic deformation behavior in chips when alpha colony size is on the same order of magnitude as the primary deformation zone, or larger. There was little or no influence on cutting forces and burr formation, however chip breakability and tool life was reduced when boron was added. Surface roughness showed a more complex behavior where 0.06 wt.% boron resulted in rougher surfaces compared to the other compositions at low feed rate.
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| 3. |
- Duhan, Alice, 1986-
(författare)
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Les langues du roman translingue : Une étude de Nancy Huston, Vassilis Alexakis et Andreï Makine
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although literary translingualism, defined as the practice of writing literature in a second language, is by no means new, it is only in the past two decades that a specialized research field has emerged around the phenomenon. Synthesizing recent developments and drawing on several existing research strands, this study sets out to examine translingual writing in French in its contemporary expressions, with a particular focus on the novel. Do contemporary writers understand their translingualism differently from their predecessors? Can translingual studies be productively put into dialogue with developments in world literature studies? And how should we understand translingual writing in relation to the theoretical “translingual turn” affecting literary studies more broadly? This dissertation argues that contemporary translingual writing in French must be understood as part of a wider shift affecting both creative and critical practices, as the forces of globalization prompt us to reassess the relationship between literature and its language(s).Following a theoretical discussion, the analysis chapters aim to shed light on contemporary understandings of translingualism as articulated in the poetics of three major authors. The chapter focusing on Nancy Huston’s bilingual novel, Danse noire, investigates forms of novelistic self-reflexivity that demonstrate a renewed attentiveness to translation as it underpins literary mimesis. What is here called her translational storytelling not only foregrounds the representation of diegetic languages, but also draws our attention to the hermeneutic processes and ethical implications of writing and reading stories which potentially reach beyond our own linguistic, geographic and social realms. The following chapter turns to the linguistic autofiction of Vassilis Alexakis. After establishing how Alexakis’ ambilingual practice – his alternation between writing in French and Greek – leads him to interrogate his own position within world literary exchanges, it analyses both his novel, Les Mots étrangers, and his collaboration on the bilingual anthology, Âtënë tî Bêafrîka. Paroles du cœur de l’Afrique, within the framework of an “uneven translingual event” (Helgesson & Kullberg). The final chapter considers the fact that Andreï Makine’s Le Testament français has come to be viewed as the archetypal French translingual novel. A reading of this novel alongside Makine’s pseudotranslations and pseudonymic works prompts an examination of the notion of translingualism as exophony, a voyage outside of the mother tongue, and of how such writing positions itself in relation to national, monolingual literary space.Previous studies of translingualism in a French context have tended to view translingual authors as language migrants, who abandon their mother tongue in favour of a monolingual literary production in French. Recent work has brought the focus back to the multilingual processes informing translingual creativity, but may have overestimated the capacity of such writing to transgress the monolingual paradigm. Drawing on work by critics such as Apter, Beecroft, Gramling and Yildiz, this dissertation shows how contemporary translingual poetics can be understood as at once the result of homogenizing forces which favour monolingual and “translatable” writing in major world languages, and as partaking in the emergence of new aesthetic practices seeking to register and respond to linguistic diversity in literature.
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| 4. |
- Fotedar, Sunney, 1989, et al.
(författare)
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A criterion space decomposition approach to generalized tri-objective tactical resource allocation
- 2023
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Ingår i: Computational Management Science. - : Springer Science and Business Media LLC. - 1619-697X .- 1619-6988. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a tri-objective mixed-integer linear programming model of the tactical resource allocation problem with inventories, called the generalized tactical resource allocation problem (GTRAP). We propose a specialized criterion space decomposition strategy, in which the projected two-dimensional criterion space is partitioned and the corresponding sub-problems are solved in parallel by application of the quadrant shrinking method (QSM) (Boland in Eur J Oper Res 260(3):873–885, 2017) for identifying non-dominated points. To obtain an efficient implementation of the parallel variant of the QSM we suggest some modifications to reduce redundancies. Our approach is tailored for the GTRAP and is shown to have superior computational performance as compared to using the QSM without parallelization when applied to industrial instances.
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| 5. |
- Fotedar, Sunney, 1989, et al.
(författare)
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A decision-making tool to identify routings for an efficient utilization of machining resources: the decision makers’ perspective
- 2020
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Ingår i: PLANs forsknings-och tillämpningskonferens.
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Konferensbidrag (refereegranskat)abstract
- In the aerospace industry, efficient management of machining capacity is crucial to meet the required service levels to customers (which includes, measures of quality and lead-times ) and keeps the tied-up working capital in check. The proposed decision-making tool, described in this paper, aims to combine information and knowledge of manufacturing and logistics experts in a company to improve flow of materials through the factory. The material flow situation is different for a large aerospace tier-1 supplier as opposed to flow-based manufacturing company; when there is no pandemic or natural calamity, having relatively stable demand due to long-term contract is common, but there exists short-term demand variability. There is a complex flow of products at GKN Aerospace, as the products share machining resources, thus, resulting in uneven loads at machines and sometimes excess loading at certain machines. This along with short-term demand variability results in long queues in-front of machines which contributes with the biggest share of the total lead-time. Thus, long waiting times at one/many machine/s is common and may lead to bottlenecks in many places in the production pipeline. So, there is potential benefit in having rerouting-flexibility for products which can help in reducing queuing. However, qualifying a product for a new machine is time-consuming activity, and thus, should be done few years in advance. We propose a mathematical model aimed at improving some of these deficiencies of commonly used methods by facilitating balanced resource loading levels, i.e. to provide more degrees of freedom to the planner to absorb demand variations. The output provided by the model includes production routings in each time period (quarter) for the next 4–5 years; new qualifications to be done by technical staff for allocation of part types/products to machines which are not yet qualified/used for a given product. We keep the resource loading levels that are above a given threshold as low as possible and reduce the time/money spent for qualifying new allocations.
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| 6. |
- Hultman, Hugo, et al.
(författare)
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Identification of variation sources for high precision fabrication in a digital twin context
- 2020
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Ingår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE). ; 2B-2020
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Konferensbidrag (refereegranskat)abstract
- The aerospace industry is increasing its focus on fabrication in manufacturing, foregoing large castings to instead assemble and join smaller parts into final products. This increases the total amount of geometrical variation introduced during the production process, since the unique variation from each individual part can add to a propagating effect putting the final assembled product outside of tolerance limits. Geometry assurance and variation simulation has traditionally been applied as a part of the design process to develop robust manufacturing concepts that are as insensitive as possible to variation. A concept for geometry assurance has been proposed where variation simulation is conducted for each individual assembly using real measurements from incoming parts, making it possible to make adaptive adjustments to production parameters to optimize results. It is however not feasible to measure and simulate every aspect of the process. This paper provides a summary of relevant sources of geometrical variation for a high precision fabrication process, based on input from a fabrication process in the aerospace industry. Variation sources are analyzed and discussed from an industrial perspective, putting them in the context of an actual fabrication process as well as in the context of digital twins for geometry assurance.
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| 7. |
- Hultman, Hugo, et al.
(författare)
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Predicting Geometrical Variation in Fabricated Assemblies Using a Digital Twin Approach Including a Novel Non-Nominal Welding Simulation
- 2022
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Ingår i: Aerospace. - : MDPI AG. - 2226-4310. ; 9:9
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Tidskriftsartikel (refereegranskat)abstract
- The aerospace industry faces constantly increasing demands on performance and reliability, especially within the vital area of engine development. New technologies are needed in order to push the limits of high precision manufacturing processes for the next generation of aircraft engines. An increased use of in-line data collection in manufacturing is creating an opportunity to individualize each assembly operation rather than treating them identically. Welding is common in this context, and the interaction between welding distortion and variation in part geometries is difficult to predict and manage in products with tight tolerances. This paper proposes an approach based on the Digital Twin paradigm, aiming to increase geometrical quality by combining the novel SCV (Steady-state Convex hull Volumetric shrinkage) method for non-nominal welding simulation with geometrical data collected from 3D scanning of parts. A case study is presented where two parts are scanned and then welded together into an assembly. The scan data is used as input for a non-nominal welding simulation, and the result of the simulation is compared directly to scan data from the real welded assembly. Three different welding simulation methods are used and assessed based on simulation speed and ability to predict the real welding result. The segmented SCV method for welding simulation shows promising potential for this implementation, delivering good prediction accuracy and high simulation speed.
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| 8. |
- Hultman, Hugo, et al.
(författare)
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Towards a digital twin setup for individualized production of fabricated components
- 2021
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Ingår i: ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE). ; 2B-2021
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Konferensbidrag (refereegranskat)abstract
- As the aerospace industry continues its shift towards digital manufacturing, an increased use of inline sensors and data collection is creating an opportunity to further optimize the production process. Measurements from individual parts make it possible to adapt each process to current conditions rather than running all processes nominally. This is sometimes described as individualized production as opposed to traditional mass production. The concept of a digital twin for manufacturing has recently gained more attention as a promising method for individualized production. A digital twin collects data from a real environment to create a virtual copy of a physical phenomenon, which can be used to predict how its real counterpart is going to behave. The approach has been proposed for a manufacturing environment where it would be used to predict the outcome of a production process. This could prove particularly useful for fabrication processes, a method used for making aero engine parts by joining large assemblies of smaller parts through welding. This paper presents functionalities that can be used to implement a digital twin in a high precision fabrication process, outlining different approaches for data collection, data analysis, and adaptive process adjustments. An example is shown where physical measurements are used to improve the predictive capabilities of a welding simulation in order to enable more accurate process adjustments.
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| 9. |
- Malakizadi, Amir, 1983, et al.
(författare)
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The role of microstructural characteristics of additively manufactured Alloy 718 on tool wear in machining
- 2021
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Ingår i: International Journal of Machine Tools and Manufacture. - : Elsevier BV. - 0890-6955. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to provide a fundamental understanding of the role of microstructural characteristics influencing tool wear when machining Alloy 718 fabricated using Powder Bed Fusion (PBF). The effects of preferred crystallographic orientation (texture), shape and distribution of grains, local misorientation, type and amount of precipitates as well as the type, size and amount of abrasive carbides, nitrides and oxides on tool wear are investigated in as-built condition and after the standard solutionising and double-aging treatment. The microstructures of workpiece materials and the surfaces of worn tools were examined using different material characterisation techniques, including Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). A dislocation-based approach was used to reveal the cumulative effects of the microstructural characteristics on deformation behaviour and the thermo-mechanical loads on the tools during cutting. The analyses suggest that texture and the extent of material work-hardening prior to the onset of crack formation markedly influence the amount of plastic work and thus heat generation when machining Electron Beam Powder Bed Fusion (EB-PBF) material. The higher heat generation in the cutting zones provokes thermally-induced wear mechanisms like diffusion-dissolution and oxidation. In addition, the larger amount of hard oxide inclusions present in EB-PBF material leads to higher wear by abrasion. In contrast to the prevailing experimental approaches in this field, the present investigation is built on a physics-based framework to understand the fundamental aspects that govern material deformation and heat generation in cutting and, consequently, tool wear mechanisms. This framework can be used for machinability assessment of any alloy manufactured by different additive manufacturing (AM) technologies and for optimising the process-chain, including printing strategies and thermal post-treatments, to improve the machinability of AM alloys by tailoring their microstructure.
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| 10. |
- Moberg, Christina, et al.
(författare)
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De unga gör helt rätt när de stämmer staten
- 2022
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Ingår i: Aftonbladet. - 1103-9000.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- 1 620 forskare och lärare i forskarvärlden: Vi ställer oss bakom Auroras klimatkrav
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| 11. |
- RAZANICA, SENAD, 1988, et al.
(författare)
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FE modeling and simulation of machining Alloy 718 based on ductile continuum damage
- 2020
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Ingår i: International Journal of Mechanical Sciences. - : Elsevier BV. - 0020-7403. ; 171
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Tidskriftsartikel (refereegranskat)abstract
- A novel model for rigid visco-plastic flow and continuous damage evolution is proposed for the modeling and simulation of chip formation of the alloy 718. The model draws from a recent thermodynamically consistent damage coupled to elasto-visco-plasticity framework for ductile failure, which is advanced to purely dissipative flow stress problems in the DEFORM 2D\texttrademark platform. As opposed to standard models with direct damage-plasticity coupling, the present model describes this coupling through a visco-plastic damage driving energy. The effective material response is described by the Johnson-Cook model where onset of damage evolution is controlled by a modified Cockcroft-Latham failure criterion, facilitating a flexible modeling of serrated chip formation. By comparing the proposed continuous damage degradation model to the damage drop method in DEFORM 2D\texttrademark, the role of ductile failure on the chip formation is investigated. The model is calibrated and validated against experimental machining tests, where both continuous and serrated chip formation is observed for the alloy 718 depending on the cutting speed. From the experiment, cutting forces, chip shapes and tool-chip contact lengths were analyzed and compared to the model response. A good agreement between model and experimental results is obtained.
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| 12. |
- Theissen, Nikolas Alexander, 1992-, et al.
(författare)
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Measurement for the identification of static and quasi-static rotational stiffness
- 2021
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Ingår i: Precision engineering. - : Elsevier BV. - 0141-6359 .- 1873-2372. ; 72, s. 215-223
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Tidskriftsartikel (refereegranskat)abstract
- Machine tool calibration can be employed to optimise tool path trajectories through on- and off-line compensation of anticipated deflections, which result from a process plan, and to assess the machine tools capability to comply with the geometric dimensions and tolerances of a process plan.This work presents a measurement for the identification of static and quasi-static rotational stiffness of a rotational joint of 5-axis machining centres. This work shall serve as a basis towards the calibration of translational as well as rotational stiffness of 5-axis machining centres. The novelty of this work lies partly in the measurement procedure for the quasi-static rotational stiffness, which relies on multiple circular trajectories, as well as in the comparison of the static and quasi-static rotational stiffness of machine tools, which is usually identified using finite element approaches. The measurement procedure for the static rotational stiffness consists of inducing a static load directly, from an overhead factory crane, to a single rotational joint and measuring its deflection with both three LVDTsLinear Variable Differential Transformers (LVDTs) as well as three Non-Contact Capacitive Probes (NCCPs). While the measurement for the quasi-static rotational stiffness induces quasi-static loads indirectly from the Loaded Double Ball Bar, with different magnitudes and radii from the axis of rotation, between the tool centre point and the machine tool table. The quasi-static measurement procedure measures the deflection with both three LVDTs as well as three NCCPs while the spindle tracks circular trajectories inscribed by the movement of the rotary axis. The measurement procedures are implemented in two case studies on 5-axis machining centres with significantly different kinematic configurations to be able to highlight and discuss the limitations of the applicability of the method. The presented method works well for machining centres with symmetric and acceptably with asymmetric structures due to the corresponding symmetry of the deflection field.Finally, the manuscript concludes with a contextualisation of the introduced measurement procedure towards fully calibrated machine tool models, i.e. translation and rotation as well as static and dynamic, which together with customised post-processors and process models, might form the future basis of a stiffness volumetric compensation system.
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