| 1. |
- Goldhahn, Joerg, et al.
(författare)
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Evidence for anti-osteoporosis therapy in acute fracture situations-Recommendations of a multidisciplinary workshop of the International Society for Fracture Repair
- 2010
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Ingår i: BONE. - : Elsevier BV. - 8756-3282. ; 46:2, s. 267-271
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Tidskriftsartikel (refereegranskat)abstract
- The International Society for Fracture Repair convened a multidisciplinary workshop to assess the current evidence around the interaction between anti-osteoporosis drugs and the healing of incident fractures, with a view to making recommendations for clinical practice. The consensus was that there is no evidence-based reason to withhold anti-resorptive therapy while a fracture heals, whether or not the patient was taking such therapy when the fracture occurred. The workshop also considered existing models of service provision for secondary prevention and concluded that the essential ingredient for reliable delivery is the inclusion of a dedicated coordinator role. Several unresolved issues were defined as subjects for further research, including the question of whether continuous long-term administration of anti-resorptives may impair bone quality. The rapidly changing area requires re-assessment of drugs and their interaction with fracture healing in the near future.
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| 2. |
- Leidermark, Daniel, 1980-, et al.
(författare)
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The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen
- 2012
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 51:1, s. 273-280
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Tidskriftsartikel (refereegranskat)abstract
- Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g.gas turbine components, where great care must be given with respect to high temperature fatigue. Due tothe large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As aconsequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigatethis variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens,where placements and orientations of the grains were randomised. Furthermore, each grain wasmodelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion infatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-basesuperalloys may show a considerable variation, which cannot be captured by one single deterministicanalysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitudethat it needs to be taken into account in industrial applications where highly stressed coarse grainedmaterials are used.
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| 3. |
- Asnafi, Nader, 1960-, et al.
(författare)
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3D Metal Printing from an Industrial Perspective : Product Design, Production and Business Models
- 2018
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Ingår i: Metal Additive Manufacturing Conference 2018 Proceedings. - Vienna, Austria : ASMET. ; , s. 304-313, s. 304-313
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Konferensbidrag (refereegranskat)abstract
- This paper is focused on automotive stamping tools and dies and the impact of 3D metal printing and metals related 3D printing on design and production of such tools and dies. The purpose has been to find out the current industrial potential of 3D printing, as far lead time, costs, shapes, material usage, metal piece size, surface roughness, hardness, strength, and machinability are concerned. The business transformational impact of 3D printing is also addressed in this paper. The obtained results show that the lead time can be halved, the costs are somewhat higher, and the strength, hardness, surface roughness and machinability of the 3D printed metallic tools and dies are as good as those of the conventionally made. The maximum size of a metal piece that can be 3D printed today by Powder Bed Fusion (PBF) is in the best case 500 mm x 500 mm x 500 mm. 3D printing can also be used to make the pattern used to make the mold box in iron and steel casting. It is also possible to eliminate the casting pattern, since the mold box can be 3D printed directly. All this has started to have a large business impact and it is therefore of great significance to outline and execute an action plan almost immediately.
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| 4. |
- Asnafi, Nader, 1960-, et al.
(författare)
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3D Metal Printing from an Industrial Perspective : Product Design, Production, and Business Models
- 2019
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Ingår i: Berg- und Huttenmännische Monatshefte (BHM). - Vienna : Springer. - 0005-8912 .- 1613-7531. ; 164:3, s. 91-100
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Tidskriftsartikel (refereegranskat)abstract
- This paper is focused on automotive stamping tools and dies as well as the impact of 3D metal printing and metals related 3D-printing on design and production of such tools and dies. The purpose has been to find out the current industrial potential of 3D-printing as far as lead time, costs, shapes, material usage, metal piece size, surface roughness, hardness, strength, and machinability are concerned. The business transformational impact of 3D-printing is also addressed in this paper. The obtained results show that the lead time can be halved, the costs are somewhat higher, and the strength, hardness, surface roughness, and machinability of the 3D-printed metallic tools and dies are as good as those of the conventionally made. The maximum size of a metal piece that can be 3D-printed today by Powder Bed Fusion (PBF) is, in the best case, 500 mm × 500 mm × 500 mm. 3D-printing can also be used for the pattern to make the mold box in iron and steel casting. It is also possible to eliminate the casting pattern, since the mold box can be 3D-printed directly. All this has started to have a large business impact, and it is therefore of great significance to outline and execute an action plan almost immediately.
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| 5. |
- Asnafi, Nader, 1960-, et al.
(författare)
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Automotive Stamping Tools & Dies and Injection Mold made by Additive Manufacturing through Laser-based Powder Bed Fusion
- 2019
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Ingår i: Metal Additive Manufacturing Conference.
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Konferensbidrag (refereegranskat)abstract
- Design and production of tools, dies and moulds are two important steps in the development of new components/products. These steps determine both the lead time (Time-To-Production/-Market) and the size of the investments required to start the production. This paper deals with design and production of stamping tools & dies for sheet metal components and injection moulds for plastic components. Laser-based Powder Bed Fusion (LPBF) is the additive manufacturing (henceforth even called 3D printing) method used in this investigation.The stamping tools & dies should withstand the requirements set in stamping of hot-dip galvanized DP600. Solid and topology optimized forming and cutting/blanking/trimming tools made in maraging steel (DIN 1.2709) by LPBF are approved/certified for stamping of 2 mm thick DP600. A working station in a progressive die used for stamping of 1 mm thick DP600 is 3D-printed in DIN 1.2709, both with a honeycomb inner structure and after topology optimization, with successful results. 3D printing results in a significant lead time reduction and improved tool material efficiency. The cost for 3D-printed stamping tools and dies is somewhat higher than the cost of those made conventionally. DIN 1.2709 is certified in this study as tool material for stamping of hot-dip galvanized DP600.The core (inserts) of an injection mould is 3D-printed in DIN 1.2709, conformal cooling optimized and 3D-printed in Uddeholm AM Corrax, and compared with the same core made conventionally. Additive manufacturing results in localized tool production and lower total costs. The cooling and cycle time can be improved significantly, if the injection moulding core (inserts) is optimized and 3D-printed in Uddeholm AM Corrax. The best results are obtained, if the 3D-printed core is NOT only an optimized copy of the conventionally designed and manufactured version. The best results are obtained, if the core is redesigned to utilize the full potential of 3D printing.This paper accounts for the results obtained in the above-mentioned investigations.
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| 6. |
- Asnafi, Nader, 1960-, et al.
(författare)
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Design and Validation of 3D-Printed Tools for Stamping of DP600
- 2019
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Ingår i: 38th International Deep Drawing Research Group Annual Conference, IDDRG 2019. - : Institute of Physics Publishing (IOPP).
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Konferensbidrag (refereegranskat)abstract
- This paper is focused on automotive stamping tools & dies and the impact of 3D metal printing on design and production of such tools & dies. Forming (U-bend) and trimming/cutting/blanking tools & dies designed both conventionally and by topology optimization were 3D-printed, using Laser-based Powder Bed Fusion (LPBF), in the maraging steel DIN 1.2709. These 3D-printed tools were then used to form (U-bend) and trim/cut/blank 2-mm thick hot-dip galvanized DP600. An approval of the forming tool required that 50,000 U-bends were formed in 2-mm thick DP600 without any surface scratches on the sheet metal part. An approval of the trimming/cutting/blanking tool required 100,000 trimming strokes with this tool, where the maximum (sheet metal) burr height was lower than 0.2 mm (lower than 10% of the sheet thickness (2 mm in this study)). The 3D-printed forming and trimming/cutting/blanking tools & dies - both the conventionally designed and the topology optimized versions – managed the criteria mentioned above and were therefore approved. The approval means that these concepts can now be used to make production stamping tools and dies. This paper describes the topology optimization, the forming & trimming/cutting/blanking testing, the results yielding an approval of the 3D-printed tool concepts, and the 3D-printed production tools for stamping of DP600.
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| 7. |
- Asnafi, Nader, 1960-, et al.
(författare)
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Production Tools Made by Additive Manufacturing Through Laser-based Powder Bed Fusion
- 2020
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Ingår i: Berg- und Huttenmännische Monatshefte (BHM). - : Springer. - 0005-8912 .- 1613-7531. ; 165:(3), s. 125-136
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the design and production of stamping tools and dies for sheet metal components and injection molds for plastic components. Laser-based Powder Bed Fusion (LPBF) is the additive manufacturing method used in this investigation. Solid and topology optimized stamping tools and dies 3D-printed in DIN 1.2709 (maraging steel) by LPBF are approved/certified for stamping of up to 2‑mm thick hot-dip galvanized DP600 (dual-phase steel sheet). The punch in a working station in a progressive die used for stamping of 1‑mm thick hot-dip galvanized DP600 is 3D-printed in DIN 1.2709, both with a honeycomb inner structure and after topology optimization, with successful results. 3D printing results in a significant lead time reduction and improved tool material efficiency. The cost of 3D-printed stamping tools and dies is higher than the cost of those made conventionally. The core (inserts) of an injection mold is 3D-printed in DIN 1.2709, conformal cooling optimized and 3D-printed in Uddeholm AM Corrax, and compared with the same core made conventionally. The cooling and cycle time can be improved, if the injection molding core (inserts) is optimized and 3D-printed in Uddeholm AM Corrax. This paper accounts for the results obtained in the above-mentioned investigations.
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| 8. |
- Aspenberg, David, et al.
(författare)
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An evaluation of the statistics of steel material model parameters
- 2012
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Ingår i: Journal of Materials Processing Technology. - : Elsevier. - 0924-0136 .- 1873-4774. ; 212:6, s. 1288-1297
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Tidskriftsartikel (refereegranskat)abstract
- In robustness studies, variations of material properties are often represented by simple assumptions, such as scaling of stress-strain relations, often due to lack of knowledge or deeper understanding of the material physics and the material model applied. By performing material characterisation tests on several batches of a DP600 steel and fitting a phenomenological material model to each batch, this paper studies the dispersion of material model parameters, as well as correlations between both experimental and model parameters. It is concluded that some of the charcterisation tests may be omitted in the future, due to correlations found between parameters. The results may also be applied in a robustness study by inversely using the retrieved statistics to generate reasonable new sets of material model parameters. The methodology presented may be adopted for any other type of material characterisation process.
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| 9. |
- Aspenberg, David, et al.
(författare)
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Robust optimisation of front members in a full frontal car impact
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In the search of a lightweight design of automobiles, it is necessary to assure that a robust crashworthiness performance is achieved. Structures that are optimised to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimisation process. This paper presents an approach to optimisation where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using Artifical Neural Networks and polynomials, respectively. The features of the robust optimisation approach are displayed in an analytical example, and further demonstrated in a large scale design example of front side members of a car. Different optimisation formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimisation puts higher demands on the FE model performance than normally.
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| 10. |
- Aspenberg, David, 1979-
(författare)
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Robust optimisation of structures : Evaluation and incorporation of variations in simulation based design
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the robustness of structures considering various uncertainties. The overall objective is to evaluate and develop simulation based design methods in order to find solutions that are optimal both in the sense of handling typical load cases and minimising the variability of the response, i.e. robust optimal designs. Conventionally optimised structures may show a tendency of being sensitive to small perturbations in the design or loading conditions. These variations are of course inevitable. To create robust designs, it is necessary to account for all conceivable variations (or at least the influencing ones) in the design process. The thesis is divided into two parts. The first part serves as a theoretical background for this work. It includes introductions to the concept of robust design, basic statistics, optimisation theory and metamodelling. The second part consists of five appended papers on the topic.The first and third papers focuse on the evaluation of robustness, given some dispersions in the input data. Established existing methods are applied, and for paper three, comparisons with experimentally evaluated dispersions on a larger system are made.The second and fourth paper introduce two new approaches to perform robust optimisation, i.e. optimisations where the mean performance and the robustness in the objectives are simultaneously optimised. These methods are demonstrated both on an analytical example and on a Finite Element model design example. The fifth paper studies the variations in mechanical properties between several different batches of the same steel grade. A material model is fitted to each batch of material, whereby dispersions seen in test specimens are transferred to material model parameter variations. The correlations between both test and material model parameters are studied.
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