| 1. |
- Gomez-Gallegos, A. A., 1983-, et al.
(författare)
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A comparative study assessing the wear behaviour of different ceramic die materials during superplastic forming
- 2017
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Ingår i: Materialwissenschaft und Werkstofftechnik. - : Wiley-VCH Verlagsgesellschaft. - 0933-5137 .- 1521-4052. ; 48:10, s. 983-992
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Tidskriftsartikel (refereegranskat)abstract
- Superplastic forming is an advanced manufacturing process where metallic sheets are heated to their superplastic region to be then blow formed within a die set. The process allows for the forming of complex parts but it is typically restricted to low volume production and high value pieces. Despite their brittle nature, ceramic dies are a developing technology for superplastic forming as they offer lower production costs and shorter lead times than conventional metallic dies, thus reducing process costs. This work presents a method to assess ceramic die wear by means of a novel test rig developed a at the Advance Forming Research Centre of the University of Strathclyde, Scotland, UK where the superplastic forming die-part interaction can be replicated at laboratory scale. Controllable normal load tests at standard superplastic forming conditions on three different reinforced ceramic materials are carried out with a view to understanding their wear mechanisms and to ultimately identify methods to improve their wear resistance.
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| 2. |
- Gomez-Gallegos, A. A., 1983-, et al.
(författare)
-
Surface finish control by electrochemical polishing in stainless steel 316 pipes
- 2016
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Ingår i: Journal of Manufacturing Processes. - : Elsevier. - 1526-6125. ; 23, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical machining (ECM) is a non-conventional machining process which is based on the localised anodic dissolution of any conductive material. One of the main applications of ECM is the polishing of materials with enhanced characteristics, such as high strength, heat-resistance or corrosionresistance, i.e. electrochemical polishing. The present work presents an evaluation of the parameters involved in the ECM of Stainless Steel 316 (SS316) with the objective of predicting the resulting surface finish on the sample. The interest of studying ECM on SS316 resides on the fact that a repeatable surface finish is not easily achieved. ECM experimental tests on SS316 pipes of 1.5 (0.0381 m) diameter were conducted by varying machining parameters such as voltage, interelectrode gap, electrolyte inlet temperature, and electrolyte flow rate. The surface finish of the samples was then evaluated in order to find the significance of each of these parameters on the surface quality of the end product. Results showed that overvoltage, which is dependent on the interelectrode gap and the electrolyte temperature, is one of the main parameters affecting the surface finish; additionally there is a strong relationship between the resulting surface finish and the electrolyte flow. The interelectrode gap and inlet electrolyte temperature also affect the resulting surface finish but their influence was not so evident in this work. Finally, the variation of the electrolyte temperature during the process was found to have a great impact on the uniformity of the surface finish along the sample. We believe that this contribution enables the tailoring of the surface finish to specific applications while reducing manufacturing costs and duration of the ECM process.
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| 3. |
- Bylya, Olga, et al.
(författare)
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Al-Li Alloys : The Analysis of Material Behaviour during Industrial Hot Forging
- 2017
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Ingår i: International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom. - : Elsevier. ; , s. 7-12
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Konferensbidrag (refereegranskat)abstract
- Al-Li alloys are a promising class of aerospace materials that combine light weight with high strength, comparable to those of steels. In the case of critical components, it is well known that providing the required reliability is impossible without tailoring the output microstructure of the material. This, in turn, requires a clear understanding of the logic behind microstructure formation depending on the total processing history (especially temperature and strain-rate history). However, uniaxial isothermal laboratory tests provide very limited information about the material behaviour. Real forging processes, especially involving complex geometries, sometimes develop quite complicated temperature-strain-rate paths that vary across the deformed part. A proper analysis of the microstructural transformations taking place in the material under these conditions is therefore very important. In this paper, the correlation between the loading history and microstructural transformations was analysed for AA2099 alloy using the hot forging of a disk-shaped component at selected forging temperatures and strain rates. The obtained results were compared to industrial processing maps based on uniaxial tests.
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| 4. |
- Gomez-Gallegos, Ares Argelia, 1983-, et al.
(författare)
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3D multiphysics model for the simulation of electrochemical machining of stainless steel (SS316)
- 2018
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Ingår i: The International Journal of Advanced Manufacturing Technology. - : Springer. - 0268-3768 .- 1433-3015. ; 95, s. 2959-2972
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Tidskriftsartikel (refereegranskat)abstract
- In electrochemical machining (ECM)—a method that uses anodic dissolution to remove metal—it is extremely difficult to predict material removal and resulting surface finish due to the complex interaction between the numerous parameters available in the machining conditions. In this paper, it is argued that a 3D coupled multiphysics finite element model is a suitable way to further develop the ability to model the ECM process. This builds on the work of previous researchers and further claims that the overpotential available at the surface of the workpiece is a crucial factor in ensuring satisfactory results. As a validation example, a real-world problem for polishing via ECM of SS316 pipes is modelled and compared to empirical tests. Various physical and chemical effects, including those due to electrodynamics, fluid dynamic, and thermal and electrochemical phenomena, were incorporated in the 3D geometric model of the proposed tool, workpiece, and electrolyte. Predictions were made for current density, conductivity, fluid velocity, temperature, and crucially, with estimates of the deviations in overpotential. Results revealed a good agreement between simulation and experiment and these were sufficient not only to solve the immediate real problem presented but also to ensure that future additions to the technique could in the longer term lead to a better means of understanding a most useful manufacturing process.
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| 5. |
- Gomez-Gallegos, A. A., 1983-
(författare)
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Electrochemical machining: towards 3D simulation and application on SS316
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrochemical machining (ECM) is a non-conventional manufacturing process, which uses electrochemical dissolution to shape any conductive metal regardless of its mechanical properties and without leaving behind residual stresses or tool wear. Therefore, ECM can be an alternative for machining difficult-to-cut materials, complex geometries, and materials with improved characteristics, such as strength, heat-resistance or corrosion-resistance. Notwithstanding its great potential as a shaping tool, the ECM process is still not fully characterised and its research is an on-going process. Various phenomena are involved in ECM, e.g. electrodynamics, mass transfer, heat transfer, fluid dynamics and electrochemistry, which occur in parallel and this can lead to a different material dissolution rate at each point of the workpiece surface. This makes difficult an accurate prediction of the final workpiece geometry. This problem was addressed in the first part of the present thesis by developing a simulation model of the ECM process in a two-dimensional (2D) environment. A finite element analysis (FEA) package, COMSOL multiphysics® was used for this purpose due to its capacity to handle the diverse phenomena involved in ECM and couple them into a single solution. Experimental tests were carried out by applying ECM on stainless steel 316 (SS316) samples. This work was done in collaboration with pECM Systems Ltd® from Barnsley, UK. The interest of studying ECM on stainless steels (SS) resides on the fact that the application of ECM on SS typically results in various different surface finishes. The chromium in SS alloys usually induces the formation of a protective oxide film that prevents further corrosion of the alloy, giving the metal the special characteristic of corrosion resistance. This oxide film has low electrical conductivity; hence normal anodic dissolution often cannot proceed without oxide breakdown. Partial breakdown of the oxide film often occurs, which causes pits on the surface or a non-uniform surface finish. Therefore the role of the ECM machining parameters, such as interelectrode gap, voltage, electrolyte flow rate, and electrolyte inlet temperature, on the achievement of a uniform oxide film breakdown was evaluated in this work. Experimental results show that the resulting surface finish is highly influenced by the over-potential and current density, and by the characteristics of the electrolyte, flow rate and conductivity. The complexity of experimentally controlling these parameters emphasised the need for the development of a computational model that allows the simulation of the ECM process in full. The simulation of ECM in a three-dimensional (3D) environment is crucial to understand the behaviour of the ECM process in the real world. In a 3D model, information that was not visible before can be observed and a more detailed realistic solution can be achieved. Hence, in this work a computer aided design (CAD) software was used to construct a 3D geometry, which was imported to COMSOL Multiphysics® to simulate the ECM process, but this time in a 3D environment. This enhanced simulation model includes fluid dynamics, heat transfer, mass transfer, electrodynamics and electrochemistry, and has the novelty that an accurate computational simulation of the ECM process can be carry out a priori the experimental tests and allows the extraction of enough information from the ECM process in order to predict the workpiece final shape and surface finish. Moreover, this simulation model can be applied to diverse materials and electrolytes by modifying the input ECM parameters.
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| 6. |
- Gomez-Gallegos, A. A., 1983-, et al.
(författare)
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Studies on Ti54M Titanium Alloy for Application within the Aerospace Industry
- 2018
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Ingår i: Superplasticity in Advanced Materials - ICSAM 2018. - : Trans Tech Publications. - 9783035733457 - 9783035713459
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Since the development of the Ti54M titanium alloy in 2003, its application within the aerospace sector has gradually increased due to the combination of properties such as improved forgeability and machinability, low flow stress at elevated temperatures, and superplastic characteristics. However, for the successful exploitation of Ti54M a comprehensive understanding of its mechanical characteristics, microstructure stability, and superplastic behaviour is required. The superplastic forming of titanium alloys is characterised by high deformation at slow strain rates and high temperatures which influence the material microstructure, and in turn, determine the forming parameters. These mechanisms make the prediction of the material behaviour very challenging, limiting its application within the aerospace industry. Even though Ti54M has been commercially available for over 10 years, further studies of its mechanical and superplastic properties are still required with the aim of assessing its applicability within the aerospace industry as a replacement for other commercial titanium alloys. Therefore, in this work a study of the mechanical and superplastic properties of Ti54M, in comparison with other commercial titanium alloys used in the aerospace industry - i.e. Ti-6AL-4V, and Ti-6-2-4-2 - is presented. The final objective of this study, carried out at the Advanced Forming Research Centre (AFRC, University of Strathclyde, UK), is to obtain material data to calibrate and validate a model capable of estimating the behaviour and grain size evolution of titanium alloys at superplastic conditions.
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| 7. |
- Gomez-Gallegos, A. A., 1983-, et al.
(författare)
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Studies on titanium alloys for aerospace application
- 2018
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Ingår i: Diffusion and defect data, solid state data. Part A, Defect and diffusion forum. - : Trans Tech Publications. - 1012-0386 .- 1662-9507. ; 385, s. 419-423
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Tidskriftsartikel (refereegranskat)abstract
- Since the development of the Ti54M titanium alloy in 2003, its application within the aerospace sector has gradually increased due to the combination of properties such as improved forgeability and machinability, low flow stress at elevated temperatures, and superplastic characteristics. However, for the successful exploitation of Ti54M a comprehensive understanding of its mechanical characteristics, microstructure stability, and superplastic behaviour is required. The superplastic forming of titanium alloys is characterised by high deformation at slow strain rates and high temperatures which influence the material microstructure, and in turn, determine the forming parameters. These mechanisms make the prediction of the material behaviour very challenging, limiting its application within the aerospace industry. Even though Ti54M has been commercially available for over 10 years, further studies of its mechanical and superplastic properties are still required with the aim of assessing its applicability within the aerospace industry as a replacement for other commercial titanium alloys. Therefore, in this work a study of the mechanical and superplastic properties of Ti54M, in comparison with other commercial titanium alloys used in the aerospace industry - i.e. Ti-6AL-4V, and Ti-6-2-4-2 - is presented. The final objective of this study, carried out at the Advanced Forming Research Centre (AFRC, University of Strathclyde, UK), is to obtain material data to calibrate and validate a model capable of estimating the behaviour and grain size evolution of titanium alloys at superplastic conditions.
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