Latest Developments in Industrial Hybrid Machine Tools that Combine Additive and Subtractive Operations

Hybrid machine tools combining additive and subtractive processes have arisen as a solution to increasing manufacture requirements, boosting the potentials of both technologies, while compensating and minimizing their limitations. Nevertheless, the idea of hybrid machines is relatively new and there is a notable lack of knowledge about the implications arisen from their in-practice use. Therefore, the main goal of the present paper is to fill the existing gap, giving an insight into the current advancements and pending tasks of hybrid machines both from an academic and industrial perspective. To that end, the technical-economical potentials and challenges emerging from their use are identified and critically discussed. In addition, the current situation and future perspectives of hybrid machines from the point of view of process planning, monitoring, and inspection are analyzed. On the one hand, it is found that hybrid machines enable a more efficient use of the resources available, as well as the production of previously unattainable complex parts. On the other hand, it is concluded that there are still some technological challenges derived from the interaction of additive and subtractive processes to be overcome (e.g., process planning, decision planning, use of cutting fluids, and need for a post-processing) before a full implantation of hybrid machines is fulfilledSpecial thanks are addressed to the Industry and Competitiveness Spanish Ministry for the support on the DPI2016-79889-R INTEGRADDI project and to the PARADDISE project H2020-IND-CE-2016-17/H2020-FOF-2016 of the European Union's Horizon 2020 research and innovation program

Laser Metal Deposition enhancement by holistic simulation of powder mass flow and deposition into the melt pool

El contenido de los capítulos 3, 4 y 5 está sujeto a confidencialidad. 251 p.En el presente trabajo de investigación se ha desarrollado una metodología para la mejora del proceso de aporte por láser mediante la modelización del mismo. El problema se ha abordado en diferentes pasos. Primero de todo, se ha desarrollado un cabezal de aporte que cumple con todos los requerimientos del proceso mediante un software comercial de CFD. Posteriormente, se ha fabricado y validado el mismo. Además, con el objetivo de mejorar la eficiencia de la boquilla e incrementar la estabilidad del proceso, se ha desarrollado un sistema novedoso de regulación del caudal del polvo. El cabezal de aporte ha sido empleado satisfactoriamente para la reparación y fabricación de diversas piezas. En lo que respecta a la modelización, se ha desarrollado un modelo que considera los fenómenos fluido-dinámicos que se producen dentro del baño fundido generado por un haz láser. Una vez se ha validado el modelo, se ha empleado para evaluar la importancia de considerar u omitir el movimiento del material fundido. Los resultados obtenidos indican que la influencia del movimiento del material fundido es mínima en el proceso de aporte por láser y pueden ser omitidos sin que ello suponga una pérdida de precisión. Basándose en esta última afirmación, se ha desarrollado un modelo tridimensional que simula el proceso de aporte por láser al completo. Este modelo calcula la transferencia de calor por conducción dentro de la pieza y la geometría del material aportado. Además, en función de los ciclos de calentamiento y enfriamiento que sufre el material, es capaz de predecir las propiedades mecánicas resultantes, tales como dureza, microestructura o la formación de poros

Laser Metal Deposition enhancement by holistic simulation of powder mass flow and deposition into the melt pool

El contenido de los capítulos 3, 4 y 5 está sujeto a confidencialidad. 251 p.En el presente trabajo de investigación se ha desarrollado una metodología para la mejora del proceso de aporte por láser mediante la modelización del mismo. El problema se ha abordado en diferentes pasos. Primero de todo, se ha desarrollado un cabezal de aporte que cumple con todos los requerimientos del proceso mediante un software comercial de CFD. Posteriormente, se ha fabricado y validado el mismo. Además, con el objetivo de mejorar la eficiencia de la boquilla e incrementar la estabilidad del proceso, se ha desarrollado un sistema novedoso de regulación del caudal del polvo. El cabezal de aporte ha sido empleado satisfactoriamente para la reparación y fabricación de diversas piezas. En lo que respecta a la modelización, se ha desarrollado un modelo que considera los fenómenos fluido-dinámicos que se producen dentro del baño fundido generado por un haz láser. Una vez se ha validado el modelo, se ha empleado para evaluar la importancia de considerar u omitir el movimiento del material fundido. Los resultados obtenidos indican que la influencia del movimiento del material fundido es mínima en el proceso de aporte por láser y pueden ser omitidos sin que ello suponga una pérdida de precisión. Basándose en esta última afirmación, se ha desarrollado un modelo tridimensional que simula el proceso de aporte por láser al completo. Este modelo calcula la transferencia de calor por conducción dentro de la pieza y la geometría del material aportado. Además, en función de los ciclos de calentamiento y enfriamiento que sufre el material, es capaz de predecir las propiedades mecánicas resultantes, tales como dureza, microestructura o la formación de poros

A novel numerical framework for simulation of multiscale spatio-temporally non-linear systems in additive manufacturing processes.

New computationally efficient numerical techniques have been formulated for multi-scale analysis in order to bridge mesoscopic and macroscopic scales of thermal and mechanical responses of a material. These numerical techniques will reduce computational efforts required to simulate metal based Additive Manufacturing (AM) processes. Considering the availability of physics based constitutive models for response at mesoscopic scales, these techniques will help in the evaluation of the thermal response and mechanical properties during layer-by-layer processing in AM. Two classes of numerical techniques have been explored. The first class of numerical techniques has been developed for evaluating the periodic spatiotemporal thermal response involving multiple time and spatial scales at the continuum level. The second class of numerical techniques is targeted at modeling multi-scale multi-energy dissipative phenomena during the solid state Ultrasonic Consolidation process. This includes bridging the mesoscopic response of a crystal plasticity finite element framework at inter- and intragranular scales and a point at the macroscopic scale. This response has been used to develop an energy dissipative constitutive model for a multi-surface interface at the macroscopic scale. An adaptive dynamic meshing strategy as a part of first class of numerical techniques has been developed which reduces computational cost by efficient node element renumbering and assembly of stiffness matrices. This strategy has been able to reduce the computational cost for solving thermal simulation of Selective Laser Melting process by ~100 times. This method is not limited to SLM processes and can be extended to any other fusion based additive manufacturing process and more generally to any moving energy source finite element problem. Novel FEM based beam theories have been formulated which are more general in nature compared to traditional beam theories for solid deformation. These theories have been the first to simulate thermal problems similar to a solid beam analysis approach. These are more general in nature and are capable of simulating general cross-section beams with an ability to match results for complete three dimensional analysis. In addition to this, a traditional Cholesky decomposition algorithm has been modified to reduce the computational cost of solving simultaneous equations involved in FEM simulations. Solid state processes have been simulated with crystal plasticity based nonlinear finite element algorithms. This algorithm has been further sped up by introduction of an interfacial contact constitutive model formulation. This framework has been supported by a novel methodology to solve contact problems without additional computational overhead to incorporate constraint equations averting the usage of penalty springs

Computational Multiphase Fluid Dynamics Analyses and Systems-Level Model Development for a Reactor Core Isolation Cooling System Terry Turbine

The Reactor Core Isolation Cooling (RCIC) system found in certain boiling water reactor (BWR) power plants is intended to provide make-up coolant to the reactor pressure vessel (RPV) when it is isolated from the power-producing steam turbine and condenser. Since the Fukushima-Daiichi nuclear power plant accident in March of 2011, the RCIC system has drawn special attention from members of the nuclear industry and government regulators for its apparent role in removing residual decay heat at units 2 and 3 for far longer – 70 and 20 hours, respectively - than the 4 to 8 hours typically credited. The RCIC system in units 2 and 3 mitigated severe accident progression under circumstances well outside its own design basis, delaying core damage for a time. These observations suggest the RCIC system is perhaps a more robust and capable safeguard against core damage than previously thought, especially in the context of beyond-design-basis accidents like short-term or long-term station blackout events. As such, the RCIC system merits further study in pursuit of an increased level of understanding. If better analytical methods are developed and applied, the findings may lead to revised severe accident management strategies and more resilient nuclear power plants in the United States and abroad. The goals of this dissertation are essentially to develop, implement, apply, and validate sufficiently detailed mathematical models of the RCIC system that it may be better understood. This analysis occurs at two disparate levels of physical detail: the computational multiphase fluid dynamics (CMFD) level and the systems level. For CMFD level analyses, a quasi-two-fluid dispersed phase flow model was developed for implementation into STAR-CCM+. Results were validated to the extent possible via experimental benchmarks. Data useful for systems level modeling purposes was obtained from CMFD, including several factors for MELCOR turbine velocity stage and pressure stage modeling. For systems level analyses, RCIC system Terry turbine mathematical models (for the pressure and velocity stages) were developed for implementation into MELCOR as was a new centrifugal pump model (homologous pump model). New systems-level model capabilities were demonstrated with example problems. Some important observations were made regarding RCIC system performance under off-normal conditions, namely that: 1) the RCIC turbine could be capable of operating with a wide-open governor valve without reaching its mechanical over-speed set-point, and 2) the RCIC system could be capable of self-regulating under two-phase flow conditions resulting from a cyclic pattern of reactor pressure vessel re-fill and over-fill. The new MELCOR models developed herein will certainly enable users to investigate RCIC system thermal-hydraulic response in greater detail and with higher fidelity

3d Scanning And The Impact Of The Digital Thread On Manufacturing And Re-Manufacturing Applications

3D laser line scanners are becoming a powerful technology for capturing point cloud datasets and collecting dimensional information for many objects. However, the use of point cloud is limited due to many factors. These include the lack of on deep understanding of the effect of point cloud parameters on scan quality. This knowledge is critical to gaining an understanding of the measurement in point cloud. Currently, there are no adequate measurement procedures for 3D scanners. There is a need for standardized measurement procedures to evaluate 3D scanner accuracy due to uncertainties in 3D scanning, such as surface quality, surface orientation and scan depth [6]. The lack of standardized procedures does not allow the technology to be fully automated and used in manufacturing facilities that would allow 100% in-line inspection. In this dissertation I worked on accomplishing four tasks that will achieve the objective of having a standardized measurement procedure that is critical to develop an automated laser scanning system to avoid variations and have consistent data capable of identifying defects. The four tasks are: (1) linking the robot workspace with the scanner workspace; (2) studying the effect of the scanning speed and the resolution on point cloud quality by conducting an experiment with systematically varied scan parameters on scan quality; (3) studying the overall error of that is associated with the transformation of the point cloud in a remanufacturing facility using additive manufacturing. The parameters that were tested are the effect of view angle, standoff distance, speed, and resolution. Knowing the effect of these parameters is important in order to generate the scan path that provides the best coverage and quality of points collected. There is also a need to know the impact of all the scanning parameters especially the speed and the resolution; (4) modeling a machine learning tool to optimize the parameters of different scanning techniques after collecting the scanning results to select the optimal ones that provide the best scan quality. With the success of this work, the advancement and practice of automated quality monitoring in manufacturing will increase

Supportless Fabrication, Experimental, and Numerical Analysis of the Physical Properties for a Thin-Walled Hemisphere

Although multi-axis bead deposition-based additive manufacturing processes have been investigated in many aspects in the literature, a general process planning approach to address collision detection and prevention still needs to be developed to fabricate complex thin-wall geometries in a supportless fashion. In this research, an algorithm is presented that partitions the surfaces of the part and finds the appropriate tool orientation for each partition to avoid collisions. This algorithm is applied to segment the surface of a thin-wall hemisphere dome and fabricate it without the need of support structures. Two main fabrication strategies are developed: wedge-shaped partitioning, and a rotary toolpath. A five-axis toolpath and a 2+1+1-axis toolpath is introduced to fabricate the partitioned build scenarios. A rotary (1+3-axis) toolpath is also developed. It is concluded that planar slicing brings limitations to reduce the number of partitions that can be modified by a constant step over toolpath. On one hand, the partitioning strategy provides an opportunity to fabricate geometries in a supportless fashion by direct energy deposition additive manufacturing, on the other hand, it introduces physical properties challenges such as surface roughness and hardness variations. Process planning, data collection, and experimental/numerical procedures are implemented to investigate the surface roughness variations (Ra measurement) of fabricated domes. Hence, two solutions are developed using Matlab programming. A mount solution uses the magnified pictures of the exposed surface edges of mount samples as input data. The other solution uses a 3D point cloud of the surface. The innovation of the 3D point cloud solution is the distance factor that is applied in the calculations. The results of this solution are compared to the mount solution. Since the input data of the mount solution is more accurate, the results are more reliable than the 3D point cloud method. The Ra variation diagrams show lower Ra values for the 5-axis sample and the highest values for the rotary sample. Large surface irregularities are noticed at the transition points between partitions, which escalates the roughness values drastically in the region. The sudden alteration of the tool orientation between partitions causes these surface irregularities. Additionally, process planning, data collection, and experimental/numerical analyses are developed to explore hardness variations of the fabricated domes along the slicing direction. The hardness diagram of the 2+1+1-axis sample shows a recognizable pattern for partitions 2-4. The hardness is around 200 (HV) within the partitions but drops to 150 (HV) at the transition points between partitions. Partitions 5-8 show a less recognizable pattern. Although the rotary sample is fabricated in 3 intermittent fabrication sections, it does not show any significant pattern related to the sectioning. The statistical analysis of the hardness shows the highest standard deviation for the 5-axis sample and the least for the rotary one. Finite element analysis of the hardness and residual stress are performed by the ESI Sysweld software for 144 beads of the 2+1+1-axis sample. To reduce the calculation time (a factor of 15 times), a variable mesh size of the beads and substrate are introduced. This means that the element size of the beads grows for the regions farther from the measurement region. The resultant hardness diagram predicts the peak and valley of the experimental diagram for the partitions 1-4, but it misses some patterns for partitions 5-8. Fast Fourier transformation analyses of the surface roughness and experimental/numerical hardness data show a repetitive pattern by the wavelength of the partition length. The preparation time and accuracy of the finite element analysis results reveal that an experimental fabrication and measurement test is preferred at this time, or a new method of numerical analysis is required. This research clearly illustrates the challenges associated with building a complex component and understanding its characteristics. On one hand, splitting the part geometry by different partitioning shapes facilitates the fabrication of the geometries in a supportless fashion. However, this fabrication strategy introduces inconsistency in the mechanical properties. Hardness variations generated by a partitioning strategy needs to be dealt with (possibly by a post-heat treatment). Surface quality at the transient points needs to be investigated more. This foundational research highlights the process planning challenges associated with metal bead based deposition processes, and highlights relevant challenges for similar process families

Internationales Kolloquium über Anwendungen der Informatik und Mathematik in Architektur und Bauwesen : 20. bis 22.7. 2015, Bauhaus-Universität Weimar

The 20th International Conference on the Applications of Computer Science and Mathematics in Architecture and Civil Engineering will be held at the Bauhaus University Weimar from 20th till 22nd July 2015. Architects, computer scientists, mathematicians, and engineers from all over the world will meet in Weimar for an interdisciplinary exchange of experiences, to report on their results in research, development and practice and to discuss. The conference covers a broad range of research areas: numerical analysis, function theoretic methods, partial differential equations, continuum mechanics, engineering applications, coupled problems, computer sciences, and related topics. Several plenary lectures in aforementioned areas will take place during the conference. We invite architects, engineers, designers, computer scientists, mathematicians, planners, project managers, and software developers from business, science and research to participate in the conference

Aeronautical engineering: A continuing bibliography with indexes (supplement 296)

This bibliography lists 592 reports, articles, and other documents introduced into the NASA scientific and technical information system in Oct. 1993. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics