| 1. |
- Björnsson, Andreas
(författare)
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Automated layup and forming of prepreg laminates
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Composite materials like carbon fiber-reinforced polymers (CFRPs) present highly appealing material properties, as they can combine high strength with low weight. In aerospace applications, these properties help to realize lightweight designs that can reduce fuel consumption. Within the aerospace industry, the use of these types of materials has increased drastically with the introduction of a new generation of commercial aircraft. This increased use of CFRP drives a need to develop more rational manufacturing methods.For aerospace applications, CFRP products are commonly manufactured from a material called prepreg, which consists of carbon fibers impregnated with uncured polymer resin. There are two dominant manufacturing technologies for automated manufacturing using prepreg, automated tape layup and automated fiber placement. These two technologies are not suitable for all types of products, either due to technical limitations or a combination of high investment costs and low productivity. Automation alternatives to the two dominant technologies have been attempted, but have so far had limited impact. Due to the lack of automation alternatives, manual manufacturing methods are commonly employed for the manufacturing of complex-shaped products in low to medium manufacturing volumes.The research presented in this thesis aims to explore how automated manufacturing systems for the manufacturing of complex CFRP products made from prepreg can be designed so that they meet the needs and requirements of the aerospace industry, and are suitable for low to medium production volumes. In order to explore the area, a demonstrator-centered research approach has been employed. A number of demonstrators, in the form of automated manufacturing cells, have been designed and tested with industrial and research partners. The demonstrators have been used to identify key methods and technologies that enable this type of manufacturing, and to analyze some of these methods and technologies in detail. The demonstrators have also been used to map challenges that affect the development of enabling methods and technologies.Automated manufacturing of products with complex shapes can be simplified by dividing the process into two steps. Thin layers of prepreg are laid up on top of each other to form flat laminates that are formed to the desired shape in subsequent forming operations. The key methods and technologies required to automate such a system are methods and technologies for automated prepreg layup, the automated removal of backing paper and the forming of complex shapes. The main challenges are the low structural rigidity and tacky nature of prepreg materials, the extensive quality requirements in the aerospace industry and the need for the systems to handle a wide array of prepreg shapes.The demonstrators show that it is possible to automate the manufacturing of complexshaped products using automated layup and forming of prepreg laminates. Tests using the demonstrators indicate that it is possible to meet the quality requirements that apply to manual manufacturing of similar products.
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| 2. |
- Hällgren, Sebastian, 1971-
(författare)
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Some aspects on designing for metal Powder Bed Fusion
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM) using the Powder Bed Fusion (PBF) is a relatively new manufacturing method that is capable of creating shapes that was previously practically impossible to manufacture. Many think it will revolutionize how manufacturing will be done in the future. This thesis is about some aspects of when and how to Design for Additive Manufacturing (DfAM) when using the PBF method in metal materials. Designing complex shapes is neither easy nor always needed, so when to design for AM is a question with different answers depending on industry or product. The cost versus performance is an important metric in making that selection. How to design for AM can be divided into how to improve performance and how to improve additive manufacturability where how to improve performance once depends on product, company and customer needs. Using advanced part shaping techniques like using Lattices or Topology Optimization (TO) to lower part mass may increase customer value in addition to lowering part cost due to faster part builds and less powder and energy use. Improving PBF manufacturability is then warranted for parts that reach series production, where determining an optimal build direction is key as it affects many properties of PBF parts. Complex shapes which are designed for optimal performance are usually more sensitive to defects which might reduce the expected performance of the part. Non Destructive Evaluation (NDE) might be needed to certify a part for dimensional accuracy and internal defects prior use. The licentiate thesis covers some aspects of both when to DfAM and how to DfAM of products destined for series production. It uses design by Lattices and Topology Optimization to reduce mass and looks at the effect on part cost and mass. It also shows effects on geometry translation accuracies from design to AM caused by differences in geometric definitions. Finally it shows the effect on how different NDE methods are capable of detecting defects in additively manufactured parts.
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| 3. |
- Jansson, Anton, 1986-
(författare)
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More Than a Shadow : Computed Tomography Method Development and Applications Concerning Complex Material Systems
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The complexity of the components fabricated in today's industry is ever increasing. This is partly due to market pressure, but it is also a result from recent progress in fabrication technologies that open up new design possibilities. The increased use of additive manufacturing and multi-material systems, especially, has driven the complexity of parts to new heights. The new complex material systems bring benets in many areas such as; mechanical properties, weight reduction, and multifunctions. However, the increased complexity also makes inspection and dimensional control more dicult. In additive manufacturing, for example, internal features can be fabricated which cannot be seen or measured with conventional tools. There is thus a need for non-destructive inspection methods that can measure these geometries. Such a method is X-ray computed tomography. Computed tomography utilizes the X-rays ability to penetrate material to create 3D digital volumes of components. Measurements and material investigations can be performed in these volumes without any damage to the investigated component. However, industrial computed tomography is still not a fully mature method and there are many uncertainties associated with the investigation technique. In this work, a dual-energy computed tomography tool has been developed with the aim to increase the performance of computed tomography when investigating complex geometries and material combinations. This method has been applied to various phantoms and an industrial case. Also, in this work, complex lattice structures fabricated with additive manufacturing have been investigated and analysed using computed tomography. The results show that the new DECT method improves measurement results and can be utilized to inspect multi-material components. The results also show that computed tomography can be used successfully to gain knowledge about complex lattices.
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| 4. |
- Jonsson, Marie, 1979-
(författare)
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On Manufacturing Technology as an Enabler of Flexibility : Affordable Reconfigurable Tooling and Force-Controlled Robotics
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In order to survive in today’s global market many manufacturing companies seek flexibility to reduce product lead times and meet changing market demands. Manufacturing equipment forms the base of the production system and manufacturing technology with the capability to adapt to any changes in prerequisites is thus a key enabler of flexibility. Industrial robots and fixtures are common in all types of manufacturing. Robots are versatile re-programmable units capable of performing many tasks, such as welding, part transfer, etc. Industrial robots have traditionally been unable to handle disturbances and lack of constraints of input. This has led to manual operations often being preferred to automation when some level of flexibility is needed. One way to enhance manufacturing equipment’s capability to handle unknown events is to integrate different kinds of sensors to gain more knowledge of the manufacturing environment. Force sensors, for example, can be used to close the feedback loop and, together with an adequate control system, enable the robot to react to force stimuli. This is useful in manufacturing applications like assembly and deburring, which have previously been difficult to automate.Fixtures are devices that hold and position parts during a manufacturing process. Traditionally many fixtures have been dedicated, i.e. designed for a specific part and purpose. This means that fixtures have not been able to handle different products in the same unit, thus hindering flexibility. Sensors, like measurement systems, can be used together with fixtures to de-couple the structure of the fixture from the accuracy, which is the traditional approach to fixturing. This reasoning forms the base of the Affordable Reconfigurable Tooling (ART) concept, developed at Linköping University. The ART concept aims at increasing flexibility in manufacturing, while ensuring affordability and efficiency.This thesis explores how common manufacturing equipment, like industrial robots and fixtures, combined with sensor input, can enhance flexibility in manufacturing. The research shows that force-controlled robots, reacting to force stimuli, produce consistent results in assembly of compliant structures and in complex deburring. Force control also makes the system more robust, as it is able to handle variance in the assembled and deburred parts which adds to system flexibility. It also lessens the need for accuracy in other equipment used, such as grippers and fixtures, and makes programming easier and safer. Force control would, however, benefit if parameter tuning was simplified in order to fit an industrial environment and if presented user information is tailored for the intended user.Using measurement sensors to build fixtures, new ART devices aimed at increased flexibility in fixtures have been developed. These devices reduce the resources needed for fixture build and reconfiguring between products and also open up for making fixtures more active in manufacturing and similar to robots, while still being affordable. ART also reduces resources needed for design, as shown by the developed design aid programs. ART also supports concurrent design, as fixture specifications may be finalized before the product specifications are fully set.The overall results indicate that the explored sensors in combination with today’s emerging technologies can give additional benefits for applications like assembly and deburring and for fixtures. Furthermore, it is shown that it is possible to increase flexibility on different levels in a manufacturing system by using sensors in combination with industrial robots and fixtures.
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| 5. |
- Wiberg, Anton, 1991-
(författare)
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Towards Design Automation for Additive Manufacturing : A Multidisciplinary Optimization approach
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent decades, the development of computer-controlled manufacturing by adding materiallayer by layer, called Additive Manufacturing (AM), has developed at a rapid pace. The technologyadds possibilities to the manufacturing of geometries that are not possible, or at leastnot economically feasible, to manufacture by more conventional manufacturing methods. AMcomes with the idea that complexity is free, meaning that complex geometries are as expensiveto manufacture as simple geometries. This is partly true, but there remain several design rulesthat needs to be considered before manufacturing. The research field Design for Additive Manufacturing(DfAM) consists of research that aims to take advantage of the possibilities of AMwhile considering the limitations of the technique.Computer Aided technologies (CAx) is the name of the usage of methods and software thataim to support a digital product development process. CAx includes software and methodsfor design, the evaluation of designs, manufacturing support, and other things. The commongoal with all CAx disciplines is to achieve better products at a lower cost and with a shorterdevelopment time.The work presented in this thesis bridges DfAM with CAx with the aim of achieving designautomation for AM. The work reviews the current DfAM process and proposes a new integratedDfAM process that considers the functionality and manufacturing of components. Selectedparts of the proposed process are implemented in a case study in order to evaluate theproposed process. In addition, a tool that supports part of the design process is developed.The proposed design process implements Multidisciplinary Design Optimization (MDO) witha parametric CAD model that is evaluated from functional and manufacturing perspectives. Inthe implementation, a structural component is designed using the MDO framework, which includesComputer Aided Engineering (CAE) models for structural evaluation, the calculation ofweight, and how much support material that needs to be added during manufacturing. Thecomponent is optimized for the reduction of weight and minimization of support material,while the stress levels in the component are constrained. The developed tool uses methodsfor high level Parametric CAD modelling to simplify the creation of parametric CAD modelsbased on Topology Optimization (TO) results.The work concludes that the implementation of CAx technologies in the DfAM process enablesa more automated design process with less manual design iterations than traditional DfAM processes.It also discusses and presents directions for further research to achieve a fully automateddesign process for Additive Manufacturing.
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| 6. |
- Zekavat, Amir Reza, 1986-
(författare)
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Application of X-ray Computed Tomography for Assessment of Additively Manufactured Products
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM) is a novel method for fabricating parts from three-dimensional model data, usually by joining materials in layer upon layer fashion. The freedom of design in this method has resulted in new possibilities for fabrication of parts with complex geometries. Manufacturing nearnet- shape parts as well as geometrically complex components such as periodic cellular structures that are used in lightweight structural components, has made AM a promising manufacturing method in industry.Despite the numerous advantages of the AM methods, the imperfections associated with the manufacturing processes has limited the application of additively manufactured parts. Porosity and surface texture of AM parts especially those fabricated using Laser Powder Bed Fusion (LPBF) methods, have been studied in this thesis. It was observed that the mentioned imperfections have a considerable impact on the mechanical performance of thin-wall structures that are the constituting units of surface-based periodic cellular structures. The quality of internal structure in components fabricated using Fused Deposition Modelling (FDM) and its effect on the strength of those components were the other issues investigated in this thesis.In order to investigate the mechanical strength of AM parts, as the result of mentioned mesoscale imperfections, appropriate evaluation methods that are capable of quantitatively assessing these imperfections are required. X-ray Computed Tomography (CT), a non-destructive evaluation method, has shown high capabilities for providing useful and reliable geometrical information of both internal and external features of AM components. The challenges involved with the application of CT for assessment of AM component are also studied in this thesis.Apart from the contributions of this thesis on how CT may be used in AM field, the results of this thesis has provided insight into the design process of cellular structures. This thesis has provided essential information about the strength dependency of thin-walls as the result of mesoscale fabrication defects and how these defects are dependent on the selected material and design of the structure.
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| 7. |
- Anderberg, Staffan, 1981-
(författare)
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A study of process planning for metal cutting
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Process planning as a function for competitiveness is often neglected. However, as an intermediary between product development and manufacturing, it holds a key function in transforming product specifications and requirements into a producible process plan. Demands and requirements should be met concurrently as manufacturing costs and lead times are minimised. The focus of this thesis is the act of process planning, where the use of better methodologies, computer-aids and performance measurements are essential parts. Since process planning has the function of transforming demands and requirements, changing customer and regulative requirements are vital to regard. Since environmentally benign products and production increases in importance, the research presented in this thesis includes a CNC machining cost model, which relates machining costs to energy consumption. The presented results in this thesis are based on quantitative and qualitative studies in the metal working industry. This thesis has contributed to an enhanced understanding of process planning to achieve better performance and important areas for improvements. Despite a 50 year history of computerised process planning aids, few of these are used in the industry, where manual process planning activities are more common. Process planning aids should be developed around the process planner so that non-value adding activities, such as information management and documentation are minimised in order to allow more resources for value adding activities, such as decision making. This thesis presents a study of systematic process planning in relation to perceived efficiency. This correlation could however not be verified, which opens up for further studies of other possible explanations for process planning efficiency. Process planning improvements in the industry are difficult to make, since there is little focus on process planning activities and limited knowledge about actual performance hereof. This means that measures taken regarding process planning development are difficult to verify.
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| 8. |
- Jansson, Anton, 1986-
(författare)
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Only a Shadow : Industrial computed tomography investigation, and method development, concerning complex material systems
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The complexity of components fabricated in today's industry is ever increasing. This increase is partly due to market pressure but it is also a result from progress in fabrication technologies that opens up new possibilities. The increased use of additive manufacturing and multi-material systems, especially, has driven the complexity of parts to new heights. The new complex material systems brings benefits in many areas such as; mechanical properties, weight optimisation, and sustainability. However, the increased complexity also makes material integrity investigations and dimensional control more difficult. In additive manufacturing, for example, internal features can be fabricated which cannot be seen or measured with conventional tools. There is thus a need for non-destructive inspection methods that can measure these geometries. Such a method is X-ray computed tomography. Computed tomography utilizes the X-rays ability to penetrate material to create 3D digital volumes of components. Measurements and material investigations can be performed in these volumes without any damage to the investigated component. However, computed tomography in material science is still not a fully mature method and there are many uncertainties associated with the investigation technique. In the work presented in this thesis geometries fabricated by various additive manufacturing processes have been investigated using computed tomography. Also in this work, a dual-energy computed tomography tool has been developed with the aim to increase the measurement consistency of computed tomography when investigating complex geometries and material combinations.
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| 9. |
- Sundqvist, Jesper
(författare)
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Heat conduction effects during laser welding
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the invention of the laser in 1960, its use has been growing steadily. New laser sources with high beam power and high beam quality provide potential for further growth. High quality beams can be shaped by optical tools, such as scanners or Diffractive Optical Elements, DOE, to almost any beam shape, enabling innovative laser process solutions. For welding in particular, a tailored beam can be used to control the melt pool and to optimise the temperature field and cycle. For example, joining of electrical components like battery cells becomes more common due to the shift to electrical vehicles. This is a field of applications where laser welding with a tailored beam has high potential due to the need of tightly controlled design tolerances or processing temperatures and in turn electrical and mechanical properties. The research presented in the thesis encompasses the heat flow generated from tailored laser beams, the thermal effects on the weld shape and on other quality criteria, the generated residual stress and its influence on fatigue crack propagation. For the sake of simplicity, melt flow was not considered in the calculations, which was discussed, too. The first three papers apply predictive mathematical modelling for the temperature field while the fourth paper experimentally derives the thermally induced residual stress distribution back from measured fatigue crack propagation.Paper I contains a FEM-based numerical heat flow study of a conduction mode laser welding case where a C-shaped overlap joint is desired. The quality criteria demand the welding process to be tightly controlled in terms of laser power and pulse time. Contrary to expectations, the joint geometry can significantly deviate from the laser beam C shape. As a continuation, in Paper II various quantitative indicators were derived and studied as part of the numerical simulation, in order to identify a suitable beam shape and in turn a DOE-design.Paper III presents a semi-analytical mathematical model that was developed for the heat flow in pulsed conduction mode welding for spatially and temporally shaped laser beams. As an alternative to FEM, the model is fast due to its analytical nature, which enables iterative beam shape optimization and DOE-design. By studying different beam shapes and the induced temperature fields, the potential and limits of the model were demonstrated and discussed. Paper IV is a study on residual stress that is thermally induced during the heating and cooling cycle of laser keyhole welding. Acceleration measurement of the crack propagating across the weld during fatigue testing turned out to be a suitable method to derive the residual stress distribution along the crack, including its alteration during the cracking. Comparisons with FEM-based stress analysis provide a link back to the temperature field induced by the laser, which enables optimization, e.g. by beam shaping.
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