| 1. |
- Adegoke, Olutayo
(författare)
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Processability of Laser Powder Bed Fusion of Alloy 247LC : Influence of process parameters on microstructure and defects
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about laser powder bed fusion (L-PBF) of the nickel-based superalloy: Alloy 247LC. Alloy 247LC is used mainly in gas turbine blades and processing the blades with L-PBF confers performance advantage over the blades manufactured with conventional methods. This is mainly because L-PBF is more suitable, than conventional methods, for manufacturing the complex cooling holes in the blades. The research was motivated by the need for academia and industry to gain knowledge about the processability of the alloy using L-PBF. The knowledge is essential in order to eventually solve the problem of cracking which is a major problem when manufacturing the alloy. In addition, dense parts with low void content should be manufactured and the parts should meet the required performance. Thus, the thesis answered some of the important questions related to process parameter-microstructure-defect relationships.The thesis presented an introduction in chapter 1. A literature review was made in chapter 2 to 4. In chapter 2, the topic of additive manufacturing was introduced followed by an overview of laser powder bed fusion. Chapter 3 focused on superalloys. Here, a review was made from the broader perspective of superalloys but was eventually narrowed down to the characteristics of nickelbased superalloys and finally Alloy 247LC. Chapter 4 reviewed the main research on L-PBF of Alloy 247LC. The methodology applied in the thesis was discussed in chapter 5. The thesis applied statistical design of experiments to show the influence of process parameters on the defects and microstructure, so a detail description of the method was warranted. This was given at the beginning of chapter 5 and followed by the description of the L-PBF manufacturing and the characterization methods. The main results and discussions, in chapter 6, included a preliminary investigation on how the process parameters influenced the amount of discontinuity in single track samples. This was followed by the results and discussions on the investigation of voids, cracks and microhardness in cube samples (detail presentation was given in the attached paper B). Finally, the thesis presented results of the microstructure obtainable in L-PBF manufactured Alloy 247LC. The initial results of the microstructure investigation were presented in paper A.
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| 2. |
- Agic, Adnan, 1967-
(författare)
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Analysis of entry phase in intermittent machining
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cutting forces and vibrations are essential parameters in the assessment of a cutting process. As the energy consumption in the machining process is directly affected by the magnitude of the cutting forces it is of vital importance to design cutting edges and select process conditions that will maintain high tool performance through reduced energy consumption. The vibrations are often the cause of poor results in terms of accuracy, low reliability due to sudden failures and bad environmental conditions caused by noise. The goal of this work is to find out how the cutting edge and cutting conditions affect the entry conditions of the machining operation. This is done utilizing experimental methods and appropriate theoretical approaches applied to the cutting forces and vibrations. The research was carried out through three main studies beginning with a force build-up analysis of the cutting edge entry into the workpiece in intermittent turning. This was followed by a second study, concentrated on modelling of the entry phase which has been explored through experiments and theory developed in the first study. The third part was focused on the influence of the radial depth of cut upon the entry of cutting edge into the workpiece in a face milling application. The methodology for the identification of unfavourable cutting conditions is also explained herein. Important insights into the force build-up process help addressing the correlation between the cutting geometries and the rise time of the cutting force. The influence of the nose radius for a given cutting tool and workpiece configuration during the initial entry is revealed. The critical angle i.e. the position of the face milling cutter that results in unfavourable entry conditions has been explained emphasizing the importance of the selection of cutting conditions. Finally, the theoretical methods utilized for the evaluation of the role of cutting edge geometry within entry phase dynamics has been explored. This has revealed the trends that are of interest for selection of cutting conditions and cutting edge design.
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| 3. |
- 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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| 4. |
- Aryal, Pradip
(författare)
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Gas Metal Arc Melt Pool Modelling : Effect of welding position and electromagnetic force mode
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gas metal arc is a high-efficiency and widely used heat source for metal processing applied predominantly in welding and additive manufacturing. In this study, it was applied to welding. It offers high productivity, low production and investment cost, as well as suffers from some drawbacks such as humping or undercut when welding large parts that are curved and impose changing the orientation of the welding torch along the joint path. Deeper process understanding was therefore sought to mitigate these drawbacks. The difficulty is then the non-lineardependence of the process to the welding parameters and material properties. Besides, visual observation of this process is also difficult. For instance, the elevated temperature and the intense radiative emission from the electric arc, smoke, spatter, as well as the non-transparency of the processed alloy can hinder in-process observation or limit it. Process simulation provides a complementary means to reach process knowledge. It was thus the approach used in this study. For this, a thermo-fluid melt pool model that can predict melting and solidification, track free surface deformation, metal transfer, and coalescence with the melt pool was developed. Two main research questions were identified and addressed.The first one led to studying the effect of the substrate orientation during multilayer welding of a V-groove joint with INVAR and gas metal arc. It was foundthat the force balance in the melt pool changes significantly when the workpieceorientation is changed, resulting in distinct melt flow patterns, melt pool and bead geometries, and in some conditions defect initiation such as humping, undercut, and lack of fusion. As a result, multi-layer welding with flat substrate and downhill welding of a 20◦ inclined substrate are recommended with these process conditions. On the contrary, welding of a side inclined substrate and uphill welding of a 20◦ inclined substrate are not recommended. The second question gave rise to the comparative investigation of the three electromagnetic force models commonly used when modelling a melt pool produced by an electric arc. The underlying modelling assumptions were retrieved and investigated. It was found that each of these three models predicts a different melt flow pattern, different heat convection, melt pool shape, free surface oscillation, and interaction with the transferred metal drops, and thus result in different bead geometry. All these models can be adjusted to predict the penetration depth, however, only the most complete of them is recommended for developing a predictive melt pool model. For this, it is proposed as a future work to improve this model through predicting an electromagnetic force that takes also into account the local deformation of the free surface.
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| 5. |
- Baghdadchi, Amir, 1994-
(författare)
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Laser Welding and Additive Manufacturing of Duplex Stainless Steels : Properties and Microstructure Characterization
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Duplex stainless steels (DSS), with a ferritic-austenitic microstructure, are used ina wide range of applications thanks to their high corrosion resistance and excellent mechanical properties. However, efficient and successful production and joining of DSS require precise control of processes and an in-depth understanding o frelations between composition, processing thermal cycles, resulting microstructures and properties. In this study laser welding, laser reheating, and laser additive manufacturing using Laser Metal Deposition with Wire (LMDw) ofDSS and resulting weld and component microstructures and properties are explored.In the first part a lean FDX 27 duplex stainless steel, showing the transformation induced plasticity (TRIP) effect, was autogenously laser welded and laser reheated using pure argon or pure nitrogen as shielding gas. The weld metal austenite fraction was 22% for argon-shielding and 39% for nitrogen-shielding in as-welded conditions. Less nitrides were found with nitrogen-shielding compared to argonshielding. Laser reheating did not significantly affect nitride content or austenite fraction for argon-shielding. However, laser reheating of the nitrogen shieldedweld removed nitrides and increased the austenite fraction to 57% illustrating the effectiveness of this approach.Phase fraction analysis is important for DSS since the balance between ferrite and austenite affects properties. For TRIP steels the possibility of austenite tomartensite transformation during sample preparation also has to be considered. Phases in the laser welded and reheated FDX 27 DSS were identified and quantified using light optical microscopy (LOM) and electron backscatter diffraction (EBSD) analysis. An optimized Beraha color etching procedure was developed for identification of martensite by LOM. A novel step-by-step EBSD methodology was also introduced, which successfully identified and quantified martensite as well as ferrite and austenite. It was found that mechanical polishing produced up to 26% strain-induced martensite, while no martensite was observed after electrolytic polishing.In the second part a systematic four-stage methodology was applied to develop procedures for additive manufacturing of standard 22% Cr duplex stainless steel components using LMDw combined with the hot wire technology. In the four stages, single-bead passes, a single-bead wall, a block, and finally a cylinder with an inner diameter of 160 mm, thickness of 30 mm, and height of 140 mm were produced. The as-deposited microstructure was inhomogeneous and repetitive including highly ferritic regions with nitrides and regions with high fractions ofaustenite. Heat treatment for 1 hour at 1100 ̊C homogenized the microstructure, removed nitrides, and produced an austenite fraction of about 50%. Strength, ductility, and toughness were at a high level for the cylinder, comparable to those of wrought type 2205 steel, both as-deposited and after heat treatment. The highest strength was achieved for the as-deposited condition with a yield strength of 765 MPa and a tensile strength of 865 MPa, while the highest elongation of 35% was found after heat treatment. Epitaxial growth of ferrite during solidification, giving elongated grains along the build direction, resulted in anisotropy of toughness properties. The highest impact toughness energies were measured for specimens with the notch perpendicular to the build direction after heat treatment with close to 300 J at -10oC. It was concluded that implementing a systematic methodology with a stepwise increase in the deposited volume and geometrical complexity can successfully be used when developing additive manufacturing procedures for significantly sized metallic components.This study has illustrated that a laser beam can successfully be used as heat source in processing of duplex stainless steel both for welding and additive manufacturing. However, challenges like nitrogen loss, low austenite fractions and nitride formation have to be handled by precise process control and/or heat treatment.
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| 6. |
- Balachandramurthi, Arun Ramanathan
(författare)
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Fatigue Properties of Additively Manufactured Alloy 718
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Additive Manufacturing (AM), commonly known as 3D Printing, is a disruptive modern manufacturing process, in which parts are manufactured in a layer-wise fashion. Among the metal AM processes, Powder Bed Fusion (PBF) technology has opened up a design space that was not formerly accessible with conventional manufacturing processes. It is, now, possible to manufacture complex geometries, such as topology-optimized structures, lattice structures and intricate internal channels, with relative ease. PBF is comprised of Electron Beam Melting (EBM) and Selective Laser Melting (SLM) processes.Though AM processes offer several advantages, the suitability of these processes to replace conventional manufacturing processes must be studied in detail; for instance, the capability to produce components of consistent quality. Therefore, understanding the relationship between the AM process together with the post treatment used and the resulting microstructure and its influence on the mechanical properties is crucial, to enable manufacturing of high-performance components. In this regard, for AM built Alloy 718, only a limited amount of work has been performed compared to conventional processes such as casting and forging. The aim of this work, therefore, is to understand how the fatigue properties of EBM and SLM built Alloy 718, subjected to different thermal post-treatments, is affected by the microstructure. In addition, the effect of as-built surface roughness is also studied.Defects can have a detrimental effect on fatigue life. Numerous factors such as the defect type, size, shape, location, distribution and nature determine the effect of defects on properties. Hot Isostatic Pressing (HIP) improves fatigue life as it leads to closure of most defects. Presence of oxides in the defects, however, hinders complete closure by HIP. Machining the as-built surface improves fatiguelife; however, for EBM manufactured material, the extent of improvement is dependent on the amount of material removed. The as-built surface roughness, which has numerous crack initiation sites, leads to lower scatter in fatigue life. In both SLM and EBM manufactured material, fatigue crack propagation is transgranular. Crack propagation is affected by grain size and texture of the material.
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| 7. |
- Bennulf, Mattias, 1992-
(författare)
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A User-Friendly Approach for Applying Multi-Agent Technology in Plug & Produce Systems
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents methods for simplifying the use of multi-agent systems in Plug & Produce. The demand for customized products and low volume production is constantly increasing. The industry has for many years used dedicated manufacturing systems where it is difficult and expensive to adapt to new product designs. Instead, factories are forced to use human workers for certain tasks that demand high flexibility and rapid adaption for new product designs. Several solutions have been proposed over the years to create highly flexible automation systems that automatically handles rapid adaption for new products. A concept called Plug & Produce aims at creating a system where resources and parts can be added in minutes rather than days in dedicated systems. One promising solution for implementing Plug & Produce is the distributed approach called multi-agent systems, where each resource and part get its own controller that communicates with each other to reach manufacturing goals. The idea is that the system automatically handles the adaption for new products. However, still today the use of such systems is extremely limited in the industry. One reason is the lack of mature multi-agent systems that are easy to use and that hides the complexity of the underlying agent system from the users. This is a huge problem since these systems tend to be more complex than traditional approaches. Thus, this thesis focuses on simplifying the use of multi-agent systems by proposing various methods for bringing the multi-agent technology for Plug & Produce closer to the industry.
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| 8. |
- Bernhard, Irene
(författare)
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E-government and e-governance : Swedish case studies with focus on the local level
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The concepts of e-government and e-governance are used interchangeably in most research and there is no single definition of these terms. The objective of this licentiate thesis is to provide a deeper understanding of these concepts through empirical studies in a Swedish context. Further, it aims to analyse whether – and if so in what way – the implementation of local contact centres (CC) affect conditions for local planning. This is reported in three articles. In this thesis e-government is defined to as the use of tools and systems by governmental bodies made possible by ICT that affect the organization of public administration. E-governance is defined as the ICT-based networks of services and administration in New Public Management settings including both public and private actors. Case study methodology is used as research method, including interviews, focus group studies, document studies, and some participatory observations. The analysis is partly built on an inductive methodological approach, since this is a new, emerging field of innovative policy and practice. Based on a theoretical discussion of New Public Management in the digital era, findings show that there is a difference between the concepts of e-government and e-governance from the perspective of e-administration and e-services and that the terms should not be used interchangeably. The study indicates that there are examples of implementation that are referred to the e-governance setting. Further the study indicates that local municipal contact centres may be referred to not only as an implementation of e-government but as a combination of e-governance and e-government. The findings indicate that there is a potential for positive impact on the conditions for local planning through the implementation of municipal contact centres.
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| 9. |
- Bernhardsson, Lennarth, 1954-
(författare)
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An Eye for an I : Focus on integration in WIL
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis describes the development and change of forms within a course with a focus on Work-Integrated Learning (WIL). For several years I have been responsible for a course and at the same time author of the syllabus for the course and seen how weak the integration is, and how it is perceived by the students, between theoretical knowledge and the practical work during an internship period. This has resulted in two interventions and processing of the syllabus and above all the methods and pedagogy used for the implementation of the course.In the beginning, the internship period contained four presentation seminars where the result was only a joint listening to the other students' stories and presentations. This resulted in a discussion and conceptual paper that focused on the importance of integration and how this can be made visible. The first change in curricula was inspired by Flipped Classroom, where students had to submit their narratives in advance in an online shared document. Prior to the seminar, it was assumed that they would then read each other's text and reflect on similarities and differences in experiences and learning in the workplace where they had their internship period. This resulted in a more reflective conversation during the seminars which can be called Peer Reflections where the conversation was always based on previous reflections and each other's thoughts.The second intervention was carried out in implementation at the same time as it was to be compared with the student's experiences of seminars in a control group that carried out a similar course structure with presentation and examining seminars. The change was inspired by a model from Australia that they call Huddles. This is a concluding seminar as a briefing of the practice. The issues that are discussed are carefully selected in collaboration with the students and have a clear anchoring in their experiences during the practice. The change, which was then implemented, after inspiration from Huddles in one group, with as before four seminars during the internship with carefully selected themes. At the same time, I was inspired by models for evaluating differences in teaching when technology is introduced, such as the SAMR model (substitution, augmentation, modification, and redefinition) and how this could be seen as a form of progression if technology was changed to AIL. The SOLO taxonomy was also the inspiration for describing the assignments and themes before each seminar.The research questions presented in this licentiate thesis focus on the students' experiences of how these changes contribute to a better understanding of the integration of what is taught at the university in the form of theory and the practical knowledge they learned in the internship.Qualitative data collection has taken place through observations and focus groups in both the group where changes have been implemented and in the group that conducted accounting and examining seminars. The results show that the integration in the students' understanding of theory and practice increases. They also experience a progression in their reflections and the seminars, while the students in the control group experience their seminars as scattered and they do not contribute to any knowledge development.The licentiate thesis also contributes to considering WIL as a complex concept with different areas of responsibility. The university teaches on the theoretical side, Work-Integrated Education (WIE) while on the other side of the dichotomy theory and practice where students are largely responsible for Workplace learning (WPL). Between these, several different activities can be carried out, including Huddles, which can be described as work-based learning (WBL). The university can contribute to these activities with, for example, simulations, the teaching of relevant software used by companies and organizations in the field. Workplaces can also contribute with concrete assignments in the form of various projects that the students are allowed to carry out or perhaps with guest lectures and concrete cases. Seeing WIL as an umbrella covering different forms of activities with different organizational responsibilities can make it easier to see the importance of the different activities and these can be integrated. WIL is not only WIE.In addition to the view that AIL is an umbrella concept with several different types of activities, ideas are also given on how Huddles can be introduced as a pedagogical method and how progression can be developed within Work-integrated Education and Learning with inspiration from different models.
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| 10. |
- Bonilla Hernández, Ana Esther
(författare)
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Analysis and direct optimization of cutting tool utilization in CAM
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The search for increased productivity and cost reduction in machining can be interpreted as the desire to increase the material removal rate, MRR, and maximize the cutting tool utilization. The CNC process is complex and involves numerous limitations and parameters, ranging from tolerances to machinability. A well-managed preparation process creates the foundations for achieving a reduction in manufacturing errors and machining time. Along the preparation process of the NC-program, two different studies have been conducted and are presented in this thesis. One study examined the CAM programming preparation process from the Lean perspective. The other study includes an evaluation of how the cutting tools are used in terms of MRR and tool utilization.The material removal rate is defined as the product of three variables, namely the cutting speed, the feed and the depth of cut, which all constitute the cutting data. Tool life is the amount of time that a cutting tool can be used and is mainly dependent on the same variables. Two different combinations of cutting data might provide the same MRR, however the tool life will be different. Thereby the difficulty is to select the cutting data to maximize both MRR and cutting tool utilization. A model for the analysis and efficient selection of cutting data for maximal MRR and maximal tool utilization has been developed and is presented. The presented model shortens the time dedicated to the optimized cutting data selection and the needed iterations along the program development.
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