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  • Balachandramurthi Ramanathan, Arun
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Fatigue Properties of Additively Manufactured Alloy 7182018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

  • Karimi Neghlani, Paria
    University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.
    Electron beam melting of Alloy 718: Influence of process parameters on the microstructure2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Additive manufacturing (AM) is the name given to the technology of building 3D parts by adding layer-by-layer of materials, including metals, plastics, concrete, etc. Of the different types of AM techniques, electron beam melting (EBM), as a powder bed fusion technology, has been used in this study. EBM is used to build parts by melting metallic powders by using a highly intense electron beam as the energy source. Compared to a conventional process, EBM offers enhanced efficiency for the production of customized and specific parts in aerospace, space, and medical fields. In addition, the EBM process is used to produce complex parts for which other technologies would be either expensive or difficult to apply. This thesis has been divided into three sections, starting from a wider window and proceeding to a smaller one. The first section reveals how the position-related parameters (distance between samples, height from build plate, and sample location on build plate) can affect the microstructural characteristics. It has been found that the gap between the samples and the height from the build plate can have significant effects on the defect content and niobium-rich phase fraction. In the second section, through a deeper investigation, the behavior of Alloy 718 during the EBM process as a function of different geometry-related parameters is examined by building single tracks adjacent to each other (track-by-track) andsingle-wall samples (single tracks on top of each other). In this section, the main focus is to understand the effect of successive thermal cycling on microstructural evolution. In the final section, the correlations between the main machine-related parameters (scanning speed, beam current, and focus offset) and the geometrical (melt pool width, track height, re-melted depth, and contact angle) and microstructural (grain structure, niobium-rich phase fraction, and primary dendrite arm spacing) characteristics of a single track of Alloy 718 have been investigated. It has been found that the most influential machine-related parameters are scanning speed and beam current, which have significant effects on the geometry and the microstructure of the single-melted tracks.

  • Abdulla, Zine
    University West, Department of Engineering Science, Division of Mathematics, Computer and Surveying Engineering.
    Varför blir inte detaljplanelagd mark för bostadsändamål bebyggd?2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    According to Boverket's housing market survey 2018, which is a result of a national survey of the housing market in Sweden, there is a deficit in housing in 243 of Sweden's 290 municipalities. In order to meet increased demand for housing, increased housing construction is needed. Detailed development plans govern the rights, construction rights, which indicate what and to what extent property owners can build land. Detailed development plans are the legally binding documents that are established and adopted by municipalities in order to determine, among others, the use of land and water areas. There are several reasons for housing shortage and one is that Sweden's population continues to increase, both due to natural population growth and because of immigration. A growing population entails, for instance, an increase in housing demand, which in turn places demands on the housing market. The demand and supply of housing need to match each other. Another reason is that today it is the private sector that accounts for the majority of housing supply. The private sector does not have the responsibility that municipalities have in terms of meeting the residents' housing needs. The private actors intend to make a profit. Consequently, privately owned construction and housing companies build when it is economically beneficial and not just because there is a housing requirement. Due to the fact that there are still housing shortages in most municipalities, which is problematic, it is interesting to investigate which factors are important for housing construction.

    Current detailed development plans for housing purposes were studied. The detailed development plans that had not been implemented were used as starting material during interviews with relevant actors.

    The purpose of the study was to try to find out what factors affect the fact that detailed development plan land for housing purposes is not built.

    The study's results show that among the factors it is primarily the market situation, high business activity and recession, which affect whether housing construction is going to start or not. There are also factors such as construction law handling times that affect how soon a residential building can get started.

    The conclusion of the study was, among other things, that the market situation seems to be the most influential factor and because the market is governed by profit-dependent players, supply and demand will not always meet. Other conclusions that were drawn were that what is being built is not what is requested and that the building permits take longer than is required by plan- och bygglagen.