| 31. |
|
|
| 32. |
- Heralic, Almir, 1981-
(författare)
-
Towards full Automation of Robotized Laser Metal-wire Deposition
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal wire deposition by means of robotized laser welding offers great saving potentials, i.e. reduced costs and reduced lead times, in many different applications, such as fabrication of complex components, repair or modification of high-value components, rapid prototyping and low volume production, especially if the process can be automated. Metal deposition is a layered manufacturing technique that builds metal structures by melting metal wire into beads which are deposited side by side and layer upon layer. This thesis presents a system for on-line monitoring and control of robotized laser metal wire deposition (RLMwD). The task is to ensure a stable deposition process with correct geometrical profile of the resulting geometry and sound metallurgical properties. Issues regarding sensor calibration, system identification and control design are discussed. The suggested controller maintains a constant bead height and width throughout the deposition process. It is evaluated through real experiments, however, limited to straight line deposition experiments. Solutions towards a more general controller, i.e. one that can handle different deposition paths, are suggested.A method is also proposed on how an operator can use different sensor information for process understanding, process development and for manual on-line control. The strategies are evaluated through different deposition tasks and considered materials are tool steel and Ti-6Al-4V. The developed monitoring system enables an operator to control the process at a safe distance from the hazardous laser beam.The results obtained in this work indicate promising steps towards full automation of the RLMwD process, i.e. without human intervention and for arbitrary deposition paths.
|
|
| 33. |
- Holmberg, Jonas, 1976-
(författare)
-
Surface integrity on post processed alloy 718 after nonconventional machining
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a strong industrial driving force to find alternative production technologies in order to make the production of aero engine components of superalloys even more efficient than it is today. Introducing new and nonconventional machining technologies allows taking a giant leap to increase the material removal rate and thereby drastically increase the productivity. However, the end result is to meet the requirements set for today's machined surfaces.The present work has been dedicated to improving the knowledge of how the non-conventional machining methods Abrasive Water Jet Machining, AWJM, Laser Beam Machining, LBM, and Electrical Discharge Machining, EDM, affect the surface integrity. The aim has been to understand how the surface integrity could be altered to an acceptable level. The results of this work have shown that both EDM and AWJM are two possible candidates but EDM is the better alternative; mainly due to the method's ability to machine complex geometries. It has further been shown that both methods require post processing in order to clean the surface and to improve the topography and for the case of EDM ageneration of compressive residual stresses are also needed.Three cold working post processes have been evaluated in order to attain this: shot peening, grit blasting and high pressure water jet cleaning, HPWJC. There sults showed that a combination of two post processes is required in order to reach the specified level of surface integrity in terms of cleaning and generating compressive residual stresses and low surface roughness. The method of high pressure water jet cleaning was the most effective method for removing the EDM wire residuals, and shot peening generated the highest compressive residual stresses as well as improved the surface topography.To summarise: the most promising production flow alternative using nonconventional machining would be EDM followed by post processing using HPWJC and shot peening.
|
|
| 34. |
- Hosseini, Vahid, 1987-
(författare)
-
Influence of multiple welding cycles on microstructure and corrosion resistance of a super duplex stainless steel
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Super duplex stainless steel (SDSS) has found a wide use in demanding applications such as offshore, chemical and petrochemical industries thanks to its excellent combination of mechanical properties and corrosion resistance. Welding of SDSS, however, is associated with the risk of precipitation of secondary phases and formation of excessive amounts of ferrite in the weld metal and heat affected zone. The present study was therefore aimed at gaining knowledge about the effect of multiple welding thermal cycles on the microstructure and possible sensitization to corrosion of welds in SDSS.Controlled and repeatable thermal cycles were produced by robotic welding. Oneto four autogenous TIG-remelting passes were applied on 2507 type SDSS plates using low or high heat inputs with pure argon as shielding gas. Thermal cycles were recorded using several thermocouples attached to the plates. Thermodynamic calculations and temperature field modelling were performed in order to understand the microstructural development and to predict the pitting corrosion resistance. Etching revealed the formation of different zones with characteristic microstructures: the fused weld zone (WZ) and the heat affected zone composed of the fusion boundary zone (FBZ), next to the fusion boundary, and further out Zone 1 (Z1) and Zone 2 (Z2). The WZ had a high content of ferrite and often nitrides which increased with increasing number of passes and decreasing heati nput. Nitrogen content of the WZ decreased from 0.28 wt.% to 0.17 wt.% after four passes of low heat input and to 0.10 wt.% after four passes of high heatinput. The FBZ was reheated to high peak temperatures (near melting point) and contained equiaxed ferrite grains with austenite and nitrides. Zone 1 was free from precipitates and the ferrite content was similar to that of the unaffected base material. Sigma phase precipitated only in zone 2, which was heated to peak temperatures in the range of approximately 828°C to 1028°C. The content of sigma phase increased with the number of passes and increasing heat input. All locations, except Z1, were susceptible to local corrosion after multiplere heating. Thermodynamic calculations predicted that a post weld heat treatment could restore the corrosion resistance of the FBZ and Z2. However, the pitting resistance of the WZ cannot be improved significantly due to the nitrogen loss. Steady state and linear fitting approaches were therefore employed to predict nitrogen loss in autogenous TIG welding with argon as shielding gas. Two practical formulas were derived giving nitrogen loss as functions of initial nitrogen content and arc energy both predicting a larger loss for higher heat input and higher base material nitrogen content. A practical recommendation based on the present study is that it is beneficial to perform welding with a minimum number of passes even if this results in a higherheat input as multiple reheating strongly promotes formation of deleterious phases.
|
|
| 35. |
- Javidi Shirvan, Alireza, 1978-
(författare)
-
Modelling of Electric Arc Welding : arc-electrode coupling
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Arc welding still requires deeper process understanding and more accurateprediction of the heat transferred to the base metal. This can be provided by CFD modelling.Most works done to model arc discharge using CFD consider the arc corealone. Arc core simulation requires applying extrapolated experimental data asboundary conditions on the electrodes. This limits the applicability. To become independent of experimental input the electrodes need to be included in the arcmodel. The most critical part is then the interface layer between the electrodesand the arc core. This interface is complex and non-uniform, with specific physicalphenomena.The present work reviews the concepts of plasma and arc discharges that areuseful for this problem. The main sub-regions of the model are described, andtheir dominant physical roles are discussed.The coupled arc-electrode model is developed in different steps. First couplingsolid and fluid regions for a simpler problem without complex couplinginterface. This is applied to a laser welding problem using the CFD softwareOpenFOAM. The second step is the modelling of the interface layer betweencathode and arc, or cathode layer. Different modelling approaches available inthe literature are studied to determine their advantages and drawbacks. One ofthem developed by Cayla is used and further improved so as to satisfy the basicprinciples of charge and energy conservation in the different regions of thecathode layer. A numerical procedure is presented. The model, implementedin MATLAB, is tested for different arc core and cathode conditions. The maincharacteristics calculated with the interface layer model are in good agreementwith the reference literature. The future step will be the implementation of theinterface layer model in OpenFOAM.
|
|
| 36. |
|
|
| 37. |
- Johansson, Anders
(författare)
-
Money talks while volume and value should run the show : An evaluation of financial parameters for decision making duringmanufacturing system acquisition
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Market economic values have for the last decades been given an increasing role with the establishment of financial institutes and global organisations with a capitalistic focus as a consequence. As a counter reaction, the concept of sustainable development has emerged complementing the economic focus with environmental and social aspects. However, there are still challenges on how to make balanced decisions based on all three view points and consequently the decision makers still primarily reside to the established tangible financial data. Within the industrial setting there is no difference. The manufacturing system design is based on multiple criteria and requirements, but commonly the final investment decision is primarily based on what can be financially justified. Longterm solutions probably lies in combining the tangible economy with the less tangible soft values that cannot be valued in monetary means. Therefore, to find this sweet spot, the purpose of this research is to in-depth investigate the world of economy, but from an engineers' point of view. A financial analysis is done to understand the economical components and how these are related to the manufacturing system. Furthermore, to connect cost with contributed value of the manufacturing system, a holistic business value chain analysis is done to ensure that less tangible aspects can be understood and utilised. The result of this research, highlights for example that sales volume has a larger impact on the manufacturing profitability, than that of the initial investment cost. Therefore, manufacturing systems should also be evaluated on the bases of how well it can meet the volatility in market demands. Another result presented is a portfolio of new graphical representation used as a support tool for investment decisions. Furthermore, to be able to invest in manufacturing systems that contribute to a more competitive company, the wider business value with manufacturing is discussed.
|
|
| 38. |
- Kajonius, Petri, 1974-
(författare)
-
The Impact of Care Process on Satisfaction with Elderly Care
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis is based on the growing interest in Swedish elderly care. The aim of this thesis is to investigate what generates satisfaction with elderly care among older persons. The dominant ideology in both privately and publically run elderly care is individualized care, also called person-centered care, which holds the older person’s satisfaction as one of the main quality indicators. The proportion of older people is increasing and to maintain high levels of satisfaction with elderly care will require more knowledge. Data from the National Board of Health and Welfare’s (2012) nationwide survey on seniors’ experiences with elderly care was collected. Statistical analyses of this sample formed the basis for the results of the thesis and were reported in two papers. Study I used Donabedian’s (1988) model of quality of care in terms of structure, process, and outcome, and all municipal units in Sweden were included (N = 324). The results showed that structural variables (i.e. budget, staff, and training level) have minimal or no relationships with older persons’ satisfaction with care, while process variables (i.e. experiences of respect, information, and influence) have strong relationships with satisfaction with care. Study II made use of the long-standing person versus situation- model in social psychology, and was analyzed on an individual level (N = 95,000). The results showed that care process factors (i.e. experiences of treatment, safeness, staff- and time-availability) had a stronger relationship, than individual factors (i.e. health, anxiety, and loneliness) with satisfaction with care. The results also showed that older persons with home care generally felt better treated than older persons in nursing homes, but also felt less safe. Mediational analyses, based on this comprehensive elderly data, suggest that the individual aging condition of loneliness can be countered by providing safeness and treatment, resulting in high satisfaction with care. In conclusion, satisfaction with elderly care in Sweden today can largely be explained from a psychological perspective by the older persons’ perception of the care process, not by the amount of structural resources or the conditions of the aging persons. These findings could help facilitate the future quality development in municipalities and care organizations.
|
|
| 39. |
- Karimi Neghlani, Paria, 1986-
(författare)
-
Electron beam melting of Alloy 718 : Influence of process parameters on the microstructure
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 40. |
|
|
