No description available.

This thesis presents an investigation into the laser cladding process using CO2 and Nd:YAG lasers. The work is divided into four papers: Paper one is a literature review of the subject of laser cladding. This presents a general overview of the subject from a practical and theoretical point of view. Paper two is an investigation about the energy redistribution during CO2- laser cladding. Experimental absorption measurements by calorimetry were carried out to separate and analyse how much of the energy is lost by reflection etc. It was found that approximately 60% of the original laser power is lost by reflection. Paper three extends the work of paper two and compares the process efficiency of Nd:YAG and CO2 laser cladding. The energy redistribution during cladding has been analysed for both processes. The Nd:YAG laser cladding process was found to be considerably more energy efficient than CO2- laser cladding process. Paper four presents preliminary experimental results from two new processes; Laser casting and Laser clad-casting. Laser casting is a process similar to blown powder laser cladding but without the final product joined to the substrate. The substrate acts as a mould and the casting retains topological features of the substrate. Laser clad-casting involves the production of a clad layer between machined copper blocks. Clad tracks can therefore be achieved with large depth to width ratios and pre determined cross sections. / Godkänd; 2002; 20070222 (ysko)

Preservation of cultural property in the form of historical artefacts for the future is an important interest in our society. The information which can be obtained from these materials is a valuable key to understand the past. One of the aims of any conservation procedure is to preserve both aesthetic and physical conditions of irreplaceable artefacts. Conservation involves a number of different steps. Cleaning is one of the critical steps needed to stabilise the material and to recover hidden details on the surface. It is therefore very important to choose suitable techniques and methods when cleaning to avoid damage to the artefact. Research and development to find more suitable conservation techniques are still going on. One of the new techniques under investigation is laser cleaning which has shown a good potential as a cleaning tool for many material categories met in conservation work. This thesis presents an investigation of the laser cleaning of metal artefacts using Nd:YAG and TEA CO2 lasers. The first part is a general overview of the laser technique applied to metal conservation and an outline of the practical work. The thesis then continues with four papers. Paper A concerns the removal of adhesives and coatings from iron samples using pulsed TEA CO2- and Nd:YAG-lasers. Trial samples were treated with different kinds of adhesives and coatings typically used in metals conservation and then cleaned using the lasers. The results were compared with cleaning using a conventional technique, micro blasting. Comparison of the different laser-cleaned surfaces was also performed by optical microscopy and Raman-spectroscopy. The comparative study showed that the best cleaning result was achieved by the TEA CO2 laser. The coatings were removed entirely without damage to the substrate. Paper B deals with cleaning of corroded iron samples using pulsed TEA CO2- and Nd:YAG-lasers. TEA CO2 lasers were successfully used to remove organic materials and rust. The Nd:YAG laser was able to clean the corroded samples, however, the risk for surface damage was found to be higher than using the TEA CO2 laser. Analysis of the surfaces cleaned by the two types of lasers was carried out by optical- and scanning electron microscopy, X-ray spectrometry and Raman-spectrometry. Paper C is a comparative study of the cleaning of iron samples using TEA CO2- and Nd:YAG lasers. In the first experiment a comparison of Nd:YAG laser and micro blasting for the cleaning of rust was made. The second experiment dealt with the removal of a wax coating from iron samples using a TEA CO2 laser with different power densities. The first experiment shows that the samples cleaned by pulsed laser retain a better surface structure than those cleaned by micro blasting. The second experiment showed how different energy densities affect the same surface. Paper D is an investigation of the cleaning of silver threads in textile using Nd:YAG laser at wavelengths of 1064 nm, 532 nm and 266 nm. The goal of this work was to find a technique to clean the tarnished silver without damaging the underlying silk. This was necessary since the conventional chemical treatment for cleaning tarnished silver is problematic to apply in this specific instance. The laser wavelength of 266 nm was found to be most appropriate for cleaning the silver threads without causing any damages either the silver or the underlying silk. However, the 1064 nm wavelength caused damage such as melting and burning of both the silver and silk. / Godkänd; 2002; 20070224 (ysko)

This thesis presents an investigation of the interaction mechanism involved in processing of different engineering materials using pulsed TEA CO2- and Nd:YAG lasers. Several methods were used. Digital Speckle Photography (DSP) or Speckle Correlation was used to detect micro-structural changes in the material surface during laser irradiation. Scanning Electron Microscopy (SEM) and optical microscopy were used to obtain information about hole quality; entrance and exit diameters, amount of spatter, cracking etc., when laser drilling. Optimum processing parameters, for example wavelength, pulse repetition frequency and pulse energy were established and are presented in this thesis. In Papers A and B, an evaluation of the interaction mechanism using Digital Speckle Photography (DSP) is presented. Paper C focuses more on the influence of the laser irradiation parameters on the quality of laser drilled holes. To find optimum processing parameters, SEM and optical microscopic investigations of thermoplastic polymers, and thermoset polymers exposed to laser irradiation with different wavelengths were carried out. Thermoplastics PMMA and Polycarbonate and a thermoset epoxy matrix reinforced by glass and graphite fibres were used. The results from the first paper showed that microstructural changes caused by laser pulse impact can be visualised. The results of other two papers showed that, for hole drilling, short wavelengths are most suitable since these give good hole quality in most engineering materials including metals and composites. / Godkänd; 2004; 20070128 (ysko)

This thesis describes the state-of-the-art of off-line programming (OLP) for co-ordinate measuring machines (CMM's) and explores two important aspects of OLP systems; automatic generation of inspection programmes, probing points and movements between these, and data transfer from computer aided design (CAD). A method of generating inspection programmes using a 'feature' based definition of component geometry is described. This has been implemented as both free standing code and as a prototype, known as the Inspection Planning Assistant (IPA), which is based upon the robot simulation software GRASP. Current neutral data exchange formats such as IGES and DMIS are limited in their ability to transfer a toleranced 3D CAD model to OLP systems. The new standard for the exchange of product model data (STEP ISO 10303) offers the potential to resolve these problems. The scope and application of a STEP application protocol for inspection process planning is described / Godkänd; 1996; 20080328 (ysko)

No description available.

Godkänd; 1995; 20080330 (ysko)

Additive manufacturing is an increasingly popular industry that has gained significant traction in the last decade. Today there exists no way to predict how a powder will spread in a powder bed additive manufacturing machine or how well it will form into thin layers. This is important because major costs can be saved by using a test that predicts the spreading behaviour of powder. This ability to be spread will be given the name spreadability. To test the spreadability of powder, a machine that mimicked the pushing of the powder in powder bed additive manufacturing was used. Since there exist no metric for spreadability, the study decided to attempt to quantify the spreadability with the help of image analysis. In the image analysis the area of the powders was measured, and through a comparison of the area against a bounding geometry, a measurement for spreadability can theoretically be attained. To further validate the results and simultaneously search for possible correlations, the experimental data was compared against flowability data obtained from angle of repose and Hall flowmeter. The results showed that the method of choice worked well for measuring the area and gave data that could be used to interpret spreadability. The data also showed what seems to be a correlation with the flowability data. While no definitive conclusions could bedrawn due to a small sample size, the collected data does seem promising for future work. / Additiv tillverkning är en alltmer populär industri som har fått stor uppmärksamhet under det senaste decenniet. Idag så finns det inga sätt som man kan förutse hur ett pulver kommer att bredas ut i en pulverbädds additiv tillverkningsmaskin eller hur bra den är på att bilda tunna lager. Detta är en viktig kunskap att förstå då stora kostnader kan sparas in genom att använda ett test som förutser utbredningsförmågan av pulver. Denna förmåga får namnet spridbarhet. För att kunna testa spridbarheten hos pulver, används en maskin som härmar puttandet av pulver i en pulverbädds additiv tillverkningsmaskin. Eftersom det inte finns någon metod att mäta spridbarhet med, så valde denna studie att försöka kvantifiera spridbarheten via en bildanalys. Med denna bildanalys kunde arean av pulver mätas och genom att jämföra denna mot en avgränsande geometri kan mätdata för spridbarheten teoretiskt fås fram.För att kunna validera resultatet, och samtidigt se om det finns en korrelation, jämfördes det med flytbarhetsdata från rasvinkelmätare och Hall flödesmätare. Resultaten visade att metoden klarade av att mäta arean, och gav resultat som kan användas för att tolka spridbarhet. Den data som framtogs visade också att det möjligtvis kan finnas en korrelation mellan spridbarhet och flytbarhet. Även om något klart svar inte kan ges på grund av en liten provstorlek, så verkar resultaten vara lovande för framtida arbeten.

In last ten years, the size range of dimensions program has increased and therefore the hot rolling process needs to be analysed and improved. The bar mill at Ovako Sweden AB in Hofors intends to increase the current roll diameter to improve the rolling capacity and to remove the existing bottleneck within the production flow. Therefore, this project is carried out to study the hot working of ingots within the current rolling setup, aiming to evaluate the subsequent change on ingot central deformation and porosity related to roller dimension. In this project, two plant trials are executed at Ovako Sweden AB and after the trials; analyses on ingot central deformation and central porosity are performed respectively with samples from the two trials. The results suggest that, after the first rolling stage, larger diameter rolls results in less pore defects but gives similar central deformation. Indicated from the results, the ingot is likely to have less central porosity but equal central deformation by increasing the roll diameter. After this project, we get a better perspective of the potential to boost the rolling capacity with a new larger roll and the subsequent quality benefits.

Additive Manufacturing became a major research topic and part of industrial production in the past years. Numerous techniques now allow to build 3D structures with a wide choice of materials. When it comes to processing of metals, a laser beam is often used as a heat source to melt either a wire or powder, where the trajectory of spatters and powder particles can be affected by the laser beam radiation. Laser beam irradiation is partly absorbed by the material, and is then converted to heat, which can cause melting and even vaporization. The vaporization of material induces a recoil pressure on the melt pool, which affects its geometry and dynamics. However, the effects of the recoil pressure on airborne objects such as drops and powder particles are still relatively unknown. Their different sizes and boundary conditions compared to a melt pool might affect their behaviour under high laser beam radiation.  Therefore, this thesis aims at better understanding the effects of the recoil pressure on metal drops and powder particles, as well as their impacts on Additive Manufacturing processes, especially Directed Energy Deposition and Laser Metal Wire Deposition. In the three adjoined papers, high-speed imaging was used to observe (i) powder blown through a laser beam, (ii) drops falling in a laser beam, and (iii) drops detaching from a wire in a laser beam. The videos enabled to calculate the acceleration of powder particles and drops of different sizes, the density map of the powder stream, and the detachment direction of the drops. The experimental results were completed with theoretical calculations of thermodynamics, recoil pressure and surface tension.  These studies allowed to conclude that the acceleration induced by the recoil pressure on a drop or a powder particle increases with decreased size. Moreover, the recoil pressure causes a slight deviation of the powder stream in Directed Energy Deposition that can induce a better powder focusing. The recoil pressure can also cause the disintegration of powder particles in the laser beam. Finally, it was shown that the recoil pressure can be used to detach drops on demand from a wire and accelerate them towards the substrate where they can be strategically deposited for building additive structures.