Search results

The paper aims to discuss the inverse heat conduction methodology in solution of a certain parameter identification problem. The problem itself concerns determination of the thermophysical properties of a thin layer coating by applying the laser flash apparatus.

The modelled laser flash diffusivity data from the three-layer sample investigation are used as input for the following parameter estimation procedure. Assuming known middle layer, i.e. substrate properties, the thermal diffusivity (TD) of the side layers’ material is determined. The estimation technique utilises the finite element method for numerical solution of the direct, 2D axisymmetric heat conduction problem.

The paper presents methodology developed for a three-layer sample studies and results of the estimation technique testing and evaluation based on simulated data. The multi-parametrical identification procedure results in identification of the out of plane thin layer material diffusivity from the inverse problem solution.

The presentation itself is limited to numerical simulation data, but it should be underlined that the flake graphite thermophysical parameters have been utilised in numerical tests.

The developed methodology is planned to be applied in detailed experimental studies of flake graphite.

In the course of a present study, a methodology of the thin-coating layer TD determination was developed. In spite of the fact that it has been developed for the graphite coating investigation, it was planned to be universal in application to any thin–thick composite structure study.

The thermal history during laser exposure determines part properties in selective laser sintering (SLS). The purpose of this study is to introduce a new measurement technique based on a CO₂ laser unit combined with a high-speed DCS. A first comparison of the thermal history during laser exposure measured with Laser-high-speed-(HS)-differential scanning calorimetry-(DSC) and in SLS process is shown.

This Laser-HS-DSC allows an imitation of the SLS-process in a very small scale, as the sample is directly heated by a CO₂ laser. For this study, the laser power and the impact time is varied for determining temperature and achieved heating rates. Consequently, the temperature levels measured by the Laser-HS-DSC are compared with measurements in SLS-process.

The influence of laser power and impact time on resulting maximum temperatures und heating rates during laser exposure are investigated. With increasing laser power and impact time the maximum temperature rises up to approximately 450°C without material degradation. The heating rate increases up to an impact time of 3 ms and stays almost equal for higher durations.

The Laser-HS-DSC experiments are based on few particles limiting a complete comparison with SLS process. In SLS, one volume element is exposed several times. In this study the PA12 material was exposed only once.

For the first time, laser sintering experiments can be transferred to a laboratory scale to analyze the influence of laser exposure on resulting temperature field during laser exposure without superimposing effects.

The purpose of the present research is to examine very small-sized samples of approximately 2-mm diameters. For samples of this size, the holder must make contact with the entire perimeter surface of the sample, and the sample is held in place by friction. This necessitates a mathematical model for the direct solution which accommodates the holder and a contact resistance between the holder and the sample.

Most flash diffusivity testing is performed on samples which are nominally 12-13 mm in diameter and are held by only a small contact area around the perimeter of the sample in a holder. With an experiment set up in this way, the effects of conduction between the sample and the holder are normally ignored.

This research examines the effects of the holder and the contact resistance on the measured thermal diffusivity of the sample and includes experimental results from laboratory measurements.

This work provides a method for finding thermal diffusivity for extremely small samples. This capability is important in cases involving precious materials or highly toxic materials where only small samples are available.

This paper aims to propose an analytical thermal three-dimensional model that allows an efficient evaluation of the thermal effect of the laser-scanning path. During manufacturing by laser powder bed fusion (LPBF), the laser-scanning path influences the thermo-mechanical behavior of parts. Therefore, it is necessary to validate the path generation considering the thermal behavior induced by this process to improve the quality of parts.

The proposed model, based on the effect of successive thermal flashes along the scanning path, is calibrated and validated by comparison with thermal results obtained by FEM software and experimental measurements. A numerical investigation is performed to compare different scanning path strategies on the Ti6Al4V material with different stimulation parameters.

The simulation results confirm the effectiveness of the approach to simulate the thermal field to validate the scanning strategy. It suggests a change in the scale of simulation thanks to high-performance computing resources.

The flash-based approach is designed to ensure the quality of the simulated thermal field while minimizing the computational cost.

This work aims to investigate the direct production of electrical discharge machining (EDM) electrodes by means of the selective laser sintering (SLS) technique using a new non-conventional metal-matrix composite material (TiB₂-CuNi). The influence and optimization of the main SLS parameters on the densification behavior and porosity is experimentally studied. EDM experiments are also performed to evaluate the electrodes performance.

The new EDM electrode material used was a powder system composed of TiB₂ and CuNi. Making use of a designed systematic experimental methodology, the effects of layer thickness, laser scan speed and scan line spacing were optimized, where aspects such as densification behavior, porosity and surface morphology of the samples were analyzed through microstructural and surface analysis. EDM experiments were conducted under three different regimes in order to observe the electrodes behavior and performance. The results were compared with copper powder electrodes manufactured by SLS and EDMachined under the same conditions.

The experimental results showed that the direct SLS manufacturing of composite electrodes is feasible and promising. The laser scan speed has a high effect on the densification behavior of the samples, while the effect of scan line spacing on the porosity is more visible when the overlapping degree is considered. Surface morphology was not affected by the scan line spacing, whereas balling phenomenon was reported, regardless of the scan line spacing. The EDM results showed that the TiB₂-CuNi electrodes had a much superior performance than the copper powder electrodes made by SLS, regardless of the EDM regime applied.

Generally, the machine tool itself promotes some restrictions to the SLS process optimization. It is normally attributed to the characteristics of the laser type and the amount of energy that can be delivered to the powder bed. The present investigation could not cover all the optimization potential involved with the studied material due to limitations of the SLS machine tool used.

Significant results on the direct SLS manufacturing of a new non-conventional composite material, which has a great technological potential to be used as an EDM electrode material, are presented. Valuable guidelines are given in regard to the SLS optimization of TiB₂-CuNi material and its performance as an EDM electrode. This work also provides a systematic methodology designed to be applied to the SLS process to produce EDM electrodes.

Prompted by the reliability and robustness of the previously proposed method of non-destructive measurement of thermal conductivity (TC) for anisotropic materials, the enhanced approach is presented in this study. The main improvement lies in the substitution of the analytic solution of direct problem solver with a numerical one. This solver, used during the inverse procedure that fits measurement data into simulated ones, is proposed to be a numerical one (finite volume method). Moreover, the purpose of this study is to show the applicability of the reduce order model for retrieving thermal conductivity of solid body.

In the proposed methodology, both the laser heat source and temperature measurements are performed on the same side of the sample material, which is the main difference with respect to the classic Parker flash method. To speed up the computational time, the full numerical model used in the course of inverse solution is replaced by the proper orthogonal decomposition (POD)-radial basis function (RBF) reduced order model, which is fast and accurate.

The TCs measured using the proposed methodology are in good agreement with the well established (but destructive) measurement methods. The advantage of the proposed approach lies in the optimal approximation properties of the POD approximation basis used in reduced order model, as well as in its regularization properties.

The proposed technique has high application potential in the design of novel apparatus for non-destructive measurement of TCs for both isotropic and anisotropic materials.

This is the first time when the POD-RBF reduced order model is used in the procedure of non-destructive TC measurement for anisotropic bodies.

This work is focused on the investigation of direct production of electrical discharge machining (EDM) electrodes through the selective laser sintering (SLS) technique using a new metal-matrix composite material made of molybdenum and a copper-nickel alloy (Mo-CuNi). The influence and optimization of the main SLS parameters on the densification behavior and porosity is experimentally studied. Additionally, EDM experiments are performed to evaluate the electrodes performance under different machining conditions. The paper aims to discuss these issues.

The new EDM electrode material used was a powder system composed of Mo and pre-alloyed CuNi. A systematic experimental methodology was designed to evaluate the effects of layer thickness, laser scan speed and hatch distance. The densification behavior, porosity and surface morphology of the samples were analyzed through microstructural and surface analysis. EDM experiments were conducted under three different regimes in order to observe the electrodes behavior and performance. The results were compared with copper powder electrodes manufactured by SLS and solid copper electrodes EDMachined under the same conditions.

The experimental results showed that the direct SLS manufacturing of composite electrodes is feasible and an adequate combination of parameters can produce parts with good quality. The laser scan speed has a great effect on the densification behavior of the samples, while the effect of hatch distance on the porosity is more visible when the overlapping degree is considered. The overlapping also had a significant effect on the surface morphology. The EDM results showed that the Mo-CuNi electrodes had superior performance to the copper powder electrodes made by SLS for all the EDM regimes applied, but inferior to those achieved with solid copper electrodes.

Significant results on the direct SLS manufacturing of a new material which has a great technological potential to be used as an EDM electrode material are presented. Valuable guidelines are given in regard to the SLS optimization of Mo-CuNi material and its performance as an EDM electrode. This work also provides a systematic methodology designed to be applied to the SLS process to produce EDM electrodes.

The purpose of this paper is to investigate the selective laser melting (SLM) of Inconel 625 using pulse shape control to vary the energy distribution within a single laser pulse. It aims to discuss the effectiveness of pulse shaping, including potential benefits for use within SLM.

Laser parameters were varied in order to identify optimal parameters that produced thin wall parts with a low surface roughness without the use of pulse shape control. Pulse shape control was then employed to provide gradual heating or a prolonged cooling effect with a variety of peak power/pulse energy combinations. Properties of pulse shaped and nonpulse shaped parts were compared, with particular attention focused on part surface roughness and width.

High peak powers tended to reduce top surface roughness and reduce side roughness as recoil pressures flatten out the melt pool and inhibit melt pool instabilities from developing. Ramp up energy distribution can reduce the maximum peak power required to melt material and reduce material spatter generation during processing due to a localized preheating effect. Ramp down energy distribution prolonged melt pool solidification allowing more time for molten material to redistribute, subsequently reducing the top surface roughness of parts. However, larger melt pools and longer solidification times increased the side roughness of parts due to a possible lateral expulsion of material from the melt pool.

This paper is the first of its kind to employ laser pulse shape control during SLM to process material from powder bed. It is a useful aid in unveiling relationships between laser energy distribution and the formation of parts.

The purpose of this paper is to investigate how electronic components can be utilized and integrated into polymeric optical fibre (POF) textiles to refine the design aesthetic, tactile quality and initiate the interaction of textiles with the users; and to study the design process of interactive products by using a novel design process model.

Fashion and textile design methods, textile technology are used in combination with modern technologies such as laser engraving, sensing, short-distance communication technology, throughout the entire process of development of interactive photonics creations.

The results of evaluation indicate that the engineered prototypes can enhance the interactive function of interior furnishing. The usability of interactive POF cushions is optimized by innovative design methods considering both design and technology.

This research explores to combine knowledge from different disciplines, including textile, electronics, sensor and laser to create interactive soft furnishings. The inter-disciplinary research provides a new perspective on how POF fabric can be utilized as a new media to change the way people interact with their living surroundings. The interior soft furnishings are no longer unresponsive to people, but can react to them, adapt to their behaviors, change color according to their preferences and therefore merge into our daily life. The developed prototypes reshape interior soft furnishing, and therefore have both theoretical and practical significance.

All measurements of EHD film thicknesses were carried out in simulated test machines. This study uses an actual bearing. A test rig which used a 65mm bore radial cylindrical roller bearing was constructed with a specially designed sapphire window in the outer track. Full loads, and speeds to 3000 rpm were applied. With specially polished rollers and chromic oxide coating on the window excellent interferometric film thickness measurements were found possible. A Xenon flash lamp was used and a Xenon Iaserof0–50pps,pulse half width of 150ns and peak power of 100 watts was developed for this research. A microscope and 35mm camera as well as video tape were used for recording results. Arrangements were made to study any chosen roller and the side of the bearing was also open to view. First the film measurements, when corrected for inlet zone viscous heating, agreed admirably with theoretical predictions for mid and exit film thickness. The effect of inlet boundary length on the film was then investigated in some depth. Studying the effect of the multiple roller system, a number of techniques were used to demonstrate that the inlet boundary length, which controls the lubricant film thickness, was itself controlled by the film thickness between the rollers and track in the unloaded zone. The ribs of oil, formed at either edge of the roller, are only secondary sources of oil for replenishment of the inlet film. It is in fact usual (as shown by the convex shape of the inletzone) for oil to feed out of the inlet zone into the ribs. Oil globules were sometimes observed riding on an air cushion at the entry to the roller‐track conjunction, though completely inoperative as providers of oil.