Analysis and Modeling of the Forces Exerted on the Cookware in Induction Heating Applications

We present a semianalytical model for calculating the forces exerted on cookware in domestic induction heating applications. The developed model is based on the Maxwell''s stress tensor and is also based on the existing semianalytic expressions of the electromagnetic fields in planar induction heating systems, which are expressed in terms of Fourier-Bessel series. Taking advantage of the axial symmetry of usual domestic induction heating systems, the flux of the vertical component of the Maxwell''s stress tensor is analytically integrated and the vertical force is obtained. The proposed model captures both eddy currents and magnetization that occurs in typical ferromagnetic cookware. The model is verified by means of two-dimensional Finite Element simulations and also is tested by means of measurements of the change of the weight experimented by cookware due to the forces during the heating process

Proceedings of the First Workshop on Containerless Experimentation in Microgravity

The goals of the workshop were first to provide scientists an opportunity to acquaint themselves with the past, current, and future scientific investigations carried out in the Containerless Science programs of the Microgravity Science and Applications Div. of NASA, as well as ESA and Japanese Space Agencies. The second goal was to assess the technological development program for low gravity containerless experimentation instruments. The third goal was to obtain recommendations concerning rigorous but feasible new scientific and technological initiative for space experiments using noncontact sample positioning and diagnostic techniques

Recent Developments and Future Challenges in Incremental Sheet Forming of Aluminium and Aluminium Alloy Sheets

Due to a favourable strength-to-density ratio, aluminium and its alloys are increasingly used in the automotive, aviation and space industries for the fabrication of skins and other structural elements. This article explores the opportunities for and limitations of using Single- and Two Point Incremental Sheet Forming techniques to form sheets from aluminium and its alloys. Incremental Sheet Forming (ISF) methods are designed to increase the efficiency of processing in low- and medium-batch production because (i) it does not require the production of a matrix and (ii) the forming time is much higher than in conventional methods of sheet metal forming. The tool in the form of a rotating mandrel gradually sinks into the sheet, thus leading to an increase in the degree of deformation of the material. This article provides an overview of the published results of research on the influence of the parameters of the ISF process (feed rate, tool rotational speed, step size), tool path strategy, friction conditions and process temperature on the formability and surface quality of the workpieces. This study summarises the latest development trends in experimental research on, and computer simulation using, the finite element method of ISF processes conducted in cold forming conditions and at elevated temperature. Possible directions for further research are also identified

40 K Neon liquid energy storage unit

Cryocoolers have been progressively replacing the use of the stored cryogens in cryogenic chains used for detector cooling, thanks to their higher and higher reliability. However, the mechanical vibrations, the electromagnetic interferences and the temperature fluctuations inherent to their functioning could reduce the sensor’s sensitivity. In order to minimize this problem, compact thermal energy storage units (ESU) are studied, devices able to store thermal energy without significant temperature increase. These devices can be used as a temporary cold source making it possible to turn the cryocooler OFF providing a proper environment for the sensor. A heat switch is responsible for the thermal decoupling of the ESU from the cryocooler’s temperature that increases when turned OFF. In this work, several prototypes working around 40 K were designed, built and characterized. They consist in a low temperature cell that contains the liquid neon connected to an expansion volume at room temperature for gas storage during the liquid evaporation phase. To turn this system insensitive to the gravity direction, the liquid is retained in the low temperature cell by capillary effect in a porous material. Thanks to pressure regulation of the liquid neon bath, 900 J were stored at 40K. The higher latent heat of the liquid and the inexistence of triple point transitions at 40 K turn the pressure control during the evaporation a versatile and compact alternative to an ESU working at the triple point transitions. A quite compact second prototype ESU directly connected to the cryocooler cold finger was tested as a temperature stabilizer. This device was able to stabilize the cryocooler temperature ((≈ 40K ±1 K) despite sudden heat bursts corresponding to twice the cooling power of the cryocooler. This thesis describes the construction of these devices as well as the tests performed. It is also shown that the thermal model developed to predict the thermal behaviour of these devices, implemented as a software,describes quite well the experimental results. Solutions to improve these devices are also proposed.Fundação para a Ciência e a Tecnologia - SFRH/BD/70427/2010 scholarship; PTDC/EMEMFE/ 66533/2006; PTDC/EME-MFE/101448/2008; PEst-OE/FIS/UI0068/2012-2014); FCT-Embaixada de França — Programa Pessoa 2011/201

Metal Micro-forming

The miniaturization of industrial products is a global trend. Metal forming technology is not only suitable for mass production and excellent in productivity and cost reduction, but it is also a key processing method that is essential for products that utilize advantage of the mechanical and functional properties of metals. However, it is not easy to realize the processing even if the conventional metal forming technology is directly scaled down. This is because the characteristics of materials, processing methods, die and tools, etc., vary greatly with miniaturization. In metal micro forming technology, the size effect of major issues for micro forming have also been clarified academically. New processing methods for metal micro forming have also been developed by introducing new special processing techniques, and it is a new wave of innovation toward high precision, high degree of processing, and high flexibility. To date, several special issues and books have been published on micro-forming technology. This book contains 11 of the latest research results on metal micro forming technology. The editor believes that it will be very useful for understanding the state-of-the-art of metal micro forming technology and for understanding future trends

Laser cladding for epitaxial nickel base superalloys turbine blades

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2014.A prosperidade e larga utilização da aviação como meio de transporte civil, nacional e internacional, exige seriedade no condicionamento das aeronaves. A manutenção preventiva é um ponto fundamental para que sejam evitados desastres aéreos. A verificação dos motores é indispensável e, devido ao alto valor agregado, corresponde aos custos mais elevados de recondicionamento. As turbinas, por estarem sujeitas a elevada temperatura e pressão, geralmente apresentam o maior número de componentes danificados. Por esta razão há o interesse no desenvolvimento de técnicas para o reparo eficaz de pás de turbina. Erosão e formação de trincas são danos comuns que necessitam de recondicionamento. A recente aplicação de pás monocristalinas (SX), no lugar de policristalinas, apresenta vantagens por suportar melhor as elevadas temperaturas e com isto aumentar a eficiência dos motores [1, 2]. No entanto, não há um método reconhecido para o reparo das pás monocristalinas. A proposta deste trabalho consiste na aplicação de laser cladding com injeção de pó, devido a características como o tratamento localizado e controle de material fornecido. Este processo é apropriado devido principalmente à flexibilidade e baixo nível de diluição. Foram desenvolvidos dois métodos para promover o reparo de tais defeitos. Um método consiste na remoção completa de camadas de material onde estão situadas as trincas. O outro prevê a remoção de apenas um pequeno volume da estrutura afetada, através de um entalhe que retira o volume danificado. Com isto, a perda de material, o tempo de trabalho e os custos de manutenção podem ser drasticamente reduzidos. O entalhe tem de ser soldável e também permitir a solidificação de material no mesmo plano orientado como a microestrutura inicial. Para isto, um gradiente de temperatura deve ser introduzido a fim de orientar o crescimento de grão. No entanto, existem desafios para alcançar uma estrutura de cristal único sem rachaduras e poros, devido à distribuição de energia no interior do entalhe. Progressos atingidos e novos desafios são apresentados neste trabalho.Abstract : The prosperity and widespread use of aviation as a civil national and international transport requires seriousness in the aircraft conditioning. Preventive maintenance is the key to avoid disasters. For that, is essential the check of engines, which corresponds to the higher reconditioning costs. The turbines, due to elevated temperature and pressure, usually have the highest number of damaged parts. For this reason, there is an interest in developing techniques for the efficient repair of turbine blades. Erosion and crack formation are common damages that require refurbishing. The recent application of single crystal (SX) turbine blades, instead of polycrystalline, present better withstands in high temperatures and thus increases the efficiency of the engines [1, 2]. However, a recognized method for the repair of SX turbine blades has to be developed. The proposal of this work involves the application of laser cladding with powder injection, due to characteristics such as localized treatment and control of the material injected. This process is particularly suitable due to flexibility and low dilution levels. There are two techniques developed to promote the repair of such defects. One way is by the removal of complete layers in which the cracks are located. Another possibility is to remove just a small volume of the affected microstructure. Therewith the loss of material and working time may be drastically reduced as well as the maintenance costs. The notch must be weldable and permit the material solidification in the same oriented plane as the original structure. For that, a temperature gradient has to be introduced in order to guide the grain growth. However, there are challenges to achieve a SX structure without cracks and pores due to energy distribution inside the notch. Current achievements and further challenges are presented in this work

Modeling of directional solidification of multicrystalline silicon in a traveling magnetic field

Melt flow plays an important role in directional solidification of multicrystalline silicon influencing the temperature field and the crystallization interface as well as the transport of impurities. This work investigates the potential of a traveling magnetic field (TMF) for an active control of the melt flow. A system of 3D numerical models was developed and adapted based on open-source software for calculations of Lorentz force, melt flow, and related phenomena. Isothermal and non-isothermal model experiments with a square GaInSn melt were used to validate the numerical models by direct velocity measurements. Several new 3D flow structures of turbulent TMF flows were observed for different melt heights. Further numerical parameter studies carried out for silicon melts showed that already a weak TMF-induced Lorentz force can stir impurities near to the complete mixing limit. Simultaneously, the deformed temperature field leads to an increase of the deflection of crystallization interface, which may exhibit a distinct asymmetry. The numerical results of this work were implemented in a research-scale silicon crystallization furnace. Scaling laws for various phenomena were derived allowing a limited transfer of the results to the industrial scale

Field quality analysis to monitor the industrial series production of the dipole magnets for the Large Hadron Collider

In superconducting accelerator magnets, the field quality is mainly determined by conductor position inside the coil. For the LHC, the dipolar field homogeneity must be assured up to 10-5 of the main field component, imposing strict manufacturing tolerances. Magnetic measurements at room temperature provide a fast and economical way to find out assembly errors or the use of faulty components. In order to compute control bounds for the industrial series production, the magnetic measurements performed at room temperature on 27 pre-series collared coils have been statistically analyzed in this work. An automatic tool has been implemented to single out anomalous values of the magnetic field in the measurements. Such cases have been analyzed using a magnetostatic code to work out errors in the manufacturing process and the possible cures