Development of a Powder Management Mechanism for an SLS/SLM Machine

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Συστήματα Αυτοματισμού

The Synthesis and Properties of Advanced Aluminium and Copper Based Metal Matrix Composites

This thesis studies the influence that submicrometric alumina particles (α-Al2O3) and milled carbon fibres (MCFs) have on the microstructure, hardness, mechanical properties, and wear of aluminium and copper matrices. The direct use of particulates (micrometric and nanometric scale) and carbon fibres (continuous and chopped) as reinforcement materials in Al-based and Cu-based alloys can potentially result in significant improvements in their property compared to existing Al-based and Cubased alloys. In this research, dual phase and hybrid (three-phase) composites were manufactured by introducing hard ceramic particles (α-Al2O3) and recycled MCFs (\u3c 100 μm long) into Al and Cu matrices. An advanced powder metallurgy processing method was also developed to prepare precursor powder blends for consolidation by uniaxial hot pressing, after which their performance was investigated and compared. This research is divided into, (i) the preparation of precursor composite powders using the magnetically Uniball controlled milling technique, (ii) a synthesis of monolithic aluminium and copper composites using the uniaxial hot pressing technique, (iii) advanced characterisation X-ray diffractometry, field emission scanning electron microscopy (FSEM) equipped with energy dispersive spectroscopy (EDS), Archimedes density, electrical conductivity, resistivity, universal compression testing, Vickers micro-hardness, Ultra-micro indentation testing (UMIS), and wear testing. All the mechanical testing and wear testing of monolithic products was carried out at ambient temperature and atmosphere

Interfacial coefficients in powder metal compaction

A study has been made of the die compaction of metal powders and in particular the problems associated with friction between sliding surfaces have been examined. Friction which results from adhesion or welding, plays an important role in powder consolidation and is greatly influenced by the condition of the surfaces concerned. Attention has been focused upon the compact die interface and the interactions occurring within this region. In particular information has been obtained for friction coefficients between the sliding surfaces and the role of lubricants in affecting these parameters. An assessment has been made of the effect of admixed lubricant level upon the laboratory scale compaction of a reduced iron powder. Ejection forces have been measured and the effects of lubricant content and characteristics evaluated. Die material and surface finish has been shown to be of importance during compaction and ejection. Compact surfaces and strengths have been examined and correlated with the ejection stress data. [Continues.

Development of an inexpensive guidance system for agricultural purposes

Robotics is a rapidly growing technology and robots have pervaded into most of the industries. Robotics and automation are designed to remove the human factor from the labor intensive and monotonous work and thereby decrease the associated costs. The application of robotics to agriculture is fairly recent. Robotic applications in agriculture vary from autonomous row-guidance tractors to fruit picking robots. Similarly, soil testing and soil sampling is one area in agriculture where automation of tasks and the employment of an autonomous robot would be of great use to consultants and farmers employing site specific farming techniques. Soil testing is an important part of farming used to determine the average nutrient status in a field and to obtain a measure of nutrient availability in the field. Fertilizers and other nutrients are applied to the fields based on different soil tests. Site specific farming is greatly dependent on soil testing and can result in increased yield, reduced cost and reduced water pollution. Soil testing requires a lot of soil samples and soil sampling is a time consuming, laborious process and expensive process. Most of the consultants employing site specific techniques use ATVs to get around large fields when sampling. The development of an autonomous guidance system for an ATV to perform soil sampling would be greatly beneficial to them. Labor costs would be significantly reduced and the operators would be subjected to fewer environmental elements. The use of ATVs ensures that no extra capital is needed to buy a vehicle. The use of a small vehicle like an ATV also causes less soil compaction. A WAAS enabled Differential GPS with accuracies to within 9.84 feet was used as the position sensor. Pocket PCs are more portable than a laptop computer and are more suitable for farm conditions. Shape files were used to provide the sampling points as input to the guidance program. A guidance program was made to operate on a PDA and provide guidance instructions. A microprocessor was programmed to read the guidance instructions and actuate the different components like throttle and steering. Tests were conducted to test the accuracy and consistency of the system. The offsets of each stop point from the test point were documented and analyzed. The results indicated that the system was as accurate as the GPS used for guidance. They also indicated that a guidance system can be realized with the use of very few components and an accuracy needed for soil sampling can be achieved. Avoidance routines for obstacles within the field were indicated as future developments

Interconnect yield analysis and fault tolerance for field programmable gate arrays

Imperial Users onl

Effect of Graphene addition on the mechanical and tribological behavior of nanostructured AA2124 /Graphene self-lubricating metal matrix composite

In the current research, the mechanical and tribological behavior, and structural evolution of AA2124-3 and 5-wt.% graphene (G) composites prepared by a combination of ball milling and hot extrusion were investigated. Mixing followed by energy ball milling of the powders was conducted under argon atmosphere. Hot extrusion of the green compacts was carried out at 0.46 and 0.68 of the alloy melting temperature. Properties such as macro and micro-hardness, nanohardness, tensile and lattice strain were characterized. Wear rates, coefficient of friction (COF) were characterized using dry pin-on-disc test under loads of 50, 100N and 150N. Nanoscratch testing were employed to investigate the self-lubricating tribological behavior. X-ray diffraction, optical and scanning electron microscopy were used to determine the influence of the G-content on the crystallite size variation and the lattice strain for the ball milled powders compared to the hot extruded rods. Density measurements and optical microscopy (OM) were employed to investigate the consolidation degree and porosity variation as a function of increasing G- of the G and Al-matrices for the variable conditions. Bulk texture variation was analyzed to evaluate the influence of the extrusion temperature. AA 2124-3 wt.% G composites displayed the highest tensile properties, highest hardness and lowest wear rates and COF, as well as lowest scratch width and depth compared to the 5 wt.%G and the plain alloy. The uniform distribution of the G-particles within the Al-matrices for the 3wt.% containing composites hindered grain coarsening by the induced lattice strain compared to that of 5 wt% G ones. Moreover, addition of 3 wt.% G smeared thin uniform tribofilm on the surfaces of the worn composite rods. The formed layer reduced friction and wear. Increasing the G content up to 5 wt.% resulted in segregation and clustering of the G-particles within the Al-matrices, which caused microplouging and sever plastic deformation wear mechanism and excessive delamination. IV Lower consolidation temperatures of 300oC produced composites with lower wear rates due to the excessive strain hardening effect. Extrusion at 300oC produced a continuous G-encapsulating layer around the Al-matrix compared to an interrupted G-layer for the 450oC extrusions. The G-layer morphology influenced the dominating mechanism of the composite during deformation. Texture analysis of the AA2124-3 wt.%G extruded at low and high temperatures proved that both the Cu-and Shear are the dominating texture components, while increased texture intensities from 1.2-to-1.76 occurred with increasing the extrusion temperature

Belle II Technical Design Report

The Belle detector at the KEKB electron-positron collider has collected almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2 /s luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. A new international collaboration Belle-II, is being formed. The Technical Design Report presents physics motivation, basic methods of the accelerator upgrade, as well as key improvements of the detector.Comment: Edited by: Z. Dole\v{z}al and S. Un

Spaceborne sensors (1983-2000 AD): A forecast of technology

A technical review and forecast of space technology as it applies to spaceborne sensors for future NASA missions is presented. A format for categorization of sensor systems covering the entire electromagnetic spectrum, including particles and fields is developed. Major generic sensor systems are related to their subsystems, components, and to basic research and development. General supporting technologies such as cryogenics, optical design, and data processing electronics are addressed where appropriate. The dependence of many classes of instruments on common components, basic R&D and support technologies is also illustrated. A forecast of important system designs and instrument and component performance parameters is provided for the 1983-2000 AD time frame. Some insight into the scientific and applications capabilities and goals of the sensor systems is also given

Aluminium Based Material Extrusion Through Mathematical Contoured Die: Numerical & Experimental Investigation

The metal forming process is preferable for manufacturing the parts of moderate complexity and greatly diversified profiles for the larger volume of productions to reduce the tooling cost. Energy saving, less scrap generation and near net shape production with better mechanical properties along with high production rate have enhanced the specific forming process, extrusion, for the production of long straight metal products. The huge demand of aluminium alloy in the extrusion industry for fulfilling the market requirements in the sector of building and architecture, construction, automobile and transport system, electrical and electronics, aerospace, and heat exchangers tends to optimize the process for improved process efficiency as well as product quality. Prediction of the influence of process parameters is very difficult owing to the concealed material deformation during extrusion. Due to this reason, an illustrious finite element analysis tool (DEFORM TM) was adopted to investigate the process. The simulations were performed to ascertain extrusion load, effective stress, effective strain and temperature distribution for square to square extrusion process. To decipher the effect of die length, ram velocity and extrusion ratio in the process, simulations were carried out by varying the variables in a wide range with different types of dies. The process was also employed for the investigation of the round to square extrusion considering the same parameters along with punch shape for Al-6063 alloy. Influence of die profile plays a predominant role in predicting the ultimate load requirements and flow characteristics. Considering the die profile an important component, the profile for round to square shape has been developed by following cosine, linear converging, elliptic, hyperbolic and 3rd order polynomial laws. Considering the above die profiles the simulations were conducted with optimised process parameters to find out a suiatable die profile. The simulations were validated with high-temperature experimentations. To improve the product properties, aluminium metal matrix composites (AMMC) prepared by powder metallurgy (PM) route has been extruded. Four different reinforcing elements of 2 wt. % (Zn, Ti, Soda lime silica glass and ZrO2) were added to Al / 5 wt. % of Mg / 1 wt. % of Gr matrix. To avoid the product defects, mathematically contoured cosine profiled die was used for the thermo-mechanical treatment. The improvement of the product properties has been studied. The optimum parameters before experimentation can be set by utilising the finite element tool successfully. Computerised finite element techniques are the best suitable technique to understand the concealed operations like extrusion. The optimum ranges for the extrusion of simple square bar section from the same shape billet and round to square extrusion has been established. The cosine profiled die for both kinds of extrusion as well as PM composite was found suitable as it generates lesser velocity relative difference at die exit. A significant amount of property improvement was observed in the AMMC after thermo-mechanical treatment