The Feature Resolution and Dimensional Control in Freeform Solidification of Alumina Systems by Stereolithography

Metal additive manufacturing technology of layer-wise stacking of 2 dimensional patterns is emerging in engineering components manufacturing. Nevertheless, limited materials selectivity is a critical hurdle for industrial adoption. Hard engineering components are good market penetration point because product design is limited by machining cost. Near net shaped product with complex design will be advantageous though net shape products cannot be manufactured by current state AM technology. In this context, applicability of a Fe base powder with multiple components for laser powder bed fusion AM was assessed. Powder layer was pre-placed on STS build platform and layer thickness was set to be 25 um. 2 dimensional patterns were overlaid according to continuous irradiation mode with outer contour formation. Laser input parameters were selected from pre-screening step with 5x5x3 mm3 model. After that, 10x10x10 mm3 samples were prepared with laser powder and laser scan rate changing. According to laser parameters, phase compositions and microstructures were reported. Optimum process window for the powder feedstock is reported. With respects to formation of defects such as distortion, interlayer debonding, cracking, and pores, solidification crack, non-uniformity of powder layer, and primitive bead characteristics were considered. In addition, effects of phase composition on corrosion behavior were investigated by anodic polarization.

A finite-element analysis of magnetically driven recirculating flow in electromagnetic near net shape casting

Powder metallurgy (P/M) is the processing of parts from metal powders. In (P/M) technology can be produce homogenous and net shape products, to generate properties not attainable through conventional metal working processes or to manufacture parts to net shape, this reason has motivated the need to find a cost effective technological production method for these composites. In this study the effect of Sintering Temperature and Silicon Carbide Percent on the Compression Properties of the aluminum silicon carbide produced by powder metallurgy is investigated by using the heat treatment of the composite. This method produce a local fusing and welding of the aluminum particles while using aluminum powder with thick oxide layer surrounding the particles prevents the all melting of the composite. Sintering temperatures between 500 and 850 °C were applied after cold compaction on samples containing (0%, 5%, 10%, 15%, 20%, 25% 30% and 35%) of silicon carbide powder then the specimens examined to study the compression properties. The results show that the compression properties of the samples increases with increasing the silicon carbide percent and sintering temperature. Also, to obtain good compression properties the sintering temperature are found to be 600°C for the aluminum with no silicon carbide content, 700 °C for composite containing both 5% and 10% SiC, 750°C for composite containing 15% SiC, 800 °C for composite containing 20%, 25% SiC, 850°C for composite containing 30%, 35% SiC.

The powder metallurgy technique is a well established process for the cost effective production of near net shape products in long series. Soft magnetic materials utilise the premix and compacting techniques of powder metallurgy. High purity powder particles with high compressability are required to ensure good soft magnetic properties. Improvements in the compressability of the powder combined with advances in compacting techniques such as warm compacting result in high density components suitable for commercial production. High induction in powder based products is dependant on the density. In order to ensure low eddy current loss at medium frequency a continuous insulation layer between particles is applied. The thickness of the insulation layer should be minimised in order to maintain the compressibility of the powder and resultant induction. The insulation layer should remain intact after compacting at high pressure. Additives are a normal requirement in the mass production of powder components as lubrication for easy removal of the component from the tool is required. In the case of insulated powder particles where the thin insulation layer must be maintained, additives may also be used to increase the strength. In the case of conventional irregular particle form, the magnetic and thermal properties which can be achieved are isotropic. This permits the design of motors with three dimensional flux and limits the constraints imposed by anisotropic materials.

Development of a computer-aided concurrent net shape product and process development environment

Cold forging of high strength aluminum alloys and the development of new thermomechanical processing

31 - Design of Plastic Parts

Electric discharge aided surface post-treatment of laser powder bed fused non-planar metallic components for enhanced form accuracy

Near single phase zirconolite ceramics, prototypically CaZrTi2O7, were fabricated by reactive spark plasma sintering (RSPS), from commercially available CaTiO3, ZrO2 and TiO2 reagents, after processing at 1200 °C for only 1 h. Ceramics were of theoretical density and formed with a controlled mean grain size of 1.9 ± 0.6 μm. The reducing conditions of RSPS afforded the presence of paramagnetic Ti3+, as demonstrated by EPR spectroscopy. Overall, this study demonstrates the potential for RSPS to be a disruptive technology for disposition of surplus separated plutonium stockpiles in ceramic wasteforms, given its inherent advantage of near net shape products and rapid throughput.

In cold forming several options exist to meet the requirements of producing specific products, e. g. tool shape and lubrication. In the field of micro cold working such measures are not available. When geometrical tool dimensions become smaller the microstructure of the tool materials can interfere with tool making and the forming process, respectively. Aim of this work was to produce hypereutectoid Cr-steels by spray forming and selective laser melting to provide adapted tool materials. Spray forming is regarded as a fast primary forming process with subsequent hot working steps. Selective laser melting is a rapid tooling process for producing near net shape products from powder. Both techniques are known to deliver fine and homogeneous microstructure due to rapid solidification. Powder from spray forming overspray was used as feedstock for selective laser melting. Results are shown from alloy variations in vanadium, niobium and carbon of the steel X110CrMoV8-2 and their effect on microstructure, mechanical properties and friction coefficient of the materials using the strip-pulling test after hardening and tempering. The generated materials with hardness up to 63 HRC are micro-machinable to micro swaging tools with working diameter of less than 1 mm.

In semi-solid forging, it is necessary to control the forming variables accurately in order to make near net shape products. Generally, the defects of products may occur due to liquid segregation that can be caused by deformation, strain rate, and condition of friction. The liquid segregation is to be predicted by flow analysis. This paper presents upper bound analysis model using the new yield function proposed by Doraiveluet al. The model has been applied to analyze the simple compression process of semi-solid Sn-15%Pb alloys to confirm the usefulness of the yield function. The radial distribution of the liquid fraction at various strains, strain rates, and friction conditions between die and workpiece has been estimated.

Effect of in-situ processing parameters on microstructure and mechanical properties of TiC particulate reinforced Al–4.5Cu alloy MMC fabricated by stir-casting technique – Optimization using grey based differential evolution algorithm

Imbalanced data generation and fusion for in-situ monitoring of laser powder bed fusion

Examples of the role interfacial phenomena can play in materials processing are highlighted in the description of a number of recent research studies conducted at Imperial College. Interfacial phenomena play critical roles in increasing or retarding the rates of chemical reaction and in promoting or hindering wetting and dispersion of phases in each other.The reduction of ilmentite to iron and titanium carbide or titanium oxycarbide has been studied with the ultimate aim of achieving separation of the titanium and its subsequent conversion to pigment grade titanium dioxide. The need to achieve good separation of iron from other reaction products is then a prime concern. The effects of reducing conditions on the wetting of titanium carbides and oxycarbides by iron alloys has therefore been studied. It seems that associative adsorption of titanium and carbon may be responsible for the observed effects of dissolved titanium and carbon on the wetting of TiC by liquid iron alloys.As a result of this work a further project has been generated involving the identification of conditions for achieving good dispersions of refractory carbides including titanium carbide in iron alloys. The major motivation behind this work was the desire to develop a cheap casting based process for the production of iron based metal matrix composites capable of producing near net shape products. As a result of this work a novel rapid testing technique for the assessment of the wettability and compatibility of potential filler materials with liquid metal matrices has been developed. The technique employs levitation and quenching of liquid metal drops containing added filler materials to permit assessment of alloy composition, filler coatings and temperature on matrix/filler interactions. The levitation technique has been further utilised in a study of the conditions required for dispersion or non dispersion of second phase particles in liquid superalloys. In this case the cleanliness of the superalloys achieved during recycling procedures is determined by the ease with wich inclusions can be removed. Some observations with ternary oxides also indicate the importance of the associative adsorption phenomenon.The importance of interfacial considerations has also been highlighted by our studies on the production of aluminium-titanium-boron grain refining master alloys from fluoride fluxes. Entrapment of the products can result from emulsification occurring during the reduction reactions. A detailed study of this phenomenon has been conducted using a modified sessile drop technique. The results obtained indicate the critical role that interfacial tension plays in determining the ease of metal-flux separations and in determining whether products are dispersed in the metal or slag.The kinetics of metal-salt reactions were also found to be of importance. Fast transfer of Ti and B to the metal results in the build up to TiAl3. TiB2 or AlB12 at the interface. These compounds when present at the interface can be wet by the flux and result in emulsion formation. Inhibition of emulsification can be achieved by the presence of surface active elements such as magnesium and calcium.The role of interfacial phenomena in influencing the kinetics of the reduction of slags has been studied in an investigation of the kinetics of alkali metal oxide release from silicate melts. The kinetics of K2O and Na2O release during heating in graphite crucibles has been studied from binary alkali oxide-silicon dioxide melts and from a wide range of CaO-Al2O3-SiO2 slags. The contribution of the wetting of the graphite by the slag towards influencing reaction kinetics represents a notable feature of the study.

Analysis of the spray deposition process