No description available.

No description available.

Casting is a metal forming process: Pouring the melt metal into a desired shaped mould wait it solidifies. It is often used to manufacture complex parts, which are too expensive or time consuming to produce by other methods. However, casting probably is one of the most challenging manufacturing process. It is a highly technical engineering process requiring deep scientific understanding. A typical modern casting process contains six different stages, which named as melting, alloying, moulding, pouring, solidification and finishing respectively. At each stage, high level and precision of process control is required. Casting process also is one of the most energy intensive manufacturing processes. The metal melting consumes over half of the energy in a casting process. Therefore, the expenses on the casting process has been a significant concern due to the rising of the energy prices. A new casting process, CRIMSON (Constrained Rapid Induction Melting Single Shot Up-casting), has been developed by teams from Cranfield University and the N-TEC Ltd. It can improve the energy efficiency of a casting process without reducing the quality. The process, firstly, uses the rapid induction furnace to melt just enough metal for one single casting; then transfer the molten charge to a computer controlled counter gravity casting platform. Finally, the highly controlled metal flow is pushed into the mould to finish the pouring and solidification. Such process reduces the defect generation and energy consumption by rapid melting, minimum holding and smooth filling of the mould. Since the CRIMSON process is a relatively new casting production process. The main objective of this dissertation is to validate the CRIMSON process by different approaches. Firstly, the concept of the sound casting running system design and the principle of the novel CRIMSON process has been introduced. Secondly, Flow3D (A comprehensive, general-purpose computational fluid dynamics software) has been used to investigate the filling patterns of the novel CRIMSON process and the gravity sand casting process. Thirdly, life cycle assessment (LCA) method has been used in this project to review the energy consumption of the conventional casting sector and the novel CRIMSON process. The inventory data was used to assess the environmental impacts of the both casting processes. Moreover, this project investigated the productivity of the CRIMSON process. The productivity of the CRIMSON process for certain range of the casting product has been investigated and compared with the conventional casting process. Finally, the cost of the CRIMSON process has been estimated. The total variable cost of the CRIMSON process was investigated and compared with the conventional casting process as well. Key conclusions can be addressed as below:  Because of the geometry requirement, the gravity poured running system cannot avoid generating double oxide film defect during the filling.  For the CRIMSON process, all the important parameters (such as temperature, time, and velocity) are under control. The piston only needs to move at low speed to guarantee the liquid metal is delivered smoothly and the double oxide films are not formed or entrapped.  The material flow and the embedded energy of the casting making can be evaluated by the lift cycle inventory data collection method. The embedded energy of the sand casting is about 55 MJ/kg. However, to consider the recycling and reusing the internal material, the energy burden of the CRIMSON and the conventional sand casting are 16 MJ/kg and 18 MJ/kg respectively. Considering the energy burden for saleable casting, the CRIMSON process consumes 230 MJ/kg to make saleable casting; the conventional process consumes 449 MJ/kg to make saleable casting.  By using the collected inventory data, the environmental impact assessment can be carried out for both the casting process. The results indicate that the CRIMSON process is environmental friendly compared with the conventional sand casting process.  A complete foundry model was developed in order to investigate the productivity of the CRIMSON process. The WITNESS simulation tool was used to assess the productivity investigation. For casting size less than 2 kg, the conventional sand casting process is productive. However, as the casting size increases, the CRIMSON process becomes more productive.  Cost estimation also carried out for the CRIMSON process. The total variable cost of the casting process was investigated. It was found that the most expensive variable cost is the raw material cost, which can be 80% of the total variable cost. Furthermore, it is concluded that the CRIMSON process has less variable cost compared with the conventional sand casting process under most of the circumstances.

There is an interest in industry in cost reduction. Tool wear constitutes an important element in the cost of many metal working processes, not only because of the cost of the tool, but also because of the cost of machine downtime. Saltbath nitriding of high speed steel tools adds only about 1% to the cost of a finished tool, but has been found to confer benefits considerably in excess of this over a range of cutting conditions . A series of cutting tests is described, during which cutting forces and tool temperatures were recorded simultaneously using microcomputer based instrumentation developed at the Polytechnic as part of this study. The shear mechanism for tools with a nose radius is investigated, and methods for evaluating the primary shear plane area are proposed and discussed. The variation in primary shear plane area with chip flow angle is evaluated. The method for predicting chip flow angle from tool geometry is presented, and results from this analysis compared with experimental data . A method for predicting primary shear angle from tool geometry, force measurements and workpiece material properties is developed. A number of methods for measuring tool temperature are described . Temperature distributions obtained from finite element heat transfer analysis are presented, and a mechanism for the catastrophic failure of the toolnose is proposed. A range of cutting conditions is described, over which the performance of high speed steel cutting tools is enhaced by saltbath nitriding.

This thesis examines the capabilities of different Rapid Prototyping (RP) manufacturing processes for producing sound metallic parts incorporating features in the micrometre range using the Investment Casting (IC) process. RP has been growing in the past twenty years and is nowadays widely employed in the area of precision investment casting since the technology offers the possibility of manufacturing wax patterns which can be directly implemented into investment casting. Owing to the steady improvements of the technology, some of the recently developed RP building machines offer the possibility of manufacturing small parts incorporating micro-features. In this work, a detailed description of the accuracy and capabilities of the IC process regarding its potential for producing sound meso/micro components is given using two types of conventional RP machines. The results of this analysis are then compared through a benchmarking study with a recently developed RP process suitable for the direct manufacture of ceramic moulds. The different technological chains are compared regarding their overall accuracy, surface finish, the amount of structural defects present in the castings and their relative production costs and lead-time. Finally, the potential of the investment casting process for manufacturing sound micro-castings with high aspect ratio is approached from a structural point of view. Through a metallographic analysis study, the research investigates the size-scale effect of cast micro-components upon their microstructure and the subsequent changes in their mechanical properties.

The continuing maturation of metal laser-sintering technology has presented the opportunity to de-risk the engine design process by experimentally down-selecting high pressure nozzle guide vane (HPNGV) cooling designs using laboratory tests of laser-sintered - instead of cast - parts to assess thermal performance. Such tests are very promising as a reliable predictor of the thermal-paint-engine-test, which is used during certification to validate cooling system designs. In this thesis, conventionally cast and laser-sintered parts are compared in back-to-back experimental tests at engine-representative conditions over a range of coolant mass flow rates. Tests were performed in the University of Oxford Annular Sector Heat Transfer Facility. The aerothermal performance of the cast and laser-sintered parts is shown to be very similar, demonstrating the utility of laser-sintered parts for preliminary engine thermal assessments. It can be shown that in most situations counter-current heat exchanger arrangements outperform co-current arrangements. This concept, though familiar in the heat exchanger community, has not yet been applied to hot-section gas turbine cooling. In this thesis, the performance benefit of novel reverse-pass cooling systems - that is, systems in which the internal coolant flows substantially in the opposite direction to the mainstream flow - is demonstrated numerically and experimentally in film-cooled HPNGVs. It is shown numerically that reverse-pass cooling systems always act to flatten lateral wall temperature variation and to reduce peak metal temperature by maximising internal convective cooling at the point of minimum film cooling effectiveness. Reverse-pass cooling systems therefore require less coolant than other internal flow arrangements to maintain acceptable metal temperatures. The benefits of reverse-pass cooling can be fully realised in systems with long, undisturbed surface length, such as the suction-side (SS) of a HPNGV, afterburner liners, HPNGV platforms, and combustor liners. Three engine-scale HPNGVs with SS reverse-pass cooling systems were subsequently designed using bespoke numerical conjugate heat transfer and aerodynamic models to satisfy engine-realistic aerothermal and manufacturing constraints. The reverse-pass HPNGVs were metal laser-sintered and tested in back-to-back experiments with conventionally cooled HPNGVs in the Annular Sector Heat Transfer Facility. The reverse-pass HPNGVs are shown to reduce peak engine metal temperature by 30 K and reduce mean SS engine metal temperature by 60 K compared to conventionally cooled HPNGVs with the same cooling mass flow. A physically-based infra-red thermography procedure was implemented which takes into account the transmittance of the external optics, the surface emissivity of the object, the black-body temperature-radiometric characteristics of the camera, and the time-varying surrounding radiance. Failure to account for surrounding radiance is shown to result in an absolute error in overall cooling effectiveness of 0.05. A new experimental facility - the Coolant Capacity Rig - was developed in order to measure row-by-row, compartmental and total coolant capacity of HPNGVs to a precision of 0.03%, over a large range of pressure ratios and mass flows using a differential mass flow measurement technique, bypass system, and calibrated mass flow orifice. A novel method for estimating internal loss coefficients from the coolant capacity measurements has been devised which, uniquely, does not require internal pressure measurement.

A review of damage mechanisms in dies used for aluminium casting revealed that erosion due to the molten/semi-solid aluminium droplets entering the die was a major cause of wear. It was also clear that no laboratory tests were available to simulate the die/aluminium interactions. Existing test methods use actual casting machines which is time consuming and expensive. The aim of this work was to develop a laboratory test and then to use it to evaluate current die materials as well as possible treatments/coatings that could be used to reduce the problem. A test was developed that used a shot blaster to propel aluminium balls at flat or cylindrical specimens (to cover possible die geometry variations). It was also possible to heat the specimens. A pulsed method was used for the ball application to simulate multiple castings. Ball motion was evaluated and specimen wear characterised across a range of ball impact velocities. Different impact angles were used for flat specimens and for cylindrical specimens central and eccentric ball flows were used. High speed video was used to investigate the actual impact velocities and also observe the behaviour of the aluminium balls impacting at different angles to see how the wear mechanisms actually occurred. Four regimes of particles behaviour: impact only, impact and sliding, sliding only and pressed only were seen. Wear testing showed that wear increased with impact velocity, but different effects were seen when varying the impact angle as seen previously in studies on erosive wear of spherical solid particles for ductile materials. At 30o impacts, a higher erosion rate was seen than those at 60o and 90o impact angle. Zig zag indentations were seen at high impact angles indicating a higher displacement and removal of material by plastic flow keeps advancing downstream until the individual peaks and valleys meet. Wear rate results highlighted four periods with exposure time: incubation period, acceleration or accumulation period, deceleration period and steady-state period. Tests on cylindrical H13 specimens showed that a high amount of wear occurred at an eccentric position due to increased cutting action. The effects of elevation the temperature in the system on the erosion behaviour were also studied. At high temperature materials soften and the erosion increased. Treated surfaces were also studied to evaluate selected candidate coatings and generate data on their wear resistance. The results showed that coating can have a large effect on erosion damage. The knowledge gained by experiment has contributed to the understanding of die failure and will increase die lives as well as reducing maintenance, machine downtime and labour costs.

The purpose of this research is the development of guiding principles and rules for the design of running systems for aluminium castings, employing both the "virtual" experiment, a computational modelling package, and the "physical" experiment, the real-time X-ray radiography study. "Diverging-Bend" geometry has an essential feature in which the flow rate of the system could achieve the maximum and the velocity of advancing flow could reduce without developing surface turbulence. In liquid aluminium, the surface tension becomes more significant compared to water during the flow transformation from supercritical to subcritical velocities. To describe the phenomenon of hydraulic jump for liquid aluminium it is necessary to include the surface tension, giving the relation pV 2 = (pxgxH) + (4T/H) where p: density, V: average velocity, g: gravitational acceleration, H: the height of the hydraulic jump, and T: surface tension. Guidelines for the designing of L-junctions are developed. Five geometries of L-junctions can be applied and assembled in the design of runners and multiple-gate system. Progressive filling along the L-junction geometry can be achieved by reducing the area of the "dead zone". In a multiple-gate system uniform distribution of flow rate through each gate into the mould cavity is achieved. Quantification of a running system is established by the measurement of coefficient of discharge Cd. The loss coefficient K for individual component of runners is also estimated.

A literature survey on the whole field of pore formation is assembled into the form of a general theory of the causes of porosity in castings. The conventionally accepted modes of feeding are assessed: liquid-, mass-, and interdendritic- feeding; and two further mechanisms are proposed: burst- and solid-feeding. The latter is investigated theoretically using various flow models: elastic-plastic, viscous, creep and Bingham flow. A new theory is proposed for the origin of layer porosity in castings. Experimental work on a wide variety of alloys: Al-Cu, Fe-C, Complex Ni- and Co-base alloys, cast both in air and in vacuum are investigated for the effect of section thickness, taper, and mould and metal temperatures. The formation of porosity appears to change from a non-nucleation to a nucleation mechanism as section thickness increases. A new method of interpreting radiographs based upon a longitudinal line count reveals that solid feeding becomes important in reducing porosity at high mould temperatures. Experiments on the effect of composition of an alloy on porosity cast doubt on the widely accepted theory that the presence of non-equilibrium eutectic liquid reduces porosity, but indicate that the non-equilibrium freezing range of the alloy may be the critical parameter. The effect of pressure on porosity is investigated utilising pressures below atmospheric; the results are inadequately explained by current theories and are discussed in terms of the nucleation and growth of pores; the effect would also appear to have considerable industrial potential for reducing porosity in vacuum cast components.

No description available.