Numerical optimization of gating systems for light metals sand castings

This thesis proposed an optimization technique for design of gating system parameters of a light metal casting based on the Taguchi method with multiple performance characteristics. Firstly, the casting model with a gating system was designed and exported as International Graphics Exchange Standard (IGES) models by Unigraphic NX4.0. Based on the IGES models of the casting, Finite Element (FE) Models were generated using Hypermesh software. Then, mold filling and solidification processes of the castings were simulated with the MAGMASOFT. Finally, the simulation result can be converted to numerical data according to the 3D coordinates of the FE model by MAGMALink module of MAGMASOFT . The various designs of gating systems for the casting model were generated and the simulated results indicated that gating system parameters significantly affect the quality of the castings. To obtain the optimal process parameters of the gating system, the Taguchi method including the orthogonal array, the signal to noise (S/N) ratio, and the analysis of variance (ANOVA) were used to analyze the effect of various gating designs on cavity filling and casting quality using a weighting method. The gating system parameters were optimized with evaluating criteria including filling velocity, shrinkage porosity and product yield

NEMS by sidewall transfer lithography

A batch fabrication process for nano-electro-mechanical systems (NEMS) based on sidewall transfer lithography (STL) is developed and demonstrated. The STL is used to form nanoscale flexible silicon suspensions entirely by conventional lithography. A two-step process is designed for single-layer STL to fabricate simple electrothermal actuators, while a three-step process is designed to allow nanoscale features intersecting with each other for more complicated device lay-outs. Fabricated nanoscale features has a minimum in-plane width of approx. 100nm and a high aspect ratio of 50 : 1. Combined structures with microscale and nanoscale parts are transferred together into silicon by deep reactive etching (DRIE). Suspensions are achieved either by plasma undercut or HF vapour etch based on BSOI. The STL processes are used to form nanoscale suspensions while conventional lithography is used to form localised microscale features such as anchors. A wide variety of demonstrator devices have been fabricated with high feature quality. Analytic models have been developed to compare with experimental characterization and finite element analysis (FEA) predictions. Lattice structures fabricated by multi-layer STL have also be investigated as a novel type of mechanical metamaterial. Thus, the process could allow low-cost and mass parallel fabrication of future NEMS with a wider range of potential applications.Open Acces

Advanced digital SAR processing study

A highly programmable, land based, real time synthetic aperture radar (SAR) processor requiring a processed pixel rate of 2.75 MHz or more in a four look system was designed. Variations in range and azimuth compression, number of looks, range swath, range migration and SR mode were specified. Alternative range and azimuth processing algorithms were examined in conjunction with projected integrated circuit, digital architecture, and software technologies. The advaced digital SAR processor (ADSP) employs an FFT convolver algorithm for both range and azimuth processing in a parallel architecture configuration. Algorithm performace comparisons, design system design, implementation tradeoffs and the results of a supporting survey of integrated circuit and digital architecture technologies are reported. Cost tradeoffs and projections with alternate implementation plans are presented

Automated NDT inspection for large and complex geometries of composite materials

Large components with complex geometries, made of composite materials, have become very common in modern structures. To cope with future demand projections, it is necessary to overcome the current non-destructive testing (NDT) bottlenecks encountered during the inspection phase of manufacture. This thesis investigates several aspects of the introduction of automation within the inspection process of complex parts. The use of six-axis robots for product inspection and non-destructive testing systems is the central investigation of this thesis. The challenges embraced by the research include the development of a novel controlling approach for robotic manipulators and of novel path-planning strategies. The integration of robot manipulators and NDT data acquisition instruments is optimized. An effective and reliable way to encode the NDT data through the interpolated robot feedback positions is implemented. The viability of the new external control method is evaluated experimentally. The observed maximum position and orientation errors are respectively within 2mm and within 1 degree, over an operating envelope of 3m³. A new software toolbox (RoboNDT), aimed at NDT technicians, has been developed during this work. RoboNDT is intended to transform the robot path-planning problem into an easy step of the inspection process. The software incorporates the novel path-planning algorithms developed during this research and is shaped to overcome practical limitations of current OLP software. The software has been experimentally validated using scans on real high value aerospace components. RoboNDT delivers tool-path errors that are lower than the errors given by commercial off-line path-planning software. For example the variability of the standoff is within 10 mm for the tool-paths created with the commercial software and within 4.5 mm for the RoboNDT tool-paths, over a scanned area of 1.6m². The output of this research was used to support a 3-year industrial project, called IntACom and led by TWI on behalf of major aerospace sponsors. The result is a demonstrator system, currently in use at TWI Technology Centre, which is capable of inspecting complex geometries with high throughput. The IntACom system can scan real components 2.8 times faster than traditional 3-DoF scanners deploying phased-array inspection and 6.7 times faster than commercial gantry systems deploying traditional single-element inspection.Large components with complex geometries, made of composite materials, have become very common in modern structures. To cope with future demand projections, it is necessary to overcome the current non-destructive testing (NDT) bottlenecks encountered during the inspection phase of manufacture. This thesis investigates several aspects of the introduction of automation within the inspection process of complex parts. The use of six-axis robots for product inspection and non-destructive testing systems is the central investigation of this thesis. The challenges embraced by the research include the development of a novel controlling approach for robotic manipulators and of novel path-planning strategies. The integration of robot manipulators and NDT data acquisition instruments is optimized. An effective and reliable way to encode the NDT data through the interpolated robot feedback positions is implemented. The viability of the new external control method is evaluated experimentally. The observed maximum position and orientation errors are respectively within 2mm and within 1 degree, over an operating envelope of 3m³. A new software toolbox (RoboNDT), aimed at NDT technicians, has been developed during this work. RoboNDT is intended to transform the robot path-planning problem into an easy step of the inspection process. The software incorporates the novel path-planning algorithms developed during this research and is shaped to overcome practical limitations of current OLP software. The software has been experimentally validated using scans on real high value aerospace components. RoboNDT delivers tool-path errors that are lower than the errors given by commercial off-line path-planning software. For example the variability of the standoff is within 10 mm for the tool-paths created with the commercial software and within 4.5 mm for the RoboNDT tool-paths, over a scanned area of 1.6m². The output of this research was used to support a 3-year industrial project, called IntACom and led by TWI on behalf of major aerospace sponsors. The result is a demonstrator system, currently in use at TWI Technology Centre, which is capable of inspecting complex geometries with high throughput. The IntACom system can scan real components 2.8 times faster than traditional 3-DoF scanners deploying phased-array inspection and 6.7 times faster than commercial gantry systems deploying traditional single-element inspection

The use of stereolithography and related technologies to produce short run tooling

ThesisWhere material properties are critical to a polymer part, rapid prototype (RP) models are inappropriate for evaluation purposes and actual parts moulded in a range of materials are required for evaluation. Conventional tool making processes have extremely long lead times considering that numerous iterations may be required. The aim of this project was to generate polymer parts, utilising various approaches to Rapid Tooling (RT) , including Stereolithography or related technologies, as part of the process. The objective was to establish decision-making criteria for deciding on the appropriateness of various processes and the risks involved to assist prospective users of these technologies. The first phase of the project focused on the process validation of utilising Stereolithography as a direct means to generate injection mould tooling inserts, which were fitted into an injection mould designed for the trial purposes. The objective was to obtain process information with regard to insert generation for Stereolithography. A three dimensional model of the part was generated with CAD and the associated mould was generated around the part. The insert halves were processed and solid epoxy inserts were generated with the 3D Systems SLA500 Stereolithography machine. These inserts were post-finished and fitted to the injection mould . Additional features were added to the inserts to test cooling and gating and wear resistance of the cavity material. The author attended the basic injection tool setting course of the Plastics Federation to enable him to contribute more directly to this process. This also highlighted some of the design issues to facilitate ease of production . Initial difficulties were experienced in finding optimal process parameters. A total of 70 parts were produced, with measurable insert degradation. During the author's training at 3D Systems in the USA, he obtained additional insight in current methods of insert modelling and insert generation. If these process problems could be overcome, it would be possible to produce in excess of a 100 parts with one set of inserts, assuming a tolerance specification of 0.2mm. The cost of producing the inserts was approximately 50% that of conventional tooling fabrication . The time lapse between growing of the inserts and production of parts was one week compared to 6 to 8 weeks tool manufacture time with conventional methods. The second phase of the project focused on methods to enhance the cavity surface. Electroplating of inserts and inserts generated from Aluminium filled epoxy were tested , to investigate the effects that plating has on tool life, dimensional accuracy, temperature distribution, and the cost implications for these subsequent process steps. Stereolithography inserts were generated, taking into account the design considerations. Aluminium filled epoxy inserts were subsequently cast from silicone moulds drawn off the Stereolithography master patterns. Two sets of Stereolithography inserts were plated with 20 ~m of electrolytic nickel plating. One set of aluminium filled epoxy inserts were plated with electrolytic copper followed by electroless nickel. The mould sets were subjected to the same injection moulding trials using Polypropylene. The third phase of the project evaluated the use of Stereolithography investment casting masters to produce tool steel inserts, through the QuickCast process. Porosity was evident, with substantial machining required to fit the inserts. Not all the detail was retained during the casting process. Thin rib features on the part were thus lost. Due to the porosity the cooling was changed to copper tubes fitted into the rear of the tool and back-filled with aluminium epoxy. As the Stereolithography patterns were not polished the metal inserts had to be hand finished. This was a time consuming process and skill is required to obtain a good finish. A cost comparison indicated that machining aluminium inserts would be more cost effective. The tool manufacture time and eventual cost is not significantly less than conventional machining . In fact, trials with aluminium High speed CNC machining proved to be more time, finish and cost effective. This is discussed as part of the trial examples. Wax injection into AIM tooling was investigated on behalf of a client, with good results . As ceramic and polymer injection are very similar, apart from the ceramic being far more abrasive, it is the author's opinion that AIM tooling would be applicable, taking into account that fewer parts may be achieved. The KelTool process was also investigated during the author's USA visit. The licensing fees and additional equipment are extremely costly due to the Rand IDollar exchange rate. Issues related to this process are documented in this report. Clearly the deciding factors remain the quantity of parts required and the complexity of form. Each manufacturing process has a certain level of risk involved. Accumulative risk not only sets manufactured parts at risk but could jeopardise project time scales and iterations of a process have significant impact on a project budget

Achieving ship's mission flexibility through designing, printing and operating unmanned systems with additive manufacturing and delayed differentiation

The design, print and operate (DPO) concept of operations (CONOPS) is proposed in this thesis as a new means of equipping ships with the appropriate capabilities. A companion concept of delayed differentiation is also introduced. In coupling the two concepts, additive manufacturing of capabilities in-situ becomes a possibility through the equipping of operational units with three building blocks: additive manufacturing systems and their raw materials, commercial off-the-shelf items and field programmable gate arrays. A concept of operations on uses of additive manufacturing was developed to illustrate the flexibility that the nexus of DPO CONOPS and delayed differentiation can engender. A tactical unmanned aerial vehicle (UAV) was used as an illustration to contextualize the concept of operations to enhance the littoral combat ship's survivability when operating in the littorals. Assessments were then made on the feasibility of DPO CONOPS for shipboard uses. A tactical UAV was used as it was assessed to be operationally relevant and significant. Analytical models that could be iterated to achieve the specific-to-mission requirements were developed to analyze and assess the implementation approach. The models focused on the UAV's reliability in fulfilling the mission as well as the build-time of the UAV.http://archive.org/details/achievingshipsmi1094550484Military Expert 6, Republic of Singapore NavyApproved for public release; distribution is unlimited

Bearing condition monitoring using acoustic emission and vibration: The systems approach

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.This thesis proposes a bearing condition monitoring system using acceleration and acoustic emission (AE) signals. Bearings are perhaps the most omnipresent machine elements and their condition is often critical to the success of an operation or process. Consequently, there is a great need for a timely knowledge of the health status of bearings. Generally, bearing monitoring is the prediction of the component's health or status based on signal detection, processing and classification in order to identify the causes of the problem. As the monitoring system uses both acceleration and acoustic emission signals, it is considered a multi-sensor system. This has the advantage that not only do the two sensors provide increased reliability they also permit a larger range of rotating speeds to be monitored successfully. When more than one sensor is used, if one fails to work properly the other is still able to provide adequate monitoring. Vibration techniques are suitable for higher rotating speeds whilst acoustic emission techniques for low rotating speeds. Vibration techniques investigated in this research concern the use of the continuous wavelet transform (CWT), a joint time- and frequency domain method, This gives a more accurate representation of the vibration phenomenon than either time-domain analysis or frequency- domain analysis. The image processing technique, called binarising, is performed to produce binary image from the CWT transformed image in order to reduce computational time for classification. The back-propagation neural network (BPNN) is used for classification. The AE monitoring techniques investigated can be categorised, based on the features used, into: 1) the traditional AE parameters of energy, event duration and peak amplitude and 2) the statistical parameters estimated from the Weibull distribution of the inter-arrival times of AE events in what is called the STL method. Traditional AE parameters of peak amplitude, energy and event duration are extracted from individual AE events. These events are then ordered, selected and normalised before the selected events are displayed in a three-dimensional Cartesian feature space in terms of the three AE parameters as axes. The fuzzy C-mean clustering technique is used to establish the cluster centres as signatures for different machine conditions. A minimum distance classifier is then used to classify incoming AE events into the different machine conditions. The novel STL method is based on the detection of inter-arrival times of successive AE events. These inter-arrival times follow a Weibull distribution. The method provides two parameters: STL and L63 that are derived from the estimated Weibull parameters of the distribution's shape (y), characteristic life (0) and guaranteed life (to). It is found that STL and 43 are related hyperbolically. In addition, the STL value is found to be sensitive to bearing wear, the load applied to the bearing and the bearing rotating speed. Of the three influencing factors, bearing wear has the strongest influence on STL and L63. For the proposed bearing condition monitoring system to work, the effects of load and speed on STL need to be compensated. These issues are resolved satisfactorily in the project.Royal Thai government and the Department of Physics, Faculty of Science, Chulalongkorn Universit

Novel pneumatic circuit for the computational control of soft robots

Soft robots are of significant research interest in recent decades due to their adaptability to unstructured environments and safe interaction with humans. Soft pneumatic robots, one of the most dominant subsets of soft robots, utilize the interaction between soft elastomeric materials and pressurized air to achieve desired functions. However, the systems currently used for signal computation and pneumatic regulation often make use of rigid valves, pumps, syringe drivers, microcontrollers et al. These bulky and non-integrable devices limit the performance of pneumatically-driven soft robots, carrying challenges for the robot to be miniaturized, untethered, and agile. This DPhil aims to develop pneumatic circuits that can be integrated into the soft robot bodies while performing both onboard computation and control. This thesis presents our contributions towards the aforementioned objective step by step. Firstly, we designed a 3D-printable bistable valve with tunable behaviours for controlling soft pneumatic robots. As an integrable control device, the valve stores one bit of binary information without requiring a constant energy supply and correspondingly controls a pneumatic chamber. Secondly, in order to reduce the number of valves required to control multi-chamber soft robots, we introduced a modular approach to design multi-channel bistable valves based on the previous work. Thirdly, in order to achieve continuous pressure modulation with integrable devices, we designed a soft proportional valve, utilizing the continuous deformation of Magnetorheological Elastomer (MRE) under magnetic flux. Apart from the analogue activation manner, this design also ensures a fast response time, operating at a time scale of tens of milliseconds, much shorter than the mechanical response time of most soft pneumatic actuators. Fourthly, to achieve onboard proportional control of multi-chamber soft robots, we developed an MRE valve array with an embedded cooling chamber. Physical experiments showed that our MRE valve array ensured the independence and accuracy of each valve unit within it, with a significantly lowered temperature of 73.9 $^o$C under 5 minutes of operation. Lastly, we developed an open-source software toolbox supporting the design of integrable pneumatic logic circuits to enhance their accessibility and performance. The toolbox comes with a graphical user interface (GUI) to take users' desired logic functions in the form of a truth table and a set of 2D space constraints related to the available space onboard the robot. It then schedules the pneumatic circuit which performs the desired computation within the space constraints and produces a 3D-printable CAD file that can be fabricated and used directly. The work presented in this thesis enables the community to simplify the process of integrating control devices into soft pneumatic robots, thereby paving the way for a new generation of fully untethered and autonomous soft robots