Mechanical Engineering - Theses
Permanent URI for this collection
Search Results
1 - 10 of 16
-
ItemMiscibility, morphology and physical properties of blends of polycarbonate with a range of thermoplastic polyesters(University of Melbourne, 1991)This study aims to gain an understanding of the relationship between miscibility, morphology and physical properties of polycarbonate (PC)/thermoplastic polyester blends. Blends of PC with 6 polyesters were prepared. The blends were compounded using a single screw extruder and then injection moulded to form test pieces. A transesterification inhibitor was added to prevent transesterification occurring during the melt processing. The miscibility of the blends was determined using Differential Scanning Calorimetry and Dynamic Mechanical Thermal Analysis. The blends exhibited a range of miscibilities from completely miscible to almost immiscible. The miscibility of some of the blends was found to be dependent on the method of blend preparation, and whether or not transesterification had occurred. Transmission Electron Microscopy of Ruthenium Tetroxide stained sections of the blends was used to study their morphology. As would be expected, the partially miscible blends showed phase separation, whereas the miscible ones did not. The morphology of the partially miscible blends was found to be dependent on the viscosities of the homopolymers and the shear rate applied to the blend during melt processing. Small Angle X-ray Scattering was used to study how the spherulitic morphology of the semicrystalline polyesters was effected by blending them with PC. As the miscibility of the blend increased, an increasing amount of PC became incorporated between the lamellae of crystalline polyester. The resistance to fracture of the blends was determined under both constant strain rate and impact conditions. Tensile tests and Scanning Electron Microscopy of fracture surfaces was used to aid the interpretation of the fracture results. Under constant strain rate conditions, the fracture toughness of the partially miscible blends was dependent on the adhesion between its phases. If the adhesion was poor, the blend had a low resistance to fracture. If the adhesion was good, the fracture toughness was dependent on the morphology of the blend and the relative ductilities of the homopolymers. If the blend consisted of domains of ductile material dispersed through a brittle matrix, its fracture toughness was synergistic. However, if the blend consisted of rigid domains dispersed through a ductile matrix, its resistance to fracture was poor. If the two phases had similar ductilities, the fracture toughness of the blend was additive. Miscible blends were found to have poor resistance to fracture under constant strain rate conditions. These blends had greater than additive densities, indicating that they contain less free volume than their corresponding homopolymers. This results in reduced molecular mobility, which embrittles the material, because it is unable to undergo energy dissipative plastic deformation. The fracture toughness of one particular miscible blend was further reduced by the poor adhesion between the crystalline phase of one of the polymers and the mixed amorphous phase. The impact strength of the blends was found to increase as the miscibility of the blend increased.
-
ItemDesign of a prosthetic anterior cruciate ligament( 1999)Injury to the knee can have a dramatic effect on a person's lifestyle. Participation in sports and exercise, general mobility, and even commonplace activities like walking up stairs can all be restricted or prevented completely if knee joint function is impaired. A common form of knee injury, estimated to affect roughly one in three thousand people per year, involves damage to the anterior cruciate ligament (ACL). The ACL passes through the centre of the knee, connecting the femur ('thigh bone') and tibia ('shin bone'). Rupture of the ACL can lead to instability of the knee, potentially resulting in knee pain, limitation of mobility and long term joint damage.This thesis describes the design and preliminary testing of a prototype prosthetic ACL intended to restore natural knee motion after ligament injury. The functional characteristics of the human ACL are established, and the major failure modes of previous prosthetic ligaments are identified as fatigue, abrasion, creep and joint inflammation due to particulate wear debris.
-
ItemSculpturing surfaces with robot manipulators( 1993)A six freedom robot manipulator can position and orientate a tool anywhere within in its workspace. This enables the manipulator to traverse an oriented cutting tool across surfaces whose topography require the use of all six freedoms. Although the tracing of a general curve within the reachable workspace is theoretically possible, kinematic and control limitations often preclude this. The degree of such limitations may impede the successful generation of a specific surface shape. This research investigated specific surfaces and sculpturing strategies to evaluate the kinematic limitations posed by manipulators. In the assessment of whether a strategy will be successful or not, the manipulator's structural configuration, cutting tool geometry, location of the surface in the workspace, and the trajectory generation method must be taken into consideration. The range of end-effector orientations possible at a single position within the manipulator's workspace was defined as the orientation envelope and provides a measure of manipulator dexterity. The orientation envelope can be used to predict whether a manipulator based sculpturing system can kinematically complete a sculpturing strategy. Surfaces that cannot be sculptured continuously, either due to orientation envelope or dexterity limitations, may be divided into patches, each involving a different strategy. At a special configuration the rank of a six freedom manipulator's Jacobian is less than six because at least two joints lose their linear independence. Special configurations are likely to be encountered during sculpturing of highly curved surface regions and can prevent continuous sculpturing. To permit continuous sculpturing in a. region which contains special configurations, the trajectory curves for the manipulator are either steered away from singular positions on the surface or made to move smoothly through them by adjusting the trajectory path. A system based interface between the Cincinnati Milacron T3-726 controller and an external host computer was written to test the accuracy of the T3-726 in locating end- effector geometries in its workspace during tracing experiments. The T3-726 controller introduced a substantial systematic error which caused end-effector locational errors that tended to increase as the manipulator actuated its joints away from their home positions. Manipulator based sculpturing can only be performed reliably with external joint space control. A novel method of trajectory curve generation is proposed in which only a surface and an initial surface curve description is needed. The evolution of the initial surface curve is driven by the curvature of the curve and the surface to which it is constrained and subsequently generates a family of intermediate trajectory curves.
-
ItemGeometrical analysis and CAD/CAM software for twist drills( 1997)The drilling process is one of mankind's earliest machining achievements and remains a most widely used operation in modern manufacturing industry. It has been reported in a recent CIRP keynote paper that drilling operations account for 22% of all the processing time spent in material removal with conventional machining operations. It has long been argued that because of the extensive use of drilling even a slight improvement in the general level of drill performance would yield important practical and economic benefits to individual firms and manufacturing industry as a whole. The importance of drilling operations is also witnessed by the continual research and development of the drill design geometry and tool materials aimed at improving the technological and economic performance of drills and drilling noted in the literature. Among the many better known and reported findings and improvements are included the development of the twist drill geometry initially patented by Morse in 1863, the recognition of the effect of the geometrical features on drill performance, the selection of appropriate values of these features to optimise the drill performance for each workpiece material, the development of a general purpose twist drill with a compromise set of drill point feature values to yield an acceptable performance when drilling a range of work materials commonly used in engineering practice and the development of standard specifications of the twist drill geometry. Among the less known, and often insufficiently emphasised in the research literature, developments and contributions are those made by the drill manufacturer in reducing the cost and improving the quality at twist drills through innovations in manufacturing methods. These include the ingenious design and use of special purpose machines for fluting and point sharpening suitable for batch production and automation. More recently CNC machine tools for twist drill manufacture have been developed and are being introduced although the use of such computer-based technology in cutting tool design and manufacture appears to have lagged behind that for general component manufacture. The lack of detailed drill design and manufacturing information reported in the literature appears to be partly due to the special and complex nature of the machine tools used, the ambiguously specified drill geometry given in standards and handbooks and the proprietary nature of the information. As a consequence the drill manufacturers have retained much of the control of the nominal or design values and tolerances of the specified features and geometry of the popular general purpose twist drills. With the advent of CNC machine tools and flexible automation in discrete part manufacturing predictable and consistent drill performance, which is dependent on the drill geometry, is essential for economic optimization of drilling operations as well as to offset the high investment and overhead cost of modem computer based manufacturing. The introduction of this technology in drill manufacture also requires a precise knowledge of the twist drill geometry and offers the opportunity and competitive advantage to produce drills with the optimal drill point feature values for each work material as well as the general purpose drills as 'standard' products. An ongoing research programme at the University of Melbourne has involved investigations into the general purpose drill geometry, specification, manufacture and performance modelling as well as process capability studies during drill production since the 1970's. These investigations have highlighted the need to delve into the traditional domain of the drill manufacturers to study the drill geometry from the drill design and manufacturing points of view to identify, and if possible eliminate, any ambiguities and establish models of the precise geometry for use in drill specifications and performance modelling as well as for machine settings and geometrical control during drill manufacture. It has also been shown that there is considerable scope for developing mathematical models and associated computer programs of the generated drill geometry of use in CAD/CAM applications and for reducing the excessive geometrical variability of 'as produced' drills to achieve predictable performance essential for modem flexible manufacturing. In this thesis detailed analyses and associated computer software of the flute generation process will be developed based on a typical fluting machine design used in drill production. Both forward and backward analyses will be developed to enable the generated flute profile to be established for a given cutter profile and machine settings and to determine the cutter profile required given the intended or design flute profile geometry and the machine setting respectively. The computer models will also incorporate point sharpening analyses based on the straight lipped conical grinding method and a simplified conical grinding method recommended in Chinese and Russian sources. The fluting and sharpening models will be used to study the adequacy of the general purpose drill specification for uniquely describing the drill geometry, the intended or design flute geometry and its suitability for straight lip production and the extent to which the generated geometry is dependent on the manufacturing method and settings used in production. Apart from gaining a deeper understanding of the geometrical specification, design and manufacture of twist drills this project will provide useful software for CAD/CAM application essential for introducing CNC technology in drill production.
-
ItemModelling heat pump grain drying systems( 1990)Drying is a common process in a number of industries. Products such as furs, wools, textiles, clay, timber, grains, fruits, and vegetables, at some stage, require drying. Review of the literature reveals that commercial dryers are highly inefficient due to various factors. One such factor is that commercial dryers are generally not equipped with heat recovery facilities. Heat pumps can provide a very efficient means of recovering both sensible and latent heat, hence energy loss can be substantially reduced. Furthermore, a heat pump always delivers more heat than the work input to the compressor. These two salient features render heat pump drying a premium alternative for efficient use and conservation of energy in drying industries.
-
ItemA ground coupled heat pump system with energy storage( 1996-09)A Ground Coupled Heat Pump System (GCHP) is a heat pump with or without any thermal storage which uses soil as a heat source or sink. Soil, due to its large thermal capacity and inertia, can serve as a heat source or sink, thus offering relatively constant operation conditions for a heat pump. The soil temperature at a depth of about 2.0m fluctuates slightly around the yearly average air temperature at any given location. This offers a lower and stable sink temperature in the cooling mode operation and a higher and stable source temperature in the heating mode operation. The major consequence of this fact for a GCHP operation is a lower energy consumption as compared with a standard air-source heat pump.
-
ItemPredictive models for forces, power and hole oversize in drilling operations( 1994-12)Drilling is one of the most commonly used material removal processes for producing holes in the manufacturing industry. Despite the long history of design and developments of hole making tools, the modern twist drill, which undertakes most of the hole making tasks, is largely based on Morse’s geometrical design patented in 1863. however, considerable improvements in the technological performance of drilling operations as assessed by the forces, power, drill-life and hole quality have been achieved through the use of stronger and more wear resistant tool materials, better selection of the salient drill point features and improvements in drill manufacturing methods involving increased automation and geometrical control of drill variability. A variety of drill point modifications and designs have also been proposed and made commercially available although the modern conventional general purpose twist drill design still remains the standard product of drill manufacturers commonly available in stock. The improvement of the technological performance of twist drills has traditionally been the domain of the drill manufacturers who provide technical information and advice often in the form of machining feed and speed recommendations for use in practice. Such machining recommendations or data may also be found in special handbooks which sometimes include drilling performance data such as thrust, torque and power requirements or the expected drill-life in the form of tables, monographs or empirical equations which include the obvious process variables such as the feed and speed. (For complete introduction open document)
-
ItemHigh-Performance Visual Closed-Loop Robot Control( 1994)This thesis addresses the use of monocular eye-in-hand machine vision to control the position of a robot manipulator for dynamically challenging tasks. Such tasks are defined as those where the robot motion required approaches or exceeds the performance limits stated by the manufacturer. Computer vision systems have been used for robot control for over two decades now, but have rarely been used for high-performance visual closed-loop control. This has largely been due to technological limitations in image processing, but since the mid 1980sadvances have made it feasible to apply computer vision techniques at a sufficiently high rate to guide a robot or close a feedback control loop. Visual servoing is the use of computer vision for closed-loop control of a robot manipulator, and has the potential to solve a number of problems that currently limit the potential of robots in industry and advanced applications. This thesis introduces a distinction between visual kinematic and visual dynamic control. The former is well addressed in the literature and is concerned with how the manipulator should move in response to perceived visual features. The latter is concerned with dynamic effects due to the manipulator and machine vision sensor which limit performance and must be explicitly addressed in order to achieve high-performance control. This is the principle focus of the thesis. In order to achieve high-performance it is necessary to have accurate models of the system to be controlled (the robot) and the sensor (the camera and vision system).Despite the long history of research in these areas individually, and combined in visual servoing, it is apparent that many issues have not been addressed in sufficient depth, and that much of the relevant information is spread through a very diverse literature. Another contribution of this thesis is to draw together this disparate information and present it in a systematic and consistent manner. This thesis also has a strong theme of experimentation. Experiments are used to develop realistic models which are used for controller synthesis, and these controllers are then verified experimentally.
-
ItemMachine scheduling problems with setup times( 1993)In this thesis the problem of scheduling a single stage flowshop with setup times is analysed. All the jobs are assumed to be divided into several mutually exclusive classes and a setup task is required when processing switches from jobs of one class to jobs of another class and the setup time is sequence independent. Chapter 1 gives an introduction to the flowshop scheduling problem and discusses the issue of NP-completeness. The second chapter is a review of the literature in this field. In the third chapter a new heuristic is presented for scheduling a single machine with setup times. Its performance is compared with the other known heuristics. The next chapter extends the analysis to parallel machines and some new heuristics for scheduling parallel machines with setups are compared. This section of the research is driven by a problem found in a printing factory in Melbourne. The final chapter presents the conclusions and explores possible future extensions of this research.
-
ItemOptimization strategies and CAM software for rough turning operations( 1991)Among the various manufacturing processes, one of the major important methods of shaping components is by the metal removal operations. A survey carried out in the United Kingdom in 1971 has indicated that 85% of all types of machine tools were used for metal removal operations [1]. Further investigation on metal cutting machine tools has revealed that about 21% of these machine tools used in the U.S.A. in 1973 were lathes [2], while statistical information on component shapes manufactured has shown that more than 50% were geometrically cylindrical which could be suitably processed on lathes [3]. Therefore turning operations contribute a significant proportion of all metal removal operations and capable of manufacturing a high percentage of component shapes required by industrialized nations. Within the manufacturing industry, metal removal or generally metal machining occupies a high ranking position in dollar volume capacity. It is estimated that US$60 billion is spent annually in the U.S.A. on labour and overhead costs for operating metal cutting machine tools [2]. Investigation on machine tool utilization has shown that although only about 5% of the total time is available for operating conventional machine tools, this represents about 47% of the manufacturing costs [4]. Hence even a small percentage improvement in machining costs or production rates can prove to be economically significant in financial savings. While such a huge amount of financial investment allocated on metal machining has been claimed to be justified in conventional manufacturing systems, where less than 5% of the total available production time is spent on machining components, this percentage is expected to increase to more than 70% in modern computer-based manufacturing systems and NC/CNC machine tools [5]. Furthermore, in view of the very high capital and operating costs of computer-based manufacturing systems, the optimization of machining conditions in process planning assumes even greater importance than in the past. While few CAM systems incorporate software packages for the optimization of machining conditions, such advanced machining software will prove indispensable to improve the efficiency and competitiveness of firms investing in capital intensive high technology manufacturing equipments and CAM systems. In this thesis, the popular and important rough turning operations will be considered. Optimization analyses and strategies for the selection of cutting conditions for single pass and multi-pass rough turning operations will be developed. The analyses will be based on criteria typified by the maximum production rate and minimum cost per component and will incorporate various practical constraints of importance in rough turning. Attempts will also be made to develop an interactive and user-friendly software package for both single pass and multi-pass turning for eventual use in CAM support systems in manufacturing industry.