Dissertationen zum Thema „Plastic machining“

Global manufacturing trend and competition challenge every industry to seek new manufacturing methods to improve their business processes and speed up the product development cycle [Conolly, 2004a and Knights, 2001]. Among the candidates, layer manufacturing (LM) technologies appear to be a potential solution [Plam, 2002, and Grimm, 2004]. Recent LM technologies have led to a demanding application for developing production tools to manufacture parts, known as rapid tooling (RT). Selective laser sintering (SLS) is one of the leading LM systems available today in RT to manufacture injection mould (core/cavity) inserts [Kruth, 1998, Chua, 1999, Dormal, 1999, and Grenda, 2005]. However, the current capabilities of the SLS in producing metal parts have not yet fulfil the requirements of the injection mould inserts, especially in dimensional accuracy and surface finish quality [Francis, 2002 and Dalgamo, 2001 a]. The aim of this research is to use indirect SLS and high speed machining (HSM) in developing production-quality plastic injection moulding (core/cavity) inserts. The idea is that the indirect SLS process is utilised to build a near-net-shape inserts, while HSM is then utilised to finish the inserts to production specifications. Benchmark studies have been carried out to characterise the capabilities of both SLS and HSM with reference to the typical requirements of injection mould inserts. Utilising the study results, new developments of the mould inserts have been implemented on three major industrial case studies. Their performances have been evaluated and measured by comparing them with its respective original inserts. Furthermore, a set of design rules has been derived from best practices of the case studies, and have been validated by developing a new design for each case studies inserts. The results have demonstrated that the indirect SLS process has a capability III manufacturing a near-net shape of the insert which requires further related finishing to achieve final production specifications. The insert performances in some case studies have indicated significant improvements in process productivity and energy consumption as well as economic benefits to using the inserts. Regarding the significant considerations in realising the design, a recommendation on further strategic design rules and manufacturing process are highlighted so that the development of the insert using the selected approach can be more effective and efficient. Moreover, a utilisation of computer analysis software and further durability trial is also highlighted in order to predict and evaluate the optimum overall performance.

The credit card industry is huge with over two and a half billion cards shipped annually. A local card manufacturer, with a production volume in excess of forty million cards annually, approached the University of Canterbury to design and develop advanced card manufacturing technology. The motivation behind this development was the desire of the sponsoring company to keep abreast of new technologies and to have the ability to manufacture and supply cards with this new and emerging technology into a highly competitive world market. This thesis reports the research surrounding the development of a dedicated new machine tool explicitly designed to implement the emerging technologies found in the international credit card industry. The machine tool, a dedicated milling machine, was not developed in its entirety within these pages; however, three major constituents of the machine were researched and developed to a point where they could be implemented or become the subject of further research. The three areas of interest were; • A machine table system that avoided the increased zonal wear to which linear bearings are subject, typically due to short high frequency traversals, and also the high friction and mass generally found in dovetail slides. • Design requirements demanded the use of a single commercially available carbide cutter to produce 1500 components per hour. Therefore, a purpose built high (revs per minute) rpm spindle and drive system specifically for use with polymeric materials, (R-PVC in particular) was deemed necessary. • Tracking the cutter depth in relation to an RFID aerial track embedded within the credit card core. The aerial tracking was to be dynamic and occur during the machining process with the machine “remembering” the depth of cut at contact with the aerial. Each of the three areas was researched via an in-depth literature review to determine what and if any material had been published in these fields. For the development of the machine table a novel flexure hinge idea was considered. Considerable material was discovered about flexures, but very little was found to be relevant to the application of high displacement metal flexures necessary to meet the required levels of table movement. In effect the proposed machine table system and research in this field would be novel. The high performance spindle investigation became directed into a much narrower focus as it progressed; that of determining the power consumption required to machine the integrated circuit pockets in an R-PVC work piece. This was due to the lack of information pertaining to the physical properties of polymeric materials, in particular the specific cutting pressure. The depth following sensor array was configured using capacitance detection methods to determine the distance between the cutter?s end and the aerial tracks. Capacitance sensing methods, whilst not new, were developed into a novel arrangement to meet the specific cutter tracking requirements of the proposed new machine tool. Each of the respective development areas had concept designs completed and were prototyped before being tested to determine the effectiveness of the respective designs. The outcomes from the testing are reported herein, and show each constituent part to be basically feasible, in the application. The results were sufficient to indicate that each development showed distinct potential but further development and integration into the machine tool should ensue.

The aim of this diploma thesis is to design a single-purpose machine for machining steering wheel lever from PUR. The problem with the current state was the need of manpower for machine a large number of levers. The automated machining process eliminates the problem. The result of the work is a detailed 3D model of a single-purpose machine created in the Onshape program, drawing documentation of several parts of the equipment, economic evaluation and risk analysis of the machine. The conclusion of the thesis contains an evaluation of the whole project.

The diploma thesis Rationalization technology of production tools is divided into two parts. The first part is focused on injection molding of plastic materials and analysis current status of production injection tools. The second part contains proposal of rationalization steps in the production process and evaluation of rationalization.

Carbon fiber-reinforced plastics (CFRPs) have gained widespread popularity as a lightweight, high-strength alternative to traditional materials. The unique anisotropic properties of CFRP make processing difficult, especially using conventional methods. This study investigates laser cutting by ablation as an alternative by comparing two near-infrared laser systems to a typical mechanical machining process. This research has potential applications in the automotive and aerospace industries, where CFRPs are particularly desirable for weight savings and fuel efficiency. First, a CNC mill was used to study the effects of process parameters and tool design on machining quality. Despite high productivity and flexible tooling, mechanical drilling suffers from machining defects that could compromise structural performance of a CFRP component. Rotational feed rate was shown to be the primary factor in determining the axial thrust force, which correlated with the extent of delamination and peeling. Experimental results concluded that machining quality could be improved using a non-contact laser-based material removal mechanism. Laser machining was investigated first with a Yb:YAG fiber laser system, operated in either continuous wave or pulse-modulated mode, for both cross-ply and woven CFRP. For the first time, energy density was used as a control variable to account for changes in process parameters, predicting a logarithmic relationship with machining results attributable to plasma shielding effects. Relevant process parameters included operation mode, laser power, pulse overlap, and cross-ply surface fiber orientation, all of which showed a significant impact on single-pass machining quality. High pulse frequency was required to successfully ablate woven CFRP at the weave boundaries, possibly due to matrix absorption dynamics. Overall, the Yb:YAG fiber laser system showed improved performance over mechanical machining. However, microsecond pulses cause extensive thermal damage and low ablation rates due to long laser-material interaction time and low power intensity. Next, laser machining was investigated using a high-energy nanosecond-pulsed Nd:YAG NIR laser operating in either Q-Switch or Long Pulse mode. This research demonstrates for the first time that keyhole-mode cutting can be achieved for CFRP materials using a high-energy nanosecond laser with long-duration pulsing. It is also shown that short-duration Q-Switch mode results in an ineffective cutting performance for CFRP, likely due to laser-induced optical breakdown. At sufficiently high power intensity, it is hypothesized that the resulting plasma absorbs a significant portion of the incoming laser energy by the inverse Bremsstrahlung mechanism. In Long Pulse mode, multi-pass line and contour cutting experiments are further performed to investigate the effect of laser processing parameters on thermal damage and machined surface integrity. A logarithmic trend was observed for machining results, attributable to plasma shielding similar to microsecond fiber laser results. Cutting depth data was used to estimate the ablation threshold of Hexcel IM7 and AS4 fiber types. Drilling results show that a 2.2 mm thick cross-ply CFRP panel can be cut through using about 6 laser passes, and a high-quality machined surface can be produced with a limited heat-affected zone and little fiber pull-out using inert assist gas. In general, high-energy Long Pulse laser machining achieved superior performance due to shorter pulse duration and higher power intensity, resulting in significantly higher ablation rates. The successful outcomes from this work provide the key to enable an efficient high-quality laser machining process for CFRP materials.

Dissertação para obtenção do Grau de Doutor em Engenharia Mecânica
The tremendous growth which occurs at a global level of demand and use of composite materials brings with the need to develop new manufacturing tools and methodologies. One of the major uses of such materials, in particular plastics reinforced with carbon fibres, is their application in structural components for the aircraft industry with low weight and high stiffness. These components are produced in near-final form but the so-called secondary processes such as machining are often unavoidable. In this type of industry, drilling is the most frequent operation due to the need to obtain holes for riveting and fastening bolt assembly of structures. However, the problems arising from drilling, particularly the damage caused during the operation, may lead to rejection of components because it is an origin of lack of resistance. The delamination is the most important damage, as it causes a decrease of the mechanical properties of the components of an assembly and, irrefutably, a reduction of its reliability in use. It can also raise problems with regard to the tolerances of the assemblies. Moreover, the high speed machining is increasingly recognized to be a manufacturing technology that promotes productivity by reducing production times. However, the investigation whose focus is in high speed drilling is quite limited, and few studies on this subject have been found in the literature review. Thus, this thesis aims to investigate the effects of process variables in high speed drilling on the damage produced. The empirical models that relate the delamination damage, the thrust force and the torque with the process parameters were established using Response Surface Methodology. The process parameters considered as input factors were the spindle speed, the feed per tooth, the tool diameter and the workpiece thickness. A new method for fixing the workpiece was developed and tested. The results proved to be very promising since in the same cutting conditions and with this new methodology, it was observed a significant reduction of the delamination damage. Finally, it has been found that is possible to use high speed drilling, using conventional twist drills, to produce holes with good quality, minimizing the damage.

The thesis deals with electron beam micromachining of nonmetallic materials like glass, ceramics and plastics. A brief description of the device on which the experiments were carried out is included; the author has participated on its development. Main topic is experimental study of influence of main electron beam parameters on results of machining. Examined parameters include accelerating voltage, beam current, focusing and speed of machining. Influence of beam deflection is analyzed. Method of sequential machining by repeated passes of the electron beam is presented. Main examined materials are quartz glass, alumina and selected plastics. The usefulness of the technology is shown by several practical applications.

The diploma thesis deals with the influence of machining technologies (turning, milling, grinding and polishing) on the surface texture of functional surfaces of selected materials from technical plastics. In the first part of the thesis there is a theoretical analysis of the possibilities of machining plastic materials. Furthermore, an analysis of the most commonly used parameters for evaluating the roughness of the machined surface and their effect on functionality is performed. The experimental part of the thesis describes samples preparation, analysis of measured data and subsequent evaluation with benefits for machinery industry.

碩士
國立臺灣科技大學
機械工程系
102
Post-processing on plastic products of quality has become the trend in current manufacturing. Because it is difficult to create non-circular features, such as square holes with sharp corners, on plastic materials with traditional machining, and the non-conductive plastic cannot be processed with non-traditional machining such as wire electrical discharging machining or electrical discharge machining, the objective of this research was to study the uses of ultrasonic machining on plastic materials to fabricate square holes. PMMA was selected to be the material of the plastics. The ultrasonic machine tool used in this research was a self-made one-axis ultrasonic machine, which consists of an ultrasonic spindle, a one-axis linear motion platform, a slurry supply system, and a force measurement system. Because the resonance frequency of the ultrasonic system is influenced by the geometry and the mass of the ultrasonic tool, finite element analysis software was utilized as a tool at the design stage. In order to increase the efficiency of processing PMMA, Taguchi’s methods were used in the experiment to determine the optimal machining conditions. Control factors are types of abrasive, feed rate, tool materials, and types of tool. Accuracy is the target of the experiment. Results from analysis of variance show that types of abrasive, feed rate, tool materials, and types of tool are significant factors. Furthermore, types of abrasive had the greatest contribution. According to the single-to-noise ratio results, we can obtain the optimal factor combination, for which abrasive is Al2O3, the feed rate is 0.02 mm/s, the tool material is stainless steel, and the tool design is pointed.

碩士
國立中興大學
機械工程學系所
107
In the recent year, people are increasingly interested in the use of composite material in the booming industry such as aerospace industry and sports equipment. Carbon fiber Reinforced Plastic(CFRP) is light in weight, fatigue resistance, corrosion resistance, low thermal expansion coefficient and impact resistance. It has occupied a very important position; But because of these characteristics, the CFRP has poor processability, and it faces various problems in conventional processing, such as poor workpiece quality, poor processing efficiency, and short tool life. The experiment is divided into two parts. The first part is the ultrasonic vibration assisted side milling processing of thermoplastic carbon fiber composites. The ultrasonic vibration and the quality of the hole after the side milling (burr phenomenon, surface roughness, etc.) are discussed. First use the Taguchi method to find the best processing parameters (cutting speed, feed per revolution, ultrasonic power), and analyze the variance and do the confirm experiment. Finally, compare the ultrasonic vibration assisted processing. The second part is the experiment of ultrasonic carbon fiber composites with or without ultrasonic vibration assisted drilling, and to discuss the influence of burr phenomenon and tool wear on carbon fiber composites under the presence of ultrasonic vibration assisted drilling. In the milling experiment, it was found that the best processing parameters of milling by the Taguchi method. In the ultrasonic milling experiment, the ultrasonic assisted milling can shorten the burr and reduce the surface roughness of the hole wall. The chips are also short and crumb-like; in the ultrasonic drilling experiments, ultrasonic-assisted drilling can also reduce the length of the burr, the tool wear and the maximum of spindle power, and greatly reduce the chip length.

碩士
國立臺灣科技大學
機械工程研究所
83
The large deformation - large strain finite element theory, and the Upadted Lagrangian Formulation (U.L.F) and step by step principles were used in this paper to develope a 3D elastic- plastic analytical model. At the same time, the strain-energy density theory and a material constant (strain-energy density critical value) were introduced as the reference criteria for chip separation during the cutting process of metals. Furthermore ,the twin-node processing method was added to work with the material constant of strain-energy density critical value. Then the chip separation criterion for the continuous chip during the metal cutting process can be appropriately established. Based on this criterion, an orthogonal and oblique cutting elastic-plastic large deformation model can be further established . In this paper, the second-order strain rate scheme was used in the model and computer program of the large deformation finite element theory to serve as the basis for determining whehter the simulation results are converged or not. Finally,the numberical analysis model developed in this paper was used to analyze the shape changes of the workpiece and chip, the distribution of stess and strain in the workpiece and chip, the distribution of stress and strain in the workpiece and chip, and the process of cutting changes of mild steel under isothermal condition, three dimensional orthogonal and oblique cutting condition. At the same time, initial analyses of the effects of different cutting speeds and residual stress were explored so as to understand th effects of cutting conditions on processed workpiece.

碩士
國立中興大學
機械工程學系所
103
Technical products have characteristics such as short life cycle, high surface quality request and large quantity. Therefore, manufacturing factories gradually tend to use general types machine tool equipped with intelligent management, intelligent design and monitoring systems. Recently, with technological development, there are more and more indirect sensors which are normally used, and computer efficiency is higher than the past. The obstacles of hardware are gradually removed. Accordingly, in the field of manufacturing, many researchers use artificial neural networks (ANNs) to predict the surface roughness. They use milling experiment data for training ANNs, and get the relationship between inputs and outputs. In most of cases, well trained ANNs can predict workpiece surface roughness effectively. The prediction system can achieve the intelligentization of rising process quality. However, when their systems got the prediction of workpiece surface quality, the data did not be further used. This research project will investigate the use of ANNs with sensor fusion to construct an effective surface quality prediction system by making use of force and acoustic emission signals. The prediction system was then optimized under the constraint that the workpiece surface roughness must be lower than the requested surface roughness. The optimization system determined the best parameter combination by maximizing the material removal rate (MRR), and then relaying this information to the machine tool controller. The optimization system experiments show that the maximum error of is about 11%, and the Mean absolute percentage error is about 5.2%, and each optimization operation takes around 110 sec. The performance of system is excellent. The optimization system can be modify and setup on pc-based CNC controller. Let manufacturing industry field can achieve the intelligentization of rising process efficiency.

碩士
國立勤益科技大學
機械工程系
105
Carbon fiber, having the characteristics of light weight, high strength, high modulus, chemical resistance, low coefficient of thermal expansion and so on, has the potential to replace metallic materials, with its application market focusing on heavy industries such as automobile, aerospace, national defense, etc. Currently carbon fiber, which is considered as one of the ten potential materials under the future trend, is the most used material for aerospace building materials, sports equipment, and 3C products, and is recently being used in the automobile industry and wind energy industry. However, Due to its anisotropy and its excellent characteristics, its processing is difficult. For example, delamination occurs while drilling, which could be reduced to some extent, but could not be completely overcome by using ultrasonic assistance. To overcome the said problem, we need to put sacrifice material under the carbon fiber, which, however, increases processing costs, and may cause severe damage to the fiber surface due to excessive cutting resistance, whereby a whole piece of fiber is peeled off and the internal fibrous tissue is pulled out. Additionally, excessively high tool nose temperature could burn the carbon fiber surface and dissolve the resin, which greatly deteriorates the surface quality, and this issue needs to be addressed. This study was divided into two parts. The first part, concerned with ultrasonic-assisted drilling (UAD) of carbon fiber reinforced plastics (CFRP), investigated the influence of ultrasonic amplitude on export quality. The optimal amplitude was selected for subsequent experiments, where the axial thrust and export quality of general drilling and UAD were compared at different feed speeds. Finally an optical microscope was employed to determine the export quality and the measurement tool wear. The second part, concerned with ultrasonic-assisted milling (UAM), mainly explored the influence of amplitude on surface roughness, as well as the influence of three different cooling mechanisms and two different tool geometries on surface topography and surface roughness. Subsequently an optical microscope was used to measure the tool wear and to observe the cutting forms of different processing methods. The results verified that ultrasound could reduce the delamination phenomenon, reduce axial thrust, and reduce tool wear. However, high-amplitude waves degraded the export quality, while low-amplitude waves were ineffective. Better export quality could be achieved at a frequency of 25 KHz, an amplitude of 5.76μm, a spindle speed of 3185rpm, and a feed speed of 5mm/min. A higher feed speed greatly reduced tool wear, but caused severe delamination. In terms of milling, employing ultrasound-assisted techniques and high-efficiency milling cutters could greatly improve the surface quality, where using a four-blade end mill and carbon dioxide-based low-temperature cooling could achieve a surface roughness of 0.703μm. However, as regards tool wear, they did not achieve as good an effect as does the MQL technique. Using air cooling without assistance of ultrasound mostly resulted in unsatisfactory results. In addition, with the introduction of ultrasound-assisted techniques, the winding problem caused by cutting was resolved, and segmental chips were mostly formed during machining, which was most significant for the MQL processing method.

The demand for materials with high mechanical performances such as Carbon Fiber Reinforced Plastics (CFRP) is increasing. However, there are major challenges in machining CFRP as it involves delamination, fiber pullouts, and extreme cutting tool wear. Analysis of chip formation mechanisms and prediction of associated cutting forces in CFRP machining enables one to address these challenges. This study proposes a mechanistic cutting force model for milling operations of the CFRP workpiece, considering its non-homogeneity and anisotropy, by taking into account variations of fiber cutting angle during machining. A mechanistic model of cutting force constants is obtained from a number of experimentally measured unidirectional CFRP milling forces. The obtained mechanistic force model predictions are verified against experimentally measured milling forces with arbitrary tool path indicating the accuracy of the proposed mechanistic model in predicting cutting forces. The proposed mechanistic cutting force model is capable of being integrated into the manufacturing process to allow optimized machining of quality certified CFRP work-pieces.
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