Dissertations / Theses on the topic 'Cryogenic Milling of Polymers'

Résumé : Les principaux challenges de l’industrie du futur sont de satisfaire à toujours plus d’exigences en termes de développement durable, d’optimisation des coûts et des délais. Les secteurs industriels fabriquant des produits à haute valeur ajoutée tels que l’aéronautique et le spatial, sont dans une perspective continue d’amélioration des produits manufacturés et des procédés. L’emploi de matériaux tels que des alliages de titane ou les superalliages à base de nickel devient courant. Ils sont cependant « complexes à usiner ». Les difficultés comme l’usure prématurée des outils, les déformations de pièces ou encore les mauvaises qualités de surface deviennent problématiques. C’est dans cette perspective que l’assistance cryogénique en usinage peut répondre aux diverses problématiques. Cette technologie peut apporter les réponses aux exigences d’industrialisation : limitation des élévations de température, pas de nettoyage post-usinage et pas d’utilisation de fluides de coupe nocifs pour les opérateurs. Cela induit pourtant de nouvelles questions tel que l’acheminement du fluide cryogénique vers les zones souhaitées, l’optimisation du procédé ou encore l’impact du grand froid sur les outils et les pièces. De nouveaux verrous technologiques et scientifiques apparaissent. Cette thèse propose de les étudier<br>Abstract: The main challenges facing the industry are to satisfy ever more demands in terms of sustainable development, optimization of costs and deadlines. The industrial sectors manufacturing products with high added value in aeronautics and space, are continously in a perspective of improvement the manufactured products and processes. The use of materials such as titanium alloys or nickel-based superalloys is common. Its are "complex to machine". Difficulties in the use of tools, parts deformations or poor surface qualities become problematic. It is in this perspective that the cryogenic assistance in machining can answer the various problems. This technology can provide answers to the industrialization requirements: limiting the rising temperature, no post-machining cleaning and no use of cutting fluids, harmful, for operators. This leads to new questions such as the routing of the cryogenic fluid to the desired zones, the optimization of the process or the impact of a cold fluid on the tools and the parts. New technological and scientific locks are emerging. This PhD thesis propose to study them

Polymer matrix composites (PMCâ s) are now being used more and more extensively and over wider ranges of service conditions. Large changes in pressure, chemical environment or temperature influence the mechanical response of such composites. In the present effort, we focus on temperature, a parameter of primary interest in almost all engineering applications. In order to design composite structures without having to perform extensive experiments (virtual design), the necessity of establishing theoretical models that relate the macroscopic response of the structure to the microscopic properties of the constituents arises. In the first part of the present work, a new stiffness versus temperature model is established. The model is validated using data from the literature. The influence of the different polymerâ s properties (Molecular weight, crystallinity, and filler content) on the model are studied by performing experiments on different grades of four polymers PMMA, PEEK, PPS, and PB. This statistical model is proven to be applicable to very different polymers (elastomers, thermoplastics, crystalline, amorphous, cross-linked, linear, filled, unfilledâ ¦) over wide temperature ranges (from the glassy state to the flow region). The most attractive feature of the proposed model is the capability to enable a description of the polymerâ s mechanical behavior within and across the property transition regions. In order to validate the feasibility of using the model to predict the mechanical response of polymer matrix composites, the stiffness-temperature model is used in various micromechanical models (rule of mixtures, compression models for the life prediction of unidirectional PMCâ s in end-loaded bendingâ ¦). The model is also inserted in the MRLife prediction code to predict the remaining strength and life of unidirectional PMCâ s in fatigue bending. End-loaded fatigue experiments were performed. A good correlation between theoretical and experimental results is observed. Finally, the model is used in the Classical Lamination Theory; some laminates were found to exhibit stress reversals with temperature and behaved like thermally activated mechanical switches.<br>Ph. D.

Orientador: Nivaldo Lemos Coppini<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-25T08:53:06Z (GMT). No. of bitstreams: 1 Martins_FranciscoRomeo_D.pdf: 4084610 bytes, checksum: 81ef4e100b6b8932d54977aa580c82cb (MD5) Previous issue date: 2014<br>Resumo: O objetivo deste trabalho é caracterizar o material composto PRFC (Polímero Reforçado com Fibras de Carbono) em relação ao seu comportamento durante o processo de fresamento cilíndrico tangencial simétrico. Foi usado um método experimental. Uma fresa com oito milímetros de diâmetro e com seis arestas de corte de metal duro ISO K10 foi usada para usinagem placas (PRFC) com 4 mm de espessura. Todo o limite da máquina foi explorado em termos de velocidade de corte que variou entre de 100 em 100 m/min na faixa de 100 a 600 m/min. A profundidade de usinagem (espessura da chapa) foi de 4 mm. Dois avanços por dente da fresa foram utilizados em parte das experiências nos valores de 0,075 e 0,1 mm/rot. Este trabalho se justifica pelo fato de que a utilização de materiais compósitos tem crescido substancialmente e os seus métodos de produção se tornaram mais populares. Estes materiais vêm sendo cada vez mais utilizados em aplicações das mais diversas áreas industriais, tais como: aeroespacial, aviação comercial, indústria naval, automobilística, indústrias de máquinas ferramentas e equipamentos desportivos. Os materiais compósitos (PRFC) são importantes materiais de componentes estruturais, devido às suas propriedades de alta resistência, elevada rigidez, elevado grau de amortecimento, baixa expansão térmica e boa estabilidade dimensional. Entretanto, devido à sua anisotropia, este material pode apresentar problemas durante a usinagem. Pode ocorrer ruptura de fibra, trincas, descolamento fibra, degradação térmica e delaminação. Os resultados obtidos mostraram que o mecanismo de desgaste ocorreu principal seguido por aderência cuja influência foi desprezível. Os valores dos coeficientes de vida de Taylor permitiram verificar que o material compósito é fácil de fresar. Os resultados das forças e potências de corte, instantâneas e médias também mostram ser um material fácil de cortar, principalmente quando comparado com um ferro fundido de baixa resistência. Os desgastes apresentaram comportamento não convencional e este fato foi evidenciado após a comparação feita com resultados obtidos para os mesmos tipos de materiais compósito disponíveis na literatura. Não foi observada a presença de delaminação ou qualquer tipo de dano, pois, foi observada uma boa rugosidade da superfície fresada<br>Abstract: The purpose of this work is to characterize the composite Carbon Fiber Reinforced Plastic (CFRP) with respect to its behavior during symmetric cylindrical milling process. It was used an experimental method. Eight millimeters milling cutter diameter with six cutting edge of cemented carbide ISO K10 was used to mill (CFRP) plates with 4 mm thick. The entire Machine limit was explored in terms of cutting speed from 100 to 600 m/min, 100 by 100 m/min steps. Other parameters were depth of cut 4 mm (plate width), feed rate per tooth 0,075 and 0,1 mm/rot. The focus of the present work is justified by the fact that the use of composite materials has been growing substantially and their manufacturing methods have become more popular and they are now being increasingly used in industrial applications such as aerospace, commercial aircrafts, ships, automobiles, machine tool and sports equipments. Composite materials such as carbon fiber reinforced plastics (CFRP) are important materials for structural components owing to their excellent properties such as high specific strength, high specific stiffness, high damping, low thermal expansion and good dimensional stability. However, due to its anisotropy, (CFRP) poses problems in machining such as fiber breakage, matrix cracking, fiber/matrix debonding, fiber pullout, thermal degradation, and delamination. The results showed that the main wear mechanism was abrasion followed by attrition that showed to be absolutely not important. The Taylor¿s tool life coefficients showed that to cut the composite material was very easy. Instantaneous and medium cutting power and cutting forces determined during the tests showed that the composite material is easier to cut when compared, for instance, with a low resistance casting iron. The wear evolution showed not conventional behavior and this fact was evidenced after comparison made with similar results from the literature. It was not observed delamination or any kind of damage and it was observed a good surface roughness<br>Doutorado<br>Materiais e Processos de Fabricação<br>Doutor em Engenharia Mecânica

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<br>國立臺灣大學<br>機械工程學研究所<br>100<br>The use of liquid carbon dioxide to assist cutting so as to improve the encountered difficulties in micro end milling Ti-6Al-4V titanium alloy was proposed in this study. To confirm the effects of the proposed approach, experimental results were compared with those under dry cutting, high pressure air jet, minimum quantity lubrication (MQL), and wet conditions. It was found that the machined roughness decreased with the cutting speed as observed in the conventional cutting when a larger diameter end milling cutter (D = 0.5 mm) was used. On the contrary, the chips produced were tiny and broken when a smaller diameter cutter (D = 0.3 mm) was used. Under high cutting speed condition these chips could adhere on the machined surface and led to an increase of surface roughness.The application of liquid carbon dioxide assisted micro milling can effectively decrease cutting temperature, which in turn reduce the amount of chips adhering on the machined surface and lower the tool flank wear. The surface roughness Ra at a cutting speed of 70 m/min was improved from 0.09 μm under dry cutting to 0.04 μm under the proposed liquid carbon dioxide assisted cutting. And there were no flank wear at feed of 4 μm/tooth, depth of cut 20 μm and cutting length of 1200 mm. In addition, there were very few burrs left on the machined surface. The height of the burr was only 23% of that under dry cutting. In the end, the use of liquid carbon dioxide and MQL to assist cutting to improve the lubrication in the use of liquid carbon dioxide. The experimental results show that this method provided the lowest cutting force, burr height and surface roughness among all the cooling/lubrication conditions employed. And there were no chips adhere on the machined surface.

碩士<br>正修科技大學<br>機電工程研究所<br>107<br>Cutting tools are important to manufacturing industry and affect production efficiency, quality and part accuracy. Tungsten carbide is one of the most commonly used in cutting tools. TiAlN is often coated on the cutting tool because it has high wear resistance and high temperature oxidation resistance. Cryogenic treatment has been widely used in tools, cutting tools and mold industry, etc., which can improve material properties by decreasing residual stress, stabilizing dimensional accuracy and increasing the wear resistance. The purpose of this study is to discuss the feasibility of cryogenic treatment to improve the TiAlN tungsten carbide milling cutter life for cutting the Inconel 625. Tool life test results exhibit that, without cryogenic treatment, chip and wear with the largest range exist in cutter tools. However, with cryogenic treatment, the wear range is narrow and no chipping. These verify that cryogenic treatment can enhance life of tungsten carbide milling cutter. According to the XRD result, the residual stress is less after cryogenic treatment. The optical microscope and scanning electron microscope (SEM) results indicate that after cryogenic treatment, the microstructure is denser and the adhesion of coating and tungsten carbide is better. From the above test results, it is shown that the service life of TiAlN coated milling cutter after cryogenic treatment can be effectively improved due to the denser microstructure、less residual stress and better adhesion.

Preliminary investigations of mechanical attrition (MA) resulted in particle size reduction, amorphization of semicrystalline polymers, and relatively insignificant effects on PEO or PVP molecular weight distributions. Cryogenic mechanical alloying (CMA) was extensively used to blend immiscible polymers. Globar FT-IR confirmed that no chemical compatibilizaton occurred during CMA, while a novel chemical mapping protocol developed with synchrotron FT-IR microspectroscopy allowed for qualitative and quantitative estimation of blend heterogeneities. The uniqueness of the PS/PET system led to extensive study of domain characteristics, the extent of compatibilization, and changes in PET crystallizability with CMA. Various PS/PET blend compositions (nominal 30, 50, and 70 weight percent PET) were processed by CMA and extrusion and studied comparatively. CMA compatibilized PS and PET more efficiently and controllably than extrusion. These results agreed with trends observed for domain size distribution, and CMA also created nonspheroidal domains, i.e., an efficient way to increase interphase contact. CMA, in effect, created a rigid amorphous PET phase that served the dual purpose of enhancing compatibility and stabilizing the morphology during post-CMA heating<br>acase@tulane.edu

Bulk commercially pure titanium was prepared by powder metallurgy, namely by cryogenic milling and spark plasma sintering, with aim to produce ultra-fine grained material with enhanced strength. The microstructure of milled powders was investigated in detail by a novel method called transmission EBSD, which allowed the first direct observation of texture within the powder particles. This texture is similar to rolling texture, because of the similar nature of the defor- mation during milling. Microstructure observations revealed grains with the size under 100 nm. The influence of sintering parameters on material properties were studied by scan- ning electron microscopy including EBSD, X-ray diffraction and by microhardness measurements. The trade-off relationship between porosity and grain size was identified, fully dense material with ultra-fine grained microstructure could not be produced. Increased oxygen content was identified as a main strengthening factor, while porosity has significant deteriorating effect on mechanical properties. The texture of powder was retained in the bulk material. The possibility of stabilizing the microstructure by mechanical alloying of Ti with yttrium oxide nanoparticles was investigated with mixed results. The stabiliza- tion was successful, but several issues...

Yes<br>A novel process chain for serial production of polymer-based devices incorporating both micro- and nano-scale features is proposed. The process chain is enabled by the use of Zr-based bulk metallic glasses (BMG) to achieve the necessary level of compatibility and complementarity between its component technologies. It integrates two different technologies, namely laser ablation and focused ion beam (FIB) milling for micro-structuring and sub-micron patterning, respectively, thus to fabricate inserts incorporating different length scale functional features. Two alternative laser sources, namely nano-second (NS) and pico-second (PS) lasers, were considered as potential candidates for the first step in this master-making process chain. The capabilities of the component technologies together with some issues associated with their integration were studied. To validate the replication performance of the produced masters, a Zr-based BMG insert was used to produce a small batch of micro-fluidic devices by micro-injection moulding. Furthermore, an experimental study was also carried out to determine whether it would be possible by NS laser ablation to structure the Zr-based BMG workpieces with a high surface integrity whilst retaining the BMG's non-crystalline morphology. Collectively, it was demonstrated that the proposed process chain could be a viable fabrication route for mass production of polymer devices incorporating different length scale features.