Green micromachining of ceramics: Feasibility and machinability
Başlık çevirisi mevcut değil.
- Tez No: 539712
- Danışmanlar: Prof. Dr. BURAK ÖZDOĞANLAR
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2018
- Dil: İngilizce
- Üniversite: Carnegie Mellon University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 165
Özet
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Özet (Çeviri)
Ceramics o er many unique mechanical, thermal, electrical and chemical properties that make them ideal materials for a broad range of applications. However, the same properties that make ceramics attractive materials also bring strict limitation to their manufacturability. The manufacturability limitations are further exacerbated at the microscale: although there are many potential applications for micro-scale features, components and devices made from ceramics, those applications cannot be realized without e ective approaches for micro-manufacturing of ceramics. Towards addressing the challenge of micromanufacturing of ceramics, in this thesis, we are proposing an approach referred to as green micromachining (GMM). Green micromachining involves fabricating micro-scale features green-state ceramics (ceramic particles mixed with a polymer binder and compacted into simple shapes) using mechanical micromachining, and subsequently debinding their binder and sintering them to obtain solid ceramics with micro-scale features. Since the strong bonds between the ceramic particles are not generated in the green state, mechanics of material removal is dominated by the binder, and thus, becomes signi cantly easier|producing considerably lower forces and tool wear. If done e ectively, the GMM approach promises signi cant advantages in geometric and shape capabilities, and in both lead time and cost of fabrication. However, realizing this potential of GMM requires understanding process-property relationships and associated quality metrics. This doctoral research investigates the feasibility of green micromachining to fabricate micro-scale features in various ceramics. The overarching research objective of this doctoral thesis is to determine the e ect of GMM parameters on process forces, microtool wear, and resulting quality of the fabricated micro-scale features on ceramics. The research involves both theoretical and experimental analyses of the GMM process and a post-sintering assessment of features fabricated using the GMM approach. The speci c objectives of this work are to (1) analyze green micromachinability of ceramics through experimental analyses; (2) characterize micromachining mechanics and forces via orthogonal machining; (3) develop a mechanistic model for forces arising from GMM; (4) characterize the wear of microtools under di erent process conditions and for di erent tool materials and coatings; and (5) evaluate geometric and shape characteristics of features fabricated through GMM on sintered ceramics. Toward addressing the research objectives, rst, GMM of ceramics is experimentally investigated. Similar to other manufacturing processes, there is a strong correlation between process conditions and output quality in GMM. To quantify the e ect of process parameters (cutting velocity, feed rate, depth of cut) and material conditions on green micromachining outputs, various powder/binder combinations of two important ceramics (SiC and AlN) are green micromachined using a design of experiments approach. The resulting surface roughness, cutting forces, speci c energies, burr formation, and tool wear are qualitatively or quantitatively evaluated. Second, process mechanics and the associated process forces during GMM are analyzed. Forces measured during micromachining reveal essential characteristics of the process from material removal mechanisms to tool wear. Due to the complexity of cutting geometry and kinematics of the process, micro-endmilling does not provide a clear connection between machining forces and process inputs. To better understand the nature of process mechanics and the associated forces, orthogonal machining1 (planing) experiments are conducted. The relationship between machining parameters and GMM forces are explored for both a rounded tool and a sharp tool. The speed-dependent characteristics of speci c energies in cutting and thrust direction considering uncut chip thickness are identi ed. Third, a mechanistic (i.e., semi-empirical) force model for GMM is developed and experimentally validated. Micromachining forces are also critical to avoid tool breakage, excessive tool de ection, and damage to the miniature machine tool system used for GMM. As such, it is critical to predicting the e ect of process parameters on GMM forces. To predict the uncut chip thicknesses accurately, a comprehensive chip thickness model considering process kinematics, workpiece elastic recovery, and tool-trajectory errors is developed. Next, a calibration approach is developed: the approach requires a minimum number of micromachining (micromilling) experiments and uses a genetic algorithm approach to identify the calibration parameters from the experimental forces. Finally, the model is validated under varying experimental conditions on AlN and SiC workpieces. 1Orthogonal cutting process simpli es the cutting process kinematics, thereby allowing detailed analysis of process mechanics and forces Fourth, an investigation of micro-tool wear during GMM is performed. Understanding tool wear mechanism and its progression is critical towards assessing the feasibility of GMM. The objective of this work is to observe the wear mechanism and measure the wear progression during GMM using coated and uncoated microtools. For this purpose, the tool wear during GMM of SiC and AlN is evaluated to identify the wear characteristics when micromachining workpieces with di erent powder and binder combinations. The change in speci c energies and burr formation with wear progression is explored. Subsequently, a comprehensive investigation of micro-tool wear on green SiC is conducted. Uncoated and coated (AlTiN and nanocrystalline diamond coatings) carbide micro-endmills are used to fabricate channels on SiC blanks. At speci ed lengths of cut, each tool is imaged to determine changes in tool geometry and cutting-edge radii that result from progression of tool wear. More detailed scanning electron microscopy (SEM) images of the fresh and worn tools are also obtained. Cutting forces are also measured during the experiments. In addition to quantitative assessments on changes in tool diameter and edge radii, qualitative assessments related to tool chipping or other catastrophic failure is performed through imaging. Fifth, a study on GMM-based micro-manufacturing of Zirconia is presented. The purpose of this study is to demonstrate the entire process ow, including the fabrication of the green blanks through die pressing of powdered Zirconia, GMM, debinding, and sintering, resulting in micro-scale ceramic features. After obtaining the blanks with die pressing, a study on the green micromachinability of Zirconia is completed to identify favorable process parameters. Subsequently, a range of geometries, including three-dimensional shapes, pyramids, pillars, walls, and channels are fabricated to demonstrate both the shape and the minimum size capabilities. The binder in green micromachined samples are then thermally removed, and the ceramic parts are sintered. Although optimization of sintering temperature pro le is beyond the scope of this work, a favorable temperature pro le that results in crack-free samples with uniform shrinkage is identi ed and used during sintering. A set of speci c features in both their green-micromachined and sintered states are characterized to determine how sintering a ects dimensions (uniform and non-uniform shrinkage ratios), shapes (e.g., rounding of corners) and surface roughness of micro-scale features fabricated by GMM. The thesis concludes with a discussion of future work that is needed for improving the current understanding of GMM-based fabrication process and accelerating the applicability of GMM approach for achieving reproducible manufacturing of wide range of ceramics with micro-scale details.
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