リンカイ エンセイ ハカイ キジュンチ ノ ケッテイ ト センダン ウチヌキ カコウ ニオケル ハカイ カイシテン ノ ヨソク

博士(工学)佐賀大

Development of hybrid micro machining approaches and test-bed

High precision miniature and micro products which possess 3D complex structures or free-form surfaces are now being widely used in industry. These micro products require to be fabricated by several machining processes and the integration of these various machining processes onto one machine becomes necessary since this will help reduce realignment errors and also increase the machining efficiency. This thesis describes the development and testing of several hybrid machining approaches for machines which are typically used to produce micro products such as micro fluidic moulds, solar concentrator moulds, micro grooves in brittle materials and micro structured milling cutters. These are: (a) micro milling and laser deburring; (b) micro grinding involving laser pre-heating; (c) micro milling and laser polishing. The hybrid micro milling/ laser deburring process was tested during the fabrication of a micro fluidic injection mould. Micro burrs on the channel of micro fluidic mould generated during micro milling were completely removed by developed laser deburring process. This approach can achieve a good surface finish on a micro fluidic mould. The hybrid laser assisted micro grinding process was investigated by fabricating a set of micro grooves on brittle materials, including Al2O3 and Si3N4. The workpiece was pre-heated by laser to increase its temperature above that of the brittle to ductile transition phase interface. It was found that lower cutting forces were apparent in the grinding process when used to machine brittle materials. It was also found that laser assisted grinding helped achieve a very good surface finish and reduced subsurface damage. The final hybrid machining approach tested involved micro milling and laser polishing to fabricate solar concentrator moulds. Such a mould requires a good surface finish in order to accurately guide light focusing on a target. The laser polishing process was successfully used to remove any unwanted cutting marks generated by a previous micro milling process. Abstract iii As a novel extension to this hybrid machine world, a focussed ion beam (FIB) fabrication approach was researched regarding the generation of microstructures on the rake faces of milling cutters with the aim of reducing cutter cutting forces and increasing tool life. The tool wear resistance performance of these microstructured tools was evaluated through three sets of slot milling trials on a NAK80 specimen with the results indicating that micro structured micro milling cutters of this kind can effectively improve the tool wear resistance performance. A microstructure in a direction perpendicular to the cutting edge was found to be the best structure for deferring tool wear and obtaining prolonged tool life. This approach can potentially be further integrated into a hybrid precision machine such that micro structure cutters can be fabricated in-situ using a laser machining process. The conceptual design of a 5-axis hybrid machine which incorporates micro milling, grinding and laser machining has been proposed as a test-bed for the above hybrid micro machining approach. Through finite element analysis, the best configuration was found to be a closed-loop vertical machine which has one rotary stage on the worktable and another on machining head. In this thesis, the effectiveness of these novel hybrid machining approaches have been fully demonstrated through machining several microproducts. Recommendations for future work are suggested to focus on further scientific understanding of hybrid machining processes, the development of a laser repairing approach and the integration of a controller for the proposed hybrid machine

Study of angular cutting conditions using multiple scratch tests onto low carbon steel: An experimental-numerical approach

Multiple parallel scratches are often analyzed to understand the material removal mechanisms due to abrasion. However, successive scratches with different orientations may represent better the conditions found in machining processes, such as honing and belt finishing. The objective of this work was to analyze the cutting forces and the phenomena of material removal due to abrasion, arising from angular scratches in low carbon steel. Experimental and numerical techniques were considered. In both, analyses considered the presence of an initial set of parallel scratches, followed by a second set of scratches with different orientations (10, 20 or 30°) with respect to the previous one. The cutting action was performed by a tool representing an abrasive particle, which had a cono-spherical geometry with 235μm tip radius and 30° apex angle. The cutting settings were: 50m/min scratch velocity and 100μm depth of cut. In the experimental part, scratches were conducted using a shaper machine tool equipped with a tungsten carbide (WC-Co) stylus. Tests were conducted on a Kistler platform, which allowed force measurement. Surfaces were later analyzed with an optical profilometer. The numerical simulations considered a ductile damage model with element deletion to provide the material removal during the scratches. Experimental and numerical results showed that the angle affects the cutting forces, especially when one scratch crosses a previously scratched region. The 20° case was the most critical, especially in terms of the cutting forces, due to the accentuated material strain-hardening for this condition. Likewise, this fact was corroborated by numerical results, which indicated a higher energy necessary to plastic deformation, and a reduced material removal at 20°

Three-Dimensional Finite Element Analysis of Conventional and Ultrasonic Vibration Assisted Micro-Drilling on PCB

Recent advancement in society’s demands has forced industries to produce more and more precise micro parts. With an advancement in engineering sciences, current manufacturers in various fields such as aerospace, medical, electronics, automobile, biotechnology, etc. have achieved the potential to fabricate miniaturized products, but with numerous technical challenges. Dimensional accuracy and surface integrity of the machined components are the key challenges and at the same time, cost minimization is strongly desired. To meet these challenges and demands, improvements in machining regarding new procedures, tooling, tool materials and modern machine tools are highly essential. Micromachining has shown potential to achieve the fast-growing needs of the present micro manufacturing sector. Additionally, new machining techniques like ultrasonic machining, laser drilling, etc. have been developed as an alternative source to reduce obstructions caused during macro/micro machining. The present research aims to perform three-dimensional (3D) finite element dynamic analysis for micro-drilling of multi-layer printed circuit boards (PCBs). Both conventional and ultrasonic vibration assisted micro-drilling (UVAMD) FE simulations have been compared to predict and evaluate the effect of process parameters on the output responses like stress generation and reaction forces and burr formation on the workpiece surfaces. The Lagrangian based approach is followed for the FE simulation including the mass and inertial properties of the proposed FE model. The predicted FE results are compared with the past experimental work for thrust force evaluation and burr formation on workpiece surfaces. The present work is supported with modal and harmonic analysis of stepped and conical horns along with micro drill bit. Here, horns made up of Aluminum 6061-T6, Titanium and Mild steel are chosen with micro drill bit of 0.3 mm diameter with varying tool materials (Tungsten carbide and High speed steel). The effects of natural frequencies with different mode shapes within the range of 15-30 kHz are shown. The frequency responses of micro drill with displacement conditions have been presented for longitudinal modes. The present simulation results will be helpful to conduct proper experimentation in order to achieve efficient machining and surface finish. The results enumerate that the drilling parameters have a strong influence on thrust forces and stresses occurring in micro-drilling. Ultrasonic assisted micro-drilling has a good potential in reduction of forces generated by vii selecting proper machining parameters. The FE simulation of UVA micro machining can further be enhanced and extended to various materials like plastics, sheet metal, other PCBs, etc. to predict the performance with varying machining and geometrical parameters

Study on Burr Formation at the Top Edge in Rectangular Groove Cutting

Previous research on burr formation in machining operations has usually been limited to the study of the rollover burr in the cutting direction. In this paper, a 3D finite element model to simulate rectangular groove cutting operation has been developed using commercial finite element software, employing experimentally determined mechanical properties at elevated strain rates and temperatures. The plastic deformation behavior and three-dimensional burr formation during rectangular groove cutting is investigated. The simulated burr profile and cutting force prove that the developed model can capture the thermo-mechanical mechanisms in rectangular groove cutting and can simulate burr development with considerable accuracy. The study concentrates on the influence of cutting parameters on burr formation which are also conducted. The results show that the feed rate and rake angle are the cutting parameters which have a major influence on burr size in the groove cutting operation. And the effect of cutting velocity and minor clearance angle in the traditional range on burr size are quite limited

A Micro-milling cutting force and chip formation modeling approach for optimal process parameters selection

Las últimas décadas evidencian una demanda creciente por componentes miniaturizados con dimensiones reducidas y tolerancias estrechas, lo cual ha conllevado al desarrollo de la micro y nanotecnología. El micro-fresado, dentro de los procesos de micro-mecanizado, tiene el potencial de ser uno de los procesos de remoción de material más costo-efectivos y eficientes debido a su facilidad de aplicación, variedad de materiales de trabajo y flexibilidad geométrica. Se enfrenta a unos retos complejos debido al efecto de tamaño, vibraciones y otros factores incontrolables. Este estudio analiza dicho proceso orientado hacia desarrollar una mejor comprensión de la mecánica del micro-corte para ser aplicada en la optimización de parámetros de proceso. Se propone un acercamiento al modelado híbrido en forma novedosa, que permite una evaluación numérica a priori para evaluación de fuerzas y esfuerzos, combinado con experimentación para evaluar parámetros relevantes a la industria (formación de rebabas, desgaste de herramientas, entre otros).DoctoradoDoctor en Ingeniería Mecánic

Deformation in shear slitting of polymeric webs

Shear slitting of a 25.4 μm thick polypropylene web was conducted on a laboratory slitter using a pair of rotary blades at a constant speed up to 5.08 m/s under controlled tension. The effect of web speed on the slit-edge burr height of the web is investigated for the thick polypropylene web. A profilometer was employed to measure the edge profile. Experimental results indicate that the burr height decreases with web speed when other slitting parameters are fixed. To overcome the difficulty in observing the in-situ shear slitting process of the polypropylene web, a rubber sheet was also used in the present study for the observation of the deformation process during shear slitting, and the surface deformation field of the rubber was measured by a digital image correlation method. The finite element simulation of the early stage of rubber slitting process was performed using commercial ABAQUS code and numerical results are in good agreement with those observed in experiments. The experimental observation and the numerical simulation show that shear slitting of rubber initiates with an indentation process, followed by deformation localizations around the slitter blades; the final stage is a tearing process.Mechanical and Aerospace Engineerin

Burrs understanding, modeling and optimization during slot milling of aluminium alloys

Nowadays due to global competition, manufacturing industries must provide high quality products on time and within the cost constraints to remain competitive. High quality mechanical parts include those with better surface finish and texture, dimension and form accuracies, reduced tensile residual stress and burr-free. The burr formation is one of the most common and undesirable phenomenon occurring in machining operations, which reduces assembly and machined part quality. Therefore, it is desired to eliminate the burrs or reduce the effort required to remove them. Amongst machining operations, slot milling has a more complex burr formation mechanism with multiple burrs appear in machined part edges with non-uniform dimensions. The ultimate goal of this research work is burr minimization in slot milling operation. To this end, new strategies for understanding, modeling and optimizing burrs during slot milling of aluminum alloys are proposed for improving the part quality and ultimately reducing the non-value added expenses caused by deburring processes. In order to have a better understanding of slot milling burr formation mechanism, multi-level experimental studies and statistical methods are used to determine the effects of machining conditions, tooling and workpiece materials on burrs size (height and thickness) when using dry high speed condition. It was found that optimum setting levels of process parameters to minimize each burr are dissimilar. The analysis of results shows that cutting tool, feed per tooth and depth of cut have certain level of influence on slot milling burrs. However most of the burrs are strongly affected by interaction effects between process parameters that consequently complicate developing burr size prediction models. An analytical model is proposed to predict the thickness of the largest burr during slot milling of ductile materials. The model is based on the geometry of burr formation and continuity of work at the transition from chip formation to burr formation, which also takes into account the effect of the cutting force involved in the machining process. A computational model is also developed to predict the exit up milling side burr thickness based on the use of cutting parameters and material properties such as yield strength and specific cutting force coefficient, which are the only unknown variables in the model. Both analytical and computational models are validated using experimental results obtained during slot milling of 2024-T351 and 6061-T6 aluminium alloys. Machining parameters optimization to minimize the burr size could have a negative impact on other machining performance characteristic, such as surface finish, tool life and material removal rate. Therefore, surface finish is also investigated with burr formation in this research work. For simultaneous multiple responses optimization, a new modification to the application of Taguchi method is suggested by proposing fitness mapping function and desirability index. The proposed modification is validated by simultaneous minimization of surface roughness and thickness of five burrs during slot milling of 6061-T6 aluminium alloy. The optimization results demonstrate the potential and capability of the proposed approach

Laser assisted micro-milling of titanium alloy

The interest in applying Additive Manufacturing (AM) technology has grown due to its ability to produce complex parts with high flexibility, serving as an alternative to conventional manufacturing processes. However, the poor surface quality and limited dimensional accuracy of AM parts often necessitate post-processing such as machining, grinding, and polishing. Titanium, specifically Ti6Al4V alloy, is frequently used in AM technology. This study compares the machinability of AM Ti6Al4V parts produced by Electron Beam Melting (EBM) with extruded Ti6Al4V parts, focusing on cutting forces, specific cutting energy, burr formation, and surface quality in the micro-milling process. Despite the higher hardness of EBM Ti6Al4V, no significant difference in cutting forces was observed at chip thicknesses between 7.4 μm and 37.3 μm. However, at chip thicknesses below 7.4 μm, EBM parts exhibited lower cutting forces and specific cutting energies, and finer surface roughness. Both materials formed continuous wavy-type burrs of comparable size during micro-milling. The study also underscores the significance of Laser-Assisted Machining (LAM) in reducing machining forces and increasing Material Removal Rate (MRR). Instead of the traditional LAM method, a pico-second laser (USPL) was used to pre-structure the Ti6Al4V parts, impacting uncut chip thicknesses during micro-milling. A kinematic model was developed to understand the influence of workpiece structuring on uncut chip thicknesses, identifying structure density and depth as critical parameters. Experimental tests showed a significant reduction in cutting forces with pre-structured workpieces, without notable changes in surface roughness. The orientation of structure lines relative to the helix angle affected the surface roughness. Pre-structuring led to controlled subsurface damage and less material removal during milling, resulting in better machinability

A finite element study of the mechanics of micro-groove machining of 4340 steel

Microgroove features have been widely used in hot embossing molds, micro-heat exchangers, optical lithography masks, micro-forming dies, engineered surface textures, etc. The challenge of achieving such feature is the control of the process parameters to minimize the side burr that often damages the microgroove. Besides, there is a limitation of the experimental study on gathering the cutting performance information such as temperature, stress, and chip formation for the purpose of process improvements. Therefore, a 3D Finite Element (FE) model was developed to study the microgroove cutting process. However, the frictional heat has not been considered in the previous FE models and could have big impact on predictions of the side burr height, chip thickness, temperature in the chip, and the cutting force experienced by the tool. To better understand the process mechanics of micro-groove cutting, the 3D finite element model for microgroove machining of steel developed previously has been enhanced to include the friction heat generation. The side burr and chip formation were predicted and validated with experimental results in AISI 4340 steel, which showed that the model predicted side burr height within 6.7% and chip thickness within 3.3 % error. Various process mechanics including temperature distribution in the chip, cutting force predictions, and stress distribution in the workpiece were studied. It was found that coupling the thermal and mechanical effects, and including the friction heat improved the prediction of the cutting performance. It was also noticed that the cutting tool with a small edge radius and a larger rake angle experienced lower temperature, lower stresses, and smaller cutting forces on its rake face