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

Axial strategy for ultraprecise single point cutting of V-grooves Case 1: constant chip thickness

47th SME North American Manufacturing Research Conference, NAMRC 47, June 10-14, 2019, Pennsylvania, US

Reduction of cutting forces by elliptical vibration in multi-pass ultraprecise single point axial cutting of V-grooves

48th SME North American Manufacturing Research Conference, NAMRC 48 (Cancelled due to COVID-19

Plasmonic lenses for tunable ultrafast electron emitters at the nanoscale

Simultaneous spatiotemporal confinement of energetic electron pulses to femtosecond and nanometer scales is a topic of great interest in the scientific community, given the potential impact of such developments across a wide spectrum of scientific and industrial applications. For example, in ultrafast electron scattering, nanoscale probes would enable accurate maps of structural dynamics in materials with nanoscale heterogeneity, thereby leading to an understanding of the role of boundaries and defects on macroscopic properties. On the other hand, advances in this field are mostly limited by the brightness and size of the electron source. We present the design, fabrication, and optical characterization of bullseye plasmonic lenses for next-generation ultrafast electron sources. Using electromagnetic simulations, we examine how the interplay between light-plasmon coupling, plasmon propagation, dispersion, and resonance governs the properties of the photoemitted electron pulse. We also illustrate how the pulse duration and strength can be tuned by geometric design and predict that sub-10-fs pulses with nanoscale diameter can be achieved. We then fabricate lenses in gold films and characterize their plasmonic properties using cathodoluminescence spectromicroscopy, demonstrating suitable plasmonic behavior for ultrafast nanoscale photoemission

Microengineered structures for rapid automatic loading of optical fibre segments

We present a technique to rapidly and automatically produce sections of optical fibre and load them into arrays such that they can be nano-imprinted in parallel. The technique makes use of automated fibre feeding, cutting and alignment with microfabricated groove arrays. The system is analyzed and optimized and it is found that the geometry of the arrays themselves is a critical factor. Three types of array are investigated-simple grooves, grooves with lateral funnels at the input, and bulk silicon machined V-groove arrays with funnels in both lateral and vertical dimensions. It is found that the incorporation of funnels significantly increases the accuracy of loading, overcoming the need for precise alignment, such that a throughput nearing 1000 fibre segments an hour can be achieved. This system forms part of a sequence of novel processes for the production of nano-photonic sensors

Hybrid micro-machining processes : a review

Micro-machining has attracted great attention as micro-components/products such as micro-displays, micro-sensors, micro-batteries, etc. are becoming established in all major areas of our daily life and can already been found across the broad spectrum of application areas especially in sectors such as automotive, aerospace, photonics, renewable energy and medical instruments. These micro-components/products are usually made of multi-materials (may include hard-to-machine materials) and possess complex shaped micro-structures but demand sub-micron machining accuracy. A number of micro-machining processes is therefore, needed to deliver such components/products. The paper reviews recent development of hybrid micro-machining processes which involve integration of various micro-machining processes with the purpose of improving machinability, geometrical accuracy, tool life, surface integrity, machining rate and reducing the process forces. Hybrid micro-machining processes are classified in two major categories namely, assisted and combined hybrid micro-machining techniques. The machining capability, advantages and disadvantages of the state-of-the-art hybrid micro-machining processes are characterized and assessed. Some case studies on integration of hybrid micro-machining with other micro-machining and assisted techniques are also introduced. Possible future efforts and developments in the field of hybrid micro-machining processes are also discussed

Theoretical and experimental investigations on conformal polishing of microstructured surfaces

Microstructured surfaces play a pivotal role in various fields, notably in lighting, diffuser devices, and imaging systems. The performance of these components is intricately related to the accuracy of their shapes and the quality of their surfaces. Although current precision machining technologies are capable of achieving conformal shapes, the post-machining surface quality often remains uncertain. To appropriately address this challenge, this paper introduces a novel conformal polishing methodology, specifically designed to enhance the surface quality of microstructured surfaces while maintaining their shape accuracy. As part of the investigations, specialized tools, namely the damping tool and profiling damping tool, are methodically developed for polishing rectangular and cylindrical surfaces. A shape evolution model is established based on the simulation of individual microstructures, incorporating the concept of finite-slip on the microstructured surface. The findings reveal that principal stresses and velocities experience abrupt variations at the convex and concave corners of rectangular surfaces as well as at the ends of cylindrical surfaces. The numerically predicted surface shape errors after polishing demonstrate reasonably good agreement with experimental results such that their discrepancies are less than 1 μm. Additionally, this method is able to successfully eradicate pre-machining imperfections such as residual tool marks and burrs on the microstructured surfaces. The arithmetic roughness (Ra) of the rectangular surface is measured to be an impressively low 0.4 nm, whereas the cylindrical surface exhibits Ra = 6.2 nm. These results clearly emphasize the effectiveness of the conformal polishing method in achieving high-quality surface finishes