Abstracts:A novel approach of precision polishing based on the reversal growth property is proposed for potassium dihydrogen phosphate (KDP) crystal. The approach utilizes the unsaturated growth solution of KDP crystal to polish the crystal itself. The reversal growth property and its influence factors are studied. For this precision polishing approach, the mechanism of surface planarization is analyzed. Some preliminary investigations on the surface planarization performance are also carried out. Results show that the reversal growth property of the KDP crystal is closely related to the characteristic of KDP solution, namely, temperature, concentration, and flowability. With the appropriate coordination of these factors, the reversal growth of KDP crystal can be achieved under a highly controlled manner. By using this novel polishing approach, the macrostructures on the KDP crystal workblank can be removed efficiently. Additionally, through a multiple-stage polishing process, the surface rms roughness of the KDP crystal declines from 5702.4 nm to 17.1 nm in 2 min, meanwhile, the average material removal rate is 51.7 μm/min.

Abstracts:Long range, high precision, XY stages have a multitude of applications in scanning probe microscopy, lithography, micro-AM, wafer inspection and other fields. However, finding cost effective precision motion stages with a range of more than 12 mm with a precision better than one micron is a challenge. This study presents parametric design of the two XY flexure-based stages with a travel ranges of up to 50 mm and sub-micron resolution. First, the fabrication and testing of a two-axis double parallelogram flexure stage is presented and the results obtained from FEA and experimental measurements are shown to be in good agreement with the analytical predictions for this stage. A modified stage design with reduced higher order modes and same range, is also presented. This modified design is shown to be capable of achieving an open loop resolution of 100 nm with a travel range of greater than 50 mm. Higher order modes of the modified stage have been shown to be shifted from 25 Hz in the double parallelogram flexure (DPF) stage to over 86 Hz in the modified DPF stage making it much simpler to design a high speed (>10 Hz) controller for the modified stage.

Abstracts:This article presents a new and individual way to generate opto-mechanical components by additive manufacturing, embedded in an established process chain for the fabrication of metal optics. The freedom of design offered by additive techniques gives the opportunity to produce more lightweight parts with improved mechanical stability. The latter is demonstrated by simulations of several models of metal mirrors with a constant outer shape but varying mass reduction factors. The optimized lightweight mirror exhibits 63.5% of mass reduction and a higher stiffness compared to conventional designs, but it is not manufacturable by cutting techniques. Utilizing selective laser melting instead, a demonstrator of the mentioned topological non-trivial design is manufactured out of AlSi12 alloy powder. It is further shown that – like in case of a traditional manufactured mirror substrate – optical quality can be achieved by diamond turning, electroless nickel plating, and polishing techniques, which finally results in < 150 nm peak-to-valley shape deviation and a roughness of < 1 nm rms in a measurement area of 140 × 110 μm². Negative implications from the additive manufacturing are shown to be negligible. Further it is shown that surface form is maintained over a two year storage period under ambient conditions.

Abstracts:Damping plays an important role in suppressing modal vibration in a flexure-based mechanism due to its lightly damping characteristics. This paper develops a novel damped circular hinge with integrated comb-like substructures, and derives a mathematical model of loss factor of the flexure hinge and builds its pseudo-rigid body model with damping. The damped flexure hinges can be fabricated in a hybrid process with additive material manufacturing or mounting, and damping-material filling by means of some designed aided tools. For the actual fabricated damped circular hinges, their modal loss factors in a specified sandwiched-damping-layer configuration are obtained based on experimental modal analysis, as indicate that sandwiched damping can effectively suppress the bending modal vibration and the damping can be reinforced progressively with a damping-layer number. Meanwhile, based on finite element analysis, loss factor of the damped flexure hinge and its mathematical model are verified. The actual and simulation experimental results indicate that the presented comb-like damped substructures can be effectively functioned as a modular damper for a circular hinge and the damped flexure hinge can be designed independently of its damping and stiffness when low elastic viscoelastic material adopted.

Abstracts:This paper shows that the radial flow caused by the collision of the metal vapor jets generated from the surfaces of the tool electrode and workpiece serves as one of the material removal mechanisms in electrical discharge machining (EDM). Material removal per single discharge of a steel workpiece was larger using the tool electrode made of materials with lower boiling point. Observation of the discharge gap using a high-speed video camera showed that molten material on the workpiece was swept away more significantly and larger amounts of debris was removed using the tool electrode materials with lower boiling point. The molecular dynamics simulation showed that the radial velocities of the vapor atoms removed from the workpiece were higher using the tool electrode with lower boiling point because the jets from the tool electrode were more intensive. Furthermore, the discharge reaction force acting on the wire electrode in a single pulse discharge in air was measured from the wire vibration. The results showed a larger discharge reaction force using a zinc coated brass wire compared with a non-coated wire. Thus, it can be concluded that the shear force caused by the jets serves as one of the material removal mechanisms in EDM. Furthermore, one of the reasons for the higher material removal rate obtained using zinc coated wire electrode in wire EDM is the ease of boiling of the zinc coating layer on the wire surface.

Abstracts:Signals obtained in metal cutting are often non-linear and non-stationary, so that an appropriate signal-processing technique is needed for the process monitoring. In this paper, machining stability is evaluated by Hilbert–Huang transform (HHT), which can extract the features of vibrating signals. End-milling tests are conducted with thin-walled workpieces to demonstrates the feasibility of HHT in the monitoring for ever-changing state of machining processes. The experimental results obtained are as follows: HHT separated the signal containing chatter from others and can acquire the transition of frequency spectrum during the milling operation. Then, the effect cutting fluid and the influence by biting of hard material are investigated by HHT.

Abstracts:Accuracy in manufacturing microchannels is important in order to achieve their intended function. Smooth and high aspect ratio microchannels on silicon wafer substrate are needed in the heat removal application in various microelectronic components. Generally, etching techniques are used to fabricate silicon microchannels; however, the maximum achievable limit for the channel depth is a major concern. Micro-ultrasonic machining (micro-USM) is capable of machining high aspect ratio microchannels on hard and brittle material such as silicon, glass, ceramics, etc. However, achieving reasonable form accuracy and surface roughness of the microchannels is challenging. Overcut and edge damage (stray cut) are undesirable for precision machining while surface roughness of the microchannels can be set at an optimized value to attain maximum heat transfer. In the present study, silicon microchannels were fabricated using the micro-USM technique. In order to improve the precision and quality of the fabricated silicon microchannels in terms of surface roughness, overcut and stray cut; viscous fluids with different viscosities were considered for investigation in combination with other machining conditions. The experimental investigation revealed that using low viscous fluids yields better surface roughness compared to high viscous fluid; however, overcut and stray cut were minimized while using high viscous fluids. Machining at higher feed rates could minimize the surface roughness, over cut and stray cut irrespective of the abrasive concentration percentage. Possible interactions between the tool, abrasive and workpiece in the machining zone were analyzed vis-à-vis the experimental results.

Abstracts:Irradiation of a single-crystal diamond tool was performed with a picosecond pulsed laser to produce a tool with a microgrooved edge. This tool was then used in a metal cutting process to transfer the edge grooves onto a workpiece. Suitable conditions for laser irradiation on the diamond tool were experimentally investigated in terms of groove shape and laser-induced damage to diamond. Two different kinds of cutting experiments were performed; a uniformly grooved surface and a hierarchically structured surface were obtained. The chip formation mechanisms in the metal grooving process were examined. A copper workpiece was rapidly machined the surface of which had microgrooves with a pitch of a few micrometers. An increase of the contact angle was observed on the grooved surface, indicating the improvement of water repellency. This study presents an efficient method to machine microgrooves on metal materials for functional surfaces.

Abstracts:Dry machining is undesirable to produce precision surface due to thermal adversities especially for a low melting point material such as Al 6061-T6. Likewise, the conventional flood cooling is neither economically viable nor eco-friendly. In this context, three novel cooling-lubrication (C/L) technologies namely the nitrogen gas cooling (NGC), nitrogen gas assisted minimum quantity lubrication (NGMQL) and Ranque-Hilsch vortex tube (RHVT) NGMQL are investigated along with the air cooling (AC) in turning with an attempt to reduce surface roughness (Ra ) and tool flank wear (VBmax ). The machining was conducted using uncoated WC insert at two-levels of cutting speed and feed rate; and, as medium of cooling/lubrication the nitrogen gas and/or canola oil is employed. The SEM and 3D topographic images were analyzed for the machined surfaces, worn tool surfaces and chips. Results showed that the RHVT-NGMQL revealed the least surface roughness and tool wear (∼75% improvement compared to other C/Ls). Notable wear modes were: in dry cutting the plastic deformation, BUE and adhesion; in NGC the BUE; in NGMQL the rubbing and adhesion; in RHVT-NGMQL the adhesion. In micro-level, no significant difference in chip structure was found for the studied C/L methods In addition, the Composite Desirability optimization was adopted to systematically minimize Ra and VB max concurrently. It was found that the optimum speed vc  = 160 m/min and feed rate f = 0.06 mm/rev under RHVT-NGMQL C/L condition has the potential to generate a precision surface with a roughness value <1.0 μm.