Hemi-Ellipsoidal microlensed fiber based on polishing and polymer technology

This paper represents a development of a new advanced technology to fabricate and characterize micro-collimators with hemi-ellipsoidal microlenses at single-mode fibers outputs. The proposed method utilizes the controlled mechanical micromachining technique based on the variation of the speed of the fiber around its axis in both X and Y directions followed by the injection of a quantity of polydimethylsiloxane (PDMS) to form the hemi-ellipsoidal microlenses. The experimental results show that this technique allows to obtain a wide variety of ellipticity diameters ratios from 0.68 to 0.84. An elliptical ratio of radii of curvature Ry/Rx in a range of 0.51 at 0.86 is also obtained. In this investigation a mode field diameters MFD in an interval between 3.26 µm and 9.93 µm have been realized. The measurement results demonstrate that the proposed technology allows to fabricate hemi-ellipsoidal microlenses having an MFD ellipticity ratios of about 0.60 to 0.97 in near field promising for micro-collimator suitable to match an elliptical laser beam to the circular one of a fiber.

Manufacturability and Surface Characterisation of Polymeric Microfluidic Devices for Bio-medical Applications

Microfluidic devices fabricated through mechanical micromachining techniques have already been reported to be highly economical when compared to other techniques. Direct mechanical machining processes are generally classified as a one-step manufacturing process, having the advantages of rapid prototyping and batch production. Though there are advancements in ultra-precision machining techniques, the real challenge of direct machining polymeric microfluidic channels is the occurrence of poor surface integrity owing to the change in mechanical as well as viscoelastic properties. This forms the key objective of the present research work, where the major emphasis has been given to understand the applicability of micro-milling techniques in fabricating microfluidic devices, especially for bio-applications. In this research, the mechanical micro-milling technique was used to create microscale channels on polymethylmethacrylate (PMMA) and polycarbonate (PC) materials; wherein the process capability was mainly assessed based on the surface characteristics of the micro features. Furthermore, for the quantitative analysis, a comparative study was also performed by measuring the surfaces roughness and surface energy of the microchannels made by various fabrication routes such as hot embossing and lithography. The experimental results indicate that the micro-milling of PMMA is the preferable choice for fabricating microfluidic devices when compared to PC. Also, for showing the manufacturability of the mechanical micromachining technique, microfluidic channels with serpentine channels were machined with a depth and width of 50µm and 200µm respectively. The applicability of the fabricated microfluidic devices was further validated by evaluating the functioning of these devices for blood cell separation at different dilution rates.

Experimental characterization and finite element modeling of the residual stresses in laser-assisted mechanical micromachining of Inconel 625

Laser-assisted mechanical micromachining offers the ability to machine difficult-to-cut materials, like superalloys and ceramics, more efficiently and economically by laser-induced localized thermal softening prior to cutting. Laser-assisted mechanical micromachining is a micromachining process with localized laser heating which could affect the cutting forces and the machined surface integrity. The residual stresses obtained in the laser-assisted mechanical micromachining process depend on both mechanical loading and the laser heating. This article focuses on the experimental process characterization and prediction of the cutting forces and the residual stresses in a laser-assisted mechanical micromachining–based orthogonal machining of Inconel 625. The results show that the laser assistance reduces the mean cutting forces by ∼25% and enhances the normal compressive residual stress at the surface by ∼50%. Since microscale residual stress measurement is very time-intensive, a coupled-field thermo-mechanical finite element model of laser-assisted mechanical micromachining has been developed to predict the temperature, cutting forces and the residual stresses. The cutting forces and residual stresses’ predictions are in good agreement with the measured values during machining. In addition, parametric simulations have been carried out for laser power, cutting speed, cutting edge radius, rake angle, laser location and laser beam diameter to study their effect on cutting forces and surface residual stresses.

Development of Tool Based Micromilling/Microdrilling Machine with Piezoactuated Workpiece Feeding System

Tool based mechanical micromachining technology is gaining importance in MEMS device fabrication because of its ability to machine 3D micro features on different engineering materials. This paper presents the development of tool based mechanical micromachining center with piezoactuated workpiece feeding system. A high speed spindle is used to rotate the micromilling/drilling tool at a speed of 12,000 to 60,000 rpm. A thermoelectric based liquid cooling system is developed to control the temperature of the high speed spindle at a set value. Along with the X-Y positioning system, the workpiece is also mounted on a piezoactuator to provide Z-axis motion during machining operation. An electrical continuity based tool-workpiece contact detection system is developed to overcome premature tool failure during initial tool registration with the workpiece. Based on the developed tool-workpiece contact sensor, an in-situ measurement system is developed to measure the micromachining depth. Experiments were conducted to measure the performance of spindle cooling system and in-situ measurement system.