Papers by Keyword: Microstructured Surface

Abstract: A microstructured surface was created on a steel surface by whirling electrical discharge texturing (WEDT) since it was considered that the microstructures could act as lubricant reservoirs to assist the formation of a lubricating film, resulting in reduced friction. In this study, friction tests under engine oil were carried out over a range of loads and sliding speeds. In addition, the surface characteristics of the microstructured surface were also investigated to optimize the friction characteristics of the textured surface through pin-on-disc friction tests. It was found that under the mixed lubrication condition near the boundary condition, textured surfaces with texture-area ratio of approximately 6% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient. However, a texture-area ratio of approximately 4% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient under the mixed lubrication condition near the elastohydrodynamic lubrication condition. It was considered that when the normal load decreased, the lubrication region changed from the mixed lubrication condition to the hydrodynamic lubrication condition, which meant that the actual contact surface area decreased. The decrease in the actual contact surface area with decreasing texture-area ratio led to a reduction in the friction coefficient. Finally, it was clarified that the friction coefficient was reduced under the optimized conditions of the microstructured surface through a pin-on-disc friction test.

Abstract: In this paper, a five-axis ultra precision machine tool for fabrication of microstructured surfaces is presented. This machine consists of two rotary axes (C&B) and three linear axes (X&Y&Z). High precision aerostatic bearing and torque motor are adopted in C axis (main spindle) and B axis. X axis and Z axis use the hydrostatic guideway and are driven by linear motors. Y axis is driven by torque motor and precision ball screw. This machine is able to realize multiple processing methods, including ultra precision diamond turning, ultra precision milling, fly-cutting, fast tool servo and slow tool servo diamond turning.Furthermore, a large number of experiment researches are carried out. Some typical microstructure surfaces are manufactured, for sinusoidal grid surface, the surface roughness Ra is 11.9nm, which is machined by slow tool servo diamond turning. Micro pyramid array surface is fabricated by using fly-cutting, which performs well both in the profile accuracy and the repeatability. These experiment researches prove that this ultra precision machine is superior in accuracy and system reliability.

Abstract: In recent years microfluidic devices became of great interest, as they offer a wide range of bio-analytical and fluid processing applications through the utilization of size effects. Especially a mass manufacturing of disposable polymeric microfluidic devices by hot embossing or injection molding is expected to have high economic potential. It is known, that channels and areas showing a localized change in wettability can considerably improve fluid processing tasks like mixing or droplet generation. Chemical approaches, like the polymerization of lauryl acrylate, were successfully shown to achieve hydrophobic coatings for micro channels but are not suitable for a mass manufacturing. Since microstructures are known to provide water repellent properties of surfaces, this paper focuses on the applicability of diamond grooving and Diamond Micro Chiseling (DMC) processes for the manufacture of microstructured areas in brass molds inserts, in order to achieve hydrophobic properties of their replica. Major design features of structures, like a height range of 6 to 16μm or aspect ratios in between 0.5 and 3.2 are derived from the natural example of the lotus leaf. Molding is carried out by using a two component silicone filler. The performance of the replicated hydrophobic surfaces is evaluated by droplet contact angle measurements. After presenting methodology and results, the paper will conclude on how to transfer the investigated microstructuring methods to the manufacture of mold inserts for the replication of polymeric microfluidic chips with localized hydrophobic areas and channels.

Abstract: The depth of cut changed periodically along the contour of the cutting surfaces. The diamond tool of sharp point tip was used in diamond cutting microstructured surfaces with Fast Tool Serve (FTS). All reported the cutting force model were not suitable for accurately predicting cutting force. A cutting forces model concerned with edge radius, spring back and dynamic shear angle was proposed for diamond cutting microstructured surfaces. The model was verified with a series of experimental results. The results showed that the proposed model was able to exactly predict the cutting force.

Abstract: Based on the ultra precision machine tool, using Matlab/Simulink and considering the linear and nonlinear factors of the processing such as environmental vibration, machine movement, servo control technology, work piece material, cutting force and built-up-edge, the simulation system of ultra precision machining for microstructured surface based on fast tool servo (FTS), which integrated machine control system, machine mechanical system and surface generation, was established and verified by processing sinusoidal microstructured surfaces. The experimental results showed the simulation output errors were 15 % or so, and the simulation system could predict the microstructured surface morphology, optimize the processing parameters and provide support for follow up studies.

Abstract: High sensitive biosensing is required in many research fields and our lives. In this paper, we describe the fabrication of microstructured silicon (Si) surface to increase surface area and the evaluation by a highly sensitive immunoassay on that surface. Microstructured Si surface was fabricated by etching a Si wafer with a mask of self-assembled microparticles. The surface area of the microstructured surface was 1.5 times larger than that of flat surface. And the surface area was variable by changing particle diameter and etching time. An immunoassay was performed on this surface. It was confirmed that sensitivity was increased approximately 3.9 times with increase in surface area.

Abstract: Fast tool servo diamond turning is a promising machining method for precision and complex micro-structured surfaces with spatial wavelength above tens of microns. It is crucial to measure and characterize the micro-structured surfaces to sub-micrometer form accuracy. The general purpose measurement instruments are not able to evaluate the true form accuracy between the measured surface and designed surface. Therefore, in this paper an automatic surface characterization method is proposed to evaluate the form accuracy for micro-structured surfaces. The fabricated surfaces can be measured by any high-resolution measurement instruments. After the surface measurement, an iterative closest point (ICP) algorithm is modified to align the measured surfaces to the designed surfaces with the form error evenly distributed over the whole surface. After alignment, the designed surface height corresponding to each measured point is calculated to form the areal error map. 3D surface parameters are chosen and calculated from the error map to characterize the surface form error. Experimental results demonstrate the effectiveness of the proposed surface characterization method.

Abstract: Increasing demand for ultraprecision components with micro-structured surfaces has attracted focus on diamond turning research. In this paper, a fast tool servo (FTS) based diamond turning machine is presented for fabricating micro-structured surfaces with high accuracy. A design criterion is established to serve as a guide in choosing or designing a suitable type of FTS for a micro-structured surface. Experiments on fabricating sampled micro-structured surfaces are carried out to demonstrate the effectiveness of the designed FTS based diamond turning machine.

Abstract: Tool wear in diamond cutting sinusoidal mircostructured surfaces may be quite different from that in conventional diamond turning as the sharp point tip tool is used and the depth of cut changes cyclically along the profile of the cutting surfaces. In present paper, the diamond tool geometry requirements for cutting sinusoidal microstructured surfaces were analyzed. A series of controlled cutting tests of LY12 were executed on a 2-aixs bench type ultra-precision turning machine which equipped a fast tool servo (FTS). Tool wear patterns were investigated with varied feed speed in diamond cutting sinusoidal microstructured surfaces. The scanning electron microscope (SEM) examination results of tool wear showed that the visible wear was occurred after a short cutting distance. The gradual wear around tool tip and along cutting edges was predominant wear pattern with a low feed speed. The catastrophic fracture wear at tool tip was happened with a high feed speed and the wear of sharp point tip of tool was more serious than that of cutting edges of tool.

Abstract: This paper presents a high precision AFM for nanometrology of large area micro-structured surfaces. A PZT with a stroke of 100 microns is used as the Z-directional actuator for the AFM cantilever. Two capacitance-type displacement probes are aligned at two sides of the PZT along the movement direction. The displacement as well as the tilt motion of the PZT can be accurately measured and compensated for based on the probe outputs. It was confirmed that the tilt motion of the PZT was approximately 32 arcseconds over the 100 micron stroke. The sample is moved by two linear stages for scanning in the X- and Y-directions over an area of 50 mm x 40 mm. The angular error motions of the stages that influence the AFM accuracy are measured by an autocollimator for compensation. A piezo-resistive cantilever, which can output the atomic force signal by itself, was employed instead of the conventional optical force sensing device for compactness of the AFM structure. A large area sinusoidal metrology surface has been successfully measured by the developed high-precision AFM.