Application of Design of Experiment Method for Thrust Force Minimization in Step-feed Micro Drilling.

Micro drilled holes are utilized in many of today's fabrication processes.Precision production processes in industries are trending toward the use of smaller holeswith higher aspect ratios, and higher speed operation for micro deep hole drilling. However,undesirable characteristics related to micro drilling such as small signal-to-noise ratios,wandering drill motion, high aspect ratio, and excessive cutting forces can be observedwhen cutting depth increases. In this study, the authors attempt to minimize the thrustforces in the step-feed micro drilling process by application of the DOE (Design ofExperiment) method. Taking into account the drilling thrust, three cutting parameters,feedrate, step-feed, and cutting speed, are optimized based on the DOE method. Forexperimental studies, an orthogonal array L27(313) is generated and ANOVA (Analysis ofVariance) is carried out. Based on the results it is determined that the sequence of factorsaffecting drilling thrusts corresponds to feedrate, step-feed, and spindle rpm. Acombination of optimal drilling conditions is also identified. In particular, it is found in thisstudy that the feedrate is the most important factor for micro drilling thrust minimization.

Experimental Study on the Effects of Alumina Abrasive Particle Behavior in MR Polishing for MEMS Applications.

Recently, the magnetorheological (MR) polishing process has been examined asa new ultra-precision polishing technology for micro parts in MEMS applications. In theMR polishing process, the magnetic force plays a dominant role. This method uses MRfluids which contains micro abrasives as a polishing media. The objective of the presentresearch is to shed light onto the material removal mechanism under various slurryconditions for polishing and to investigate surface characteristics, including shape analysisand surface roughness measurement, of spots obtained from the MR polishing process usingalumina abrasives. A series of basic experiments were first performed to determine theoptimum polishing conditions for BK7 glass using prepared slurries by changing the processparameters, such as wheel rotating speed and electric current. Using the obtained results,groove polishing was then performed and the results are investigated. Outstanding surfaceroughness of Ra=3.8nm was obtained on the BK7 glass specimen. The present resultshighlight the possibility of applying this polishing method to ultra-precision micro partsproduction, especially in MEMS applications.

Micro Fluidic Channel Machining on Fused Silica Glass Using Powder Blasting.

In this study, micro fluid channels are machined on fused silica glass via powder blasting, a mechanical etching process, and the machining characteristics of the channels are experimentally evaluated. In the process, material removal is performed by the collision of micro abrasives injected by highly compressed air on to the target surface. This approach can be characterized as an integration of brittle mode machining based on micro crack propagation. Fused silica glass, a high purity synthetic amorphous silicon dioxide, is selected as a workpiece material. It has a very low thermal expansion coefficient and excellent optical qualities and exceptional transmittance over a wide spectral range, especially in the ultraviolet range. The powder blasting process parameters affecting the machined results are injection pressure, abrasive particle size and density, stand-off distance, number of nozzle scanning, and shape/size of the required patterns. In this study, the influence of the number of nozzle scanning, abrasive particle size, and pattern size on the formation of micro channels is investigated. Machined shapes and surface roughness are measured using a 3-dimensional vision profiler and the results are discussed.

Micro Dot Patterning on the Light Guide Panel Using Powder Blasting.

This study is to develop a micromachining technology for a light guidepanel(LGP) mold, whereby micro dot patterns are formed on a LGP surface by a singleinjection process instead of existing screen printing processes. The micro powder blastingtechnique is applied to form micro dot patterns on the LGP mold surface. The optimalconditions for masking, laminating, exposure, and developing processes to form the microdot patterns are first experimentally investigated. A LGP mold with masked micro patternsis then machined using the micro powder blasting method and the machinability of themicro dot patterns is verified. A prototype LGP is test- injected using the developed LGPmold and a shape analysis of the patterns and performance testing of the injected LGP arecarried out. As an additional approach, matte finishing, a special surface treatment method,is applied to the mold surface to improve the light diffusion characteristics, uniformity andbrightness of the LGP. The results of this study show that the applied powder blastingmethod can be successfully used to manufacture LGPs with micro patterns by just singleinjection using the developed mold and thereby replace existing screen printing methods.

Magnetostrictive Micro Mirrors for an Optical Switch Matrix.

We have developed a wireless-controlled compact optical switch by siliconmicromachining techniques with DC magnetron sputtering. For the optical switchingoperation, micro mirror is designed as cantilever shape size of 5mm×800µm×50µm.TbDyFe film is sputter-deposited on the upper side of the mirror with the condition as: Argas pressure below 1.2×10-9 torr, DC input power of 180W and heating temperature of up to250°C for the wireless control of each component. Mirrors are actuated by externallyapplied magnetic fields for the micro application. Applied beam path can be changedaccording to the direction and the magnitude of applied magnetic field. Reflectivity changes,M-H curves and X-ray diffractions of sputtered mirrors are measured to determine magneto-optical, magneto-elastic properties with variation in sputtered film thickness. The deflectedangle-magnetic field characteristics of the fabricated mirror are measured.