Ultra-precision Micro Research Articles

Influence of Feed Rate Response (FRR) on Chip Formation in Micro and Macro Machining of Al Alloy

In this paper, the investigation of chip formation of aluminum alloy in different machining strategies (i.e., micro and macro cutting) is performed to develop a holistic view of the chip formation phenomenon. The study of chip morphology is useful to understand the mechanics of surface generation in machining. Experiments were carried out to evaluate the feed rate response (FRR) in both ultra-precision micro and conventional macro machining processes. A comprehensive study was carried out to explore the material removal mechanics with both experimental findings and theoretical insights. The results of the variation of chip morphology showed the dependence on feed rate in orthogonal turning. The transformation of discontinuous to continuous chip production—a remarkable phenomenon in micro machining—has been identified for the conventional macro machining of Al alloy. This is validated by the surface crevice formation in the transition region. Variation of the surface morphology confirms the phenomenology (transformation mechanics) of chip formation.

Design and dynamic optimization of an ultra-precision micro grinding machine tool for flexible joint blade machining

Ultra-precision micro machine tool (UPMMT) has always been a high-precision machine tool for microscale/mesoscale mechanical components. It has demonstrated many advantages in small footprint, low cost of energy, low operational cost, high machining precision, etc. However, developing UPMMT is always a complicated, labor-consuming work and lacks scientific approach and guidelines. This paper is devoted to introduce a detailed design method of a micro grinding machine tool used for flexible joint blade machining. The micro grinding machine tool was built up with a combined support structure of both advantages of gantry column and single column structure, allowing more work zone and better static stability. In order to improve the dynamic performance of the machine tool, an optimization design method based on sensitivity analysis was proposed. The weakest link of the machine tool structure was identified and selected as the optimization target, and an optimization equation was established with the nature frequency as the optimization goal, mass and size as the constraint condition. The results showed that the first six nature frequencies of the machine tool were increased with different degrees and the first nature frequency was increased by about 10%. The biggest resonance peak of the machine tool was reduced in the x direction by 8.6%, in the y direction by 6.4%, and in the z direction by 10.1%. Based on the optimization results, a prototype was built, and machining tests were carried out on flexible joint blade machining to evaluate the machining performance of this machine tool.

Actuarial calculation of the squareness errors for ultra-precision micro v-groove machine tools

A v-groove structure is extensively used for planar optical-fiber alignment because of its unique features. To obtain low connection loss, the core pitch tolerance of a v-groove structure should be within submicrons. The squareness errors have great influences on the machining precision of micro v-grooves. Therefore, the actuarial calculation of squareness errors is of great significance for ultra-precision micro v-groove machine tools. In view of the disadvantages of the squareness error analysis method basing on small angle error assumption, the actuarial calculation of squareness error is implemented. A more precise geometric error model basing on the actuarial calculation of squareness error is established. The transformation between actuarial calculation of squareness error and improvement of machining precision is achieved through the geometric error modeling. The results show that the actuarial calculation of squareness error is effective and practical.

Finite Element Simulation and Experimental Study on Micro-Milling Cobalt-Based Alloy

Elgiloy is a cobalt-based alloy with excellent physical and chemical performance, which is used widely in medical and industrial applications. In this paper, the professional finite element analysis software for metal cutting is used to establish the finite element simulation model of micro cutting this kind of cobalt-based alloy, and the effect of feed rate, which is considered as the most important processing parameter, on the cutting force of micro cutting Elgiloy is analyzed. The cutting force measurement system based on ultra-precision micro milling machine tool is established for experimental study on the cutting force of micro milling Elgiloy by using ultra-fine gain tungsten carbide micro milling tool. The cutting force is measured with different feed rate parameters and the influence of the parameters on the cutting force is analyzed. The simulation and experimental results show that the trends observed at the micro scale are the same as the trends for machining at the macro scale, which implies that the Elgiloy material behaves in a similar manner at both length scales.

A study of single kinematic errors accurate fitting for ultra-precision micro v-groove machine tools

V-groove structure is extensively used for planar optical-fiber alignment, and its quality is critical to the functionality of the fiber connector. The core pitch of v-groove structure is the most important machining parameter, which determines the v-groove quality. And its machining precision is dominated by the machine tool motion precision in the z-axis direction. Six single kinematic errors derived from the multi-body system theory are the main factors affecting the accuracy of the machine tool motion in the z-axis direction. Therefore, this paper presents a single kinematic errors accurate fitting methodology for the micro v-groove machine tools. A function is fitted with a set of data using the existing fitting method and verified by another set of data measured at other testing points. Each set of test points have the same intervals, but their starting points are different from each other. The fitted function is constantly upgraded in the process of the verification. And the accurate fitted function is finally obtained by the recycling verification process. The results show that the accurate fitting method is effective and practical.

Ultraprecision Micro Grooving on Brass for Surface Wettability Control

Fine micro grooves of various depths and pitches were fabricated on brass surface by ultraprecision micro cutting, and the effects of groove geometry and orientation on surface wettability were investigated. Results showed that the contact angle of a liquid drop changes significantly with the depth and orientation of the grooves. By optimizing the grooving conditions, the contact angle was increased to about twice that of a flat surface. Effects of crystal grain boundaries in the workpiece material and effects of cutting conditions on burr formation during micro grooving were studied by both experiments and finite element simulation.

Transient liquid phase diffusion bonding for micro PCD tool fabrication

In this study, K30 (W 90 wt%, Co 10 wt%) and DX5 (W 84 wt%, Co 16 wt%) tungsten carbide were used as base metals for transient liquid-phase diffusion bonding (TLPDB). The filler metal was MBF20, a type of nickel alloy used to minimize the residual stresses that occur due to the differences in the expansion coefficients of the metals. MBF20 contained B, Si, and Cr, which reduced the melting point of the nickel alloy and enhanced its mechanical properties. The base metal and filler metal surfaces were cleaned by mechanical polishing and cleaning. Diffusion bonding was performed under vacuum at 1,000–1,500 K under low pressure than buckling load conditions. The microstructure on the localized bonded surface was analyzed using scanning electron microscope (SEM) and optical microscopy. Result of no significant change was observed in the diffusion bonding in the low-to-mid temperature range due to insufficient filler metal or base metal dissolution at the bonding site. However, at high temperatures, the filler completely melted and bonded to the base metal on both sides. Our results showed that temperatures approaching the recrystallization temperature were required to provide high-quality welds for ultra-precision joints and micro polycrystalline diamond (PCD) tool fabrication.

Size Effect in Sintering of Micro Metal Injection Molded Part

Micro gears with different dimension were fabricated by micro metal injection molding and sintering behavior of the micro gear was investigated. For this, ultraprecision micro molds were prepared by micro electroforming. The sintered micro gears had outer diameter of 470μm and 250 μm, respectively. From the sintering results at 1200°C and 1250°C, the grain growth and the degree of thermal etching depend dominantly on the size of micro part rather than micro feature size. The sintering temperature of micro parts should be lower than that of macro components.

Xanthan Gum으로 코팅된 Carbonyl Iron Particle를 이용한 자기유변유체 연마특성에 관한 연구

A polishing method using magnetorheological (MR) fluid has been developed as a new precision technique to obtain a fine surface. The process uses a MR fluid that consists of magnetic carbonyl iron (CI) particles, nonmagnetic polishing abrasives, water and stabilizers. But the CI particles in MR fluids cause a severe corrosion problem. When coated with Xanthan gum, the CI particles showed long-term stability in corrosive aqueous environment. The surface roughness obtained from the MR polishing process was evaluated. A series of experiments were performed on fused silica glass using prepared slurries and various process conditions, including different polishing times. Outstanding surface roughness of Ra=2.27nm was obtained on the fused silica glass. The present polishing method could be used to produce ultra-precision micro parts.

Advanced Micromanufacturing for Ultra Precision Part by Soft Lithography and Nano Powder Injection Molding

Recently, the advanced technologies that offer high precision product, relative easy, economical process and also rapid production are needed to realize the high demand of ultra precision micro part. In our research, micromanufacturing based on soft lithography and nanopowder injection molding was investigated. The silicone metal pattern with ultra thick and high aspect ratio succeeds to fabricate Polydimethylsiloxane (PDMS) micro mold. The process followed by nanopowder injection molding (PIM) by a simple vacuum hot press. The 17-4ph nanopowder with diameter of 100 nm, succeed to be injected and it forms green sample microbearing with thickness, microchannel and aspect ratio is 700µm, 60µm and 12, respectively. Sintering process was done in 1200 C for 2 hours and heating rate 0.83 o C/min. Since low powder load (45% PL) was applied to achieve green sample fabrication, ~15% shrinkage happen in the 86% relative density. Several improvements should be done to produce high accuracy and full density sintered part.

S1302-2-5 反応焼結SiCの超精密マイクロ切削に関する研究(超精密加工(2))

S1302-2-5 反応焼結SiCの超精密マイクロ切削に関する研究(超精密加工(2))

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.

A Study on Tool Deflection Trend Using Real Captured Images in Micro Endmilling Process

Recently, ultra-precision micro patterns and shapes have been widely used in optical field. Various methods which are based on semi-conductor fabrication methods are nowadays used in fabrication of micro shapes and patterns, but micro endmilling technology has lately attracted considerable attention because of various available materials, flexibility of process and high-productivity. For the precision micro endmilling process, analysis of micro cutting error is mandatory. In general, tool deflection is a major factor which causes cutting error and limits realization of the high-precision cutting process. Specially, in micro endmilling process, micro tool deflection generates very serious problems compared to macro tool deflection. In this paper, it is performed to observe the real tool deflection shapes in micro endmilling process, so the trend of micro tool deflection was analyzed using real captured images in this study. To get the real images of micro tool deflection, micro slot cutting processes were executed under various cutting conditions using micro endmill and the real images of tool deflection were obtained during cutting process by high-speed camera. Finally, the extent of tool deflection was calculated by the deflection angle according to cutting conditions and two trends (the point of first tool contact and the cutting stage) of micro tool deflection were analyzed.

High frequency bandwidth measurements of micro cutting forces

The miniaturization of machine components is perceived by many as a core requirement for the future technological development of a broad spectrum of products. One of the challenges in micro engineering is the development of economical micro systems that are flexible, functional and made of appropriate engineering materials. The mechanical removal of materials using miniature tools, known as a micro machining process, has unique advantages in creating 3D components using a variety of engineering materials, when compared with photolithographic processes. Since the diameter of miniature tools is very small, excessive forces and vibrations will significantly affect the overall part and tool quality. In order to improve the part and tool quality, accurate measurement of micro cutting forces is imperative. In this paper, we focus on the development of an ultra precision micro milling system and the measurement of micro cutting forces using a three-axis miniature force sensor and accelerometers. Since the inherent dynamics of the workpiece and overall machine tool affects the frequency bandwidth, we employ the Kalman filter approach to fuse the sensor signals and compensate for unwanted dynamics, in order to increase the bandwidth of the force measurement system. Based on accurate cutting force measurement, we can come up with the optimal process parameters to maintain desired tolerances and also monitor the process to prevent failures.

Study on Precision Grinding of Micro Aspherical Surface (4th Report)

Needs of digital devices increase rapidly in recent years, and the demand for a micro axis-symmetric aspherical glass lens of large numerical aperture is expanding rapidly especially in that device. Moreover blue lasers have been increasingly used to make wavelengths short and the maximum tangent angle of the aspheric shape has increased. Therefore ultra-precision grinding technology of ceramic dies became to be a core technology. Authors have successfully developed the 45 degrees tilted grinding method, and ultra-precision micro aspherical shape has been obtained. The improvement of the form accuracy will be required because the specifications of micro lenses become more and more strict in future. However, the shape correction cannot be done satisfactorily, because the wheel wear is not equal and the grinding point on the wheel moves. In this paper, a new grinding method is proposed to solve the above problems. In this method, three-axes (X, Y, Z) are controlled simultaneously so that the position of the grinding point on the diamond wheel is fixed. Then the grinding system was developed and grinding experiments using micro symmetric aspherical dies of tungsten carbide were carried out.

2912 6 軸超精密複雑形状金型加工機の開発とその加工効果

We have developed a "Nano-Precision Machining System" which machines have produced metal die for ultra precision micro lens and liquid crystal optical wave guides etc. The developed machine is mainly composed of the high stiffness machine frame, NC controller, air hydrostatic spindles and supporting devices such as oil tanks and temperature control units. The machine has 6 axes. Three linear axes (X, Y and Z-axes) can be controlled at a feeding resolution of 1 nm under full closed feedback. The maximum workpiece size is 220 mm × 170 mm along the X and Y axes. In this paper, the concept of the "Nano-Precision Machining -System" are proposed and introduced. The system configuration, features, and specifications were described.

高アスペクト比形状の超精密マイクロ切削加工

In recent years, the ultraprecision micro machining technology is greatly expected in a variety of fields such as optical instruments, electronic devices, medical equipments, etc. At the time, it is essential to meet the requirement of producing various shapes, one of which is a structure with a high aspect ratio. Such a structure is applicable, for example, to a shaft of micro robot, a long part of micro actuator and micro machine, a micro needle for syringe, etc. However, it is extremely difficult to fabricate the structure with a high aspect ratio since it is easily crooked and broken during cutting. Thus, it is at first intedned to produce prismatic micro tower with a high aspect ratio, which has never been fabricated until now, by applying the ultraprecision milling technology with a single crystal diamond cutting tool. This method enables to accurately create a variety of micro structures with a high aspect ratio. In addition, the study also proposes a new machining method to create micro pin array, avoiding the contact of cutting edge with already machined parts again. Micro pin array may be applied to painless micro needles for syringe. As a result, it is found that the proposed method has the potential of producing a variety of micro structures with a high aspect ratio.

Development of Ultraprecision Micro Grooving. Manufacture of V-Shaped Groove.

The study deals with the manufacture of microgrooves with sharp edges and smooth oblique and / or curved surfaces by means of an ultraprecision milling machine and single crystal diamond endmills. Fine microgrooves are key components to fabricate mivrograting, micrograting lens and so on. Conventional groove fabrication methods such as etching and lithography are difficult to make grooves without burr. The new machining method proposed in the study allows to produce V-shaped grooves of 100 μm in pitch with enough shape accuracy and surface roughness of 48 nm (P-V value). The method also makes it possible to form the microgroove of 1 μm in pitch with sharp edge and without burr. In addition, the method is experimentally found effective to produce R-shaped groove and trapozoid-shaped one without burr.

Ultaprecision Diamond Cutting of Hardened Steel by Applying Elliptical Vibration Cutting

Elliptical vibration cutting, which has been proposed by the authors, is applied to ultraprecision diamond cutting of hardened steel in the present research. Since steel cannot be cut by the ordinary cutting method with a diamond cutting tool due to excessive tool wear, performance of the elliptical vibration cutting is examined in comparison with the conventional vibration cutting. The experimental results show that the proposed method has superior performance, i.e. low cutting force, high quality surface finish and long tool life. Based on these advantages, the elliptical vibration cutting is successfully applied to ultraprecision cutting of hardened steel, such as ultraprecision turning of a spherical die and a flexible micro structure, and ultraprecision micro grooving.

Development of Ultraprecision Micro Grooving. Manufacture of V-Shaped Groove.

The study deals with the manufacture of microgrooves with sharp edges and smooth oblique and/or curved surfaces by means of an ultraprecision milling machine and single crystal diamond endmills. Fine microgrooves are key components to fabricate micrograting, micrograting lens and so on. Conventional groove fabrication methods such as etching and lithography are difficult to make grooves without burr. The new machining method proposed in the study allows to produce V-shaped grooves of 100 μm in pitch with enough shape accuracy and surface roughness of 48 nm (p-v value). The method also makes it possible to form the microgroove of 1 μm in pitch with sharp edge and without burr. In addition, the method is experimentally found effective to produce R-shaped groove and trapozoid shaped one without burr.