Ultraprecision Machining Center Research Articles

An experimental investigation of double-side processing of cylindrical rollers using chemical mechanical polishing technique

Cylindrical roller bearings have been widely used in the mechanical industry due to the high radial load capacity. In some precision applications, high accuracy of cylindrical rollers, such as high profile accuracy and excellent surface quality, is strongly demanded and is even indispensable for the operational reliability of bearings. In this paper, on the basis of a lapping process, chemical mechanical polishing (CMP) technique was used to prepare cylindrical rollers with a low roundness and a nanoscale surface roughness Ra on a double-side cylindrical ultra-precision processing device, which was developed by the Ultra-precision Machining Center of Zhejiang University of Technology. Firstly, the effects of the experimental conditions, such as the rotating speeds and the down force, on the processing performance were studied. The simulation results reveal that, using the optimized rotating speeds, with the processing time going, the processing trajectory gradually distributes uniformly on the cylindrical surface of the roller along both the circular and the axial directions, and thereby, the uniform material removal can be realized; with the increase of the down force, the material removal rate (MRR) of the cylindrical roller almost linearly increases. Specially, the down force of the CMP process was set to 20 N/roller to obtain a better polishing performance. Then, on the basis of a lapping process, CMP technique was used to further improve the surface quality of the cylindrical rollers to nanoscale roughness. The results show that, after a two-step CMP process including a rough polishing step and a fine polishing step, the cylindrical surface of the rollers changes from rough and uneven state into smooth and free of micro-scratches state, and the surface roughness Ra decreases from initial 76 to 16.6 nm, and the roundness decreases from initial 0.97 to 0.40 μm. Finally, the material removal mechanism of the cylindrical rollers was investigated. During the lapping process, the material removal is predominantly driven by the mechanical abrasion from the α-alumina particles; while during the CMP process, the material removal is realized by the alternating cycles of “oxidation/complexation/passivation-abrasion-oxidation/complexation/passivation” process. In sequence, the mechanism of the roundness improvement was proposed. During the lapping and the CMP processes, the MRR at the protrudent point is larger than that at the recessed point due to the larger contact stress, and as a result, the actual surface profile of the circular section gradually reaches the average circle, and the roundness decreases.

Finite Element Analysis and Optimization of Thermal Deformation of Resin Concrete Manufacturing Bases

Resin concrete generally has good mechanical properties, excellent thermal stability and great vibration resistance, the model of the ultra-precision machining center bed is established to study the thermal stability of the resin concrete using virtual reality and collaborative simulation technology based on Pro/E and ANSYS Workbench. The main factors that affect the machine tool bed thermal deformation were found through analyzing the deformation results and the materials and restrain conditions were optimized. The results proved that the optimized machine tool bed has good thermal stability and theoretical basis was provided to improve the thermal stability of the ultra-precision machining centers.

Novel micro-optical collector design for a gas chromatographic detector based on atomic emission spectroscopy

We report a novel micro-optical systems approach for gas chromatographic detection based on plasma excitation of the eluate and subsequent emission spectroscopic evaluation. Specifically, we propose a detector architecture that integrates a microhollow cathode setup and an optical collector system on a common planar microsystems platform. The collector consists of an array of identical imaging systems that surround the microplasma and couple the emitted light side-on into fibers via which it can be fed into a spectrometer. Elliptically shaped reflector profiles ensure nearly aberration-free achromatic imaging and hence a high coupling efficiency. This is confirmed by ray-tracing simulations. An experimental demonstration of the detector module is assembled. The elliptical profiles are milled out of aluminium with diamond tools on an ultraprecision machining center. Experimental tests with a He plasma prove that a higher optical coupling efficieny than with the traditional end-on signal pickup scheme can be achieved.

On-Machine Cutting Edge Profile Measurement for Micro Milling Tool (2nd Report, Micro Endmill (.PHI.300.MU.m) Wear Measurement and Evaluation)

The extremely precise level of cutting work's demand has been increasing, recently. Therefore, the establishment of a supreme measurement technology for micro endmills during operating on ultra-precision machining center plays an important role in many micro fabrication industries. The “Diffraction Gauge Method”, a novel measuring technique based on far-field laser diffraction, has been proposed to measure cutting-edge profiles of micro tools (φ<500μm) with repeatability of better than 100 nm even though on-machine surroundings. In this paper, cutting-edge profile measurement of worn micro endmills (φ300μm), which operated side-milling on graphite work material, is carried out. Agreement of the measured profiles with SEM image confirms the high accuracy of the measurement technique. Subsequently, the tool wear evaluations in various cutting lengths of micro endmills before and after cutting notify the relationship between increase in tool wears and cutting length. These experimental results verify the validity of our novel micro endmill measurement technique, which can be applied into ultra-precision machining center in the near future.

1414 集束レーザ光を用いた三次元微細形状の加工(S80-2 特殊加工プロセス(2),S80 特殊加工プロセス)

Development of a high-speed microfabrication technique using focused laser beam was conducted. Conventional CAD/CAM system was used and the beam was scanned mechanically by attaching both optical mirror arrays and a focal lens to the column of an ultraprecision machining center. Measured groove width and pocket depth obtained by grooving and pocket machining were used as a tool diameter and an axial depth of cut. A glass-like carbon having over 80% laser beam absorptivity and 650MHv hardness was employed as a workpiece. It was verified through the machining test that pseudo 3 dimensional concave prisms could be fabricated by digging square pockets with different square sizes and the same pocket depth to negative Z direction. Shifting laser focal point from the work surface could control a depth of the square pocket, so that a high-speed roughing by adjusting focal point on the work surface could be conducted. In addition, the laser micromachining system could be adapted to a high-speed finishing by shifting focal point from the work surface.

Improvement of Machining Accuracy of 5-Axis Control Ultraprecision Machining by Means of Laminarization and Mirror Surface Finishing

Air bearings are often used in ultraprecision machine tools requiring high accuracy. With increasing the high accuracy for machine tools, it is required to pay attention to microvibration with nanometer order. The fluctuation in compressed air applied to air bearings causes the air turbulence, which results in the microvibration. The study presents the laminarization by the optimal design of piping and air bearing surfaces as well as mirror surface finishing, so that the laminarization can be realized to suppress the microvibration. From experimental results, it is found that the surface roughness of workpieces can be drastically improved by using a revised ultraprecision machining center.

Creation of Ultraprecision V-shaped Microgrooves Using Non-Rotational Cutting Tools

The study deals with the creation of ultraprecision microgrooves using non-rotational diamond cutting tools with angle of 90 degrees, which are mounted on an ultraprecision machining center. Machining experiments of micro grooves were conducted to find the optimal value of cutting speed, depth of cut, rake angle, changing the cutting speed from 1mm/min to 200mm/min, the depth of cut from 0.1m to 10m and the rake angle from -5 degrees to 30 degrees. Workpieces were machined with the cutting tool submerged in the cutting fluid to know the influence of cutting fluid supply method. From the experimental results, the adequate cutting condition is obtained such as the rake angle of 10 degrees to 20 degrees, the finish cutting speed of 1mm/min and the depth of cut in rough cut and finish cut of 1m and 0.5m respectively. As the cutting fluid supply method, workpiece submerged in the cutting fluid is effective. Using the cutting condition, fine V-shaped microgrooves are obtained in various materials. In addition, frontlight optical plate and micro Fresnel lens with the designed micro grooves were designed and manufactured by non-rotational diamond cutting method. As a result, it is also found that the non-rotational diamond cutting method enables to accurately and neatly manufacture microgrooves without any burr generation.

126 Improvement of Ultraprecision Machining Center by Means of Laminarization

126 Improvement of Ultraprecision Machining Center by Means of Laminarization

Creation of 3-D tiny statue by 5-axis control ultraprecision machining

The study deals with the creation of a 3-dimensional (3-D) complicated tiny statue by means of a 5-axis control ultraprecision machining center and a pseudo ball end mill of single crystal diamond. In recent years, 3-D microstructures are required to provide components for micromechanism as well as metal molds and dies. Thus, as an example of complicated 3-D microstructures, a Buddha head of 3 mm in size was created, based on the scanned data of an actual statue. A control program developed in the study enables a diamond tool to feed around the head and to move from the top of the head to the neck not only by 4-axis control but also by 5-axis control to prevent the tool and its holder from colliding with a workpiece. As a result, a tiny Buddha head could be created with high surface quality.

Non-adhesive direct bonding of tiny parts by means of ultraprecision trapezoid microgrooves

The study proposes a new method of bonding two small parts without the use of any adhesive by making use of ultraprecision trapezoid microgrooves on the surfaces of each part. These trapezoid microgrooves allow small parts to be bonded together with high positioning accuracy due to a wedge effect and an adhesion phenomenon between the mating surfaces. Ultraprecision trapezoid microgrooves are created by using an ultraprecision machining center having 1 nm positioning resolution and a diamond milling cutter. From experimental and simulated results, it is found that the bonding strength in general increases with decreasing wedge angle. The effect of the wedge length on bonding strength varies with the wedge angle where the strength increases with increasing length for wedge angles greater than 8° but increases with decreasing length for wedge angles less than 8°.

マイクロＶ溝を利用した微小部品の直接接合 ２方向溝を用いた高精度位置決め

The study proposes a new method to accurately bond two small parts without any adhesives by makinguse of ultraprecision V-shaped microgrooves created on the surfaces of each part. These V-shaped microgrooves, whose depth and dihedral angle are 20μm and 13 degree respectively, allow small parts to be tightly bonded together with high positioning accuracy dueto a wedge effect and an adhesion phenomenon between two mating surfaces. In the study, ultraprecision V-shaped microgrooves having two different directions are created by using an ultraprecision machining center with 1 nm positioning resolution and a single crystal diamond milling cutter. From experimental results, small parts of 4 mm x 4 mm x 4 mm that have V-shaped micro-grooves in two directions could be tightly bonded with 0.380 mm positioning accuracy. In addition, the new method has a possibility to bond different materials with each other. Two small parts with V-shaped microgrooves that are made of oxygen-free copper and aluminum are subjected to bonding test. The test shows the accurate and strong bonded result. As a result, the proposed bonding method is found to be effective to connect small parts accurately.

非回転工具を用いた超精密マイクロ溝の創成

This study deals with the creation of ultraprecision microgrooves using non-rotational diamond tools mounted on an ultraprecision machining center. Two types of non-rotational V-shaped diamond tools with the same inclined angle of 90 degree were prepared, with rake angles of 0 and 10 degrees respectively. Microgroove machining experiments were conducted to find the value of the optimal cutting speed, changing the cutting speed from 5 mm/min to 100 mm/min. The optimal condition is judged by investigating the burr generation and shape of chips. Up to the total depth of cut of 10 pm, straight-shaped chips came out, and the surface roughness was good, although burrs were generated. On the other hand, with a total depth of cut up to 20μm, wave-like chips came out and a good surface roughness was obtained. In addition, no buns were found on the machined surface. However, the use of cutting fluid led to the generation of wave-like chips and no burrs up to the total depth of cut of 20μm. From the experimental results, it is found that the adequate cutting condition is that the rake angle is 0 degrees and cutting speed of 40 mm/min with the cutting fluid kerosene dripped. Using this cutting condition, cross, parallel and curved V-shaped microgrooves were machined. As a result, fine microgrooves were obtained, which are applicable to micro optical devices.

マイクロＶ溝を利用した微小部品の直接接合

The study proposes a new method of bonding two small parts without the use of any adhesive by making use of ultraprecision V-shaped microgrooves on the surfaces of each part. These V-shaped microgrooves allow small parts to be bonded together with high positioning accuracy due to a wedge effect and an adhesion phenomenon between the mating surfaces. Ultraprecision V-shaped micro-grooves are created by using an ultraprecision machining center having 1 nm positioning resolution and a diamond milling cutter. From experimental and simulated results, it is found that the bonding strength in general increases with decreasing wedge angle. The effect of the wedge length on bonding strength though varies with the wedge angle where the strength increases with increasing length for wedge angles greater than 8 degrees but increases with decreasing length for wedge angles less than 8 degrees.

Development of Ultraprecision Machining Center with Closed-Loop Structure and Its Control

A high stiffness is required to reduce the relative displacement between workpiece and cutting tool due to the cutting force even for ultra-precision machine tools. Thus, a lathe-type ultra-precision milling machine was designed with a pseudo ball endmill as a cutting tool. The study deals with the further improvement of stiffness by upgrading the milling machine to that with a closed-loop structure. Thus, two constraint axes are employed to form the closed-loop structure, and are able to move in cooperation with X and Z-axis movements. The effect of the closed-loop structure is confirmed experimentally as well as with FEM analysis.

Development of Ultraprecision Machining Center with Closed-Loop Structure and Its Control.

High stiffness is required to reduce the relative displacement between workpiece and cutting tool due to the cutting force, even for ultraprecision machine tools. From the viewpoint of the structure with high stiffness, a gate-type structure is desirable. However, it is in general difficult to construct, and is liable to have a large size. In terms of ease of construction, a lathe-type ultraprecision milling machine has already been made, together with a pseudo ball endmill of single-crystal diamond as a cutting tool. The study deals with the further improvement of stiffness by upgrading the lathe-type ultraprecision milling machine to that with a closed-loop structure. Thus, two constraint axes are employed to form the closed-loop structure, and are able to move in cooperation with x-and z-axis movements using the newly developed control software. The effect of the closed-loop structure is experimentally confirmed as well as in FEM analysis.