Ultra-precision Milling Research Articles

Creation of Ultra-precision Microstructures with High Aspect Ratios

In recent years, ultra-precision micromachining technology has been used in a variety of fields such as optical instruments, electronic devices, medical equipments, etc. At present, it is essential to meet the requirement of producing various shapes, one of which is a structure with a high aspect ratio. Such structures are applied, for example, to a shaft of micro robot, a long part of microactuator and micromachine, a microneedle for syringe, etc. However, due to its fragile nature, it is extremely difficult to fabricate the structure with a high aspect ratio since it is easily damaged during cutting. It is intended to produce micro towers with high aspect ratios by applying the ultra-precision milling technology using a single crystal diamond cutting tool. The method enables accurate creation of a variety of microstructures with high aspect ratios. In addition, the study also proposes a new machining method to create microneedle arrays, avoiding the contact of cutting edge with already machined parts again. As a result, it is concluded that the proposed method has the potential of producing a variety of microstructures with high aspect ratios.

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.

Metal Mold Manufacturing of Fresnel Lens by Use of Micro Grooving Technology.

The study deals with cutting of metal mold for a tiny Fresnel lens which is composed of circular micro grooves. Conventional methods such as photolithography and cutting by a lathe often lead to the burr generation due to a reduction of cutting speed, especially at the center of lens, and to low surface quality such as step-like cross-section of groove by photolithogrphy. The employment of a rotational diamond cutting tool is expected to eliminate the above problems. Thus, a workpiece of Fresnel Lens is set on the main spindle of a lathe-type ultraprecision milling machine, which has the positioning accuracy of 1 nm. The diamond cutting tool is rotated by a high speed air turbine spindle. According to the cutting experiment, no burr was found at the edge of grooves, and the surface roughness of a slope in the groove was 80 nm (Rmax). The cross section of lens groove is slightly curved due to the unique way of cutting, which made a profile of lens get closer to the ideal one.

Application of Ultraprecision Microgrooving to Manufacturing Diffraction Grating for a Small Encoder.

This study deals with the manufacture of a small high-resolusion rotary encoder for a feed-back sensor of small actuators to move a small robot arm in the near future. A laser diffraction grating is desirable to exert the diffraction efficiency. Thus, the encoder with 32786 V-shaped grooves radiately around a track of 10 mm in diameter is designed to obtain a resolution of two million pulses for a rotation. Smooth and correct V-shaped grooves are created by means of ultraprecision micromachining technology, where a rotational diamond cutting tool is fed on an ultraprecision milling machine having 1 nm positioning accuracy. In order to obtain a good encoder, diamond tool wear was monitored, servomotors were tuned to reduce the tracking error, and the master encoder was compensated to eliminate the periodical positioning error. However, a phase mismatch took place at the point, where the cutting starts and finishes. This is mainly due to the thermal disturvance since it takes about ten hours to complete the cutting. Thus, the cutting order was modified so as to make the influence of thermal disturbance uniformly distribute around the track of encoder. As a result, it is proved that the way of cutting enables the encoder to have enough optical performance.

Development of a 5-Axis Control Ultraprecision Milling Machine for Micromachining Based on Non-Friction Servomechanisms

The study addresses the development of a 5-axis ultraprecision milling machine to create tiny 3-dimensional workpieces as well as microstructures. 3-axis control ultraprecision milling machines allow microstructures on tiny workpiece surfaces to be manufactured; however it is difficult to create 3-dimensional workpieces such as very small heads, statues etc., which will be important in micromanufacturing in the future. Thus, a 5-axis milling machine consisting of three translational and two rotational axes has been developed benefitting from the use of non-friction servomechanisms. 5-axis micromachining was conducted to create a half cylindrical workpiece. It was found that the ultraprecision milling machine is accurate enough to machine tiny 3-dimensional workpieces.

Manufacture of diffraction grating on tiny parts by means of ultraprecision milling

The study deals with the manufacture of diffraction grating by applying the ultraprecision microgrooving technology. Microgrooving is performed by the use of a lathe-type ultraprecision milling machine having 1 nm positioning accuracy, together with a rotating diamond cutter. As an example of microgroove, a diffraction grating with 32 768 V-shaped grooves is fabricated in a pitch of 1 μm and a depth of 0.5 μm around the circumference of copper disk of 12 mm in diameter. The high-speed rotating cutter allows the microgrooves to be sharply machined without burrs and accumulative pitch errors, taking account of cutting order. The surface roughness of machined grooves is 1 nm (Ra), which experimentally shows good optical properties.

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.

マイクロ溝加工技術を用いたフレネルレンズ金型加工

The study deals with cutting of metal mold for a tiny Fresnel Lens which is composed of circular micro grooves. Conventional methods such as photolithography and cutting by lathe often lead to the burr generation due to a reduction of cutting speed, especially at the center of lens, and to low surface quality such as step like cross-section of groove by photolithography. The employment of a rotational diamond cutting tool is expected to eliminate the above problems. Thus, a workpiece of Fresnel Lens is set on the main spindle of a lathe-type ultraprecision milling machine, which has the positioning accuracy of 1 nm. The diamond cutting tool is rotated by a high speed air turbine spindle. According to the cutting experiment, no burr was found at the edge of grooves, and the surface roughness of a slope in the groove was 80 nm. The cross section of lens groove is slightly curved due to the unique way of cutting, which made a profile of lens get closer to the ideal one.

Special Issue on Emerging Technology in Manufacturing

Manufacturing yields value from worthlessness. Thus, in recent years, manufacturing technologies have been undergoing rapid change in order to produce products of high quality, at a low cost and with short lead times. Improvements and innovations, with regard to manufacturing technologies, range from the fundamentals to large-scale systems. Therefore, the guest editor would like to introduce the new manufacturing technology, together with the latest research results. One of the most recent key technologies is the so-called rapid-prototyping technology. It shortens the development period of new products from the design stage. Many rapid-prototyping technologies are being developed concurrently. In this issue, the state of the art is explained clearly by an expert in the field. For mechanical products, manufacturing capabilities are highly dependent upon machine tools. In this issue, there is a research paper concerned with a design method for multi-purpose machine tools that can fabricate a variety of products. Machining efficiency is strongly influenced by the positioning accuracy and feed velocity of the axis movement of the machine tools. A control algorithm that can achieve high speed and accuracy is proposed in a paper in this issue. In order to make the most of NC machine tools, it is essential to provide NC data rapidly However, it is difficult to generate NC data, especially for multi-axis control machine tools capable of machining workpieces with complicated shapes. The development of 6-axis control CAM software for creating sculpted surfaces is reviewed in the issue. Another paper deals with NC data generation for sculpted surface processing using virtual reality. In FA systems, the nature of the programming/execution environment is shifting from a concentrated one to a distributed one, and a worker-friendly manufacturing environment is required for the workers. Two papers are presented for realizing such environments. Recently, ultra-precision machining and micro-machining technologies have been attracting great interest as a result of their ability to produce micro-mechanisms and micro-robots. One paper describes production of a prototypical tiny part with a sculpted surface using an ultra-precision milling machine. Another is related to simulation of an atomic level cutting mechanism that applies molecular dynamics. Manufacturing technology is making tremendous progress, and is putting promising new technologies into use toward the goal of realizing intelligent manufacturing systems, IMS. The guest editor heartily hopes that this issue aids in comprehension of the emerging technology in the manufacturing field.

Manufacture of Micropropellers by Means of Ultraprecision Milling Machine

The requirement for producing metallic microparts for use in micromachines and/or micromechanisms will continue to increase. This study deals with the manufacturing of tiny parts, of mm-size, using micromachining technology and an ultraprecision milling machine, which consists of a z-motion table, a positionable spindle on it as the c-rotational axis, and an x-motion table. The spindle, which has a pseudo ball end mill composed of a single crystal diamond, is mounted on the x-table. A new manufacturing procedure is devised in order to create a propeller, 3 mm in diameter, as a representative micropart, based on the CAD data of the propeller. As a result, it was found that a functional machined propeller, with a surface roughness of 0.1 μm, can be mounted onto a micromotor shaft, 0.7 mm in diameter.

Advanced Three-Dimensional Micromachining by Means of Ultraprecision Milling. 2nd Report. High-Precision Tool Chuch System.

This study deals with the improvement of ultraprecision micromachining technology by devising a tool chucking mechanism. A lathe-type ultraprecision milling machine equipped with an improved pseudo ball end mill as a cutting tool was designed to create tiny parts with nm-order surface roughness. The dimensional accuracy and surface roughness are significantly influenced by the rotational accuracy of the pseudo ball end mills, which are mounted on the spindle using a chucking mechanism. To meet the requirement, a new chucking mechanism was devised as a substitute of a three-jaw-type chuck to improve the setting repeatability of the tool. The new chucking mechanism enables the tool to be rightly positioned within the range of 0.2 μm. As a result, the ultraprecision milling machine equipped with the chucking mechanism and the tool was able to produce a traditional Noh mask on a copper surface of 1 mm in diameter with a surface roughness of 58 nm (p-v). In addition, it was found that the contour line pattern observed on the mask surface was due to a three dimensional cutter mark.

超精密フライス加工機による微小部品加工の試み

The requirement of producing metallic micro-parts for micro-machine and/or micro-mechanism will be increased. The study deals with manufacturing of tiny parts in mm-size by use of micro-machining technique of an ultra-precision milling machine. The ultra-precision milling machine, consisting of Z-motion table, positional spindle on it as C-rotational axis, X-motion table, is equipped with a pseudo-ballend mill composed of a single crystal diamond tool mounted at the top of high speed air spindle on X-motion table. A new manufacturing procedure is devised to manufacture a propeller of 3 mm in diameter as an example of micro-parts by use of ultra-precision milling machine. On the basis of CAD data of a propeller, two kinds of NC data, for front face and back one, are generated to machine the whole shape together with preparation of jig. It is found that the machined propeller mounted to the micro motor shaft works.

Ultraprecision 3D Micromachining of Glass

It has been theoretically and experimentally confirmed that brittle materials can be machined in the ductile mode under the certain small depth of cut. However, it is extremely difficult to obtain tiny 3D workpiece shapes of brittle materials with high surface accuracy. The study deals with the ultraprecision 3D micromachining of glass workpiece by means of a lathe-type ultraprecision milling machine and pseudo ball end mills. As a result, it is possible to obtain a glass mask of 1 mm in diameter with the surface roughness of 50 nm.

Micro-Machining of Sculptured Surfaces by Lathe-type Ultra-precision Milling Machine.

Micro-machining technology is in general well known in the field of photolithography technique, where most of material to be used are brittle ones such as silicon-oxide. From now on, however, the requirement of producing micro-machine and/or micro-mechanism with metal materials will be increased since a variety of workpiece configurations can be easily made. Thus, the study deals with the micro-machining of metal workpieces with sculptured surface by use of an ultra-precision milling machine newly developed. The lathe-type ultra-precision milling machine, consisting of Z-motion table, positionable spindle on it as C-rotational axis, X-motion table and B-rotational table on it, is equipped with a pseude ball endmill composed of a single crystal diamond tool mounted at the top of high speed air spindle on B-rotational table. Two control programs were developed to carry out 3-axis and 4-axis control micro-machining respectively. 3-axis control program enables the tool to produce a human face-like surface with the surface roughness of 77 nm(Rmax) within the area of 3.5 mm square. On the other hand, 4-axis control is to cope with the machining of workpieces with a steep incline, changing the tool attitude by B-rotational table. The cutting experiment shows the potential of 4-axis control ultra-precision milling of workpieces with a steep incline. As a result, the possibility of generating ultra-precision sculptured surfaces is experimentally confirmed with metal workpieces.

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.

Ultraprecision Milling. Sculptured Surface Generation.

This study deals with the development of an ultraprecision milling machine, which allows the production of workpieces with sculptured surfaces. To date, a variety of precision parts have been produced by ultraprecision diamond turning machines. However, they cannot cope with the fabrication of sculptured surfaces, which have stricter requirements. The ultraprecision milling machine developed here consists of an air spindle with a milling tool and a three-axis feed mechanism. As a milling tool, a pseudo-ball-endmill is designed by slightly offsetting a conventional diamond tool having a nose radius. It is found that the ultraprecision milling machine can produce workpieces with a sculptured surface and surface roughness of about 70 nm Rmax.

Generation of Sculptured Surfaces by Means of an Ultraprecision Milling Machine

Summary The study deals with the development of an ultra-precision milling machine, which allows the production of workpieces with sculptured surfaces. Until now, a variety of precision parts have been produced by ultra-precision diamond turning machines. However, they can not cope with making sculptured surfaces, which have higher requirements. The ultra-precision milling machine developed consists of an air spindle with a milling tool and a three-axis feed mechanism. As a milling tool, a pseudo ball-endmill is designed by slightly offsetting a conventional diamond tool having a nose radius. It is found that the ultra-precision milling machine can produce workpieces with sculptured surface in surface roughness of 70 nm Rmax.

Study of Ultraprecision Milling. Structure of Ultraprecision Milling Machine and Machining.

The study deals with the development of ultraprecision milling machine, which allows to produce workpieces with sculptured surface. Until now, a variety of precise parts such as optical lens, laser reflective mirror, disc substrate and so on have been produced by ultraprecision turning lathes. However, the ultraprecision lathe can not cope with making sculptured surface, whose requirement is considered to increase. The ultraprecision milling machine developed in the study consists of an air spindle with a milling tool and a three-axis feed mechanism on which a workpiece is mounted. As a milling tool, a pseudo ball-endmill is designed by slightly offsetting a conventional diamond tool having a nose radius. It is found that the ultraprecision milling machine can produce workpieces with curved surface in surface roughness of 78 nm Rmax.