Papers by Author: Eiji Kondo

Abstract: For a cutting process using a low-rigidity end mill, it is very important to be able to estimate the machining error caused by the deflection of the tool. The purpose of this study is to establish a method for the real-time estimation of the machining error caused by the deflection of the tool at the cutting point of a ball-end mill. The method was verified by comparing the estimated deflection and the machining error when milling an inclined surface. It was concluded that the machining errors in ball-end milling of inclined surfaces can be estimated from the normal force at the moment when the radial direction of the peripheral cutting edge is normal to the feed direction of the tool.

Abstract: As titanium alloys have a high strength-to-weight ratio and superior corrosion resistance, they are widely used in the aerospace, biomedical, and automotive industries. However, these alloys exhibit very poor machinability, which results in problems such as short tool life. This study investigates the effect of the cutting atmosphere on tool wear during high-speed end milling of the titanium alloy Ti6Al4V. Dry cutting, cold air jet cutting, cutting fluid mist jet cutting, and cutting fluid flush cutting were considered in order to determine the optimum cutting atmosphere and conditions. For down-cutting speeds of 200−300 m/min, the cutting atmosphere and cutting speed were adopted as experimental parameters. Down-cutting was performed in order to measure the width of the tool flank wear land as the cutting length was increased. The results indicated that the optimum cutting method was cold air jet cutting. For a cutting length of 500 mm, this method produced a narrower flank wear land than dry cutting. In addition, for longer cutting lengths of up to 4000 mm, the wear rate for cold air jet cutting was less than or equal to that for dry cutting, and no chipping or excessive wear was observed.

Abstract: Large wear of diamond tools for ultra-precision cutting of soft metals deteriorates quality of machined surface, and the worn tools have to be replaced with new tools when the tool wear reaches limited wear land width of cutting edge generating finished surface. However, it is difficult to predict the tool life since all cutting tools have individual tool life. Therefore, the purpose of this study is to estimate wear land width of cutting edge of a single crystal diamond tool having large nose radius by using static cutting forces during machining. As a result of the cutting tests and measurements, it was found that the ratio of thrust force to principal force had good relation with the ratio of flank wear land area to cutting cross section area. Furthermore, according to some detailed observation of flank wear, width of flank wear land was greatly related to uncut chip thickness obtained under different cutting conditions and it was found that width of flank wear land could be estimated by measured static cutting forces and cutting conditions.

Abstract: For a cutting process using a low-rigidity end mill, it is very important to be able to estimate the degree of machining error caused by the deflection of the tool. The purpose of this study is to establish a method of estimating, in real time, the machining error caused by the deflection at the cutting point of an end mill. To this end, in this research, a method for estimating the machining error caused by the deflection of the tool used for the ball-end milling of a hemispherical surface was verified by comparing the estimated and measured deflections of the tool. As a result, it was found that the machining errors in ball-end milling could be estimated from the normal force at the moment when the radial direction of the peripheral cutting edge is normal to the feed direction of the tool.

Abstract: A lot of studies on the ultra-precision cutting of single crystal silicon have been reported and they used the single crystal diamond cutting tools having the sharp cutting edge. However, the diamond cutting tools having small chamfer at the cutting edge are usually used in practical machining shops. In addition, studies on the relationship between the tool wear and the machined surface have been reported little although the relationship is important in practical applications. In this study, ultra-precision cutting of single crystal silicon, using cutting fluids, feed rate, and depth of cut as experimental parameters, were carried out by using the single crystal diamond cutting tools having small chamfer and large nose radius, and effects of the cutting fluids, the feed rate, and the depth of cut on the machining accuracy and tool wear were studied. As a result, the optimum cutting conditions was obtained as follows: the cutting fluid was kerosene, the feed rate was 2.0μm/rev, and the depth of cut was 1.0μm.

Abstract: In order to investigate the effect of humidity on fatigue strength of an extruded and age-hardened Al alloy 7075-T6, rotating bending fatigue tests were carried out using plain specimens in environments of controlled relative humidity of 25%, 50%, 75% and 85% and distilled water. The cross section of the alloy has a marked texture of (111) plane. Although fatigue strength was decreased by high humidity, the decrease by high humidity was very small when the humidity was lower than about 60% -70% and fatigue strength was largely decreased over the humidity. Both of initiation and propagation of a crack were accelerated by high humidity. In high humidity, a crack propagated in a shear mode macroscopically and it was ductile in company with many glide planes and voids microscopically. That is, the propagation was not a tensile mode with brittle facets even in water. The shear mode propagation inclined about 35° to the extruded direction and fracture surface was (100) plane, meaning that the shear mode propagation of a crack was mainly caused by the marked texture of the alloy. The propagation mode of a crack was affected by not only environment but also stress level.

Abstract: This paper presents a system of 3-D micro structure measurement that uses an optical fiber probe of 5 µm in diameter. The probe is deflected when it comes into contact with a measured surface, and this deflection is measured optically. In this research, we optimize design parameters of optical system using ray tracing, and a prototype of the measuring system is fabricated on trial to verify the simulation results. Then, its measuring accuracies are examined by using the basic experimental apparatus. As a result, it is clarified that the resolution of the fiber probe is better than 10 nm. Also, the utility of this system is confirmed by measuring the shape of a 600 µm diameter ruby sphere.

Abstract: In the ultra-precision machining, the smaller the undeformed chip thickness is, the more the machined surface integrity is affected by the cutting edge roundness of the cutting tool. In this research, the work hardened surface layer was dealt with as an evaluation of the machined surface integrity and the effect of the mechanical factors on work hardening was investigated experimentally in orthogonal cutting. In the case of a rounded cutting edge, unlike a sharp one, it makes the generation mechanism of the work hardened surface layer complicated. In this research, the mechanical dominant factors were investigated by comparing the effect of the rounded cutting edge on the work hardened surface layer, which counts for much in ultra precision machining involved in small undeformed chip thickness, with that of the sharp cutting edge.

Abstract: In order to investigate the influence of grain size on notch sensitivities in fatigue of a fine-grained carbon steel, rotating bending fatigue tests were carried out using specimens with a V-grooved circumferential notch of commercial fine-grained carbon steel with grain size of 6.5µm. The results were compared with those of a larger grain sized carbon steel (grain size: 20 µm) and the notch sensitivities were evaluated based on Linear notch mechanics proposed by Nisitani. Notch sensitivities for both of fatigue limits for a crack initiation and its propagation of the fine grained steel were high. The results were discussed from the view points of the size of area related to crack initiation and the crack growth resistance.

Abstract: Rotating bending fatigue tests were carried out to investigate the effects of temperature on the fatigue strength and the fracture mechanism of an 18 % Ni maraging steel at room and elevated temperatures of 473K and 673K. Fatigue strength was higher at elevated temperatures than at room temperature, though static strength was decreased by softening at elevated temperature. There was no effect of temperature on crack morphology and fracture mechanism. On the other hand, during fatigue process at elevated temperature, the specimen was age-hardened and the specimen surface was oxide. That is, the increase in fatigue strength at elevated temperature was mainly caused by the increase in hardness due to age-hardening and suppression of a crack initiation due to surface oxidation.