Papers by Author: Masayuki Nunobiki

Abstract: This research proposes the application of laser forming to repair dents made in stainless steel sheets. Stainless steel sheets are widely used for the exterior coverings of trains or automobiles. When dents are made in an exterior sheet, it is necessary to detach the panel and strike the sheet from the inside with a hammer. This research indicates that dents were repaired by irradiating them from the outside with a laser beam. It is effective to repair dents without detaching the exterior sheet from the body of the vehicle. In the proposed method, a laser was scanned along the shape of the dent under the condition that the sheet bent by the temperature gradient mechanism or upsetting mechanism. In our experiments, circular dents were made in a 1-mm-thick SUS304 sheet. The laser was scanned along several circular scan lines on the circular dent with a diameter of approximately 20 mm. The depth of approximately 1.5 mm of the dent decreased by 85% using this technique.

Abstract: In this research, deformation behavior of titanium sheet in laser forming was simulated. In preliminary experiments, we had carried out single-straight-line bending and investigated the relationship between the bended angle and the laser processing conditions. It was clarified that the bended angle formed by laser forming to the free edge became larger than the angle formed by laser forming to the center, even if laser scanned in same processing conditions. To investigate the influence of the free edge, heat-transfer analysis and structural analysis were carried out by using a finite element analysis software ANSYS 11.0. It was confirmed that the bended at the free edge became large because the plastic strain of the lower surface has decreased greatly more than the strain of the upper surface decreases.

Abstract: The effects of cutting conditions on the surface roughness in a micro-end-milling process of a mold material are described in this paper. Micro-end-milling operations were performed under different cutting conditions such as feed rate and depth of cut, in order to investigate the factors that had the greatest influence on the finished surface during micro-end-milling. It was revealed that the surface roughness begins to deteriorate when the radial depth of the cut exceeds the tool radius. In addition, it was found that this phenomenon is peculiar to micro-end-milling processes.

Abstract: This study deals with the cutting characteristics of titanium materials when milled by a small-diameter end mill, or a micro end mill. It is well known that titanium is difficult to cut by conventional means. However, its cutting characteristics have not yet been made sufficiently clear in cases where a micro end mill less than 1 mm in diameter is used. This study chiefly involves the experimental investigation of tool wear and surface roughness of micro-end milling of Ti-6Al-4V. The findings were that tool wear did not increase much when the cutting speed was increased from 50 m/min to 200 m/min. Furthermore, the cutting force required to cut decreased at high speeds and during wet cutting. In wet cutting, the surface had a roughness (Rz) of only 0.3 μm at 200 m/min in contrast to 0.6 μm at 50 m/min.

Abstract: This paper deals with laser forming procedure to bend pure titanium sheets along arbitrary curved shape. In preliminary experiments, single straight-line bending was carried out and the relationship between bending angle and laser irradiation conditions was investigated. It was clarified that the bending angle was able to control with scanning velocity and the number of scanning passes. With use of obtained experimental formula for the bending angle, we tried to bend the Ti sheet along given parabola shape with a multi straight-line bending. The experimental result was corresponding to the target shape well. This paper proposed a laser forming procedure for curved shapes which include both convex curve and concave curves. It was confirmed that it was able to curve a titanium sheet along arbitrary curved surface with proposed method.

Abstract: This paper describes the cutting characteristics of lithium niobate, which is used for surface acoustic wave type micropumps, regarding the formation of micro grooves by direct cutting. Since lithium niobate is a brittle material with a strong crystal orientation dependency, significant differences were observed in the characteristics of the finished surface according to different directions of cutting. The ductile mode cutting of lithium niobate was found to be feasible with cutting depths of approx. 5 μm or less. Also, results of the study show the feasibility of the formation of minute grooves through the cutting of lithium niobate, using milling with an end mill.

Abstract: This paper proposed an on-machine laser deburring method for narrow slits made by laser cutting. Burrs are generally unwanted materials which remain at the cutting edge after machining operations, such as grinding, drilling, milling or turning. A cost necessary to remove burrs becomes a significant portion of the machining costs. In laser cutting, dross removal was significant problem. It is difficult to prevent completely dross from adhering in laser cutting for stainless sheets. In laser cutting for adornments, it is necessary to remove the dross and to chamfer the cutting edges in order not to injure the hand. It is difficult to remove the dross and to chamfer the edges of a narrow slit by machine work or handwork. We irradiated the defocused laser beam to the slits again for these post-processing. To control the depth and width of the removal area, we examined the relationship between the removal area and the deburring conditions. It was clarified that the width and depth of removal area can be controlled by irradiation time and energy fluence.

Abstract: When many products were cut out from a wide base sheet by laser cutting in some conditions, an error occurred in a height regulator by the sheet's greatly bending. It is necessary to avoid occurring the error at unmanned processing. We paper investigated local deformation around cutting edge. The cutting path consists of piercing point, terminal point, straight lines, cranks and curves. We measured local deformation around terminal point, crank and straight line. It was clarified that base sheet bent greatly around terminal points and crank and the sheet curved gradually along the straight line. We investigated relationship between global deformation of the base sheet and the local deformation. It was able to presume the entire deformation of base sheet by overlapping the individual deformations around cutting edge.

Abstract: This study deals with behaviour of bending deformation in CO2 laser forming process of titanium. CO2 laser forming technique was applied for a pure titanium plate with thickness of 1 mm to aim the development of new bending process. The experiments of laser forming were carried out with a CO2 laser machine. The bending angle and the temperature of workpiece were examined under the condition of various laser power, feed speed and laser spot diameter. Based on the experimental results, it was found that the bending deformation behaved greatly depending on the laser power and the laser spot diameter. The bending angle increased with an increase in the laser power. The bending direction tended to change from the laser irradiation side to its opposite side when the large laser spot diameter was applied.

Abstract: This study aims at clarifying the relationship between the surface integrity of PTFE finished by an ultra-precision diamond cutting and the adhesion strength of a metal thin film. As the first step of this study, the basic properties such as surface integrity in the diamond cutting of PTFE and the effect of the surface roughness on the textile water repellency are demonstrated in this report. The following remarks were found. The measured roughness of finished surface largely exceeded the theoretical roughness, while the cutting force was very small comparing with aluminum and the flow type chips were formed. The surface with a smaller roughness tended to repel water.