Papers by Author: Hiroyuki Sasahara

Abstract: The objective of this paper is to clarify the effect of grinding surface characteristics in the grinding of a titanium alloy with a coolant supply from the inner side of the grinding wheel. In this paper, we selected a white aluminum oxide (WA) vitrified bonded grinding wheel and a green silicon carbide (GC) vitrified bonded grinding wheel, and compared their grinding characteristics. As a result, in the case of the GC vitrified bonded grinding wheel, the surface roughness decreased by about 54% and the compressive residual stress increased by about 128%.

Abstract: The objective of this paper is to clarify the effect of the difference of grinding fluid supply method on grinding surface characteristics during the curved surface machining of titanium alloy. The convex and concave type workpieces were machined by internal coolant supply and external coolant supply, and the surface characteristics were compared. The internal coolant supply could supply the grinding fluid directly to the machining point through the grinding wheel pores. One nozzle or seven nozzles were used for external coolant supply. As a result, the surface roughness of the concave surface decreased by about 10 % compared with the one nozzle was used when the grinding fluid was supplied from the inner side of the grinding wheel. In the case of the convex surface, the surface roughness decreased about 20 % compared with the single nozzle was used, and it decreased about 9 % compared with the seven nozzles were used.

Abstract: To predict accurate cutting forces and residual stresses while machining products or to design optimum machining conditions like friction stir welding (FSW), FEM analyses are effective because they can reduce the cost of product design and improve product qualities. In order to conduct these FEM analyses precisely, it is necessary to determine accurate flow stresses of workpieces used for the constitutive equations of analyses that generally have a wide range of temperatures and strain rates. Correct identification of flow stress can lead to better analysis results close to actual phenomenon. In this study, focusing on 6061-T6 aluminum alloy used for objects such as civil engineering structures and railway vehicle bodies, we investigated the properties for machining the material. For this, we carried out an inverse analysis to understand the flow stress of 6061-T6 machined at high-strain rates and high temperatures. Then, we used this identified flow stress in the constitutive equation of FEM models, and inspected the accuracy of material properties conducting verification experiments and analyses to check the cutting forces and chip temperature while machining. As a result, we obtained good correlations between verification experiments and an analysis, which means the identified flow stress can be used for precise FEM analyses when machining materials.

Abstract: Grinding is a machining technology for plane surfaces and cylindrical surfaces in general. In comparison with cutting, higher accuracy can be provided and it is easier to manufacture high-hardness materials using grinding. However, the grinding wheel surface state changes during grinding, and grazing, clogging and shedding may then lead to problems. As these problems degrade the accuracy and productivity of grinding and the surface integrity of the work material, it is important to select an appropriate grinding condition to avoid the problems. In this study, a novel in-process system for monitoring the grinding wheel surface temperature and grinding state in real time, was proposed. A thermocouple is embedded in the grinding wheel in the developed system. The measured temperature data are transmitted to the external terminal equipment by a wireless transmitter built into the tool shank. Grinding wheel surface temperature was measured on four kinds of grinding wheels using the developed system. As a result, the grinding wheel surface temperature was measured successfully. In addition, it was clarified that the temperature transition largely depends on the grinding state.

Abstract: In grinding, the moving trajectories of abrasive grains are almost straight to the motion of the rotation and feed of the grinding wheel, so that grinding marks are formed continuously. As a result, surface roughness is dependent on grain size and organization of the grinding wheel. If the trajectory of the abrasive grain is wavy, the peak lines of the grinding marks will be partially removed by following the abrasive grain. This improves surface roughness. The objective of this study is to develop a mechanism to give axial vibration to the grinding wheel by the pulsation of the plunger pump, and thus to improve the surface roughness of the machined surface.

Abstract: Direct metal lamination using arc discharge was applied to the repair of metal components such as metallic parts, dies and molds by adding equivalent metal to them. In this method, a heat-affected zone which has different mechanical properties from the base metal is formed near the laminated metal. This is because the rapid temperature change by welding heat input can cause phase transformation or metallic structure change. Therefore, the mechanical properties of the laminated metal, heat-affected zone and base metal after repair by direct metal lamination need to be explored. In addition, the region which needs to be repaired must be removed in advance because worn and defective parts aren’t adequate as the base for lamination of further layers. Thus, the most suitable removal shape for repair by direct metal lamination was investigated. Finally, the hardness distribution and toughness of the metal components after repair was explored. It was found that the hardness distribution of metal components after repair was uneven. However, the toughness of the heat-affected zone was found to be comparable to those of the laminated metal and the base metal.

Abstract: In this paper, driven rotary cutting of maraging steel was carried out and the influence on tool wear of difference cutting conditions was investigated. As cutting conditions, different coolant conditions, cutting speeds, circumferential velocity ratios, tool inclination angles, tool rotation directions and normal rake angles were tested. We found that as the coolant quantity decreased and cutting speed increased, the width of flank wear increased. It was also found that the circumferential velocity ratio, tool inclination angle, tool rotation direction and normal rake angle have optimal conditions that decrease wear. Optimal conditions were chosen, and a tool life test was carried out. As a result, driven rotary cutting was achieved with 11 or more times the tool life of conventional turning.

Abstract: Nowadays, numerical simulation technique is used to predict machining states such as cutting forces, stresses and temperature distribution. However, it is difficult to simultaneously estimate the stress-strain relationship of the workpiece and friction characteristics between tool-chips during cutting process. The aim of this study is to propose a new method to identify friction characteristics and flow stress of 0.45% carbon steel for FEM simulation during cutting process. Shear friction equation had been applied to estimate the friction characteristics and the Johnson-Cook (JC) constitutive equation work flow stress model was considered as a function of strain, strain rate and temperature to determine characteristics of workpiece flow stress. As a result, friction characteristics and flow stress of 0.45% carbon steel during cutting process had been estimated applying this proposed method.

Abstract: Generally, grinding fluid is supplied from a nozzle to a grinding point. However, it is difficult to supply sufficient coolant to the deep grinding point of a hole. Therefore, we have proposed an alternative coolant system that supplies grinding fluid from the inner side of the grinding wheel utilizing the spindle through the supply system of the machining center. In this study, a new tool for small and deep holes was developed to supply grinding fluid in this way. The inside of a 0.45%C steel cylinder was then machined under various grinding conditions. Higher form accuracy and surface roughness were obtained under all conditions by supplying grinding coolant from the inner side of the grinding wheel. In addition, the system prevented tears on the machined surface and loading on the grinding wheel.

Abstract: We explored the effect of supplying coolant from the inner side of a grinding wheel on the residual stress caused by grinding. Effect of depth of cut on grinding temperature and residual stress was also studied. Results clarified that grinding with an internal coolant supply induced a larger compressive residual stress compared to a conventional external grinding fluid supply when depth of cut was large. In addition, grinding temperature in the internal grinding fluid supply was lower than in the external grinding fluid supply, as measured by infrared thermograph camera. Findings suggested that large compressive residual stress was obtained in the case of the coolant supplied from the inner side of the grinding wheel because temperature was lower than external coolant supply.