原田 泰典

<p>The improvement of fatigue life in inconel alloy by microshot peening was investigated. Shot peening is a widely used surface treatment method for improving fatigue life. This process imparts compressive residual stresses on the surface, thus improving the fatigue life of the machine parts. To reduce the surface roughness, the peening treatment with fine particles attracts attention. The size of the particle is very small and it is normal a one-tenth. In the peening process, the equipment were used an air-type machine. The microshot used were high-carbon cast steel and high hardness steel with an average diameter of 0.1 mm. The surface hardness data showed that work hardening extended deeper than the mean diameter of the media. In addition, when the workpiece was peened by high hardness steel powders, the surface hardness increased. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by microshot peening. The higher effect was found in the peening by using high hard steel powders, because a work-hardened layer was formed deeper in the material.</p>

<p>The formability of the laminated titanium sheet was investigated to control the ears in the deep drawn cup. Planar anisotropy causes ears to form in drawn cups. To control the occurrence of the ears, the deep drawing of the laminated sheet in consideration of anisotropy was carried out. In the experiment, the blank was pure titanium JIS1. The initial thickness and diameter of the sheet was 0.5 mm and 70 mm, respectively. The laminated sheet was constituted in two titanium sheets. Two sheets were located in the direction where varied in a rolling direction. Each sheet in stacked condition was not joined each other. Also please note that lubricant was not applied on the contact planes of sheets. In the deep drawing process, the laminated sheet was employed and a flat sheet blank was formed into a circle by a punch. A punch diameter is 40mm, and the drawing ratio is about 1.7. For the prevention of seizure in contact area between a drawing tool and titanium, titanium blank was treated by oxide coating. The clearance between the punch and die was set to be equal to the thickness of the laminated sheet. The lubricant used was the solid powders of molybdenum disulfide. The number of ears produced was four. The height of the ears decreased with increasing surface roughness. When it was located in the 45 degrees direction for a rolling direction, the ears of the drawn cup was controlled most.</p>

<p>Aiming to enhance functionality of titanium cup, the formability of titanium/mesh/titanium laminated sheet by deep drawing was investigated. In the experiment, the materials were pure titanium and stainless steel mesh. The laminated sheet was constituted by interposing mesh between two titanium sheets. Each sheet in stacked condition was not joined each other. In the deep drawing process, the laminated sheet was employed and a flat sheet blank was formed into a circle by a punch. The deep drawing was carried out to investigate the formability. The laminated sheet was successfully drawn without the cracks.</p>

<p>The fatigue improvement of titanium alloy by microshot peening and ultrasonic peening was investigated. In the peening process, the equipment were used an air-type machine and ultrasonic peening machine. The microshot used were high-carbon cast steel with an average diameter of 0.1mm. The surface hardness data showed that, in the case of microshot peening, work hardening extended deeper than the mean diameter of the media. In addition, in the case of ultrasonic peening, the surface hardness increased slowly with the projection time. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by both treatments.</p>

<p>Cladding is the bonding together of dissimilar metals. One of clad products is the titanium clad steel sheet. It is effective to cover with pure titanium sheet to improve the corrosion resistance of the steel sheet. Titanium clad steel sheets are often achieved by rolling sheets together under high pressure. In the current study, the formability of pure titanium clad sheet by multistage deep drawing was investigated to enhance corrosion resistance of steel cup. In the experiment, the materials were pure titanium sheets TP270, ultralow-carbon steel SPCC, and stainless steel SUS316L. The initial thickness of the sheet was 0.2 to 0.5 mm in thickness. A total plate thickness of the blank was 1.0 mm. In the deep drawing process, the blank was employed and a flat sheet blank was formed into a circle by a punch. Various cups were drawn by exchanging the punch and die. The die was a conical shape without a blankholder in the subsequent stages. For the prevention, pure titanium blank was treated by oxide coating. By oxide coating, the titanium sheet has sufficient ability in preventing the seizure in multistage deep drawing. It was found that the titanium clad cups were successfully drawn.</p>

<p>Magnesium alloys are widely used in the automotive and aircraft fields. They have excellent physical and mechanical properties, such as low density and high strength-to-weight ratio. However, their poor corrosion resistance has been the main impediment in their applications. Surface modification is the main methods to control the degradation rate of magnesium alloys. This problem has been studied by many researchers. The authors have proposed a lining process of metals with thin aluminium foils using shot peening. In this method, the foil can be bonded to the workpiece surface bringing about large plastic deformation. The pressure generated by the hit of many shots is utilized for the bonding. In the present study, to improve the surface characteristics of magnesium alloy, the formation of an Fe-Al intermetallic compound film on magnesium alloy by compound treatment combining shot lining method and heat treatment was investigated. Shot peening was performed with a centrifugal-type machine using cast steel ball. The lined sheet is aluminum foil with pure iron powders, and the workpiece was the commercial magnesium alloy AZ31. The lining experiment was performed at 573 K in air. The lined workpieces are heat treated by laser in air. The Vickers hardness test was performed with a microhardness tester. It was confirmed that the present method could be used for the formation of functional films on magnesium alloy.</p>

<p>The effect of microshot peening on the surface hardness and fatigue strength of titanium alloy was investigated. Shot peening is a widely used surface treatment method for improving fatigue life. This process imparts compressive residual stresses on the surface, thus improving the fatigue life of the machine parts. In the peening process, the equipment were used an air-type machine and ultrasonic peening machine. The microshot used were high-carbon cast steel with an average diameter of 0.1mm. The surface hardness data showed that, in the case of microshot peening, work hardening extended deeper than the mean diameter of the media. In addition, in the case of ultrasonic peening, the surface hardness increased slowly with the projection time. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by both treatments. The higher effect was found in the ultrasonic peening treatment, because a work-hardened layer was formed deeper in the material.</p>

<p>The effects of projection conditions on the surface hardness and fatigue strength of stainless steel was investigated. In the peening process, the equipment were used an air-type machine and ultrasonic peening machine. The microshot media used were high-carbon cast with an average diameter of 0.1mm. The surface hardness data showed that, in the case of microshot peening, work hardening extended deeper than the mean diameter of the media. In addition, in the case of ultrasonic peening, the surface hardness increased slowly with the projection time. The rotary bending fatigue tests were carried at a frequency of 3150 cycles/min. Improvement of the fatigue strength was observed by both treatments. The higher effect was found in the ultrasonic peening treatment, because a work-hardened layer was formed deeper in the material.</p>

<p>In press forming, pure titanium sheet has sufficient ductility. However, the seizure tends to occur during the deep drawing due to high reactivity with die materials. The authors reported that the heat oxided sheets were treated by oxide coating so as to get oxide surface layer effective for preventing the seizing. In the current study, the square titanium cups were formed by multistage deep drawing using oxided titanium sheets for preventing seizing. The sheets were employed and a flat sheet blank is formed into a square by a punch. Various cups were drawn by exchanging the punch and die. The die was a funnel shape without a blankholder in the subsequent stages. The effects of the oxide layer and die shape on the occurrence of seizure in multistage deep drawing were examined. The square cups were successfully drawn by oxide coating. As the number of drawn cups increases, the thickness strain increases at the corner of cups. However, the seizure did not cause even for cups of the 12th stage. It was found that the oxide titanium sheets have sufficient ability in preventing the seizure in multistage deep drawing processes.</p>

<p>In press forming, pure titanium sheet has sufficient ductility. However, the seizure tends to occur during the deep drawing due to high reactivity with die materials. In the current study, by using the resin composite die, the titanium cups were formed by deep drawing for preventing seizing. In the experiment, the material was pure titanium sheet TP340. The initial thickness of the sheet was 0.5 mm in thickness. The sheets were employed and a flat sheet blank is formed into a cylindrical by a punch. The effect of the die shape on the deep drawability was examined. The cups were successfully drawn by the resin composite die. Even if the number of drawn cups increased, the thickness strain hardly changed. The seizure did not cause in the case of 100 times of processing number of times. It was found that the resin composite die has sufficient ability in preventing the seizure in deep drawing processes.</p>