A simple material contact sensor on the forming tool was devised for sheet hydroforming. The applicability was investigated for the shallow forming of aluminum alloy sheet. A flat bottom axisymmetric ...die or a conical one was used. An antistatic electric tape was used as contact sensor. It is flexible and attached to the die cavity in the radial direction. Electrical resistance of the tape between the center and the contact position of the material changes as the forming progresses. The change in voltage of the resistance part corresponding to the contact length was captured continuously. The strain at the center of the circular test piece was also continuously measured using a strain gage for large deformation. A short contact length was captured for the flat bottom die, since the test piece deforms into a dome shape, and the tip of the dome contacts to the center of the die cavity. On the other hand, the captured length was longer in the forming with the conical die. The repetitive separation and contact motion of the test piece to the die in impact forming due to the impulsive water pressure was successfully captured by the contact sensor. The accuracy was relatively coarse due to that the diameter of the die cavity was small. However, it was found that the simple contact sensor can be applied to evaluate the deformation behavior of the material. The measured maximum strain of the test piece was larger in impact forming, and the strain concentration occurred. This may be due to the negative strain rate sensitivity of the material.
The drilling characteristics and availability of a diamond-coated carbide drill for drilling holes in ceramics were investigated and verified. An alumina and yttria-stabilized zirconia ceramics were ...used as workpiece materials. The drilling characteristics were evaluated based on the cutting-edge behavior, thrust force, integrity of the inner surface of the drilled hole, and chip morphologies. Alumina drilling had appropriate drilling conditions under which the diamond coating did not flake; under these conditions, extremely long tool life was obtained. Even when the diamond coating flaked off, the thrust force was reduced owing to the sharp cutting edges on the remaining coating ridgelines on the flank face. This flaking occurred around the corner edge region and expanded toward the thinning and chisel edge region with an increase in the number of holes drilled. In addition, the diamond flaking on the rake face occurred earlier when the feed rate of the drill was increased. In drilling alumina, the surface roughness of the inner surface deteriorated as the feed rate increased but improved as the diamond coating flaked off. Whereas in drill zirconia, a considerably better inner surface was obtained, regardless of the flaking of the diamond coating and drilling conditions. In both ceramics, thinning the diamond coating from 20 to 10 μm resulted in premature flaking of the coating. The drill life was reached when the flaking region reached the chisel edge from the corner side. The results of this investigation will assist with the drilling of holes in brittle ceramics using a diamond-coated carbide drill.
•Showed availability of diamond-coated carbide drill for drilling holes in ceramics.•Clarified self-sharpening mechanism due to coating flaking during drilling progress.•Studied coating flaking effect on cutting force, surface integrity, and drill life.•Showed clear difference in machinability depending on ceramics properties.•Revealed drilling conditions and coating thickness to achieve good drill life.
Several types of multiple straight convex shapes were formed on a thin aluminum sheet with a grooved die using impulsive water pressure. The maximum pressure was 160 MPa in the high-speed forming, ...wherein a drop hammer testing machine was used, whereas it was 100 MPa in the low-speed forming because of the limitations of the press machine. The effects of the forming speed, cross-sectional shape, and pitch of the grooves on the deformation behavior were investigated. The increase in the impulsive water pressure was found to be affected significantly by the compressibility of water. The symmetricity of the convex shape in the cross-section decreased at both ends for a smaller pitch because of the imbalance of the material flow at both peripheries of the groove. The concave surface profile of the pressure side was more rounded in the high-speed forming than that in the low-speed forming when semicircular and rectangular grooved dies were used. This may be attributed to the fact that the plastic deformation becomes more uniform owing to the positive strain rate sensitivity of the test material. In the forming with rectangular grooves, fracture occurred under the low- and high-speed conditions, wherein the maximum pressure was set to 100 MPa. However, the material did not fracture during high-speed forming with a pressure of 160 MPa, where the convex shape was higher and the material contacted the bottom of the groove. This behavior may be because the dislocation density of the material did not increase rapidly owing to the strain rate being maintained high until the material suddenly stopped deforming in the latter condition. In forming with a trapezoidal grooved die, the formed profiles were considerably similar under all conditions because the strain was considerably smaller than that with the other grooves.
The aim of this study is to show the effect of the strain-rate on the forming limit strain of an aluminum alloy A5052 sheet and a mild steel sheet SPCC. Biaxial stretching test was carried out. The ...prescribed strain path was linear path or that with directional change in straining. The sheet was pre-strained by uniaxial tension in the latter path. The deformation speed was set to be quasi-static or high speed whose strain-rate was about 300 /s using the dedicated high speed stretching device. The forming limit strain of the A5052 sheet for the linear strain path was larger in the high speed stretching than that under the quasi-static condition. For the case with strain path change the forming limit strain was further large. This may be due to the softening phenomenon which occurs by aging treatment, because the stretching experiment was conducted about two weeks after the pre-straining operation. On the other hand, the forming limit strain of the SPCC under the high speed condition was smaller than that under the quasi-static condition in the linear strain path. This is attributed to the decreased strain hardening exponent when the strain-rate increases. Further, in the equi-biaxial stretching of the pre-strained specimen, large difference of the forming limit strain between the deformation speeds was found. It is concluded that A5052 aluminum alloy sheet has a good adaptability to high speed forming, on the other hand, attention should be paid in increasing the forming speed of SPCC.
The drilling characteristics of alumina ceramics during through-hole drilling with a diamond-coated carbide drill were investigated experimentally. The drilling characteristics were evaluated by ...cutting edge behavior, cutting force (thrust force and torque), and chipping state at the exit side of the drilled hole in relation to the number of drilled holes. Additionally, the effects of the diamond-coating thickness and drill feed rate were investigated. The drills had a typical twist shape and were made of tungsten carbide base material with diamond coatings at 10 μm and 20 μm thick. The drilling machine was a standard machining center with a simple unidirectional drill feed without vibration. In through-hole drilling, as in blind-hole drilling, the coating on the rake face flaked during the initial stage of drilling, resulting in a sharp cutting edge on the diamond-coating ridge remaining on the flank face. However, flaking of the diamond coating on the rake face was observed earlier during through-hole drilling than in blind-hole drilling. Although the chipping area increased with increasing drill feed rate, coating flaking on the rake face significantly suppressed it at all feed rates. There was a clear correlation between the chipping area and cutting force since the chipping area decreased with decreasing thrust force. Before the theoretical hole penetration, hat-shaped chipping was observed with two crack propagation directions, accompanied by a sharp decrease in thrust force. Moreover, even after observing a sharp decrease in thrust force, a gradual decrease in thrust force was observed in the case of a good chipping state. The chipping area was significantly improved by reducing the coating thickness, and the thrust force was reduced.
The aim of this study is to experimentally determine the solid fraction at the cessation of the flow of a molten Al-Si-Mg alloy (JIS-AC4CH) ceases. In this study, an experimental apparatus to measure ...the melt temperature during flow was developed and was used to perform highly accurate temperature measurements. An immersion-type optical-fiber radiation thermometer without emissivity correction was used for the temperature measurement device in this apparatus. The solid fraction was calculated from the area of primary crystals when the molten metal at any temperature was quenched. The melt temperature at flow cessation was higher than the eutectic reaction temperature, and the solid fraction in the melt front was approximately 0.2. However, the maximum solid fraction was found at a position slightly away from the melt front toward the pouring gate, and was approximately 0.3. It was inferred for this Al-Si-Mg alloy, that the flow cessation mechanism was a mixture of skin formation and mushy formation types.
Joining of pure copper C1100 and aluminum alloy A6061-T6 plates of 5 mm thickness was investigated. The method was developed by one of the authors, in which the newly created surfaces of a pair of ...plates obtained by high-speed shear were immediately in contact with a sliding motion with a small overlap length. The total processing time was just about a few milliseconds. To create the new surface, high-speed shaving was also tested. The joining was not possible for the full thickness of the plates. A sharp notch was observed at the joint boundary due to a large shear droop in the copper. Shaving decreased the shear droop, and the joint length through the plate thickness became longer. The joining performance was evaluated by a uniaxial tensile test. The joint efficiency reached 100% using the specimen cut out from the really joined boundary. The affected zone of joining was confirmed by the hardness distribution near the boundary. It was about 30% of the thickness of the plate, which was much smaller than that in welding by heat, and no softened zone was found in both materials.
To explore the influence of the release agent on the fluidity of the aluminum alloy melt, continuous experiments were carried out. First, through a flat mold filling experiment, the aluminum alloy ...melt and temperature change of the flat mold were obtained via measurements under the condition in which the mold was coated with a powder mold release agent. Stable and minimal, the excellent thermal insulation performance of heat transfer coefficient. Then, fluidity measurement experiments and computer simulation were conducted to verify the influence of the density change of the powder mold release agent on the fluidity of the aluminum alloy melt during the casting process. It was found that this relationship was affected by the temperature difference between the mold and aluminum alloy melt. The experimental results showed that changes in the powder mold release agent density changed the distribution density of its components through the thickness of the coating, thereby affecting the fluidity and thermal insulation function.
This study investigated a method for accurately predicting the residual stress in die castings manufactured using aluminum alloy. To account for the mechanical properties caused by the material ...composition differences that occur in the thickness direction of the die castings, a model split in the thickness direction was used in the simulation model. Norton’s law was applied to the constitutive equation of the material, and the stress relaxation phenomenon was examined. The composition of Al-Si-Cu alloy (JIS-ADC12) die castings in the thickness direction were analyzed using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS), and differences in composition were confirmed. As a result of calculating the residual stress using the simulation, it was possible to calculate the residual stress that could not be reproduced by the simulation model of uniform composition. This suggested that the difference in mechanical properties of die castings in the micro-region influences the residual stress.
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