Yukio Kasuga

An application of ultrasonic vibration to the deep drawing process

Abstract An experimental apparatus with the blank-holder or die plate vibrated in a radial mode was constructed in order to make the apparatus compact. The application of 20 and 28 kHz oscillation increases the LDR from 2.68 to 3.01, from 2.58 to 2.94 and from 2.38 to 2.77 respectively, in the case of cold rolled steel for deep drawing, cold rolled steel and 304 stainless steel. greater accuracy and deeper cups can be formed by stopping the oscillation after the maximum punch load rather than applying the oscillation throughout the deep drawing process. The radial vibration induces the axial vibration in the blank-holder or die plate and the axial vibration contributes strongly to the rise in the limiting drawing ratio (LDR) rather than the radial one. When one of the blank-holder and die plates is vibrated, the vibration in anti-phase is induced in the other. This means that both the blank-holder and the die plate should be simultaneously vibrated in anti-phase. Seasoning cracks of drawn cups can be avoided when the vibration is applied to the deep drawing process of 304 stainless steel sheets.

Effects of Sintering Conditions on the Mechanical Properties of Alumina Particle Dispersed Magnesium SPS Compacts

To enhance the mechanical properties of Mg alloys, 0-30vol% Al2O3/Mg powders were formed by ball milling powder mixtures of pure Mg and Al2O3 particles, and then Spark plasma sintering (SPS) compacts (Al2O3/Mg discs) were made by the Al2O3/Mg powders. The effect of the cooling conditions in the SPS process on the mechanical properties of the Al2O3/Mg discs was investigated. From the results of SEM, XRD and TEM-EDS, the microstructures of the Al2O3/Mg discs were identified to consist of α-Mg solid solution, Al2O3 particles, refined MgO particles and refined needle-like Mg17Al12 ( more than 20vol% Al2O3 content). The mechanical properties of the discs were able to control by the regulation of the cooling conditions (cooling rate (vc) and applied pressure in the cooling (pc)) in SPS process, and as a result, the SPS discs possessing the mechanical properties beyond HP compacts were obtained under the cooling conditions of “vc= 0.83K/sand pc = 20MPa”. Main factor that the cooling conditions in SPS process effect on the mechanical properties of the Al2O3/Mg discs are considered to be the compresive residual stress generated in the α - Mg solid solution by the thermal stress associated with deference of the coefficients of thermal expansion between the α - Mg and ceramics particles (Al2O3 and MgO) in the discs.

Effect of cutting conditions on press cutting of a square pipe

Abstract In press cutting of a square pipe, effects of cutting parameters such as the top angle of the punch, wall thickness, side length and material of the pipe on the distortion of the cross-section and surface decline of the cut end to the axis are discussed. Cutting force is also measured and discussed. When cutting with the top angle 60°, the first indentation into the top corner makes the material apart. And the surface at the side corners are rough, while this does not occur for the other angles. In the case of 90°, the shearing force becomes largest in the latter half of the cutting process. For 180°, the distortion of the cross-section is the largest. The measured and observed results show that the better top angle may be 120°. Surface decline of the cut end, which expresses the perpendicularity to the axis, becomes larger, as the wall thickness is increased with the ratio of the tool clearance to the wall thickness unchanged. In estimating the cutting force, the model when calculating the shear force in sheet shearing with a shear-angled punch is used. The estimated formula is also available in cutting the square pipe.

Change in shape of a cold formed and annealed stainless steel sheet and joining with use of this change

Abstract An austenitic stainless steel sheet with thickness 1.0 mm is V-bent, U-O press formed and roll-formed. Metastable austenitic stainless steel is partly transformed into martensite when cold formed and is reversed in annealing, followed by a volume change. Taking this into consideration, V-bend angle and outer diameter are measured before and after annealing of the V-channel and the pipe obtained. By evaluating the change, effects of the punch radius, reduction in outer diameter, stability of austenite, rolling direction and annealing temperature on the opening of the channel and the swelling of the pipe are made clear. For comparison a uniaxial tensile test is also performed and the volume fraction of martensite is measured. Maximum change in V-bend angle for 301 stainless steel is 5° when the punch radius is 10 mm and the V-channel is annealed at 1023K. For 301 stainless steel, 50% of the material is transformed into martensite and 80% of the transformed martensite is reversed at 1023K. Also for the roll-formed or U-O formed pipe, outer diameter of the pipe is changed by some 0.2%. Taking advantage of this change, the pipe can be joined with the carbon steel pipe and the obtained joining strength is about 25 MPa.

Characterization of deformation-induced metallurgical change in austenite stainless steel sheet with acoustic microscopy

This article reports on the non-destructive evaluation (NDE) of metallurgical changes induced by the deformation processes. In particular, the martensite and reversed austenite states of a meta-stable austenitic stainless steel sheet were evaluated. The sheet was elongated up to 40% at room temperature, and was then brought below room temperature to produce martensite. This was then followed by annealing for reversion. First, martensite content was measured with a Feritscope. Second, the surface acoustic wave (SAW) velocity was measured with a high numerical aperture spherically focused ultrasonic beam with a frequency equal to 600 MHz. The measured SAW velocity values were found to be dependent on the elongation, the ambient temperature during elongation, and the annealing temperature. A useful trend was found in the correlation between the measured SAW velocity and the martensite content as measured with the Feritscope. Second, using a high frequency (i.e., 800 MHz) acoustic imaging technique, the deformed and annealed grain structures were mapped. In comparing the acoustic images with the optical images, the deformed grains shown in the acoustic images were found to be significantly clearer than those shown in the optical images. These studies reveal the importance of NDE, in connection with the forming of stainless steel structures, to map the deformation induced metallurgical changes. Here, unique NDE techniques are seen to be effective in mapping the changes with the use of hypersonic SAW velocity measurements and imaging.

Fabrication Of Double Wall Tube By U‐O Press Forming And Pulsed Gas Tungsten Arc‐welding

Double walled tubes were trially fabricated by press‐forming and arc‐welding, as difficulty in fabrication was anticipated in the case of roll‐forming. U‐O press‐formed double walled sheets are TIG arc‐ welded. For determination of welding conditions, overlapped flat sheets were employed and butt‐welded including pulsed arc‐welding. Pulse from 1 to 100Hz is effective to obtain penetrated weld bead. With this, the double walled tube could be arc‐welded, which could not be achieved by conventional TIG arc‐welding.

Joining of Polycarbonate Ring/Disk to Metal Sheet/Shaft and its Easy Disassembly

For the possibility of easy disassembly of a joint assisted by strain recovery, the joint is fabricated with a cold rolled circular polycarbonate (PC) disk embedded in the center of an aluminium or a PC disk. Also, a shaft and a hollow circular disk are assembled by compressing or press fitting a cold rolled PC ring into the gap between them. First, the cold rolled polycarbonate disk is heat treated and the change in geometry is examined. Secondly, in order to evaluate joint strength, shear force and torque of the assembled joints are discussed with regard to reduction in thickness, tool clearance and interference. Lastly, joints are heat treated and the disassembly is checked. The cold rolled disk is recovered with the temperature 190°C for 20min. In embedding, disk compression in addition to rolling reduction is effective in increasing joint strength. In fabricating the shaft/disk joint, deformation of polycarbonate was not effective due to the recovery in room temperature after joining, while press fitting of the polycarbonate ring could fabricate the assembly. Heat treatment helped the joint to be automatically disassembled. The directly joined parts became completely apart, but the shaft/disk joint was disassembled only between the ring and the disk.

Finite Element Analysis of V-Bending of Polypropylene Using Hydrostatic-Pressure-Dependent Plastic Constitutive Equation *

Finite element analysis of V-bending process of polypropylene was performed using hydrostatic-dependent elastic-plastic constitutive equations proposed by the present authors. Kinematic and isotropic hardening rule was employed for the plastic constitutive equations. The kinematic hardening rule was more suitable for the expression of the stress reversal in uniaxial stress - strain relation than the isotropic hardening. For the result of the finite element analysis of V-bending, the kinematic hardening rule was able to predict the experimental behavior of springback more properly than the isotropic hardening. Moreover, the effects of hydrostatic pressure-dependence were revealed by examining the calculated distribution of bending plastic strain, bending stress and the width of the bent specimen.

Evaluation of Deformation-Induced Transformation and Reversion Processes of Stainless Steel With Scanning Acoustic Microscopy

An objective of this article is to evaluate deformation-induced martensite and reversed austenite of a metastable austenitic stainless steel sheet with scanning acoustic microscopy. The sheet was elongated up to 40% at and below the room temperature to produce martensite, followed by annealing for reversion. First, martensite content was measured by a Feritscope. Second, using a complex V(z) curve technique with a spherically focused ultrasonic beam of frequency at 600MHz, surface acoustic wave (SAW) velocity of a specimen was measured. We found that the measured SAW velocity was dependent on the elongation, ambient temperature in elongation, and the annealing temperature. There was a trend in the correlation between the measured SAW and the content measured by the Feritscope. The measured value of the SAW velocity was compared with the theoretical one which was calculated by Young’s modulus, Poisson’s ratio, and the density of the material. The measured SAW velocity agreed well with the theoretical one. Third, using high frequency (i.e., 800MHz) acoustic imaging technique, the deformed and annealed grain structures were observed. Furthermore, the acoustic images were compared with the optical images. We found that deformed grains shown in the acoustic images were clearer than those shown in the optical images.© 2003 ASME

Evaluation of deformation-induced transformation and reversion processes of stainless steel by acoustic microscope

Deformation-induced martensite and reversed austenite of a metastable austenitic stainless steel sheet were evaluated by a scanning acoustic microscope with frequencies 600MHz and 800 MHz. The sheet was elongated up to 40 percent at and below the room temperature to produce martensite, followed by annealing for reversion. First martensite content was measured by a Feritscope. Next using a complex V(z) curve, leaky Rayleigh wave velocity was measured. The deformed and annealed grain structure s were observed with the frequency 800MHz and compared with those by the optical microscope. Rayleigh wave velocity is dependent on the elongation and ambient temperature in elongation and the annealing temperature, which agrees well with the one by the Feritscope. Deformed grains are more clearly observed by the scanning acoustic microscope with 800MHz. The measured value of the velocity is compared with the theoretical one which can be calculated by Youngs modulus, Poissons ratio and the density. The measured Rayleigh wave velocity is well agreement with the theoretical one.