Shunro Yoshioka

Surface Modification of Steel by a Small-Diameter Plasma Arc

A plasma arc, which is produced through a small diameter nozzle, is applied to surface modification of steel. The nozzle diameters are 0.2 and 0.3 mm; the arc diameter is so small that the power density is of the order of 106 W/cm2. This is applicable to small area surface modifications. In case of surface hardening due to self-quenching, Vickers hardness of 1000 is obtained for AISI 1045; melting does not occur. In case of alloying with SiC particles, Vickers hardness of 1200 is obtained for AISI 1010; furthermore, the wear resistivity is increased by a factor of several tens.

Thin-Plate Welding by a High-Power Density Small Diameter Plasma Arc

High-power-density plasma arc of 10 4 W/mm 2 (10 6 W/cm 2 ) is applied to welding of stainless steel plate of 0.1 and 0.3 mm in thickness. Practical conditions required for successful welding and welding capability of this new equipment are discussed. Welding capability does not depend on the working distance defined as the distance between exit of nozzle and workpiece surface. Furthermore, even though the plasma torch is deviated from the right position, appropriate welding can be successfully carried out because the workpiece is the anode in this process and thus all power is supplied to the workpiece.

Small diameter nozzle plasma arc as a processing tool

High‐power‐density plasma arc equipment with a small diameter nozzle of 0.1–0.3 mm has been developed, which produces power density of about 104 W/mm2 at the exit of the nozzle. The density is comparable to those produced by electron and laser beams. In the present article, development procedure, power density on the target surface, and processing capability in comparison to the conventional electron and laser beams are described. The power density as the processing heat source depends on the kind of processing. The apparent power density in cutting is of the order of 104 W/mm2; on the other hand, that in surface hardening is of the order of 102 W/mm2. The processing capability for causing melting such as cutting and welding does not depend on the working distance, which is defined as the distance between the torch and target material; furthermore, the deviation of the torch from the correct position does not affect the processing capability. The equipment developed is suitable for an automated production...

Forming characteristics of thin metal plate with diode laser beam

Diode laser beam of 20 W is applied to bend forming of thin metal plates. Bending characteristics are discussed on the basis of the experimental results for various bending conditions such as laser power, beam diameter, plate thickness, position of laser irradiation and so forth; furthermore, several kinds of metals are adopted as targets, i.e., AISI 304, iron, copper, molybdenum, nickel and aluminum. The bending angles strongly depend on the kind of materials; in particular, materials with low thermal conductivity bends with large angles. This seems to be caused by the high temperature rise due to low thermal diffusion. AISI 304 plates bend both away from and toward the beam under the same experimental conditions. The beam diameter has a strong effect on the bending direction; in case of forming of AISI 304 plate of 0.1 mm thickness, it bends away from the beam with higher possibility with larger diameter beam.Diode laser beam of 20 W is applied to bend forming of thin metal plates. Bending characteristics are discussed on the basis of the experimental results for various bending conditions such as laser power, beam diameter, plate thickness, position of laser irradiation and so forth; furthermore, several kinds of metals are adopted as targets, i.e., AISI 304, iron, copper, molybdenum, nickel and aluminum. The bending angles strongly depend on the kind of materials; in particular, materials with low thermal conductivity bends with large angles. This seems to be caused by the high temperature rise due to low thermal diffusion. AISI 304 plates bend both away from and toward the beam under the same experimental conditions. The beam diameter has a strong effect on the bending direction; in case of forming of AISI 304 plate of 0.1 mm thickness, it bends away from the beam with higher possibility with larger diameter beam.

Laser forming of thin foil by a newly developed sample holding method

A sample holding method is newly developed for laser forming, in which the target material is held between two transparent plates. During laser beam scanning on the target, the target foil is kept flat. After the scanning is finished, the foil is detached from the holder; the foil bends toward the beam scanned surface. Experiments are carried out with a Nd:yttrium–aluminum–garnet laser beam for a spot size of 25μm and for a traverse speed of 10 mm/s. A bending angle of about 30° is obtained for stainless steel (AISI 304) foil of 10 μm in thickness with a power of 0.3 W and a scanning repetition number of 20. On the other hand, if the laser beam is focused and scanned on the convex side along the ridge line of a curved foil, it bends toward the concave side and the bending angle increases. The increment angle of about 20° for a prebent angle of 45° is obtained for stainless steel foil 20 μm in thickness under the conditions of the power of 1.3 W and scanning repetition number of 10. If the sample is rotate...

Forming of thin plate with diode laser

Diode laser is applied to bend forming of thin stainless steel plate (AISI 304); the power is 10 W with the spot size of about 1 mm and the plate thickness is 0.1 mm. The bending characteristics depend on the conditions of the plate material, scanning speed of the beam, pre-bending and so forth. At low speed, there is possibility of bending both toward and away from the beam. The occurrence probability of bending away from the beam is about 0.1 to 0.3. As to a plate with pre-bending, the irradiation direction of the beam on the plate does not affect the bending direction; the plate always bends toward the same direction of the prebending even if the beam is supplied on the opposite surface. Furthermore, this is effective within some deviation distance from the ridge of the bent plane; the distance depends on the beam spot size. The characteristics are very useful for making complicated structure of thin plate; various shapes are formed and some of them are demonstrated.Diode laser is applied to bend forming of thin stainless steel plate (AISI 304); the power is 10 W with the spot size of about 1 mm and the plate thickness is 0.1 mm. The bending characteristics depend on the conditions of the plate material, scanning speed of the beam, pre-bending and so forth. At low speed, there is possibility of bending both toward and away from the beam. The occurrence probability of bending away from the beam is about 0.1 to 0.3. As to a plate with pre-bending, the irradiation direction of the beam on the plate does not affect the bending direction; the plate always bends toward the same direction of the prebending even if the beam is supplied on the opposite surface. Furthermore, this is effective within some deviation distance from the ridge of the bent plane; the distance depends on the beam spot size. The characteristics are very useful for making complicated structure of thin plate; various shapes are formed and some of them are demonstrated.

Removal Characteristics of Processing with SPM

Abstract SPM (Scanning Probe Microscope) can be used as a processing tool. In the present paper, processings are carried out with AFM and STM in air at room temperature. In case of AFM processing with silicon tips, no depression is formed in gold workpiece; however, it is formed in silicon workpiece, which seems to be caused by strong adhesion between the same materials. In case of STM processing with tungsten tips, although depressions are formed in the gold workpiece, the reproducibility is low with hand-made tips; however, field evaporation processing is carried out with high reproducibility.

Laser bending of thin metal plate: Effects of two beams and single line beam on bending characteristics based on buckling mode

Two diode laser beams are applied to laser forming of stainless steel of about 0.1 mm in thickness. Beam diameter is about 1 mm so that bending is due to buckling mechanism. In this mechanism, the bending direction is not fixed so that the target is bent toward or away the laser beam. In the present study, two spot beams or a line beam are used to control the bending direction for the buckling mode bending; the laser beams are focused into two spots on the surface of a target plate, or the laser beam is focused in a line shape on the target. The experimental results show that the bending direction can be controlled under some conditions even in the buckling mode bending of thin plates with large diameter beams.Two diode laser beams are applied to laser forming of stainless steel of about 0.1 mm in thickness. Beam diameter is about 1 mm so that bending is due to buckling mechanism. In this mechanism, the bending direction is not fixed so that the target is bent toward or away the laser beam. In the present study, two spot beams or a line beam are used to control the bending direction for the buckling mode bending; the laser beams are focused into two spots on the surface of a target plate, or the laser beam is focused in a line shape on the target. The experimental results show that the bending direction can be controlled under some conditions even in the buckling mode bending of thin plates with large diameter beams.

Monitoring of YAG laser spot welding-detection of porosity defect by acoustic signal-

Sound is generated during laser spot welding; this is useful for monitoring the welding operation. In the present experiments, the sound is detected by a microphone for inspecting the generation of porosity defect in YAG laser spot welding. Laser beam conditions are the energy of 2.0 J and pulse duration of 5 ms; the welding is done on plates of stainless steel of 1.0 mm in thickness by single pulse. The Short Time Fourier Transform (STFT) analysis is applied for obtaining the time dependence of the generated sound. Though great difference cannot be observed in the sound signals detected by the microphone, the clear difference can be observed by the STFT. The intensity of 11-15 kHz is lower in the welding with defect than in without defect. This is also confirmed in the welding by laser beams of 2 J, 4 ms, 2 J, 3 ms and 1.8 J, 3 ms. The result shows a possibility of detecting the welding defect by the sound analysis in the production systems.Sound is generated during laser spot welding; this is useful for monitoring the welding operation. In the present experiments, the sound is detected by a microphone for inspecting the generation of porosity defect in YAG laser spot welding. Laser beam conditions are the energy of 2.0 J and pulse duration of 5 ms; the welding is done on plates of stainless steel of 1.0 mm in thickness by single pulse. The Short Time Fourier Transform (STFT) analysis is applied for obtaining the time dependence of the generated sound. Though great difference cannot be observed in the sound signals detected by the microphone, the clear difference can be observed by the STFT. The intensity of 11-15 kHz is lower in the welding with defect than in without defect. This is also confirmed in the welding by laser beams of 2 J, 4 ms, 2 J, 3 ms and 1.8 J, 3 ms. The result shows a possibility of detecting the welding defect by the sound...

Monitoring of YAG laser spot welding

Sound is produced during laser spot welding. In the present experiments, the sound is detected by a microphone for monitoring YAG laser spot welding of stainless steel sheets of 0.3 and 1.0mm in thickness. Laser beam conditions are the energy of 2J and pulse duration of 5ms; the welding is done by a single pulse. To analyze the time dependence of the sound variation, the short-time fast Fourier transform analysis method (SFFTA) is adopted. The difference between the sounds in full penetration welding for thin sheet and in partial penetration welding for thick sheet is studied. Though great difference cannot be observed in the sounds detected by the microphone, the clear difference can be observed in SFFTA. The lap spot welding is successfully carried out for the gap less than 0.05mm; the results obtained by SFFTA are similar to the result for the bead on plate welding of a thick plate. On the other hand, the welding cannot be made in the gap greater than 0.1mm; the result obtained by SFFTA is similar to the result for the bead on plate welding of a thin sheet. The results show the possibility of monitoring the quality of the lap welding by sound analysis for production systems.Sound is produced during laser spot welding. In the present experiments, the sound is detected by a microphone for monitoring YAG laser spot welding of stainless steel sheets of 0.3 and 1.0mm in thickness. Laser beam conditions are the energy of 2J and pulse duration of 5ms; the welding is done by a single pulse. To analyze the time dependence of the sound variation, the short-time fast Fourier transform analysis method (SFFTA) is adopted. The difference between the sounds in full penetration welding for thin sheet and in partial penetration welding for thick sheet is studied. Though great difference cannot be observed in the sounds detected by the microphone, the clear difference can be observed in SFFTA. The lap spot welding is successfully carried out for the gap less than 0.05mm; the results obtained by SFFTA are similar to the result for the bead on plate welding of a thick plate. On the other hand, the welding cannot be made in the gap greater than 0.1mm; the result obtained by SFFTA is similar to t...