森田 昇

The aim of the present study is to understand material removal mechanism in nanometer scale by carrying out single grain scratching experiments using AFM mechanism. A microcantilever for the scratching tool have been developed by anisotropic etching of single crystal silicon, and the scratching experiments were performed with the cantilever mounted on a commercial AFM system. As a result, it was confirmed that the newly developed cantilever tool could machine an obvious scratch.

In this study, which is aimed at understanding machining characteristics and tribological phenomena in vacuum, a machining system in a vacuum chamber which pressure is 6.0×10^<-5> Pa, is developed and diamond cutting experiments using aluminum workpieces are carried out. The cutting system is a face turning composed of a high speed spindle with a magnetic bearing, that revolves at 22000rpm in vacuum, and a diamond tool with rake angle 0 deg and flank angle 5 deg. Cutting behaviors in vacuum are similar to those in argon gases, and also those in air and oxygen are in a similar way. For instance, the cutting force in vacuum and in argon gases is larger than that in air and oxygen, and phenomena like a built-up edge generate in air and oxygen, but that is not observed in vacuum and argon gases. The similarity depends on the pressure or absence of oxygen. It is found that those results depend on the pressure or absence of oxygen.

This paper describes the influence of tool angles, especially rake angles, on the surface integrity of mirror cutting material. In this study, strain distribution in damaged layer is measured by a newly developed method. This method is applied electron beam lithography to drawing Au micro grids on the surface of oxygen free copper. Orthogonal cutting of specimen using various rake angle tools are carried out using a micro cutting device. It was found that strain distribution had close connection with tool geometry, and that highly compressed strain to vertical direction from machined surface was shown on the condition of negative rake angle tool. This method is effective to visualize cutting mechanism and material deformation at microscopic structure.

Defocusing of a laser beam is one of the most important factors to control the feature of drilling holes in ceramic materials. This suggests that laser beam energy is delivered and focused on the bottom of the drilling hole by multi-reflection from the internal wall surface of the hole. The deep hole drilling process of silicon nitride ceramics was simulated by a newly developed analysis model. The ray tracing method for a laser power intensity distribution analysis and difference method for thermal analysis were combined. The drilling hole is processed mainly by energy reflected from the internal wall surface of the hole. In this process laser beam intensity becomes higher in the center of the hole since the laser beam is focused by the wall-reflecting effect. The defocusing position from the material surface has direct effects upon the drilling process, which depends on the reflection angle of a laser beam at the internal wall surface of the hole. The reflection angle controls the wall-focusing effect and determines the hole shape.

This paper describes a mechanism of deep hole drilling of covalent bond-ceramics using a pulsed YAG laser. The deep hole drilling process was simulated by the newly developed analysis method. It was combined the ray tracing method for a laser power intensity distribution analysis and difference method for a thermal analysis. It assumed that laser beam energy was delivered by reflection from the internal wall surface of a hole in the ray tracing model. Sublimation process of silicon nitride was considered during the thermal analysis. The deep drilling hole was processed mainly by energy reflected from the internal wall surface of the hole. In this process laser power intensity became higher in the center of the hole since the laser beam was focused by the wall-reflecting effect.

The laser-induced thermal shock test and thermal stress analysis by a finite element method were carried out for explaining the generation and propagation behavior of thermal cracks in ceramics such as silicon nitride, alumina and zirconia caused by high-power-laser irradiation. Different features of crack propagation were observed depending on the ceramic species, probably depending on their thermal properties. Maximum tensile stress in every axis direction was observed at certain locations, where the stress intensity factor was also largest. It was found that cracks might generate right under the center of a heat source circle and at the outside of the circle, and might propagate from right under surface towards the radial direction. The initial point of cracks seems to be grain boundary phases which soften at high temperatures.

This study analyzes the effect of temperature and load rate on brittle-ductile transition (B-D- T). The purpose is to control grinding conditions on the basis of an understanding of the micro mechanism of B-D-T. In the study, both indentation and scratching experiments were carried out under various temperatures. The specimen is heated by CO2laser beam up to 750°C. The relationships among crack length, temperature and load rate are discussed. The load rate is larger under conditions of low temperature, high speed and heavy load. Larger load rate will cause occurrence of brittle fracture. As a result, it is clarified that B-D-T is affected directly by a specimen&#039;s temperature and load rate in addition to the critical depth of cut. © 1992, The Japan Society of Mechanical Engineers. All rights reserved.

This paper describes the dynamic behavior of laser-produced ionizing vapor in laser-processing the covalent bond-ceramics. The distribution of laser-ionized vapor is determined by the measurements of electrical potential using newly developed small pin-type electric probes. The desity of ionized vapor is highest around a laser beam axis above the workpiece. The distribution and motion of ionized vapor is successfully controlled under the external electric field.

To achieve a damage-free grinding surface of brittle materials, the characteristics of brittle-ductile transition must be realized and the surface texture of the grinding wheel must be adequately controlled. In the study, a grinding wheel is truncated by grinding cast iron after dressing. The peak-valley value of the cross-sectional profile of the truncated wheel is much better than the dressed one. Moreover, after analyzing the surface texture results from various experiments, it is found that the statistic mean value of the critical depth of cut dcis approximately 40 nm by the truncated wheel with up cut grinding. The percentage of fracture surface is decreased with the decrease in the depth of cut in each case. The data points on the skewnesskurtosis plot of ductile mode grinding surface are relatively concentrated compared to the fracture mode surface. © 1992, The Japan Society of Mechanical Engineers. All rights reserved.

This paper describes the effect of crack-free laser processing of hot-pressed silicon nitride ceramics on fracture strength and residual stress. The fracture strength of the processed test pieces was determined by three-point bending tests. The residual stress in the processed surface was characterized by X-ray diffraction measurement. The strength of the laser-processed workpieces was reduced to 90-80% compared with that of the ground workpieces because of subsurface layer damage, which included the heat-affected layer and the residual stress layer. In particular, the latter greatly affected the fracture strength because the higher compressive residual stress layer generated during grinding was released by laser processing. It is concluded that the newly developed crack-free processing technique has great industrial possibilities.

This paper describes the fracture mechanism and the prevention of crack propagation in laser-processing of the hot-pressed silicon nitride ceramics using the pulsed YAG laser. The crack formation mechanism is successfully explained by the thermal stress and fracture strength distribution. The laser pulses controlled at below the critical duration and frequency are effective for the purpose of crack-free processing because the thermal stress is localized only in the laser-heated shallow region. © 1992, The Japan Society for Precision Engineering. All rights reserved.

This paper describes the effects of laser heating on the electroless plating process. In the experiment, a focused YAG laser beam and a copper electroless plating solution were used. In the analysis, the temperature distribution was calculated by the solution of the heat conduction equation. In the first stage on the laser-induced plating, the rapid heating effect induces the nucleation reaction. In the second stage, the partially heating effect enhances the reduction reaction based on the micro-convection, which depends on the sharp temperature profile.

Aluminum nitride (AIN) ceramics decomposes into aluminum vapor and nitrogen gas at about 2790 K. Peculiarly, The aluminum metallic phase is formed in laser processing of AIN ceramics. This is probably caused by the existence of high [ressure Aluminum vapor at high temperature. This paper describes the vapor pressure measurement for the purpose of explanation of the metallic phase formation mechanisms.

This paper describes the effect of crack-free laser processing of hot-pressed silicon nitride ceramics on the fracture strength and residual stress. The fracture strength was determined by three-point bending tests. The residual stress in the processed surface was characterized by X-ray diffraction measurement. The strength of the laser-processed test pieces is reduced to 90-80% compared with that of the ground test pieces because of surface layer damages, which are the recast layer and the residual stress layer. In particular, the latter greatly affects the fracture strength because the higher compressive residual stress layer generated during grinding is removed by laser machining. © 1991, The Japan Society of Mechanical Engineers. All rights reserved.

This paper describes the dynamic behavior of the vapor pressure and plasma potential to investigate the metallic phase formation mechanism in laser-processing of the covalent bond-ceramics. The vapor pressure was measured with a high sensitivity acceleration sensor. The plasma potential was detected with electrical probes, which have been newly developed. The vapor pressure increases linearly with the peak power to about 39.2 MPa. The plasma propagation speed is higher than the velocity of sound nearby the target. © 1991, The Japan Society for Precision Engineering. All rights reserved.

Thermal-stress-induced cracks are generated during the laser-processing of ceramics. This paper describes the temperature profile and thermal stress propagation for silicon nitride ceramics heated by Gaussian heat flux. The thermal stress distribution is calculated with consideration of the temperature dependence on material properties, the influence of laser pulse duration and its repetition rate using FEM. The tensile stress in circumferential, radial and axial directions induces the radial, lateral and median cracks, respectively. The use of short laser pulses below 20 μs with a repetition frequency under 10 kHz is experimentally recommended to reduce thermal stress and to avoid crack formation. © 1991, The Japan Society of Mechanical Engineers. All rights reserved.

This paper describes the effects of laser heating on the electroless plating process. In the experiment, a focused YAG laser beam and a copper electroless plating solution were used. In the analysis, the temperature distribution was calculated by the solution of the heat conduction equation. In the first stage on the laser-induced plating, the rapid heating effect induces the nucleation reaction. In the second stage, the partially heating effect enhances the reduction reaction based on the micro-convection, which depends on the sharp temperature profile. © 1991, The Japan Society for Precision Engineering. All rights reserved.

In the laser machining of ceramics, it is difficult to avoid the formation of a recast layers and cracks. These deffects significantly spoil some excellent properties of ceramics. This paper describes the feasibility of a crack-free processing method for hot-pressed silicon nitride(Si3N4) ceramics with an yttrium aluminum garnet(YAG) laser. It is found that, in order to attain the defect-free machining, it is necessary to process the ceramics using a laser beam pulsed below 500 ns in duration and 10 kHz in repetition rate. © 1990, The Japan Society of Mechanical Engineers. All rights reserved.

This paper describes the feasibility of selective area deposition of metal thin films onto ceramic substrates by using a laser-induced plating technique. In experiments, a focused YAG laser beam and a copper electroless plating solution including CuSO4were used. For the ceramic workpieces, aluminum nitride (A1N) substrate without activation was used. As a result, a copperdeposit was produced on the ceramic surface only in regions where the laser beam was irradiated. A very high plating rate of about.2μm/s was achieved. This plating enhancement rate is about lxl03times the usual plating rate. The specific resistance of the copper film was about 3x 10-8Ωm. As an application, the direct drawing of copper lines was demonstrated with a writing speed of 0.2 mm/s. © 1989, The Japan Society of Mechanical Engineers. All rights reserved.

A new method for direct writing of conductor lines onto ceramic substrates is presented. This method consists of forming metal thin film composed of aluminum by sublimating aluminum nitride (AlN) ceramics in Ar gas atmosphere with a Q-switched yttrium aluminum garnet (YAG) laser. Thickness of this film was about 0.5 μm. The specific resistance was about 5×10^<-6>Ω・m. This metal layer was also available to electroless plating as a catalyst. With nickel (Ni) electroless plating solution, the Ni conductor lines of a specific resistance about 1×10^<-7> Ω・m were directly band selectively formed on the aluminum layer. The bonding strength between the plated film and AlN substrate was above 9.8 MPa (1 kgf/mm^2).