Keiji Yamada

Thermal damage of silicon wafer in thermal cleaving process with pulsed laser and CW laser

The laser cleaving process is a new method to cut brittle materials such as glass, silicon and ceramics. In this dry process, the material is diced only by the thermal stress induced by the laser irradiation. Therefore, the material is not contaminated with the coolant generally used in the mechanical dicing process, but teh thermal damages are caused on the irradiated surface. The objective of this paper is the prevention of thermal damages in the laser cleaving process of silicon wafer. The cleavin experiments are conducted with pulsed ND:YAG laser and cw Nd:YAG laser. In the cleaving with pulsed laser, the temperature required for crack propagation is investigated by measuring with a two-color pyrometer developed. The critical temperature at which the stress intensity factor slightly exceeds the fracture toughness depends on the pulse frequency, the pulse width, the scanning velocity of laser spot and the material properties. The temperature is also confirmed by the thermal stress analysis. And then, for the cleaving with cd laser, a refrigerating-chuck system is developed to reduce the thermal damage of workpiece. The system refrigerates the working table below the freezing point of water, and the material is fixed on the table by the frozen water between the material and the table. While the silicon oxide is caused on the surface of wafer in the room temperature, the refrigerating-chuch can prevent the thermal damage and improve the linearity of the cleaving trajectory and the reliability of the cleaving process.

The Relationship between Dynamic Components of Cutting Force and Adhesion of Tool-Chip Interface

A new method for evaluation of adhesion in cutting is proposed. Adhesion of chip induces fluctuation in chip flow or stick-slip movement of chip, so that dynamic component of cutting forces depends on the cutting conditions and properties of the work materials. In this investigation continuous turning of a medium carbon steel was carried out and dynamic components of cutting forces are measured by piezoelectric dynamometer. Fluctuation in dynamic force on rake face of the tool is considered at a range of cutting speeds under dry condition and oil-mist lubrication. Surface profiles of machined surfaces and sticking of chip on tool face were also investigated. In cutting of medium carbon steel, the dynamic components below 500Hz increased under the condition of build-up edge (BUE) formation, and gradually decreased as increase of cutting speed. Tool-edge geometry well transferred onto the machined surface when the dynamic components were low level. Smoothness of chip flow on rake face is strongly associated with good surface finish.

Forming of Microstructure on Hard Brittle Materials in Ductile Mode Cutting

The requirement of the ultra-precision machine tools for ductile cutting of hard brittle materials was examined experimentally. One of the essential factors of achieving ductile mode cutting was not only high-resolution feedback control but also the dynamic performance of the machine tool in forming solid immersion lens of monocrystalline silicon. We also proposed newly developed method for ultra-precision machine tools, which does not have enough high dynamic performance in order to achieve ductile mode cutting of the hard brittle materials. An additional device consisted of air slider on the machine tool was applied to cutting of glass in order to keep stable ductile mode cutting. We fabricated high-value added structure, which are designed a diffraction grating, consisted of micro groove on a borosilicate crown glass surface with the developed device.

Laser-Assisted Truing for Metal-Bonded Diamond Wheel

Truing and dressing are time-consuming processes in precise finishing with super-abrasive wheels because of the hard super-abrasive grains which cause extensive wear of truer. In this paper, laser-assisted truing method for super-abrasive wheels is introduced. Feasibility of the proposed method is confirmed by fundamental experiments conducted with metal-bonded diamond wheel and pulsed Nd:YAG laser. On the surface of wheel irradiated with laser beam, it is found that the abrasive grains are degraded and the machinability of surface layer is remarkably improved.

Wear Characteristics of Coated Carbide Tools in the Face Milling of Ductile Cast Iron

This study reports an experimental investigation about the wear behavior of TiN and TiCN coated carbide tools during the face milling of pearlitic and ferritic ductile cast iron. Pearlitic ductile cast iron caused the highest cutting forces and flank wear in both TiN and TiCN coated tools. Due to its protective effect, the TiCN coated carbide tool outperformed the TiN coated carbide tool regarding flank wear. The main issue when face milling ferritic ductile cast iron with TiN coated tools was notching wear. The principal reason for notch wear was pointed as adhesive wear caused for the high tendency of ferrite to adhere on the tool. The results demonstrated that the TiCN coating did not showed notching wear when face milling ferritic ductile cast iron, therefore a good choice of coating material can prevent notching wear.

Relationship between Cutting Heat and Tool Edge Temperature in End Milling of Titanium Alloy

In this study, tool edge temperature was measured by a two-color pyrometer with an optional fiber. During one revolution of spindle, the tool edge passes over the fine hole at workpiece after cutting workpiece. An optical fiber inserted into the fine hole transmits infrared ray radiated from tool edge to two detectors with different spectral sensitivities. One peak signal from each detector can be obtained by each spindle revolution. The tool edge temperature can be calculated by taking the ratio of outputs from these two detectors. The relation between cutting heat calculated from cutting force and tool edge temperature was discussed. The tool edge temperature at the same cutting heat could be compared. The wet cutting condition caused lower tool edge temperature than the others at the same cutting heat. MQL and dry showed almost same tool edge temperature. The dispersion of tool edge temperature in wet cutting is wider than that in dry cutting and MQL cutting.

Difference of Feed Marks in Cutting Fluids when Turning Stainless Steel

In this study, the difference of finished surface roughness and feed mark shape in lubricity of the cutting fluids were investigated in turning SUS440C. In the cutting speed of 20m/min, the oil having excellent oiliness caused the smallest finished surface roughness among the tested cutting fluids at the feed rate of 0.1mm/rev, while, the oil having high extreme pressure property was best at the feed rate of 0.2mm/rev. The feed marks were hardly recognized at any conditions. In the cutting speed more than 20m/min, the finished surface roughness in any lubricant conditions showed almost the same or slightly larger compared with that in dry conditions. The feed marks were recognized, and the transcription of cutting edges shape under wet conditions trended to be the same or worse than dry conditions.

Pulsed Laser Surface Treatment for Improvement of Machinability

The surface of worn dies are often machined to remove the worn layer and then to re-form its shape. But, in machining operations for hardened materials, the high cutting force sometimes yields bending deflection of low stiffness tools, and results the decrease in productivity and accuracy.In this study, surface treatment by pulsed laser is applied for the high hardness materials to improve the machinability in the machining operation. Die steels are used as work material machined with ball endmills of carbide in the experiments where the cutting force and the actual depth of cut are measured to obtain the specific cutting energy and to evaluate the machinability. In endmilling operations of the nitrided die steels, the actual depth of cut is decreased by the bending deflection of endmill. However, the surface treatment with laser moderates the decreasing of the actual depth of cut. It is confirmed that the surface of workpiece pre-treated with laser has larger roughness than un-treated ones, and the specific cutting energy is decreased by laser surface pre-treatment.

Machine Learning of Cutting Conditions in Drilling Using Artificial Neural Network

Machining has traditionally been one of the major operations within most manufacturing systems and intelligent machining will play an important role in feature manufacturing systems. This paper concerns the machine learning, specifically classification and recognition of cutting conditions in drilling process. Awareness of the cutting conditions can enhance the auto-diagnosis of an intelligent machining system. In this paper, features representing the drilling process are generated from the converted forms of thrust force and torque and extracted with wavelet packet transform (WPT) and then selected by principal component analysis (PCA). Data instances are generated from experiments with different cutting conditions including workpiece material, drill diameter, feed rate, and spindle speed. A feed-forward network trained with back-propagation method (BPNN) is applied to distinguish between the patterns of each cutting condition. The different contributions of features and the recognition results of cutting conditions are discussed.

Influence of the Cutting Fluid on Tool Edge Temperature in End Milling of Titanium Alloy

In this study, tool edge temperature was measured by a two-color pyrometer with an optional fiber and the novel method to evaluate the cooling effect of cutting fluid was proposed. After one cut, the tool edge passes over the fine hole at workpiece where inserted into an optical fiber so that the one peak signal can be obtained by each of two detectors with different spectral sensitivities in the pyrometer. The tool edge temperature can be calculated by taking the ratio of outputs from these two detectors. In previous research dealing with the cutting temperature in end milling obtained by a two-color pyrometer with an optional fiber, the average temperature calculated from some large peak values was used for an index as cutting temperature. However, this method was not suitable to estimate the tool edge temperature in wet milling. In the proposed method, the tool edge temperature was calculated only by the peak signals just after full length cut and used for an index as cutting temperature. The frequency distribution of tool edge temperature was made by the obtained temperature data. Comparing dry cutting to wet cutting, there was almost no difference in maximum temperature but obvious difference in the frequency distribution. The temperature range in wet cutting was wider than that in dry cutting.