Fumihiro Itoigawa

EXPERIMENTAL STUDY ON LUBRICATION MECHANISM IN MQL INTERMITTENT CUTTING PROCESS

Effects and mechanisms in MQL aluminium cutting are investigated by use of an intermittent turning process and by a friction test apparatus this is designed for measuring friction force between a freshly formed surface and tool material in plastic contact condition. Cutting tests are conducted using two types of lubricants that have differences in lubricity, and in speed ranges from 100 m/min to 400 m/min. Experimental results suggest that the lubrication mechanism of the MQL aluminium cutting considerably changes, depending upon the lubricant types and the temperature on the tool face. If an ester-type lubricant is used and tool surface temperature can be suppressed below a certain transition temperature of friction, a large reduction in a frictional force can be obtained at an initial stage of intervals of intermittent cutting.

Discussion on Surface Plasmon Resonance Technique in the Otto Configuration for Measurement of Lubricant Film Thickness

This study presents a novel method of in situ observation of lubricant films formed within contact interfaces, focusing on the use of the surface plasmon resonance (SPR) technique in the Otto configuration, i.e., the SPR-Otto system. First, a numerical analysis based on the multiple-beam interference theory showed that the SPR-Otto method proposed in this study exhibits high sensitivity for the measurement of lubricant film thickness, comparable to that of a well-known optical interferometry method. Additionally, the advantages and disadvantages of the SPR-Otto method were considered on the basis of the numerical results. Subsequently, a model experiment was performed using an SPR-Otto optical microscope newly developed in this study to demonstrate the predictions obtained in the numerical analysis.

Experimental Research of Micro-Textured Tool for Reduction in Cutting Force

An effect of micro-textured tool on a reduction in cutting force has reported in recent years. Some researchers have discussed that the microstructures contribute to the reduction in friction force at tool-chip interface by acting as cutting fluid reservoirs. In this study, on the other hand, a reduction in cutting force achieved by using the textured tools was confirmed even under dry condition. The results of orthogonal cutting tests employing AISI 1045 steel with non-textured and textured tools indicated that the cutting force and calculated friction coefficient at the tool-chip interface definitely reduce at relatively high cutting speed. For this friction reduction effect, effective texture patterns and optimal area ratio of concave portion to total surface were empirically suggested. Moreover, from results of the tests using tools with sectionally textured surface, it was revealed that the texture only around the position in which the chip flow separates from the tool rake face is effective to reduce the cutting force. Close observation of both tool edges and formed chips under various cutting tests indicated that changes in geometry and dimensions of dead metal formed around the cutting edge is essential for the reduction in cutting force. Finally, a mechanical cutting model having an agreement with the experimental results was discussed by employing the slip-line field method.

Starvation in Ball Bearing Lubricated by Oil and Air Lubrication System

An oil and air lubrication system for ball bearings supporting a high speed spindle maintains friction losses and temperature rises in low level comparing with other lubrication systems, e.g., oil jet or oil mist lubrication. In this study, rotating speeds of the ball in an angular contact ball bearing lubricated by the oil and air lubrication system are observed in various oil supply rates. In addition, quasi-static model analysis of the ball motion is carried out. Experiments indicate that the angular velocity of the ball varies with the oil supply rate even at the constant spindle speed. Furthermore, the model analysis suggests that the ball angular velocity is considerably concerned with an inlet film thickness. From the both results, a relationship between a starvation factor in the ball-race contacts and the oil supply rate is derived for the ball bearing under the oil and air lubrication.

Effects of Stress Distribution at the Contact Interface on Static Friction Force: Numerical Simulation and Model Experiment

This study develops a simplified model that can simulate the dynamics of a split contact interface at the transition from static to kinetic friction. The model has a contact interface formed by multiple contacting points connected to a rigid base via a spring. From a numerical analysis of this model, the effect of the stress distribution at the contact interface on the level of static friction force was investigated. Consequently, it was found that the existence of the stop-restart motion can act to increase the macroscopic (apparent) static friction force. Thus, the numerical analysis demonstrated that the macroscopic static friction coefficient could be changed without varying the local static friction coefficient. The type of tangential loading history, i.e., the existence of stop-restart motion, is an important factor for characterizing the level of the static friction force. In other words, this implies that we can adjust the level of the macroscopic static friction coefficient without changes to the local static friction. Furthermore, the above numerical prediction was confirmed by a model experiment focusing on the sliding contact interface of an object built from separated rubber blocks.

A Novel Cutting Concept of CFRP Composites for Extending the Life of Tool

This paper presents a novel concept for extending the life of the tools that are used in the milling process of carbon-fiber-reinforced plastic (CFRP) composites. Three types of tools were compared in milling tests; tool I: an uncoated tungsten carbide (WC-Co) tool, tool II: a polycrystalline diamond (PCD) tool, and tool III: a combination tool comprising a PCD layer surface with a thickness of 100 μm and a WC-Co substrate flank surface. The measurement of changes in cutting forces over cutting distance revealed that tool III had a better (tool) life performance than the other tools. Additionally, observation of changes in the edge profiles of the tools revealed that the effective edge sharpness of tool III remains constant during the milling tests. The difference between the wear rates of the PCD rake and WC-Co flank surfaces in tool III maintained a constant effective sharpness during the milling process, and it extended the tool life. Based on our findings, we concluded that using the difference between the wear rates of rake and flank surfaces is an effective technique for tool life extension in the milling process of CFRP laminates.

High Precision Turning of Hardened Steel by Use of PcBN Insert Sharpened with Short Pulse Laser

Precision grinding is one of the important processes for finishing of hardened steel parts. However, the grinding process might be quite costly providing the parts with shape complexity should be finished because a number of production steps are needed. Also, this process has some environmental issues, such as disposal of a large amount of grinding sludge and grinding fluid. Precision cutting would become a better alternative process to reduce cost and environmental burden because process steps can be simplified by use of CNC machine tools with PcBN cutting insert if deterioration of cutting tool edge by wear and chipping can be suppressed for long duration. In this study, to improve performance of a PcBN cutting insert, such as wear resistance and defect resistance by the applying of pulse laser processing to sharpen cutting edge in order to realize substitution of cutting for grinding. Precision cutting experiments for hardened steel are conducted by use of the PcBN insert with sharp and tough edges processed by pulsed laser and, for comparison, by use of the PcBN insert ground with diamond wheel. From the results of cutting experiments, it was found that precision cutting with PcBN insert processed by pulsed laser can provide a steady cutting state for a long cutting duration, and a smooth finished surface comparable to precision grindings.

Real-Contact Area Between an Elastomer and a Flat Plane Observed by Surface Plasmon Resonance: Optical Model Calculations

This study presents a novel method for high-sensitivity measurement of the area of the real contact between an elastomer surface and a rigid flat plane, using the surface plasmon resonance (SPR) technique in the Kretschmann configuration. Through numerical calculations, the sensitivity of the SPR method for determining the real-contact area is discussed and compared to other typical optical techniques, such as total internal reflection and multiple beam optical interference. The wavelength dependence of the optical reflectance is simulated, as well as its change with the elastomer-plane gap thickness and the optical properties of the gap material. Non-transparent elastomers are also studied. Consequently, it was found that the SPR method has the highest sensitivity for the measurement of real-contact area; it can detect, for example, an ultra-thin air gap (or water gap) formed between the contacting surfaces from the measurement of the intensity of reflected light from the contact region.

Edge Sharpening and Surface Modification of PcBN Cutting Tool by Pulsed Laser Grinding

PcBN cutting tools have excellent characteristics such as high degree of hardness and low chemical reactivity, so they have potential to replace high precision grinding of hardened steel with high precision cutting. PcBN might be more efficient tool material if improvement in formability, and good surface modification can be achieved. In order to solve these problems, Pulsed Laser Grinding (PLG) is applied to a shape cutting edge and to finish a rake face. After processing by the PLG, shaped cutting edges were observed with a scanning electron microscope (SEM) and measured with contact- type profilometer. As a result, cutting edges processed by the PLG are similar or shaper than that by conventional diamond grinding. In addition, as a one of effects of surface modification, The Vickers microhardness of rake faces increases by about 10 present after PLG. On the other hand, according to frictional test with lateral force microscopy, the coefficient of friction of rake face decreases by half of ordinary surface. Depending on these advantages of PLG, high precision turning of hardened steel with 58HRC in hardness by use of the tool processed by PLG can demonstrate good performance rather than a commercial tool with diamond grinding finish.

Micro Fabrication Using EDM Deposition

This paper describes a metal deposition process using micro electrical discharge machining (micro EDM) to fabricate microstructures. Steel is used for the tool electrode, and the EDM process is carried out in air. By feeding the tool electrode in the vertical direction, a micro rod with 0.14mm in diameter and 2.2mm in height is formed on the workpiece surface. A fillet-like line with uniform thickness is also drawn over the workpiece surface when the horizontal feed is applied independently of the servomechanism of the EDM machine and the horizontal feed rate is kept constant. It is considered from the observation of the discharging surface that the local gap distance at a discharge location becomes larger than that at other locations on the discharging surface and, therefore, the discharge points are not concentrated at a single point but distributed over the discharging surface.