Myung-Chang Kang

Evaluation of machinability by cutting environments in high-speed milling of difficult-to-cut materials

Abstract High-speed machining of difficult-to-cut materials generates concentrated thermal/frictional damage at the cutting edge of the tool and rapidly decreases the tool life. In this paper, the cutting environments, such as dry, flood coolant, and compressed chilly-air coolant, were investigated to improve the tool life. For this study, a compressed chilly-air system was manufactured. The experiments were performed for various hardened materials and various coated tools. The effectiveness of the developed methods on the basis of tool life was estimated. The results show that the cutting environment using compressed chilly-air coolant provided better tool life than using flood coolant or using a dry environment.

Tool wear measuring technique on the machine using CCD and exclusive jig

Abstract Recently the applications of high speed machining have increased due to the need for high precision and high accuracy machining and machining of difficult-to-cut material. However, the high speed machining also accompanies problems: the product quality can be degraded due to the tool wear and the product cost can be increased due to frequent tool replacements. Therefore, it is necessary to develop a technique of quantitative tool wear measurement to determine the precise timing for tool replacement. In this respect, this study suggests a reliable technique for the reduction of error components by developing a system using a CCD camera and an exclusive jig to be able to precisely measure the size of tool wear in a direct manner, in addition to partly introducing Taguchi method.

A study on the precision machinability of ball end milling by cutting speed optimization

Abstract This study proposes an optimization cutting speed program developed to improve the machining precision and tool life in high speed machining using the ball end mill. This program optimizes the cutting speed that varies during free surface machining. As for the technique of optimization cutting speed, the NC code generated from CAD/CAM goes through a reverse post process and cutting simulation and the effective tool diameter of the ball end mill is obtained. Then the range of critical cutting speed suitable for the workpiece is selected and the spindle revolution is changed according to the effective tool diameter within the range of the critical cutting speed. In this paper, the machining precision and tool life were compared in the free surface machining conducted by the general cutting method and the technique of optimization cutting speed.

Characteristic evaluation of Al2O3/CNTs hybrid materials for micro-electrical discharge machining

The characteristic evaluation of aluminum oxide (Al2O3)/carbon nanotubes (CNTs) hybrid composites for micro-electrical discharge machining (EDM) was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. Al2O3 composites with different CNT concentrations were synthesized. The electrical characteristic of Al2O3/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the characteristics of machining were analyzed using field emission scanning electron microscope (FESEM). The electrical conductivity has a increasing tendency as the CNTs content is increased and has a critical point at 5% Al2O3 (volume fraction). In the machining accuracy, many tangles of CNT in Al2O3/CNTs composites cause violent spark. Thus, it causes the poor dimensional accuracy and circularity. The results show that conductivity of the materials and homogeneous distribution of CNTs in the matrix are important factors for micro-EDM of Al2O3/CNTs hybrid composites.

A study on the kinematics and dynamics of a 3-DOF parallel machine tool

Abstract A new kind of 3-DOF parallel machine tool has been developed to apply in billet snag grinding by Northeastern University, China. It has the advantages of simple structure, higher stiffness, higher ratio of force-to-weight, larger working space, simple kinematics equations, no motion coupling and no singular pose. This robot can be used for grinding, milling, polishing and other machining process with suitable tools. In this paper, its structure and degree of freedom, the workspace, the kinematics and accuracy analysis, the static and dynastic analysis, the simple robot and its parameters are introduced.

Surface effects of hybrid vibration-assisted femtosecond laser system for micro-hole drilling of copper substrate

Abstract The ultrafast laser based hybrid machining system was studied and a novel approach was demonstrated to improve laser machining quality on metals by vibrating the optical objective lens with a low frequency (500 Hz) and various displacements (0–16.5 μm) during a femtosecond laser machining process. The laser used in this experiment is an amplified Ti:sapphire femtosecond (10−15 s) laser system that generates 100 femtosecond pulses having an energy of 3.5 mJ/pulse with a 5 kHz repetition rate at a central wavelength of 790 nm. It is found that both the wall surface finish of the machined structures and the aspect ratio obtained using the frequency vibration assisted laser machining are improved compared with those derived via laser machining without vibration assistance.

Machining characteristics of complex prism pattern on electroplated roll by copper

Abstract The BLU (back light unit) is the core component of the LCD for notebook, mobile-phone, navigation, as well as large sized TV, PID (public information display), etc. In order to enhance optical efficiency of LCD, optical films with the uniform prism patterns have been used for BLU by stacking two films up orthogonally. In this case, light interference-phenomenon occurred such as Morie, wet-out, u-turning, etc. It caused several problems such as low brightness, spots and stripes in LCD. Recently, the high-luminance micro complex prism patterns are actively studied to avoid the light interference-phenomenon and enhance the optical efficiency. In this study, the roll master to manufacture complex micro prism pattern film was machined by using the high precision lathe. The machined patterns on the roll master were 50, 45, 40, 35, 30, 25, 20, 15, 10 and 5 μm in the pitch with 25.0, 22.5, 20.0, 17.5, 15.0, 12.5, 10.0, 7.5, 5.0 and 2.5 μm in the peak height, respectively. The roll was 2 000 mm in length and 320 mm in diameter. The electroplated roll by copper and the natural single crystal diamond tool was used for machining the patterns. The cutting force was measured and analyzed for each cutting condition by using the dynamometer. The chips and the surfaces after being machined were analyzed by SEM and microscope.

Comparative study on discharge conditions in micro-hole electrical discharge machining of tungsten carbide (WC-Co) material

WC-Co is used widely in die and mold industries due to its unique combination of hardness, strength and wear-resistance. For machining difficult-to-cut materials, such as tungsten carbide, micro-electrical discharge machining(EDM) is one of the most effective methods for making holes because the hardness is not a dominant parameter in EDM. This paper describes the characteristics of the discharge conditions for micro-hole EDM of tungsten carbide with a WC grain size of 0.5 μm and Co content of 12%. The EDM process was conducted by varying the condenser and resistance values. A R—C discharge EDM device using arc erosion for micro-hole machining was suggested. Furthermore, the characteristics of the developed micro-EDM were analyzed in terms of the electro-optical observation using an oscilloscope and field emission scanning electron microscope.

Improvement of machining quality of copper-plated roll mold by controlling temperature variation

Abstract Micro prism film used in LCD industry can be manufactured by roll to roll method with copper-plated roll mold. As copper-plated roll mold is getting larger, pitch error is getting severer. The pitch error drops the quality of micro prism film. The main cause of the pitch error was investigated during machining large roll mold whose machined length was 1 200 mm. The temperature of machining system was elevated during machining roll mold, and this elevation induced thermal expansion of the system. The temperature variation around the roll mold also made thermal expansion of the roll mold. The amount of thermal expansion had strong relationship to the amount of pitch error. Therefore, the roll mold was machined after warming-up of machining system and precise temperature controller around copper-plated roll mold was installed, which minimized the temperature variation. Finally, precise micro prism patterns without pitch error were machined on the large roll mold.

The influence of counterface materials and humidity on the tribological behavior of arc ion plated TiN films

Abstract TiN films were deposited onto AISI D2 steels by an arc ion plating (AIP) technique. The effects of atmospheric humidity and counterface materials on the tribological behavior of the AIP-TiN layer have been investigated using a conventional ball-on-disc wear apparatus. In the case of a steel counterface, the average friction coefficient increased with increasing relative humidity due to tribochemical interaction of the steel with moisture. At low relative humidity (2% RH) condition, the TiN coating layer rather gained mass due to the seizure of steel on the layer without the tribochemical reaction. For the higher humidity condition above 25% RH, the mass loss of the TiN coating layer occurred and was accelerated with the increase of the relative humidity as the tribochemical reaction was progressively dominant. In the case of the alumina counterface, the friction coefficient decreased with increasing relative humidity from 2% RH to 25% RH. This behavior was explained by the formation of the aluminum–hydrated oxide phase between counterface materials. On the other hand, the increasing relative humidity up to 85% RH induced a large increase of both average friction coefficient and its deviation, in addition, increased the wear rates of both counterface layers. This behavior was explained with the accelerated fracture of the alumina ball due to the reduced flexural strength in moist conditions.