As products life cycles are becoming shorter, the reduction of die and mold manufacturing cost and time is becoming more crucial in the machinery, automotive, and electronics industries. Over the past decades, many initiatives have been made to develop high performance free-machining steels without significant degradation of mechanical properties. To develop a modified AISI P20 free-machining steel, we studied the effects of B, N, and S additives on the variations of the cutting forces and metal structures such as grain size, density, and distribution of free-machining inclusions. From a set of experiments, it was observed that an appropriate addition of B and N additives reduces the resulting cutting force by approximately 6.3% and delays the tool wear progress. During the solidification B and N additives form hBN precipitates, with a layered and planar structure, within the steel matrix. The hBN precipitates’ weak shear strength results in lowering the required milling force. It is also confirmed that machinability is prominently improved when a large number of microsized hBN precipitates are distributed uniformly in the steel matrix. This study could contribute to the development of high performance BN-added free-machining steels for die and mold applications.

Development of five axis tool grinding machine and CAD/CAM systems increase tool design flexibility. In this research, investigated are cutting characteristics of ball-end mill with different helix angle. Special WC ball-end mills with 0o, 10o, 20o, 30o helix angles are designed and used in various cutting tests. Machining performance according to helix angle variation is evaluated from cutting forces, surface roughness, tool wear, produced chip shape, and vibration characteristics. The ball-end mill with 10o helix angle shows the best cutting performance due to appropriate chip load distribution and smooth chip flow. This research can be used for cutting edge geometry optimization and novel design of ball-end mill.

The feasibility of electrochemical drilling and milling on stainless steel are investigated using tungsten microelectrode with 10μm in diameter. For the development of environmentally friendly and safe electrochemical process, citric acid solution is used as electrolyte. A few hundred nanoseconds duration pulses are applied between the microelectrode and work material for dissolution localization. Tool fracture by Joule heating, micro welding, capillary phenomenon, tool wandering by the generated bubbles are observed and their effects on micro ECM are discussed. Occasionally, complex textures including micro pitting corrosion marks appeared on the hole inner surface. Metal growth is also observed under the weak electric conditions and it hinders further dissolutions for workpiece penetration. By adjusting appropriate pulse and chemical conditions, micro holes of 37μm in diameter with 100μm in depth and 26μm in diameter with 50 μm in depth are drilled on stainless steel 304. Also, micro grooves with 18 μm width and complex micro hand pattern are machined by electrochemical milling.

Micro electrochemical machining (ECM) is conducted on stainless steel 304 using non-toxic electrolyte of citric acid. Electrochemical dissolution region is minimized by applying a few hundred second duration pulses between the tungsten SPM tip and the work material. ECM characteristics according to citric acid concentration, feeding velocity and electric conditions such as pulse amplitude, pulse frequency, and offset voltage are investigated through a series of experiments. Micro holes of 60㎛ in diameter with the depth of 50㎛ and 90㎛ in diameter with the depth of 100㎛ are perforated. Square and circular micro cavities are also manufactured by electrochemical milling. This research can contribute to the development of safe and environmentally friendly micro ECM process.

Machining accuracy is closely related with tool deflection induced by cutting forces. In this research, cutting forces and tool deflection in end milling are expressed as a closed form of tool rotational angle and cutting conditions. The discrete cutting forces caused by periodic tool entry and exit are represented as a continuous function using the Fourier series expansion. Tool deflection is predicted by direct integration of the distributed loads on cutting edges. Cutting conditions, tool geometry, run-outs and the stiffness of tool clamping part are considered together for cutting forces and tool deflection estimation. Compared with numerical methods, the presented method has advantages in prediction time reduction and the effects of feeding and run-outs on cutting forces and tool deflection can be analyzed quantitatively. This research can be effectively used in real time machining error estimation and cutting condition selection for error minimization since the form accuracy is easily predicted from tool deflection curve.

In this research, micro fabrication technique using localized electrochemical deposition (LECD) with ultra short pulses is presented. Electric field is localized near the tool tip end region by applying a few hundreds of nano second pulses. Pt-Ir tip is used as a counter electrode and copper is deposited on the copper substrate in 0.5 M CuSO₄ and 0.5 M H₂SO₄ electrolyte. The effectiveness of this technique is verified by comparison with LECD using DC voltage. The deposition characteristics such as size, shape, surface, and structural density according to applied voltage and pulse duration are investigated. The proper condition is selected from the results of the experiments. Micro columns less than 10 ㎛ in diameter are fabricated using this technique. The real 3D micro structures such as micro pattern and micro spring can be fabricated by this method. It is suggested that presented method can be used as an easy and inexpensive method for fabrication of microstructure with complex shape.

A method for form error prediction in side wall machining with a flat end mill is suggested. Form error is predicted directly from the tool deflection without surface generation by cutting edge locus with time simulation. Developed model can predict the surface form error about three hundred times faster than the previous method. Cutting forces and tool deflection are calculated considering tool geometry, tool setting error and machine tool stiffness. The characteristics and the difference of generated surface shape in up milling and down milling are discussed. The usefulness of the presented method is verified from a set of experiments under various cutting conditions generally used in die and mold manufacturing. This study contributes to real time surface shape estimation and cutting process planning for the improvement of form accuracy.

Tungsten carbide microshaft can be used as various micro-tools for MEMS because it has high hardness and high rigidity. In this study, experiments are performed to produce tungsten carbide micro-shaft using electrochemical etching. H₂S0₄solution is used as electrolyte because it can dissolve tungsten and cobalt simultaneously. Optimal electrolyte concentration and machining voltage satisfying uniform shape, good surface quality, and high MRR of workpiece are experimentally found. By controlling the various machining parameters, a straight micro-shaft with 5 ㎛ diameter, 3 ㎜ length, and 0.2° taper angle was obtained.