Recently, lightweight materials centered on the future mobility industry are used in various parts such as battery housings and EV platform frames to improve fuel efficiency of automobile engines. Polycrystalline Diamond (PCD) tools are in demand by parts processing companies to improve productivity for machining lightweight parts. PCD drills have excellent cutting performance and wear resistance in high-speed machining. They are expected to grow in the global cutting tool market in the future. Research is needed to improve their performance. In this study, PCD gun drill and twist drill were respectively manufactured using brazing technology. Comparative machining experiments were then conducted. The PCD gun drill is a straight-shaped tool with a PCD tip brazed to a tool body groove for the tip to enter the cutting edge. The PCD twist drill is a spiral-shaped tool with a PCD drill blank brazed to a V-shaped butt joint with the tool body and an internal groove. Both PCD drills were successfully manufactured and evaluated for dimensional accuracy and surface quality by machining aluminum alloy materials with MCT equipment. In the future, we will evaluate not only aluminum materials, but also various machining materials.

Silicon carbide (SiC) is chemically stable, highly heat-resistant, and resistant to thermal shock. SiC having excellent characteristics in a high temperature and high voltage environment is used in high-power semiconductors, highprecision mechanical devices, optical components, etc. As it is used in various industries, there is a growing demand for processing fine holes or grooves in silicon carbide. In this study, micro holes and grooves were machined on 4HSiC and sintered SiC using electrical discharge machining (EDM). Silicon carbide which has very high hardness can be easily processed by EDM as compared with mechanical processes. As a tool material, a polycrystalline diamond (PCD) which has high wear resistance was used and a micro tool of a diameter of 100 μm was fabricated by wire electrical discharge grinding (WEDG). In the EDM of SiC, the machining characteristics such as surface roughness, discharge gap, and tool wear were investigated.

The mole, symbol mol, is the International System of Units (SI) unit of the amount of substance which is the quantity referring to a measure of the number of specified elementary entities, such as chemical elements or compounds in a sample. In the current SI, the mole is defined by specifying the mass of carbon-12. But this base unit is not an invariant of nature because the mass is defined by the material artefact. According to efforts to define the base units in SI using true invariants of nature, the mole will be redefined by fixing the numerical value of a fundamental constant, the Avogadro constant. In the new SI, the definition of the mole can be realized through the experiments that lead to the determination of the Avogadro constant. The best experimental value of the Avogadro constant has been obtained by the X-ray crystal density experiment using silicon-28 highly enriched silicon sphere in the frame work of the International Avogadro Coordination. In this paper, the current definition of the mole and practical aspects of this unit are introduced, then the principle and technical challenges in X-ray crystal density experiment for redefinition of the mole are discussed.