For precision machining of fuel injection nozzles, a micro-drilling process to drill micro-holes <0.2 mm in diameter is required. In this study, a non-step drilling method for high-efficiency processing is developed. Previously, the effects of drill feed rate were verified to measure thrust force and torque during drilling, and the results indicated that a high feed rate capable of keeping chips to a continuous form was optimal. Here, the cutting performance of the non-step drilling method was investigated by experiments. Machining tests indicated that use of a diamond-like carbon (DLC)-coated drill for chip exhaust out of the drilling hole of the micro-drill allowed a higher feed rate to be applied.

View full abstract

Cemented carbide is used for cutting tools and cold forging molds because it has excellent wear resistance. However, in the case of soft metal processing, the cemented carbide may be worn. In this study, the wear behavior of cemented carbide against copper alloy was investigated using a pin (cemented carbide)-on-plate (Cu alloy) reciprocating friction tester. The results indicated that the wear depth and the mechanism of wear of the cemented carbide were different in the initial-wear region and the steady-state region. In addition, the wear depth of the copper alloy was different in the initial-wear region and the steady-state region. The change in wear mechanism with the number of cycles influenced the transfer situation and amount of copper alloy transferred to the cemented carbide.

View full abstract

Peri-implantitis is a site-specific infectious disease that causes an inflammatory process in soft tissues and loss of bone supporting an osseointegrated dental implant. The pathogenesis of peri-implantitis involves microorganisms in the dental plaque on an abutment of the implant. Therefore, removal of plaque on the surface of abutment is clinically required for long-term function of the implant. Conventional treatment of peri-implantitis by debridement includes a method of scaling on the titanium abutment surface using a curette-style titanium or plastic scaler, because the hardness of the surface of titanium abutment is not sufficient to prevent damage and the increase in surface roughness by conventional debridement with a stainless steel scaler. However, few studies have examined damage to the implant abutment surface caused by a hand scaler. This study was performed to evaluate the surface changes on a cylindrical pure titanium surface curetted using a curette-style stainless steel scaler. The curette-style stainless steel scaler markedly damaged the cylindrical pure titanium surface. The arithmetic mean surface roughness (Ra) of the curetted surface was significantly (13-fold) higher than the Ra of the initial surface. Deep flaws were observed in the curetted surface.

View full abstract