• 한국기계가공학회지
• /
• 제19권3호
• /
• pp.8-13
• /
• 2020

Carbon fiber-reinforced plastics (CFRPs) are extremely strong and light fiber-reinforced plastics containing carbon fibers. CFRPs can be expensive to produce, but are commonly used wherever high strength-to-weight ratio and rigidity are required, such as in the aerospace, automotive, and ship superstructure industries. In CFRP drilling, the tool performance greatly varies depending on the tool shapes, cutting conditions, and diamond coating. This study developed a new type of tungsten carbide drill with multi-blade edges to evaluate the surface quality of CFRP materials according to the coating thickness of diamond-coated drills. Experiments on tool wear, surface roughness, and burr formation were conducted. The bore exit quality of a 12 mμ -coated drill was better than that of a 6 mμ -coated drill. The superior effects of the 12 mμ -coated drill and the good surface quality of CFRP were also demonstrated.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2003년도 춘계학술대회 논문집
• /
• pp.533-537
• /
• 2003

Compared to sintered polycrystalline diamond (PCD), the deposited thin film diamond has a great advantage on the fabrication of cutting tools with complex geometries such as drills. Because of high performance in high speed machining non-ferrous difficult-to-cut materials in the field of automobiles industry, aeronautics and astronautics industry, diamond-coated drills find large potentialities in commercial applications. However, the poor adhesion of the diamond film on the substrate and high surface roughness of the drill flute adversely affect the tool lift and machining quality and they become the main technical barriers for the successful development and commercialization of diamond-coated drills. In this paper, diamond thin films were deposited on the commercial WC-Co based drills by the electron aided hot filament chemical vapor deposition (EACVD). A new multiple coating technology based on changing gas pressure in different process stages was developed. The large triangular faceted diamond grains may have great contribution to the adhesive strength between the film and the substrate, and the overlapping ball like blocks consisted of nanometer sized diamond crystals may contribute much to the very low roughness of diamond film. Adhesive strength and quality of diamond film were evaluated by scanning electron microscope (SEM), atomic force microscope (AFM), Raman spectrum and drilling experiments. The ring-block tribological experiments were also conducted and the results revealed that the friction coefficient increased with the surface roughness of the diamond film. From a practical viewpoint, the cutting performances of diamond-coated drills were studied by drilling the SiC particles reinforced aluminum-matrix composite. The good adhesive strength and low surface roughness of flute were proved to be beneficial to the good chip evacuation and the decrease of thrust and consequently led to a prolonged tool lift and an improved machining quality. The wear mechanism of diamond-coated drills is the abrasive mechanical attrition.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2003년도 춘계학술대회 논문집
• /
• pp.161-166
• /
• 2003

The micro-extruding die is a die for manufacturing of fine-wire by extruding process. The fine-wire made from the micro-extruding can be effectively applied to fields of semiconductor parts and medical parts etc. It is predicted that the demand of fine-wire in industry is more and more increasing. In this study $\phi50\mu m$ micro-drill which is coated with diamond is used for drilling of super micro-hole sizes. For the machining of taper parts of entrance and exit, drill having $\phi50\mu\textrm{mm}$ inclination angle $20^{\circ}$and angle $30^{\circ}$ is used. This is useful for anti tool-breakage and excessive too-wear in drilling process. After micro-drilling, the polishing process by diamond abrasive and polishing wood s carried out for increasing surface roughness.

• Composites Research
• /
• 제24권4호
• /
• pp.23-28
• /
• 2011

최근 항공용 재료 산업 분야에서 널리 사용되고 있는 CFRP의 활용이 증가되고 있다. 하지만, CFRP와 같은 복합재료 부품의 결합 시에 단점이 있다. 복합재료를 이용한 다양한 구조를 제조하기 위해선 많은 홀 가공이 필요하다. 일반적으로 CFRP 홀 가공시 내구성이 매우 강한 polycrystalline crystalline diamond (PCD) 드릴을 사용한다. 하지만, 단가가 비싸고 가공 속도가 느리기 때문에 내구성은 PCD 드릴에 비해 약하나 드릴 형상 변화를 통해 가공 속도를 조절 할 수 있고, 비교적 가격이 저렴한 chemical vapor deposition (CVD) 다이아몬드 코팅 드릴의 사용량이 증가 되고 있다. 본 연구에서는. PCD 드릴과 CVD 다이아몬드 코팅 드릴의 홀 가공성을 비교 평가하였다. 먼저, 홀 가공 조건 식 (날당 이송량, 절삭 속도)을 이용하여 CFRP 홀 가공성을 평가했으며, CFRP 가공 시 드릴링 과정에서 발생하는 시편 내부의 열적 손상 정도를 비교했다. 열화상 카메라 촬영한 홀 가공 시 발생되는 온도를 이용한 경험식을 만들어 두 드릴의 발열 정도에 따른 홀 가공성을 비교 평가하였다. 또한, 홀 가공 시 발생하는 칩(chip) 배출 여부에 따른 홀 내부의 상태를 평가하여 CVD 다이아몬드 코팅 드릴과 PCD 드릴의 CFRP 홀 가공성을 비교했다. 전반적으로 PCD 드릴의 홀 가공성이 CVD 다이아몬드 드릴에 비해 우수한 성능을 나타냈지만, 홀 생성 속도는 CVD 다이아몬드 드릴이 PCD 드릴에 비해 빠른 결과를 나타냈다.

• 한국정밀공학회지
• /
• 제30권1호
• /
• pp.113-119
• /
• 2013

To develop a new nuclear fuel, it needs to make a test fuel rod and carry out burn-up test in the test loop of a research reactor to check the irradiation characteristics of the nuclear fuel. At that time, several sensors such as thermocouples, LVDTs and SPNDs are needed to be attached in and out of the fuel rod and connect them with instrumentation cables. Then, the instrumentation cables deliver the signals measured by the sensors to the measuring device located outside of the reactor pool. In particular, to install a thermocouple in a fuel rod, it needs to drill off holes on the alumina blocks and sintered $UO_2$ pellets. However, because the hardness of a sintered $UO_2$ pellet is 700 Hv (or HRC 61) and that of an alumina block is 1480 Hv, a special drilling machine which adapts a diamond coated drill bit had developed. In this study, several case experiments have been carried out to find an optimal drilling condition of the drilling machine. And, using the optimal drilling condition, minimum numbers of the holes that a drill bit can drill off are verified.

• 한국정밀공학회지
• /
• 제30권2호
• /
• pp.223-230
• /
• 2013

When a new nuclear fuel is developed, an irradiation test needs to be carried out in the research reactor to analyze the performance of the new nuclear fuel. In order to check the performance of a nuclear fuel during the irradiation test in the test loop of a research reactor, sensors need to be attached in and out of the fuel rod and connect them with instrumentation cables to the measuring device located outside of the reactor pool. In particular, to check the temporary temperature change at the center of a nuclear fuel during the irradiation test, a thermocouple should be instrumented at the center of the fuel rod. Therefore, a hole needs to be made at the center of fuel pellet to put in the thermocouple. However, because the hardness and the density of a sintered $UO_2$ pellet are very high, it is difficult to make a small fine hole on a sintered $UO_2$ pellet using a simple drilling machine even though we use a diamond drill bit made by electro deposition. In this study, an automated drilling machine using a CVD diamond drill has been developed to make a fine hole in a fuel pellet without changing tools or breakage of workpiece. A sintered alumina ($Al_2O_3$) block which has a higher hardness than a sintered $UO_2$ pellet is used as a test specimen. Then, it is verified that a precise hole can be drilled off without breakage of the drill bit in a short time.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 추계학술대회 논문집
• /
• pp.202-205
• /
• 2002

The micro-extruding die is a die for manufacturing of fine-wire by extruding process. The fine-wire made from the micro-extruding can be effectively applied to fields of semiconductor parts and medical parts etc. It is predicted that the demand of fine-wire in industry is more and more increasing. In this study $\Phi$ 50${\mu}{\textrm}{m}$ micro-drill which is coated with diamond is used for drilling of super micro-hole sues. For the machining of taper parts of entrance and exit, drill having $\Phi$ 9mm inclination angle 20$^{\circ}$ is used. This is useful for anti tool-breakage in drilling process. After micro-drilling, the polishing process by abrasive is carried out for increasing surface roughness.

• Archives of Plastic Surgery
• /
• 제50권3호
• /
• pp.248-253
• /
• 2023

Metal fixation systems for cranial bone flaps cut by a drill are convenient devices for cranioplasty, but cause several complications. We use modified craniotomy using a fine diamond-coated threadwire saw (diamond T-saw) to reduce the bone defect, and osteoplasty calcium phosphate cement without metal fixation. We report our outcomes and tips of this method. A total of 78 consecutive patients underwent elective frontotemporal craniotomy for clipping of unruptured intracranial aneurysms between 2015 and 2019. The follow-up periods ranged from 13 to 66 months. The bone fixation state was evaluated by bone computed tomography (CT) and three-dimensional CT (3D-CT). The diamond T-saw could minimize the bone defect. Only one wound infection occurred within 1 week postoperatively, and no late infection. No pain, palpable/cosmetically noticeable displacement of the bone flap, fluid accumulations, or other complications were observed. The condition of bone fixation and the cosmetic efficacy were thoroughly satisfactory for all patients, and bone CT and 3D-CT demonstrated that good bone fusion. No complication typical of metal fixation occurred. Our method is technically easy and safety, and achieved good mid-term bone flap fixation in the mid-term course, so has potential for bone fixation without the use of metal plates.

• 한국표면공학회지
• /
• 제53권6호
• /
• pp.271-279
• /
• 2020

Non-ferrous metals, widely used in the mechanical industry, are difficult to machine, particularly by drilling and tapping. Since non-ferrous metals have a strong tendency to adhere to the cutting tool, the tool life is greatly deteriorated. Diamond-like carbon (DLC) is one of the promising candidates to improve the performance and life of cutting tool due to their low frictional property. In this study, a sacrificial DLC layer is applied on the hard nitride coated drill tool to improve the durability. The DLC coatings are fabricated by controlling the acceleration voltage of the linear ion source in the range of 0.6~1.8 kV. As a result, the optimized hardness(20 GPa) and wear resistance(1.4 x 10-8 ㎣/N·m) were obtained at the 1.4 kV. Then, the optimized DLC coating is applied as an sacrificial layer on the hard nitride coating to evaluate the performance and life of cutting tool. The Vickers hardness of the composite coatings were similar to those of the nitride coatings (AlCrN, AlTiSiN), but the friction coefficients were significantly reduced to 0.13 compared to 0.63 of nitride coatings. The drilling test were performed on S55C plate using a drilling machine at rotation speed of 2,500 rpm and penetration rate of 0.25 m/rev. The result showed that the wear width of the composite coated drills were 200 % lower than those of the AlCrN, AlTiSiN coated drills. In addition, the cutting forces of the composite coated drills were 13 and 15 % lower than that of AlCrN, AlTiSiN coated drills, respectively, as it reduced the aluminum clogging. Finally, the application of the DLC sacrificial layer prevents initial chipping through its low friction property and improves drilling quality with efficient chip removal.

• 한국기계가공학회지
• /
• 제14권4호
• /
• pp.160-166
• /
• 2015

Ultrasonic machining (USM) has been considered a new, cutting-edge technology that presents no heating or electrochemical effects, with low surface damage and small residual stresses on brittle workpieces. However, nowadays, many researchers are paying careful attention to the disadvantages of USM, such as low productivity and tool wear. On the other hand, in this study, a high-performance rotary ultrasonic drilling (RUD) spindle is designed and assembled. In this system, the core technology is the design of an ultrasonic vibration horn for the spindle using finite element analysis (FEA). The maximum spindle speed of RUM is 9,600 rpm, and the highest harmonic displacement is $5.4{\mu}m$ noted at the frequency of 40 kHz. Through various drilling experiments on glass workpieces using a CVD diamond-coated drill, the cutting force and cracking of the hole entrance and exit side in the glass have been greatly reduced by this system.