Earticle

The objectives of this research are (1) identifying duties of machine tool operators in small and medium enterprises; and (2) identifying tasks carried out by machine tool operators in small and medium enterprises. This research uses descriptive research method. The study participants were eight machine tool operators from five small and medium enterprises in Yogyakarta, Indonesia. Methods of data collection using document review, observation, questionnaires and focus group discussions. Data analysis using descriptive analysis. Results of research: (1) 5 duties done by machine tool operator are identified (maintain safe work environment, maintain the machine tools, analyze blueprint, perform machining operations, clean machine and workplace), and (2) 27 tasks executed by machine tool operator are identified; 22 knowledge and skills; 17 behaviours; and 18 machines, tools and equipment required by machine operators.

Recently, with the development of ultra-precision technology, the quality improvement of optical parts and various products is emerging. The need for a difficult-to-cut material that is light and exhibits high hardness and high strength physical properties is being emphasized. Ultra-precision machining processing solutions for these difficult-to-cut materials are being actively developed. In this research, experiments were performed using a DTM machine equipped with a laser-assisted machining module for ultra-precision machining of CaF2 materials that are brittle but exhibit high transmittance in a wide range from ultraviolet to infrared.

The optical fibers tend to have poor machinability because of its hardness and brittleness. In the previous study, we applied the electrochemical discharge machining to fabricate the tip of the optical fiber. We could machine the optical fiber using the electrochemical discharge machining however the machined optical fiber tip had rough surface. In this study, we use electrochemical discharge machining with rotation tool which of the rough-grinding and finishing-grinding process to obtain a smooth surface of the side firing fiber. As a result, we are able to machine the optical fiber tip with smooth surface effectively from the proposed fiber machining process and the emission from the side- firing fiber clearly demonstrated the directional emission as the emission beam was reflected at 80 ° relative to the fiber axis.

Purpose: The present study aimed to develop a resin-free computer-aided design/computer- aided manufacturing wax block and evaluate its milling accuracy and manual modifiability. The null hypothesis was that there would be no significant difference in the milling accuracy between the developed resin-free wax block (NPD) and the commercial LDPE-based wax block (LPD). Methods: An NPD block was fabricated using an optimized wax composition. Mandibular molar crowns (n=16 per group) were produced via five-axis dry milling. Milling accuracy was assessed through 3D superimposition (root mean square values) and one-way analysis of variance (α=0.05). Manual modifiability was qualitatively evaluated by an expert using an electric carver and optical microscopy. Results: The NPD group achieved stable dry milling without thermal deformation. No significant difference in milling accuracy was observed between the NPD and LPD groups (p>0.05), thereby supporting the null hypothesis. In the qualitative assessment, the NPD group exhibited superior carving properties and seamless fusion with modeling wax compared to the LPD group. Conclusion: The newly developed resin-free wax block maintains high precision comparable to commercial products while allowing greater manual modifiability. It serves as a practical alternative for enhancing efficiency in digital dental workflows.

A magnetic abrasive finishing process was proposed for improving the surface accuracy of microscale -diameter STS 304 bar used in many applications such as, medical, aerospace, and nuclear industries. Most of the previous research has already explored the conventional finishing technique to improve the accuracy of material in terms of the surface roughness. However, their results are still not good enough for the requirement in the today’s engineering industry. Especially, when the workpiece is a material of microscale-diameter, use of such conventional processes becomes impossible because they entail the application of high pressures that may damage the surface to be finished. Moreover, less control is available over these conventional finishing processes. In this study, an ultra-high-precision magnetic abrasive finishing process was applied to the precision machining of microscale-diameter STS 304 bar and the experimental work are performed with many critical parameters such as, different workpiece revolution speeds, abrasive grain sizes, different finishing temperatures, and pole vibrations. The results showed that in The initial surface roughness of 0.20 µm (Ra) was decreased to 0.025 µm with 0.5 µm of abrasive grain size and pole vibration 12Hz at 40,000 rpm.

Machining center(MCT) which is operated at night without any operator is utilized widely. Its shaft and other elements rotate with high speed and high temperature is generated, due to the friction. Also, gas generated by cutting fluids and metal dust mix up together, which become the ignition source. The combustion process which leads to the ignition is investigated by measuring the rising time of the frictional heat and the safety standards applied to the electric discharge machine are reviewed. Frictional heat temperature variations in the process of metal machining are surveyed for the machining methods, metals and rpm, which will be very useful to make fire protection policy.

Recently, various efforts to make more speedy and precision machine tool to improve productivity and also various efforts to solve environmental problem are going on, so that dry cutting in manufacturing industry, which needs environmental conscious design and development of manufacturing technique, is becoming a very important assignment to solve. Because dry cutting does not use cutting fluid, we need other methods that can be used instead of cutting fluid, which does cooling, lubricating, chip washing, and anti-corrosion. Especially, because turning is a continuous work, the consideration of tool life and surface roughness due to continuous heat and poor lubrication is important. The purposes of this paper are the consideration of how well the compressed air can work instead of cutting fluid, and also the development of the method to select the optimum machining condition by the minimum numbers of experiments through the Taguchi method.

기계 분야에서는 빠른 가공 정보 전달을 위해 설계자가 원격지 CNC에 직접 가공 정보를 설정하고 가공을 제어하는 기술 을 사용한다. 이 기술 활용은 기계 납품의 적시성을 높일 수 있지만, 가공 정보의 기밀성 유지에는 취약하다. CNC는 다수의 설계자가 접속할 수 있으며, 여기서 악의적 공격자는 목표한 가공 정보에 접근하여 이를 변조하거나 외부에 유출할 수 있다. 본 연구에서는 이러한 보안 위협에 대응하기 위해 CNC에 저장된 가공 정보를 보호하기 위한 다중 사용자 환경의 원격 CNC 가공 정보 기밀성 보호 기술을 제안한다. 제안한 기술은 암호 알고리즘을 적용하여, CNC에 업로드된 가공 정보의 기밀성을 보장할 수 있다. 본 연구에서 제안한 기술에 따라 실증 구현 후 단위 기능을 검증한 결과, 목표한 기능이 정상 동작하는 것을 확인하였다. 다만 본 연구에서 제안하는 기술은 저장된 가공 정보만 보호할 수 있으므로, 활용되고 있는 상태에서 가공 정보 의 기밀성을 보장하기 위한 추가 연구가 필요하다.

In the mechanical engineering field, designers use a function to directly set machining information on a remote CNC for fast machining information transmission. This function usage can increase the timeliness of machine delivery, but it is vulnerable to maintaining the confidentiality of machining information. CNC can be accessed by multiple designers, and malicious attackers can access the targeted machining information and modify or leak it to the outside. In this study, we propose a remote CNC machining information confidentiality protection technique for a multi-user environment to protect machining information stored in the CNC to respond to such security threats. The proposed technique can guarantee the confidentiality of machining information uploaded to the CNC by applying an encryption algorithm. After verifying the unit function after the demonstration implementation according to the technology proposed in this study, it was confirmed that the targeted function operates normally. However, since the technology proposed in this study can only protect the stored machining information, additional research is needed to ensure the confidentiality of the machining information while it is being used.

Purpose: This study aimed to observed changes in the shape of dental barrels based on application time. Machinability measures the angle of alloy specimens. Polishing performance measures the surface roughness of alloy specimens. Methods: The dental barrel polishing equipment used in this study was a Snow Barrel (DK Mungyo). Three types of cobalt-chromium alloys for partial dentures were used as specimens (BC CAST R [BP]; Bukwang, Vera PDI [VP]; Aalbadent, and GM 800+ [GP]; Dentaurum). Specimens were prepared in the form of plates (10 mmx10 mmx2 mm). Dental barrel polishing was performed at 450 rpm for 60 minutes with intervals of 5 minutes. The processing angle was measured using a microscope (SZ61; Olympus). Results: For the angle measurement, the VPC specimen was measured at 78.64°, 36.00° for the VP60 specimen, 79.57° for the BP control (BPC) specimen, 28.07° for the BP60 specimen, 75.01° for the GPC specimen, and 39.92° for the GP60 specimen. For the surface roughness measurements, the average surface roughness of the VPC and VP15 specimens were 1.09 μm and 0.26 μm, respectively. The average surface roughness of the BPC and BP20 specimens were 1.77 μm and 0.29 μm, respectively. The average surface roughness of the GPC and GP15 specimens were 1.08 μm and 0.27 μm. Conclusion: The results were excellent after about 20 minutes of dental barrel polishing conditions presented in this study.

In this research, the magnetic abrasive finishing process using (Nd-Fe-B) permanent magnet was applied to confirm the performance and to find the optimum conditions. The STS304 bar was used as the specimen in this experiment. In order to confirm the performance of magnetic abrasive finishing process, the surface roughness (Ra) and diameter reduction were measured when the specimens were processed under the conditions of rotational speeds, frequencies, and magnetic pole shapes. The rotational speeds were varied at 8000rpm, 15000rpm, 20000rpm, and 25000rpm. And the frequencies were changed to 0Hz, 4Hz and 10Hz. Also the shapes of the magnetic pole were changed to flat edge, sharp edge and round edge. It can be concluded that the surface roughness (Ra) and diameter reduction were found to be the best at 25000rpm, 4Hz, flat edge.

Demand for precision optical system is increased due to the rapid development of aerospace, defense, and imaging fields. Research to produce high precision reflector mirror is being carried out. In particular, confocal off-axis reflecting optical system can be applied to various fields due to the advantage of being able to implement a short focal length and a large field of view. The axis of freeform reflector is asymmetrical, so ultra precision machining which is possible to accurately controls over three- axis is required for the reflector. Precision machining of free-form reflectors is more difficult than precision machining of symmetrical reflector. In this study, effect of mirror mounting structure on cutting characteristics was researched by finite element analysis(FEA) to set the reference plane using the machining and measurement of the freeform mirror. The mirror mounting has been divided into four types of squares, hexagons, octagons, and dodecagon. This study of FEA shows that there are not much difference in stress on the surface of the mirror for rotating and cutting forces. It was confirmed that deflection have great different over 5 times according to mounting structure. The analysis results are expected to be useful in the assembly part design and production to minimize the manufacturing tolerances of the freeform mirror.

ABS브레이크시스템은 휠측으로 전해지는 제동유압을 주기적으로 단속하여 휠의 슬립현상을 방지할 수 있도록 한 것으로, 휠 실린더와 연계된 브레이크 유압라인의 솔레노이드 밸브가 주기적으로 개폐되면서 단속적인 제동압력이 형성되도록 한 것이다. 솔레노이드 밸브시트의 핵심기술은 오리피스 볼 플란저의 정밀도이며, 브레이크 작동시 유로의 차단과 형성에 대한 정밀도와 신뢰성이다. 유로의 차단과 형성은 자기장운동과 스프링플런저의 초미세 운동으로 반복되며, 이는 오리피스 볼 플란저의 가공정밀도와 밀접한 관계가 있다. 본 연구는 입자유동가공법을 적용하여 오리피스 볼 플란저의 정도를 얻기 위한 초정밀가공 기술의 개발이다.

ABS brake system of a vehicle controlled braking oil pressure to be handed down in wheel periodically, and a slip phenomenon of a wheel was prevented, and a solenoid valve of brakes hydraulic line cooperated with wheel cylinder was opened and closed periodically and it was acted on intermittent braking pressure. Core technology of a solenoid valve sheet is accuracy of orifice ball flanger, and one of the important ultraprecision function characteristics as opposed to interception to oil and the formation at the time of brake operation. Interception to oil and the formation are repeated by a motion of magnetic field and ultra-micro-motion of a spring flanger and an accuracy of orifice ball flanger to be closely related. In this study was development of a process design to effective accuracy of orifice ball flanger by abrasive flow method.

Intelligent machines respond to external environments on the basis of decisions that are made by sensing the changes in the environment and analyzing the obtained information. This study focuses on the construction of a knowledge base which enables decision making with that information. Approximately 70% of all errors that occur in machine tools are caused by thermal error. In order to proactive deal with these errors, a system which measures the temperature of each part and predicts and compensates the displacement of each axis has been developed. The system was built in an open type controller to enable machine tools to measure temperature changes and compensate the displacement. The construction of a machining knowledge base is important for the implementation of intelligent machine tools, and is expected to be applicable to the network based intelligent machine tools which look set to appear sooner or later.

Tool tips of the circular saw for the steel cutting have commonly applied to brazing type welded the saw body to tips. In this case, when the tool tip is required to the exchange, many problems were occurred as the exchange cost is high and its time is long. In this study, to resolve the brazing type circular saw, the insert type circular saw has designed and made. Also, to confirm the performance of new type circular saw, the various experiments were carried out under condition of tip's shape and machining conditions.