• 한국공작기계학회논문집
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• 제11권5호
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• pp.73-80
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• 2002

In this study, work materials of the ree form surface shape was machined by ball end mill cutter according to the change of cutting location and depth, and the acquired data of cutting force, tool deflection and shape accuracy were analyzed. Cutting force results were obtained with tool dynamometer and tool deflection values were measured by a couple of eddy-current sensors. Shape accuracy was obtained by roundness tester and surface profile measuring machine. As inclination angle was decreased, cutting force was increased. Cutting force showed large value at $105^{\circ}$ and $150^{\circ}$. Tool deflection was less at down milling than at up milling, decreased at 45$^{\circ}$ and 120$^{\circ}$, and shown large tool deflection at $150^{\circ}$. Roughness values were found to be bad in the inside of surface shape tool deflection. Surface accuracy was obtained better precision in down milling than in up milling.

• Journal of Magnetics
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• 제8권3호
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• pp.124-127
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• 2003

HDDR (hydrogenation, disproportionation, desorption, recombination) and mechanical milling processes have been applied to the $SmCo_{5}$ alloy in an attempt to produce a highly coercive powder. The $SmCo_{5}$ alloy had very high structural stability under the hydrogen atmosphere and the 1:5 phase was only partially disproportionated under up to 10 kgf/$\textrm{cm}^2$ hydrogen gas. The partially disproportionated material was recombined not into 1:5 phase after the HDDR, but rather into multi-phase mixture consisting of 1:5, 2:17, 2:7 and 1:7 phases. The $SmCo_{5}$ alloy HDDR-treated with hydrogen up to 10 kgf/$\textrm{cm}^2$ had poor coercivity. For a useful HDDR to prepare a high coercivity $SmCo_{5}$ alloy powder, much higher hydrogen pressure well exceeding 10 kgf/$\textrm{cm}^2$ would be required. The $SmCo_{5}$ alloy lump was amorphized by an intensive mechanical milling, and it was crystallised ultra-finely by a subsequent optimum annealing. The optimally annealed material had very high coercivity, and it was found that the mechanical milling followed by an annealing was an effective way of producing highly coercive $SmCo_{5}$ alloy powder.

• 한국공작기계학회논문집
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• 제13권2호
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• pp.17-24
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• 2004

In end milling process, undeformed chip thickness and cutting forces vary periodically with phase change of the tool. Recently, a model has been proposed to simulate the shear and friction characteristics of an up-end milling process in terms of the equivalent oblique cutting to this. In the current study, a down-end milling process has been replaced with the equivalent oblique cutting process. And shear and tool-chip friction characteristics variation of SM45C steel has been studied using the end-mills of different helix angles. The specific shear and friction energy consumed with helix angle of $50^{\circ}$ is somewhat larger than those of$30^{\circ}$ and $40^{\circ}$. The specific shear energy consumed is about 76-77% of the specific cutting energy regardless the helix angles.

• Archives of Metallurgy and Materials
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• 제65권4호
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• pp.1329-1333
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• 2020

In this study, we have developed Sn-Ag alloy by a simple high energy ball milling technique. We have ball-milled the eutectic mixture of Sn and Ag powders for a period of 45 h. The milled powder for 45 h was characterized for particle size and morphology. Microstructural investigations were carried out by scanning electron microscopy and X-ray diffraction studies. The melting behavior of 45 h milled powder was studied by differential scanning calorimetry. The resultant crystallite size of the Sn(Ag) solid solution was found to be 85 nm. The melting point of the powder was 213.6℃ after 45 h of milling showing depression of ≈6℃ in melting point as compared to the existing Sn-3.5Ag alloys. It was also reported that the wettability of the Sn-3.5Ag powder was significantly improved with an increase in milling time up to 45 h due to the nanocrystalline structure of the milled powder.

• Journal of Magnetics
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• 제16권2호
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• pp.104-107
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• 2011

In the present study, we systematically investigated the effect of mechanical milling on the magnetic properties of $Sm_2Fe_{17}N_x$ powders produced by the reduction-diffusion process. The Sm-Fe powders obtained by the reduction-diffusion process were composed of an $Sm_2Fe_{17}N_x$ single phase. After nitrogenation, the coercivity and saturation magnetization of the powders were 0.48 kOe and 13.32 kG, respectively. The particle size largely decreased down to less than $2\;{\mu}m$ in diameter after ball milling for 30 hours. However, there is no evidence that the $Sm_2Fe_{17}N_x$ was decomposed to Sm-N and ${\alpha}$-Fe even after ball milling for 30 hours. The coercivity was significantly improved up to 8.82 kOe after milling for 60 hours. However, the magnetization decreased linearly with the ball milling time.

• 한국전기전자재료학회논문지
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• 제20권12호
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• pp.1039-1043
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• 2007

In this paper, in order to develop low temperature sintering ceramics for multilayer piezoelectric actuator application, PMN-PZN-PZT ceramics were fabricated using $LiCO_3,\;Bi_2O_3$ and CuO as sintering aids. And also, their piezoelectric and dielectric properties were investigated according to the milling time. All the specimens sintered at $930\;^{\circ}C$ showed tetragonal phases without secondary phases. With increasing milling time, piezoelectric and dielectric characteristic of specimens increased up to 60 hours milling time and then decreased due to the agglomeration of fine particle. Accordingly, it seems that 60 hour is optimum milling condition. At the sintering temperature of $930\;^{\circ}C$ and milling time of 60 hour, density, dielectric constant(${\varepsilon}_r$), electromechanical coupling factor (kp), mechanical quality factor (Qm), piezoelectric d constant showed the optimum value of $7.95\;g/m^3$, 1382, 0.546, 1749, 330 pC/N, respectively for multilayer piezoelectric actuator application.

• 한국정밀공학회지
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• 제14권4호
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• pp.78-87
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• 1997

In machine tools, frictional force exists between the table and the guideways, and in ballscrews. In this paper, feed motor current measured by a hall sensor is used to calculate the motor torque. Some frictional phenomena are studied in feed drive systems, such as the relationship between feedrate and frictional torque, and chip cover effects on frictional torque. Considering frictional phenomena, the relation- ship between the feed froce and the feed motor current id obtained. Feed force can be well estimated by feed motor current measurement considering frictional behavior. The relationship between the cutting force and the feed motor current is slightly different between up milling and down milling due to the effect of y direc- tional cutting force on frictional torque.

• 한국정밀공학회지
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• 제19권8호
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• pp.63-70
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• 2002

In end milling process, the undeformed chip section area and cutting forces vary periodically with phase change of the tool. However the real undeformed chip section area deviates from the geometrically ideal one owing to cutter runout and tool shape error. In this study, a method of estimating the real undeformed chip section area which reflects cutter runout and tool shape error was presented in up end milling process using measured cutting forces. The average specific cutting resistance, Ka is defined as the main cutting force component divided by the modified chip section area. Ka value becomes smaller as the helix angle increases from $30^circC \;to\;40\circC$. But it becomes larger as the helix angle increases from $40^\circ$to 50 . On one hand, the Ka value shows a tendency to decrease with increase of the modified chip section area and this tendency becomes distinct with smaller helix angle.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.767-770
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• 2000

In order to reduce lean-time and cost, recently the technology of Rapid Prototyping and Manufacturing(PR/M) has been used widely. So various RP/M methods have been developed and these systems commercialized several years ago. The machining process is one of these methods. It also offers advantages such as precision and versatility. But there are some considerations during machining. The most important problem among them is the fixturing. So we have to overcome the limitation because the fixturing time is depend on the complexity of geometry to be machined. In this paper, we have developed the fixturing technique using filling process that can be widely useful for rapid products within a short time. So we have carried out some kinds of rapid products such as plastic knob and metal fan using our fixturing process. In fixturing step, the filling material might chosen a resin or a alloy according to wether the work material is plastic or metal respectively. Also we developed the set-up equipment attachable on the table of the milling machine that provided practicable quality during a series of machining operations, named by two step milling process.

• Journal of the Korean Wood Science and Technology
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• 제16권4호
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• pp.61-69
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• 1988

Recently the automization of wood manufacturing and the development of CNC machine tools becomes the center of interest. Cutting mechanism, tool wear and the roughness of machined surface have been studied. In the studies about wood for special uses, concrete data of cutting is desired. While Pinus densiflora is characterized that heartwood develops as age increases, Chunyang District has the characteristic of strength, red color, relatively regular chap and high heartwood - percentage. But there is no data about cutting this wood, Chunyang District. In this study face milling by sintered carbide tool was excuted to Chunyang District. Cutting force, Surface roughness and states were investigated with regard to cutting speed. Example results were as follows; 1) Mean cutting resistance against lateral component force and longitudinal component force decreased rapidly up to cutting speed of 155 m/min, and remains constant above this speed. 2) The surface roughness of cutting surface lowered as cutting speed increased, regardless of fiber formation. Radial rougness of fiber is larger than lineal surface roughness. 3) Increase in Cutting speed made machining mark restrained. Down-milling showed larger marks than up-milling.