• 한국정밀공학회지
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• 제16권7호
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• pp.188-195
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• 1999

Cutting edge plays an important role in generating machined surface. In order to consider the geometric effects of the cutting edge on mechanical states, the concept of ploughing force and stagnation point was introduced which explains the generating mechanism of machined surface during cutting. The effects of edge radius and nose radius of cutting tool on the distribution of residual stresses of the machined surface having several hardness were studied. Good machined surface having high compressive residual surface stresses can be achieved if cutting tools having large edge radius and small nose radius are used for cutting work materials having high hardness with high depth of cut. The magnitude of edge radius and the hardness of work material also affected the shape of the chip in orthogonal cutting.

• 한국정밀공학회지
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• 제13권1호
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• pp.53-61
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• 1996

A clear understanding of the surface formation mechanism due to cutting is very important to help produce a good quality surface. Much of the roughness along the length of a bar being cut in a lathe can be explained in terms of macroscopic tool shape and feed rate. However, the roughness along the direction of cutting requires a different explanation. The formation of surface roughness is a problem in flow and fracture of materials in the vicinity of the tool edge. On a microscopic scale the cutting edge is rounded because it is impossible to grind a perfectly sharp cutting edge. Even if a perfectly sharp cutting edge were obtained it would soon become dull as a result of rapid breakdown and wear of the cutting edge. A research project is proposed in which in the main object is to model the surface formation mechanism due to cutting. The tool was assumed to be dull, that is, its edge has a finite radius. In order to study the effect of the radius of cutting edge on the surface formation, tools having different cutting edges were used. For orthogonal cutting experiment, cast iron and glass were chosen as brittle materials. Plowing forces acting in the cutting edge were estimated and its effect on the surface roughness was studied by observing the machined surface using optical microscope.

• 한국정밀공학회지
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• 제21권1호
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• pp.61-70
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• 2004

Generally, ceramics are very difficult-to-cut materials because of its high strength and hardness. The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Ceramics can be machined with traditional method such as grinding and polishing. However, such processes are generally cost-expensive and have low material removal rate. Thus, in this paper, to overcome these problems. BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 5,10,15,20,25 and 30%. And, mechanical properties, R-curve behavior and machining tests are carried out to evaluate the machining properties of the manufactured machinable ceramics.

• 소성∙가공
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• 제19권5호
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• pp.290-295
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• 2010

Shaving technology is one of the significant metal forming technologies which can make the smooth and fine sheared surface of products after shearing process. The sheared surface on the side wall of the cutting edge is very important because it functions as a basic surface for measuring the dimensions of product. Effective sheared surface after shaving can be influenced by several working variables such as shaving allowance, shaving clearance, type of material and profile of cutting edge. The influence of these variables on shaving characteristics was investigated in this study. A cut-off die to make the simplified gear-shaped products was manufactured. Three kinds of sheet metals (AL5052, SPCC and SAPH440) of 3mm thickness were firstly sheared and then shaved for four shaving allowances and three sharing clearances. It was shown through experiments that the optimum working condition to give the maximum effective sheared surface in shaving was found ; Shaving allowance is 0.2mm and Shaving clearance is 0.01mm.

• 한국정밀공학회지
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• 제19권2호
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• pp.106-113
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• 2002

Stencil is used normally as a mask for seeder pasting on pad of PCB. The objective of this study is to develop stencil cutting system and determine optimal conditions which make good-quality stencil by using a Nd:YAG laser. The effects of process parameters such as laser power, type of mask, gas pressure, cutting speed and pulse width old the cut edge quality were investigated. In order to analyse fille cut surface characteristics(roughness, kerf width, dross) optical microscopy, SEM photography and roughness test were used. As a result, the optimal conditions of process parameters were determined, and the practical feasibility of the proposed system is also examined by using a commercial Gerber file for PCB stencil manufacturing.

• 한국안전학회지
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• 제24권2호
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• pp.7-12
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• 2009

The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Thus, traditional ceramics are very difficult-to-cut materials. Generally, ceramics are machined using conventional method such as grinding and polishing. However these processes are generally costly and have low MRR(material removal rate). To overcome such problems, in this paper, h-BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 10 and 15%. The purpose of this study is an analysis of endmill's rake angle for appropriate tools design and manufacturing for the machinable ceramics. In this study, Experimental works are executed to measure cutting force, surface roughness, tool fracture, on different axial rake angle of endmills. Cutting parameters, namely, feed, cutting speed and depth of cut are used to accomplish purpose of this paper. Required experiments are performed, and the results are investigated.

• 한국정밀공학회지
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• 제12권12호
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• pp.72-80
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• 1995

Ultraprecision machining technology has been playing a rapidly increasing and important role in manufacturing. However, the physics of the micromachining process at very small depth of cut, which is typically 1 .mu. m or less is not well understool. Shear along the shear plane and friction at the rake face dominate in conventional machining range. But sliding along the flank face of the tool due to the elastic recovery of the workpiece material and the effects of plowing due to the large effective negative rake angle resultant from the tool edge radius may become important in micromachining range. This paper suggests an orthogonal cutting model considering the cutting edge radius and then quantifies the effect of plowing due to the large effective negative rake angle.

• 한국추진공학회지
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• 제24권5호
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• pp.43-55
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• 2020

가스터빈 블레이드의 핀-휜 배열의 냉각 성능을 향상시키기 위하여 분절핀을 설치하여 효과를 분석하였다. 분절핀의 위치에 따른 유동 및 열전달 특성 변화를 수치해석을 통해 분석하였다. 분절핀이 설치되지 않은 엇갈림 핀-휜 배열인 기존형상 와 분절핀이 X₂/D_p=1.25 간격 떨어진 분절핀적용형상 1과 X₃/D_p=1.75 간격 떨어진 분절핀적용형상 2 를 비교하였다. 해석 결과 분절핀의 설치로 인해 핀-휜 배열 전단부에서 발생하는 말발굽와류의 세기가 강화되는 것을 확인하였다. 또한 핀-휜 배열 후단부에서 발생하는 멤돌이 와류의 세기가 약해지는 것을 확인하였다. 이로 인해 바닥면의 열전달 분포가 크게 상승하는 것을 확인 하였다. 반면 분절핀의 설치로 인해 압력손실은 증가하였으나, 열성능계수는 분절핀 적용형상 2 에서 최대 23.8% 가량 증가하는 것을 확인하였다. 이를 통해 향후 가스터빈 핀-휜 냉각 유로 설계 시 분절핀을 설치하면 냉각 성능이 증대 될 것으로 판단된다.

• Elastomers and Composites
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• 제36권4호
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• pp.255-261
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• 2001

Precut을 가지고 있는 고무 시편에서 서로 다른 온도에서 인장 강도의 영향을 조사하였다. 온도 조건에 따라 precut이 있는 시편과 precut이 없는 시편의 인장 강도는 서로 다른 거동을 보였다. $80^{\circ}C$에서는 임계 Precut 크기보다 더 큰 precut를 가지는 시편은 상온에서 시편보다 높은 인장 강도를 보였다. 상온에서 측정한 시편에 비하며 $80^{\circ}C$에서 측정한 시편은 잘 발달된 2차 균열들을 가지고 있는 반면, $110^{\circ}C$에서 측정한 시편의 경우 2차 균열들이 명확하게 발달하지 못하였다. 서로 다른 온도에서 인장강도의 차이는 인장시 발달된 결정화도와 균열 끝 부분에서 형성된 미세 균열 형상과 관계가 있는 것으로 보인다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1996년도 추계학술대회 논문
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• pp.64-74
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• 1996

The meachanism for cutting epoxy resins specimens which were specially provided was experimentally investigated to obtain a fine surface finish. the specimens were cut the three-dimensional undrer dry conditions using a lathe. the relationship between the topography of the cut surface due to the change rate of temperature of the cutting condition using sintered carbides (P20, K10, KT150) was investigated. the main results obtained are as follows: 1) The change rate of temperature of the cutting edge is increased in nearly proportion ot cutting speed feed rate depth of cut. 2)The profile of surface roughness were regulated k10 but irregulated P20 KT150. 3) The surface roughness value decreased K10 rather than P20 KT150. 3) The surface roughness value decreased K10 rather than P20 KT 150.4)The cutting resistance increased thrust force rather than cutting force due to the visco-elastic material of epoxy resins.