• 소성∙가공
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• 제11권4호
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• pp.349-354
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• 2002

In order to find the effect of lubricant viscosity, sheet surface roughness, tool geometry, and forming speed on the frictional characteristics in sheet metal forming, a sheet metal friction tester was designed and manufactured and friction test of various sheet were performed. Friction test results showed that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, the friction coefficient is relatively high. The result also show that as the punch radius and punch speed becomes bigger, the friction coefficient is smaller. Using experimental results, the mathematical expression between friction coefficient and lubricant viscosity, surface roughness, punch comer radius, or punch speed is also described.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.349-355
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• 2017

프레스금형(press dies)에 의한 굽힘가공(bending work) 이라는 것은 평평한 블랭크(blank)를 필요로 하는 각도(角度)로 굽히는 것이다. 굽힘가공을 하면 굽혀진부분(flange)과 굽혀지지 않은 부분(web)으로 구분되며, 굽힘라인(bending line) 부분에는 굽혀진 각도(bending angle)와 굽힘반지름(bending radius)이 내측과 외측으로 성형된다. 이때, 내측 굽힘반지름의 크기는 제품의 재질별로 최소치수가 제시 된다. 제시된 최소치수 보다 작게 굽히면 절단면 굽힘부위에 덧살이 발생 하거나 외측 굽힘반지름 부위에는 균열(crack)이 생긴다. 굽힘가공에서의 외측 굽힘반지름은 자연적으로 생긴다. 그래서 외측 굽힘반지름 치수를 굽힘펀치와 다이블록으로 조정하면서 필요한 치수로 굽힐수 없다. 굽힘가공에는 V-굽힘, U-굽힘, Z-굽힘, O-굽힘, P-굽힘, 에지굽힘(edge bending), 트위스트굽힘(twist bending), 크림핑(crimping) 등이 있다.이 중에서 Z-굽힘은 굽힘라인이 2개로써 블랭크의 상면(上面)과 하면(下面)에 설정하여 상향(上向)굽힘이나 하향(下向)굽힘으로 작동되는 금형을 사용한다. Z-굽힘을 크랭크굽힘(crank bending) 이라고도 한다. 이런 구조의 금형으로 Z-굽힘가공을 하면 내측반지름은 표준치수로 굽혀진다. 표준치수라는 것은 굽힘가공에서 굽힐 수 있는 최소 굽힘반지름 치수로서 굽힘펀치의 각(角)반지름(Rp)를 뜻한다. 그런데 산업현장에서는 외측 굽힘반지름 치수를 굽힘펀치와 다이블록으로 굽힐수 없는 미세한 샤프에지(sharp edge) 형상인 매우 작은 치수(R=0.2mm)를 필요로하고 있는 바, 본 논문에서는 외측 굽힘반지름 치수를 0.2mm 이하로 굽힐수 있는 Z-굽힘가공 공법을 개발 하고자 하였다.

• 소성∙가공
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• 제13권5호
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• pp.461-465
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• 2004

Based on the experimental observation, the mathematical friction model, which is an essential information for analyzing the forming process of sheet metal, is developed considering lubricant viscosity, surface roughness and hardness, punch comer radius, and punch speed. By comparing the punch load found by FEM with a proposed friction model with experimental measurement when the coated and uncoated steel sheets are formed in 2-D geometry in dry and lubricant conditions, the validity and accuracy of the developed friction model are demonstrated.

• 소성∙가공
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• 제11권6호
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• pp.503-512
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• 2002

The drawbead is used to control material flow into the die during the binder wrap process and the stamping process in the sheet metal forming process. Since the dimension of drawbead is relatively small in comparison with the typical dimensions, it is difficult to include drawbeads in finite element analysis of the sheet metal forming process. It is because the mesh system has to be fine enough to describe the drawbead and the computation time is drastically increased. In this paper, simulation of drawbead forming has been carried out to obtain the equivalent boundary conditions in the binder wrap process and the stamping process. In order to investigate the effect of various die geometries, parameter studies are performed with the variation of parameters such as the blank length, the drawbead depth, the drawbead radius, the inclination of die and the friction coefficient.

• Design & Manufacturing
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• 제13권3호
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• pp.19-23
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• 2019

In the mold industry, CAM software has been introduced to solve the impossible or time-consuming part of the mold industry because the increase in labor costs, the drop in mold price, and the short delivery time are tasks to be solved not only in the manufacturing industry but also in the mold industry as a whole. In order to reduce the processing time and improve the surface roughness, we have been conducting various researches for efficient machining. This study was carried out to compare the ball end mill and radius end mill tools with the Power mill software and NC brain software under the same conditions and to find out the most efficient method of machining the smooth drafting surface and improving the surface roughness. (1) By machining the smooth drafting surface using radius end mill, the machining time is 23.7% faster than when using ball end mill. (2) Surface roughness when machined with radius end mill is smoother than when using ball end mill. Based on these results, it can not be applied to all shapes, but if it is a relatively wide and simple gradient shape, the raster machining method using radius end mill can be more effective in terms of delivery and quality than machining with ball end mill.

• 소성∙가공
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• 제9권3호
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• pp.284-292
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• 2000

Optimization of the process parameters is carried out for process design in sheet metal forming processes. The scheme incorporates with a rigid-plastic finite element method for the deformation analysis and response surface methodology for the optimum searching of process parameters. The algorithm developed is applied to design of the draw bead force and the die radius in deep drawing processes of rectangular cups. The present algorithm shows the capability of designing process parameters which enable the prevention of the weak part of fracture during processes.

• 소성∙가공
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• 제21권6호
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• pp.348-353
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• 2012

Micro-drawn parts have received wider acceptance as products become smaller and more precise. The subject of this study was the deformation characteristics of ultra thin sheet metal in micro drawing of a rectangular shaped part. The influence of drawing speed and blank holding force on the product quality was investigated in micro-drawing of ultra thin sheet of beryllium copper (C1720) alloy. The specimen had a diameter of 4.8 mm and a thickness of $50{\mu}m$. Experiments were carried out in which, different blank holding force and drawing speed were considered. The product quality was evaluated by measuring the thickness and hardness along two specified directions, namely, the side and diagonal directions. The distribution of the thickness strain showed severe thinning especially around the punch radius in both directions. In the diagonal direction, thickening occurred in the flange area due to the axi-symmetric drawing mode. The increase of blank holding force and/or drawing speed was found to cause severe thinning around the punch radius. The blank holding force had a greater effect on thinning of the product than the drawing speed.

• 한국정밀공학회지
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• 제27권11호
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• pp.7-16
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• 2010

In this study, wire was used as the filler material for the laser repair welding, and the phenomenon in which the supplied filler material was melted and beaded down into the specimen was examined with varying laser powers and welding speeds. The optimal processing condition was found to be the laser power of 1,300 W, the welding speed and feed wire supply speed of 0.5 ml/in and the defocused distances of +2mm. At this time, the heat input(E) was $65{\sim}75\;J/mm^2$, and no internal defect occurred. When repair welding was carried out as the optimal processing for the part that had an external defect with the radius of 2mm, the filler metal was melted, resulting in the volume smaller than the defect part and thus causing the part unfilled. Therefore, it was found to be necessary to carry out repair welding two to three times by multiple passes rather than does it only once by single pass.

• 한국기계가공학회지
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• 제8권2호
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• pp.60-68
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• 2009

The objective of this paper is to design stamping die of inner reinforcement panel with DL 950 advanced high strength steel as stamping materials through numerical analyses and experiments. The stamping process was designed as bending dominant process consisting of 1 step of notching and 4 steps of bending processes. In order to obtain a proper design of the stamping die, various three-dimensional elasto-plastic finite element analyses were performed using a commercial code AUTOFORM V4.2. Design parameter of stamping die was chosen as the corner radius of the stamping die for each step. From the results of the FE analysis, feasible corner radii of the stamping die, which can minimize the deviation of corner angle of the stamped part from design data, and forming load for each part were estimated. Stamping experiments were carried out using the manufactured stamping die according to the proposed die design. The results of experiments were shown that the stamping die can successfully manufacture the inner reinforcement panel with DL 950 advanced high strength steel as base stamping material.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.283-287
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• 2003

In recent years, design of an optimal blank shape is very important for sheet metal forming process in the automobile industry because the raw material cost rate is significant part in the automobile industry. With the design of an optimal blank shape, the engineer can protect a blank from an excessive holding force to improve the quality and reduce the ratio of material scrap. Therefore design of an optimal blank shape is inevitable in sheet metal forming process. However, if it causes a complicated shape of blank, it may be difficult to do the blank layout optimally. In this study, we developed software of optimal blank layout connected with the software of optimal blank shape design which was created in the past by the present authors. And by using these softwares, we would like to present the method in order to get optimal utilization ratio easily and precisely within short time for the sequence of works from design to blank layout.