Sung Ho Chang

Simulation of an Aspheric Glass Lens Forming Behavior in Progressive GMP Process

Recently, GMP(Glass Molding Press) process is mainly used to produce aspheric glass lenses. Because glass lens is heated at high temperature above Tg (Transformation Temperature) for forming the glass, the quality of aspheric glass lens is deteriorated by residual stresses which are generated in a aspheric glass lens after forming. In this study, as a fundamental study to develop the mold for progressive GMP process, we conducted a aspheric glass lens forming simulation. Prior to a aspheric glass lens forming simulation, compression and thermal conductivity tests were carried out to obtain mechanical and thermal properties of K‐PBK40 which is newly developed material for precision molding, and flow characteristics of K‐PBK40 were obtained at high temperature. Then, using the flow characteristics obtained, compression simulation was carried out and compared with the experimental result for the purpose of verifying the obtained flow characteristics. Finally, a glass lens press simulation in progressive GMP process was carried out and we could forecast the shape of deformed glass lenses and residual stresses contribution in the structure of deformed glass lenses after forming.

An Experimental Study on Flow Characteristics of PBK-40 for Glass Molding Press Simulation

Remarkable progress had been made in both technology and production of optical elements including aspheric lens. Especially, requirements for machining glass materials have been increasing in terms of limitation on using environment, flexibility of material selection and surface accuracy. In the past, precision optical glass lenses were produced through multiple processes such as grinding and polishing, but mass production of aspheric lenses requiring high accuracy and having complex profile was rather difficult. Against such a background, the high-precision optical GMP process was developed with an eye on mass production of precision optical glass pasts by molding press. This GMP process can produce with precision and good repeatability special form lenses such as for cameras, video cameras, aspheric lenses for laser pickup, f-θ lens for laser printer and prism, and fine glass parts including diffraction grating and V-grooved base. Generally, GMP process can be classified into batch and progressive type. In these types, because progressive type has many merits in that productivity is higher and repair/retouch of mold is easier than batch type, progressive GMP process is mainly used to produce aspheric glass lenses these days. In this paper, as a fundamental study to develop the multi-cavity mold for higher productivity of progressive GMP process used in fabrication of aspheric glass lens, compression tests for K-PBK40, which is the material of aspheric glass lens, were conducted at high temperature. As a result, flow characteristics of K-PBK40 were obtained for aspheric glass lens press simulation.

Study on the Roller-Bending Simulation to Promote Productivity in the HINGE STRAP Forming System

The purpose of present study was to increase productivity and to promote the quality of the part in the forming system for hinge strap in automobile. So the roller-bending simulation was carried out to develop the forming system for the hinge strap. A square tube used in the roller-bending for the hinge strap was fabricated using process of the sheet forming and the welding. So study on the mechanical properties of the original metal sheet (SPCC 1.6t) and weld-line (including a HAZ) were performed before the roller-bending simulation. And the body forces of the roller (rigid body) in the roller-bending process simulation were calculated to make an accurate estimate the capacity of the oil pressure cylinder for a pressure device. Then the roller-bending process was divided into 5 steps for the simulation for validating the effect of the bending velocity on the springback. At the end, the shape after springback was estimated. The result was adopted in the design for the bending die.

A Study on Die Roll Height of Special Automobile Seat Recliner Gear According to Die Chamfer Shape in Fine Blanking Tool

In this paper, the effect of die chamfer shape on the die roll height was studied by fine blanking experiments for imaginary special automobile seat recliner gear. The three die inserts with different die chamfer shapes were machined, and fine blanking tool was manufactured. Using the fine blanking tool, three experiments were conducted on the 650 ton fine blanking press. Each die roll height was measured, analyzed and we found the tendency of die roll heights on imaginary special automobile seat recliner gear to increase with increasing die chamfer angle, with the horizontal distance of die chamfer being constant. This result can be used to minimize the die roll height of fine blanking gear parts when designing die chamfer of fine blanking tool.

A Study on the Relation between Die Roll Height and Die Chamfer Shape in Fine Blanking for Special Gear

In this paper, the relation between die roll height and die chamfer shape was studied by fine blanking experiments for imaginary special gear. The three die inserts with different die chamfer shapes were machined, and fine blanking tool was manufactured. Using the fine blanking tool, three experiments were conducted on the 650 ton fine blanking press. Each die roll height was measured, analyzed and we found the tendency of die roll heights on imaginary special gear to increase with increasing die chamfer angle, with the horizontal distance of die chamfer being constant. This result can be used to minimize the die roll height of fine blanking gear parts when designing die chamfer of fine blanking tool.

A Study on the Effect of V-Ring Position on the Die Roll Height in Fine Blanking for Special Automobile Seat Recliner Gear

In this paper, the relation between die roll height and V-ring position was studied by fine blanking experiments for imaginary special automobile seat recliner gear. The three die inserts and three guide plate inserts with different V-ring positions were machined, and fine blanking tool was manufactured. Using the fine blanking tool, three experiments were conducted on the 650 ton fine blanking press. Each die roll height was measured, analyzed and we found the tendency of die roll heights on imaginary special gear to increase with increasing the distance between V-ring position and contour of gear. This result can be used to minimize the die roll height of fine blanking gear parts when designing V-ring of fine blanking tool.

Study on the Friction Characteristics for AZ31 Sheet as Various Surface Treatment of SKD11

Abstract The material used is a commercial magnesium based alloy AZ31(Mg-3Al-1Zn) sheet with a thickness of 0.8 mm. Friction tests at various temperatures(R.T. to 200℃) and at various holding forces in the 4 type molds were carried out to investigate the coefficient of friction. A warm drawing process with a local heating and cooling technique was developed in the Mg alloy sheet forming to improve formability because it is very difficult for Mg alloy to deform at room temperature by the conventional method. So, the coefficient of friction at various mold surface treatment conditions in this study was needed to develop the Mg alloy sheet forming technology. Key Words : Coefficient of Friction, AZ31, Holding Force, Warm Drawing 1. 서 론 마그네슘 합금의 경우 가열된 상태에서는 소성가공성이 상당히 향상되는 특성을 갖기 때문에 최근 들어 온간 프레스 금형에 의한 부품 생산이 큰 주목을 받고 있다. 그러나 마그네슘 합금은 상온에서의 소성가공이 좋지 않아 주로 주조 또는 다이 캐스팅에 의해서 제품이 생산되고 있다. 그러나 성형물의 기계적 강도 미흡, 높은 후처리 비용, 박육 제품 성형의 어려움 등의 이유로 그 적용 범위에 제약이 따르는 상황이다. 이와 관련하여 최근 마그네슘 합금 판재의 성형성이 향상되는 온간 성형에 따른 마그네슘 합금 판재의 온간 특성 및 성형성 평가에 대한 연구가 진행되었다. Choo등[1]은 금형의 후처리 및 온도변화에 따른 마그네슘 합금의 성형성을 평가하였고, Kim등[2]은 마그네슘 합금 판재에 대해 온도 및 변형률 속도를 변화 하면서 기계적 물성 및 성형성을 파악을 하였다. 또한 Choi등[3]은 마그네슘 합금 판재 성형성 극대화를 위한 최적의 금형 온도를 구하기 위한 연구를 하였다. 이와 같이 마그네슘 합금의 온간 성형성 및 기계적 물성 파악에 대한 연구는 다양하지만 판재 성형에서의 주요 변수중의 하나인 마찰 특성에 대한 연구는 미흡한 실정이다. 본 논문에서는 마찰 시험기 제작하고 냉간금형 합금공구강인 SKD11 금형을 이용하여 표면처리를 달리한 뒤 마그네슘 합금인 AZ31 시편에 대해 인출속도, 가압력, 금형의 온도 변화에 따라 프레스 성형시 홀더와 다이간에 생기는 Galling 등 모든 변수를 고려한 마찰 특성을 파악하고자 한다. Table 1은 금형 소재인 SKD11 합금 조성표이다.

Study on the Manufacturing of Zirconia Cutting Square Tools by PIM and Hot Isostatic Pressing Process and Test Cutting

The purpose of present study was to increase productivity and to reduce the polution of dust for making of endmill by conventional method such as grinding process. The micro scale endmill manufactured by powder injection molding, the molding (green part) was debinded and sintered. After that decreasing the porosities of the parts sintered, HIP process was adapted. After HIP process the relative density was shown more than 99% of the tools sintered. Finally, the micro cutting experiment using manufactured tool by PIM and HIP were implemented for verifying the feasibility of the tool. The ware of zirconia micro tool was observed very small, but the concentricity is less than the conventional tool made by grinding process. This type of tool is adequate to use in rough milling.

Effect of Melt Treatment on Forming and Brazing Characteristics of 4343/3003/4343 Aluminum Clad Sheet

In this study, it was aimed to investigate the effects of grain refining of 3003 core alloy on forming and brazing characteristics of 4343/3003/4343 aluminum clad sheet. Ti inoculation level was changed up to 0.1wt% by adding Al-10Ti master alloy into 3003 aluminum melt as grain refiner. The three-layer aluminum clad sheets of 0.7 mm thickness were fabricated by hot roll bonding process. The forming and brazing characteristics were evaluated by measuring FLD (forming limit diagram), bonding strength and sagging resistance.

Injection Molding Characteristics of COC and PP in Micro Rib Structure

The demand for the miniaturization and high-precision of machine part has recently increased in new technology like biotechnology(BT) and nanotechnology(NT). The purpose of this study is to analyze the molding characteristics according to injection conditions by measuring the filling height in micro injection molding of the polypropylene(PP) and cyclic olefin copolymer(COC). The result shows that the filling effect of COC is better than that of PP in micro rib structure with injection molding process.