Young Moo Heo

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.

The Cutting Process Monitoring of Micro Machine using Multi Sensor

Recently, the monitoring technology of machining process is very important to improve productivity and quality in manufacturing filed. Such monitoring technology has been performed to measurement using vibration signal, acoustic emission signal and tool dynamometer. However, micro machining is limited small-scale parts machining because micro tool is very small and weakness to generate signal in micro machining process. Therefore, this study has efficient sensing technology for real monitoring system in micro machine that is proposed to supplement a disadvantage of single-sensor by multi sensor. From experimental result, it was evaluated tool wear and cutting situation according to repetitive slot cutting condition and changing cutting condition, and it was performed monitoring spindle rpm and condition according to compare acceleration signal with current signal.

Indirect Prediction of Surface Damage for a Press Die with Wear Characteristics and Finite Element Stamping Analysis

The damage level of the die surface was predicted by estimating the surface roughness with a finite element analysis and the wear characteristics. Wear and friction tests were conducted to compare the wear characteristics for three kinds of surface treatments – CrN, TiAlN and AlCrN coatings. A prediction model was derived from the surface roughness results with respect to contact pressure and sliding speed which were obtained from the wear test. Surface roughness values for the damage regions of the die surface were compared between the experiments and the prediction model, which shows fairly good agreement with each other.

A Comparative Study of Failure Criteria for Magnesium Alloy Sheet under Warm Press Forming Condition

Magnesium sheet alloys possess limited plastic formability at room temperature but their formability is substantially improved at elevated temperatures and optimum strain rates. In the present paper, three different types of failure criteria, namely, strain-based, stress-based, and work-based criteria, are compared for their applicability to warm press forming of magnesium sheet alloys. Warm deep-drawing experiments were conducted on AZ31 alloy sheet, and the results were used to assess the strength and weakness of the failure criteria.

An Experimental Study of V-Ring Position on the Die Roll Height in the Fine Blanking of Special Part with Corner Shapes

In this paper, the relation between die roll height and V-ring position of a fine blanking tool was studied by experimenting on a special part with various corner shapes. Three guide plate inserts with different V-ring positions and a die insert with constant die chamfer were machined, and a fine blanking tool was manufactured for the fine blanking experiments. Three experiments were conducted on a 650-ton fine blanking press. Each die roll height was measured and analyzed. We found the tendency of the die roll heights on the corner shapes of fine blanked parts to increase with increasing the distance between the V-ring position and the contour of the special part, and to decrease with increasing corner radius and angle. These results can be used to minimize the die roll height of fine blanking parts with corner shapes when designing the V-ring of a fine blanking tool.

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.

An Experimental Study on Molding Factor for Spiral Type Micro Injection Product

In recent industry, with the miniaturization and high-precision of machine part, the development of mold manufacturing technology for mass production is accompanied by the development of new technology such as IT and BT In this study, the spiral type injection mold with a thickness is made to. investigating the influence of injection molding parameter and the flow length is measured through an experiment. Besides, Taguchi method is used in this experiment and the obtained data are analyzed using ANOVA method.

Comparison analysis on the properties of the phosphor film according to the various composition ratio of phosphor slurry

The conventional method of making a phosphor layer on the LED package by using a dispensing method is difficult to implement the specific color coordinate, color temperature and optical efficiency because the thickness of the phosphor layer is non-uniform due to precipitation of the phosphor. Besides, the dispensing method consume a large amount of phosphor and silicone to fill the LED package. Thus, studies that manufacture phosphor layer with a uniform thickness such as spray coating, screen printing, electrophoresis are active recently. The purpose of this study is to perform the basic research about the change of the characteristics of phosphor film that is molded with uniform thickness using the phosphor slurry according to various silicone resin and phosphor composition ratio. It is expected to be used as useful information for the fabricating properties when production environment of phosphor layer is changed dispensing method into phosphor film fabrication. In the experiment, it was selected three...

Improvement in mechanical and barrier properties of polyethylene blown films using atomic layer deposition

Recently, thin films deposited on polymer substrates have been widely utilized as encapsulation barriers in electronic applications such as flexible displays, packaging films, and organic light-emitting diodes. The barrier and mechanical properties of these films are critical aspects when using them for protecting the inner modules of electronic devices from environmental factors such as moisture, oxygen, and sunlight. In particular, polymers can be degraded or decomposed more easily than other materials under such environmental conditions. Therefore, polymer films can be deposited using thin functional materials; however, suitable deposition methods for polymers are scarce owing to many limitations such as low melting/glass transition temperature, thermal degradation, and oxidation. In this study, a thin alumina oxide film was deposited on a high-density polyethylene blown film by using atomic layer deposition. The mechanical and barrier properties of the alumina oxide film deposited on the polyethylene ...

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.