Sung Woon Cha

Influence of mould temperature on the thickness of a skin layer and impact strength in the microcellular injection moulding process

The thickness of a skin layer on the parts made by a microcellular injection moulding process may influence its properties, including impact and tensile strength, density and sound transmission. Therefore it is necessary to study the variations in skin layer thickness with processing parameters. In this paper, the influences of temperatures in the mould cavity on the skin layers thickness are addressed. In addition, the relationship between the temperature distributions across the cavity of the mould, with impact strength on parts made using a microcellular injection moulding process, was addressed. *TSL, the temperature at which the skin layer forms, was proposed. According to previous studies, TSL is expected to be similar to the polymer melting point for semi-crystalline polymer and the glass transition temperature for amorphous materials. In addition, a method to predict variations in skin layer thickness with mould temperature is discussed.

Performance enhancement of an ionic polymer metal composite actuator using a microcellular foaming process

Recently, the study of electroactive polymers that can be operated by electrical energy has attracted a great deal of attention. One type of electroactive polymer consisting of ionic polymer metal composites (IPMCs) is important because of its low driving voltage and fast response time, but the driving force gives limitations to the characteristics of IPMCs. In this research, we developed a high-performance IPMC using a new manufacturing process through a microcellular foaming process. Nafion (ionic polymer) films, foamed using a microcellular foaming batch process, and un-foamed Nafion films had a uniform thickness of platinum (Pt) deposited on them by electroless plating. To evaluate performance of the fabricated IPMCs, we tested changes in blocked force and free bending displacement of an IPMC actuator according to changes in applied voltage, water content and thickness of the sample. The foamed IPMC (fIPMC) actuator demonstrated 50% increased free bending displacement and twice larger blocked force than the normal (non-foamed) IPMC actuator. This result shows that the feasibility of attaining the same performance as a non-foamed IPMC with a lower applied voltage and of developing higher-performance IPMC actuators. Thus, we show the possibility of high-performance fIPMC actuators that may be useful in various fields.

The Effect of Microcellular Plastics on Light Transmission

There has been rapid progress in the industrial application of high-molecular-weight materials. Plastics, in particular, are in wide demand owing to their low prices and high performance. With the likely exhaustion of their petroleum raw materials, more effective ways of utilizing plastics are being sought. The microcellular foaming (MF) process has proved a growth industry. It enables a considerable reduction in the amount of plastic used, while preserving its desirable mechanical properties. A major advantage of the MF process is in the production of lightweight products. This study examined the optical properties of MF plastics that become white on foaming. This alters the optical properties of the parent plastic, such as from semitransparency to opacity, with a direct reduction in light transmission. A series of experiments that show the quantitative changes in light transmission that occur on microcell generation in polyethylene terephthalate (PET) and polycarbonate (PC) are reported.

Improvement of the Mechanical Properties of Biodegradable Polymers Using a Microcellular Foaming Process and Natural By-Products

Biodegradable plastics based on biomass are currently the subject of active research. However, they have shortcomings that include weak mechanical properties and high prices. Therefore we added wood powder and rice bran, which are generated as by-products from natural raw materials. In addition, a microcellular foaming process was applied to form pores inside the plastics. Various coupling agents were assessed and compared, and appropriate coupling agents were selected for each polymer. In addition, we studied the effect of porosity and natural by-product content on the mechanical properties of the biodegradable plastics. We also confirmed that environmentally friendly plastics could be made lighter and their mechanical strength could be improved through the addition of by-products from natural raw materials.

Parameter Design of a Coaxial Cable Insulation Manufacturing Process Using Axiomatic Design and the Taguchi Method

In modern industries, the development of communication mediums requires high-frequency communication networks in which signal reduction by dielectric loss is increased. Accordingly, the need for an insulator with low permittivity also has grown, making the production of highly foamed insulators now necessary. Considering the mechanical and electrical properties of such insulators, benefits can be seen in multiresponse problems with higher densities of uniform-specific cell size. In this paper, we describe the applicability of a highly foamed polyolefin extrusion process to the manufacturing of insulation for coaxial cable. Moreover, a combination of axiomatic design and the Taguchi method was utilized for solving the multiresponse problem. Through this technique, we propose a new method for optimizing multiresponse problems. Development of manufacturing processes for insulating coaxial cable, and responses for each process variable, become possible with this method.

Development of a Multilayered Optical Diffusion Sheet Using Microcellular Foaming Technology

The superior optical performance of a sheet developed using microcellular foaming technology is demonstrated through the development and commercialization of a reflector. In this study, the cell morphology characteristics of reflectivity, transmittance, and haze were analyzed to develop diffusion sheet. A basic concept of a multilayered diffusion sheet was derived using axiomatic design, and the design was tested and validated using a microcellular foaming batch process. Diffusion sheet transmittance and haze values were compared with commercialized products. The results show the multilayered diffusion sheet manufactured using a microcellular foaming process increased transmittance by 40% compared to that of existing products.

A Study on Optimizing the Mechanical Properties of Glass Fiber-Reinforced Polypropylene for Automotive Parts

Many currently produced plastic automotive parts use glass fiber reinforced plastic for enhanced strength and reduced vehicle weight. Apart from glass fiber, there are many manufacturing process factors concerning the production of the glass fiber reinforced plastic parts and their characteristics. This paper employed Taguchis method, a correlation analysis, and an axiomatic design to study the optimizing process for glass fiber-reinforced plastic parts. The major factors affecting the characteristics of the plastic-based automotive parts were determined, and the optimal conditions for the parts were deduced.

Changes in the Reflectivity and Color Characteristics of Microcellular Foamed Plastics

As the use of plastics has increased in various industries, research on microcellular plastics has increased as well. The microcellular foaming process helps produce lighter plastic and reduces material consumption. This process also affects the optical properties. The primary purpose of this study is to measure the visible changes occurring in polymer samples by comparing changes in the samples before and after the microcellular foaming process. To measure the changes in color characteristics, colored PC samples were utilized for the experiments. Changes in the color characteristics were indicated using the Munsell color system.

Conceptual Design of Microcellular Plastics Bumper Parts Using Axiomatic Approach

Society is increasingly demanding automobiles centered on environmental factors and fuel efficiency. Accordingly many studies have examined the use of Al, Mg and composites for lightweight automobiles. We implemented a microcellular plastic (MCP) designed for a lightweight automobile using axiomatic design. The results show that the physical properties of MCPs are most affected by the size and uniformity of the MCPs, and that a weight reduction of about 15% is possible by applying MCPs to bumper covers. In conclusion, the MCP bumper design was proved to be a decoupled design, demonstrating the applicability of MCPs to bumpers.

Studies of the Variation in the Dielectric Constant and Unique Behaviors with Changes in the Foaming Ratio of the Microcellular Foaming Process

MCPs have many advantages, such as favorable mechanical, optical, acoustical, and electrical properties due to the size of the cells. Porous plastics also share the advantages of plastics processed by existing conventional foaming technologies. This study focuses on the electrical properties by examining the variation of the dielectric constant. Samples with different foaming ratios were created. Tests in this research proved that the dielectric constant was inversely proportional to the foaming ratio. In some cases, however, an inverse proportion was not observed. Therefore, this study investigated the characteristics and cell morphology of the MCPs to reveal the factors influencing.