• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.1
• /
• pp.105-112
• /
• 2010

Weldlines are generated during the injection molding process when two or more melt flows are brought into contact. The weldlines are unavoidable in the cases of presence of holes or inserts, multi-gated delivery systems, significant thickness change, etc. At the welded contact region, a 'V'-shaped notch is formed on the surface of the molded part. This 'V'-notch deteriorates not only surface appearance but also mechanical strength of the molded part. To eliminate or reduce weldlines so as to improve the weldline strength, the mold temperature at the corresponding weld locations should be maintained higher than the glass transition temperature of the resin material. The present study implements high-frequency induction heating in order to rapidly raise mold surface temperature without a significant increase in cycle time. This induction heating enables to local mold heating so as to eliminate or reduce weldlines in an injection-molded plastic part. The effect of induction heating conditions on the weldline strength and surface appearance of an injection-molded part is investigated.

• Design & Manufacturing
• /
• v.7 no.1
• /
• pp.60-63
• /
• 2013

Recently, Silicone that one of the thermo-sets is used to making optical products such as LED lenses because of excellent thermal properties. LED lenses are required to keep the precise dimensions, so they must be molded to have the minimum deformation. Thermo-sets have the expansion characteristic on the part of thermal property, it is important to optimize the cure condition so that the deformation of the part become minimum. In this study, to investigate the relationship between the shrinkage by the curing and expansion by the thermal properties of the resin, reactive injection experiment was performed by setting the variables such as mold setting temperature, cure time. As a result, it was confirmed that there was a interval while the thermal properties were transferred to more active during the cure process. It is expected to help in determining the reactive injection molding conditions of the thermo-set parts as well as LED lens in order to reduce the amount of deformation.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.2
• /
• pp.185-192
• /
• 2012

The paper presents the development of a cooling circuit design system that automatically creates 3D cooling circuit on a given section plane conforming to design specifications, generates 3D solid model of cooling line segments defined on a 2D sketch plane, and verifies interference of 3D cooling channel with the molding die surface. The system was developed mainly for designing plastic injection molding die of vehicular lamp, which helps the mold designer to rapidly construct cooling circuits but also reduce designer's unintended mistakes by conforming to the dimensional design specifications. It is used by an injection molding die manufacturing company in Korea, and reported approximately 20% reduction of cooling channel design time.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2002.02a
• /
• pp.253-259
• /
• 2002

Micro cell structures with high aspect ratio were fabricated by injection molding method. The mold inserts had dimension $1.9cm\times8.3cm$ composed of a lot of micro posts and were fabricated by LIGA process. The size of the micro posts was $157{\mu}m\times157{\mu}m\times500{\mu}m$ and the gaps between two adjacent posts were $50{\mu}m$. Using Polymethylmethacrylate (PMMA) injection molding was performed. The key experimental variables were temperature, pressure, and time. By controlling these, good shaped mim cell structures with $50{\mu}m$ in wall thickness and $500{\mu}m$ in depth were obtained. In order to understand micro molding mechanism, shape changes of molded PMMA were studied with experimental variables. And the durability of mold insert was investigated, too. The results show that the most important factor in molding processes was the mold temperature that is closely related to the filling of the melt into the micro cavity. And the holding time before cooling showed a great effect on the quality of molded PMMA.

• Journal of the Korean Society of Industry Convergence
• /
• v.4 no.3
• /
• pp.267-273
• /
• 2001

In this study, the survival rate of fiber is investigated by nozzle size difference in injection/mold sides. The survival rate of fiber is influenced about the nozzle size differ. Also, The mechanical properties of short carbon glass fiber reinforced polypropylene are experimentally measured as functions of fiber volume fraction and nozzle size difference. These mechanical properties are compared with the survival rate of fiber and fiber volume fraction using image analysis after pyrolytic decomposition. The survival rate of fiber as well as fiber volume fraction is influenced by injection processing condition, the used materials, mold conditions and nozzle sides difference, etc, In particular, the survival rate of fiber is great influenced when injection/mold nozzle sides are different more than that of the same. Consequently, the mechanical properties of short carbon/glass fiber reinforced polypropylene arc improved as the nozzle sides are the same in injection mold sides.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.4 s.97
• /
• pp.110-115
• /
• 1999

The surface gloss of an injection molded part is one of the most significant point for evaluating the quality of products appearance. The effects of process condition on the gloss of ABS(Acrylonitrile-Butadiene-Styrene) molded part were investigated in this work. The measurements of gloss and morphology on the surface of molded part were carried out with different melt temperature, mold temperature, mold surface roughness, injection pressure and holding pressure. Gloss had a maximum value with melt temperature in the range of 210 to 220 ${^\circ}C$ and with mold temperature 40 to 50${^\circ}C$ and with injection pressure 80~90 MPa, respectively. Melt temperature was shown to have the largest effect on gloss in our work. Gloss was not improved in the region of melt temperature 240${^\circ}C$ above and of mold temperature 60${^\circ}C$ above. It was concluded that the variation of gloss was mainly caused by rubber particles migration under shear stress not by their aggregation or necklace.

• Design & Manufacturing
• /
• v.11 no.3
• /
• pp.1-7
• /
• 2017

The fabrication process of micro pattern structure with high precision and high aspect ratio using powder injection molding (PIM) is developed. In the PIM process, the metal powder is mixed with the binder systems and the mixture is injected into the metal mold. The injection molded green parts are debinded and sintered to reach final shape and properties. In this method, the optimization of physical properties such as fluidity and strength of the binder system is essential for perfect filling the high aspect ratio micro-pattern. For this purpose, the correlation between the properties of the binder system and feedstock and ${\mu}-PIM$ process was investigated, and a binder system with low viscosity at low temperature(about $110^{\circ}C$) and high strength after cooling was investigated and applied. Employing this process, high precision parts with line type micro pattern structure which has pattern size $160{\mu}m$ and aspect ratio more than 2 can be manufactured.

• Design & Manufacturing
• /
• v.9 no.2
• /
• pp.30-33
• /
• 2015

In injection molding, many kinds of defects have occurred because of a characteristic of plastics injection molding. Weld line is one of the defects is formed when separated melt fronts recombine together during the mold filling stage. That is one of problems in injection molding. Weld lines in the appearance of plastics parts can deteriorate visible quality. And most importantly, the local mechanical strength in the weld line area can be significantly weaker. It could be one of the most problems for structural applications. In this study, the mold available two-shot-molding of same polymers have been designed, and a series of experiment about tensile strength in weld line area has been conducted using Taguchi's design of experiment to optimize injection molding conditions decreasing of weld strength and find out a factors affected weld strength in two-shot- molding.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.18 no.6
• /
• pp.76-81
• /
• 2019

In the mold-manufacturing field, various methods of advanced production technology are being used in the production of industrial-grade gear pulleys. Among the current methods are injection molding, hoop molding, insight molding, two-material molding, compound-mold molding, as well as engineering plastic mold. Currently, casting pulleys are inexpensive because they are produced in small quantities. However, they produce complications during the manufacturing process, are very unreasonable for mass production, and are disadvantageous in cost competitiveness. Pulleys are divided into hundreds of kinds and thousands of kinds, so the production methods vary. As these pulleys are made of a single material by a casting and welding method, they are not manufactured using injection molds consisting of different materials. In this research, pulleys, shafts, and reinforced plastic materials were incorporated using ANSYS software, and a low-cost, lightweight technology was applied for trial production with optimum design and extrusion technology.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2010.11a
• /
• pp.283-284
• /
• 2010