• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.6
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• pp.1490-1500
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• 1995

Compression molding of SMC (Sheet Molding Compound) in a thin plaque with substructures like a rib is involved with the formation of surface defect along the centerline over the rib area called by sink mark depending on process parameters. The surface quality of the external panels in automotive manufacturing is so critical that this kind of defect should be eliminated during manufacturing stages. The effect of process parameters on sink mark formation and the distribution of chopped fiberglasses in the compression molded thin plaque with a rib was experimentally investigated in the present study. In order to estimate the effect of the molding parameters such as molding temperature, mold closing speed, depth of the rib, corner radius of the rib, and final molded part thickness of flat portion on the depth of sink mark and the distribution of fiberglasses in the molded SMC part with the rib under the present experimental conditions, the molding parameters used in experiments were non-dimensionalized equation for predicting the depth of sink mark was determined through dimensional analysis based on the experimental data. The orientation and distribution of fiberglasses and fillers which directly affect the formation and depth of sink mark were investigated by taking the photographs of the cross-sectional area of the molded specimen using scanning electron microscope. The experimental results proposed from this investigation are useful in understanding the formation of sink mark and predicting the depth of sink mark in compression molding of SMC with substructures.

• Design & Manufacturing
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• v.2 no.2
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• pp.33-37
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• 2008

This paper describes the optimization of injection molding conditions to minimize sink marks. Sink marks, which refer to a small depression on the surface opposite a thick wall thickness, are often encounted in injection molded plastic parts. Part geometry, material properties and processing conditions during injection molding can affect the sink mark depth. We designed the runner system which is possible balanced filling to cavities using CAE program and then obtained optimal processing conditions by Taguchi's Robust Design technique. By actual injection molding using optimized mold and molding conditions, it confirmed that sink mark depth decreased zero compared to 1mm level in the conventional mold and process.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.7
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• pp.111-115
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• 2008

This paper describes the optimization of injection molding conditions to minimize sink marks. Sink marks, which refer to a small depression on the surface opposite a thick wall thickness, are often encounted in injection molded plastic parts. Part geometry, material properties and processing conditions during injection molding can affect the sink mark depth. We designed the runner system which is possible balanced filling to cavities using CAE program $Moldflow^{TM}$ and then obtained optimal processing conditions by Taguchi's Robust Design technique. By actual injection molding using optimized mold and molding conditions, it confirmed that sink mark depth decreased zero compared to 1mm level in the conventional mold and process.

• Design & Manufacturing
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• v.6 no.2
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• pp.1-5
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• 2012

Weld line in injection molded part is one of the defects in injection molding process. Weld line deteriorates not only appearance quality but mechanical property. In this study, ABS and PP were used as experimental materials. And weld line length, depth and strength have been examined according to the injection molding conditions. As the results of experimental studies, weld line length increased as flow rate increases for all materials. And the flow rate is most influenced to the creation of weld line length. Also weld line strength increased, as flow rate and melt temperature increase for all materials. The whole experiment results was similar to CAE analysis results.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.115-119
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• 2008

Weld line in injection molded part is one of the defects in injection molding process. Weld line deteriorates not only appearance quality but mechanical property. In this study, ABS and PP were used as experimental materials. And weld line length, depth and strength have been examined according to the injection molding conditions. As the results of experimental studies, weld line length increased as flow rate increases for all materials. And the flow rate is most influenced to the creation of weld line length. Also weld line strength increased, as flow rate and melt temperature increase for all materials. The whole experiment results was similar to CAE analysis results.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.149-153
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• 2008

The cavity of mold is exposed to high pressure during injection molding operation. Injection molded articles with deep depth are often demanded as design variety increases. Mold becomes weak and deformation increases as the mold depth increases. Thus the injection molds for deep depth articles should be designed to hold out high pressure or stress and large deformation. Through this study, equation for mold design was examined and suggested novel method to determine equation for mold design with deep depth. Novel equation developed in this study was consisted with cantilever and two points bending while previous equation was modified from just cantilever bending. The validity of novel equation was verified through computer simulation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.200-203
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• 2001

Micromolding methods such as micro-injection molding and micro-compression molding are most suitable for mass production of plastic micro-optics with low cost. In this study, plastic micro-optical components, such as refractive microlenses and diffractive optical elements(DOEs) with various grating patterns, were fabricated using micro-compression molding process. The mold inserts were made by ultrapricision mechanical machining and silicon etching. A micro compression molding system was designed and developed. Polymer powders were used as molded materials. Various defects found during molding were analyzed and the process was optimized experimentally by controlling the governing process parameters such as histories of mold temperature and compression pressure. Mim lenses of hemispherical shape with $250{\mu}m$ diameter were fabricated. The blazed and 4 stepped DOEs with $24{\mu}m$ pitch and $5{\mu}m$ depth were also fabricated. Optical and geometrical properties of plastic molded parts were tested by interferometric technique.

• Design & Manufacturing
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• v.6 no.1
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• pp.5-11
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• 2012

The sink mark on boss parts is generated by the volumetric shrinkage that is caused by both the molding thickness and the boss wall thickness. The volumetric shrinkage is caused by packing pressure and its amount tends to decrease by increasing the packing pressure. The packing pressure can therefore increase the flow rate to a boss part and causes the depth of sink mark to increase. As the molding thickness and the boss wall thickness in the boss part can increase the part volume, these may yield bad solidifying and also extend the molding cycle. In this paper, both the injection molding test and the flow analysis were carried out to investigate the effect of sink mark that was generated in the boss wall thickness of injection molded products. The sink mark could also be caused by thickness ratio of boss part. For a given thickness ratio of boss, several molding process parameters such as packing pressure, packing time and melt temperature, affecting to generation of the sink mark were discussed.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.103-109
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• 2008

The sink mark on boss parts is generated by the volumetric shrinkage that is caused by both the molding thickness and the boss wall thickness. The volumetric shrinkage is caused by packing pressure and its amount tends to decrease by increasing the packing pressure. The packing pressure can therefore increase the flow rate to a boss part and causes the depth of sink mark to increase. As the molding thickness and the boss wall thickness in the boss part can increase the part volume, these may yield bad solidifying and also extend the molding cycle. In this paper, both the injection molding test and the flow analysis were carried out to investigate the effect of sink mark that was generated in the boss wall thickness of injection molded products. The sink mark could also be caused by thickness ratio of boss part. For a given thickness ratio of boss, several molding process parameters such as packing pressure, packing time and melt temperature, affecting to generation of the sink mark were discussed

• Transactions of Materials Processing
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• v.20 no.3
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• pp.250-256
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• 2011

Vacuum-assisted thermoforming is one of the critical steps for the successful application of film insert molding(FIM) to parts of complex shapes. If the thickness distribution of the formed film is non-uniform, cracking, deformation, warping, and wrinkling can easily occur at the injection molding stage. In this study, the effects of processing parameters, which include the film heating time, plug depth, plug speed and vacuum delay time, on film thickness distribution were investigated. It was found that the film thickness at the part sidewall decreases with increasing the film heating time and plug depth, but the thickness at the bottom was found to exhibit the opposite behavior. The film thickness of the sidewall was observed to increase at higher plug speed and vacuum delay time of 0 ~ 0.3sec.