• Design & Manufacturing
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• 제16권3호
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• pp.28-33
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• 2022

The recent increasing application rate of advanced high-strength steel(AHSS) for automotive parts makes it difficult to ensure the durability of forming tools. Significant load and friction generated during the piercing process of AHSS increase the wear rate and the damage degree to dies. These harsh process conditions also yield product failures, such as dimensional inconsistency of pierced holes and insufficient quality of hole's sheared edge. This study analyzed the effect of punch wear on the sheared surface of pierced parts and the forming load during the piercing process. Wear-shaped punches showed approximately 20% higher piercing load than normal-shaped punches, and the rollover ratio of the sheared surface also increased. It is considered that the dull edge of wear-shaped punches does not penetrate directly into the material but shears after tensioning it in a piercing direction. In addition, wear-shaped punches experienced compressive load even after completing the piercing process during the down-stroke and tensile load during the up-stroke. This load variation is related to the smaller diameter piercing holes produced by wear-shaped punches compared to normal-shaped punches. Thus, we demonstrated the predictability of the wear level of dies through a comparative analysis of the piercing load pattern.

• 한국산학기술학회논문지
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• 제16권6호
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• pp.3667-3671
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• 2015

PCB(Printed circuit board) 장착을 주목적으로 하는 포밍공정에서 주름을 발생시키지 않으면서, 실험을 통하여 재료의 두께 변화를 고찰하였다. 실험결과 제 1공정의 포밍 높이는 제 2공정에서의 재료두께 변화에 크게 영향을 미치는 것으로 나타났으며, 제 1공정에서 다이의 입구 모서리는 제품높이 50%정도의 라운드를 가져야 하며, 포밍의 높이는 원래의 제품보다 재료의 두께만큼 높게 하여야 한다. 또한 제 1공정에서 포밍형상을 구현하면 재료의 두께가 85%로 얇아지고 제 2공정에서 리스트라이킹시 재료의 두께가 80%로 얇아진다. 그러므로 정확한 형상을 구현하기 위해서는 재료가 얇아지는 것을 고려하여 다이는 원제품의 형상을 유지하고 펀치는 원제품의 깊이에 재료 두께의 20%이상 더한 값만큼 길이를 길게 하여야 압축의 효과를 얻을 수 있다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.279-284
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• 2005

The casting defects that are caused by molten metal were cold shut formation, entrapment of air, gas, and inclusion. But the control of casting defects has been based on the experience of the foundry engineers. In this thesis, the computer simulation analyzed the flow of molten metal. The quantitative analyses which proposed the effective mold design was executed Flow patterns of 0.15-0.16m/s molten metal in 15 mm thin plate casting were investigated in order to optimize die-casting process. As increasing ingate velocity in thin plate casting, cold shot was decreased. The parameters of runner shape that affected on the optimized conditions that was calculated with simple equation were investigated. These die casting process control techniques of automobile valve body mid-plate have achieved good agreement with the experimental data of tensile strength, hardness test, and material structure photographies satisfactory results.

• Design & Manufacturing
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• 제13권2호
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• pp.17-21
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• 2019

In this study, selective laser sintered 3D printing mold core and metal core were used to investigate the difference of the thickness shrinkage from the gate of the injection molded part at a constant interval. SLS 3D printing mold core was made of nylon-based PA2200 powder and the metal core was manufactured by conventional machining method. As the PA2200 powder material has low strength, thermal conductivity and high specific heat characteristics compared with metal, molding conditions were set with the consideration of molten temperature and injection pressure. Crystalline resin(PP) and amorphous resin(PS) with low melting temperature and viscosity were selected for the injection molding experiment. Cooling time for processing condition was selected by checking the temperature change of the cores with a cavity temperature sensor. The cooling time of the 3D printing core was required a longer time than that of the metal core. The thickness shrinkage of the molded part compared to the core depth was measured from the gate by a constant interval. It was shown that the thickness shrinkage of the 3D printing core was 2.02 ~ 4.34% larger than that of metal core. In additions, in the case of metal core, thickness shrinkage was increased with distance from the gate, on the contrary, in the case of polymer core showed reversed aspect.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 The 8th Asian Symposium on Precision Forging ASPF
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• pp.143-146
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• 2003

In this paper, a new preform design method is proposed to eliminate the excessive flash in metal forging process. After carrying out finite element simulation of the process with an initial billet, backward particle tracing is performed from the outlet of the flash. Then, the region which belongs to the flash is easily found .. The process is analyzed again with the redesigned billet which is removed that region the above mentioned region. The optimal preform shape which minimizes the amount of flash without changing the forgibility can be obtained in several iterations.

• 한국기계가공학회지
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• 제2권3호
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• pp.90-95
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• 2003

The W-EDM is very important In precision machining of die, punch and small parts of precision products, so this machining method is widely used in various fields of industry. In this study, machining characteristics of Hand Drum Form and surface roughness are investigated experimentally. As Hand drum form has great effect on straightness of cut-surface of workpiece, its evaluation is very important in precision cutting. As experimental material, the mold material, STD11 is used and machined by CNC wire-EDM using the 025mm wire in diameter with repeated cutting up to 6 times. The thickness of workpiece is vaned in 20, 40, 60, 80, 100mm Hand drum form and surface roughness are measured after each cutting. Experimental results show that four times-cutting is optimum in the point of hand drum form and surface roughness.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.426-430
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• 2008

Hot shear-welding is a process of bonding two plates together by using shearing stress in a controlled manner. This study dealt with the hot shear-welding process of two aluminum plates. These two plates were piles up in the shear-welding mold. Due to the shearing stress, these two plates were cut off longitudinally, and meantime they were welded together. During this process the control of the surplus material flow is very important, and it can be realized by designing the overlapping length and the shape of the cavity. The commercial software Deform-3D was employed to predict the effect of these two factors. The overlapping length and the shape of the cavity that presents the optimum design was then developed to get a good shear-welding process.

• Journal of Welding and Joining
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• 제34권1호
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• pp.75-81
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• 2016

This study applied laser surface melting process using CW(Continuous wave) Yb:YAG laser and cold-work die steel SM45C and investigated microstructure and hardness. Laser beam speed, power and beam interval are fixed at 70 mm/sec, 2.8 kW and $800{\mu}m$ respectively. Depth of Hardening layer(Melting zone) was a minimum of 0.8 mm and a maximum of 1.0 mm that exceeds the limit of minimum depth 0.5 mm applying trimming die. In all weld zone, macrostructure was dendrite structure. At the dendrite boundary, Mn, Al, S and O was segregated and MnS and Al oxide existed. However, this inclusion didn't observe in the heat-affected zone (HAZ). As a result of interpreting phase transformation of binary diagram, MnS crystallizes from liquid. Also, it estimated that Al oxide forms by reacting with oxygen in the atmosphere. The hardness of the melting zone was from 650 Hv to 660 Hv regardless of the location that higher 60 Hv than the hardness of the HAZ that had maximum 600 Hv. In comparison with the size of microstructure using electron backscatter diffraction(EBSD), the size of microstructure in the melting zone was smaller than HAZ. Because it estimated that cooling rate of laser surface melting process is faster than water quenching.

• 대한안전경영과학회지
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• 제13권4호
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• pp.101-108
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• 2011

In this paper deals with strength of glass fiber reinforced plastics produced by shouting machine was investigated by universal testing instrument. We can obtain following results by performing the strength evaluation of polymer composite material according as varied environment temperature. The effect of environmental temperature on Strength properties was more sensitive in the weld specimen than parent. When changed environmental temperature, variation of strength in the parent was much bigger than it of weld specimen, that is, matrix in the parent, orientation in the specimen ware more sensitive to environmental strength. Tensile strength of polycarbonate matrix was similar regardless of mold temperature.

• 마이크로전자및패키징학회지
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• 제20권4호
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• pp.59-63
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• 2013

In this paper, the impact of the copper densities of substrate layers on IC package warpage is studied experimentally and numerically. The substrate strips used in this study contained two metal layers, with the metal densities and patterns of these two layers varied to determine their impacts. Eight legs of substrate strips were prepared. Leg 1 to leg 5 were prepared with a HD (high density) type of strip and leg 6 to leg 8 were prepared with UHD (ultra high density) type of strip. The top copper metal layer was designed to feature meshed patterns and the bottom copper layer was designed to feature circular patterns. In order to consider the process factors, the warpage of the substrate bottom was measured step by step with the following manufacturing process: (a) bare substrate, (b) die attach, (c) applying mold compound (d) and post reflow. Furthermore, after the post reflow step, the substrate strips were diced to obtain unit packages and the warpage of the unit packages was measured to check the warpage trends and differences. The experimental results showed that the warpage trend is related to the copper densities. In addition to the experiments, a Finite Element Modeling (FEM) was used to simulate the warpage. The nonlinear material properties of mold compound, die attach, solder mask, and substrate core were included in the simulation. Through experiment and simulation, some observations were concluded.