• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.33-34
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• 2010

• Transactions of Materials Processing
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• v.19 no.4
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• pp.203-209
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• 2010

In the hot press forming process (HPF), a martensitic structure is obtained by controlling the cooling rate when cooling a boron sheet that is heated up to over $900^{\circ}C$. The HPF process has various advantages such as the improvement in formability and material properties and minimal spring back of the deformed materials. The factors related to the cooling rate depend on the heat transfer characteristics between heated materials and dies. Therefore, in this study, the cooling rate is controlled by adjusting the heat transfer coefficient of the material at the pressing process. And, the mechanical properties and microstructure of the deformed material is demonstrated during the HPF process where cold dies are used to form the heated steel plate. This is achieved by varying the major forming conditions that control the cooling rate regarded as the most important process parameter.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.3
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• pp.130-134
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• 2016

Due to the need for advanced technologies in the automotive industry, the demand for lighter and safer vehicles has increased. Even though various nonferrous metals, like Aluminum, Magnesium and also Carbon Fiber Reinforced Plastic (CFRP), have been implemented in the automotive industry, a lot of technical research and development is still focused on ferrous metals. In particular, the market volume of High Strength Steel (HSS) parts and Ultra High Strength Steel (UHSS) by hot press forming parts has expanded significantly in all countries' automotive industries. A new tool steel, High Thermal-Conductivity Tool Steel (HTCS), for stamping punches and dies has been developed and introduced by Rovalma Company (Spain), and it is able to support better productivity and quality during hot press forming. The HTCS punches and dies could help to reduce cycle time due to their high thermal conductivity, one of the major factors in hot press forming operation. In this study, test dies were manufactured in order to verify the high thermal conductivity of HTCS material compared to SKD6. In addition, thermal deformation was inspected after the heating and cooling process of hot press forming. After heating and cooling, the test dies were measured by a 3D scanner and compared with the original geometry. The results showed that the thermal deformation and distortion were very small even though the cooling time was reduced by 2 seconds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.1-6
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• 2018

Hydro-forming technology has spread dramatically throughout automotive industry over the last 20 years. This technology has many advantages for automotive applications in terms of better structural integrity of the parts, lower cost from fewer parts, material savings, weight reduction, lower springback, improved strength, durability, and design flexibility. In this study, various simulation technologies were developed to investigate the formability of hydro-forming components. Through this technology, to establish the effective forming process for appropriate components design, the bending process, pre-forming process, die closing process, etc. were considered for good forming. This paper proposes the forming amount, section length (corresponding to the hydro-forming press capacity), and minimum curvature (curvature effect evaluation according to the hydro-forming pressure) among the considerations in the design of the hydro-forming part. In addition, a design method is proposed for hydro-forming molding by carrying out cross section analysis of a real sub-frame part for automobiles. The effects of pre-bending, axial feed, hydraulic pressure, press load, and friction among the hydro-forming process parameters were analyzed. Therefore, whether these processes are necessary factors for hydro-forming were examined.

• Transactions of Materials Processing
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• v.19 no.6
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• pp.378-386
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• 2010

Nowadays there has been great interest in using heat treated cast material for press dies due to several advantages like reduction in die production costs. However, in hot press forming processes H13 forged tool steel is mostly used. Cooling performance of dies in hot press forming processes is considered as an important factor of study and also the IHTC parameter between cast material die and sheet metal should be considered as an essential. In the present study, the IHTC was calculated for the sheet metal in the hot press forming process with cast and forged material dies. The temperature measurements were performed for the sheet metal, casting and forged material dies by applying various contact pressure in hot press forming. IHTC was calculated and studied by adopting the inverse heat convection method in DEFORM-2D. Each IHTC was considered as a function of contact time and contact pressure. The experimental data were compared with calculated data obtained from the proposed equation and references.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.539-542
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• 2008

Recently, GMP(Glass Molding Press) process is mainly used to produce aspheric glass lenses. Because glass lens is heated at high temperature above Ty (yielding point) for forming glass, the quality of aspheric glass lens is deteriorated by residual stresses which are generated in a aspheric glass lens after forming. Before this study, as a fundamental study to develop forming conditions for progressive GMP process, compression, strain relaxation and thermal conductivity tests were carried out to obtain the visco-rigid plastic, the visco-elastic and thermal properties of K-PBK40 which is newly developed and applied for precision molding glass material, In this study, using the experimental results we obtained, a glass lens forming 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.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.353-356
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• 2008

Tool design is carried out for a press forming of a cross member in the rear suspension assembly based on the result of the finite element analysis. The analysis simulates the two-stage stamping process with the initial design and it fully reveals the unfavorable mechanism which develops inferiorities during forming. In this paper, a new design guideline is proposed to modify the process and tool shapes for a single-stage forming process. With the improved tool design, this study fabricates prototypes that satisfy the durability requirement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.12
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• pp.3559-3566
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• 2009

Heating and cooling plate are separately used for heating and cooling cast dies for footwear parts. However, this has a disadvantage that it takes a long time to manufacture footwear parts etc.. In the present study, the pipe-inserted cast die for press forming process was proposed to substitute heating and cooling plate. The temperature distribution on the pipe-inserted cast die was analyzed by numerical work using a FEM. And its temperature was measured by LabView. A manufacturing by the pipe-inserted cast die for press forming process was effectively verified, especially in a productivity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.450-453
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• 2009

In order to overcome drawbacks of the advanced high strength steel such as inferior formability and large springback, the hot press forming process(HPF) has been being applied for forming of automotive sheet parts. Good formability and dimensional accuracy without springback as well as good crash performance of final products are the advantages of the HPF process. In this work, a method to characterize the mechanical properties of the HPF steel was developed based on the simple tension test at high temperatures and its finite element analysis, while it was applied to obtain strain rate and temperature dependent flow curves of the HPF steel. The final flow curves were represented by utilizing the Johnson-Cook type equation both in uniform and post-uniform deformation regions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.493-496
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• 2008

The residual stress generated in the boron steel blank formed via hot press forming process was predicted by JMatPro, a material property modeler, and Abaqus. The numerical predictions were compared by the experimental measurements obtained by the instrumented indentation. Both the predicted and measured principal stresses monitored at the outer surface of central bending position were qualitatively in good agreement. It was concluded that the residual stresses generated from hot forming process is not negligible as it has been generally assumed, although the spring back deformation is quite small. This should be specially considered from the part design stage since the tensile nature of the residual stress exhibited on the surface may lead to the stress corrosion cracking.