• Design & Manufacturing
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• v.10 no.2
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• pp.12-17
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• 2016

Recently, lightweight material is attracting attention as a solution to the problem of fuel efficiency and increasing the need for development. CFRP has been attracting attention as lightweight materials for automobile because it has a high specific stiffness and specific strength compared to steel material. CFRP have a wide range of mechanical properties depending on the laminate condition. In this paper, study on the forming analysis of double-dome model was performed considering CFRP prepreg laminate condition and coefficient of friction. After forming analysis, the result has compared with wrinkling area and vertical strain of fiber to the laminated condition. And then compared with inflow of blank to the laminate condition. Through this paper, we propose the forming analysis methods of CFRP material.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.3
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• pp.165-172
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• 2004

Compared with the hydroforming technology for steel, the hydroforming technology for aluminum has not been actively investigated. Recently, the hydroforming of high strength aluminum tubes has attracted great interest because of its good strength to weight ratio. In this study, front side member (FSM) is fabricated with the hydroforming of aluminum tube and the mechanical properties and dimensional accuracy of the hydroformed FSM is investigated. For hydroforming process, extruded aluminum tubes with ribs to improve the structural rigidity are used. To ensure the mechanical properties, the aluminum tubes are T6 heat-treated before hydroforming.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.5
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• pp.100-106
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• 2006

NiTi alloy known as its shape memory effect also has superelastic characteristic, which makes it possible to be elastic under large deformation. Since the tensile strength of the alloy is very high and density is low compared to carbon steel, it can be applied to lightweight structural design. In order to design structures with shape memory alloy, finite element analysis is used and a constitutive algorithm based on Aurrichio's model is added to LS-DYNA as a user subroutine. Explicit time integration and shell element formulation are used to simulate thin-walled structures. The algorithm uses Drucker-Prager type loading condition to calculate martensite volume fraction during the transformation. The implemented algorithm is verified in uni-axial loading condition and martensite phase transformation can be detected well with the algorithm. In this study, as a energy absorbing structure, thin-walled tube is modeled with finite elements and the deformation behavior is studied. Simulation results has shown that the martensite transformation was generated in loading condition. After plastic deformation reached, the load decreases linearly without reverse martensite transformation.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.79-89
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• 2008

With the increased use of surface textured steel sheet in body-in-white assembly, resistance spot weldability of these steels is considered to be an important subject. This study evaluated nugget formation and weldability by measuring dynamic resistance with various weld pressure, current, and weld time for steel sheet with two different surface roughnesses. The surface roughness for T-H steel ($R_{a}=1.70\;{\mu}m$) was higher than that for T-L steel ($R_{a}=1.33\;{\mu}m$), and resulted in increased contact resistance and heating for T-H steel spot welding. Therefore, at low weld current and weld cycle ranges, the T-H steel showed better weldability over the T-L steel. The evaluations of weld interface showed that the fusion zone in the T-H steel sheet was continuous in contrast to discontinuous fusion zone for T-L steel sheet at the same welding conditions. A comparison of dynamic resistance and tensile-shear strength (TSS) between T-H and T-L steel sheet suggested that high surface roughness provided larger heating at early cycle of welding and larger TSS.

• Journal of Welding and Joining
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• v.31 no.4
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• pp.17-22
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• 2013

The excellent beam quality of high power fiber lasers are commonly used for remote welding applications in body job applications. The Welding speed and productivity is unmatched with any other welding technology including resistance spot welding or traditional laser welding. High tooling cost for clamping and bulky safety enclosures are obstacles which are limiting the use. With the newly developed Laser stitch welding gun we have an integrated clamping in the process tool and the laser welding is shielded in a way that no external enclosure is needed. Operation of this laser welding gun is comparable with resistance spot welding but 2-times faster. Laser stitch welding is faster than spot welding and slower than remote welding. It is a laser welding tool with all the laser benefits like welding of short flanges, weld ability of Ultra High Strength steel, 3 layers welding and Aluminium welding. Together with low energy consumption and minimum operation cost of IPG fiber laser it is a new and sharp tool for economic car body assembly.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.18-22
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• 2015

The importance of emotional quality of car is getting higher in these days. Noise takes great portion in emotional quality because it is detectable problem with just a few rides. The sources of car noise during operation are various and the related technical issues are vast. Sometimes weldments of auto body are referred as the source of noise and the suspicious weldment shows unsatisfactory welding quality in most cases. In this research, cases of noise making weldments are investigated to figure out the solution for welding quality improvement. They are categorized into several groups in according to the inferred types of the error source then appropriate solutions are suggested. Auto body has weldments of resistance spot welding and gas metal arc welding in general. Therefore the solutions are suggested as adjustment of welding process variables and related machineries. Inevitable error source is also referred which is originated from thermal expansion rate difference between ultra high strength steel and mild steel. This new approach is validated through simple calculation then more concrete investigation with numerical analysis is remained as further works to be done.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.353-359
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• 2010

For achieving economical fuel consumption, an increase in the load bearing capacity, and for environmental conservation, there is a constant demand for lightweight frames of commercial vehicles used in the transportation industry. In this study, a structural analysis of the frame of a heavy flat-bed trailer was performed to determine the optimal design of a new lightweight frame made of high-strength steel. To identify the key design parameters of the trailer frame, Taguchi's orthogonal array was used in the experiments. Using ANSYS, a commercial FEA program, the frame structure was optimized with respect to stress, deflection, and torsional stiffness by performing stress and vibration analyses. A physical model of the trailer was also built to verify the validity of the numerical analyses. Finally, an on-road fatigue test of the new lightweight frame made of the high-strength steel, ATOS80, was performed to confirm the durability of the new design.

• Journal of Welding and Joining
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• v.31 no.2
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• pp.30-36
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• 2013

Recently the use of ultra high strength steels(UHSS) in structural and safety component is rapidly increasing in the automotive industry. Furthermore, it commonly use in tailor welded blank laser welding process before hot stamping to reduce lightweight vehicle. However TWB process is to be a problem about welded strength after hot stamping because it's welded before heat treatment. Therefore, in this study, laser welds of TWB after heat treatment were analyzed for changes in the characteristics, especially the impact on the oxidation and decarburization in order to prevent pre-coated Al-Si layer welds on the properties for intensive investigation. As a result, the degradation of the TWB weldments changes in the heat treatment conditions alone, without any pre-treatment of the coating layer has confirmed that there is a limitation on the improvement. Furthermore Al-Si elements are overall distributed on the weldment and it specially concentrated along the fusion line. Hardness value of Al-Si segregation area is less than 350Hv and tensile strength showed just 78~83% compared with substrate. Accordingly, we proved that both side Al-Si coating should be removed in order to ensure the strength of the substrate.

• Design & Manufacturing
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• v.12 no.3
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• pp.25-30
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• 2018

Recently The automotive industry is trying to increase the energy efficiency by reducing the weight of the car body and engine components as a way to achieve high energy efficiency. In particular, the reduction of the weight of the vehicle through the weight reduction of the vehicle body has the advantage that the fuel consumption and the output can be improved. But at the same time, there is the disadvantage that the strength becomes weak due to the reduction of the material thickness. Therefore, in order to overcome these disadvantages, materials with high strength according to the unit thickness have been actively developed, and researches for applying them have also been increasing. In this study, we will investigate the application of cold rolled steel sheet, which is a lightweight material, to a horn bracket that secures a installed in an automobile engine room. The horn bracket secures the horn on the car engine and is bolted to the outer wall of the engine. The momentum is acted on the bracket due to the distance between the bolt fastening part and the car horn installed on the bracket end side. Therefore, the body part of the bracket is more likely to be destroyed by the influence of the continuous stress. In this paper, design optimization for weight reduction and strength enhancement was performed to solve this problem, and possibility of applying the rolled steel sheet material as lightweight material by tensile test and fabrication was confirmed.

• Journal of the Korean Society for Heat Treatment
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• v.29 no.3
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• pp.103-108
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• 2016

In recent years, TRIP steels which are composed of ferrite, bainite, and retained austenite have drawn much attention for automotive sheets due to excellent combination of strength and ductility. The effect of two-step isothermal heat treatment of bainitic transformation on microstructures, especially retained austenites and tensile properties in the conventional TRIP steel was investigated. A two-step isothermal heat treatment, in which 50% bainitic transformation occurred at high temperature, followed by bainitic transformation at low temperature, improves tensile properties, resulting from enhanced mechanical stability of retained austenite against external plastic deformation due to refinement of retained austenites, compared to single-step isothermal heat treatment.