• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.6
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• pp.201-208
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• 2013

Recently, there has been an active study about weight reduction for automotive. This study is prediction and evaluation of one pice type steering component, which is universial joint. Steering system is a core of major safe device in vehicle. Universial shaft adopted in steering system transmit steering torque between olumn and steering gear. Conventional universial shaft is produced by welding process because of geometric complexity. But welding process has some weakness such as deflection on surface, residual stress, and deteronration of material properties so it can deteriorate durability of vehicle.

• Proceedings of the KWS Conference
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• 2008.05a
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• pp.36-36
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• 2008

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.274-276
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• 2006

Weldability of high Cr ferritic steel for $620^{\circ}C$ grade turbin casing were investigated. The effect of carbon content on the cold and hot cracking susceptibility and HAZ softening was determined. The cast steel with higher carbon content showed higher HAZ hardness because of the dissolution of cabonitrides during welding thermal cycle. Moreover, it showed higher solidification cracking sensitivity because of the little S-ferrite formation in weld metal. Both steels showed HAZ softening at $900^{\circ}C$ peak temperature after PWHT.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.610-615
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• 2016

Diverse accessories are used in automobiles, such as navigation systems, front and rear cameras, spoilers, and sun visors. Sun visors block sunlight so that drivers can drive safely with a better view, and they are used in many automobile designs. However, when large plastic products are manufactured using injection molding, there are many difficulties that develop, like weld lines, short shots, flow marks, imperfections, and distortion. In this study, a CAE simulation was conducted based on previous results to predict potential problems in the injection molding of large products. The flow characteristics up to complete charge for the melting resins were captured using a computer-aided engineering simulation. The temperature departure on the front part of a flow was about $10^{\circ}C$ and very stable. The practical ejecting time of the cold runner was about 70 seconds in the simulation. Finally, the capability of a suitable injection machine was calculated and recommended by prediction of the injection pressure and the die clamping force.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.80-84
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• 2011

The weight reduction of the transportations has become an important technical subject Al and Al alloys, especially Al 5052 alloys have been being applied as door materials for automobile. One of the most widely known car weight-reduction methods is to use light and corrosion-resistant aluminum alloys. However, because of high electrical and thermal conductivity and a low melting point, it is difficult to obtain good weld quality when working with the aluminum alloys. Also, Pulse MIG welding is the typical aluminum welding process, but it is difficult to apply to the thin plate, because of melt-through and humping-bead. In order to enhance weld quality, welding parameters should be considered in optimizing the welding process. In this experiment, Al 5052 sheets were used as specimens, and these materials were welded by adopting new Cold Metal Transfer (CMT) pulse process. The proper welding conditions such as welding current, welding speed, torch angle $50^{\circ}$ and gap 0~1mm are determined by tensile test and bead shape. Through this study, range of welding current are confirmed from 100A to 120A. And, the range of welding speed is confirmed from 1.2m/min to 1.5m/min.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.3
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• pp.120-126
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• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range$({\Delta}K)$ region and faster in high ${\Delta}K$ region than that of the base metal specimens.

• Journal of Welding and Joining
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• v.31 no.1
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• pp.51-57
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• 2013

Residual stress caused in the weldments with high restraint force are often observed during welding in the weldments of Inner and outdoor materials or radial tanks. The reason is that quantitative analysis about thermal stresses during laser welding is lacking for this weldments. To verify Finite Elements Method (FEM) theory, the temperature was measured with thermocouple in a real time in this paper. Also analysis of the thermal stress for welding condition is performed by Comsol program package on various welding condition in SCP1-S butt welding. The principal stress in laser welding process is seen through the width direction. Also, it was confirmed that a change in base metal by thermal expansion made the stress in width direction stronger. Base metal close to the weld bead as the process progresses to the tensile stress in the compressive stress was varied. It was shown that the change of stress was quantitative from the bead at a certain distance.

• Journal of Welding and Joining
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• v.33 no.5
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• pp.53-60
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• 2015

Laser surface Melting Process is getting hardening layer that has enough depth of hardening layer as well as no defects by melting surface of substrate. This study used CW(Continuous Wave) Yb:YAG and STD11. Laser beam speed, power and beam interval are fixed at 70mm/sec, 2.8kW and 800um respectively. Hardness in the weld zone are equal to 400Hv regardless of melting zone, remelting zone overlapped by next beam and HAZ. Similarly, microstructures in all weld zone consist of dendrite structure that arm spacing is $3{\sim}4{\mu}m$, matrix is ${\gamma}$(Austenite) and dendrite boundary consists of ${\gamma}$ and $M_7C_3$ of eutectic phase. This microstructure crystallizes from liquid to ${\gamma}$ of primary crystal and residual liquid forms ${\gamma}$ and $M_7C_3$ of eutectic phase by eutectic reaction at $1266^{\circ}C$. After solidification is complete, primary crystal and eutectic phase remain at room temperature without phase transformation by quenching. On the other hand, microstructures of substrate consist of ferrite, fine $M_{23}C_6$ and coarse $M_7C_3$ that have 210Hv. Microstructures in the HAZ consist of fine $M_{23}C_6$ and coarse $M_7C_3$ like substrate. But, $M_{23}C_6$ increases and matrix was changed from ferrite to bainite that has hardness above 400Hv. Partial Melted Zone is formed between melting zone and HAZ. Partial Melted Zone near the melting zone consists of ${\gamma}$, $M_7C_3$ and martensite and Partial Melted Zone near the HAZ consists of eutectic phase around ${\gamma}$ and $M_7C_3$. Hardness is maximum 557Hv in the partial melted zone.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.693-700
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• 2012

In this study, the Charpy impact test along with metallurgical observation was conducted to evaluate low temperature impact toughness of structural steel welds with different welding processes to find out the optimal welding process to guarantee the required impact toughness at low temperatures. The welding processes employed are shield metal arc welding (SMAW) and flux cored arc welding(FCAW), which are commonly used welding methods in construction. The Charpy impact test is a commercial quality control test for steels and other alloys used in the construction of metallic structures. The test allows the material properties for service conditions to be determined experimentally in a simple manner with a very low cost. To investigate the impact toughness at low temperatures of the steel welds, specimens were extracted from the weld metal and the heat affected zone. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The low temperature impact performance was evaluated based on the correlation between the absorbed energy and the microstructure. Analysis of the results showed that the optimal welding process to ensure the higher low temperature impact toughness of the HAZ and the weld metal is SMAW process using the welding consumable for steels targeted to low temperature use.

• Journal of Welding and Joining
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• v.34 no.1
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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.