• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.1
• /
• pp.58-65
• /
• 2010

For the improvement of fuel consumption, the study on the use of lightweight material or thinner sheet have been carried out in automotive industry. With the need for the use of thinner sheet, the dent resistance became one of the major concern in th design of exterior panels in automotive industry. Many studies have been carried out for the dent resistance by experiment or quasi-static numerical simulation. In this study, the dent formation behavior is investigated by dynamic finite element analysis using ABAQUS. Dent formation may be affected by many factors such as sheet thickness, material properties, pre-strain, and sheet curvature. The effect of these factors on dent resistance is investigated. From the analysis following three conclusions are derived. First, dent resistance become hard as the sheet curvature radius increases. Second, dynamic dent resistance is mainly affected by bending stress rather than tensile stress. Third, the pre-strain itself do not give any guidance for dynamic dent resistance and dynamic dent resistance have to be decided considering the strain hardening and thickness reduction together. The results are considered to be reliable and useful to improve the dent damage of automotive panels.

• Transactions of Materials Processing
• /
• v.23 no.1
• /
• pp.23-28
• /
• 2014

The aspect ratio of a hole is defined as the ratio of the thickness to the diameter of the sheet metal. Most holes in the sheet metal industry are made by piercing. However, for thick sheets, which have an aspect ratio greater than 2, a machining process like drilling instead of piercing is usually used to make holes. In the current study, piercing, which is a shearing process, is evaluated to punch a hole with a high aspect ratio by using a newly designed die set-up. The piercing die was manufactured to prevent the punch from buckling and also to improve the alignment between the die components. An aluminum alloy sheet was selected for the experiments. The influence of several process parameters such as sheet thickness, clearance and stripping force were investigated. Experimentally, a hole with an aspect ratio of 5 was pierced. The resulting hole had a clean surface and the dimensional accuracy of pierced hole was considerably improved with decreasing clearance between punch and die. It is also shown that the larger penetration depth of the effective sheared surface can be achieved for high aspect ratio piercing relative to conventional piercing with a low aspect ratio.

• Journal of Power System Engineering
• /
• v.11 no.3
• /
• pp.47-52
• /
• 2007

Punching, blanking, trimming and slitting are widely used in shearing processes in sheet metal forming of automotive parts. In this paper the effects of clearance, cutting angle and tool sharpness on the formation of burr were investigated by experimental method in shearing processes of steel sheets, SPCEN and SPRC35E. The amount of burr and the shapes of burr were different between two kinds of steel sheets. It has been shown that the cutting angle of the shearing blade had no effects on the height of burr when the clearance was below the 10% of the steel sheet thickness, and also that the height and shape of burr were not affected by the cutting angle when the wear of shearing blade was below the 10% of the steel sheet thickness. It was known that there had been existing the critical clearance of 10 to 15% for the tested steel sheet, SPCEN and SPRC35E.

• Transactions of Materials Processing
• /
• v.24 no.2
• /
• pp.115-120
• /
• 2015

Deep drawing of cylindrical cups is one of the most fundamental and important processes in sheet metal forming. Circular cups are widely used in industrial fields such as automobile and electronic appliances. Some of these cups are formed by a one-stage process, others such as battery cases and beverage cans are made by a multi-stage process. In the current study the multi-stage deep drawing of aluminum sheet metal is examined. The process consists of two deep drawing operations followed by two ironing operations. The press die, which can be used for the four-stage forming process, was manufactured allowing punch and die components to be easily changed for various experiments. The rolling direction of both the sheet and the drawn cups was always positioned toward the horizontal x-direction on the die face to minimize experimental errors during the progressive forming. The dimensional accuracy of the cylindrical cups formed at each stage and the earing defect due to the anisotropy of sheet were investigated. The influence of anisotropy on the thickness distribution was also examined. Both the thickness and the outer diameter of the cups were measured and compared for each set of experimental conditions. It was found that the dimensional accuracy of cups rapidly improves by employing the ironing process and also by increasing the amount of ironing.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.627-631
• /
• 2005

In this study, low fatigue behavior of laser welded sheet metal were investigated. Before welding, the cross section of butt joint was prepared only by fine shearing without milling process. Specimens were same sheet metal and welding condition that using automobile manufacturing company at present. Butt joint of cold rolled sheet metal was welded by $CO_2$ laser. It is used that welding condition such as laser welding speed was 5.5m/sec and laser output power was 5kW for 0.8mm and 1.2mm sheet metal. The laser weldments were machined same or different thickness and same or different material. In order to mechanical properties of around welding zone, hardness test was performed. Hardness of welding bead is about 2 times greater than base material. We performed the low cycle fatigue tests for obtaining fatigue properties about thickness and the weld line direction of specimen. The results of strain controlled low cycle fatigue test indicate that all specimens occur cyclic softening, as indicated by the decrease in stress to reach a prescribed strain.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.27 no.12
• /
• pp.1852-1858
• /
• 1990

The sheet resistance and thickness of Ti-Silicides treated RTA at 600, 700, 800\ulcorner was measured with amount of BF2 implanted in Si substrate. And the profile of BF2 was studied by SIMS. The formation of TiSi2 starts at 700\ulcorner. The Ti-Silicides almost consist of TiSi2 and have a low resistivity about 16列 cm at 800\ulcorner. The sheet resistances of Ti-silicides increase and thicknesses of it decrease with increasing dose of BF2. Considering the results of SIMS and the thickness of native oxide, the decrease of thickness of Silicides chiefly results from the increase of native oxide thickness with increasing dopants.

• Journal of the korean Society of Automotive Engineers
• /
• v.15 no.2
• /
• pp.121-129
• /
• 1993

Plane strain punch stretching test (PSST) was developed to evaluate stamping formability of sheet materials. In this test, the rectangular specimen of sheet material is uniformly stretched up to fracture by raising a specially designed punch to certainly assure plane strain stretching deformation along the longitudinal direction of the specimen. The stamping formability was evaluated by limit punch height(LPH) in plane strain punch stretching test compared to limit dome height(LDH) in hemispherical punch stretching test. LPH-value in PSST well ranks the stamping formability of various material and correlates with press performance. Moreover by using ultrasonic thickness gauge the plane strain intercept-limit plane strain(FLCo)-in forming limit curve can be accurately determined from thickness measurement around the fracture area. The FLCo derived from thickness measurement well correlates with the results from circle grid analysis for the deformed circle grid marked on the surface of the specimen.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.84-86
• /
• 2007

Aluminum sheets were asymmetrically cold rolled without lubrication by using different roll velocities of upper and lower rolls in order to intensify the shear deformation. During asymmetrical cold rolling of aluminum sheets, a reduction per a rolling pass, initial sheet thickness, roll diameter, roll velocity ratio were varied to investigate the effect of rolling parameters. The formation of through thickness shear texture was related to the ratio of the contact length between the roll and sample($l_c$) to the sheet thickness(d). The strain states associated with asymmetrical rolling were investigated by the finite element method (FEM) simulation. FEM results indicated that the evolution of deformation texture in a thickness layer is strongly governed by integrated values of strain rates $\dot{\varepsilon}_{13}$ and $\dot{\varepsilon}_{11}$ along the streamline in the roll gap.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.03b
• /
• pp.273-279
• /
• 1999

In this paper the stress and strain behaivor in near homogeneous isotropic matrix of metal like steel was studied roll forming of thin steel sheet for cylindrical pipe. Analytical results reveals a body which is on the area of square thickness along and perpendicular to the width of thin steel sheet is in the state of plane strain during roll forming. As a result construction of analytical method for calculating deformation load and stably deformed length along the width of strained steel sheet was established. Also loads applied during roll forming were analyzed using two typical thin steel sheet 12.3m thick steel sheet with 42.5kg /mm2 yield strength of pipe and 5.3mm thick steel sheet with 32.5kg/mm2 yield strength of pipe. Through this analysis applicability of the analytical method for deformation load during roll forming of cylindrical thin steel pipe was evaluated with a study of necessary production technology for roll forming and design technology for roll forming machine.

• Journal of Welding and Joining
• /
• v.28 no.2
• /
• pp.74-78
• /
• 2010

In this paper, a non-contact method of evaluating the thickness reduction in an aluminum sheet caused by corrosion and friction using SH-EMAT (shear horizontal, electromagnetic acoustic transducer) is described. Since this method is based on the measurement of the time-of-flight and amplitude change of guided waves caused from the thickness reduction, it provides information on the thinning defects. Information was obtained on the changes of the various wave features, such as their time-of-flight and amplitude, and their correlations with the thickness reduction were investigated. The interesting features in the dispersive behavior of selected guided modes were used for the detection of thinning defects. The measurements of these features using SH waves were performed on aluminum specimens with regions thinned by 7.2% to 29.5% of the total thickness. It is shown that the time-of-flight measurement provides an estimation of the thickness reduction and length of the thinning defects.