• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.64-67
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• 2009

Vibrational micro-forming of pyramidal shape patterns was conducted for an Al superplastic alloy, Al 5083 and a Zr-based bulk metallic glass, $Zr_{62}Cu_{17}Ni_{13}Al_8$. A vibrational micro-forming system was specially designed for generating vibrational load by combining a PZT actuator with a signal generator. Single crystal Si micro dies with wet-etched pyramidal patterns were used as master dies for vibrational micro-forming. The micro-formed pattern height was increasing with increasing the frequency of the vibrational load. In particular, the vibrationally-microformed pattern height was similar or even higher than the statically-microformed pattern height when the load frequency exceeded about 125 kHz. It was also observed that the crystal grains affect the surface quality of the microformed pattern and the distribution of the pattern height in the die cavity array.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.6
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• pp.3667-3671
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• 2015

Through experiment that does not cause wrinkles in the forming process for the primary purpose for install PCB(Printed circuit board) the thickness variation of the material was investigated. Experimental results was showed that the forming height of the first process had Influence Material thickness variation in the second process, in the first process, the Entrance corner of the die must have round of the product height of 50%, and The height of forming should be as high as the thickness of the material than the original forming. Also as do implement the forming shape in the first process, the thickness of the material is thinned to 85%, Restriking in the second process was that The thickness of the material is thinned to 80%. Therefore, In order to implement a precise shape, Thinking that the material thinning, The die was maintain the shape of the original product, and It was obtain the effect of the compression that the punch is to be longer, as the sum of more than 20% of the material thickness in the depth of the original product.

• Transactions of Materials Processing
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• v.13 no.4
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• pp.342-349
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• 2004

The form-joining process (or clinching) uses a set of die and punch to impose the plastic deformation-induced geometric constraint on a sheet metal pair. The joining strength from the process ranges 50-70 percent of that of the resistance spot welding. In this paper, a new form-joining process with the aid of an adhesive is proposed in which an epoxy adhesive is applied to a sheet metal pair, and before it cures the pair is clinched to cause the geometric constraint in the form of a protrusion. In order to reduce the forming load and the height of protrusions, a new die and punch set with a very small clearance is devised to reduce the depth of drawing and the forming load. Taguchi method is employed to find the optimal values of design parameters. To implement each case of the orthogonal array, the finite element method is used. The experiments show that in the tensile-shear test, the bonding strength of the new form-joining process with an epoxy adhesive is approximately the same as that of the resistance spot welding; and in comparison with the other two form-joining processes with an epoxy adhesive, the height of protrusions is reduced by more than 65 percent and the forming load by 50 percent.

• Transactions of Materials Processing
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• v.16 no.6
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• pp.457-462
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• 2007

The drawbeads, which are used for controlling the flow of the sheet into die cavity by imposing the tension and for preventing the forming defects like wrinkling, springback, etc. during the sheet forming process, affect the formability strongly because of the differences in the restraint and opening forces according to the drawbead shapes and dimensions. In this study, the experimental device enabling to measure the drawbead restraining and opening forces is manufactured and the drawing forces of circular, square, and step drawbeads are measured. The drawbead restraining and opening forces of a circular drawbead are increased as its drawbead height is increased. Similarly, those of a square drawbead are increased as its height is increased and shoulder radii decreased. The drawbead forces obtained from the experiment were compared with those calculated in the numerical simulation of stamping process of automotive fender. Good agreement was found so that the experimental measurements can be used in the simulation of auto-body stamping process.

• Design & Manufacturing
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• v.2 no.2
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• pp.29-32
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• 2008

A back light unit (BLU) is a key module of a thin film transistor liquid crystal display (TFT-LCD), frequently utilized in various mobile displays. In this study, we experimentally characterize transcription and optical properties of concave and convex microlens arrays (MLAs) of light guide plate (LGP) fabricated by injection molding with polycarbonate as a LGP substrate material. Nickel mold inserts were manufactured by electroforming on the MLA which was fabricated by the thermal reflow of photoresist microstructures patterned by UV-photolithography. For the case of convex microlens, the height of replicated microlens was less than that of the mold insert while maintaining almost the same microlens diameter of the mold insert as the location of the microlens is far from the gate. In contrast, for the concave microlens, the diameter of replicated microlens was larger than that of mold insert, while showing almost the same microlens height as the mold insert. From the optical examination of replicated convex and concave MLAs, it was found that a higher luminance of the LGP was achieved by the concave MLAs compared to the convex MLAs (about 30% enhancement in this case)due to the utilization of a larger amount of light provided by the light sources.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.431-433
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• 2007

The drawbeads, which is used for controlling the flow of the sheet by imposing the tension and for preventing the springback in the sheet metal forming process, affects a lot the formability because of the differences in the restraint and opening forces according to the drawbead shapes and dimensions. In this study, the experimental device enabling to measure the drawbead restraining and opening forces was manufactured and the drawing forces of circular, square, and step drawbeads are measured. The drawbead restraining and opening forces of a circular drawbead are increased as its drawbead height is increased. Similarly, those of a square drawbead are increased as its height is increased and shoulder radii decreased. Also, those of a step drawbead are increased as its height and difference in their heights are increased.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.10
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• pp.1877-1889
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• 1992

Upsetting is performed in open-die press forging to deform metal in all directions in order to enhance soundness of a product and reduce directionality of properties caused by casting. It is necessary to ensure sufficient forging ratio for subsequent cogging operations and consolidate the void along the centerline. To obtain these benefits, the upper die shape (dome and dished shape) is considered as an upsetting parameter. Thermo-viscoplastic finite element analysis has been carried out so as to understand the influence of upper die shape on the effective strain, hydrostatic stress and temperature in the upset-forged ingots without internal defects. The analysis is focused on the investigation into internal void closure in ingots with pipe holes and circular voids. The computational results have shown that the volume fraction of the void is independent of the circular void size and the closure of internal voids is much more influenced by the effective strain than the hydrostatic stress around the void. It is finally suggested that the height reduction must be over 35% for consolidation of internal voids.

• Design & Manufacturing
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• v.13 no.4
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• pp.23-27
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• 2019

People's interest in the environmental problems of the Earth is growing as they come to the modern world, and research is being actively conducted on how to protect the environment. As a result, the automobile industry, one of the causes of environmental pollution, is also affected. Therefore, research is being conducted to improve the fuel economy and light weight of cars, development of pollution-free cars such as electric cars, and aluminium materials that are lighter than ordinary steel sheets and easier to recycle are gaining attention. In this experiment, the material was formed to form a form of aluminium and the material reduction rate of the side wall of the foam was tested according to the amount of side wall. The material used in the experiment was A3003-O, which is less plastic than normal steel plates, but has excellent corrosion resistance, plasticity and weldability compared to aluminium materials, but has poor tensile strength. For tensile testing, a certain array of Forming Shapes was molded and the height of the Forming was set to 5mm, and the height of the Forming was 4.7mm, indicating that the difference between the first 5mm Forming and the height was not large. In addition, the material reduction rate was tested by giving 15, 0, and -0.15 teas, respectively, and was found to be valuable as a product only for -0.15.

• Transactions of Materials Processing
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• v.19 no.8
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• pp.486-493
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• 2010

A shape error of the sheet metal product made by a flexible stretch forming process is occurred by a various forming parameters. A die used in the flexible stretch forming is composed of a punch array to obtain the various objective surfaces using only one die. But gaps between the punches induce the shape error and the defect such as a scratch. Forming parameters of the punch size and the elastic pad to prevent the surface defect must be considered in the flexible die design process. In this study, tendency analysis of shape error according to the forming parameters in the flexible stretch process is conducted using a finite element method. Three forming parameters, which are the punch size, the objective curvature radius and the elastic pad thickness, are considered. Finite element modeling using the punch height calculation algorithm and the evaluation method of the shape error, which is a representative value for the formability of formed surface, are proposed. Consequently, the shape error is in proportion to the punch size and is out of proportion to the objective curvature radius and the elastic pad thickness.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.1084-1087
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• 1997

In this paper, we developed the micro NCT system for punching the thin plates, which is driven is driven by the standalone type microprocessor. In order to adjust the alignment between the punch and die in-situ punching procedures, the non-contact type laser sensor for measuring the burr and micro-driving system for punching die with using the differential screw are developed. The height of burr in four directions in the punched hole of test specimen are measured, and the measured data are transferred to the personal computer by RS232C serial communication technology. In the personal computer, by using the graphic user interface type monitoring program and data handling procedures which includes the filtering algorithms, the direction and length of movement of the die position is decided and these data are transferred back to the microprocessor. The microprocessor drives the micro positioning stage based on these data. Even if this method is not a perfect solution for the in-situ alignment in micro punching, but this alignment methodology is accomplished in the same stage just after the punching that we hope to solve the alignment problem in the punching system based on this technology.