• Transactions of Materials Processing
• /
• v.30 no.2
• /
• pp.69-73
• /
• 2021

This paper addresses the product shape modification for spring-back reduction in the sheet metal forming process of the cabin sunroof which is applied to the construction equipment. Initially, the anisotropic material properties are measured in order to calculate the degree of spring-back by the numerical simulation of the sheet metal forming process. To reduce the spring-back of the stamped part, several design modifications are suggested according to the geometrical bead arrangement on the planar region. The degrees of spring-back are confirmed for various product designs with different use of the geometrical bead. Finally, the spring-back improvement was validated by manufacturing the tryout product with the modified die set for the optimized product shape.

• Transactions of Materials Processing
• /
• v.8 no.4
• /
• pp.384-392
• /
• 1999

In metal forming, there are problems with recurrent geometric characteristics without explicitly prescibed boundary conditions. In such problems, so-called recurrent boundary conditions must be introduced. In this paper, as a practical application of the proposed method, the precision cold forging of a helical gear has been simulated by a three-dimensional rigid-plastic finite element method and compared with the experiment. The application of recurrent boundary conditions to helical gear forging analysis is proved to be effective and valid. the elastic stress analysis of the die for helical gear forging has been calculated by using the nodal force at the final stage obtained from the rigid-plastic finite element analysis. In order to obtain more precise gear products, the elastic analysis of the die after release of punch and the elastic spring-back analysis of product after ejection have been performed, and the final dimension of the computational product has been in good agreement with that of the experimental product.

• Journal of the Korean Society for Precision Engineering
• /
• v.12 no.11
• /
• pp.118-124
• /
• 1995

In the paper, we have proposed a new technique to determine the initial billet for the forged products using a function approximation in neural network. A three-layer neural network is used and a back propagation algorithm is employed to train the network. An optimal billet which satisfied the forming limitation, minimum of incomplete filling in the die cavity, load and energy as well as more uniform distribution of effective strain, is determined by applying the ability of function approximation of the neural network. The amount of incomplete filling in the die, load and forming energy as well as effective strain are measured by the rigid-plastic finite element method. This new technique is applied to find the optimal billet size for the axisymmetric rib-web product in hot forging. This would reduce the number of finite element simulation for determining the optimal billet of forging products, further it is usefully adopted to physical modeling for the forging design

• Journal of Sericultural and Entomological Science
• /
• v.10
• /
• pp.53-55
• /
• 1969

1. This experiment was made for a comparable test of five different chemicals on control effects of mulberry die back disease from the autum of 1967 to that of 1968. These chemicals were EMP, PMF, lime sulfur, chlon, and PMA. 2. The experiment showed the EMP and PMF were the best chemicals among those for controling it, and the others no significance comparing with the control. 3. The best way was a twice sprang of 150$\ell$ EMP(1/1500 con.) per 10ar to the base of branches to the full extent through september and october.

• Design & Manufacturing
• /
• v.13 no.1
• /
• pp.36-41
• /
• 2019

A large plastic molding requires an injection molding with a large clamping force. However, it could not be prepared in the manufacturing at any time. In order to solve the problem, the injection molding analysis study was conducted on the back cover of 55 inch LED TV. The study compared the case of applying the existing flow system such as hot runner, the improvement of the hot runner lay-out and the precise control of the gate operation time, From the results of using the improved flow system, it was found that the welding and the clamping force were considerably improved as compared with before the improvement. In particular, the clamping force was reduced by 50% compared with before the improvement.

• Journal of the Korean Society for Heat Treatment
• /
• v.35 no.6
• /
• pp.319-326
• /
• 2022

Direct extrusions of an aluminum 7075 alloy were carried out using 1500 ton machine with and without die cooling system. Cooling of extrusion die has been performed by the flow of liquid nitrogen and controlled by laser thermometer. Billet was 180 mm in diameter and 500 mm in length. The preheating temperatures of billet, container and die were 390℃, 400℃ and 450℃, respectively. Ram speed was kept with 1.25 mm/sec first. The change of ram speed was carried out during extrusion according to the observation of surface defects such as crack or tearing. Extrudates of 8.3 m in length, 100 mm in width and 15 mm in thickness were obtained to observe and analyze surface defects by optical microscopy and EBSD (Electron BackScattered Diffraction). In case of extrusion without die cooling cracks on the surface and tearing in the corner of extrudate occurred in the middle stage and developed in size and frequency during the late stage of extrusion. At the extrusion with die cooling the occurrence of defects could be suppressed on the most part of extrudate. EBSD micrographs showed that cracks and tearings have been resulted from the same origin. Surface defects were generated at the boundaries of grains formed by secondary recrystallization due to surface overheating during extrusion.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.26 no.1
• /
• pp.59-65
• /
• 2017

A seat track product is a car seat part that provides a base for vehicle seats. An ultra-high strength steel sheet is used to reduce the weight of vehicle body parts. However, the formability of an ultra-high strength steel sheet is poor because of its very low elongation and very high elastic deformation. For this reason, a new forming technology of an ultra-high strength steel sheet is required. The influence of spring-back of seat track parts on the shape freeze in forming processes was investigated to be solved by adjusting the appropriate tool design such as minus clearance between punch and die, and punch angle. This paper describes how to apply the spring-back prevention technique for improving shape freeze by using the ultra-high strength steel sheet with 980MPa to develop lightweight seat tract parts.

• Transactions of Materials Processing
• /
• v.21 no.5
• /
• pp.291-297
• /
• 2012

In this paper, the effect of back tension in multi-pass drawing or wiredrawing on the central bursting defect is investigated using finite element predictions. A rigid-plastic finite element method was used together with the McClintock damage model. Central bursting defects under different back tension stress values ranging from 0% to 20% of the yield strength of the material were predicted and they were compared to understand the effect of the back tension stress values on the central bursting defect. It is found that the level of back tension has a strong influence on the cumulative damage. Thus, higher back tension raises the possibility of the central bursting defect occurring, even though it decreases the interfacial pressure between the die and the work piece.

• Transactions of Materials Processing
• /
• v.9 no.1
• /
• pp.52-58
• /
• 2000

Hot precision forging with a back pressure was investigated for manufacturing of compressor parts made of Al-Si alloy. Disk-shaped blank made of Al-Si alloy was hot forged, and ribs were formed by loading back pressure on their top. The influence of the back pressure and die temperature on forgeability and properties of parts made of Al-Si alloy were examined. Using the F.E.M. simulation, we found the optimum vallue of back-pressure. The prototypes of scroll parts were forged into the near-net shape and satisfied the required properties.

• Journal of Korean Society of Forest Science
• /
• v.87 no.4
• /
• pp.557-561
• /
• 1998

A die-back fungus isolated from Pinus koraiensis was identified as Cenangium ferruginosum. Mycelial growth of the fungus was the best on PDA among five media tested. Mycelial growths on agar media supplemented with extracts from coniferous trees were relatively better than those on media with extracts from non-coniferous trees. Optimum temperature and pH for the mycelial growth of C. ferruginosum on PDA were $10^{\circ}C$ and pH 5, respectively. When five-years-old P. koraiensis seedlings were artificially inoculated with the fungus for the pathogenicity test of this fungus, 80% of seedlings were infected. and the same symptoms and signs were developed as those of naturally-infected trees.