• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1998.03a
• /
• pp.88-93
• /
• 1998

The service life of tools in metal forming process is to a large extent limited by wear, fatigue fracture and plastic deformation. In warm forging processes wear is the predominant factor for operating lives of tools. To predict tool life by wear, Archard's wear model is generally applied. Usually hardness of die is considered to be a function of temperature in Archard's wear model. But hardness of die is a function of not only temperature but also operating time of die. To consider softening of die by repeated operations, it is necessary to express hardness of dies by a function of temperatures and operating time. By experiment of reheating of dies, die softening curves were obtained. Finally modified Archard's wear model in which hardness of die was expressed as a function of main tempering curve was proposed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.10a
• /
• pp.23-26
• /
• 2004

The deformation behaviors of fully annealed or T6-treated 6061 and 7075 aluminum tubes are investigated at elevated temperature using uniaxial tensile test. Fully annealed 6061 and 7075 tube, and T6-treated 7075 tube do not show sharp local necking with an elongation of $50\%$ at tensile temperature of $300^{\circ}C$, accordingly, it is expected that warm hydroforming process can be applied. The increase of tensile temperature does not significantly affect the total elongation of T6-treated 6061 tube.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1998.06b
• /
• pp.8-18
• /
• 1998

The effect of press warm forming in cylindrical deep drawing of stainless-aluminum clad sheet metals are examined . The temperature of die and blank holder is varied from room temperature to 20$0^{\circ}C$, while the punch is kept cooled during test to increase the fracture strength of workpiece on the punch corner area. Test materials chosen for experiments are STS304-Al050-STS304, STS304-A1050-STS430-, STS304 and Al050 metals and teflon film as a lubricant is used on both sides of a workpiece. The limit drawing ration as well as quality of drawn cups (distribution of thickness and hardness)are investigated and discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.10a
• /
• pp.255-258
• /
• 2005

In this study, the effect of heat treatment conditions and deformation temperature on the formability were investigated in warm hydroforming of Al 6061 tube. Full annealing and T6-treatment for heattreatment of Al6061 tube were used in this study. To evaluate the hydroformability, uniaxial tensile test and bulge test were performed between room temperature and $300^{\circ}C$. And measured flow stress was used to simulate the hydroforming of Al 6061. A commercial FEM code, DEFORM2D, was used to calculate the damage and strain variation. The calculated values were efficient to predict the forming limit in hydroforming for real complex shaped part.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.10a
• /
• pp.139-142
• /
• 2005

Cu-Ni-Zr-Ti bulk amorphous thin strips were produced by multi-pass warm rolling of the amorphous powder at temperatures in the supercooled liquid region. Process variables for rolling of the bulk amorphous strips were properly controlled to prevent onset of crystallization and failure during rolling up to three passes. During rolling of the amorphous powder, both the deformation and densification took place and the newly developed surface on the deformed amorphous particles enhances the consolidation leading to an increase in the strength. The strain state during rolling was analyzed by FEM.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2002.05a
• /
• pp.184-186
• /
• 2002

The evolution of texture and microstructure during warm rolling and subsequent annealing in aluminium 3004 alloy sheet was investigated by X-ray texture measurements and microstructure observations. Warm rolling at 250$^{\circ}C$ led to the development of strong through thickness texture gradients with shear textures at the surface layer and a regular rolling texture in the center of the sheets. FEM simulations indicated that these texture gradients are caused by pronounced strain gradients throughout the sheet thickness. Upon recrystallization annealing, in the sheet center the characteristic cube-recrystallization texture developed, while in the surface layers with a pronounced shear texture continuous recrystallization took place which led to the formation of a very fine grained microstructure. It is concluded that the very complex strain history in the near-surface layers together with the resulting high work-hardening rate gave rise to the formation of the ultra-fine grains with an average size smaller than 2$\mu\textrm{m}$.

• Proceedings of the Korean Society of Fisheries Technology Conference
• /
• 2000.05a
• /
• pp.181-182
• /
• 2000

Due to the instability of the EKWC, the oceanic conditions in the East Sea are affected by the fluctuations of the moving paths of the TWC, polar fronts, and warm eddies. In particular, warm eddies play an important role in spreading the surface water of the East Sea from its southern coastal region to its interior region (Isoda, 1994). However, the fluctuation characteristics of the meandering TWC and the warm eddies in the East Sea are not yet known due to the instability of the TWC. Hideaki(1999) showed that the moving paths and features of the TWC in the coastal regions of Japan were not constant. (omitted)

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.306-309
• /
• 2007

Recently, magnesium alloys have been widely used in automotive, aerospace and electronic industries with the advantages such as lightweightness, high specific strength and stiffness. However, magnesium alloy has quite low formability at room temperature due to its hexagonal close-packed crystal structure. Warm deep drawing is one of the forming technologies to improve the formability of magnesium alloy sheet and the lubrication condition is an important process parameter in that. In this study, the drawing tests of AZ31 alloy sheet at elevated temperature for various kinds of lubricant were carried out and the effects of lubrication conditions on drawbility were investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.230-233
• /
• 2007

Due to their low density, high specific strength and electromagnetic interference shielding, magnesium alloy sheets are used increasingly more often in automotive, aerospace, and electronics industries. However, magnesium ally sheets should be usually formed at elevated temperature because of their poor formability at room temperature. For the use of magnesium alloy sheets for an industrial, their mechanical properties at elevated temperature and appropriate forming process conditions have to be developed. In this study, the warm deep drawing process of AZ31 sheets is studied numerically by non-isothermal simulation. The difference between the isothermal simulation results and the non-isothermal simulation results and the progress of warm forming are discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2007.10a
• /
• pp.242-245
• /
• 2007

In the present investigation, the multi-stage warm drawing process was applied to the magnesium alloy AZ31 sheet to examine the feasibility of multi-stage forming process as a high formability product making process. For that purpose, a multi-stage drawing die system with heating module was developed, and the AZ31 sheets of different sizes were consecutively drawn by the multi-stage drawing die. The obtained drawn cups of AZ31 showed that the multi-stage drawing provided the better formability than the single stage drawing in terms of drawing depth without cup defects such as wrinkles or fractures. The sheet formability improvement by using the multi-stage drawing die system against the single stage was also analyzed in terms of the finite element analysis of material state variables evolution.