• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.195-196
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• 2006

In recent years, demands for sintered ferrous material with higher strength are increasing. To satisfy these demands, studies and commercial use of the die wall lubrication method, the warm compaction method and the combination of both methods are widely carried out to achieve high density. The die wall lubrication warm compaction method makes it possible to achieve high density by reducing internal lubricant through die wall lubrication, although the method involves several issues such as prolonged cycle time due to lubricant spraying and difficulty in spraying lubricant in the case of compacting with complicated geometry. Meanwhile, the conventional warm compaction method requiring no die wall lubricant application cannot achieve such a high density as in the case of die wall lubrication warm compaction due to higher volume of internal lubricant. However, this report discloses our study result in which the possibility of improving density is exhibited by using a lubricant type with superior dynamic ejection property that can reduce volume of lubricant additive.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.750-751
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• 2006

We investigated the mechanism how the high green density can be provided during die lubricated warm compaction (WD). We observed and analyzed the densification processes of iron powders including different contents of an inner lubricant, and measured the lateral pressure at the die wall during WD in comparison with conventional compaction and warm compaction. As a result, the high density in WD was due to not only the particles-deformation enhanced by warming powders but also the particles-rearrangement promoted by reducing an amount of the inner lubricant rather than the die lubrication.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.53-57
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• 1998

In order to investigate the effects of the variables during the stamping process upon the side wall curl behavior, experiments and finite element analyses were done using a 90 degree draw-bending test. The variables considered were the die radius, the forming speed, the restraint force, the lubrication and the sheet grade. The experiments and simulation conditions were selected according to the design of experiment (DOE) approach. The effects of the restraint force, the lubrication and the forming speed were the same for both high strength and mild steels, but the effects of the die radius on the side wall curl were dependent on the magnitude of the die radius and the sheet grade. A straight side wall was observed for both high strength and mild steels when the die radius was about 2∼3 times of the sheet thickness. It was recommended that the restraint force, the forming speed and the friction be increased in order to reduce the side wall curl.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.197-198
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• 2006

The high pressure compaction without internal lubricant and the high green density even with the pore free density were achieved by the newly developed die wall lubricant for warm compaction. This developed die wall lubricated warm compaction followed by high temperature sintering resulted in not only the superior mechanical property but also the low dimensional change. In this paper, the effects of increasing the green density on the sintered density, the dimensional change and the mechanical property are mainly discussed

• Journal of the korean Society of Automotive Engineers
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• v.11 no.4
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• pp.35-42
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• 1989

The major purpose of this paper is a study on the effect of die profile radius on the formability of spring-type blankholder system in deep drawing process. By drawing the various materials, formability is studied by means of checking the drawing force, blankholding force variation, limiting drawing ratio and wall wrinkling phenomenon. As the die profile radius increases, the maximum drawing force and maximum blankholding force decrease regardless of lubrication condition. Because better lubrication induces blankholding force to rise, spring type blankholder system is better to protect flange wrinkling phenomenon than constant pressure type. And wall wrinkling phenomenon was not detected in experimental die radius range, so the Miyakawa's upper wrinkling limit is understimated in case of material tested.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1173-1174
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• 2006

Improvement of the strength is one of the most important subjects on soft magnetic composite (SMC) to increase the applica ble items. In this study, lubricants for inner lubricating SMC, which can be produced in lower cost than die wall-lubricatin g SMC, varied to investigate their effect on the strength. The newly developed SMC with self-lubricating resin shows high st rength equivalent to that of SMC obtained by die wall lubrication.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.1
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• pp.117-125
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• 2013

Variations of springback in stamped parts are induced by the uncontrollable noises including the variation of incoming material properties, lubrication and other forming process parameters. Reduction of springback variation is very important during springback compensation processes on stamping dies and assembly processes. To reduce the variation of springback, a robust optimization methodology which uses complex method combined with orthogonal array is proposed. The proposed method is applied to the robust design of U-channel die for the reduction of side wall curl. It is shown that the drawbead and die radius of U-channel draw die can be effectively optimized by the proposed method.

• Transactions of Materials Processing
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• v.11 no.8
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• pp.668-675
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• 2002

The circles deform into various shape during deformation, the major and minor axes of which indicate the direction of the major and minor principal strains. Likewise, the measured dimensions are used to determine the major and minor principal strain magnitudes. This circular grid technique of measuring strains can be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, of incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

• Transactions of Materials Processing
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• v.11 no.8
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• pp.682-690
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• 2002

The formation of adiabatic shearband in tungsten heavy alloys(WHA) was studied in this investigation. Five prismatic specimens were loaded by high velocity impacts and treated as plane strain problems. To find out the effect of particle's volume ratio, specimens containing 81%, 93% and 97% volume percents of tungsten particles were used. Also the effects of particle's geometry and size on the formation of shearband were studied for 81% volume percent alloys by small size particle model, large size particle model and undulated particle models, and the results were discussed.be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, or incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.