• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.97-103
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• 2009

The process design of forward Extrusion and Upsetting of Axi-symmetric part has been studied in this paper. During the cold forging product; auto transmission Solenoid Valve part, the defects such as folding and under-fill can be appeared by the improperly controlled metal flow. In this study, to reduce the folding and under-fill the design of experiments has been used to find out the significant design variables in the design of forging process. This paper deals with an Process Planning with which designer can determine operation sequences even after only a little experience in Process Planning of Multi-Former products by multi-stage former working. The approach is based on knowledge-based rules, and a process knowledge-base consisting of design rules is built. Based on the systematic procedure of process sequence design, the forming operation of cold forged auto transmission Solenoid Valve part is analyzed by the commercial Finite Element program, DEFORM/2D.

• Transactions of Materials Processing
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• v.7 no.6
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• pp.620-630
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• 1998

Conventional hot forging and thixoforging of Al 7075 alloy have been compared with respect to microstructures, formability and hardness. Two distinctive temperature-strain rate ranges for hot forging of Al 7075 alloy were observed from the results of simple compression tests with strain rates of 10-3∼101 sec-1 in the temperatures between $250^{\circ}C$ and $500^{\circ}C.$ In the dynamic recovery range (low temperature-high strain rate range) multi-stage forging was necessary to form a complex shape part due to the lack of formability. In the high temperature-low strain rate range, in which dynamic recrystallization takes place a complex shaped park could be formed by single-stage forging. About 50% cold working in the SIMA process was necessary to get a fine and homogeneous microstructures. Microstructural study suggest that thixoforged Al 7075 part has fine grains and homogeneous microstructures. Its hardness number is almost same to that of conventional hot forged part after aging treatment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.199-202
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• 2005

In this paper, the six sigma scheme is employed together with the rigid-viscoplastic finite element method to obtain the optimal metal flow lines in hot press forging. In general, the six sigma process is consisted of following five steps : define, measure, analyze, improve and control. Each step Is investigated in detail to meet customer's requirements through improvement of product quality. A forging simulator, AFDEX-2D, is used for analysis of the metal flow lines of a multi-stage hot forging process under various conditions of major factors, determined at each step of the six sigma process. The analyzed results are examined in order to reveal the effects of major factors on the metal flow lines and the formed shapes. The effects are used to find an optimal process and the optimal process with die is devised and tested. The comparison between required metal flow lines and experiments shows that the approach is effective for optimal process in hot forging design considering metal flow lines.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.4
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• pp.118-124
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• 1998

The die wear is one of the main factors affecting die accuracy and tool lifetime. It is desired to reduce die wear by developing simulation method to predict wear based on process variables, and then optimizing the process. Therefore, this paper describes methodology of preform design for minimizing wear of finisher die in multi-stage cold forging processes. The finite element method is combined with the routine of wear prediction. The cold forging process is analyzed using developed simulation method. In order to obtain preform to minimize die wear, the Flexible Polyhedron Search(FPS) algorithm is used. The optimal preform shape is found from iterative deformation analysis and wear calculation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.06a
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• pp.47-54
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• 1995

Rotary forging process has many advantages such as compacting of machine, low price of facilities and good quality of products. The last presented was a technical report about rotary forging press in the 100-ton class, which has the only orbital motion limited to the forming of axisymmetric parts. In this paper, the newly developed rotary forging press is introduced. The maximum capacity of forming load is 280 ton and five locking motion, this is, orbital, straight pivot, spiral and two kinds of clover can be available. This machine consists of transmission, double eccentric bush, rocking shaft, die set and hydraulic unit. Especially, the supports of rocking shaft and double eccentric bush are so crucial that hydrostatic bearings are adopted. Finally, it is expected that the technical know-how obtained in this research can be applied to the manufacturing of the another machine with large capacity.

• Transactions of Materials Processing
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• v.8 no.2
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• pp.216-221
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• 1999

In this paper, an application-oriented approach to piercing analysis in automatic forging simulation by the rigid-viscoplastic finite element mehtod is presented. In the presented approach, the accumulated damage is traced and the piercing instant is determined when the accumulated damage reaches the critical damage value. A method of obtaining the critical damage value by comparing the tensile test result with the analysis one is given. The presented approach is verified by experiments and applied to automatic simulation of a sequence of 6-stage forging processes.

• Transactions of Materials Processing
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• v.27 no.4
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• pp.250-256
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• 2018

Oxygen-free copper (OFC) was prepared as a 90 mm cube and then processed with Multi-Axial Diagonal Forging - Initialization of Prior manufacturing History (MADF). The MADF process has been newly developed as a severe plastic deformation method. The MADF process consists of upset forging with a thickness reduction of 30% and diagonal forging with a diagonal angle of $135^{\circ}$. 1 cycle process consists of a 12 passes forging process. In order to analyze the characteristic changes according to the number of iterations, 1, 2, and 3 cycles of the MADF process were performed. The OFC specimens were MADF processed without surface cracks up to 3 cycles. The microstructure, hardness and tensile test of processed materials were analyzed to study the change of material properties according to the amount of MADF process. The results showed that the MADF process effectively refined the microstructure and increased the strength of OFC. In the case of specimens processed for more than 2 cycles, the grains of all measurement regions were refined to be less than $7{\mu}m$ of grain size. The 1 cycle MADF processed OFC showed the highest mechanical properties with the hardness of 132 HV and tensile strength of 395 MPa. Hardness and strength seemed to be saturated when processed over 2 cycles.

• Transactions of Materials Processing
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• v.27 no.6
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• pp.347-355
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• 2018

This study investigated the effects of the processing number of multi-axial diagonal forging (MADF) on the microstructural changes of OFC fabricated by MADF processes. The as-extruded OFC was cut to $25mm^3$ cube for the MADF processes. The MADF process consists of plane forging with a thickness reduction of 30% and diagonal forging with a diagonal forging angle of $135^{\circ}$. In order to analyze the microstructural evolutions according to the number of repetitions, 1, 2, 3 and 4 cycles of the MADF process were performed. OFC specimens were successfully deformed without surface cracking for up to 4 cycles of MADF. The grain size, average misorientation and average grain orientation spread (GOS) of MADF processed materials were analyzed using EBSD technique and their Vicker's hardness were also measured. The results showed that MADF process effectively refined the microstructure of OFC with initial average grain size of $84.2{\mu}m$. The average grain sizes of specimens MADF processed for 1, 2, 3, 4 cycles were refined to be $8.5{\mu}m$, $2.2{\mu}m$, $1.5{\mu}m$, $1.1{\mu}m$, respectively. The grain refinement seemed to be saturated when OFC was MADF processed over 2 cycles. In the case of specimens subjected to two or more cycles of MADF, the degree of decrease in average grain size was drastically reduced as the number of cycles increased due to softening phenomena such as dynamic recovery or dynamic recrystallization during processing. The degree of increase in average Vicker's hardness was also dramatically reduced as the number of cycles increased due to the same reason.

• Transactions of Materials Processing
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• v.28 no.2
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• pp.63-70
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• 2019

This study investigates the effects of multi-axial diagonal forging (MADF) processing number on the microstructures of AA1100 fabricated using MADF processes. The cast AA1100 was annealed at $400^{\circ}C$ for 3hrs in $N_2$ atmosphere and cut into $25mm^3$ cubes for the MADF processes. The MADF process consist of plane forging with a thickness reduction of 30% and a diagonal forging with a diagonal forging angle of 135 degrees. In order to analyze the microstructural variations based on the number of repetitions, 1, 2, 3 and 4 cycles of the MADF process were performed. AA1100 specimens were successfully deformed without cracking of the surface for up to 4 cycles of MADF. The grain size, average misorientation and average grain orientation spread (GOS) of MADF processed materials were analyzed using EBSD technique. The results showed that MADF process effectively refined the microstructure of AA1100 with an initial average grain size of $337.4{\mu}m$. The average grain sizes of specimens which were MADF processed for 2, 3, 4 cycles were refined to be $1.9{\mu}m$, $1.6{\mu}m$, $1.4{\mu}m$, respectively. The grain refinement appeared saturated when AA1100 got MADF processed over 2 cycles. When the specimen was subjected to two or more cycles of MADF, the degree of decrease in the average grain size drastically decreased with an increase in the number of cycle due to the softening phenomena such as dynamic recovery or dynamic recrystallization during processing.

• Transactions of Materials Processing
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• v.28 no.6
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• pp.361-367
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• 2019

Microstructure evolution and tensile properties of Al-8mass%Mg alloy casting billet by biaxial alternative forging were investigated in this study. An alternative forging system tailored in this study was used to allow continuous strain accumulations on the alloy workpiece. A finite element (FE) simulation results revealed that the strain was mainly concentrated in the core and that the shear bands developed into a form with an X shape in the cross-section of workpiece after the alternative forging using octangular rod shaped dies. With increasing the forging passes, it was observed that the Al-8mass%Mg alloy workpieces were significantly deformed, and cracks began to form and propagate on the both ends of the forged workpieces after five passes at room temperature. In as-forged microstructures taken by microscopes, twins, clustering of dislocations, and fine subgrains were found. Tensile strengths of the forged specimens showed significant increases depending on the number of forging passes, and a trade-off relationship was observed between the elongation and strength. At room temperature and 100℃ the workpieces showed similar behaviors in microstructural evolution and tensile properties depending on forging passes, while the increase range in strength was reduced at 200℃.