• 소성∙가공
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• 제28권5호
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• pp.257-265
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• 2019

Multi-axial forging (MAF), a severe plastic deformation technique, is known to be difficult to obtain materials with homogeneous microstructures. Recently, multi-axial diagonal forging (MADF) process has been developed to solve this problem. In this study, in order to compare the microstructural and mechanical homogeneities of the MAFed and MADFed samples, oxygen-free copper (OFC) cubes measuring 25 mm in length were deformed through MAF and MADF processes and the average grain size and hardness were measured at the edge, face, and center regions of the samples. In the MAFed samples, ultrafine grains were formed at the center region, but a considerable amount of coarse grains remain at the face region. Therefore, the MAFed samples showed a high inhomogeneity in regards to grain size and hardness. On the contrary, in the case of the MADFed sample, the grain sizes at the edge, face, and center regions were similar and the hardness in all the regions are almost similar. This indicates that the MADFed sample has a homogeneous microstructure and uniform mechanical properties, which can be attributed to the homogeneous distribution of the effective strain throughout the material. The results of this study suggests that the MADF is a suitable process in the fabrication of high-strength copper materials with a homogeneous and ultrafine grain structure.

• 소성∙가공
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• 제28권2호
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• pp.98-104
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• 2019

The present study numerically simulates the deformation heterogeneity developed in AA1100 during multi-axial diagonal forging (MADF) using finite element analysis (FEA). Diagonal forging type consisting of diagonal forging (DF) and return-diagonal forging (R-DF) proved to be relatively beneficial compared to plane forging type which includes plane forging (PF) and return-plane forging (R-PF) for minimizing the non-uniformity of deformation developed in workpieces. Simulation of the effective strain generated in workpieces during the two types of forging was done using 3-D FEA. FEA shows the effect of friction coefficient on the deformation behavior on workpieces. The simulation of 2 types forging with different friction coefficients revealed that the magnitude of barreling effect and strain heterogeneity in workpieces increases with an increase in the friction coefficient.

• 소성∙가공
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• 제27권4호
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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.

• 소성∙가공
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• 제27권6호
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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.

• 소성∙가공
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• 제28권2호
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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.

• 한국재료학회지
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• 제13권12호
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• pp.812-818
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• 2003

The aim of this study is to investigate the fabrication processes on the microstructual changes and mechanical properties of large 7175 aluminum die forgings. The billets range from 370 to 720 mm in diameter were homogenized and hot forged after direct chill casting. The strength and elongation of the homogenized cast billets were revealed nearly same level independent of the billet diameter. However, these properties of ø370 mm cast billet were superior to those of $\Pie720$ mm billet under$ T_{6}$ / condition. The tensile strength of die forged specimens under $T_{6}$ condition increased up to 20% than that of solution treatment, however, the elongation was reduced to 50%. The fracture toughness of die forged specimens under $T_{6}$ condition was 35.6∼39.0 MPa$.$$m^{1}$2 irrespective of the billet size and free forging processes, but this property increased up to 10% by$V_{74}$ treatment. The fracture toughness of die forged specimen manufactured with ø370 mm cast billet showed nearly same level of ø720 mm billet which was processed using MF or Cog free forging followed by die forging.

• 한국산학기술학회논문지
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• 제13권11호
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• pp.4950-4955
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• 2012

볼트의 제작 공정은 연속적인 단조 작업에 의해서 완성되는데 각 공정의 기술적, 경제적인 성공은 적절한 공정설계와 각 작업에 필요한 금형 설계에서 좌우된다. 본 연구에서는 다단 공정에 의해서 이루어지는 SCM435 볼트의 성형과정 중에서 1, 2단계의 성형을 유한요소법을 이용하여 해석하여 합리적인 공정이 이루어지도록 개선 방향을 제시하고자 하며 유한요소법을 이용하여 해석한 1, 2단계의 공정은 축대칭이 성립되므로 소재의 변형 형상이 공정에서 기대했던 치수를 만족할 수 있었으며 소재에 형성된 단류선이 전 공정을 통하여 부드럽게 연속적으로 형성됨을 알 수 있었으므로 소재의 성형 뿐 아니라 내부의 결함도 없을 것으로 예상되었다.

• 소성∙가공
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• 제30권6호
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• pp.306-310
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• 2021

In this study, IF steel, which has a body-centered cubic (BCC) crystal structure, was fabricated as a 25 mm-long cube, and then processed for one cycle without intermediate heat treatment by applying MADF Ver.1 and Ver.2 processes. MADF processing was performed with graphite lubrication for each pass at room temperature. The development of the microstructure and texture was analyzed and compared by the location of the specimen using EBSD measurements of the IF steel. Vickers hardness test and miniature tensile test were also performed to analyze the mechanical properties. The coarse grain size of 742.6 ㎛ of the as-received IF steel was refined to a grain size of 53.0 ㎛ after one cycle of MADF Ver.1 processing and 27.0 ㎛ after MADF Ver.2 processing. Vicker's hardness of the as-received IF steel at 94 Hv was increased to 185.6 Hv and 191.2 Hv after one cycle of MADF Ver.1 and Ver.2 processing, respectively.