• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.397-400
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• 2007

Recently, rheology forming technology has been interested in industrial and academic for light weight materials and to solve environmental issues. In this study, the rheology material production equipments were used to be made spiral shape by special design. And the experiment variables established stirring time 0 $\sim$ 1200 sec, stirring velocity 0 $\sim$ 100 rpm and several material temperature of semi - solid states. The rheology materials were made for established experiment conditions then measured mechanical properties. Sequence-production equipments were appended to fabrication system of rheology material for make rheology materials continually. Therefore, the development of sequence-production equipments were demanded for fine grains and for uniform globule shape rheology materials by a specially designed spiral stirrer machine.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.2019-2031
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• 2004

The least-squares formulation for rigid-plasticity based on J$_2$-flow rule and infinitesimal theory and its meshfree implementation using moving least-squares approximation are proposed. In the least-squares formulation the squared residuals of the constitutive and equilibrium equations are minimized. Those residuals are represented in a form of first-order differential system using the velocity and stress components as independent variables. For the enforcement of the boundary and frictional contact conditions, penalty scheme is employed. Also the reshaping of nodal supports is introduced to avoid the difficulties due to the severe local deformation near the contact interface. The proposed least-squares meshfree method does not require any structure of extrinsic cells during the whole process of analysis. Through some numerical examples of metal forming processes, the validity and effectiveness of the method are investigated.

• Transactions of Materials Processing
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• v.17 no.1
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• pp.9-12
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• 2008

Recently, industries and academic institutes have been interested in the rheology forming technology for light weight materials. However, this rheocasting process has advantages such as the high initial investment cost and the lower mechanical properties than thixocasting. In this study, the continuous fabrication of rheological material with a spiral stirring equipment(mechanical stirring system) was newly devised to overcome the disadvantages of rheocasting process. The experimental parameters were stirring time($0{\sim}1200sec$), stirring velocity ($0{\sim}100rpm$) and stirring temperature($650{\sim}680^{\circ}C$). The optimal conditions for fabricated rheological material of A6061 alloy were stirring time at 300sec, stirring velocity at 60rpm and stirring temperature at $650^{\circ}C$. At these results, the equivalent diameter was $45{\sim}65{\mu}m$, mean roundness was $1.4{\sim}1.6$ and Vickers hardness was 60Hv.

• Design & Manufacturing
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• v.10 no.1
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• pp.31-35
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• 2016

In sheet metal forming process, drawing is typical process. And the key factor of drawing is blank holding force (BHF) A low BHF can cause wrinkling, whereas a high BHF can cause fracture during a deep drawing process. Thus, formability can be influenced by application appropriate BHF. In this study, a variable blank holding force (VBHF) is applied to extend the forming limit by avoiding both wrinkling and fracture. To determine VBHF in drawing process, numerical simulations and statistical analysis are carried out using commercial FEM software.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.45-51
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• 2018

Roll forming refers to the production of long plate-molded products, such as panels, pipes, tubes, channels, and frames, by continuously causing the bending deformation to thin plates using rotating rolls. As the roll forming method has advantages in terms of mass production because of its excellent productivity, the size of the roll forming industry has been continuously increasing and the roll forming method is increasingly being used in diverse industrial fields as a very important processing method. Furthermore, as the roll forming method mainly depends on the continuous bending deformation of the plate materials, the time and the cost of the heterogeneous materials developed in the process are relatively large when considered from the viewpoint of plastic working because many processes are continuously implemented. The existing studies on roll forming manufacturing have reported the loss of large amounts of time and materials when the raw materials or product types were changed; further, they have stated that the use of this method can hardly guarantee the uniformity of the formed shapes and the consistency in terms of size and cannot detect all the defects occurring during the mass production and related to the dimensions. Therefore, in this research, a real-time process data-based smart roll forming method that can be applied to multiple products was studied. As a result, a roll forming system was implemented that remembers and automatically sets the changes in the finely adjusted values of the supplied quantities of individual heterogeneous materials so that the equipment setting changing time for heterogeneous material replacements or changes in the products being produced can be shortened. It also secures the uniformity of the products so that more competitive and precise slide-rail products can be mass-produced with improvements in the quality, price, and productivity of the products.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.281-285
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• 2008

Ferritic stainless steel is used for parts of exhaust system of commercial vehicle, because it has such advantages as low price and high corrosion resistant compared with austenite stainless steel. Even though ferritic stainless steel has these merits, to manufacture multi-layer bellows with complex geometry, austenite stainless steel is being used in the industry, because of it's high ductility. However, recently, the mechanical property of the ferritic stainless is getting improved and alternating austenitic stainless steel. In this paper, the possibility of mass production of bellows made of ferritic stainless steel like MH1 and 443CT is studied. Tensile test and ridging test are carried out to observe mechanical properties of STS304, MH1 and 443CT. Forming analysis using FEM is performed to investigate plastic strain during forming process. Prototype bellows has been made using STS304, MH1 and 443CT, respectively, and fatigue tests are carried out to evaluate fatigue life of bellows.

• Transactions of Materials Processing
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• v.27 no.5
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• pp.301-313
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• 2018

In this paper, tensile test was performed on pure titanium sheet (CP Ti sheet) with HCP structure in each direction to evaluate mechanical and surface properties and analyze microstructural changes during plastic deformation. We also evaluated forming limits of Ti direction in dome-type punch stretching test using a non-contact three-dimensional optical measurement system. As a result, it was revealed the pure titanium sheet has strong anisotropic property in yield stress, stress-strain curve and anisotropy coefficient according to direction. It was revealed that twinning occurred when the pure titanium sheet was plastic deformed, and tendency depends differently on direction and deformation mode. Moreover, this seems to affect the physical properties and deformation of the material. In addition, it was revealed the pure titanium sheet had different surface roughness changes in 0 degree direction and 90 degree direction due to large difference of anisotropy, and this affects the forming limit. It was revealed the forming limit of each direction obtained through the punch stretching test gave higher value in 90 degree direction compared with forming limit in 0 degree direction.

• Transactions of Materials Processing
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• v.13 no.1
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• pp.9-14
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• 2004

Recently, various bulk metallic glasses (BMG's) having good mechanical and chemical properties were developed. BMG's can easily be deformed in the supercooled liquid region, via viscous flow mechanism. By using the viscous flow, the very low pressure is needed to deform the materials. In this study, we investigated the structural transition and deformation behavior of Vitreloy 1 (Zr/sub 41.2/Ti/sub 13.8/Cu/sub 12.5/Ni/sub 10/Be/sub 22.5/) using TMA and DSC. We applied the results to the micro forming process. The forming condition was chosen based on the viscosity data from TMA, and Si wafer with micro patterns on the surface was used as a forming die. The deformed surface was analyzed by SEM and 3D Surface Profiling System. The alloy showed good replication of the patterns. Quantitative measurement of roughness was useful to evaluate the replication. Surface condition of the deformed surface was determined by the initial surface condition.

• Transactions of Materials Processing
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• v.27 no.3
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• pp.139-144
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• 2018

Many studies have been conducted on the process of forming magnesium alloy sheets to reduce the body weights of vehicles. Magnesium has a lower specific gravity than steel and also has a higher specific strength. Mg alloy sheets have low formability and a lot of springback due to their limited ductility and low young's modulus. As the temperature increases, the yield strength of the material decreases. Warm forming increases the formability and minimizes the springback of a material by heating it and the die to reduce the required load at forming. In this study, the temperature of the AZ31B sheet was controlled in order to reduce springback and increase formability. However, as the temperature increased, the deformation characteristics of the material changed and the radius of curvature of the material increased. The load and springback amount required for forming were analyzed according to the temperature and the bottoming force in the bending deformation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.547-554
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• 2013

The fuel storage vessel installed in CNG vehicles can be largely divided into 3 parts: head, cylinder, and dome. Studies of the cylinder and dome parts have already been performed, but sufficient design data is not available about the head part. Therefore, expert field engineers heavily depend upon trial-and-error methods. Therefore, FE analysis is performed to review the hot spinning process for forming the head part of the CNG vessel using the Arbitrary Lagrangian-Eulerian (ALE) method. The effects of forming factors on the load were analyzed. The values of the factors were chosen to avoid defects in the head part and buckling, and the forming feasibility of the head part was investigated. Furthermore, a bursting test was performed to evaluate the safety of the storage vessel.