Seogou Choi

Upper-bound analysis of the rotary forging of a cylindrical billet

Abstract Rotary forging, an incremental forming processes, is a cost-effective forming method for the cold forging of intricate parts to net shape. The workpiece is gradually deformed between an upper conical die having orbital motion with an inclined rotating axis, and the lower die moving upwards. For the analysis of this forging process, a simple velocity field which can satisfy all of the velocity boundary conditions is proposed. From the derived velocity field the upper-bound force is determined by minimizing the total power consumption with respect to some chosen parameters, and velocity distribution is investigated also. Experiments are carried out with carbon steel (AISI1020, AISI1045) and aluminium (6061) and the results then compared with theoretical results. The theoretical predictions of forming force are shown to be in good correspondence with the experimental measurements. Therefore, this analysis seems to be available for the prediction of the forming force and to investigate the influence of the forming parameters on the design of the forging process.

Three-dimensional rigid-plastic FEM simulation of metal forming processes

A three-dimensional finite element modeling (FEM) code for simulation of bulk forming processes has been developed. Some techniques, such as die surface description, contact judgment algorithm, and remeshing, are proposed to improve the robustness of the numerical solution. To verify the proposed method, the isothermal forging process of a cylindrical housing has been simulated. The simulation results show that the given techniques and FEM code are reasonable and feasible for three-dimensional bulk forming processes.

Application of intelligent design support system for multi-step deep drawing process

Abstract This study is concerned with the development and application of intelligent design support system for the deep drawing process of the circular cup. Developed system is composed of several modules to help process designers acquire optimal process design easily and effectively; input module, material DB module, process design module, rule customizing module, result module, etc. Adopting case reasoning scheme, design support system can suggest various possible processes for a product. Designers can easily choose the best one of them based on his experience or simulation carried out in the design support system. Design parameters can be customized in order to optimize the process design according to materials and product shape. Several applications are shown to prove the performance of developed system.

Ductile fracture in axisymmetric extrusion

Abstract A ductile-fracture criterion, which was proposed previously namely, ( Δ l/l 0 ) f at Δ σ m =( Δ l/l 0 ) f +(−1/ tan θ) Δ σ m (where (Δl/l0)f is the fracture elongation and Δσm is the mean stress variation) was made use of to study the working limit in axisymmetric extrusion. The present investigation is concerned with the application of theory on flow and fracture to the prediction of the workability of materials in axisymmetric bar extrusion, with special reference to central bursting. The influences of die geometry and manufacturing conditions on central bursting are predicted.

Finite element analysis to optimize forming conditions for lower control arm

Finite element simulations for the press forming of a lower arm are performed using the explicit dynamic finite element method (FEM) code PAM-STAMP. To optimize the press-forming conditions and secure a safe product without any failure, such as fractures and wrinkling, the FEM simulations are coupled with Taguchi’s orthogonal array experiment. Three design variables—the friction coefficient, plastic anisotropy parameter, and blank shape—are selected to be optimized. The numeric simulations reveal that the blank shape is the most important variable, and its modification is most effective in optimizing the press-forming conditions for a lower arm. In addition, the modified blank shape produces a high yield ratio for the in-come coil. The simulation results are confirmed with experimental ones.

Development of the Roll Type Incremental Micro Pattern Imprint System for Large Area Pattern Replication

Flexible display has been attracting attention in the research field of next generation display in recent years. And polymer is a candidate material for flexible displays as it takes advantages including transparency, light weight, flexibility and so on. Rolling process is suitable and competitive process for the high throughput of flexible substrate such as polymer. In this paper, we developed a prototype of roll-to-flat (R2F) thermal imprint system for large area micro pattern replication process, which is one the key process in the fabrication of flexible displays. Tests were conducted to evaluate the system feasibility and process parameters effect, such as flat mold temperature, loading pressure and rolling speed. 100 mm × 100 mm stainless steel flat mold and commercially available polycarbonate sheets were used for tests and results showed that the developed R2F system is suitable for fabrication of various micro devices with micro pattern replication on large area.

Research on the Modulating of the Desktop Micro Forming System to Micro Factory

The micro pump module is used in so many MEMS applications, such as medical, fuel cell, display and chemistry fields. The micro pump module is consisted of actuating component, chamber plate, upper/lower fluidic channel plates and thin valve. This micro pump must have a specific performance that is high compressibility and high speed operating response. A polymer thin film is used as a valve component in micro pump module. But this polymer thin film has a low elastic characteristic so cannot operate with high frequency. If this polymer thin valve can be changed to metallic material, thin valve component can operate with high frequency because metal has a high elastic characteristic. As forming components are small in size, forming equipment must also be small in size because the forming die and load must be small. The micro forming press system is high precision forming equipment that can manufacture the precision component. This precision component has a size of several micros to millimeters and precision of sub-micro to micrometer. In this paper, we research about the metallic thin foil valve manufacturing technology to have a high frequency response. This metallic valve has a 30 mum thickness and minimum pattern size of 500 mum. And we develop the miniaturized press system that has a desktop size and a precision compound die set. This compound die set can operate in piercing and blanking process.

Plastic Deformation Characteristics Of AZ31 Magnesium Alloy Sheets At Elevated Temperature

Using lightweight materials is the emerging need in order to reduce the vehicle’s energy consumption and pollutant emissions. Being a lightweight material, magnesium alloys are increasingly employed in the fabrication of automotive and electronic parts. Presently, magnesium alloys used in automotive and electronic parts are mainly processed by die casting. The die casting technology allows the manufacturing of parts with complex geometry. However, the mechanical properties of these parts often do not meet the requirements concerning the mechanical properties (e.g. endurance strength and ductility). A promising alternative can be forming process. The parts manufactured by forming could have fine‐grained structure without porosity and improved mechanical properties such as endurance strength and ductility. Because magnesium alloy has low formability resulted form its small slip system at room temperature it is usually formed at elevated temperature. Due to a rapid increase of usage of magnesium sheets in au...

Note: in situ parameter extraction from a nonlinear dynamic model for electrical characterization of organic light emitting diodes.

This Note presents a nonlinear device model for organic light emitting diodes (OLEDs), which can describe dynamic and static characteristics of OLEDs consistently. The parameters of the proposed model are estimated by using a particle swarm optimization algorithm. Some of the resulting parameters relate with physical characteristics of OLEDs. With only one set of experiments leading to a time response of an OLED device, this nonlinear model, together with all the parameters, is obtained, which can be a big advantage for the fast quality control of the OLEDs.

Experiment Study of Micro hot-embossing process using GC mold and PC substrate

Micro semi-pyramidal pattern arrays were directly created on the commercially available polymer substrate (polycarbonate, PC) by pressing a glassy carbon (GC) mold in the hot-embossing process with self-made hot-embossing machine. The micro feature of negative cavity on the GC mold was fabricated by Focus Ion Beam technique (FIB). The cavities were approximately 65times70 um at width and 42 um at depth. The space periodicity between the micro cavities is about 120times120 um. By adopting an orthogonal design of experiment method with four parameters of the micro hot-embossing process, each one at three levels was studied. The key parameters which have important influence to the forming result, such as embossing force, embossing temperature, heating time and force holding time were studied. Good forming result was obtained by using a set of optimal parameters according to analysis of experiment data.