Kyoung Hoan Na

Hole Punching onto the Zr65Al10Ni10Cu15 BMG Sheet Fabricated by Squeeze Casting

Bulk metallic glass Zr65Al10Ni10Cu15 was fabricated in a sheet form with thickness 1.5 mm by a squeeze casting method. The structure of the as-cast Zr65Al10Ni10Cu15 sheet was confirmed to be fully amorphous. The sheet was punched into a blank under high hydrostatic pressure at room temperature. A round hole was created with a possible evidence for plastic-like deformation along the edge of rim. No visible cracks were observed around the hole. This result indicates that bulk metallic glasses, which are known to be very brittle at room temperature, can be deformed in a ductile mode under hydrostatic pressure condition. Hydrostatic pressure may suppress the formation and development of micro defects leading to ductile fracture

Dimensional Characteristics of Products Using Rotary Swaging Machine with Four-Dies

Experiments under a cold rotary swaging process have been conducted to investigate the dimensional characteristics of the swaged tube and solid bar for obtaining proper product of desirable quality. Dimensional characteristics are expressed in terms of dimensional deviation and surface roughness of swaged product through the rotary swaging process. The process variables such as forming speed and percent reduction of outer diameter of the product are considered and selected because of playing a key role in the rotary swaging process. Furthermore the developed rotary swaging machine with four-split dies, named as KRSM25, is used in the swaged experiment. Based on the experimental results, it is observed that the process variables affect the quality of swaged product such as dimensional precision, surface roughness of the product. Defect could be found to occur at a value of more than 2.0 mm/rev in forming speed. The dimensional precision of swaged product depends on the percentage reduction of outer diameter and forming speed. The work presented in this paper might be used for available information in the design of the optimum rotary swaging process.

The Microstructure of AZ 31 Magnesium Alloy by Forward Extrusion with Various Extrusion Parameters

Samples of AZ31 wrought magnesium alloy are hot extruded into forward direction with various initial billet temperatures and extrusion ratios (ERs). Usually the insufficient room temperature formability of magnesium wrought alloys makes processing steps like rolling, extrusion etc. difficult, thus limiting their use for rolled or wrought parts. However, in this paper experiment is preformed under the hot forward extrusion process for AZ31 wrought magnesium alloy with different important parameters. Major process parameters such as punch speed, billet temperatures and ERs are considered and applied to the hot extrusion process with a constant value of the die land. The influence of different billet temperatures and ERs on the hot forward extrusion process is investigated and analyzed in terms of the grain flow, microstructure, grain size and hardness distribution of formed part for magnesium and Mg alloy. Maximum forming loads for various main parameters is tackled and checked to know the optimum forming load for hot forward extrusion process. Also finest grain sizes and an inhomogeneous microstructure of extruded parts seem to occur near the die land of tool-set due to the anisotropic plastic behavior during the hot extrusion process. Extrusion properties such as extrusion load, grain size, micro hardness and surface quality are compared between the main parameters during the hot forward extrusion process. In addition it is easily disclosed from the experiment results that the die land designed for safe tool-set plays a key role in improving the mechanical properties of formed product during hot forward extrusion process for AZ31 magnesium alloy.

Cold Rolling Technique for Eliminating Cutting Process in Manufacturing Precise Product Using Non-Heat-Treated Micro Alloys

In general micro alloy steel have the higher strength relative to conventional steels, which limits the utilization of conventional plastic forming processes. Incremental forming processes are more suitable for cold forming of such a high strength material. In particular, cold cross wedge rolling (CWR) can be a potential tool to fabricate axi-symmetric components with multi steps using high strength micro alloy steel. Obviously, optimization of die shape design is a crucial factor to apply cold cross wedge rolling to micro alloy steels. In this regards, a simulation-based process design using an elasto-plastic FEM has been carried out in order to obtain an optimum die shape for cold cross wedge rolling in this paper. Analysis results provided that the stretching angle and the shoulder angle at knifing and guiding zones were significant parameters for the stable forming process. It was demonstrated that proper stretching and shoulder angles reduced an excessive slip between a work piece and die in CWR process despite the condition of the low friction coefficient.

Forming Technology for Cold Forging Processes of Ball Stud Using Non-Heat-Treated Cold Forging Materials

A microalloyed (MA) forging steel is non-heat-treated materials that have been replacing for conventional quenched and tempered (Q/T) structural steels since the MA forging steels are very cost-effective compared with Q/T steels for the production of automotive parts. However, due to a high strength and low elongation, it has been difficult to apply the MA cold forging steel to the ball stud for automobile. In this study, finite element analyses were carried out to investigate the forming loads, the stress and strain distributions of the workpiece in the cold forging processes of the ball stud using the MA cold forging steel. Compression test at room temperature and fatigue test were also performed to obtain the flow stress and fatigue life, respectively. From these results, it was found that the fatigue life was greatly affected by the strength in the neck region of the ball stud and the cold forging processes should be designed to improve the fatigue life of the ball stud used the MA cold forging steel.

Particle Size Reduction of Biomaterials Using Cryogenic Milling Process

Reducing the particle size of drug materials down to submicron is an important matter in pharmaceutical industry. Cryogenic milling technology is one of the mechanical milling processes, which is mostly utilized in refining grain size of metal and ceramics at extremely low temperature environment. This technique has not been readily studied in application to medical and biotechnology. This paper, therefore, describes the application of cryogenic milling process to reduce particle size of Ibuprofen. The shape and size of the Ibuprofen particle before and after the cryogenic ball milling process were analyzed. XRD analysis was performed to examine a change in crystallinity of Ibuprofen by the cryogenic ball milling process. The results showed that the size of Ibuprofen particles was reduced to 1/10 or less of its initial size. The results also showed that the degree of crystallinity of Ibuprofen was slightly reduced after cryogenic ball milling with nitrogen.

Study on Nanolithography Process of Polycrystalline Copper Using Molecular Dynamic Simulation

Molecular dynamics simulations are performed to verify the effect of grain boundary on nanolithography process. The model with about two hundred thousand copper (Cu) atoms is composed of two different crystal orientations of which contact surfaces are (101) and (001) planes. The grain boundary is located on the center of model and has 45 degreeangle in xz-plane. The tool is made of diamond-like-carbon with the shape of Berkovich indenter. As the tool is indented and plowed on the surface, dislocations are generated. Moreover, during the plowing process, the steps as well as the typical pile-ups are formed in front of the tool. These defects propagate into the surface of the substrate. As the tool approaches to the grain boundary, the defects are seen to be accumulated near the grain boundary. The shape of the grain boundary is also significantly deformed after the tool passes it. We observed the forces exerted on the tool by the contact with substrate, so that the friction coefficients can be obtained to address the effect of the grain boundary on the friction characteristics.

Upsetting of Ultrafine-Grained Bulk Al-Mg Alloy Consolidated by Hydrostatic Extrusion

Deformation characteristics and forming limit of ultrafine-grained bulk Al-Mg alloy were examined with upsetting process. The Al-7.5%Mg alloy produced by cryogenic milling and HIP was subjected to hot hydrostatic extrusion as a final consolidation in fabricating the ultrafine-grained bulk material. Upsetting was performed to study their mechanical characteristics in a practical forming process. The extruded specimen showed that the pores remained in spite of the HIP had been collapsed and almost eliminated. The effective removal of the distributed pores resulted in significant increase of formability by preventing early cracking. Metallographic investigations showed that the size of grain remained below a few hundred nanometer scale in the processes.

Chipless Forming Process Using Rotary Swaging Machine with Four-Dies

The rotary swaging process for producing solid bars, tubes or wires is often used to obtain the chipless forming process compared with the conventional process such as the machining and welding operation. Furthermore, machined chip, dust particles, harmful gas, and surface contamination to be commonly generated at hot working during the conventional process could be eliminated as the swaging process is applied and conducted at room temperature. Experiments for swaged product were performed to analyze the influence of the swaging process on the mechanical properties and dimensional precision in terms of surface roughness, surface hardness, and deviation of formed dimension. The changes of dimensional precision in swaged product are also checked out and considered for various process parameters such as the forming speed and the reduction in the outer diameter. Based on the experimental results, the surface roughness is improved under the swaging process. The weight of rod shift is reduced by about 15 % from 223.5 g to 190.2 g. Thus the number of operations to produce the final product under the conventional process is larger than that under the swaging process to be able to omit the machining and welding operation, etc. This paper demonstrates that a rotary swaging process turns out to be an environment-friendly forming process or chipless forming process without the machined chip.

Process Conditions and Interfacial Characteristics of Al/Cu Clad Composite Formed by Hot Hydrostatic Extrusion

The relations between interfacial properties of clad composite and process conditions are studied. Adherence on interface of two materials is most significant property of clad composite. Properties of composite material are manifestation of its microstructure, and process conditions are decisive factor to the microstructure in interfacial area. In-depth understanding about the composite’s properties is only achieved through appreciation of the mechanism by which the process conditions affect the microstructure. Aluminum and copper clad composite bars are extruded at the various process conditions. Interfacial adherence of the extruded composite is examined. Microstructure of the dispersed layer and its vicinity is investigated.