Papers by Author: Joong Yeon Lim

Abstract: In order to improve the interfacial bonding with polylactic acid, Lyocell fabric’s surfaces were treated with various silanes. The silanes applied were aminoethylaminopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane, respectively. Silane was chosen since hydroxyl group (-OH) in silane always reacts with -OH in Lyocell fabric. As received fabric’s sizing was with a solution containing polyvinyl alcohol (PVA), poly acrylic acid (PAA) and water at the ratio of 3 : 1 : 96. Highest peel test results was obtained with 3wt% silane concentration (3-methacryloxypropyltrimethoxysilane). Highest tensile strength was obtained with 2wt% silane concentration (3-methacryloxypropyltrimethoxysilane). Tensile tests were carried out before analyzing the fracture surface of the composites by scanning electron microscope. FT-IR run confirmed the silane on the surface of fabric.

Abstract: A design methodology was applied to manufacturing a tub for washing machine container. The finite element method was employed to investigate the forming process. The forming process of sheet metal into a tub for washing machine container was selected as a model process to demonstrate the design of improved process sequence which has fewer operation stages than in conventional process. The design procedures made extensive use of the finite element method which can deal with elastic-plastic modeling. A one stage process sequence to form an initial blank to final product has been simulated to obtain information on metal flow requirements. Loading simulation for conventional manufacturing process sequence has been also simulated to evaluate the design criteria. From the simulation results of conventional process sequence, it is concluded that the design criteria should include thickness uniformity in finished tub and maximum punch load within the limit of available press capacity. The newly designed sequence has two forming operations and can achieve net-shape manufacturing, while the conventional process sequence has three forming operations. The design procedure proposed in this study could be considered for the method applied to the development of process sequence design in general.

Abstract: The manufacturing process sequence of a power steering worm gear blank is analyzed. The conventional process sequence for manufacturing power assisted steering (PAS) part contains three distinctive operational stages such as indentation, extrusion, and upsetting, which were originally designed by forming equipment experts. Process conditions such as reduction in area, semi die angle and upsetting ratio are carefully considered to prevent from internal or geometrical defects. The simulation results of the conventional forging process are summarized in terms of deformation patterns, load-stroke relationships and die pressures along the interface for each operational stage. Close investigation of simulation results for current forming process leads to a new process sequence in which the number of operation are reduced into just one operation. Comparisons between the existing and proposed processes are made in terms of maximum force requirement, required forming energy, and process time, respectively. Experiment has been performed to confirm that the proposed process could be applied to replace the existing conventional process sequence and proved the new process to be a safe process sequence for manufacturing PAS part.

Abstract: A finite element method for the compaction process of metallic powder is introduced in the present work. Basic equations for the finite element formulation are summarized. A yield criterion, which is modified by describing asymmetric behavior of powder metal compacts, is introduced and applied to a certain class of powdered metal compaction processes. Two-level flanged solid cylindrical components are analyzed in three different compacting methods with three different compact geometries. The simulation results are summarized in terms of relative density distribution within compacts, pressure distributions along the die-wall interfaces, load-stroke relationships of each punch, average densities as functions of height and radius of the compact, respectively, and average densities of pin and head. For each compact from different compacting method, the best pressing method is chosen for uniform density distributions within the compact.

Abstract: A finite element method for the compaction process of metallic powder is introduced in the present work. Basic equations for the finite element formulation are summarized. A yield criterion, which is modified by describing asymmetric behavior of powder metal compacts, is introduced and applied to various classes of powdered metal compaction processes. Three material parameters are involved in the yield function and determined from the behavior of sintered powder compacts as a function of relative density. The FEM simulation includes single-action and double-action pressings of solid cylinders as well as cylindrical rings of relatively long parts (Class II parts). The compaction process for multi-level flanged components (Class III and Class IV parts) is also analyzed. The predicted results from simulations are summarized in terms of density distributions within the compacts and pressure distributions exerted on the die-wall interfaces, and also in terms of effectiveness with increased relative motions with in the compacts and the effect of various compaction schemes of combination of punch motions. Results obtained in the multi-level compaction process are discussed in terms of average relative density distributions at each height.

Abstract: The cold forging processes of automobile parts such as piston-pin, valve-spring retainer(VSR) and power-assisted steering part (PAS) are analyzed by the rigid-plastic finite element method. The results of the simulation on the piston-pin are summarized in terms of the strain distribution and load-stroke relationship. Based on the analysis on the current processes of VSR and PAS, the new novel processes for improving the conventional process sequences are designed. As a design criterion, the improved processes satisfy the new condition such as an initial billet size, the production time and the limit value of forming load and pressure etc. The present simulation results and the newly developed process gave rise to an improvement in manufacturing processes for cold-forged automobile parts. Furthermore, the numerical analysis for the processes in this study provides a new design concept for forming processes and a basis for the selection of forging equipments.

Abstract: The dissimilar channel angular pressing (DCAP or CCSS) based on the equal channel angular pressing (ECAP) was numerically modeled and analyzed by means of a rigid-plastic two-dimensional finite element method. Multi-pass rolling is performed in two different manners; the feeding direction of samples into the DCAP-channel is maintained in Route A and the feeding direction is reversed in the Route B. The deformation of AA1100 sheets during the DCAP process comprises three distinct processes of rolling, bending and shearing. The shear deformation of an amount of 0.5 was concentrated at the corner of the DCAP-channel where the abrupt change in the direction of material flow occurred. Because differences in the shear deformation in Route A and Route B led to the different strain states throughout the thickness of the aluminum sheet, the strain history in the DCAP-channel was analyzed in various thickness layers by the shear and effective strain components.