Kyung-Hun Lee

Influence of Tool Shape on Hole Clinching for Carbon Fiber-Reinforced Plastic and SPRC440

Carbon fiber-reinforced plastic (CFRP) is a lightweight material that can potentially replace structural steel components in automobiles. The hole-clinching process is a mechanical clinching technique for joining brittle or low-ductility materials, such as CFRP, with ductile materials. In this study, the influence of tool shape on the hole-clinching process for CFRP and SPRC440 was investigated using FE-analysis and experiments. The parameters of the tool shape investigated were the punch corner radius and the punch diameter. The geometrical interlocking shapes of hole-clinched joints were characterized by neck thickness and undercut. Based on the desired joint strength of 2.5 kN, hole-clinching tools were designed on the basis of the relationship between joint strength and geometrical interlocking. FE-analysis and hole-clinching experiments were performed with the designed hole-clinching tools to investigate the geometrical interlocking shape as well as joinability, including neck fracture, undercut, and hole expansion, resulting from changes in tool parameters. Joint strength was evaluated to verify the effectiveness of hole clinching by a single lap shear test.

Densification simulation of compacted Al powders using multi-particle finite element method

Abstract The powder compaction simulations were performed to demonstrate deformation behavior of particles and estimate the effect of different punch speeds and particle diameters on the relative density of powder by a multi-particle finite element model(MPFEM). Individual particle discretized with a finite element mesh allows for a full description of the contact mechanics. In order to verify the reliability of compaction simulation by MPFEM, the compaction tests of porous aluminum with average particle size of 20 μm and 3 μm were performed at different ram speeds of 5, 15, 30 and 60 mm/min by MTS servo-hydraulic tester. The results show that the slow ram speed is of great advantage for powder densification in low compaction force due to sufficient particle rearrangement and compaction force increases with decrease in average particle size of aluminum.

Effects of elastic-plastic properties of materials on residual indentation impressions in nano-indentation using sharp indenter

Abstract One of the primary features of nano-indentation technique is that the contact area induced by an indenter is indirectly measured by a relationship between the penetration depth and the known geometry of the indenter. However, this indirect measurement occasionally leads to inaccurate properties of the indented material. The objective of this study is to investigate the effects of E*/σr and the strain hardening exponents n of materials on the behaviors of pile-up and sink-in in nano-indentation and to predict n values of materials from the residual indentation impressions. The relations between the residual indentation profile and n value of the indented material were identified by dimensional analysis. Also, they were numerically formulated using FE analysis of nano-indentation for 140 different combinations of elastic-plastic parameters such as E, σy and n. The parameters of hrp/hm, herp/hm, Rr/hm and HO&P/Hreal were introduced as various dimensionless parameters to represent and quantify the residual indentation profile after indentation. They were subsequently characterized as dimensionless functions using n and E*/σr values. Finally, the validity of these functions was verified through 3D FE analysis of nano-indentation for Al 6061-T6 and AISI 1010 materials.

Development of Three-Dimensional Strip Profile Model for Thin-Foil Cold Rolling

Accurately predicting the strip profile after thin-foil cold rolling is very difficult because of the thinness of the strip. In this study, a three-dimensional (3D) strip profile model was developed to improve the accuracy of a rolled thin-foil profile. The distribution of the contact pressure between rolls (i.e., the work, intermediate, and backup rolls) and the rolling pressure between the strip and work roll were calculated by using the geometric structure of a 6-high mill and boundary conditions imposed in the width direction by a numerical method. The rolling pressure distribution in the rolling direction was determined by Flecks model of thin-foil rolling. The 3D rolled-strip profile was predicted by using the pressures in the width and rolling directions. In order to investigate the effect of the rolling speed and rise in strip temperature on the lubrication, the friction coefficient was estimated through an analytical method and experiments to test the viscosity and friction. The resulting 3D strip profile was verified by a thin-foil cold rolling test and was compared with the profile obtained using the proposed 3D model and finite element simulation.

FEA technique of hot plate forming process using cell-typed die with cooling device

Abstract Hot plate forming using a cell-typed die is a process for forming a large thick plate with a spherical shape for the manufacture of a large spherical LNG tank. Cell-typed upper and lower dies made of a framework of steel plates fitted to make a grid pattern are used in this process, and an air-cooling device is separately installed inside the lower die. A finite element analysis (FEA) technique was developed, which included hot forming, air flow, cooling and thermal deformation analysis for the hot plate forming process using the cell-typed die. Further, the convective and interface heat transfer coefficients were used to reproduce analytically the effects of the cooling device in the hot plate forming analysis. A small-scale model test of the process was conducted to verify the FEA technique. The analysis results show that the curvature of the final plate agrees well with that of the designed experiment within a maximum relative error of 0.03% at the corner of the plate.

Prediction of Bending Stiffness for Laminated CFRP and Its Application to Manufacturing of Roof Reinforcement

Recently, carbon fiber reinforced plastic (CFRP) with high strength, stiffness, and lightweight is used widely in number of composite applications such as commercial aircraft, transportation, machinery, and sports equipment. Especially, it is necessary to apply lightweight materials to car components for reducing energy consumption and CO2 emissions. In case of car roof reinforcement manufactured using CFRP, superior strength and bending stiffness are required for the safety of drivers in the rollover accident. Mechanical properties of CFRP laminates are generally dependent on the stacking sequence. Therefore, research of stacking sequence using CFRP prepreg is required for superior bending stiffness. In this study, the 3-point bending FE-analysis for predicting the bending stiffness of CFRP roof reinforcement was carried out on three cases [ 0 PW ∘ ] 5 , [ 0 PW ° / 0 UD ° / 0 - PW ° ] s , and [ 0 UD ∘ ] 5 . Material properties that the six independent elastic constants are E11, E22, G12, G23, G13, and ν12 used in FE-analysis were evaluated by the tensile test in 0°, 45°, and 90° directions. Through structural strength analysis of the automobile roof reinforcement fabricated using CFRP, the effect of the stacking sequence on the bending stiffness was evaluated and validated through experiments under the same conditions as the analysis.

Fabrication of miniature helical gears by powder extrusion using gas atomized Zn−22%Al powder

Abstract Powder extrusion, which is based on the superplastic behavior of Zn–22%Al eutectoid alloy, was proposed to reduce the forming load and promises to provide fine microstructures in the manufacture of miniature helical gears. The specifications of the helical gears were as follows: module, 0.3; number of teeth, 12; and helix angle, 15°. Compacted powders were consolidated by sintering and solution heat treatment. The consolidated billets consisted of lamellar and fine-grained microstructures. Extrusion experiments were carried out under the following conditions: temperature, 250 °C; strain rates, 2.36×10 −3 s −1 and 1.18×10 −1 s −1 . The mechanical properties of the extruded helical gears were investigated by measurement of the Vickers hardness and extrusion load, and by scanning electron microscopy.

Advanced simulation of die wear caused by wire vibrations during wire-drawing process

An advanced simulation that considers the effect of wire vibrations was proposed for predicting accurately wear profiles of a die used in a wire-drawing process. The effect of wire vibrations, the changes in the wear profiles, and the generation of ringing during die approach were investigated by this simulation. Wire vibrations occurring between the die and the drum are governed by a partial differential equation called the wave equation, which is a function of the wire length, tension, density, and initial wire velocity. The wire-drawing process was simulated by the commercial code Abaqus FEA, and the die wear profiles were predicted by Archards wear model. The predicted profiles were compared with measured profiles of a worn drawing die after producing 5 t of AISI 1010 wire; the die was made of tungsten carbide with a Brinell hardness of HB 682. The profiles predicted by considering the effect of wire vibrations are in good agreement with the experimental data, indicating that the advanced simulation can be used to accurately predict the die wear profiles when ringing is observed during die approach.

Particle Behavior and Deformation During Compaction of Al Powder Using MPFEM

This paper describes multiparticle finite element model (MPFEM)-based powder compaction simulations performed to demonstrate the densification of compacted aluminum powders. A 2D MPFEM was used to explore the densification of a collection of aluminum particles with different average particle sizes under various ram speeds. Individual particles are discretized using a finite element mesh for a detailed description of contact mechanics. Porous aluminum powders with average particle sizes of and were compressed uniaxially at ram speeds of 5, 15, 30, and 60 mm/min by using an MTS servo-hydraulic tester. The slow ram speed was of great advantage to powder densification in low compaction force due to sufficient particle rearrangement. Owing to a decrease in the average particle size of aluminum, the compaction force increased.

Process Design of Trimming to Improve the Sheared-Edge of the Vehicle Door Latch based on the FE Simulation and the Taguchi Method

Automobile door latch is a fine design and assembly techniques are required in order to produce them in a small component assembly shape such as a spring, injection products, a small-sized motor. The door latch is fixed to not open the door of the car plays an important role it has a direct impact on the drivers safety. In this study, during trimming of the terminals of the connector main components of the car door latch, reduce rollover and conducted a research to find a suitable effective shear surface. Using the Taguchi method with orthogonal array of Finite Element Analysis and optimal Design of Experiments were set up parameters for the shear surface quality of the car door latch connector terminals. The design parameters used in the analysis is the clearance, the radius, and the blank holding force, the material of the connector terminal is a C2600. Trimming process optimum conditions suggested by the analysis has been verified by experiments, the shear surface shape and dimensions of a final product in good agreement with forming analysis results.Taguchi method from the above results in the optimization for the final rollover and effective shear surface improved for a vehicle door latch to the connector terminal can be seen that the applicable and useful for a variety of metal forming processes other than the trimming process is determined to be applicable.