Jae-Seung Cheon

Determination of Friction Condition by Geometrical Measurement of Backward Extruded Aluminum Alloy Specimen

The proper determination of friction condition during metal forming operations is imperative for successful process design and production of parts. Through the years, various methods of determining the friction condition have been proposed, but all methods have some drawbacks. In this study, a new type of friction test named tip test based on backward extrusion of AL6061-O is proposed. The experimental set-up of this method induces the formation of a sharp radial tip on the extruded end of the workpiece. It has been found that the simple geometrical measurement of this radial tip position can be used to effectively determine the friction condition.

Finite Element Investigation of Friction Condition in a Backward Extrusion of Aluminum Alloy

The authors wish to thank for the grant of Basic Research Fund from KAIST and BK21 project.

Simulation of clutch-hub forging process using CAMPform

Abstract An inner gear component, clutch-hub, was chosen as the object for a numerical study investigating the usefulness and effectiveness of employing numerical simulations in the design process of metal forming parts. A computer-aided design simulation tool CAMP form was employed in this study. Simulations for S10C steel using various die and workpiece geometries were carried out, and completeness of filling and load requirements were compared to determine the forming condition most suitable for production of the clutch-hub. The effect of shear friction factor on the forming process was examined using the most suitable die and workpiece geometries. Also, study on aluminum alloys Al1100-O, Al2024-T3, Al6061-T4 and Al7075-T4 with respect to their defect factors of work hypothesis, ( C 1 ) and Cockcroft and Latham ( C 2 ) were made in this paper. It was found that only Al6061-T4 could be considered as a substitute material of steel for cold forging of the clutch-hub.

Experimental and numerical study of the impact behavior of SMC plates

Abstract Steel components absorb impact energy by plastic deformation whilst composite materials absorbing it by damage mechanisms such as fiber debonding, fiber fracture, and matrix cracking. Therefore, in order to properly substitute metal components with composite ones in industrial applications, the impact property of composite materials must be well known. In this study, the impact behavior of sheet molding compounds (SMC), which is widely used in automobile industry due to its relatively low cost and high productivity, was examined both experimentally and numerically. In order to investigate the impact behavior of SMC, an experimental study was carried out by setting up a drop weight impact test system. Using this system, the dissipated impact energies of SMC flat plates were measured to investigate the influence of the mass and shape of impactor, initial velocity, and specimen thickness on the impact behavior. For numerical predictions, a modified damage model for SMC was developed and adopted in the user defined material subroutine of the commercial simulation program LS-DYNA3D. For the sake of improving efficiency of impact simulations, the SMC material property was determined in consideration of the local differences of the fiber volume fractions. The dissipated impact energies under various conditions and the reliability of the developed impact simulation process were examined through comparisons of the predicted data with the experimental results. From this comparison, it was found that, in the scope of current study, the specimen thickness is the most important parameter that should be considered in the design of SMC components for the aspect of impact behavior.

Optimal design of composite hood with reinforcing ribs through stiffness analysis

Fiber glass reinforced composites like sheet molding compounds (SMC) have recently been widely used in the fabrication of two-piece automobile hoods for passenger cars. In the present investigation, a one-piece composite hood with reinforcing ribs was optimally designed and manufactured by resin transfer molding in order to reduce manufacturing cost. In order to obtain the optimal design, stiffness analyses for deflections due to self-weight, oil canning, and torsion test conditions were carried out by applying the ABAQUS/Standard program. Based on these analyses, the thickness dimension of the composite hood required to maintain a stiffness comparable to a conventional steel hood was determined. For optimization studies of the weight reduction of the currently proposed one-piece composite hood with reinforcing ribs, IDESIGN program was employed. Based on a recursive quadratic programming technique, the thickness dimensions of the reinforcing ribs were optimized. The deflection ratios between fiber glass reinforced composite and conventional steel hoods were minimized in the optimization studies. From the present studies, it was found that the weight saving effect obtained by introducing the optimally designed one-piece composite hood was 37% compared to the conventional steel hood. This ranged approximately from 30 to 40% for composite hoods manufactured by resin transfer molding, depending on the composite materials used. Through these studies, it was confirmed that the one-piece composite hood was a preferable design and manufacture, compared to currently used composite hood made in two pieces, in terms of weight reductions and manufacturing cost without losing the stiffness required.

A Novel Technique of Friction and Material Property Measurement by Tip Test in Cold Forging

Abstract Tip test experiments and simulations showed that the relationships between the tip distance, forming load, and shear friction factor were linear for all tested materials of aluminium alloys, steel, and copper. The ratio of the shear friction factor of the workpiece-die interface to that of the workpiece-punch interface was determined to be in the range of 23–60 per cent depending on the material. Also a logarithmic relation between the ratio of these two shear friction factors and the strain-hardening exponent of the material was found in the present investigation. Finally, it was clearly demonstrated that the tip test can be used to determine effectively the material property with decoupling of the friction effect in compression tests.

Three-dimensional bulk metal forming simulations under a PC cluster environment

Abstract The design of bulk forming parts can greatly benefit from three-dimensional finite element (FE) analyses. However, three-dimensional simulations of bulk forming processes involve large computation time and memory. Advances of personal computer (PC) technology have made it feasible to use PCs for three-dimensional simulations recently. In particular, PC clusters, a group of PCs connected by local area network (LAN) for communication, have been introduced as a cheaper alternative to parallel supercomputers. The current study is an investigation of bulk metal forming analysis in a PC cluster environment. For effective use of the PC cluster, two parallel processing algorithms were investigated. At first, columns of the global stiffness matrix were distributed amongst processors and secondly physical domain of the problem was divided into sub-domains. Since the relative performance of these two approaches usually depends on the type of the problem, a pre-simulation tool that can suggest the parallel solving approach and number of processors that will lead to least computing time for a given bulk forming problem was developed based on upsetting simulations. The effectiveness of the pre-simulation tool was examined through simulation of swash plate forging. Considering the economical benefit of PC clusters, the result of current investigation should lead to the increase of three-dimensional FE simulations in the design of bulk forming processes in forming industry.

Determination of Short Glass-Fiber Volume Fractions in Compression Molded Thermoset Composites—Experimental:

Prediction of volume fraction of short glass-fibers in compression molded thermoset composites parts such as sheet molding compounds (SMC) is of importance since their distribution affects the mechanical property and surface quality. In the present study, a simple approach based on digital image processing technique was applied in determining the fiber volume fraction distribution in the compression molded flat plate of SMC. Although the present digital image processing approach does not have the resolution to distinguish individual fiber diameters, it is capable of determining fiber concentrated regions, and thus an effective means of determining the global distribution of fibers in a single process is provided. As molding conditions, two different molding temperatures and velocities as well as two different compression ratios were investigated to determine the influence of molding parameters on the glass-fiber volume fraction distributions. It was found that a rather uniform distribution of glass-fibers was obtained under the condition with smaller compression ratios and faster mold closing speeds, whilst the effect of mold temperature on volume fraction distribution being negligible. The validity of the proposed scheme was estimated by comparing the predicted volume fraction distribution with the experimental result obtained from the conventional burning-test measurement. The comparison clearly demonstrates the simplicity and capability of the digital image processing technique applied under the present condition.

Finite element simulation of SMC compression molding based on thermo-viscoplastic approach with fiber volume fraction prediction

SMC (Sheet Molding Compounds) is a thermosetting material which consists of unsaturated polyester resin and other additives reinforced with randomly distributed chopped fiberglass strands. During the compression molding cycle, it is very difficult to understand the overall effects of SMC resin components on flow characteristics and mechanical performance of the molded parts, since mold geometries and processing variables are complex. Thus, a three dimensional rigid thermo viscoplastic finite element program including chemical reaction and fiber volume fraction prediction was developed in the present study and applied to the analysis of compression molding of a SMC charge. To verify the validity of this approach, numerical fiber volume fraction predictions were compared to fiber volume fraction data measured by image processing. Three dimensional simulations under various molding conditions were carried out to obtain more thorough knowledge of the SMC compression molding process. Based on this study, it was found that the currently developed three dimensional finite element program coupled with heat transfer and chemical reaction can provide valuable information in understanding flow characteristics, fiber volume fraction distribution, and the curing behavior of SMC compression molding in detail.