Beong Bok Hwang

The Forming Characteristics of Simultaneous Radial-Forward Extrusion Processes

Numerical simulations are applied to investigate the simultaneous radial-forward extrusion process in a combined extrusion such as subsequent radial-forward extrusion after radial extrusion. Design factors for the process such as gap height, deflection angle into annular gap and frictional condition are employed in the analysis. The analysis is focused to see the influence of design factors on the maximum force requirement for the forming process. One of the selected simulation results is compared with the experiments in terms of load-stroke relationships. The pressure distributions exerted on the die-wall interfaces are also investigated to reveal if the tooling system is safe, especially the die set. The plastic stress-strain relationship is derived analytically from the material constants used in elastic deformation analysis. It is revealed from the simulation results that the influence of the deflection angle on the maximum force requirement for the process is greatest among design parameters. AA 6063 alloy is selected as a model material for the analyses in this study.

Deformation Analysis of Co-Extrusion Process of Aluminum Alloy and Copper Alloy

This paper is concerned with the analysis of plastic deformation of bimetal co-extrusion process. Extrusion is related to large deformation of material and leads to non-homogeneous deformation within work-piece material. The mechanism of plastic deformation during the composite rod extrusion is much more complicated than that in single metal extrusion. Deformation patterns of co-extrusion of two different materials are characterized by several process parameters. In this paper, the analysis is focused to investigate the effect of contact conditions along the interface between two different materials. The rigid-plastic finite element method was applied to the analysis of co-extrusion process. The selected materials are AA 1100 aluminum alloy as hard material and CDA 110 as soft one. This type of material selection was to examine the effect of hard core and soft sleeve and vice versa in terms of deformation pattern. The initial composite billets were prepared by inserting the core material in tight (0.023mm) and weak (0.012mm) interference bonding, respectively. Four different cases of co-extrusion process in terms of material combination and interference bonding were simulated to investigate the effect of material arrangement between core and sleeve, and of bonding on the plastic zones. It is concluded from the simulation results that the plastic zones in this co-extrusion process are not influenced much by the selection of material arrangements or bonding condition between construction materials. However, it was seen from the simulation results that the extrusion ratio of each construction material, i.e. homogeneity of co-extrusion, depends much on the material arrangement and the bonding condition.

An Analysis on the Forming Load of AA 2024 Aluminium Alloy in Combined and Sequence Operation Process

This paper is concerned with the analysis of the forming load characteristics of a forward-backward can extrusion in both combined and sequence operation. A commercially available finite element program, which is coded in the rigid-plastic finite element method, has been employed to investigate the forming load characteristics. AA 2024 aluminum alloy is selected as a model material. The analysis in the present study is extended to the selection of press frame capacity for producing efficiently final product at low cost. The possible extrusion processes to shape a forward-backward can component with different outer diameters are categorized to estimate quantitatively the force requirement for forming forward-backward can part, forming energy, and maximum pressure exerted on the die-material interfaces, respectively. The categorized processes are composed of combined and/or some basic extrusion processes such as sequence operation. Based on the simulation results about forming load characteristics, the frame capacity of a mechanical press of crank-drive type suitable for a selected process could be determined along with securing the load capacity and with considering productivity. In addition, it is suggested that different load capacities be selected for different dimensions of a part such as wall thickness in forward direction and etc. It is concluded quantitatively from the simulation results that the combined operation is superior to sequence operation in terms of relatively low forming load and thus it leads to low cost for forming equipments. However, it is also known from the simulation results that the precise control of dimensional accuracy is not so easy in combined operation. The results in this paper could be a good reference for analysis of forming process for complex parts and selection of proper frame capacity of a mechanical press to achieve low production cost and thus high productivity.

Influence of Punch Geometries on the Divided Material Flow in a Double Cup Extrusion Process

This paper provides an analysis of the deformation patterns in a backward can extrusion combined simultaneously with a forward can extrusion process, which is known as a double cup extrusion process. The main objective of this study is to examine the divided material flow characteristics in DCEP. Analyses were conducted in a numerical manner by employing a rigid-plastic finite element method. Among many process parameters, the major design factors chosen for analysis include the reduction in area (RAB), the wall thickness ratio (TR), the punch nose radius (R), and the friction condition. The simulation results were summarized in terms of relationships between the process parameters and the ratios of extruded length and volume, and between the process parameters and force requirements, respectively. Comparisons between a multi-stage forming process in sequential operations and one-stage combined operation were also made in terms of the forming load and pressure exerted on the tool. The force requirement and self-regulating characteristics were more greatly influenced by the wall thickness ratio among the selected major design factors. And more severe load to form the same shape is expected in sequential operations than in a combined extrusion process.

Experimental Assessment of Mechanical Properties of Geo-grid Reinforced Material and Long-Term Performance of GT/HDPE Composite

This paper is concerned with the long-term performance of geo-textile (GT) composites in terms of creep deformation and frictional properties. Composites of PVA GT and HDPE GM were made to investigate the advanced properties of long-term performance related to waste landfill applications. The same experiments were also performed for typical polypropylene and polyester GT and compared to PVA GT/HDPE GM composites. We also develop high performance GT composites with GM by using PVA GT, which is capable of improving the frictional properties and thus enhances long-term performance of GT composites. Experimental study reveals that the friction coefficient of GT composites is relatively large compared with those of polyester and polypropylene non-woven GT as long as the friction media has similar size to the particles of domestic standard earth. In addition, the geo-composites bonded with geo-grid by a chemical process were investigated experimentally in terms of strain evaluation and creep response values. Geo-grid plays an important role as a reinforcing material. Three kinds of geo-grid were prepared as strong yarn polyester and they were woven type, non-woven type, and wrap knitted type. The sample geo-grids were then coated with PVC. The rib tensile strength tests were conducted to evaluate geo-grid products in terms of tensile strength with regard to single rib. The test was performed according to GRI-GGI. It was concluded again from the experiments that the tensile and creep strains of the geo-grid showed such stable values that the geo-grid prepared in this study could protect geo-textile partially in practical structures.

An Analysis on the Surface Expansion of Aluminium Alloys in Backward Can Extrusion Process

This paper is concerned with the analysis on the surface expansion of AA 2024 and AA 1100 aluminum alloys in backward extrusion process. Due to heavy surface expansion appeared usually in the backward can extrusion process, the tribological conditions along the interface between the material and the punch land are very severe. In the present study, the surface expansion is analyzed especially under various process conditions. The main goal of this study is to investigate the influence of degree of reduction in height, geometries of punch nose, friction and hardening characteristics of different aluminum alloys on the material flow and thus on the surface expansion on the working material. Two different materials are selected for investigation as model materials and they are AA 2024 and AA 1100 aluminum alloys. The geometrical parameters employed in analysis include punch corner radius and punch face angle. The geometry of punch follows basically the recommendation of ICFG and some variations of punch geometry are adopted to obtain quantitative information on the effect of geometrical parameters on material flow. Extensive simulation has been conducted by applying the rigid-plastic finite element method to the backward can extrusion process under different geometrical, material, and interface conditions. The simulation results are summarized in terms of surface expansion at different reduction in height, deformation patterns including pressure distributions along the interface between workpiece and punch, comparison of surface expansion between two model materials, geometrical and interfacial parametric effects on surface expansion, and load-stroke relationships. It has been concluded from the present study that the geometrical condition of punch is the most significant factor among the parameters employed in this study. It is also known from the simulation results that the difference in surface expansion according to different material properties is not more or less significant.

Microscopic evaluation of commingling-hybrid yarns

Fibers made of elements such as carbon, aramid and glass have higher mechanical properties than other conventional textile fibers and they enable the production of light weight composites as end products. Furthermore, commingling hybrid yarns generally have a characteristic feature so that their components are distributed homogeneously enough over the yarn cross section. A normal air texturerising machine was modified to produce commingling hybrid yarns for test samples. Different process parameters were applied to produce the hybridized yarn samples. However, these process parameters turned out to have little effect on the filament distribution over the hybrid yarn cross section in terms of homogeneity. The analysis in this paper is focused on the pattern of mixing of filaments over a cross section of hybrid yarns according to different combinations of reinforcement and matrix filament yarns through microscopic view. The volume content of filament in hybrid yarn cross section was maintained at 50% for both reinforced and matrix, and the hybrid yarns count at 600 tex throughout experiments. It was concluded from the experiments that the diameters of reinforcement and matrix filaments have strong effects on the pattern of mixing of filaments over a cross section of hybrid yarns such that the hybrid yarns with more or less equal diameters of reinforcement and matrix filaments showed considerably even distributions over the hybrid yarn cross section.

An Analysis on the Tensile Strength of Hybridized Reinforcement Filament Yarns by Commingling Process

Carbon, aramid and glass fibers are inherently superior to conventional textile fibers in terms of mechanical properties as well as other chemical characteristics. Because of inherent advantages and disadvantages associated with each material, it is generally better to hybridize them to fully benefit of their high performance in many practical applications. In this paper, the possibility of hybridizing Carbon/Aramid-, Carbon/Glass- and Aramid/Glass- matrices has been investigated through the commingling process. In the experiment, several process parameters were selected and they include pressure, yarn oversupply-rate and different nozzle types. As a result of experiments, it was concluded that the hybridized materials has shown better performance than individual reinforced filament yarns in terms of mechanical properties. For small tensile forces, the Carbon/Glass/matrix combination turned out to be good enough for general purpose applications. However, for high tensile applications, Carbon/Aramid or Aramid/Glass with matrix combinations was better than the other material combinations. The hybridization process was also investigated under an air pressure of 5 bar, a yarn oversupply-rate of 1.5% for reinforced filaments, and 3.5% to 6% for matrix materials, respectively. It was also shown from the experimental results that Carbon/Glass/matrix combination may be desirable for small tensile force applications and Carbon/Aramid/matrix and Glass/Aramid/matrix combinations most suitable for heavy tensile force applications, respectively. As a matrix material, polypropylene and polyester have shown better performance than polyether-ether-keeton in terms of tensile property.

A Reappraisal of Various Compacting Processes for Wasted Expandable Polystyrene (EPS) Foam

Once expandable polystyrene (EPS) foam has been used out, its high volume-to-weight ratio becomes a serious problem, and it is now prototypical high-bulk/non-burnable landfill problem. This is one of main obstacles for EPS foam to be recycled. This paper is concerned with volume reduction method for wasted EPS foam. The analysis is focused on the description of importance of volume reducing method for EPS foam. Wasted EPS foam has not been recycled effectively since its volume to weight ratio is extremely high. The large volume of EPS has prevented from its proper recycling because of high cost of transportation to recycling plant. In this reason, successful recycling of wasted EPS foam results directly from successful volume reduction of wasted EPS foam in proper manner. This paper deals with various existing methods for volume reduction of wasted EPS foam. Six existing processes of volume reduction for wasted EPS has been analyzed qualitatively and compared each other in terms of expected polystyrene (PS) characteristics after volume reduction, cost effectiveness of each process, possible effects on environment caused by the volume reduction process, and applicability to possibly recycled products. The methods analyzed in this paper include thermal, solvent, far infrared, pulverization, and mechanical compaction. Analysis was concentrated to compare each process mostly in qualitative manner among existing processes.

The Forming Characteristics of AA 2024 Aluminium Alloy in Radial Extrusion Process Combined with Backward Extrusion

Numerical analysis of radial extrusion process combined with backward extrusion has been performed to investigate the forming characteristics of an aluminum alloy in a combined extrusion process. Various variables such as gap size, die corner radius and frictional conditions are adopted as design or process parameters for analysis in this paper. The main investigation is focused on the analysis of forming characteristics of AA 2024 aluminum alloy in terms of material flow into backward can and radial flange sections. Due to various die geometries and process conditions such as frictional conditions, the material flow into a can and flange shows different patterns during the combined extrusion process and its characteristics are well summarized quantitatively in this paper in terms of forming load, volume ratio etc. Extensive simulation work leads to quantitative relationships between process conditions and the forming characteristics such as volume ratio of flange to can and the size of can and flange in terms of the can height extruded backward. It is easily seen from the simulation results that the volume ratio, which is defined as the ratio of flange volume to can volume, increases as the gap size and/or die corner radius increase. However, it is interesting to note that the frictional condition has little influence on the forming load and the deformation patterns. Usually, the frictional condition is a greatest process variable in normal forging operation. It might be believed from the simulation results that the frictional conditions are not a major process parameter in case of combined extrusion processes. It is also found that the can size, which is defined as the height of billet after forming, turns out to be even smaller than that of initial billet under a certain condition of die geometry.