• Journal of the Korean Society for Precision Engineering
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• v.14 no.8
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• pp.57-64
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• 1997

The process design of backward and forward extrusion of axisymmetric part has been studied in this paper. The important factors of cold forging process with complex geometry are the design of initial billet shape, the possibility of forming by one-stage operation and the determination of preform shapes, etc. Based on the systematic procedure of process sequence design, the forming operation of cold forged part is analyzed by the commercial finite element program, DEFORM. The design criteria are forming load, geo- metrical filling without defect and a sound distribution of effective strain in final product. It is noted that one step of preform operation is required to obtain the final product. Numerical result is compared with experi- mental one. It is found that the analyzed result is in good agreement with actual forming result.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2118-2133
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• 1996

A preform is designed by the backward tracing scheme of the rigid-plastic finite element method(FEM) for net-shape shell nosing components without machining after forming. The current process of the shell nosing requires cost-consuming machining to produce final products. Here, the backward tracing scheme of the rigid-plastic FEM, a novel method for preform design of metal forming processes, derives a sound preform for net-shape shell nosing product. The current process is simulated by the rigid-plastic finite element analysis to check the metal flow involved in the forming with a trial preform and its modified preform. The two preforms are found to be inadequate for net-shape shell nosing product. The first application of the back ward tracing scheme derives a preform producing a not-shape shell nosing product. The first application of the backward tracing scheme derives a preform producing a net-shape product numerically, but it is difficult to be formed economically as a preform. Thus an improved preform is designed by the badkward tracing scheme, which is suitable for net-shape manufacturing of the shell nosing components in view of economy of production and forming characteristics of the product. The preform in the current process and a modified preform are confirmed by a series of experiments and the results give the same deformation with the numerical ones. Finally the newly designed preform by the FEM was experimentally proved to be adequate in obtaining net-shape products.

• Journal of Korean Neurosurgical Society
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• v.29 no.5
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• pp.615-622
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• 2000

Objective : Percutaneous vertebroplasty is an effective and minimally invasive procedure consisting of the injection of a PMMA(polymethyl methacrylate) into the vertebral body compression fracture with osteoporosis. Matherials and Methods : Twenty-eight procedures were performed for vertebral body compression fractures with osteoporosis in 25 patients(22 women, 3 men). The mean age was 65.9 years old. The inclusion criteria for percutaneous vertebroplasty were 1) acute vertebral body compression fracture with osteoporosis, 2) expected high operative morbidity in old age, 3) no neurologic deficits, 4) no or minimal canal enchroachment, 5) patient refusal of invasive surgery. All patients underwent MR images before the procedure. Under local anesthesia, after the percutaneous needle puncture of the involved vertebra via a transpedicular approach and venography using the water soluble contrast material, PMMA injection was introduced into the fractured vertebral body. Results : The procedure was technically successful in all patients. All patients experienced excellent pain relief (complete pain relief ; 10, marked pain relief ; 14). One patient experienced marked pain relief, however, the patient died during the follow-up period due to stomach cancer. There were twelve paravertebral tissue leaks, twelve paravertebral venous plexus leaks, four epidural leaks and one intradiskal leak, but no clinically significant complications occurred in all patients. Conclusion : Percutaneous vertebraoplasty is a valuable procedure in the treatment of vertebral body compression fracture with osteoporosis, providing immediate pain relief and early mobilization. MRI is the most reliable diagnostic tool for identifying painful fractured vertebral body.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.905-909
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• 2001

The significance of casting/forging process for reducing the production cost of large components is being noted in these days. This casting/forging process is a method of forging a workpiece preformed by casting into the final shape. In this study, the casting/forging process has been applied in manufacturing a large aluminum flange in order to determine the optimum forging condition of the aluminum flange. The optimum range of forging temperature of Al 5083 was from $420^{\circ}C$ to $450^{\circ}C$. The suitable strain rate was 1.5 $sec^{-1}$. The deformation amount of a preform in a forging process is key role in the mechanical properties of casting/forging products. In order to find the change of mechanical properties according to effective stain of cast aluminum billets, a hot upsetting test were performed with rectangular blocks and then a uniaxial tensile test was performed with specimens cut from the upsetted billets. The tensile strength and the elongation of cast/upsetted aluminum billets were increased largely until the effective strain was 0.7. FE analysis was performed to determine the configurations of cast preform and die for an aluminum flange. In the FE analysis, the forging load-limit was fixed 1500ton for the low equipment cost. The cast preform was designed so that the effective stain around the neck of a flange exceeds 0.7. In the forging experiment for an aluminum flange, it was confirmed that the optimal configuration of the cast preform predicted by FE analysis was very useful. The cast/forged products using designed preform were made perfectly without any defects.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.11 s.176
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• pp.45-50
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• 2005

In this study, the casting/forging process was applied in manufacturing a low control arm, in order to prove that application of casting/forging process to Al6061 is likely to get the effect of light weight compared with existing steel products and to reduce the cost of materials. Firstly, In order to set up the optimum casting condition of the forging material, Al6061, casting experiments were carried out by controlling pouring temperature of the aluminum for casting, mold temperature, and pouring time. $700^{\circ}C$ pouring temperature, $300^{\circ}C$ mold temperature and 10-second pouring time were taken into account as the optimum casting conditions. With respect to a hot forging test, it is practiced on the basis of a temperature of materials, strain rate, and reduction rate so as to observe each microstructure and examine strain-stress curve simultaneously; examine tensile test and hardness test; eventually set up the optimum hot forging condition. A hot forging test, tensile test, hardness experiment, and microstructure observation were carried out on condition of $70\%$ reduction rate, $500^{\circ}C$ temperature of materials, and 1 strain rate. As a result of those experiments, 330MPa tensile strength, $16.4\%$ elongation, and 122.8Hv hardness were recorded. In oder to get a sound preform which has no unfitting cavity and less flash, two preforms were proposed on the basis of volume rate of the final product; the optimum volume rate of preform for the low control arm was $115\%$. In conclusion, it is confirmed that using the forging material rather than casting materials in casting/forging process is likely to get more superior mechanical properties. Compared with Al6061, performed by means of general forging, moreover, cast/forged Al6061 can not only stimulate productivity by reducing production processes, but cut down the cost of materials by reusing forging scraps.

• Journal of Korea Foundry Society
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• v.17 no.1
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• pp.58-66
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• 1997

The main aim of the present study is to investigate the effects of several processing parameters on the characteristics of Fe-Al alloy preform manufactured by reactive sintering process. The processing parameters include preform composition of 25, 40, 50, 60 and 75at.%Al, compacting pressure of 10, 20 and $30kg/cm^2$, and mean Al particle size of 29, 66 and $187{\mu}m$. Mean Fe particle size was $39{\mu}m$. The density of preform processed under same compacting pressure was not affected by changing Al composition. The preform with Al compositions of 25, 40, 50 and 60at.% Al swelled after reactive sintering process, thus having lower density than the green compacts. The preform with Al compositions of 75at.%Al, however, shrinked after reactive sintering process, thus having higher density than the green compacts. Ignition temperature increased with increasing compacting pressure, and increased with increasing Al composition at the fixed compacting pressure. And adiabatic temperature decreased with increasing compacting pressure at the fixed Al composition, and increased with increasing Al composition at the fixed compacting pressure. The size of compound particles increased with increasing Al composition. Especially, The size of compound particles increased largely in the case of 75at.%Al. It was observed that 50at.%Al preform have three dimentional network structure having a homogeneous and fine decreasing Al particle size.

• Journal of Korea Foundry Society
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• v.13 no.1
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• pp.62-70
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• 1993

This study presents the effect of applied pressure on the preform deformation during squeeze casting of $Al_2O_3$ short fiber reinforced aluminum alloy (AC8A) metal matrix composites. A preliminary model based on the general beam theory is suggested for the prediction of the preform deformation. Two different commercially available $Al_2O_3$ short fiber (Saffil, Kaowool) were used to study the influence of the fibers on the microstructure and mechanical properties of the squeeze cast $Al/Al_2O_3$ composites. The composites were fabricated with the applied pressure of 75 MPa which was found to be the optimum condition for the squeeze casting of the composites in this study. For the amorphous Kaowool fiber, hard crystalline Mullite phase was formed with heat treatment. Both of amorphous and the crystallized Kaowool fibers were used to fabricate $Al/Al_2O_3$ composites. Microhardness of crystallized Kaowool fiber revealed higher than that of the amorphous Kaowool fiber in the squeeze cast composites. It was also found that the wear resistance of Kaowool fiber reinforced composites increased with the amount of Mullite.

• Journal of Powder Materials
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• v.5 no.3
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• pp.184-191
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• 1998

The fabrication process and properties of SiC particulate preforms with high volume fraction above 50% were investigated. The SiC particulate preforms were fabricated by vacuum-assisted extraction method after wet mixing of SiC particulates of 48 ${\mu}m$ in diameter, $SiO_2$ as inorganic binder, cationic starch as organic binder and polyacrylamide as dispersant in distilled water. The SiC particulate preforms were consolidated by vacuum-assisted extraction, and were followed by drying and calcination. The drying processes were consisted with natural drying at $25^{\circ}C$ for 36 hrs and forced drying at 10$0^{\circ}C$ for 12 hrs in order to prevent the micro-cracking of SiC particulates preform. The compressive strengths of SiC particulate preforms were dependent on the inorganic binder content, calcination temperature and calcination time. The compressive strength of SiC preform increased from 0.47 MPa to 1.79 MPa with increasing the inorganic binder content from 1% to 4% due to the increase of $SiO_2$ flocculant between the interfaces of SiC particulates. The compressive strength of SiC preform increased from 0.90 MPa to 3.21 MPa with increasing the calcination temperatures from 800 to 120$0^{\circ}C$ under identical calcination time of 4hrs. The compressive strength of SiC preform increased from 0.92 to 1.95 MPa with increasing the calcination time from 2 hrs to f hrs at calcination temperature of 110$0^{\circ}C$. The increase of compressive strength of SiC preform with increasing the calcination temperature and time is due to the formation of crystobalite $SiO_2$ phase at the interfaces of SiC particulates.

• Composites Research
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• v.12 no.1
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• pp.68-75
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• 1999

This study has observed that the dynamic behavior of Metal Matrix Composites (MMCs) in low velocity impact varies with impact velocity. MMCs with 15 fiber volume percent were fabricated by using the squeeze casting method. The AC8A was used as the matrix, and the alumina and the carbon were used as reinforcements. The tensile and vibration tests conducted yielded the yielded the tensile stress and elastic modulus of MMCs The low pass filter and instrumented impact test machine was adopted to study dynamic behaviors of MMCs corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact energy of unreinforced alloy and MM s increased as the impact velocity increased. The increase of crack propagation energy was especially prominent, but the dynamic toughness of each material did not change much. To show the relation between crack initiation energy and dynamic fracture toughness, a simple model was proposed by using the strain energy and stress distribution at notch. The model revealed that crack initiation energy is proportional to the square of dynamic fracture toughness and inversely proportional to elastic modulus.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.1
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• pp.180-185
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• 2002

Aluminum casting/forging process is used to produce an aluminum tie-rod end for the steering system of automobiles. Firstly, casting experiments were carried out to get a good preform for forging the tie-rod end. In the casting experiment, the effects of additives, Ti+B, Zr, Sr, and Mg, on the mechanical properties and the microstructure of a cast preform were investigated. And a finite element analysis was performed to determine an optimal configuration of the cast preform. Lastly, a forging experiment was carried out to make the final product of aluminum tie-rod end by using the above cast preform. In the casting experiments, when 0.2% Ti+B and 0.25% Zr were simultaneously added into molten Al-Si alloy, the highest values of tensile strength and elongation of the cast preform were obtained. When 0.04% Sr were added into the molten aluminum alloy, the finest silicon-structure was observed in the cast preform. The highest hardness was obtained when 0.2% Mg was added. In the forging experiment, It was confirmed that the optimal configuration of a cast preform predicted by FE analysis was very useful. The hardness of a cast/forged product using designed preform was superior to that of required specification.