• Transactions of Materials Processing
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• v.6 no.3
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• pp.221-226
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• 1997

Chevron crack in cold extrusion has been studied in view of deformation conditions and material characteristics. There is V formed chevron crack is occasionally occurred in core part of shaft by multistage free extrusion. Although many research results were reported and theoretical analyses were accompanied, in this study we discussed practical method to prevent chevron crack in the field of working conditions and material characteristics. We have found that chevron crack is eliminated under condition of high hydrostatic state in deformation and decreased segregation, refinement of micro structure of materials.

• Transactions of Materials Processing
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• v.12 no.6
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• pp.582-587
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• 2003

This paper is concerned with the mechanical property changes of the milli-size products manufactured by forward extrusion processes with square dies. Experiments are carried out with pure aluminum and pure copper billets. Extrusion ratio and knock-out pad are chosen as the important process parameters affecting the changes of mechanical properties such as shear strength and hardness. Shear strength tests with the extruded milli-size pin have shown the strong relation between victors hardness and shear strength in the neck of a stepped pin. As the extrusion ratio increases, the hardness on both the surface and the center line of a pin also increase. It is also noted that the hardness on the surface is a little higher than that on the center. The existence of knock-out pad in extrusion die causes the hardness in the neck of a extruded pin to increase. Finally, the approximated linear relations between shear strength and hardness of a pin are suggested.

• Restorative Dentistry and Endodontics
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• v.45 no.3
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• pp.34.1-34.7
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• 2020

Objectives: This study evaluated by using micro-computed tomography (micro-CT) the filling ability and sealer apical extrusion promoted by a new Sealer Injection System (SIS; Angelus) with side openings needle, in comparison with the conventional injection system, associated with a new ready-to-use calcium silicate-based sealer (Bio-C Sealer). Materials and Methods: Acrylic resin models containing a main curved artificial canal and 3 simulated lateral canals in apical, middle and cervical thirds were used. The main root canals were prepared using a rotary system up to size 35.05. The canals were filled with Bio-C sealer by using a single cone technique and the conventional delivery system or SIS. Samples were scanned in micro-CT. The percentage of voids throughout the entire extension of the main root canal and in each third of the lateral canals, besides the apical extrusion of the sealer was calculated. Data were submitted to t-test (p < 0.05). Results: There was no difference between both systems in the main root canals filling. Although the volume percentage of voids was similar in the apical and middle thirds of lateral canals, SIS had the greatest filling ability of the cervical third lateral canal. Moreover, the conventional system showed the highest apical extrusion of the sealer. Conclusions: The conventional and SIS obturation systems had an appropriate filling ability of the main root canal. SIS had the best filling of the cervical third of the lateral canals, besides lower sealer apical extrusion, suggesting its clinical indication.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.797-801
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• 2003

The mechanical properties such as shear strength and the hardness of milli-size products that manufactured for various process parameters by forward extrusion using square dies are investigated. Shear strength test is implemented for the observation of relation between vickers hardness and shear strength in the interface of head and shaft part of a stepped pin. When the extrusion ratios of pure aluminum and pure copper billets increase, the hardness on both the surface and the center line of a pin also increase, especially the hardness on the surface is shown to be a little higher than on the center. The existence of knock-out pad in extrusion die caused hardness increase in the interface of a extruded pin. As compared shear strength with hardness of a pin, the approximated linear relations are suggested in this study.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.562-567
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• 2006

Micro-alloyed steel or heat-treatment-free used in clean technology have been replacing for conventional quenched-and-tempered structural steels since the micro-alloyed forging steel was developed in early 1970s in Germany for saving money of heat treatment, simplified process, short delivery and good productivity. In this paper, ball stud assembled in steering system for automobile was selected to compare conventional process making heat treatment with new process using high strength micro-alloyed steel without heat treatment. The conventional process for ball stud was composed of a total of 6 steps including upsetting, forward extrusion, machining, burnishing and tread rolling with heat treatment and shot blasting. As opposed to conventional process, newly proposed process for ball stud using the clean technology without heat treatment is simplified such as forward extrusion, heading, upsetting, forming having a flange shape and tread rolling. Also net shape forming process to achieve specified process not to include machined step fur manufacturing the ball stud was applied to newly simplified process since micro-alloyed steel is difficult to be formed.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.9 s.174
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• pp.49-59
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• 2005

This paper describes a development of the extrusion process and estimation of the weldability for multi cell tubes used to cooling system of automobiles. A study on extrusion process is performed through the 3D FE simulation in non-steady state and extrusion experimentation. Also, nano-indentation test is employed to estimate the weldability of tubes. Especially, An evaluation of the weldability using the nano-indentation is accomplished as compared with nano-hardness in welded part and in the others. Finally, the pattern of the mandrel defection is investigated according to shapes of the porthole and/or chamber.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.499-502
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• 2005

A process map has been developed, which can identify the process conditions for weak mechanical bonding at the contact surface during the direct extrusion of a Cu-Ti bimetal bar. Bonding mechanism between Cu and Ti was assumed as a cold pressure welding. Then, the plastic deformation at the contact zone causes mechanical bonding and a new bonding criterion for pressure welding was developed as a function of the principal stretch ratio and normal pressure at the contact surface by analyzing micro local extrusion at the contact zone. Finite element analyses for extrusion of Cu-Ti bimetal bars were performed for various process conditions. The deformation history at the contact surface was traced and the proposed new bonding criterion was applied to predict whether the mechanical bonding at the Cu-Ti contact surface happens. Finally, a process map for the extrusion of Cu-Ti bimetal bar is suggested.

• Transactions of Materials Processing
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• v.18 no.4
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• pp.342-346
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• 2009

Forming characteristics for the bundle extrusion of Cu-Ti bimetal wires are investigated, which can identify the process conditions for weak mechanical bonding at the contact surface during the direct extrusion of a Cu-Ti bimetal wire bundle. Bonding mechanism between Cu and Ti is assumed as a cold pressure welding. Then, the plastic deformation at the contact zone causes mechanical bonding and a new bonding criterion for pressure welding is developed as a function of the principal stretch ratio and normal pressure at the contact surface by analyzing micro local extrusion at the contact zone. The averaged deformation behavior of Cu-Ti bimetal wire is adopted as a constitutive behavior at a material point in the finite element analysis of Cu-Ti wire bundle extrusion. Various process conditions for bundle extrusions are examined. The deformation histories at the three points, near the surface, in the middle and near the center, in the cross section of a bundle are traced and the proposed new bonding criterion is applied to predict whether the mechanical bonding at the Cu-Ti contact surface happens. Finally, a process map for the direct extrusion of Cu-Ti bimetal wire bundle is proposed.

• Transactions of Materials Processing
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• v.6 no.5
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• pp.446-455
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• 1997

A Combined extrusion operation consists of forward and backward extrusion forming and it is possible to make the process be simple by employing it. But the metal flow pattern induced by the operation is hard to analyze accurately because the flows are non-steady, which have at least two directions dependent upon each other. So engineers in the industrial factories had conducted the two extrusion operations separately. A new process was designed by the industrial expert for forming of an alu-minum preform using the combined extrusion operation. In this study, experiments and finite element analysis was carried out to determine the process parameters. Through the preliminary experiment, it was shown that warm forming condition was more desirable than cold or hot ones. And optimal shape of initial billet could be also determined. From the compatibility test, bonde-lube was chosen as the optimal lubricant and 20$0^{\circ}C$ as the material temperature by the inspection of micro-structure. The operation was simulated by the rigid-plastic finite element method to examine the metal flow. Disap-pearing of dead metal zone was observed as the punch fell down and desirable shape was obtained from the one operation. As a result of this study, 7 operations could be reduced and 225% of material saved.

• Transactions of Materials Processing
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• v.16 no.8
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• pp.614-620
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• 2007

Deformation characteristics and damage evolution during warm backward extrusion of bulk AZ31 Mg alloy were investigated using finite element analyses. AZ31 Mg alloy was assumed as a hardening viscoplastic material. The tensile tests of AZ31 Mg alloy in previous experimental works showed the ductile fracture even at the warm temperature of $175^{\circ}C$. In this study, damage evolution model proposed by Lee and Dawson, which was developed based on the growth of micro voids in hardening viscoplastic materials, was combined into DEFORM 2D. Effects of forming temperature, punch speed, extrusion ratio and size of work piece on formability in warm backward extrusion as well as on mechanical properties of extruded products were examined. In general, finite element predictions matched the experimental observations and supported the analyses based on experiments. Distributions of accumulated damage predicted by the finite element simulations were effective to identify the locations of possible fracture. Finally, it was concluded that the process model, DEFORM2D combined with Lee & Dawson#s damage evolution model, was effective for the analysis of warm backward extrusion of AZ31 Mg alloys.