• Journal of Powder Materials
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• v.14 no.6
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• pp.367-371
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• 2007

P/M high speed steel (1.26% C, 4.42% Cr, 6.54% W, 4.92% Mo, 3.21 % V, 8.77% Co, bal. Fe) was applied to hot former die. It showed that the die life became 2.7 times higher than that of cast/wrought SKH 55 tool steel which is commercially used. The increase of die life was corresponding to the improved hardness and transverse rupture strength of PM high speed steel due to the finer grain and carbide as well as the uniform carbide distribution. The P/M high speed steel with the promoted die life could be an alternative to the conventional SKH55.

• 전기의세계
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• v.21 no.1
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• pp.13-16
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• 1972

Dynamic Programming is regarded as a very powerful tool for solving nonlinear optimization problem subject to a number of constraints of state and control variables, but has definite disadvantages that it requires much more computing time and consumes much more memory spaces than other technigues. In order to eliminate the above-mentioned demerits, this paper suggests a news technique called Multiple Dynamic Programming. The underlying principles are based on the concept of multiple passes that, instead of forming fin lattices in time-state plane as adopted in the conventional Dynamic Programming, the Multiple Dynamic Programming constitutes, at the first pass, coarse lattices in the feasible domain of time-state plane and determines the optimal state trajectory by the usual method of Dynamic Programming, and at the second pass again constitutes finer lattices in the narrower domain surrounded by both the upperand lower edges next to the lattice edges through which the first pass optimal trajectory passes and determines the more accurate optimal trajectory of state, and then at the third pass repeats the same processes, and so on. The suggested technique insures remarkable curtailment in amounts of computer memory spaces and conputing time, and its applicability has been demonstrated by a case study on the hydro-thermal power coordination in Korean power system.

• Transactions of Materials Processing
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• v.9 no.6
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• pp.590-597
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• 2000

A finite element formulation lot the simulation of axisymmetric sheet hydroforming is proposed, and an implicit program is coded. In order to describe normal anisotropy of steel sheet, Hill's non-quadratic yield function (Hill, 1979) is employed. Frictional contacts among sheet surface, rigid tool surface, and flexible hydrostatic pressure are considered using mesh normal vectors based on finite element of the sheet. Applied hydraulic pressure is also considered as a function of forming rate and time and treated as an external loading. The complete set of the governing relations comprising equilibrium and interfacial equations is approximately linearized for Newton-Raphson algorithm. In order to verify the validity of the developed finite element formulation, the axisymmetric bulge test is simulated. Simulation results are compared with other FEM results and experimental measurements and showed good agreements. In axisymmetric hydroforming processes of a disk cover, formability changes are observed according to the hydraulic pressure curve changes.

• Journal of Korean Association for Spatial Structures
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• v.7 no.2 s.24
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• pp.45-52
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• 2007

The purpose of this study is to explore folding as a tool diversifying structures and shapes or forms, and to consider the role and possibilities as structural design sources. First, the morphological characteristics and the elements for transforming pattern of folding are investigated and the way of forming space is also shown. Secondly, the application methods and systems of folding are descrived.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.5
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• pp.45-52
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• 2001

In order to increase the productivity of electrical parts, manufacturing processes using progressive dies have been widely used in the industry. Motor cores have been fabricated using progressive stacking die with the lamination procedure for better electro-magnetic property. For the proper design off process, a prediction of the process is required to obtain many design parameters. In this work, rigid-plastic finite element analysis is carried out in order to simulate the lamination process of the motor core. The effects of the embossing depth, the amount of deviation, and the number of stacked sheets are investigated and compared with experiments. The forming process can then be predicted successfully from the results of analyses, which enables an appropriate design to be made for the die and the process.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.5
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• pp.15-23
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• 2003

A feature-based inspection planning system is proposed in this research to develop more efficient measuring methodology for the OMM(On-Machine Measurement) or CMM(coordinate Measuring Machine) for complicated workpiece having many primitive form features. This paper is proposed solution that optimum inspection sequence of the objective features. The sequences are determined by analyzing the feature information such as the nearest relationship and the possible probe-approach direction(PAD) of the features, and forming feature groups. A series of heuristic rules are developed to accomplish it. Also, each feature is decomposed into its constituent geometric elements for inspection process, and then the number of sampling points, location of the measuring points, optimum probing path are determined.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.90-94
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• 2002

In this paper, Compression in the case where dissimilar blocks are twinned variously are carried out in the condition of lubricated interface. The degree of growth is experimentally investigated. Moreover, numerical simulations are carried out by the elastic-plastic FEM for the case of the dissimilar blocks with the initial sawtooth angle of 60。. The dissimilar blocks are twinned, larger difference between material properties leads smaller growth, and the degreased interface leads smaller growth than that in the lubricated one. Furthermore, by the simulation of compression where dissimilar blocks are twinned, it is confirmed that the tendency of the general deformation pattern is very similar to the experiment.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.353-358
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• 2002

A feature-based inspection planning system is proposed in this research to develop more efficient measuring methodology for the OMM (On-machine measurement) for complicated workpiece having many primitive form features. This paper focuses on the development of the CAIP (computer-aided inspection system) methodologies. The optimum inspection sequences for the features are determined by analyzing the feature information such as the nested relations and the possible probe approaching directions of the features, and forming feature groups. A series of heuristic rules are developed to accomplish it. Also, each feature is decomposed into its constituent geometric elements, and then the number of sampling points, the locations of the measuring point, the optimum probing path are determined by applying the fuzzy logic, Hammersley's method, and the TSP algorithm. To verify the proposed methodologies, simulations are carried out and the results are analyzed.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.18 no.1
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• pp.83-89
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• 2009

In most multi-stage forging processes, the die spotting process or alignment of punch and die depends on the manual operation. It results a very tedious and inefficient procedure, thus the proper measurement system is needed to improve productivity and accuracy. This paper proposes a measurement system for alignment of die and punch which has a cylindrical holder, and describes the system concepts using 3 eddy-current displacement transducers and precise measurement jig. In order to apply this measurement system to real situations, the measuring procedures and system calibration method, etc. are proposed. Finally, the accuracy and productivity of this measurement system are investigated in this paper.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.4
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• pp.1-7
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• 2008

Fine grained superplastic Zn-22%Al alloy was extruded using a laser machined micro-die to produce a micro-gear shaft. Extrusion process was conducted under a constant pressure at constant temperatures ranging from 503 to 563K. Laser machining was capable to machine a micro-die with close tolerances and adequate surface quality. The extrusion rate increased with extrusion load under constant extrusion temperature. The rate reached a steady state and became constant after a certain period. There was a small instantaneous stroke on application of the load and then a very brief primary stage which preceded steady-state flow. The micro-extrusion process was proven to produce a micro-gear shaft successfully using a fine grained superplastic Zn-22%Al alloy.