Wyniki wyszukiwania - BazTech

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Applicability valuation for evaluation of surface deflection in automotive outer panels

Park D. H., Bae W. R., Jeong H. J., So B. S., Ko T. J., Yarlagadda P. K. D. V.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

558-564

EN

Purpose: Upon unloading in a forming process there is elastic recovery, which is the release of the elastic strains and the redistribution of the residual stresses through the thickness direction, thus producing surface deflection. It causes changes in shape and dimensions that can create major problem in the external appearance of outer panels. Thus surface deflection prediction is an important issue in sheet metal forming industry. Many factors could affect surface deflection in the process, such as material variations in mechanical properties, sheet thickness, tool geometry, processing parameters and lubricant condition. Design/methodology/approach: Numerical simulation of process was performed by the use of finite element method, paying attention particularly to the thickness distribution and surface deflection of the drawn outer panel and the outline flange during forming. Simulation procedures of automotive outer panel as large size shape are as follows; 1) Acquisition of drawing parts 2) Laser scanning for generating CAD model 3) CAD model generation 4) Simulation model operation 5) Simulation execution and analyses of simulation results. Findings: The development of automation in stamping and assembly processes of automobile manufacture will require an excellent surface quality of formed panels and also their accurate dimensions. Practical implications: The use of high strength steel sheets in the manufacturing of automobile outer panels has increased in the automotive industry over the years because of its lightweight and fuel-efficient improvement. But one of the major concerns of stamping is surface deflection in the formed outer panels. Hence, to be cost effective, accurate prediction must be made of its formability. The automotive industry places rigid constraints on final shape and dimensional tolerances as well as external appearance quality of outer panels. The numerical simulation makes it possible to design and optimize the total process to a level, which can't be reached by traditional theoretical and experimental methods. Originality/value: Computer simulations can be used to determine the influence from variations in material properties and process parameters.

2

An analytic model for tool trajectory error in 5-axis machining

So B. S., Park D. H., Cho Y., Kim T. J., Song T. S., Ko T. J.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

570-575

EN

Purpose: This paper proposes an analytical method of evaluating the maximum error by modeling the exact tool path when the tool traverses singular region in five-axis machining. Design/methodology/approach: It is known that the Numerical Control (NC) data obtained from the inverse kinematic transformation can generate singular positions, which have incoherent movements on the rotary axes. Such movements cause unexpected errors and abrupt operations, resulting in scoring on the machined surface. To resolve this problem, previous methods have calculated several tool positions during a singular operation, using inverse kinematic equations to predict tool trajectory and approximate the maximum error. This type of numerical approach, configuring the tool trajectory, requires a lot of computational time to obtain a sufficient number of tool positions in the singular region. We have derived an analytical equation for the tool trajectory in the singular area by modeling the tool operation, by considering linear and nonlinear parts that are a general form of the tool trajectory in the singular area and that are suitable for all types of five-axis machine tools. In addition, evaluation of the maximum tool-path error shows high accuracy, using our analytical model. Findings: In this study, we have separated the linear components of the tool trajectory from the nonlinear ones, to propose a tool trajectory model that is applicable to any kind of 5-axis machine. We have also proposed a method to calculate the maximum deviation error based on the proposed tool trajectory model. Practical implications: The algorithms proposed in this work can be used for evaluating NC data and for linearization of NC data with singularity. Originality/value: Our algorithm can be used to modify NC data, making the operation smoother and reducing any errors within tolerance.

3

Characteristics of semiconductive materials for power transmission cables in the content of mwcnt.

Yang H., Yang J. S., Shin D. H., Park D. H.

Prace Naukowe Instytutu Podstaw Elektrotechniki i Elektrotechnologii Politechniki Wrocławskiej. Konferencje

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2007

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Vol. 46, nr 19

270-273

EN

This paper investigated the thermal properties of carbon nanotubes, which have been used as underground power transmission cables, by changing their contents in semiconductive shields. Heat capacity (AH), glass transition temperature (Tg), and melting temperature (Tm) were measured with eight samples using DSC (Differential Scanning Calorimetry), and the temperature measurement was applied from -100 deg.C to +100 deg.C by applying heat by 4 deg C/min. High temperature, heat degradation initiation temperature and heat weight loss were also measured by TGA (Thermogravimetric Analysis) ranged from 0 deg.C to 700 deg.C by applying heat at 10 deg.C/min. As a result, the Glass transition temperatures of the samples were measured at -20 deg.C - +25 degC, and the heat capacity and melting temperature from the DSC increased according to the increase in the content of carbon nanotubes while their thermal diffusivities increased according to the increase in the content of carbon nanotubes.