Erika Fechová

Optimizing of Electric Discharge Texturing Parameters of Rolls of the Rolling Mill of Steel Sheets

The producers of components require that cuts of steel sheets for superficial parts of cars would have guaranteed surface microgeometry, minimum defects, homogenous surface over the full width and length of the belt, mat appearance, good adhesion of the Zn layer. Microgeometry of the surface of galvanized sheets for superficial parts of cars is one of the decisive factors affecting the appearance of the surface after painting and stampability of steel sheets. Requirements for microgeometry are mainly focused on the roughness parameters Ra [μm] (roughness), Pc [cm-1] (number of peaks) or Wa [μm] (undulation roughness). This paper presents the study results of the influence of selected parameters of electric discharge texturing of rolls of the rolling mill on the Ra roughness parameter and number of peaks. Reliability of the process of electric discharge texturing of work rolls was assessed according to Cpm and Cp reliability indices. Dependencies on electric discharge texturing were depicted to predict Raand Pc qualitative indices of roughness.

Effect of the Electrolyte Temperature and the Current Density on a Layer Microhardness Generated by the Anodic Aluminium Oxidation

The paper investigates the influence of the chemical composition and temperature of electrolyte, the oxidation time, voltage, and the current density on Vickers microhardness of aluminium oxide layers, at the same time. The layers were generated in the electrolytes with different concentrations of sulphuric and oxalic acids and surface current densities 1 A·dm−2, 3 A·dm−2, and 5 A·dm−2. The electrolyte temperature varied from −1.78°C to 45.78°C. The results have showed that while increasing the electrolyte temperature at the current density of 1 A·dm−2, the increase in the layer microhardness values is approximately by 66%. While simultaneously increasing the molar concentration of H2SO4 in the electrolyte, the growth rate of the microhardness value decreases. At the current density of 3 A·dm−2, by increasing the electrolyte temperature, a reduction in the microhardness of the generated layer occurs with the anodic oxidation time less than 25 min. The electrolyte temperature is not significant with the changing values of the layer microhardness at voltages less than 10.5 V.

The Influence of Strain Rate on the Curves of Natural Strain Resistance

In the area of manufacture qualities of constructional materials special emphasis on knowledge of physical fundamentals of mechanical, electrical, chemical and magnetic properties of substances is put. The paper deals with material properties of steel sheet metals at various strain rates.

Diagnostics of Strain Hardening Exponent and Material Constant of Steel Sheets

This paper deals with evaluation of n strain hardening exponent and C material constant at various velocities of the strain rate according to EN 10002-1. Dependence of tensile stress on elongation is carried out at INSTRON shredder in digital form and it is directly introduced into MATLAB working environment. To determine these material parameters suitable material models (Krupkowsky model) and MATLAB programming pack, mainly its Curve Fitting toolbox, which provides the library of standard linear, nonlinear and nonparametric models (e.g. polynomial, rational, etc.), are used. At automobile crash tests kinetic energy conversion into energy of deformation (where it is necessary to know n, C) is theoretically calculated at certain velocities so that the solid parts of the car body would be protected from damage. It would be the best to compare correctness of those calculations to the test carried out at a real model or by simulation created on the computer with necessary software equipment.

SIMULATION OF TECHNOLOGICAL PROCESS BY USAGE NEURAL NETWORKS AND FACTORIAL DESIGN OF EXPERIMENTS

The possibilities of simulation of technological process ofaluminium anodic oxidation using the methodology of Design of Experiments (DOE) and theory of neural networks in order to monitor the anodizing process under various operating conditions are presented in this paper. The influence of chemical and physical input factors on the resulting AAO (anodic aluminium oxide) layer thickness at applied current density of 1 A x dm-2 and 6 A x dm-2 has been investigated. Based on the evaluation of experimentally obtained data, the computational predictive model describing the effect of individual input factors and their mutual interactions on the AAO layer thickness was developed in the form of cubic function. This model indicates which factors are important and how they combine to influence the response, it will enable us to optimize operating conditions. The most significant benefit of our research work in this field is the fact that all relevant factors were varied simultaneously.

THE METHODS TO DETERMINE THE STRAIN RATE OF THE STEEL SHEETS USED IN THE PRODUCTION PROCESS

The paper deals with observation and description of the influence of strain rate on true stress true strain. It compares various material models that consist strain rate for deepdrawing sheets in order to work out the most accurate material models. The more accurate input to the simulation program, give the more exact output. These simulation programs introduce higher accuracy into development and production of the pressed material and reduce production costs. Computer simulation using the software programs (e.g. PAM-STAMP, ABAQUS – Explicit, DYNA 3D etc.) also presents replacement of financially expensive experiment, utilization of potential properties of materials and error detection in the production process.

Diagnostics of Material Properties of Steel Sheets from the Tensile Test Record

Nowadays it is not possible to predict material properties such as stampability and their behaviour during pressing at certain conditions without computer simulation. Reliability and accuracy of the results of numerical simulation depend on accuracy of used material model and completeness of input material parameters. The paper mainly deals with diagnostics of material properties of steel sheets from the tensile test record.