Elena Koleva

Statistical modelling and computer programs for optimisation of the electron beam welding of stainless steel

Abstract A statistical analysis of the electron beam welding of stainless steel samples was done using multiresponse statistical techniques. A model is created which includes the values of the distance between the electron gun and both the focusing plane of the beam and the sample surface as parameters. The response at work surfaces for the welding depth and width for variable beam power, welding speed, and the above two distances, determining the position of the beam focus towards the sample surface can be found. These predicted results coincide with the existing experimental experience in this technique. Computer procedures for the choice of operating conditions under some criteria for obtaining special parameters of the seam and for acquiring optimal weld parameters are also presented. It is possible to predict the geometrical characteristics of the seam when working in some chosen limited region of the welding parameters.

Calculation of weld parameters and thermal efficiency in electron beam welding

Abstract Using the model of quasi-steady thermal distribution in a solid sample, generated by a linear heat source, moving at constant welding velocity, values of the weld depth at a given weld width are calculated and compared with the experimental data. A discussion for thermal efficiency and an analysis concerning the correlation between the weld depth and weld width and the process parameters are given. The results show that the steady operating, moving linear heat source can be assumed as an approximation in the simulation of electron beam welding with a deep penetrating beam.

The role of ingot–crucible thermal contact in mathematical modelling of the heat transfer during electron beam melting

The heat exchange of different interfaces between the casting ingot and both the water-cooled crucible and the pulling mechanism is studied. Computer simulations of the process of electron beam melting and refining and regression equations for the heat flows through the boundary surfaces, as well as for the volume of the molten metal pool on the top part of the casting ingot have been performed. They are considered as functions of the coefficients of the heat transfer and the width of the heat contact ring between the casting ingot and the copper crucible. The response surface plots are drawn to visualise these dependences. They can be used for the choice of proper process conditions and for the optimisation of the heat flows, according to the requirements of the process.

Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding

Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distance between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with ...

Use of a Secondary Current Sensor in Plasma during Electron-Beam Welding with Focus Scanning for Process Control

We consider questions of building a closed-loop focus control system for electron-beam welding. As a feedback signal, we use the secondary current in the plasma that forms above the welding zone. This article presents a model of a secondary current sensor in plasma during electron-beam welding with focus scanning. A comparison of modeled results with experimental data confirms the adequacy of the model. We show that the best results for focus control are obtained when using phase relationships rather than amplitude relationships. We outline the principles for building an EBW focus control system based on parameters of the secondary current in plasma. We simulate the work of a control system’s circuits and demonstrate the stability of the synthesized system. We have conducted pilot tests on an experimental prototype.

Renewable energy and energy efficiency in Bulgaria

The interest in renewable energy sources (RESs) utilisation and energy efficiency improvement programmes in Bulgaria reflects the changes in the field of energy policy worldwide and in Europe. Now energy management becomes a great problem of inner policy of Bulgarian government. In the last few years there has been a growing attention to the RESs applications. Bulgaria has one of Southern European countries with richest renewable energy resource base. Bulgarian EU-backed target is for 16% RESs of all energy generation by 2020. The paper presents the status of renewable energy technologies and their installed capacities. The opportunities and constraints for further development and use of renewable energy are considered. There are given data for energy balance, dwellings and one illustrative example of energy efficiency improvement of one multi-dwelling panel house, typical for a lot of Bulgarian citizens in small and big towns.

Multiresponse Robust Engineering: Industrial Experiment Parameter Estimation

A new method for estimation of the mean and variance models of the responses, taking into account the correlation between the multiple responses, together with the heteroscedasticity of the observations due to errors in the factor levels is proposed. The application of this method gives us the possibility to use raw industrial data for mean and variance model estimation and leads to reduction of the predicted variance of the responses in production conditions. Recommendations for the experimental design sequential generation, based on the proposed method are made. The introduced new combined method is applied to an electron beam welding experiment.

Automation of the electron-beam welding process

In this work, the automatic control is considered of the vacuum and cooling systems of the located in the IE-BAS equipment for electron-beam welding, evaporation and surface modification. A project was elaborated for the control and management based on the development of an engineering support system using existing and additional technical means of automation. Optimization of the indicators, which are critical for the duration of reaching the working regime and stopping the operation of the installation, can be made using experimentally obtained transient characteristics. The automation of the available equipment aimed at improving its efficiency and the repeatability of the obtained results, as well as at stabilizing the process parameters, should be integrated in an Engineering Support System which, besides the operator supervision, consists of several subsystems for equipment control, data acquisition, information analysis, system management and decision-making support.

Electron beam characterization by a tomographic approach

In this paper, experimental data are analyzed for the integral current density distribution when the electron beam parameters are varied, namely, focusing current, beam current, venelt voltage and the distance to the measuring device. The 3D beam radial current density distribution is reconstructed by implementing a tomographic approach. The characterization of the electron beam is considered in connection with the estimation of the following parameters: the radial and the angular beam distribution standard deviations, the position of the beam focus and the beam emittance.

Model-Based Robust Parametric Design of Automatic Cleaning Process

The goal of pharmaceutical industry is to manufacture products that meet patients’ needs and expectations, while satisfying the regulatory requirements. The products need to meet the required quality and purity characteristics that are represented to possess. Therefore, in a multi-product manufacturing facility, appropriately designed cleaning processes are essential to avoid cross-contamination between products and ensure patients’ health and safety. The latest trend in the development of cleaning validation is using quality by design methodology (QbD) to determine the most appropriate parameters of the cleaning processes that will reduce the risks of cross-contamination. The present study highlights the model-based approach for robust engineering design in order to achieve an efficient, reliable, and cost-effective cleaning process simultaneously.