Iskanje po katalogu digitalne knjižnice

Opis: The paper deals with the dynamics of a resistance spot welding system. At the core of this system is a transformer, which is powered on the primary side by a pulse-width modulated inverter and has a full-wave output rectifier on the secondary side that provides a direct welding current. The entire system is nonlinear, due to magnetic hysteresis and electronics. The electronics prevent the current from flowing in all parts of the welding transformer at separate time intervals during the voltage supply period; therefore, not all the parameters affect the dynamic of currents and voltages all the time so the system is also time-variant. To design a high-performance welding system and to predict the maximum possible welding current at a specific load, it is necessary to know the welding and primary currents. The leakage inductances of the system can reduce the maximum welding current significantly at higher frequencies and the same load. There are several methods to determine these currents, each with its drawbacks. Measurements are time-consuming, using professional software is expensive and requires time to learn and free open-source software has many limitations and does not guarantee the correctness of the results. The article presents a new, fourth option—a theoretical derivation of analytical expressions that facilitate straightforward and rapid calculation of the welding and primary currents of the resistance spot welding system with symmetrical secondary branches. The derivation of the mathematical expressions is based on the equivalent circuits that describe the system in different operating states. The results of the numerical simulations confirmed the derived expressions completely.
Ključne besede: DC–DC converters, pulse width modulation (PWM), welding transformers, center-tapped transformers, full-wave rectifier, resistance spot welding (RSW), leakage inductance, analytical modeling, time-variant system, equivalent circuit
Objavljeno v DKUM: 08.08.2024; Ogledov: 77; Prenosov: 36
Celotno besedilo (6,72 MB)

Opis: Determining the time of execution is very important in the early stages of each project (e.g. making offers, design phase etc.), especially in the stage of planning. This paper presents our approach to estimating the welding time for the purposes of planning the manufacturing processes. The approach is based on the knowledge of welding experts from the Nieros metal d.o.o. company and standards of welding (international and internal). An expert system was developed based on semantic web technologies for calculating the welding time in the product design phase and it is strongly integrated with the main ERP system of the Nieros metal d.o.o. company. Test results are presented at the end of this article.
Ključne besede: expert systems, new product development, ontology, welding of steels
Objavljeno v DKUM: 23.08.2017; Ogledov: 1173; Prenosov: 408
Celotno besedilo (1,16 MB)
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Opis: This paper presents the results of a research related to the impact of electric arc activation onto drive welding energy and metal weld heating speed. It is confirmed that ATIG and AMIG methods, depending on metal thickness, single pass weldability and chemical composition of activating flux, enable the reduction of welding energy by 2-6 times when compared to conventional welding methods. Additionally, these procedures create conditions to increase metal weld heating speed up to 1,500-5,500 °C/s-1. Steel which can be rapidly heated, allows for a hardened structure to form (with carbon content up to 0.4%), together with a released martensitic structure or a mixture of bainitic-martensitic structures. Results of the research of effectiveness of ATIG and AMIG welding showed that increase in the penetration capability of electric arc, which increases welding productivity, is the visible side of ATIG and AMIG welding capabilities.
Ključne besede: arc welding, active flux, penetration, heating speed, driving energy
Objavljeno v DKUM: 07.07.2017; Ogledov: 1290; Prenosov: 365
Celotno besedilo (592,40 KB)
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Opis: This paper elaborates results of hardness and impact energy of thermal cycle simulated specimens of high-alloy steel P 91 and their dependence on cooling time from 800 to 500 °C. Results were obtained by measuring hardness HV 1 and by experimental testing of Charpy notched specimens. Metallographic analysis of samples was performed on scanning electronic microscope.
Ključne besede: welding, P 91, hardness, impact energy, cooling
Objavljeno v DKUM: 03.07.2017; Ogledov: 2420; Prenosov: 120
Celotno besedilo (512,44 KB)
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Opis: The influence of weld thermal cycle on the micrstructural changes in weld metal by use of the simulated microstructures. We examined the kinetics of the formation of austenite from the starting microstructure. The simulated microstructures were prepared by the application of simulated thermal cycles with different peak temperatures on a sample of real single-pass weld metal. The reproduction of thermal cycles were carried out by the SMITWELD simulator. Special attention was dedicated to the influence of thermal cycle on the formation of microstructures, which can be potential triggers of brittle fracture (local brittle zones).
Ključne besede: welding, welded joints, multi-pass weld metal, simulated microstructure, impact toughness
Objavljeno v DKUM: 03.07.2017; Ogledov: 2389; Prenosov: 141
Celotno besedilo (223,13 KB)
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