Papers by Keyword: Welding

Abstract: Hybrid joints between aluminium and steel are used sometimes in case of thin sheets for example for a car body. Resistance welding for this joining challenge is not frequently used, but the resistance welded joints basically have good mechanical properties. During resistance spot joining of these hybrid joints, fusion between the two materials cannot occur, but with the right technological parameters an intermetallic compound (IMC) appears in the joint line. The properties of the IMC have significant effect to the joint properties, because the researchers basically investigate this. The original static mechanical tests can show good, comparable results for the joint properties. If we see the dynamic tests basically really difficult to find results in case of spot welding of steels and joining of hybrid aluminium – steel joints. The aim of this paper to show the dynamic properties of these hybrid joints. During our investigation DP600 dual-phase steel was used as the steel part because this grade is frequently used in a car chassis. For the aluminium part, two types of aluminium were applied: non-heat treatable 5754-H22 alloy, and heat-treatable 6082-T6 alloy. The different aluminium alloys have different properties, so different technological parameter combinations were used. To test the resistance of hybrid joints against dynamic loading, instrumented impact tests were performed. This special impact test is considered as an impact-bending test, because the load is perpendicular to the welded point joint. Force – time diagrams of impact tests were shown too in this paper. The intermetallic compound is necessary for joint, but it is very brittle with very big hardness, but in case of dynamic testing this hardness has no significant effect, so these specimens show good result in case of dynamic loading. The two different aluminium – steel joints show different resistance against dynamic loading, and the fracture modes were different too.

Abstract: The application of high-strength steels is increasing rapidly nowadays, and steels with more than 1000 MPa yield strength are usually used in welded structures. The welding of these materials has many difficulties, so very important the precise technology planning, and disciplined work during welding. The weldability of these materials is commonly investigated field in case of joining. The application of ultra-high strength steels expands rapidly, and in the last years, it started to use them as a base material for hardfacing. Besides the wearing, there is a claim about higher strength of base materials in case of relatively extremely loaded machines. Because this ultra-high strength steel appears as a base material for hardfacing and it brings new challenges for welding technologists. In case of joining, the welding technology is complicated, usually need preheating before welding, is important to calculate and to use the right t_8/5 cooling time, and basically necessary to decrease the heat input as much as possible. The bad effect of welding heat input can be compensated by the filler material too in some cases. In contrast in case of hardfacing the base material itself usually has a big thickness, and no joint preparation, additionally important to reach deep fusion on the surface. It basically determines the heat input which has a different heat cycle as in case of joining. Therefore, the heat affected zone (HAZ) differs from the HAZ in case of joining application. In this investigation, four different hardfacing were made with four different technological parameters by robotic gas metal arc welding on S1100QL steel. During the welding parameter determination, we try to find a series of heat inputs from the lowest to the practically usable highest heat input. For the experiments, two filler materials used, one for the buffer zone, and for the hardfacing itself. Microstructural evaluation and hardness tests were made on the specimens which can show the differences between the heat affected zones.

Abstract: The aim of this study is to investigate the effect of applying various welding current parameters of shielded metal arc welding (SMAW) on microstructure and the hardness of the hardfacing overlays. The investigation was performed on a 12mm thick ASTM A36 steel plate weld overlaid by hardfacing electrode HV-450 of 3.2 mm diameter at various welding currents, 90, 110, and 130 amperes, respectively. The investigation was conducted by using optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and hardness test on the hardfacing overlay. The results showed the hardness of the hardfacing overlay is higher than the base metal, indicating higher strength of the weld overlay. From the three welding currents applied, the highest hardness in the weld overlay is obtained at the lowest current.

Abstract: API 5L Grade B steel pipe used for the oil and gas industries must meet toughness requirement of higher than 27 Joule and hardness value of lower than 248 HV. The welding process during piping installation sometimes generates lower toughness. Thus additional heat treatment was necessary to recover their superior toughness. Quenching from 900 °C into water or oil medium followed by tempering at 550 °C, 600 °C and 650 °C for 1 hour was selected in this study. Charpy impact test was used to access their toughness data, while the hardness was measured using micro Vickers hardness. It was found that the highest toughness of 168 Joule with a hardness of 166 HV_1.0 was generated in the welding zone after water quenching followed by tempering at 600 °C treatment. The metallographic investigation reveals fully martensite tempered microstructures. These acquired toughness and hardness values were in accordance with API 5L pipe standard requirements.

Abstract: This work describes the advances in manufacturing for the recovery of hydraulic turbines. One of the key components in the operation of hydraulic turbines is the blades; as they are part of the impeller, they are in constant motion and directly receive all the loads produced by the impact of the water and the abrasive effects caused by sediment. The interaction between abrasion, cavitation, and corrosion accelerates the wear of these components, so it is necessary to apply coatings to prolong their useful life. When these elements lose their hydrodynamic profile, they must be submitted to a recovery process; typically, welding is used. However, due to the advancement of additive manufacturing (AM) and the development of new materials, AM appears as a disruptive technology capable of recovering the dynamic profile and improving surface properties such as hardness and wear resistance. The results show the effectiveness of the wire and arc additive manufacturing technology for the recovery of hydraulic turbines, increasing surface hardness from 285 to 325 HB.

Abstract: The paper deals with analysing the causes of damage to the injection mould insert block to produce plastic parts. Mould insert block material has been declared as alloy tool steel for hot working 1.2344 (X40CrMoV5-1). Part of the analysis is also evaluating an attempt to repair a damaged block using welding methods temporarily. However, there was an intense cracking of the welded joint already during the welding process. Therefore, a non-destructive capillary test was used to analyse surface defects. Complex material analysis of the mould insert block was performed using light and electron microscopy methods, the chemical composition was determined based on optical emission spectrometry.

Abstract: The paper presents the main aspects regarding the qualification and certification of welders for thermoplastic materials according to the requirements of European standards. In this sense, the requirements regarding the assessment of the knowledge and practical skills of the personnel who carry out activities for the realization of welded joints using different types of processes, materials and semi-finished products are presented. Development and diversification of the field of thermoplastic materials with industrial applications, requires a rigorous personnel verification, in order to ensure the quality required for products made by welding.

Abstract: The qualification and later certification of the inspection personnel in the field of welding is more and more a necessity that determines, through the quality of the training and the qualification / certification obtained, the access of new contracts. This paper details how the qualification and certification system, developed by the International Welding Institute (IIW) for the qualification and certification of inspection personnel in the welding field, has been harmonized with the European Qualification Framework (EQF) requests. The levels of qualification and later certification for the inspection personnel are also detailed. The situation of internationally issued qualifications and the level of EQF recognition is detailed, as well as details regarding the possibility of obtaining qualifications as C-IWE, C-IWT and C-IWS. Keywords: IIW certification, NQF, EQF, welding, C-IWI.

Abstract: The requirements for sustainability and transition to a circular economy are key elements in the design and production of the components made by polymeric materials. The European Commission has issued a number of new directives with strict roadmaps to all State Members, in this regard. Some directives have already started to take effect; others are reaching their implementation deadlines. Limiting the consumption of raw materials and energy, as well as recyclability will lead to an increased reconversion of the current manufacturing technologies. However, all these goals must also take into account the quality aspects of the products. The testing methods must be adapted to certify the properties stated in the product sheets. This paper analyzes welding quality aspects in the production of hollow balls, made of polymeric materials, objects resulting from the joining of two hemispheres. As a case study, benchmarks from the cosmetic industry commonly known as deo roll balls were used. The first part of the paper presents the classic technology for manufacturing deo roll balls by extrusion blowing process. Below are some alternative technologies for manufacturing these balls by joining two hemispheres. The last part of the paper analyzes the welded joints by destructive and non-destructive testing methods. The basics that underlie the joining by welding polymeric materials as well as notions of rheology and material structure in the heat-affected zone are essential elements in explaining defect occurrence. A strict control of the welding parameters can offer good chances for implementing technologies to produce large series of spherical objects made of polymeric materials, objects that are made through alternative joining methods, more precisely by welding two hemispheres. The experiments carried out also highlighted some vulnerabilities of the proposed alternative technologies, their possible causes as well as the possibility of solving defects. These studies may underlie similar applications in which spherical objects are used.

Abstract: Current aspects of the developing of modern self-shielding flux-cored wires composition for arc welding of low-alloyed steels are considered. Advantages and disadvantages of flux-cored wires of carbonate-fluorite, oxide and oxide-fluoride types of are shown in comparison. The effectiveness of gas shielding of molten metal at welding with self-shielding flux-cored wires of carbonate-fluorite type is analyzed considering the thermal properties of their cores. It is shown that to improve reliability of gas shielding at welding using the wires of this type it is important not only to ensure generation of sufficiently large volume of shielding gases at thermal destruction of the wire core, but also to control this process, providing gas evolution at all stages of heating and melting of the wire. The results of complex thermal analysis of the wire core mixtures containing, for example, lithium carbonate show substantially large heat losses for heating and melting of the wire core, which are accompanied by the development of energy-intensive processes of thermal destruction of core components. It is shown that the limitation of lithium carbonate content in the wire at the level of not more than 2 wt. % allows not only to preserve welding arc burning stability at the acceptable level but also to provide effective gas shielding of molten metal and easy separation of slag crust. The control of thermochemical reactions in the core is achieved by selection of its proper composition to ensure favorable melting of flux-cored wire and electrode metal transfer to the welding pool. Results of metallographic examinations of distribution and composition of non-metallic inclusions in metal of the welds made with wires of the oxide and oxide-fluoride types are presented. Main properties of the developed self-shielding flux-cored wires and recommendations on welding are given in conjunction with prospective fields of their application.