Lahodzinskyi I. Additive arc surfacing of spatial products with filler wires of steels and alloys

Lahodzinskyi I.M. Additive arc surfacing of spatial products with filler wires of steels and alloys. Thesis for the scientific degree of the doctor of philosophy, the field of stydy 13 – Mechanical engineering, program subject area 131 – Applied Mechanics. – National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kyiv, 2024. The thesis consists of six chapters in which the main results are presented and substantiated. In the introduction, the relevance of topic is justified, the objectives and tasks of the research are outlined, the methods and methodologies of their implementation are provided, and the scientific novelty and practical significance of the research results are formulated. Chapter One provides a literature review of the current state of the art in Wire Arc Additive Manufacturing (WAAM) technologies for the production of spatial products. Chapter two outlines the methods for conducting experimental research to determine the geometric characteristics of additively deposited layers, the structure and physico-mechanical properties of the deposited metal, the chemical composition, and the properties of the materials used for research Technological recommendations and selected equipment for the production of products from low plasticity materials are proposed. In Chapter Three, the process of layer-by-layer deposition of low-carbon steels by GMAW-CMT/Pulse method in combination with argon-based shielding gas mixtures, as well as deposition of PAW-CW additives is experimentally investigated. Based on the analysis of the experimental data, regularities in the influence of changes in the composition of the shielding gas environment and the welding current mode on the formation and geometric characteristics of the product walls are established. Experimental studies are conducted to determine the influence of GMAW-CMT/Pulse deposition methods on the geometric characteristics of products made of aluminum alloys, austenitic stainless steels, and silicon bronzes. On the basis of the conducted experimental research, the possibility of obtaining spatial products by plasma arc deposition using rods of heat-resistant nickel alloy as filler material, manufactured according to the author's proposed methodology, is demonstrated. The Chapter Four is devoted to the investigation of the influence of GMAW-CMT/Pulse deposition methods and changes in the shielding gas environment on the formation of structure and mechanical properties of specimens made of low-carbon steel, as well as the welding current mode (GMAW-CMT/Pulse) when using silicon bronzes. In Chapter Five, finite element models are constructed, computer simulations are performed, and an analysis of the results of finite element modeling of stress-strain components in three-dimensional products during additive arc deposition of silicon bronze and heat-resistant nickel-based alloy as compact filler material is conducted. It is found that the cause of cracks in silicon bronze and GMAW pulsed deposition processes is the formation of tensile stresses exceeding the metal's strength limit in the high temperature range during multiple heating and cooling cycles in the additive deposition process. The thermal deformation processes are investigated during the layer-by-layer plasma arc deposition of the heat-resistant nickel-based filler SBM-4 in combination with two variants of deposition base materials. In order to confirm the adequacy of the results of previous calculations and the possibility of their further application, the verification of the developed finite element model and the results of computer simulation is carried out by comparing their convergence with experimental data. In Chapter Six, technological recommendations are formulated for the layer-by-layer additive manufacturing process of spatial products using electric arc heat as a heat source and compact (solid cross-section wires and rods) filler material. A methodology is proposed for determining metal losses during finishing mechanical processing of products manufactured by various additive arc deposition methods. A computerized setup for additive arc deposition of products with numerical program control based on G-codes is designed and constructed. Examples of products manufactured according to the formulated technical recommendations for additive deposition of complex spatial shapes are given. Keywords: additive technologies, layer-by-layer deposition, additive manufacturing, FDM technology, 3D printing, welded joints, heat affected zone, low-carbon steel, aluminum alloy, bronze, mathematical modeling, finite element modeling, stress-strain state, metallographic analysis, mechanical properties, structures, grain sizes.