Study On Additive Microplasma Welding Technology For Three-dimensional Metal Parts Manufacturing

Manufacturing of complex-shaped metal products by 3D-printing becomes more and more urgent in modern industry.Laser technologies(such as SLM and SLS)are most often applied for this purpose,as well as electron beam technologies(e.g.EBF3).All of them are characterized by quite high cost and low efficiency,in spite of quite high mechanical properties of finished products.During last several years there has been a tendency of application of welding technologies in 3D printing all over the world,wherein,mainly,electric arc welding processes were used.Conducted researches proved that application of welding technologies can improve the efficiency of manufacturing and decrease the cost of the process in several times.At the same time,applied electric arc technologies decrease the physical-mechanical characteristics of manufactured parts,that becomes a significant drawback of such methods.Plasma(microplasma)welding process is capable to solve this problem and to overcome the disadvantages of conventional arc welding processes.Being a mature technology plasma welding(cladding)can provide better parameters of the arc and better physical properties,that can positively affect the properties of manufactured products.In view of this,the goal of the work on the investigation of microplasma welding technology and the creation of equipment for the production of three-dimensional metal products is formulated.The main content of the thesis includes the following:(1)To carry out research on different welding technologies application,the universal laboratory stand is created for the study of additive welding technology,comprising a power source for plasma(microplasma)welding,plasma unit,apparatus for consumable electrode welding,auxiliary cooling unit,universal plasma torch for cladding with wire under the modes of microplasma and plasma welding,plasma torch for microplasma powder cladding,laboratory filler wire feeding mechanism,the powder dispenser.(2)Theoretical and experimental studies were carried out to determine the optimal design and technological parameters of the plasma torch for the microplasma welding technology of additive production.The calculation package Solidworks Flow Simulation,built on the basis of the Navier-Stokes equations system,was used to simulate the gas dynamics in plasmatrons,modified for microplasma additive cladding.The patterns of distribution and trajectories of the particles of the filler powder were studied,and the technological parameters of the multilayer surfacing process were predicted.A concentric scheme for the input of powder into the gap between the plasma-forming and focusing nozzle was chosen.Experimental studies of the parameters of a microplasma arc and a two-phase flow "microplasma-filler powder" on the dimensions of a growing part were carried out.To optimize the technological modes of additive microplasma-powder technology,the criteria for the mass of weld metal and running energy were used.(3)Comparative experimental studies of influence of conditions of microplasma powder cladding,microplasma wire cladding and electric arc cladding with a current-carrying wire on the features of formation and the structure of three-dimensional metal samples of the obtained "straight high wall" type are carried out.In the case of microplasma-powder cladding with powder of carbon structural steel,a dense structure of samples with a wall thickness of 2.5-2.8 mm and a smooth surface with a small waviness was obtained.In addition,S-08G2 C steel wire was used as a filler material to grow three-dimensional laminar samples using microplasma and electric arc MAG cladding.The microplasma wire cladding technology also provides a dense structure of samples with a thickness of about 3 mm and a smooth surface.When building-up the same samples using MAG-wire technology,a coarser dendritic microstructure of the metal is observed as well as the presence of nonmetallic inclusions and some porosity in the upper layers of the grown wall;the thickness of the obtained samples is at least 4-5 mm.(4)A prototype of the automated equipment with numerical program control(CNC)for growing three-dimensional metal products(such as a hollow cylinder,cone,square,including stiffeners,their combinations etc.)was developed considering the following criteria: the availability for wide range of consumers(relatively low cost,ease of maintenance and low cost of operation,absence of restrictions on the size of volumetric metal structures,that is inherent in welding robots,versatility(the ability to change different welding heads,except of microplasma),the possibility to use powders and wires.The set of this prototype includes a 3D positioner with a simple CNC design and dimensions of the working space 900×900×900 mm,which allows to abandon application of welding robots and occupy cheaper market segment.It is shown that the microplasma technology,despite the fact that the inferior arc MAG,MIG performance,but differs in the 2-3 times lower specific energy consumption per unit weight of the resulting product.At the same time,the microplasma technology surpasses the arc-arc technology in terms of the level of physical-mechanical characteristics of the metal products obtained(tensile strength,elastic limit,platinum,toughness),and also provides higher precision of products and lower roughness(higher degree of detail of the form features).Also,in terms of specific energy consumption per unit weight of the obtained threedimensional article microplasma welding additive technology also significantly superior to laser cladding technology.The developed technologies and equipment can serve as the basis for their wide distribution in the industry for the production of billets of large-sized parts,especially in single or small-scale production,as well as in the manufacture of large-sized structures and complex parts of high-strength non-cast steels and alloys.