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

Challenges in path planning of high energy density beams for additive manufacturing

As there are no cutting forces in High Energy Density (HED) beams like lasers and Electron Beam (EB), their speeds are limited only by their positioning systems. On the other hand, as the entire matrix of the 3D printed part has to be addressed by the thin beam in multiple passes in multiple layers, they have to travel several kilometers in tiny motions. Therefore, the acceleration of the motion system becomes the limiting factor than velocity or precision. The authors have proposed an area-filling strategy for EB to fill the layer with optimal squares to exploit analog and hardware computing. 3D printing requires uniform intensity slanged as flat hat shape whereas the default is Gaussian. The authors have proposed an optimal algorithm that takes into account the maximum velocity and acceleration for achieving a flat hat without any compromise on productivity

Modeling of the Plasma 3D Deposition of Wire Materials

The numerical modeling of the physical process of manufacturing parts using additive technologies is complex and needs to consider a variety of thermomechanical behavior. This is connected with the extensive use of the finite element computer simulation by means of specialized software packages that implement mathematical models of the processes. The algorithm of calculation of nonstationary temperature fields and stress-strain state of the structure during the process of 3D deposition of wire materials developed and implemented in ANSYS is considered in the paper. The verification of the developed numerical algorithm for solving three-dimensional problem of the production of metal products using arc 3D deposition of wire materials with the results of the experiment is carried out. The data obtained from calculations on the developed numerical model are in good agreement with the experiment

Application of Dynamic Beam Positioning for Creating Specified Structures and Properties of Welded Joints in Electron-Beam Welding

The application of electron beam sweep makes it possible to carry out multifocal and multi-beam welding, as well as combine the welding process with local heating or subsequent heat treatment, which is important when preparing products from thermally-hardened materials. This paper presents a method of electron beam welding (EBW) with dynamic beam positioning and its experimental-calculation results regarding the formation of structures and properties of heat-resistant steel welded joints (grade of steel 20Cr3MoWV). The application of electron beam oscillations in welding makes it possible to change the shape and dimensions of welding pool. It also affects the crystallization and formation of a primary structure. It has been established that EBW with dynamic beam positioning increases the weld metal residence time and the thermal effect zone above the critical A3 point, increases cooling time and considerably reduces instantaneous cooling rates as compared to welding without beam sweep. Also, the difference between cooling rates in the depth of a welded joint considerably reduces the degree of structural non-uniformity. A bainitic–martensitic structure is formed in the weld metal and the thermal effect zone throughout the whole depth of fusion. As a result of this structure, the level of mechanical properties of a welded joint produced from EBW with dynamic electron beam positioning approaches that of parent metal to a greater extent than in the case of welding by a static beam. As a consequence, welding of heat-resistant steels reduces the degree of non-uniformity of mechanical properties in the depth of welded joints, as well as decreases the level of hardening of a welded joint in relation to parent metal

Rapid Temperature Control in Melt Extrusion Additive Manufacturing Using Induction Heated Lightweight Nozzle

An approach for improving and maintaining consistent fusion quality of the deposited material during FDM 3d-printing is proposed. This approach is based on the nozzle temperature control during the printing process to adjust the polymer extrusion temperature with a speed and accuracy adequate to the FDM process. High frequency induction heating of the lightweight nozzle (<1 g) was used. To control the temperature of a lightweight nozzle, the resonant temperature measurement method based on the analysis of the high frequency eddy currents is proposed. To determine the parameters of the nozzle and the inductor as a plant, a FEM model of the inductive heating of the nozzle and a simulated model of a serial-parallel resonant circuit containing inductor were developed. Linearization of the automatic control system was performed to ensure the equal quality of regulation when operating in a wide temperature range. The quality of regulation, stability of the system, and coefficients of the PID controller were evaluated using a simulated model of the control system. A number of test samples were printed from various materials, and tensile stress testing was carried out. The developed control method reduces the nozzle temperature control error from 20 to 0.2 °C and decreases control delay by more than six times

Mathematical Model of the Layer-by-Layer FFF/FGF Polymer Extrusion Process for Use in the Algorithm of Numerical Implementation of Real-Time Thermal Cycle Control

An approach for improving and maintaining a consistent weld quality of the deposited material during the FFF printing process is proposed. The approach is based on the analysis of the printing process thermal cycle and the real-time nozzle temperature control. The mathematical model of the FFF printing process has been developed with the use of real-time control in the algorithm of numerical implementation. The successful solution of the thermal conductivity problem made it possible to determine segment-wise heating settings for use during the printing process, resulting in a high and stable quality of welding. Comparison of the results of modeling with other well-known mathematical models of the FFF printing process and experimental results showed the adequacy of the proposed model. A maximum deviation of 17.7% between the simulation results and the thermography data was observed. The proposed model was verified using rectangular 3D polylactide shapes printed with and without regulation of the power of the heat source according to the previously estimated settings. The overall quality of regulation, stability of the system, and the PI coefficients of the controller were evaluated using a simulated model of the control system. The results of the experiment fully correspond with the modeling results

Formation of Structure and Properties of Two-Phase Ti-6Al-4V Alloy during Cold Metal Transfer Additive Deposition with Interpass Forging

The paper deals with the main formation patterns of structure and properties of a titanium alloy of the Ti-6Al-4V system during additive manufacturing using cold metal transfer (CMT) wire deposition. The work aims to find the optimal conditions for layer-by-layer deposition, which provides the high physical and mechanical properties of the titanium alloy of the Ti-6Al-4V system hybrid, additively manufactured using CMT deposition. Particular attention is paid to interpass forging during the layered printing of the product. Additionally, we investigate how the heat treatment affects the structure and properties of the Ti-6Al-4V alloy that has been CMT-deposited, both with and without forging. These studies have shown that the hybrid multilayer arc deposition technology, with interpass strain hardening, allows the use of high temperature and high technology titanium alloys to obtain products of a required geometric shape. It has been proven that the interpass deformation effect during CMT deposition contributes to a significant decrease in the sizes of the primary β-grains. In addition, forging enhances the effect of microstructure refinement, which is associated with phase recrystallization in deformed areas. It is shown that the heat treatment leads not only to a change in the morphology of the phases but also to additional phase formations in the structure of the Ti-6Al-4V-deposited metal while the mechanism is realized and consists of the gradual decomposition of the martensitic α′-phase and the formation of a dispersive α2-phase. This structure formation process is accompanied by the dispersion hardening of the α-phase. The strength characteristics of the Ti-6Al-4V alloy obtained using layer-by-layer CMT with forging are given; they exceed the strength level of materials obtained with the traditional technologies of pressure treatment, and there is no decrease in plasticity characteristics. The use of the subsequent heat treatment makes it possible to increase the ductility characteristics of the deposited and forged Ti-6Al-4V material by 1.5–2 times without strength loss

Plasma Charge Current for Controlling and Monitoring Electron Beam Welding with Beam Oscillation

Electron beam welding (EBW) shows certain problems with the control of focus regime. The electron beam focus can be controlled in electron-beam welding based on the parameters of a secondary signal. In this case, the parameters like secondary emissions and focus coil current have extreme relationships. There are two values of focus coil current which provide equal value signal parameters. Therefore, adaptive systems of electron beam focus control use low-frequency scanning of focus, which substantially limits the operation speed of these systems and has a negative effect on weld joint quality. The purpose of this study is to develop a method for operational control of the electron beam focus during welding in the deep penetration mode. The method uses the plasma charge current signal as an additional informational parameter. This parameter allows identification of the electron beam focus regime in electron-beam welding without application of additional low-frequency scanning of focus. It can be used for working out operational electron beam control methods focusing exactly on the welding. In addition, use of this parameter allows one to observe the shape of the keyhole during the welding process

Microstructural Features and Microhardness of the Ti-6Al-4V Alloy Synthesized by Additive Plasma Wire Deposition Welding

Wire arc additive manufacturing (AM) is able to replace the traditional manufacturing processes of Ti alloys. At the same time, the common drawback of Ti workpieces produced by AM via wire deposition welding is the formation of a coarse-grained dendritic structure, its strong anisotropy and, consequently, lower strength as compared to a monolithic alloy. In this work, a new method is proposed for the enhancement of the strength properties of the Ti-6Al-4V alloy synthesized by AM via wire deposition welding, which involves the use of a wire with an initial ultrafine-grained (UFG) structure. The UFG wire is characterized by a large number of defects of the crystalline lattice and grain boundaries, which will enable increasing the number of “crystallization centers” of the α-phase, leading to its refinement. The macro- and microstructure, phase composition and microhardness of the Ti-6Al-4V alloy samples were investigated. The microhardness of the alloy produced by layer-by-layer deposition welding using a UFG wire was shown to be on average 20% higher than that of the samples produced by a deposition welding using a conventional wire. The nature of this phenomenon is discussed, as well as the prospects of increasing the mechanical characteristics of Ti alloys produced by additive manufacturing