Torch Motion Research Articles

Torch Motion Control based on 3D Shape Estimation of Melt Pool by Image Measurement System

Torch Motion Control based on 3D Shape Estimation of Melt Pool by Image Measurement System

Experimental Investigation on Bead Geometry Parameter and Mechanical Property of Part Fabricated by Wire Arc Additive Manufacturing

In additive manufacturing process, wire arc additive manufacturing process (WAAM) is a technique which can produce a metal 3D printed part. In Industries product are produced by wasting one third of its material, from this process time consumption and material wastage is more comparing in Subtractive Manufacturing over Additive Manufacturing. Additive Manufacturing stepped from 1925 in manufacturing industry and it has gained its remarkable growth in past few decades, as of now metal 3D oriented parts have come to play a major role in aerospace industry. This research work focused on Gas Metal Arc Welding (GMAW) welding. It has high deposition rate, ultimate build volume and good structural integrity compare with other additive manufacturing process. MACH3 controller is used to control the welding torch motion for addition of material by 3 axis movement (X, Y and Z). To identify the correct parameters for metal part we have done numbers of samples by changing values in the MIG machine from that we finalize the three parameters through visualizes on the printed materials after that a wall like structure is built and post processing like cutting the materials from base plate, grinding the uneven surface on printed materials. The printed materials are ready for material testing like bead geometry analysis of various parameter and tensile testing to identify the printed material strength, elongation, stress and strain.

Experimental Investigation on Mechanical Properties of Part Fabricated by Wire Arc Additive Manufacturing Process

Additive manufacturing process is a method of layer by layer joining of materials to create components from three-dimensional (3D) model data. After their introduction in the automotive sector a decade ago, it has seen a significant rise in research and growth. The Additive manufacturing is classified into different types based upon the energy source use in the fabrication process. In our project, we used self-build CNC machine that runs MACH3 software, as well as the MACH3 controller is used to control the welding torch motion for material addition through three axis movement (X, Y and Z). In the project we used ER70 S-6 weld wire for the fabrication and examined its microstructure and mechanical properties. Different layers of the specimen had different microstructures, according to microstructural studies of the product. Rockwell hardness tester used for testing hardness of the product. According to the observation of the part fabricated components using the Wire Arc Additive Manufacturing process outperformed the mechanical properties of mild steel casting process. The product fabricated by Wire Arc Additive Manufacturing process properties is superior to conventional casting process.

Numerical simulation of WAAM process by a GMAW weld pool model

Additive manufacturing (AM) is a high-productivity process which can make a near-net-shape structure. In this study, the focus is the wire-arc AM (WAAM) process. In the WAAM process, wire is the depositing material. The wire melts by an arc plasma and deposits layer by layer. To establish an advanced WAAM process, it is important to make a precise structure of the intended shape. In this study, a gas metal arc welding (GMAW) weld pool model is applied to WAAM process, and influence of the deposit condition on the shape of the deposition is numerically investigated. Firstly, influence of the interpass temperature is investigated. When cooling time is set appropriately, the deposition shape becomes higher and thinner. In addition, concerning influence of the welding direction, when the welding direction is reversed for each layer, the variance of the deposition height becomes small. These numerical results show that it is important to manage the temperature and torch motion for controlling the deposition shape. These numerical results have similar tendency with experimental results and show the GMAW weld pool model is a helpful tool to predict and control the WAAM process.

狭開先パルスMIG/MAG溶接における電源特性・ワイヤ送給とトーチモーションの協調制御

狭開先パルスMIG/MAG溶接における電源特性・ワイヤ送給とトーチモーションの協調制御

Numerical Simulation of MIG Weld Pool in Switchback Welding

The authors proposed a switchback welding method to make stable back beads in the first layer weld during one-side multi-layer welding. In the proposed welding method, a welding torch is moved backwards and forwards like a switchback. The torch motion is important in the control of the weld pool. In this paper, the influence of the torch motion on the weld pool shape is investigated in order to find the optimum welding parameters. Firstly, fundamental welding experiments were carried out in thin plate one-side butt welding to determine the parameters of numerical simulation. Secondly, a simple numerical model for switchback welding was constructed and a heat conduction analysis was carried out, to investigate the effect of the travel speed and backward stroke distance of the torch on the weld pool. When the travel speed of the forward stroke was faster than that of the backward stroke, the weld pool length became shorter than a constant travel speed. On the other hand, if the backward stroke distance became longer than half of the forward stroke distance, continuous back beads could be obtained, regardless of such a disturbance as fluctuation of the arc length. The validity of the switchback welding method was verified by numerical simulation and fundamental experiments.

Three Dimension Curve Welding Seam Modeling for Seam Tracking

A novel modeling method for 3D curve welding seam is presented in this paper based on a welding robot for large workpiece. The 3D curve welding seam tracking is implemented by macro and micro motion which can control translational motion of torch in a large range and implement accurate seam tracking in small range. As such, the self-teaching seam model and real-time seam model are established to accurately control position and orientation of torch. The self-teaching model is obtained by a cubic B-spline interpolation function. Then a continuous position model of a V-type seam is established by using the cubic parameter B-spline least square method. The orientation model of the seam is also established by using the position model and coordinates of seam characteristic points. These three models form the base of macro and micro translational motion control and real-time tracking control. Furthermore, in order to compare the performances of the different position modeling method, simulations have been carried out to produce the modeling results of cubic parameter B-spline least square method and polynomial least square method. The effectiveness of these seam model has been verified.

スイッチバック溶接による溶接溶融池の数値シミュレーション

The authors proposed the switch back welding method to make the stable back beads in the first layer weld during one side multilayer welding. In the proposed welding method, the torch motion is important to control the weld pool, i.e., the welding torch is moved backward and forward like switch back. It is important to investigate the behavior of the weld pool to get the optimum welding parameters such as the traveling speed, the forward distance, the backward distance, the welding current and so on. There are many welding parameters. In order to find the optimum welding parameters, the numerical simulations are useful method instead of the welding experiments. Since the deposited metal is considered in the numerical models of the welding in the thick plates, the numerical analysis becomes complicated. In order to simplify the analysis, the authors discussed the numerical simulations of the welding in the thin metal plates because the effect of the deposited metal can be minimized.First, the fundamental welding experiments were carried out in MIG welding. By using the experimental results, the numerical models in the switch back welding are determined. Next, the behaviors of the temperature are investigated under the change of the traveling speed and the backward distance. If the traveling speed is constant in the switch back welding, the weld pool size may sometimes become big. In this case, the burn trough may take place due to the flow in the weld pool. When the traveling speed of the forward movement is faster than backward movement, the weld pool length becomes shorter than the case of the constant traveling speed. Moreover, if the backward distance is longer than half of the forward distance of the switch back welding, the authors can obtain continuous back bead regardless of the disturbance such as the variation of the arc length, i.e., the stability of the weld pool is increased. The switch back welding method is useful to make the stable back bead in the MIG welding.

Image processing and control of weld pool in switch-back welding without backing plate

To achieve high quality in multilayer welding, it is important to obtain stable weld results for the first layer.1–5 For this reason, welding is usually conducted by using a backing of the same kind as the base material or a ceramic backing plate. In using a backing metal, the weight of the base material increases. Also it sometimes induces notches to occur at the weld joint between the base material and the backing. This can cause cracking. On the other hand, in using the backing plate, its removal is required after welding, and this makes the method unsuitable for automating the process. Therefore, in the authors' previous report, a proposal was made of the switch-back welding method in which welding is executed without using a backing plate, and also an investigation was made of the welding conditions for the root gap.6 In this welding method, it is necessary to adjust the wire feeding rate, the torch motion and the power property in accordance with the gap so that the back bead and the deposit can be controlled. Even if the gap is measured before welding, it may change owing to welding distortion. Hence, when welding is conducted by fixing the welding conditions, the change in the gap causes the back bead to become unstable. For this reason, in this study, a method is discussed to detect the gap on-line by processing images of the molten pool observed by a CCD camera. Then, using the results, the back bead was feed-forward-controlled in real time. Moreover, to examine the controlling performance, welding was conducted by varying the gap between 4.6 mm and 2.5 mm without tack welding. Very good weld results were obtained.

バッキングレスＶ開先溶接におけるギャップセンシングと溶融池の制御

The formation of stable back beads in the first layer weld during one side multilayer welding is important to achieve high quality welded metal joints. The authors thus employed the switch back welding method for V groove joints without backing plates. In this method, the power source, wire feed motor, and robot manipulators were controlled by the computer based cooperative control. The torch is moved backward and forward like switch back. First, the torch is moved forward with high speed. The arc is discharged to the each root edge of the groove. The droplet is deposited to each root edge, too. After that, the torch is moved backward with the same high speed. During the backward motion, the deposited metal makes the bridge between the both edges due to the surface tension. Next, the torch is moved forward with slow speed to form the bead. The mentioned torch motion is repeated. When constant welding conditions are used, the back bead becomes unstable by affection of the disturbances such as gap variations due to the welding distortion. In this method, it is important to measure the gap. The authors discuss a method to detect the gap and to get the stable back bead by using a visual sensor, the CCD camera. During the slow forward torch motion, the weld pool can be observed. The shape in the front part of the weld pool depends on the gap. It can be detected by processing the weld pool images. The authors investigate the method to take the gap from the weld pool image. The use of feed-forward control of back beads to compensate for variations of root gaps was also tested. In order to verify the performance of the feed forward controller, the gap is changing from 4.6 mm to 2.5 mm without the tack welding.

Processing parameter effects on solution precursor plasma spray process spray patterns

Solution precursor plasma spray (SPPS) is a promising process for making thermal barrier coatings (TBCs) with improved durability. The improved durability of SPPS TBCs results from the novel microstructural features, (i) absence of splat boundaries, (ii) generation of through-thickness vertical cracks (iii) existence of uniformly distributed porosity. In this process, the coating is built up by the overlapping and stacking of layers deposited in each pass of the plasma torch across the substrate. Information concerning the lamella is generally referred to as the spray pattern. The spray patterns from SPPS of 7wt.%Y 2O 3–ZrO 2 precursor were studied via a fixed scan spray method, where the plasma torch repeatedly scans on a single line across the substrate. The surface of the resulting spray patterns can be divided into adherent deposits and powdery deposits that correspond to the hot and cold regions of the plasma jet, respectively. The penetration depth of the liquid into the plasma jet has a significant effect on the position of the adherent deposits and the deposition efficiency. The structure of the adherent deposits across the section normal to the motion of plasma torch is symmetric about its center. It becomes more porous and the thickness of the deposits is reduced towards the edges. Implications of these results for understanding and improving the SPPS process are discussed.

狭開先ロボット溶接におけるギャップ変動に対する適応制御

Quality of a multi-layer welding depends on a welding in first layer. In order to get a high quality of the welding, it is necessary to make a stable back bead and to melt the base metals. In narrow gap welding, it is difficult to control the bead height (deposited metal) and the back bead (the melted area of the backside) simultaneously by using conventional welding. To improve this problem, authors propose a cooperative control of the welding equipments including the welding power source, the electrode wire feeder and the welding robot, i.e., the welding torch is not only oscillating on the groove, but also moving back and forth. To control the heat input, the power source is controlled according to the torch motion (robot motion), too. In the forward process, the arc (the heat) is given to the root edges to get a wide back bead. In the backward process, the suitable bead height is obtained. The idea of its robot motion comes from the knowledge of the skilled welding workers. Since the arc length must be kept short during the welding, the power source with a nonlinear power source characteristic is used. Welding conditions are investigated for 4 mm root gap, 5 mm root gap and 6 mm root gap by observing arc position with a high speed motion video camera, and observing the weld pool with a CCD camera. The welding conditions are stored in a database. Before the welding, the root gap at the beginning and at the end on the base metal is detected by a slit laser light and the CCD camera, and is stored into a memory in the personal computer. During the welding, the personal computer detects the torch position from the encoder pulses of the welding robot, finds the root gap at the torch position and calculates the welding conditions by using the data base, i.e., the adaptive control for the gap variation is applied. The welding experiment under the root gap variation from 6 mm to 4 mm is carried out to verify the validity of the cooperative control method.

Temperature distribution control in scanned thermal processing of thin circular parts

Scan thermal processing is enabled by guidance of the heat source trajectory during fabrication. For thin, cylindrically symmetric parts, this is performed by their rapid revolution under a radially or axially translated torch, with its power modulated so as to implement a specified thermal distribution as it sweeps the product surface, and thus to generate desirable material features. A new analytical description of the thermal field in thin disk-shaped parts, based on superposition of Green's functions, was developed for off-line analysis. A multivariable linearized model with least-squares identification of its varying parameters was also derived for real-time emissivity compensation and prediction of delayed temperature data. This model is embedded to a thermal distribution control scheme, driving the scanned torch motion and power by a new real-time simulated annealing optimization strategy, using temperature feedback from randomly sampled surface locations by an infrared pyrometer. The thermal regulator is validated computationally and experimentally.

Scanned Orbital Welding: Thermal Modeling and Lumped Adaptive Control

Scan orbital welding of cylindrical vessel, flange, and piping parts is performed by their rapid revolution under a radially or axially translated heat source, with its power modulated so as to implement a specified thermal distribution. Thus, the plasma-arc welding torch sweeps the stainless steel surface to generate a desirable temperature field and the concomitant material features. A numerical simulation of the thermal field is developed for off-line analysis. On this basis, a lumped thermal regulator of the heat-affected zone, employing infrared temperature feedback at a single spot, as well as standard PI, gain scheduling, and self-tuning control algorithms is tested. The thermal model is also employed for real-time torch efficiency identification and compensation. The numerical reference model serves as the basis for an in-process adaptive thermal control system to regulate the temperature field, using thermal feedback from the infrared pyrometer. A distributed-parameter control strategy, with guidance of the torch motion and power by a new weighted attraction strategy to randomly sampled points, is tested on scan-welded flanges. The regulator is validated computationally and experimentally, and its applicability to other scanned processing of materials is considered.

Simulation For Control Of Sequential And Scanned Thermal Processing

A thermal simulation of manufacturing processes with sequential and scanned torch motion is developed in this article and applied to the newly invented scan welding technique. The composite model consists of a numerical description of the solid conduction field, an analytical formulation of the melt circulation, and experimental calibration of the torch parameters. This simulation is used for a comparative analysis of serial and scanned thermal processing, with the latter resulting in a more uniform temperature distribution and smooth thermal gradients. In particular, scan welding deposits the entire weld bead length simultaneously at controlled solidification rates and material structure in the heat affected zone. The model serves as the foundation of thermal control systems of the torch power and motion, using real-time feedback of surface temperatures measured by infrared thermometry. The simulation is applicable to a large variety of thermal manufacturing techniques, such as arc cutting and laser machining.

Distributed-Parameter Control of the Heat Source Trajectory in Thermal Materials Processing

In thermal manufacturing processes performed by a localized, sequentially moving heat source, simultaneous regulation of multiple thermal quality characteristics requires real-time control of the temperature field developed through the distributed heat input on the part surface. Such control of the thermal field to a desired distribution employs infrared sensing and feedback of the surface temperature hill, to modulate the torch power and motion in-process. The torch trajectory is guided in real time by an efficient optimization algorithm based on the concept of moving complexes. This distributed-parameter control strategy is developed using a numerical simulation model of thermal processing, and its performance is evaluated experimentally in heat treatment of thin stainless steel plates. The thermal controller is applied to the new scan welding process, in which it drives the torch in a reciprocating motion along the weld, yielding a uniform and smooth temperature field, and thus a favorable material structure and mechanical properties. Application of such thermal control to various other material processing methods is also investigated.

アーク溶接ロボットのオフラインプログラミングシステムにおけるロボット動作軌跡処理

Utilization of conventional arc-welding robot by actual robot teaching (by a human operator) is not suitable for constructing a flexible production system, because applicability of the teaching data is limited to only the target robot.As a solution to this problem, the authors have proposed a compact computer aided welding system which consists of a personal computer and a conventional teaching-playback arc welding robot, and indicated the concept of off-line programming by a simple robot language. In the system, wled information processing is divided into four levels; task level, tool level, robot level and machine code level. At each level, necessary information is obtained from external files. In task level, source program of the weld is parsed and weld parts are extracted from the work model. In tool level, the motion of weld torch is generated on the work model at each weld line and between weld lines referring to both of work and torch models. In robot level, each angle of robot arms, which realizes required torch angle, is claculated considering the movable range of the robot. In machine code level, angle data of robot arms and weld conditions are combined together and converted into robot codes, which are transmitted to the robot controller through a communication line.Realization of torch motion in robot level is discussed for 5-axis articulated type robot. Possibility of required torch angle by the robot is checked by calculation of intersection between arm plane, in which robot's arms move, and movable range of torch rotation. Collision check and avoidance algorithm is shown, and its property was confirmed by an example program of the weld.

Application of Microcomputers to Automatic Weld Quality Control

The demand for increased productivity of welding operations has led to the expanded use of computer control to allow higher production rates while maintaining weld quality. The charateristics of the gas metal arc welding process and the relationship between welding parameters, the desired output of the welding process, and the automation of the process are discussed. A strategy for two-axis welding torch positioning and velocity control is developed based on preview control techniques. To evaluate the applicability of the proposed control method the motion of heat source along different welding paths is simulated on an analog computer with on-line control of process time constants by an LSI-11 microcomputer. The simulation results show that high quality seam tracking can be accomplished by controlling the torch motion using the proposed method. The method appears to be suitable for on-line control of welding processes.