Pool Penetration Research Articles

Model Predictive Control of GTAW Weld Pool Penetration

Weld pool penetration is a major indicator of weld integrity but it is not directly measurable. The key to solving this issue is to find or create observable phenomena that can be used to derive the penetration. An innovative method has recently been proposed/developed to derive the penetration from the reflection of projected laser from an oscillating weld pool surface. However, in addition to the penetration, the oscillation, thus the reflection determined by it, also depends on the pulse amplitude of the current, which needs to be adjusted as the control variable to feedback control the penetration as the output. This dependence imposes a constraint on the control algorithm such that the adjustment of the control variable must be relatively slow to minimize additional sources that affect the oscillation/sensor. This restriction on the control variable adjustment also brings challenges to the identification of the dynamic model of the weld process to be controlled, which has to apply a varying control signal to stimulate the dynamics. To solve these issues, this letter proposes using a low order model to catch the dominant dynamics such that a high speed variation in the control signal can be avoided when choosing the model predictive control algorithm. This allows use of relatively poor models to determine the adjustment on the pulsing amplitude, and still achieves relatively accurate control. Experimental results verified the effectiveness of the resultant penetration control system despite the restrictions imposed by the penetration sensor, which affect the identification of high order dynamics and free adjustments of control variables.

A novel electrode-arc-weld pool model for studying the keyhole formation in the keyhole plasma arc welding process

A novel electrode-arc-weld pool model considering the influence of the backside keyhole deviation on the heat source distribution, the influence of the keyhole constraint on the arc pressure and the keyhole geometry dependent plasma shear stress, is developed to study the keyhole formation in the KPAW process. The numerical and experimental results show that: the keyhole depth increases very quickly at first, then smoothly, and then quickly again. In the blind keyhole stage, the arc pressure deepens the keyhole. The plasma shear stress facilitates the fluid flow along the rear keyhole wall and decreases the curvature of the keyhole. The process between the weld pool penetration and the keyhole penetration is defined as the blasting penetration stage, in which the molten bridge under the arc is quickly broken. The pressure balance and mass conservation mechanisms are proposed to be responsible for the blasting penetration. The low melting temperature, low surface tension and bottom surface deformation promote the blasting penetration, while the high thermal conductivity suppresses the blasting penetration. In the penetrated keyhole stage, two contrary convective eddies are found inside the weld pool. At the top surface of the weld pool, the molten metal flows upward and backward near the keyhole, but obviously flows forward at the rear part of the weld pool. At the bottom surface of the weld pool, the molten metal flows downward and backward.

The effect of the molten weld pool on the non-uniform penetration of the parent metal at of surfacing

The data of the molten weld pool influence on the increasing non-uniformity of the parent metal penetration during submerged arc surfacing using one or two strip electrodes have been presented. The experimental results of the investigation show that non-uniform penetration of the parent metal is influenced by the mass and heat flow in the weld pool. The axial bottom flow of the liquid metal during surfacing with one and two strip electrodes results in non-uniform penetration of the parent metal. In the process of submerged arc surfacing using two strip electrodes, the liquid weld metal flow and the penetration of the parent metal depend on the ratio of the current in the first and second strip electrodes. When the current in the first and second strip electrodes is the same the distribution of the temperature and flow rate across the width of the weld pool is not uniform. It leads to mass and heat flow just in the middle of the weld pool and non-uniform penetration of the parent metal with the bottom flow. The non-uniform penetration of the parent metal is influenced by the axial bottom flow. It is shown that raising the fraction of the current in the second strip electrode up to 0,6 from the total current increases the intensity of the circulation of the molten slag; its temperature becomes more equal which changes the flow rate across the width of the weld pool. The difference of the value of the maximum and average temperature, enthalpy and viscosity of the molten weld pool decreases, what influences on flow rate of the liquid metal. The experiments show that the non-uniformity of the parent metal penetration decreases

An improved simulation of temperature field in VPPA–GMAW of Al–Cu–Mg alloy

The thermal properties with consideration of the phase transitions were established to simulate the temperature field of the paraxial variable polarity plasma arc (VPPA)–gas metal arc welding (GMAW) hybrid welding. A variable combined heat source model was developed to describe the heat transfer process of hybrid welding. The effects of different energy ratios of hybrid welding on the weld pool geometries and penetration depth were investigated. An appropriate increase in the VPPA welding power could improve the depth-to-width ratio of weld beads, to achieve deep-penetration welding. Experiments were performed to measure weld geometries, and the weld pool was captured in situ by a high-speed camera to verify the developed finite element model. The calculated results were in good agreement with the experimental results. The adapted matching of the VPPA and GMAW powers was determined by the numerical simulation to optimize the hybrid welding process, resulting in high-quality butt welds.

Response surface approach to minimize the residual stresses in full penetration pulsed TIG weldments of Ti-5Al-2.5Sn alloy

Pulsation of current in tungsten inert gas (TIG) welding is employed to obtain good quality weldments. Peak current, background current, and welding speed in TIG welding are important parameters and their effects on the induced residual stresses are studied using Box–Behnken design methodology. The location of maximum residual stress was found to be close to the weld centerline. Longitudinal and transverse residual stresses at this location were found to be dependent on the pulsed TIG welding input parameters. However, using design of experiment approach, welding speed was found to have the most dominant influence on the stress values. In order to minimize the residual stresses, a reduction in heat input also led to reduction of weld pool penetration. The results of multiresponse optimization showed that in order to achieve a full penetration weldment, a minimum value of 235 MPa for longitudinal and 84 MPa for transverse residual stress will be attained. A weldment with these features can be obtained by using a high value of peak current and a high value of welding speed.

Effects of helium gas flow rate on arc shape, molten pool behavior and penetration in aluminum alloy DCEN TIG welding

Helium arc bead-on-plate welding has been observed using a high-speed video filming technique. Both the arc diameter and area were compressed with increasing gas flow. The arc compressed in the radial direction and stretched in length, causing a voltage increase. There was no negative-pole atomization in the direct current electrode negative (DCEN) mode, and the helium arc could tear the oxidation film on Al alloys. The broken oxidation film flowed on the molten pool under various forces. The arc shear force and arc pressure component are the dominant driving forces to tear the oxidation film. The ability of the helium arc to tear the oxidation film decreased with gas flow rate varying from 5 to 20 L/min. Penetration increased with gas flow because of the compression effect.

Microstructure and Porosity of Laser-welded Dissimilar Material Joints of HR-2 and J75

Dissimilar laser welding of HR-2 and J75 has a wide range of applications in high-and low-temperature hydrogen storage. The porosity distributions of the welded joints were investigated at different line energies, penetration status, and welding positions (1G, 2G, and 3G). The effect of the welding position on the welding appearance was evident only at high line energies because of the essential effect of gravity of the larger and longer dwelling molten pool. The porosity of the welded joints between the solutionised and aged J75 and HR-2 at the 3G position and partial penetration was located at the weld centre line, while the porosity at the 2G position with full penetration was distributed at the weld edges, which is consistent with the distribution of floating slag. Full keyhole penetration resulted in minimum porosity, partial penetration resulted in moderate porosity, and periodic molten pool penetration resulted in maximum porosity.

Numerical analysis of two-dimensional welding process using particle method

In recent years, many structures were made by welding. On the other hand, new materials are used to improve the performance of the structure. However, the welding of a new material is difficult and it is difficult to predict the best condition of welding. It is hoped to develop a numerical analysis method to predict welding condition of a new material. The welding arc can be calculated by some grid method. But it is difficult to calculate the surface shape of welding pool by grid method because the surface shape of welding pool and weld penetration is deformed violently by some force. Moving particle semi-implicit (MPS) method is the numerical method which can be applied because the shape of surface is calculated easily. This method is good at calculation of large deformation and matches numerical analysis of welding process. In the present study, a particle simulation model is developed. The convection in welding pool was analyzed using these models. The Marangoni force is worked toward low temperature side in calculation. Then, the calculated weld penetration became wide and shallow. On the other hand, in calculation, the Marangoni force is worked toward high temperature side. The calculated penetration becomes narrow and deep.

Possibilities for compensating a higher heat input, in particular by the torch offset relative to the top sheet at the fillet weld on a lap joint

This paper deals with the use of an adaptive control system for compensating the variation in the gap height of a fillet welded lap joint. Gap bridging requires the input of additional filler material and is related to an increased energy input. Hence, the aim was a compensation of the effect of an increased heat input, in order to maintain the weld pool and excessive penetration, which can prevent consequently root reinforcement and burn-through. The findings achieved in this work show possibilities for a real-time controlled adjustments of the welding parameters in automated metal active gas (MAG) welding for compensating a higher heat input, in particular by means of the torch offset relative to the top sheet at the fillet weld on a lap joint.

Numerical Simulation of Joining Process in a TIG Welding System Using Incompressible SPH Method

An SPH simulation of a welding process is performed for TIG welding, taking account the melting and solidification of the anode metal, the free surface movement of the liquid, and the four dominant flow-driving forces; gradient of surface tension (Marangoni effect), gas drag on the liquid surface, buoyancy, and electromagnetic force (Lorentz force). The process of welding two metal blocks is computed, including the dynamic formation of weld pool which joins the gap between the blocks. The difference of material’s surface tension dependency to temperature causes a significant difference in the weld pool penetration. These results show the usefulness of this particle method in arc welding simulations.

Detection and Analysis of Weld Pool Oscillation Information for Variable Polarity Plasma Arc Welding

It is discovered the inherent rules between weld pool oscillation frequency and weld penetration though study of weld pool oscillation behavior in the case of variable polarity plasma arc perforated vertical welding of aluminum alloy 3003. During welding, the weld pool is brought into oscillation by variable polarity current, and the oscillation frequency is measured by spectral analysis of arc voltage. The weld pool models of partial penetration and full penetration are established. It is found that variation of welding current has only a small effect on the weld pool oscillation frequency, so its impact can be neglected. In order to test accuracy of the models, it is performed the analysis of theory and measurement, and the results show that two values coincide. The weld pool natural oscillation frequency is dominated by weld pool depth, width and material density and not associated with welding parameters directly. Thus, weld pool oscillation frequency indirectly reflects weld pool penetration, which provides a theoretical support for automatic control of welding quality.

Effects of External Magnetic Field on Mechanical properties of a welded M.S metal through Metal Shield Arc Welding

The aim of this study is to show the characteristic changes obtained by the deflection of welding arc in the presence of external magnetic field. The magnetic field has been applied from various orientations upon the weld bead. The welding process which has been considered under study is shielded metal arc welding on Mild steel plate. The objective of this paper is to study effect of magnetic field on the weld quality and geometry when the field is applied longitudinal to the electrode travel i.e. the field lines are perpendicular to the electrode travel. However there is lack of information for optimum parameters, very little work has been reported in this direction. A magnetic field externally applied to the welding arc, deflects the arc by electromagnetic force in the plane normal to the field lines. The magnetic field exerts force on the electrons and ions within the arc, which causes the arc to be deflected away from the normal arc path. The welding arc can be deflected forward, backward, or sideways with respect to electrode and welding direction depending upon the direction of an external magnetic field. In this paper various mechanical properties tests such as tensile strength, hardness, impact test etc. are conducted to see the effect of external magnetic field on it. It is observed that weld pool penetration reduces while the weld bead width increases thereby affecting the parameters of the process. The results and conclusions are discussed as per the observations while the tensile strength and hardness of parent materials are observed as well.

A new method to estimate heat source parameters in gas metal arc welding simulation process

Heat source parameters were usually recommended by experience in welding simulation process, which induced error in simulation results (e.g. temperature distribution and residual stress). In this paper, a new method was developed to accurately estimate heat source parameters in welding simulation. In order to reduce the simulation complexity, a sensitivity analysis of heat source parameters was carried out. The relationships between heat source parameters and welding pool characteristics (fusion width (W), penetration depth (D) and peak temperature (Tp)) were obtained with both the multiple regression analysis (MRA) and the partial least-squares regression analysis (PLSRA). Different regression models were employed in each regression method. Comparisons of both methods were performed. A welding experiment was carried out to verify the method. The results showed that both the MRA and the PLSRA were feasible and accurate for prediction of heat source parameters in welding simulation. However, the PLSRA was recommended for its advantages of requiring less simulation data.

Numerical Simulation of Aluminum Alloys Variable Polarity Plasma Arc Welding Temperature Field

Based on analysis of plasma arc shape by high-speed camera and thermogenesis mechanism in positive and reverse polarity period,the models applied with Gaussian plus double ellipsoid combine heat source model are built.Using ANSYS parametric design language(APDL) programming language achieved alternative cycles of heat load that corresponding to the actual variable polarity welding parameters,and calculating the temperature field and molten pool shape of aluminum alloys variable polarity plasma arc welding.Comparing molten pool penetration depth under different currents and welding speeds,and verifying the heat source model accuracy in actual welding.The results provides theoretical basis to the characteristics of variable polarity plasma arc heat source shape,thermogenesis mechanism and polarity plasma arc force,and conduces to select reasonable welding parameters.

Prediction Model of Twin-Arc High Speed Submerged Arc Weld Shape Based on Improved BP Neural Network

Twin-Arc high-speed submerged arc welding forming quality prediction model was developed by three layers BP (Back Propagation) neural network. In the model, twin arc current, twin arc voltage, welding speed and wire spacing are selected for the study factor, weld pool width and penetration depth are weld forming quality indicators. The adaptive learning rate and additional momentum term are introduced to improve BP algorithm. Experiments show that the network structure is reasonable of the nodes by inputting and outputting layers of 6 and 2 respectively, hidden layer nodes are 13. The developed neural network model can predict the weld geometry with high computing and predictive accuracy of maximum predictive validation error of weld width and penetration depth within 9.6%, 10.3% respectively, which can be used for real-time monitoring of the quality of welding in the twin arc high-speed submerged arc welding process.

Study on Cutting Process of Manual SHS Cutting Technology

Cutting process of manual self-propagating high-temperature synthesis (SHS) cutting technology was studied based on industrial Q235 steel specimen and cut material of cutting pen. Through research of kerf and analysis of manual SHS cutting process, three zones of base metal is formed under the cutting pen process: molten zone heated directly by cutting pen, the common active zone of cutting pen , metal flow and slag flow, metal flow and slag flow heating zone. Its cutting process can be divided into four inter-related stages as follows: the formation stage of the molten pool, the increasing stage of the pool penetration, the stage of slag blowing off and kerf formation and then the formation stage of a new pool. The way to improve efficiency of manual SHS cutting technology is proposed at the end.

Diel heat transport within the hyporheic zone of a pool‐riffle‐pool sequence of a losing stream and evaluation of models for fluid flux estimation using heat

Hyporheic water is thought to infiltrate at the head of a riffle, which in turn is complemented by upwelling back to the stream at the tail of the riffle in a pool‐riffle‐pool (PRP) sequence. Heat tracing is a potentially useful method to characterize these hyporheic flow paths and quantify associated fluxes. Temperature was monitored within a PRP sequence for several days. Temperature in the hyporheic zone reflected the diel temperature change in the river but not uniformly. The observed thermal pattern exhibited deeper penetration of thermal oscillations below the head pool and shallower penetration below the tail pool. This pattern is consistent with the conceptual model of hyporheic exchange over a PRP sequence. One‐dimensional analytical heat transport models were used at different points below the PRP sequence to estimate distributed vertical fluid fluxes. The calculated fluxes exhibit a trend that follows the expected distribution for a PRP sequence but modified for a losing stream (net fluid flux into the streambed). Deviation of both magnitude and distribution of fluxes from the conceptual “downwelling‐to‐upwelling” model is due partly to the dominantly losing conditions at the study site, but the trends are consistent with a losing stream undergoing hyporheic exchange. Violation of the assumptions in the analytical models most likely adds error to flux estimates. For this study, flux estimation methods using a temperature time‐series amplitude analysis more closely matched field measurements than phase methods.

Exploring Infrared Sensoring for Real Time Welding Defects Monitoring in GTAW

This paper presents an evaluation of an infrared sensor for monitoring the welding pool temperature in a Gas Tungsten Arc Welding (GTAW) process. The purpose of the study is to develop a real time system control. It is known that the arc welding pool temperature is related to the weld penetration depth; therefore, by monitoring the temperature, the arc pool temperature and penetration depth are also monitored. Various experiments were performed; in some of them the current was varied and the temperature changes were registered, in others, defects were induced throughout the path of the weld bead for a fixed current. These simulated defects resulted in abrupt changes in the average temperature values, thus providing an indication of the presence of a defect. The data has been registered with an acquisition card. To identify defects in the samples under infrared emissions, the timing series were analyzed through graphics and statistic methods. The selection of this technique demonstrates the potential for infrared emission as a welding monitoring parameter sensor.

Effect of adhesive on molten pool structure and penetration in laser weld bonding of magnesium alloy

Laser weld bonding (LWB) is a new hybrid technique that combines adhesive bonding with laser seam welding together, and can achieve higher joint strength than adhesive bonding or laser welding individually. Some new physical phenomena have been observed in this welding method, and the phenomena are different from the normal laser welding process, such as a remarkable deeper penetration in LWB than that in laser welding direct (LWD). The adhesive-induced gas can influence the molten pool structure in front of the keyhole, so that less energy is required for laser keyhole through the upper sheet; thus, higher laser power density can interact with the lower sheet, leading to deeper penetration. Simulation comparison experiments are set to indirectly verify these conclusions above.

Numerical simulation of heat transfer and fluid flow in GTA/Laser hybrid welding

In order to understand the temperature fields, cooling rates and mixing in the weld pool, a comprehensive, three-dimensional heat transfer and fluid flow model is developed and tested by comparing model predictions with two sets of experimental data. The first set of data was taken from the literature. The experiments varied the separation distance between the heat sources for three arc current levels at a constant laser power. The second set of experiments analysed the effect of varying laser power for a constant heat source separation distance. The results demonstrate that the distance between the two heat sources significantly affects the cooling rates. The calculated results showed that the hybrid weld pool was very well mixed with strong convection currents resulting from the interaction between the electromagnetic and Marangoni forces. The calculated and experimental results showed that hybrid welding increases the weld pool width and gap bridgability when compared with laser welding. The weld pool depth in hybrid welding was affected mainly by the characteristics of the laser beam. Hybrid weld pool penetration depth is maximised at an optimal distance between the arc electrode and laser beam. The cooling rate increases significantly when the heat sources are separated beyond a critical distance. At close separation between arc and laser, calculations show that the arc radius must be decreased to achieve the observed weld depths.