Wide Range Of Welding Parameters Research Articles

Non-destructive evaluation of the friction stir welding process, generalizing a deep neural defect detection network to identify internal weld defects across different aluminum alloys

Friction stir welding (FSW) is a solid-state welding process, which has significantly disrupted welding technology particularly for aluminum alloy applications. Due to its high-quality welds in all aluminum alloys, comparatively low heat input with high energy efficiency and ecological friendliness, FSW is used in a rapidly growing number of applications. Currently, destructive and non-destructive testing methods are attached as a separate process step to verify weld seam quality, detecting imperfections late in production and requiring costly rework or scrapping of the assembly. Various studies have shown the possibility of using deep neural networks (DNN) to evaluate weld quality and detect welding defects based on recorded data. In this study, conducted within the scope of RWTH Aachen’s Cluster of Excellence, Internet of Production, recurrent neural networks (RNN), and convolutional neural networks (CNN) were successfully trained to classify FSW force data sets, generated while joining different aluminum alloys over a wide range of welding parameters. For internal weld defects bigger than 0.08 mm, detection accuracies over 95% were achieved using bidirectional long short-term memory (BiLSTM) networks when limited to a single alloy and thickness. The classification accuracy dropped to ~ 90% when using multiple alloys and sheet thicknesses. The comparison between different network types’ classification accuracy as well as their ability to generalize the defect detection across different welding tasks with varying sheet thicknesses, respective welding tools, and different Al alloys is shown. The systems aim at offering a reliable and cost-efficient quality monitoring solution with a wide range of applicability, increasing the acceptance of the friction stir welding process as well as confidence in the resulting weld seam quality.

Deep learning approaches for force feedback based void defect detection in friction stir welding

The Friction Stir Welding (FSW) process is known as a solid state welding process comparably stable against external disturbances in its steady state. Therefore, the process is commonly applied with fixed welding parameters utilizing axial force control or position control strategies. External and internal process disturbances, introduced by the workpieces, gap tolerances, tool wear or machine/tool inadequacies are rarely monitored and no conclusion towards the weld seam quality is drawn. In most applications the sole process monitoring feature is the axial force and quality control measures are often only applied to external weld seam features. Based on prior analytic process analysis and quality models based on analytic algorithms, machine learning approaches are employed to find suitable quality criteria to detect internal weld seam defects (void defects) over a wide range of welding parameters. The recorded welding force data is examined using Long Short-Term Memory (LSTM) Networks, Bidirectional Long Short-Term Memory (BiLSTM) Networks and different versions of Convolutional Neural Networks (CNN), differing in Layer architecture and Node count (and thus resulting complexity). In an effort to reduce data and speed up development and training, manual feature extraction was performed. Features were selected based on the cyclical nature of the FSW-process and prior research into in-plane process force data quality relevancy. The features as well as raw recorded force data were used to train previously mentioned networks. Overall the viability of the approaches was shown by a high rate of correct void defect classification, with CNNs exceeding 93% test set classification rate. Network training had to be closely monitored as a small dataset and large number of input features increased the risk of overfitting.

Root formation and mechanical properties in laser keyhole welding of 15 mm thick HSLA steel

Deep penetration laser welding is promising in joining thick (> 10 mm) steel sections. Focused laser beam by drilling vapour cavity, the keyhole, generates deep and narrow welds. Full penetration single-pass joining has a persistent problem with root quality where humping is one of the most frequent imperfection. This strongly hampers the use of high-power laser for thick plate welding. A 16 kW disk laser was used for single-pass welding of 15 mm thick plates in a butt joint configuration. Root humping occurred within a wide range of welding parameters. This provides narrow processing window. By adding an arc source to the laser beam process, the tendency of root humping increases. To achieve humping-free welds and consistent root quality over length, a delicate balance of process parameters is required. High heat input (> 0.50 kJ/mm) was positive to achieve a combination of low hardness (< 325 HV) and good Charpy toughness at -50 °C (> 50 J).

Friction stir lap welding thin aluminum alloy sheets

AbstractIn this work, thin aluminum alloy sheets with thickness of 0.8 mm were friction stir lap welded using small shoulder plunge depths of 0 and 0.1 mm. The joint formation, microstructure and mechanical properties were investigated. Results show that voids appear inside the stir zone when the small plunge depth of 0 mm is used because the tool shoulder cannot exert a good material-collecting effect at such low plunge depth. A plunge depth of 0.1 mm causes tight contact between the shoulder and the material and thus results in good material-collecting effect, which is helpful to eliminate the void. Sound joints are attained at a wide range of welding parameters when using the shoulder plunge depth of 0.1 mm. No crack is observed inside the bonding ligament. The joints own higher failure loads when the retreating side (RS) of the joint bares the main load during the lap shear tests. The shear failure load first increases and then decreases with increasing the rotating and welding speeds, and the maximum failure load of 6419 N is obtained at 600 rpm and 150 mm/min. The hardness of the joint presents a “W” morphology and the minimum hardness is obtained at the heat affected zone. The joints present tensile fracture and shear fracture when the advancing side and RS bare the main loads, respectively.

Performance Evaluation of Alternating Current Square Waveform Submerged Arc Welding as a Candidate for Fabrication of Thick Welds in 2.25Cr-1Mo Heat-Resistant Steel

AbstractThe paper evaluates the performance of alternating current (AC) square waveform submerged arc welding (SAW) as a candidate technology for manufacturing thick welds for high-pressure vessels. A new mathematical formulation for calculating melting efficiency in square waveform arc welding is presented. The melting efficiency and the heat consumption are presented as a mathematical model of welding parameters, namely welding current, welding speed, current frequency, and electrode negativity (EN) ratio. The proposed approach is demonstrated through the welding of 2.25Cr-1Mo heat-resistant steel performed over a wide range of welding parameters. The investigation provides deeper insights into the interplay between process parameter, total heat consumption, and melting efficiency. The effect on flux consumption is also explained. The melting efficiency is inversely proportional to flux consumption. The welding heat does not necessarily promote the plate melting. Improper use of welding heat may lead to decreased melting efficiency and increased unwanted melting and consumption of welding flux. Compared to the conventional direct current (DC) power sources, the AC square waveform welding achieves almost the same order of melting efficiency with added advantages of better weld bead shape and flux consumption in a desirable range. The two additional parameters (frequency and EN ratio) of the AC square waveform power source provide more freedom to fine-tune the process and thereby efficiently use welding heat. The results of this investigation will be advantageous to the designers and fabricators of high-pressure vessels using AC square waveform welding.

Study on the Effect of Energy-Input on the Joint Mechanical Properties of Rotary Friction-Welding

The objective of the present study is to investigate the effect of energy-input on the mechanical properties of a 304 stainless-steel joint welded by continuous-drive rotary friction-welding (RFW). RFW experiments were conducted over a wide range of welding parameters (welding pressure: 25–200 MPa, rotation speed: 500–2300 rpm, welding time: 4–20 s, and forging pressure: 100–200 MPa). The results show that the energy-input has a significant effect on the tensile strength of RFW joints. With the increase of energy-input, the tensile strength rapidly increases until reaching the maximum value and then slightly decreases. An empirical model for energy-input was established based on RFW experiments that cover a wide range of welding parameters. The accuracy of the model was verified by extra RFW experiments. In addition, the model for optimal energy-input of different forging pressures was obtained. To verify the accuracy of the model, the optimal energy-input of a 170 MPa forging pressure was calculated. Three RFW experiments in which energy-input was equal to the calculated value were made. The joints’ tensile strength coefficients were 90%, 93%, and 96% respectively, which proved that the model is accurate.

A Semi-Analytical Nonlinear Regression Approach for Weld Profile Prediction: A Case of Alternating Current Square Waveform Submerged Arc Welding of Heat Resistant Steel

The complexity in weld profile caused by abrupt change in polarity in square waveform welding is investigated through the development of a model capable to accurately predict weld profile. A semi-analytical model is conceived wherein characteristic attributes of a composite parabolic–elliptic function, which represent the weld profile, are obtained through nonlinear regression (NLR). The proposed model is demonstrated for its efficacy in the prediction of weld profile over a wide range of welding parameters, vis-à-vis, welding current, frequency, electrode negative (EN) ratio, and welding velocity. The investigation suggests that the center and outer cores of welding arc remains more active during positive and negative polarity, respectively, that leads to distinct macroscopic zones in weld cross section and thus, necessitates a composite profile for representation of weld profile. The intersection of the zones forms a metallurgical notch which the investigation offers a method to estimate and thus control. Unlike the convention continuous arc welding, the waveform arc welding caters welding at higher velocity without compromising the weld penetration and almost abolishing the metallurgical notch as well.

Welding parameter maps to help select power and energy consumption of friction stir welding

The objectives of this work are to investigate power and energy consumption of friction stir welding over a wide range of welding parameters and to provide a welding parameter map synthesized with their relations to welding quality. Friction stir welding has been known as an energy efficient welding technology because the whole process takes place in the solid-state, i.e., no excessive heat is needed to melt the workpiece. However, the study of the energy consumption and resulting welding quality across a wide parameter window has not been established inclusively. In this work, a series of 6061-T6 aluminum butt welds were created by friction stir welding across various welding parameters (spindle speeds and weld speeds). In order to understand the overall power and energy consumption, both mechanical process power and electrical wall plug power were measured on the 3-axis CNC mill used to perform the welds. Additionally, temperatures near the workpiece surface and weld roots were measured. The resulting weld quality was assessed by conducting tensile tests of weld cross-sections to determine the location of failures. The results of the power/energy, temperatures, and tensile tests were incorporated, producing an inclusive welding parameter map. The welding parameter map helps identify minimum power and minimum energy consumption points within the process constraints needed for maintaining good welding quality. The general approach presented in this paper can be applied to different welding setups and conditions.

Process stability during fiber laser-arc hybrid welding of thick steel plates

Thick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources.

Evaluation of heat input during friction stir welding of aluminium alloys

Heat input is one of the key parameters governing the quality and service properties of friction stir welds. By using a calorimetric technique, the heat inputs generated during the friction stir welding of the aluminium alloys, 1100 and 5083, were measured over a wide range of welding parameters. An empirical equation to estimate the heat input using the welding parameters was established based on a multiple regression analysis of the results. The effect of the heat input on the final grain size of the stir zone was also investigated by the electron backscatter diffraction method. The quantitative relationships between the input variables, heat inputs, and final grain sizes in the stir zone were derived.

Reducing bubbles in friction lap welded joint of magnesium alloy and polyamide

The direct joining between AZ31B Mg alloy and MC Nylon 6 using friction lap welding (FLW) was performed over a wide range of welding parameters to clarify the effect of welding parameters on bubble formation for the purpose of obtaining high strength hybrid joints without bubbles. The volume of bubbles in the FLW joints was influenced by the amount of gases generated due to the pyrolysis of Nylon 6 and the amount of gases squeezed out of the joints during welding. An appropriate increase in welding speed, tool rotation rate and plunge depth can reduce the volume of bubbles. Strong FLW joint with area fraction of bubbles <8% was obtained after welding process optimisation.

Prediction of Flux Cored Arc Welding (FCAW) Parameters and Bead Geometry in Downhill Position (3F)

The robot can perform Flux Cored Arc Welding (FCAW) at high productivity and consistency in quality. The quality of the welding depend on the selection of welding parameter and deposition geometry. These input has to be known before the start of production, generally the welding operator will obtain the information through experimental trial and error. This project planned to develop a tool that can advise the choice of welding parameter that produce quality weld bead with desired geometry. This research focused on the correlation of heat input on weld bead geometry and the range of welding parameter for fillet design welded in downhill direction (3F). From the correlation trend-line equations and welding parameter population boundary, the weld bead geometry and welding parameter for quality deposit are predicted. Consequently two calculators were developed to display the values digitally. The deviation of predicted bead geometry from actual welding is less than 1mm. Mean Absolute Deviation (MAD) is less than 0.4mm, accuracy is good. A wide range of welding parameters can be generated for quality welding at desired bead geometry.

Friction stir welding of aluminium casting alloys

The results of testing friction stir welding quality in relation to EN AC-43200 (AK9) and EN AC-45000 (AK64) aluminium casting alloys are presented. The test joints were made with the use of a welding machine constructed on the basis of numerically controlled milling machines. The assessment of the joint quality was made based on visual inspection, mechanical testing, weldment structure analysis and hardness tests. The purpose of the investigation was to discover the possibility of friction stir welding of casting alloys and the influence of welding conditions on joint properties and structure. The test results show good weldability of aluminium casting alloys by the FSW method. Sound welds can be obtained in a relatively wide range of welding parameters while the weld strength is satisfactory. In order to obtain the highest quality joints, the workpieces must be pressed onto the other, while the welding process cannot run with excessively high speed. The best mechanical properties of the joints were achieved when the friction process was conducted at a rotational speed of the mixing tool of 900 rpm.

Joining of metal to plastic using friction lap welding

Friction lap welding (FLW) is a new conception of joining method developed in Joining and Welding Research Institute (JWRI). The efficiency of joining metal and plastic using FLW was demonstrated through a case study on aluminium alloy AA6061 and MC Nylon-6. The lap joints with high shear strength were obtained over a wide range of welding parameters. A linear relationship was observed between FLW parameters (R/ν)0.5 and the thickness of melted nylon (H). The influences of FLW parameters on bubbles and shear strength were investigated. The morphologies of the fractured surfaces of AA6061 alloy fell into seven types based on the scanning electron microscopy examination. Statistical analysis showed that the contribution to shear strength of these regions followed such an order: region II > region V > region VI > region VII > region IV > region I or III.

Influence of the beam profile formulation when modeling fiber-guided laser welding

During deep penetration laser welding, the focused laser beam determines the vapor capillary, called keyhole, and in turn the whole process physics. Beside spot diameter and Rayleigh length, the beam profile is another important but hardly explored part of the focused laser beam. The focusing of fiber-guided Yb:fiber, Nd:YAG or diode laser beams creates the complex situation that the beam has a top-hat profile in the focal plane but toward the far field transforms to a Gaussian beam. Such power density distribution was measured for a focused high power Yb:fiber laser beam and then approached by three different beam formulations. The beam formulations were then applied to model the keyhole shape during laser welding. Although a second order beam model approached the measured beam significantly more accurately, the first order Gaussian beam was similarly suitable to predict the keyhole shape as long as the central beam domains do not interact with the material, which occurs only for low focal plane positions. A hypothetical top-hat beam would cause a different, steeper keyhole shape. Consequently, a Gaussian beam is still a suitable formulation for a wide range of welding parameters.

Ultrasonic and impulse welding of polylactic acid films

AbstractThe weldability of polylactic acid (PLA) is examined in this article. Biaxially oriented PLA films of various thicknesses were joined with impulse and ultrasonic welding techniques. Relatively high weld strengths were achieved with impulse welding over a wide range of welding parameters. Ultrasonic welding produced high weld strengths with relatively short cycle times. In detail, ultrasonic welded samples had a weld factor (weld strength/base material strength) of 1 at cycle times of 0.25 sec. The weld factor was significantly lower at shorter weld times and weld times above 0.35 sec. In contrast, 100‐μm thick samples joined by impulse welding for 2–3 sec had a weld factor of 1 and a standard deviation of only ±5%. The peak temperature during the impulse welding was measured to determine the fusion temperatures of the films. Mechanical, thermal, and optical analysis was used to examine the properties of the PLA at various welding and annealing conditions. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Study on ac-PMIG welding of AZ31B magnesium alloy

Welding of AZ31B magnesium alloy is carried out using alternating current pulsed metal inert gas (ac-PMIG) welding with 1·6 mm diameter of filler wire. Typical current waveform is used to make sure arc given an accurate energy input into filler wire. The arc characteristics, metal transfer forms, microstructure and mechanical property of ac-PMIG welding of AZ31B magnesium are investigated. The results show that a stable welding procedure and continuous joints can be obtained easily under a wide range of welding parameters. The most important factors for ac-PMIG welding are negative electrode (EN) ratio and pulse rework current, which give an accurate energy input into filler wire. The grain in fusion zone is much finer and more uniform, and grain size does not grow significantly in the heat affected zone compared with base metal. The average ultimate tensile strength of weld beads is 97·2% of base metal.

Stray Grain Formation in Welds of Single-Crystal Ni-Base Superalloy CMSX-4

Autogenous welds on the single-crystal (SX) alloy CMSX-4 were prepared over a wide range of welding parameters and processes to investigate the formation and behavior of stray grains (SGs). The quantity and location of SGs in the welds were analyzed by orientation imaging microscopy (OIM). Heat- and fluid-flow modeling was conducted to understand the influence of welding parameters on the local solidification conditions and resultant SG formation tendency. The results indicate that constitutional supercooling and SG formation are generally reduced in low-power, high-travel-speed welds. Because of the complex effect of travel speed on temperature gradient and solidification velocity, the worst conditions for SG formation in alloy CMSX-4 for the conditions examined here occur at intermediate travel speeds of ~6 mm/s. These findings were corroborated with heat-transfer/fluid-flow modeling simulations that were coupled with SG predictions. These calculations also indicate that SG formation will be greatest where different regions of dendrite growth intersect, due to the so-called off-axis heat flow. For a given set of welding conditions, the amount of SGs will also vary with substrate orientation. This effect is attributed to differences in the number and location of dendrite growth intersection regions within the melt pool that occur with changes in substrate orientation.

New findings in welding of structural steels

Gas shielded arc welding is the most widely applied welding process in industry. H2 (1.0425) structural steel chosen can be welded very cost-effectively with VAC 60 welding wires in CO2 shielding gas. With only the replacement of a highly oxidising gas, i.e. CO2, with a less oxidising gas mixture, i.e. Ar+18% CO2, a nicer appearance of the weld face and a higher weld quality may be obtained. Still higher quality of welds may be accomplished by employing pulsed arc welding of structural steels. In the study and development of the existing welding process, special attention was paid to the metal transfer. In pulsed arc welding with VAC 60 wire in the protective gas mixture of Ar+18% CO2, the metal transfer is very smooth and uniform in a very wide range of welding parameters. Because of the low oxidising capability of the Ar+18% CO2 gas mixture and the very short time of droplet formation, however, in pulsed arc welding major chemical processes in the droplet will occur only in welding with a higher average welding current (281 A). Less alloyed surfacing welds with silicon and manganese will provide higher quality only because of the surfacing weld dilution resulting from the parent-metal fusion, i.e. penetration. In pulsed arc welding, a pulse shape and energy and base current may efficiently affect the degree of penetration.

Weld pool shape prediction in plasma augmented laser welded steel

A welding process that combined plasma arc welding with laser welding was used to make autogenous bead on plate welds on a sheet stock of a carbon steel. A wide range of welding parameters (arc current, laser power, weld speed) was employed. The experimental weld pool shapes were analysed and the data were used to train a neural network to predict weld pool shape as a function of process conditions. The predictions of the neural network model showed excellent agreement with the experimental results, indicating that a neural network model is a viable means for predicting weld pool shape. Using the model, a parametric study was carried out to examine the influence of process conditions on the final weld pool profile.