Small Welding Research Articles

Interface Characteristics and Mechanical Properties of 2024 Aluminum Alloy and 304 Stainless Steel Dissimilar Alloys FSLW Joint with Ni Interlayer

The composite structure of aluminum and steel (Al/steel) dissimilar metals has been applied in manufacturing industries for lightweight products, and friction stir lap welding (FSLW) has advantages for the welding of these two metals. To further enhance the strength of the Al/steel FSLW joint, a 0.02 mm thick nickel (Ni) foil was chosen as the interlayer, and slight plunging depth of a tool pin into the lower steel sheet was designed, which can respectively change the intermetallic compounds (IMCs) type and produce small welding heat. Choosing dissimilar 2024 aluminum alloy and 304 stainless steel materials as the research subject, the characteristics of the lap interface and the mechanical properties of the joint were mainly discussed. The results showed that the lap interface between the upper aluminum and lower steel sheets was made up of an AlNi3 IMCs layer, hook structure and mechanical occlusion. The AlNi3 IMCs layer with 2 μm thickness was in a reasonable range positive to the joint strength. When the rotating speed of the stirring tool increased from 800 to 1200 rpm and the welding speed of 75 mm/min was constant, the hook structure and the mechanical occlusion were both enhanced, and the tensile shear strength of the joint was decreased. A maximum joint tensile shear strength of 217 MPa was obtained at 800 rpm, and the strength value was 47.2 percent of that of the 2024 aluminum alloy base material. The Al/steel joint with shear fracture mode presented a brittle–ductile mixed fracture.

Effect of hold time on resistance spot weldability of aluminium to steel

The effects of welding hold time on weld quality of aluminium alloy to dual-phase steel resistance spot welds were studied. Results demonstrated that there existed an optimum range of hold time (350∼500 ms), within which the largest weld nugget diameter (7.6 mm), thinnest intermetallic compound (IMC) layer (1∼5 µm) and maximum tensile shear peak load (4.7 kN) were obtained. Too short hold time led to shrinkage, small weld nugget and thick IMC layer due to reduced heat dissipation after removing electrodes, thus resulting in low tensile peak load and brittle fracture along the IMC layer. While too long hold time, i.e. 750 ms, produced a smaller weld nugget diameter due to more rapid heat dissipation.

Analysis of metal transfer and weld forming characteristics in triple-wire gas indirect arc welding

Triple-wire gas indirect arc welding (TW-GIA) has the advantages of low heat input and high deposition rate. However, the simultaneous melting of triple wires makes the metal transfer mode complicated. The unknown of the metal transfer mode restricts the development of this technology. In this paper, high-speed camera systems and electrical signal acquisition sensors were used to explore the TW-GIA metal transfer mode. The static force model and the arc conductive channel model were used to discuss the droplet force and energy conversion characteristics, respectively. Results showed that the TW-GIA metal transfer modes can be divided into the following: short-circuit transfer (SCT), main wire projected transfer + side wire globular transfer (PGT), main wire streaming transfer + side wire projected transfer (SPT), and main wire streaming transfer + side wire streaming transfer (SST). Moreover, the process parameter ranges corresponding to the four modes were summarized. Due to the stable arc and the uniform metal transfer process, SPT and SST can form desirable weld seam. The gravity and z-axis components of electromagnetic force are the main forces that promote metal transfer. The x-axis and y-axis components of the electromagnetic force deviate the metal transfer path from the arc coverage. Due to the change of arc conductive channel, the energy transferred from TW-GIA to the base metal is less than that of gas metal arc welding, showing the advantages of small welding deformation, narrow heat-affected zone, and grain refinement.

Joining aluminum to steel dissimilar metals using novel resistance spot welding process

Reliable welding of aluminum to steel dissimilar metals is of great significance in the automotive industry, which promotes lightweight automobile body structure. Here we propose an innovative resistance spot welding process to weld the AA6016 aluminum alloy and press hardened steel. Experimental results shown that the expulsion pulse, intentionally set, can instantly pushed out the molten aluminum from the interface in the form of expulsion. Furthermore, the locking plate contacts the steel workpiece and/or even achieve micro-connection through forming a small steel weld nugget. After the welding current pulse was applied, the locking plate and the steel workpiece were strongly joined together and produce a large steel weld nugget with a diameter greater than 5 mm. Moreover, the aluminum workpiece was tightly locked between the locking plate and the steel, thus achieving an effective joint between aluminum and steel.

Guidance method of simulating weld trajectory between planes based on single-point laser

Abstract In the face of problems such as welding of small objects or too small welding space, an application method of welding small plane intersecting objects based on point laser was proposed. The demonstration points pointing to different planes were preset, and the laser displacement sensor was driven to measure the physical value by simulating the sharp workpiece of the welding gun. Multiple projections at different locations were made on a certain plane of the welding object, so as to ensure that the laser points were not collinear and obtain the laser point parameter set. The plane equation was solved respectively according to the planes pointed by different demonstration points, and a geometric model was built. The equation of the intersecting line between the planes in the welding object was calculated. The points on the line were obtained as the welding start points. The workpiece tip was controlled to move along the intersection direction by the mechanical arm, so as to achieve the weld effect.

Innovations in Monitoring, Control and Design of Laser and Laser-Arc Hybrid Welding Processes

With the rapid development of high power laser, laser welding has been widely used in many fields including manufacturing, metallurgy, automobile, biomedicine, electronics, aerospace etc. Because of its outstanding advantages, such as high energy density, small weld size, easy automation. Combining the two heat sources of laser and arc for welding can achieve excellent results due to the synergistic effect. Laser welding is a complicated physical and chemical metallurgical process, involving the laser beam and molten pool, keyholes and materials melting, evaporation and multiple physical process. Process monitoring and quality control are important content of research and development in the field of laser welding, which is the premise to obtain fine weld with high quality. Numerical simulation technology can describe many complex physical phenomena in welding process, which is very important to predict weld forming and quality and clarify the underline mechanism. In this paper, the research progress of process monitoring, quality control and autonomous intelligent design of laser and laser-arc hybrid welding based on numerical simulation were reviewed, and the research hotspots and development trends of laser welding in the future are predicted.

Study of the Diffusible Hydrogen Content Affected from the Welding Electrode Humidity

The influences of moisture corruption and drying considerations on diffusible hydrogen were examined in this study. Two trials were carried out on an arc welding procedure, with the first being an assessment of the results of moisture contamination and the second being a test of the impact of welding constraints on diffusible hydrogen content. For example, the dispersible hydrogen found in welds was likened to the hydrogen levels of different unused electrodes. To calculate the proper drying constraints (Time and Temperature) for an applicable moisture contamination level in the weld electrode, an empirical equation was devised. For electrodes with a small diameter and welding parameter limits typically used for out-of-position welding, the equation is appropriate.

Improvement in joint efficiency with high productivity and narrow weld formation in friction stir welding

High productivity, excellent joint strength and small weld bead make friction stir welding an emerging joining technique to join difficult to weld dissimilar aluminum alloys. Effect of rotational speed, traverse speed and shoulder diameter on the joint strength and elongation of the friction stir welded dissimilar aluminum alloys (AA7475-AA2219) is investigated. In addition, parameters are optimized to obtain joint with narrow weld bead and high joint efficiency using the entropy-weighted technique for order of preference by similarity to ideal solution method. Nine experiments are performed as per the L9 orthogonal array and mechanical properties of the welded joints are measured. Results of the study reveal that optimum values of ultimate tensile strength and percentage elongation are obtained at a rotational speed of 710 rev/min, welding speed of 250 mm/min and shoulder diameter of 10 mm resulting in good joint strength, high productivity and narrow weld bead. From the selected process parameter range, tool shoulder diameter is found to be the most significant parameter. The findings of the present study are discussed in light of the friction stir welding process mechanism, available literature, mechanical testing, microstructure and fractography.

A new online quality monitoring method of chain resistance upset butt welding based on Isolation Forest and Local Outlier Factor

Small chain resistance butt welding often has unstable welding quality due to high production frequency and short welding time. However, there is still a lack of research on online monitoring of resistance upset butt welding. This study proposes to collect the state information in the welding process and combine with the unsupervised learning method to predict the final welding quality. The collected state information includes the dynamic resistance curve, electrode displacement curve, and upset pressure curve. And state information of 308,274 welding joints was collected. Because of the high production frequency of chains, it is difficult to obtain the quality label by the destructive detection method. The commonly used supervised learning is no longer applicable. In view of this challenge, the unsupervised learning methods, Isolation Forest and Local Outlier Factor are proposed to predict the welding quality online for the first time. Another critical problem is that the unsupervised learning model lacks evaluation criteria. This paper presented the concept of separation degree between anomalous data set and normal data set to solve this problem. The classification performance of the model is judged by comparing the separation degree. According to the separation degree calculation results, the Isolation Forest's classification performance is better than the Local Outlier Factor. Finally, according to the classification results of Isolation Forest, the correlation between state information and welding quality is analyzed. It is found that the upset pressure and dynamic resistance can reflect the change of welding quality, but the correlation between electrode displacement and welding quality is not significant.

Influence of boss-backing welding to ERW pipe

Station and valve chamber design often encounter the situation of drilling hole at the main pipeline and welding boss-backing to connect the branch pipe. Boss hole location should generally be at least 100 mm away from the longitudinal weld or spiral weld. However, because the electric resistance weld (ERW) is difficult to distinguish in practice, some bosses mounting position coincide with ERW or close to. In this paper, the influence of boss-backing welding directly on the longitudinal weld to the original residual stresses of ERW pipe was studied. The microstructure of pipe body and longitudinal weld after welding was also analysis. The testing results showed that the overall residual stresses of ERW pipe were relatively small. Residual stress at the longitudinal weld region were smaller than those at the pipe body region. After the boss-backing welding, the axial residual stress at the longitudinal weld and the circumferential residual stress at the pipe body region near the intersection increased sharply to 2.5 (444 MPa) and 3.8 (433 MPa) times, respectively. The invaded width and depth to the ERW pipe after welding were about 15.167 mm and 3.376 mm. Granular bainite with necklace type M-A constituents could be observed at the invaded zone. It is suggested that small welding heat input should be adopted for boss-backing welding.

Comparative experimental study on phased array and X-ray detection of small diameter pipe weld

According to the principle of ultrasonic phased array technology, the phased array inspection technology for butt weld of small-diameter pipe is developed. The ultrasonic phased array and ray inspection tests are carried out on the sample pipe of small-diameter tube with typical specification of heating surface in Inner Mongolia thermal power plant, and the evaluation results obtained by the two inspection methods are compared and analyzed. It can be seen from the comparison of testing results that ultrasonic phased array testing has more advantages than X-ray testing in defect detection rate and defect parameter measurement. At the same time, ultrasonic phased array testing also has the advantages of environmental protection, intuitiveness and high testing efficiency.

Online porosity defect detection based on convolutional neural network for Al alloy laser welding

Porosity is one of the most serious defects in Al alloy laser welding. The online detection of the porosity can identify the weak position of weld seam and take remedial measures accordingly. In this paper, a convolutional neural network (CNN) model where the input is the signal spectrum graphs extracted by wavelet packet decomposition (WPD) is constructed to identify the porosity during Al alloy laser welding in real-time. The porosity monitoring platform is set up to obtain the keyhole opening area signal and the keyhole depth signal in the welding process. The sliding window scanning algorithm is used to scan the signals and the weld seam, and the time-frequency spectrum graphs are obtained by WPD processing on the signals in each sliding window. Through analysis, when there is porosity in a small weld seam section of the current sliding window, the signal spectrum graphs are messy at this moment, while when there is no porosity, the signal spectrum graphs are clean and the frequency bands are concentrated in low-frequency part. The CNN model is constructed to classify the signal spectrum graphs under different porosity status, thereby it can identify the porosity in the weld seam.

Laser Spot Welding and Electric Contact Points Using Copper/Single-Walled Carbon Nanotube Nanocomposite Synthesized by Laser Surface Implanting

In our previous studies, we have developed a wet process, denoted as laser surface implanting (LSI), to synthesize a copper/single-walled carbon nanotube (Cu–SWCNT) metal nanocomposite. The nanostructure of this Cu–SWCNT composite was shown to contain discernable SWCNT clusters in nanosizes inside the copper matrix. Its hardness could achieve up to three times that of pure copper, verified by micro-hardness and nano-hardness tests. A focus ion beam bombardment test and a plane strain compression test show 2.5 times toughness improvement for the Cu-SWCNT composite. Based on these strength improvements, two potential applications for the Cu-SWCNT nanocomposite are proposed and their feasibilities are verified using specially design test rigs. The first application is related to creating long lasting electric contacts. The result shows that the Cu-SWCNT nanocomposite is highly wear-resistant. The contact area of the simulated electric contacts increases after repeated impact loading, which potentially could lower the contact resistance. The second application is to use the Cu-SWCNT implants as high strength spot weld for joining copper foils. A smaller weld with a higher strength reduces the power requirement of the laser and, consequently, the thermal distortion for higher-dimensional precision. The specially designed test rig for the weld strength characterization is a new contribution, providing a new testing capability for small and non-homogeneous samples not suitable for a standard tensile test machine.

OCT Capillary Depth Measurement in Copper Micro Welding Using Green Lasers

The transition of the powertrain from combustion to electric systems increases the demand for reliable copper connections. For such applications, laser welding has become a key technology. Due to the complexity of laser welding, especially at micro welding with small weld seam dimensions and short process times, reliable in-line process monitoring has proven to be difficult. By using a green laser with a wavelength of λ=515 nm, the welding process of copper benefits from an increased absorption, resulting in a shallow and stable deep penetration welding process. This opens up new possibilities for the process monitoring. In this contribution, the monitoring of the capillary depth in micro copper welding, with welding depth of up to 1 mm, was performed coaxially using an optical coherence tomography (OCT) system. By comparing the measured capillary depth and the actual welding depth, a good correlation between two measured values could be shown independently of the investigated process parameters and stability. Measuring the capillary depth allows a direct determination of the present aspect ratio in the welding process. For deep penetration welding, aspect ratios as low as 0.35 could be shown. By using an additional scanning system to superimpose the welding motion with a spacial oscillating of the OCT beam perpendicular to the welding motion, multiple information about the process could be determined. Using this method, several process information can be measured simultaneously and is shown for the weld seam width exemplarily.

Shielded Active Gas Forge Welding of an L80 Steel in a Small Scale Shielded Active Gas Forge Welding Machine

The Shielded Active Gas Forge Welding (SAG-FW) method is a solid-state welding technique in which the mating surfaces are heated by induction heating or direct electrical heating before being forged together to form a weld. In this article, an API 5CT L80 grade carbon steel alloy has been welded using the SAG-FW method. A small-scale forge welding machine has been used to join miniature pipes extracted from a large pipe wall. The welding was performed at three different forging temperatures, i.e., 1300 °C, 1150 °C and 950 °C, in some cases followed by one or two post weld heat treatment cycles. In order to qualify the welds, mechanical and corrosion testing was performed on miniature samples extracted from the welded pipes. In addition, the microstructure of the welds was analysed, and electron probe microanalysis was carried out to control that no oxide film had formed along the weld line. Based on the complete set of experimental results, promising parameters for SAG-FW welding of the API 5CT L80 grade steel are suggested. The most promising procedure includes forging at relative high temperature (1150 °C) followed by rapid cooling and a short temper. This procedure was found to give a weld zone microstructure dominated by tempered martensite with promising mechanical and corrosion properties. The investigation confirmed that small scale forge welding testing is a useful tool in the development of welding parameters for full size SAG-FW welding.

Small-scale resistance seam welding of 304 stainless steel with capacitor discharge welding machine

In this paper, small scale resistance seam welding (SSRSEW) of 304 stainless steel sheet with a thickness of 0.1 mm with a capacitor discharge (CD) welding machine is investigated. The effect of the main parameters such as discharged energy, electrode force, and electrode speed on the quality of the weld seam was investigated. In order to control the speed of the electrode, the electrode wheel was mounted on a CNC machine. Mechanical tests such as tensile-shear and peel tests were used to evaluate the quality of the weld seam. Also, the failure modes were investigated in different welding conditions. The results show that the discharged energy has more effect on the weld seam strength and the maximum strength in the peel test is usually lower than the strength of the tensile-shear test. Also, discharge energy level of 14 ws and electrode force of 20 N and electrode speeds of 200 and 300 mm/min are the optimum welding condition for welding the 304 stainless steel sheets with a thickness of 0.1 mm.

Contact resistance prediction of zirconium joints welded by small scale resistance spot welding using ANN and RSM models

The total electrical resistance between electrodes is a major factor in small scale resistance spot welding process uncertainty. The initial resistance between electrodes is depending on the current profile, electrode force and dome radius of hemispherical electrodes. A comparison between the experimental results of the expected resistance between electrodes and the predicted values of using ANN and RSM methods is the main goal of this study. E110 zirconium alloy with a thickness of 0.25 + 0.25 mm and 440 MPa tensile strength is used. An increase in dome radius of hemispherical electrodes reduces mean resistance values for zirconium alloy. The rate of preheating current rise has no appreciable effect on stabilization of resistance between electrodes in all cases. Stepwise current rise significantly reduces dispersion of resistance values for zirconium alloy. However, their dispersion significantly decreases after preheating in comparison with initial values. The empirical model predicted by the response surface methodology (RSM) is compared with the backpropagation algorithm model of artificial neural networks (ANN). On zirconium specimens, the absolute maximum error in RSM technique was 9.92% while 4.43%in ANN. Furthermore, in most cases the absolute maximum error in ANN is lower than RSM.

Optimal weld bead profiles in the conduction mode LBW of thin Ti–6Al–4V alloy sheets

<abstract> <p>Day by day laser welding (LW) is gaining industrial importance. Good quality of weld joints can be realized through this process. Because this process yields low distortion and small weld bead. Aerospace, nuclear, automotive, and biomedical industries are opting for the lightweight and corrosion resistance titanium alloys. This paper deals with the generation of optimal weld bead profiles in the conduction mode laser beam welding (LBW) of thin Ti–6Al–4V alloy sheets. Laser beam diameter, power and welding speed are the 3 LBW parameters, whereas, bead width, depth of penetration, heat affected zone and maximum temperature are the performance indicators (PIs). 3 levels are set for each LBW parameter. Taguchi's L<sub>9</sub> OA (orthogonal array) is selected to minimize the numerical simulations. ANSYS Fluent V16.0 with Vc++ code is used to develop a generic model. %Contribution of each process variable on the PIs is assessed performing ANOVA analysis. The range of PIs is assessed adopting the modified Taguchi approach. A set of optimal LBW parameters are identified considering a multi-objective optimization technique. For these optimal LBW parameters weld bead width is minimum, and the depth of penetration is maximum. Empirical relations for PIs are developed and validated with simulations. Utilizing the Taguchi's design of experiments, empirical relations are developed for the performance indicators in laser beam welding (LBW) simulations performing few trial runs and identified the optimal LBW process parameters.</p> </abstract>

Research of multiple metal rods joining node in spatial construction, using one welding connection

Elements in the nodes of spatial bar structures can be assembled either with bolted connections or with welding. For welded nodal connections, each element should be attached separately. This complicates the process of manufacturing the structure and increases the labour input while assembling this structure. The so-called “tub welding node” does not have such flaws as several bars are joined by a single weld formed during a single pass of the welding machine. The weld of such a node is in a complex stress and strain state. It means that a relatively small weld should constantly take heavy loads. To assess the stress and strain state of the welding node, the researchers conducted numerical studies in the SolidWorks software system. The calculation model of the structural node was based on the results of a particular existing structure examination. These empirical numerical studies revealed that stresses are evenly distributed in the body of the weld, but its surface stresses exceed the stresses inside the weld. There are some areas on the weld surface that exceed the yield strength of steel. Still, the size of these areas is negligible.

Numerical Study of Stress Analysis for the Different Widths of Padding Welds

In the presented study, the cases of regeneration of the element made of C45 steel, using the MAG (Metal Active Gas) method are analysed. The base material is applied to the regeneration process. The analysis of the influence of the padding weld width (0.006 m, 0.01 m, 0.014 m) and the preheating temperature on the phase transformations and effective stresses of the regenerated layer are performed. A non-standard approach to preheating (before each padding weld after the cooling to ambient temperature) is considered. Due to the possibility of simplifying the model from 3D to 2D (symmetry of calculations for long padding welds), calculations were performed using the finite element method in the transverse to the padding direction. Each new padding weld was included as an additional area in the finite element mesh. The developed numerical model includes a temperature model, phase transformations in the liquid and solid states, and the stress model in the elastic-plastic range. The aim of the regeneration is not only to obtain the original geometry of the element, but it is also important that the filler material used (in the considered case identical to the base material) has appropriate properties. These properties largely depend on the phase composition. The used filler material affects not only the hardness, brittleness, and ductility of the material. Its kinetics and changes in the geometry can cause significant stresses and even cracks. Based on the obtained results, it can be concluded that increasing the width of the padding welds causes a decrease in the level of residual effective stress; however, it is technologically difficult to accomplish. The most unfavourable stresses occur in the initial area of the pad welding zone. For lower preheating temperatures and smaller welds, areas with possible cracks are identified. In these cases, lower preheating and tempering should be carried out, which leads to similar energy costs as at higher preheating temperatures. Due to the complex phase transformation process for medium carbon steels and the need for the process parameters control, proper regeneration is possible only in automated workstations. Keywords: computational mechanics, numerical simulation, padding weld, preheating, strain analysis, stress