Weld Bead Appearance Research Articles

Characterisation of weld bead and microhardness of SS316L weld overlays on S355J2+N steel using GTAW under E-type magnet

In this study, a three-pole (E-type) electromagnet with magnetic configurations north-south-north (NSN) and south-north-south (SNS) was installed in the GTAW process to generate a combination of two symmetrically transverse external magnetic fields around the weld arc and the molten pool. The effects of magnetic fields obtained by these two types of magnetic configurations (NSN and SNS) on the weld bead characteristics and microhardness in GTAW were analysed. In these experiments, high-strength low alloy (HSLA) S355J2+N grade with a thickness of 10 mm was selected as the substrate material and S316L as the filler wire. Using magnetic fields during the welding process successfully enhanced the weld bead appearance and shape and improved the mechanical characteristics of weld overlays. It was also observed that for different values of excitation current, magnetic fields generated with both configurations ( i.e., NSN and SNS) provide greater bead width, a higher penetration shape factor, and higher microhardness values in comparison to specimens welded with conventional GTAW. The NSN and SNS configurations of the E-type magnet improve the penetration shape factor by 58% and 46%, respectively. These configurations were more suitable for weld overlays (cladding) and hardfacing. However, the observations indicated an enhancement in microhardness for all excitation current values by employing the NSN and SNS magnetic configurations.

Taguchi-based experimental investigation into weld cladding of Ni-WC MMC overlays by CMT process

In the search for versatile and effective weld cladding processes to deposit ultra-wear-resistant Ni-WC MMC (Ni-based tungsten carbide metal matrix composite) overlays for mining applications, there is an increasing interest in exploring advanced low-heat-input cold metal transfer (CMT) method. Depositions of single weld bead tracks of Ni-WC MMCs on steel plates were performed by employing the CMT process; Taguchi’s design of experiments was used to plan the experimental investigation. All weld tracks exhibit continuous and uniform bead profile and sound metallurgical bonding to the substrate. Retained WCs are present in the overlay tracks relatively uniformly. The formation of primary WC and secondary carbides is observed depending on the level of dilution. In contrast to standard gas metal arc welding processes, the volume fraction of retained WC, which is negatively correlated with dilution level, is not directly interrelated with heat input for the CMT process and can reach a high level together with improved weld bead appearance at high deposition rate. Deposition rate has a positive correlation with average instantaneous power, which is, in turn, positively correlated with wire feed speed. The addition of oxygen into shielding gas mixtures promotes carbide transfer from cored feed wire to the weld track and increases the volume fraction of retained WC. Analysis of signal-to-noise ratios shows that it is difficult to find a single set of optimized processing parameters, and trade-offs are needed in engineering practice. The present investigation demonstrates that the Taguchi method is a powerful tool in process improvement for weld cladding of Ni-WC MMC overlays.

Improving spreadability of molten metal in MIG welding-brazing of aluminum to steel by external magnetic field

A modified metal inert gas (MIG) welding-brazing process of aluminum and steel with the assistance of external magnetic field (EMF) was proposed in this study. An alternative EMF along the welding direction was used to promote the arc and the droplet to swing along the weld width direction by producing an alternative electromagnetic force perpendicular to the welding direction. The effect of the excitation current level and frequency on weld bead appearance, spreadability of molten metal and the welding process stability was investigated by experimental observation. As the excitation current level increased, the width of the weld seam was increased and the spreadability of the molten metal was enhanced. When it was beyond a critical level, the arc stability was disrupted. Excessive excitation current caused the excessive inclination of the arc especially in base current stage, which was extremely easy to result in arc extinguishing. When the frequency of the excitation current changed from 2 Hz to 15 Hz, the weld width was decreased. If the excitation current exceeded 15 Hz, the weld width kept constant. The wetting angle of the aluminum metal was decreased as the optimized EMF was applied. Besides, the tensile strength of the joint was enhanced due to the enhancement of spreading of molten metal under the action of EMF.

Evaluation of the effect of filler metal interlayer on the weld joint quality in fiber laser welding of alloy steel (A516)

Laser welding of A516 steel was performed using the filler metal to serve as the interlayer. The effects of laser welding parameters on the melt pool microstructure, weld bead shape, dimensions of the melt pool, and temperature field around the melt pool were investigated. The results indicated that the nozzle distance had the most significant influence on the temperature around the molten pool. As the maximum energy of the laser beam was irradiated on the center of the filler, the highest value of the temperature near the fusion zone was about 360°C. The welding speed, determining the overlap factor, had a considerable effect on the weld bead shape. The laser power, therefore, could determine laser beam line energy to melt the filler volume effectively. Enhancing the laser power up to 450 W increased the temperature to about 300 °C; also, the melting rate of the filler used was almost completed and the weld bead appearance was clearly improved; therefore, the width of the melt pool was increased by about 10%. Increasing the nozzle distance from 3 to 7 mm also reduced the width of the molten pool by about 75% and 40% with and without the filler, respectively. By using the filler metal, the geometry of the welding bead changed from a concave one to a convex one. The major fusion zone microstructure of the fusion zone was an acicular ferrite characterized by needle-shaped ferrite crystallites.

Dynamic Metal Transfer Behavior in Double-Wire DP-GMAW of Aluminum Alloy Under Different Pulse Phases

Abstract The effects of pulse phase and pulse stage on the metal transfer characteristics in double-wire double pulse gas metal arc welding (DP-GMAW) of aluminum (Al) alloy were studied using high-speed camera images and current and voltage waveforms. In addition, the effects of various forces on dynamic metal transfer behavior were analyzed under different pulse phases and pulse stages. The results show that the spray transfer mode can be obtained in both the alternating pulse phase (APP) and synchronous pulse phase (SPP). The transfer pattern of the leading and trailing droplets is alternating in the APP, but changes to simultaneous metal transfer in the SPP, mainly owing to influence of the pulse phase on droplet growth. The transfer type is one drop double pulse (ODDP) during the strong pulse stage and one drop triple pulse (ODTP) during the weak pulse stage, regardless of the pulse phase. The pulse phase does, however, affect the Lorentz force between the leading and trailing droplets, causing droplet collision in the SPP, which results in a poorer weld bead appearance compared with in the APP. Finally, the droplet diameter was found to be similar during different pulse phases and pulse stages.

Grain size and viscosity behaviour of developed agglomerated fluxes during submerged arc welding

The present paper studies the physical properties such as viscosity and grain size of the newly formed submerged arc welding (SAW) fluxes. The response surface methodology (RSM) was applied to formulate the design of experiments (DOE) and fluxes were developed. These properties of developed agglomerated fluxes were used to identify their effect on weld bead appearance and quality of weld. The results were found satisfactory.

Study of high-speed GMAW assisted by compound external magnetic field

A magnetic generating device was proposed to regulate the transverse and backward flow of weld pool for high-speed gas metal arc welding (GMAW). Compound external magnetic field (EMF) was simulated to verify the feasibility of designed magnetic generating device. The highest welding speed with good weld bead appearance was 1.7 m/min with the wire feed speed of 9.0 m/min when compound EMF was applied. The effect of the compound EMF on the arc and droplet motion was studied by image acquisition system. The suppression mechanism of the compound EMF on the undercut defect of high-speed GMAW was analyzed. The mechanism of the influence of the applied compound EMF on different welding speeds and welding currents was studied by the application of the compound EMF-assisted welding process, and low-cost, high-quality, and high-speed welding technology was realized.

On the Role of Tool Tilt Angle on Friction Stir Welding of Aluminum Matrix Composites

The current study investigates the influence of tool tilt angle (TTA) on the mechanical strength of friction stir welded aluminum matrix composite (AMC). Aerospace-grade AA6092/ 17.5 SiCp- T6 plates of 6 mm thickness have been welded at different TTA of 1, 2 and 3 with fixed tool rotational speed of 1000 rpm and tool traverse speed of 1 mm/s. A conical pin-shaped tool of H13 tool steel having a hardness of 56 HRC has been used with a tool dimension of 16 mm shoulder dia., 6 mm pin root dia., and 4 mm tool tip dia. In order to study the microhardness, tensile strength, fracture toughness and fracture behavior of the joint the weld bead appearance, macrostructure and microstructure have been investigated. Results show that with an increase in TTA, the excessive flashing has been occurred in the weld bead and also affects the ratio of shoulder influenced region and pin influenced region in the macrostructure. The presence of detrimental Al2O3 has been found inside the weld at TTA of 3. It has found that the mechanical property of the joint increases as TTA increases from 1 to 2 and thereafter it decreases. The fractographic analysis shows a mixed-mode of failure for all the samples except for the TTA of 3 where it shows brittle failure. Overall the study suggests the implication of 1 to 2 TTA to get a sound weld of this particular type of AMC.

Prediction of effects of process parameters and thermo-mechanical simulation of GMAW process for welding of AISI 430 steel

The present study is focused on welding of AISI 430 steel using AISI 309L wire rod using gas metal arc welding process. The welding voltage, welding speed, wire feed rate and gas flow rate are considered as input process parameters and their ranges are found out for good appearance of weld bead. The experiments are conducted using central composite design matrix and weld bead geometry parameters like bead height, bead width and bead penetration and mechanical properties like tensile strength and hardness are measured. The mathematical models for bead geometry parameters and mechanical properties are developed and the adequacy is checked using analysis of variance. The effects of process parameters on the bead geometry parameters, mechanical properties and microstructure are found out. The thermo-mechanical simulation is carried out using ANSYS simulation software to predict the temperature and stresses distribution in the weldment.

Research and Development of a Novel TIG Welding Torch for Joining Thin Sheets

This paper aims to develop a novel tungsten inner gas (TIG) welding torch in order to join thin sheets efficiently. Using a narrowing nozzle (constricted nozzle) inside a conventional TIG torch can critically improve the position accuracy of the tungsten electrode and also the arc plasma characteristics and heat input density. In order to evaluate the efficiency of this new torch, weld bead appearance and cross-section images were examined by an optical microscope, scanning electron microscope (SEM), and electron back scatter diffraction patterns (EBSD). The results showed that in all cases, the weld bead profile was stable without undercut and burn-through. Full penetration weld was seen. The width of weld bead on the bottom surface was increased much in comparison to conventional TIG welding. However, the results from SEM and EBSD images indicated that in the case of low welding current, the blowholes were found out on the side of the thinner material (SS400). The penetration of SUS430 material to SS400 material was not good. It seems that no fusion of SUS430 material to SS400 at the bottom surface can be seen. Meanwhile, no blowholes were seen in the case of high welding current. The penetration was better, and the fusion was reached on the bottom surface.

Experimentation and weld parameter optimisation using grey fuzzy analysis

The most popular steel grade material highly used in the fabrication of industrial pressure vessels and boilers is SA516 grade 70. Submerged Arc Welding is a metal joining technique widely used in heavy fabrication industries for its high quality, reliability, attaining deeper penetration and a smooth appearance of weld bead. In this paper, Taguchi's L27 orthogonal array is used to perform welding of SA 516 grade 70 steel plates. To improve the weld quality, the optimal combination of welding parameters is chosen using grey relational analysis. Grey fuzzy optimisation of welding parameters is based on four different output performance characteristics, namely, bead reinforcement, bead width, bead penetration and dilution. From analysis of variance it is evident that electrode stick out is the most influential factor in submerged arc welding process parameters. Mechanical and metallurgical studies are performed to confirm the effectiveness of the approach.

Bead formation characteristics in laser welding of high-strength steel under subatmospheric pressures

A series of laser welding experiments were carried out on low-alloy high-strength steel specimens under subatmospheric pressure. The welding penetration and weld bead formation characteristics were evaluated by performing metallographic examination on weld bead cross sections. The effects of technological parameters such as ambient pressure, laser power, and welding speed on weld bead formation were investigated. A multi-factor regression prediction model of welding penetration was established on the basis of the above experimental investigation to evaluate the welding penetration in accordance with the adopted welding parameters under certain ambient pressures. To have more insights into the effect of dynamic behavior of molten pool on the bead formation, the laser welding on “glass-metal” composite samples was performed under varied ambient pressures, and a high-speed digital camera was employed to observe the keyhole profile and the molten pool surface during welding process. A correlation between the welding penetration and the ambient pressure for laser welding of high-strength steel was found that in the range of 101–3 kPa, the decrease of ambient pressure leads to the raise of welding penetration and a smoother weld bead appearance.

Influence of Welding Current on Formation of Weld Bead in TIG Welding for Joining Thin Plates

In this paper, a new (novel) welding technology has been applied to join 0.1 mm thin plates. An initial study on the influence of welding current on the welding properties for stainless steel SUS304 plates is discussed in this paper. The weld bead appearance on both top surface and bottom surface was observed by microscope to indicate the change of weld bead size and welding defects. The results showed that by utilizing a constricted nozzle, a good weld bead is found out when the arc length is too short (0.3 mm), welding speed is very high (3000 mm min-1) and base metal is very thin (0.1 mm) with suitable welding conditions.

Effect of phase on the behavior of metal transfer in double-wire pulsed GMAW

High-speed photography was used to record metal transfer during double-wire pulsed gas metal arc welding (GMAW) in the synchronous, alternating and independent phases, while the voltage and current waveforms were recorded simultaneously. According to the relationships between voltage, current, and metal transfer, the effect of phase on the behavior of metal transfer was analyzed. The experimental results demonstrated that metal transfer was all a “one drop per pulse” (ODPP) spray transfer mode in the three phases. ODPP was easier to achieve and metal transfer was more stable in the alternating phase. The deviation distance of droplets in the synchronous phase was larger than that in the alternating and independent phases, and the deviation distance of droplets in the alternating phase was minimum. The surfaces of weld beads acquired showed a desirable weld bead appearance that resembled fish scales. The weld bead in the alternating phase exhibited more obvious fish scales. Phase had little effect on weld width and reinforcement, though it had a significant effect on penetration. Penetration in the alternating phase was significantly deeper than penetration in the synchronous or independent phases, and penetration was minimum in the synchronous phase. The alternating phase facilitated the growth of columnar grains to be inhibited and the directions of ferrites to be disrupted. The columnar grains were discontinuous and the directions of ferrites were more chaotic in the alternating phase when compared with in the synchronous phase. And the anisotropic microstructure in the independent phase was between the synchronous and alternating phases.

Effect of axial magnetic field in the laser beam welding of stainless steel to aluminum alloy

External magnetic field has been favored in the welding, due to the beneficial effects on the weld pool dynamics. The overlapping welding in a keyhole mode with a magnetic field perpendicular to the welding direction was carried out between stainless steel 301 and aluminum alloy 5754 in this study. The results indicated that the application of the magnetic field can modify the weld bead appearance and microstructure of the weld by the Lorenz force and thermoelectric magnetic force induced in the molten pool. Furthermore, the reaction area between steel/Al decreased due to the diffusion of the Al atoms was suppressed, consequently reducing the microhardness and then strengthening the transverse tensile force by 54.6% from 1.81kN to 2.91kN.

GMA용접에서 콘택트 팁 재질에 따른 용접특성 평가

The contact tip for gas metal arc welding has important functions to transmit the welding current to the wire and to guide the wire to molten pool. If the contact tip is damaged, it is a cause of lowering the welding productivity due to removal of welding defects and replacement of contact tip. In case of the use of a contact tip for a long time the arc is unstable because the processed hole in the contact tip center is larger, and the variation of aiming position of the welding wire causes a seam tracking error. In this study, gas metal arc welding experiments using contact tip of three different materials were performed. The contact tips with Cu-P, Cu-Cr, and Cu-ODS were used at the experiments, and the welding characteristics by each contact tip were evaluated. After welding contact tip appearance, welding spatter adhesion amount of the nozzle, and weld bead appearance were evaluated. The welding current and welding voltage were measured to verify arc stability during arc welding.

Studies on Backward Median Current Waveform Control Research in Pulsed MIG Welding

The one-droplet-per-pulse transfer is widely considered to ensure the stability of the welding process in pulsed MIG welding; a peak pulse followed by a median pulse in a square wave pulse can effectively enhance droplet transfer controllability and improve weld appearance. The instantaneous current and voltage waveforms, the probability density distributions of current and voltage, and U-I graphs collected by the waveform wavelet analyzer were used to assess the welding quality and weld bead appearance. The 1.2-mm carbon steel welding wire experiments showed that under the same conditions, using a median waveform could significantly improve the welding quality. If the median current was too small or too large, the influence on the welding process was not obvious, and was only representing an increase of the base current or peak current phase. If the median time was too short, the energy accumulated was not enough to control the droplet transfer; conversely, too much median time led to globular droplet transfer. With a backward median current range of 180A-225A and duration range of 8ms-12ms, all experiments resulted in a nice weld effect.

The influence of electrochemical reactions induced by an external circuit on submerged arc weld metal

Based on electrical conductivity of molten slag, a new method of applying direct current external circuit between slag and pool to control inclusions and improve weld bead appearance was designed and tested. The results show that the effect of the external circuit can effectively reduce the size of inclusions in weld metal. As the cathode of the electric field, a W–(2wt%)Ce electrode inserted into molten slag induces electrochemical reactions and results in the reduction of sulfide inclusions in weld metal. Moreover electron emission of W–Ce electrode improves arc characteristic and makes an improved weld bead appearance.

Influence of Welding Parameters on Weld Appearance and Mechanical Properties in Twin-Wire Tandem Submerged Arc Welding of HSLA Steel

Effects of welding parameters on the weld bead appearance and mechanical properties in twin-wire tandem submerged arc welding of a high-strength low-alloy steel were investigated. Steel plates were welded using different combinations of welding current, voltage, inter-wire spacing and welding speed. The weld joints were characterized in detail by metallography. Hardness and tensile properties of the specimens were measured. The experimental analysis reveals that good weld appearance can be obtained for a range of inter-wire spacing from 55mm to 80mm. Leading wire current, trailing wire voltage and welding speed are the major factors affecting weld bead profile and microstructures in weld metal and fusion zone. Greater welding speed tends to produce higher cooling rate and favors the formation of strengthening phases like acicular ferrite and bainitic structures resulting in better mechanical properties.

Investigations on the Performance Characteristics of GMAW Power Sources

Performance evaluation of the transistorized and invertor type GMAW power source under various modes of operations as continuous, pulsed and dual pulse is discussed in this paper. The performance of the power source has been evaluated with respect to the variation of current and voltage under different wire feed rates. The data is analyzed for identification of optimum working range of current and voltage with reference to less spatter, porosity and good weld bead appearance. Based on the results, the choice of the GMAW power sources for different applications is established. This study provides wider scope for introduction of automation of welding.