Open AccessArticle

Evaluation of Continuous GMA Welding Characteristics Based on the Copper-Plating Method of Solid Wire Surfaces

Dong-Yoon Kim

and

Jiyoung Yu

Flexible Manufacturing R&D Department, Korea Institute of Industrial Technology, Songdo-dong, Incheon 21999, Republic of Korea

Author to whom correspondence should be addressed.

Metals 2024, 14(11), 1300; https://doi.org/10.3390/met14111300

Submission received: 31 October 2024 / Revised: 13 November 2024 / Accepted: 15 November 2024 / Published: 18 November 2024

(This article belongs to the Special Issue Welding and Joining of Advanced High-Strength Steels (2nd Edition))

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Figure 1
Appearance and specifications of the welding workability evaluation system. "> Figure 2
Schematic of the welding current and voltage measurement. "> Figure 3
CT results of solid wire contact condition inside the contact tip during wire feeding. "> Figure 4
Surface analysis results of the solid wire according to the plating method; drawing direction: (a) C-wire; (b) E-wire; transverse direction; (c) C-wire; (d) E-wire. "> Figure 5
Analysis of the copper surface homogeneity of the solid wire based on the plating method: (a) C-wire; (b) E-wire. "> Figure 6
Results of coating adhesion: (a) C-wire; (b) E-wire. "> Figure 7
Arc stability evaluation for C-wire during 1 h of welding (average current/voltage and standard deviation): (a) C-wire #1; (b) C-wire #2. "> Figure 8
Actual welding current/voltage waveform of C-wire (10 kHz, 10 s): (a) stable welding section (point a); (b) unstable welding section (point b). "> Figure 9
Analysis of the contact tip and wire after 48.5 min of welding with C-wire #1: (a) the contact tip inside; (b) surface of C-wire after welding. "> Figure 10
Arc stability evaluation for the E-wire during 1 h of welding (average current/voltage and standard deviation): (a) C-wire #1; (b) C-wire #2. "> Figure 11
Weld appearance during continuous welding: (a) C-wire #1; (b) C-wire #2; (c) E-wire #1; (d) E-wire #2. "> Figure 12
Appearance of the contact tip end during continuous welding. "> Figure 13
Nozzle spatter adhesion state by welding time for each solid wire during continuous welding. ">

Versions Notes

Abstract

Gas metal arc welding (GMAW) is widely used in various industries, such as automotive and heavy equipment manufacturing, because of its high productivity and speed, with solid wires being selected based on the mechanical properties required for welded joints. GMAW consists of various components, among which consumables such as the contact tip and continuously fed solid wire have a significant impact on the weld quality. In particular, the copper-plating method can affect the conductivity and arc stability of the solid wire, causing differences in the continuous welding performance. This study evaluated the welding performance during 60 min continuous GMAW using an AWS A5.18 ER70S-3 solid wire, which was copper-plated using chemical plating (C-wire) and electroplating (E-wire). The homogeneity and adhesion of the copper-plated surface of the E-wire were superior to those of the C-wire. The E-wire exhibited better performance in terms of arc stability. The wear rate of the contact tip was approximately 45% higher when using the E-wire for 60 min of welding compared with the C-wire, which was attributed to the larger variation rate in the cast and helix in the E-wire. Additionally, the amount of spatter adhered to the nozzle during 60 min, with the E-wire averaging 5.9 g, approximately half that of the C-wire at 12.9 g. The E-wire exhibits superior arc stability compared with the C-wire based on the spatter amount adhered to the nozzle. This study provides an important reference for understanding the impact of copper plating methods and wire morphology on the replacement cycles of consumable welding parts in automated welding processes such as continuous welding and wire-arc additive manufacturing.

Keywords:

GMAW; solid wire; copper plating surface; arc stability; contact tip wear rate; spatter generation

1. Introduction

In welding sites in automotive, heavy equipment, and shipbuilding industries, components are manufactured using automated systems, such as robots and carriages. The gas metal arc welding (GMAW) process is widely applied because of its high speed and productivity. The GMAW equipment consists of a welding power source, wire feeder, welding torch, cable, filler wire, and shielding gas. The current generated by the welding power source, along with the filler wire supplied by the feeder and shielding gas, passes through the cable and is delivered to the welding torch. The welding torch is the point closest to the weld and comprises various consumable parts, which include the diffuser, which distributes the shielding gas evenly over the welding area; the contact tip, which transfers current to the filler wire and feeds the wire to the base material; and the nozzle, which blocks the air and delivers the shielding gas to the weld area [1,2]. Although inexpensive, these parts are the closest to the welding area and significantly affect the weld quality. Unlike manual welding, where the operator can directly monitor the process, in an automated GMAW system, the weld quality can vary depending on the wear and condition of the consumable welding parts, making their maintenance crucial. The contact tip guides the filler wire into the weld pool and transmits the welding current to the filler wire. Prolonged use of the contact tip can result in a decline in its ability to perform these functions properly, thereby decreasing the weld quality [3]. Previous studies investigated the wear of contact tips during continuous welding.

Villafuerte [4] described the wear mechanisms of contact tips in continuous welding and suggested that abrasion at high temperatures and electrical erosion are the primary failure mechanisms. Abrasion occurs at high temperatures because the contact tip is directly exposed to the arc, which causes the temperature to increase rapidly during welding. In the GMAW process, where wire feeding is continuous, the contact tip wears faster [3,5]. Kim [6] measured the wear of contact tips during continuous GMAW using contact tips fabricated from materials containing phosphorus (Cu–P), chromium (Cu–Cr), and a combination of chromium and zirconium (Cu–Cr–Zr). During 3 h of continuous welding using solid wires, Cu–Cr–Zr exhibited a contact tip wear rate of approximately 15%, Cu–Cr (0.25% Cr) showed 40%, and Cu–P demonstrated a wear rate of 50%. Cu–Cr–Zr exhibited the least wear during continuous welding owing to the chromium and zirconium aging treatments. In contrast, work-hardened Cu–P exhibited the highest wear because the effect of work-hardening diminished under the heat generated during welding. Kim et al. [7] used contact tips created from oxide dispersion-strengthened copper (Cu–ODS), which exhibited excellent hardness at high temperatures, for continuous welding. During 10 min of welding, the contact tip wear rates were 2.3% for Cu–ODS, 2.6% for Cu–Cr, and 3.1% for Cu–P, indicating that Cu–ODS exhibited superior resistance to contact tip wear. Research has been conducted to reduce abrasion by changing the contact tip material to those with strengthening effects at high temperatures [8,9,10]. None of the previous studies provided information about the plating of solid wires.

Electrical erosion refers to the phenomenon in which an arc forms at the tip end, where the wire and contact tip make contact, causing a portion of the tip’s surface to melt and adhere to the wire surface [4,11,12]. Yamada et al. [12] observed a phenomenon in GMAW in which the wire feeding speed momentarily fluctuated and the wire and contact tip melted. They reported that the wire did not feed smoothly when this occurred, which resulted in arc instability during welding.

Many welding materials are used to produce components. Solid wires are particularly used in the fabrication of welding parts for automotive and heavy equipment. The mechanical properties and chemical composition of the solid wires are selected based on the mechanical characteristics of the target components [13,14,15]. A solid wire is a welding wire that does not contain flux and is manufactured using melting, rolling, and drawing. It is a fully metal-filled wire with no hollow centers. The Fe content is increased or various alloying elements are added to improve the mechanical properties of the solid wire [16,17]. Additionally, copper plating the surface of the wire enhances electrical conductivity, thereby improving arc stability, and contributes to maintaining weld quality by preventing surface corrosion of the wire. The copper plating of solid wires is primarily performed using either chemical or electroplating methods. Chemical plating methods form a coating on a metal surface via a chemical reaction without an electrical current. This method results in complex shapes and generally produces thick coatings [18,19]. However, this method may be inferior to electroplating in terms of uniformity. In contrast, electroplating uses an electrochemical process to deposit metal ions onto the surface, forming a thin and uniform coating. This enhances electrical conductivity and surface smoothness, thereby improving feedability. However, if the wire surface has contaminants, coating adhesion problems may occur [18,19]. These differences in plating methods affect the arc stability, spatter generation, and contact tip wear during welding, directly affecting the continuity and quality of the weld.

Previous studies have addressed contact tip materials and failure mechanisms [4,11,12] but have yet to evaluate how these mechanisms differ under various plating methods for solid wires. Similarly, the studies by Kim [6] and Kim et al. [7] focused on the material properties of contact tips. Still, they did not explore the impact of wire plating methods on wear rates and arc stability during prolonged welding. In particular, more attention should be given to the effects of chemical and electroplating methods for solid wires on contact tip wear and welding performance. Additionally, studies on contact tip wear were conducted long ago, with a focus primarily on consumable welding components.

Recently, with active research on welding automation [20] and wire-arc additive manufacturing (WAAM) [21,22,23,24], the continuous welding performance of GMAW, considering consumable components such as the contact tip and solid wire, should be evaluated. Molochkov et al. [25] developed an algorithm to correct wire deflection caused by contact tip wear in robotic GMAW-based WAAM processes. Qiang Zhan et al. [26] developed a method to monitor and control wire bending in WAAM using a welding camera. While previous studies of WAAM primarily focused on the wire position, they did not evaluate welding quality in continuous weldings, such as arc stability and spatter generation caused by contact tip wear. Furthermore, continuous welding is again emphasized in emerging technologies like WAAM.

Fully understanding how the coating process of solid wires affects critical factors such as arc stability, spatter generation, and contact tip wear rates in continuous welding operations like WAAM and automation remains challenging. This highlights the need for a more comprehensive analysis of the interaction between solid wire plating methods and contact tip performance in continuous GMAW, emphasizing the importance of consumable parts in industrial applications.

This study specifically investigated the differences in the welding performance of copper-plated solid wires manufactured using chemical and electroplating methods. The effects on contact tip wear, spatter generation, and arc stability during continuous welding were compared, aiming to provide insights into the configuration of consumable components when designing automated GMAW systems. The welding performance of continuous GMA welding was compared and evaluated using AWS A5.18 ER70S-3 solid wires copper-plated through chemical and electroplating methods. A 60 min continuous welding experiment was conducted to analyze the current and voltage waveforms and measure the contact-tip wear rate and spatter generation. The impact of the two plating methods on welding quality was comprehensively evaluated. The results of this study are expected to serve as valuable reference materials for improving the quality of the welding process and for selecting wires for automated and continuous welding operations.

2. Experimental Procedure

2.1. Welding Wire and Contact Tip

The solid wire used was an AWS A5.18 ER70S-3 in spool form with a diameter of 1.2 mm. The chemical composition and mechanical properties are presented in Table 1, and the wire manufacturer provided this information. Solid wires with copper surface coatings were applied using chemical plating (C-wire) and electroplating (E-wire) methods. The fully solid metal portions had identical chemical and mechanical properties.

The welding workability was evaluated using a deoxidized high-phosphorus copper (Cu–P) contact tip. The chemical compositions and mechanical properties of the Cu–P contact tips are presented in Table 2. The chemical composition was analyzed using an inductively coupled plasma optical emission spectrometer (ICP–OES, Integra XL dual GBC, Melbourne, Australia). To evaluate the mechanical properties, the contact tip was cut in half, and Vickers hardness (MicroWiZhard, Kawasaki, Japan) was measured. A load of 1.96 N was applied with a dwell time of 10 s, and 20 random points inside the contact tip were measured and averaged. The chromium-containing (Cu–Cr) contact tip is some of the most commonly used contact tip. However, it wears out quickly owing to heat from the arc. As part of the workability assessment proposed in this paper, the Cu–P contact tip, which was expected to have the fastest wear rate during the same welding time, was selected. The weight and hole diameter of 10 randomly selected contact tips were measured. The Cu–P contact tip had a length of 45.0 mm and a weight of 17.0 g. The hole diameter through which the 1.2 mm wire passes ranged from 1.25 to 1.32 mm. The Cu–P contact tip underwent work hardening, and the average hardness of the contact tip at room temperature was 135 HV. After heat treatment at 450 °C for 1 h, the hardness decreased to 60 HV, representing a reduction of about 44% compared with the room temperature hardness.

2.2. Analysis of Copper Coating on Welding Wire

The copper coating characteristics of the C-wire and E-wire were analyzed before continuous welding. The wires were cut vertically and horizontally, and the cross-sections were polished. Polishing was performed using abrasive papers up to #2000 grit, followed by diamond paste polishing down to 1 µm to achieve a smooth surface. No etching solution was used. The overall coating condition of the two wires was examined using a scanning electron microscope (SEM, Thermo Fisher Scientific, Eindhoven, The Netherlands), and the coating uniformity was observed using an optical microscope (OM, BX51M, Olympus, Tokyo, Japan).

A SEM equipped with focused ion beam (FIB) functionality (FIB-SEM, Thermo Fisher Scientific, Eindhoven, The Netherlands) was used to irradiate the surface of the solid wire with an ion beam, enabling the adhesion state between the metal and copper coating to be examined. The ion beam, which was 15 µm × 15 µm, was irradiated for 5 min at an intensity of 30 kV and 20 nA. The coating adhesion was evaluated by measuring the cutting depth under identical ion beam conditions and dimensions.

2.3. Configuration of the Welding Workability System and Welding Conditions

Continuous welding was required to evaluate the welding workability of the solid wire; therefore, a carriage-type welding system was configured, as shown in Figure 1. A pipe filled with water, 400 mm (diameter) × 1000 mm (length) × 15 mm (thickness), was rotated, and the welding torch was moved to prevent thermal deformation. The carriage and pipe were configured to enable continuous welding for over an hour. The power source was DM500 (Daihen Co., Osaka, Japan) equipped with a Cu 60 square welding torch and ground cables. The welding torch cable length was 3.0 m and the grounding cable length was 5.0 m. The Cu–P contact tip was mounted on the torch end along with a nozzle with a diameter of 20.0 mm. Water was collected to prevent heat damage to the nozzle during continuous welding.

The welding conditions were fixed as follows to perform bead-on-plate (BOP) welding. The welding control used constant-voltage characteristics with a wire feed speed of 9.0 m/min, welding voltage of 30.0 V, and welding speed of 50 cm/min. The shielding gas was 80% Ar + 20% CO₂ at a flow rate of 20 L/min, and the contact tip-to-workpiece distance was 20 mm. The welding conditions were determined by referencing those used by heavy equipment manufacturers with high solid wire consumption. Continuous welding was performed for 1 h using the C-wire and E-wire, and the experiment was repeated twice.

2.4. Welding Workability Evaluation Methods

Current and voltage measurements, contact tip wear rate, and amount of spatter adhered to the nozzle were monitored to evaluate the workability based on the solid wire plating method during welding. First, the current and voltage were measured during welding based on the type of wire plating used to assess the real-time arc stability. The method and location for measuring the welding current and voltage are schematically shown in Figure 2. The data acquisition (DAQ) module comprised a CompactDAQ chassis (cDAQ-9714, National Instruments, Austin, TX, USA) and an analog input module (NI-9229, National Instruments, Austin, TX, USA). The current and voltage were measured at 10 kHz, and the recorded signals were averaged at 30 s intervals and plotted. The welding current was measured at the grounding cables, whereas the welding voltage was measured between the torch cable end and pipe to minimize the influence of the cables.

Second, the wear rate at the contact tip was checked at 30 min intervals during 1 h continuous welding. The contact points of the spool-type solid wire inside the contact tip were examined using computed tomography (CT, RayScan 250 Light, RayScan Technologies GmbH, Merseburg, Germany) scanning. The CT results were analyzed in the direction of the contact tip hole and the perpendicular direction to the contact tip hole. Figure 3 shows the necessity to check the wear rate at the end of the contact tip. The solid wire passed through the torch cable and into the contact tip, where it initially made surface contact with the contact tip but transitions to point contact at the tip end. In addition, the current supplied by the power source predominantly flowed through the wire at the end of the contact tip close to the weld material, between the contact tip’s end and the welding material, and then into the base material. During welding, the most severe wear is expected to occur at the contact tip owing to wire feeding and current flow. This wear can result in poor electrical contact and inadequate wire feeding at the desired location. Therefore, the wear rate at the end of the contact tip was assessed using the method described in Equation (1).

W e a r r a t e (%) = \frac{A_{1} - A_{0}}{A_{0}} \times 100

(1)

where

A_{0}

represents the hole area at the end of the contact tip before welding, and

A_{1}

represents the worn hole area at the end at 30 min intervals.

Finally, the amount of spatter adhered to the nozzle was measured at 30 min intervals during the 1 h welding process. The amount of spatter on the nozzle was considered indirect of the actual amount of spatter generated.

3. Results and Discussion

3.1. Analysis of Coating State and Adhesion of the Solid Wire

Figure 4 and Figure 5 show the copper-plating conditions of the chemically plated (C-wire) and electroplated (E-wire) wires. Figure 4a,b show the drawing direction, whereas Figure 4c,d show the transverse direction. In the C-wire, larger voids were observed between the plating layer and the steel sheet than in the E-wire. The surface roughness of the copper plating was smoother in the E-wire than in the C-wire, and the homogeneity was superior in the E-wire (Figure 5).

The adhesion of the coating to a solid wire was also analyzed using FIB-SEM. Figure 6 shows the cut depth when the ion beam was applied to the C-wire and E-wire. The cut depth of the C-wire, at 5.08 um, was deeper than that of the E-wire (3.94 um) for the same irradiation time. Because the mechanical properties of the fully solid metal alloy in the solid wire were similar, the amount of material cut by the ion beam during the same irradiation time was expected to be comparable. However, the Cu coating on the surface of the C-wire was cut faster than that on the E-wire, resulting in more steel alloys being cut. The greater depth indicates that the Cu coating on the C-wire has weaker adhesion than the E-wire, allowing the ion beam to remove material more efficiently [27,28]. The results demonstrate that the coating adhesion of the E-wire was superior to that of the C-wire.

3.2. Evaluation of Arc Stability Based on Copper Coating Methods

A 1 h continuous welding experiment was conducted twice using 20 kg spools of C-wire and E-wire. In the repeated welding experiments, the wires used were newly unpacked and not used in any previous welding. Figure 7 shows continuous welding with a C-wire over 1 h, the average current/voltage waveform, and the standard deviation over 30 s. In the first weld using the C-wire (Figure 7a, C-wire #1), stable welding was achieved at an average of 290 A/30.2 V at the beginning of the welding process. After 20 min, the average current decreased, whereas the average voltage increased. After 24 min, the average current decreased to 256 A, whereas the voltage increased to 30.7 V. At 25 min, the average current and voltage were 293 A and 30.2 V, respectively, which were similar to the levels at the start of welding. However, the standard deviations of current and voltage increased. Figure 8 shows a section of the actual welding current and voltage waveforms measured at 10 kHz for 10 s at points a and b in Figure 7a. Typical welding waveforms of spray droplet transfer were observed throughout all welding sections. However, the fluctuations in current and voltage at point b were greater than those at point a. At 48.5 min after the start of welding, an arc interruption occurred, resulting in a halt in the welding experiment. From 46.5 min, the average welding current gradually decreased, reaching 198 A at the min point, whereas the standard deviation of the current significantly increased. In contrast, the welding voltage was observed to increase to 31.4 V. Figure 8 shows an analysis of the interior of the contact tip and the wire surface at the point where welding was completed. The contact tip used for 48.5 min of welding was cut, and at the point where the contact tip and wire touched, traces of copper torn off from the contact tip were observed (Figure 9a). Electrical erosion was observed at the tip end where the wire and contact tip make contact, with an arc causing part of the tip surface to melt and fuse onto the wire surface [11,12]. The copper plating on the surface of the C-wire was also stripped off (Figure 8b), confirming that arcing occurred between the contact tip and wire. Consequently, the contact tip and wire fuse momentarily, preventing the wire from feeding smoothly. This caused arc instability, which ultimately stopped the welding process.

The second welding session (Figure 7b, C-wire #2) was performed for up to 1 h. At the start of welding, an average current of 306 A and voltage of 30.3 V were recorded. As the welding process progressed, the welding current decreased. After 30 min of welding, the average current and voltage were 275 A and 30.5 V, respectively. At the end of the welding process, the average welding current was 265 A, and the voltage remained at 30.5 V, confirming a decrease in the welding current. The welding current decreased because to the wear of the contact tip, which increased the resistance as the protruding wire length between the contact tip and the base material increased. In the constant-voltage control mode, this resulted in a reduction in the welding current [7]. The standard deviations of the welding current and voltage exhibited a smaller range of variation, indicating that the arc stability was superior to that in the first experiment (Figure 7a, C-wire #1).

Figure 10 shows the average current, voltage, and standard deviation for continuous welding using the E-wire. The standard deviation of the welding current/voltage in the two repeated welding experiments confirmed that continuous welding was more stable with the E-wire than with the C-wire. At the start of welding, the average welding current/voltage was 299 A/30.1 V (E-wire #1) and 297 A/30.1 V (E-wire #2), which was approximately 10 A higher than that of the C-wire. As welding progressed, the welding current decreased; after 60 min, it decreased to 271 A (E-wire #1) and 273 A (E-wire #2). The welding voltage remained similar to the initial value, at 30.2 V for E-wire #1 and 30.3 V for E-wire #2. The decrease in welding current was attributed to the wear of the contact tip, which increased the protruding length of the wire and resistance, resulting in a decrease in current.

Figure 11 shows the end of the weld bead after continuous BOP welding on a pipe, depending on the solid wire plating method. In C-wire #1 (Figure 11a), humping beads occurred when welding was interrupted owing to arc instability. With the exception of C-wire #1, continuous welding maintained a smooth appearance until completion.

3.3. Evaluation of Contact Tip Wear Rate Based on the Copper Plating Method

The worn appearance at the end of the contact tip after long-term welding is shown in Figure 12. The contact tip wear rates at 30 min and at the end of welding were calculated based on Equation (1) and are listed in Table 3. The contact tip wear rate of the E-wire was higher than that of the C-wire at both 30 and 60 min (Table 3). A contact tip wore because of the continuous feeding of the wire, combined with the softening of the contact tip caused by arc heat and the passage of electrical current during welding. The copper-plated surface is the part of the wire that comes into direct contact with the contact tip during wire feeding. Although the copper plating on the C-wire was rougher than that on the E-wire, the amount of wear on the contact tip was greater for the E-wire than the C-wire during the same continuous welding period. Therefore, it was determined that the copper coating conditions and other aspects of the wire could influence contact tip wear. The variation in the wear rate of the contact tip was likely influenced by the morphological changes of the wire caused by its spool form. A solid wire is wound in multiple layers on a spool, and when this tension is released, the wire exhibits cast and helix properties [29]. When a wire is unwound and laid on a flat surface, the natural circle it forms is called a cast. The larger the cast, the smoother and straighter the wire uncoils. Conversely, the smaller the cast, the more the wire tends to bend. A helix refers to the height at which the ends of a wire naturally rise when a 1 m length of wire is cut. The smaller the helical value, the straighter the wire, which improves the feedability of the wire. Table 4 shows the cast and helix values measured by cutting a 1.0 m length of solid wire at the beginning and end of welding, as well as the variation rate for these values. The variation rate was calculated by dividing the change in the initial values. The variation rate for the cast decreased by 3.8% and 5.5% for the C-wire, whereas for the E-wire, it decreased by 11.3% and 16.3%, respectively. The variation rates for the helix increased by 42% and 71% for the C-wire, whereas for the E-wire it exhibited a significant increase of 300% and 122%, respectively. When examining the variation rate for the cast and helix, the E-wire exhibited a larger variation than the C-wire. It was considered that the morphological changes in the solid wire as it was spooled had a more significant impact on contact tip wear than the roughness of the copper-plated surface. The increase in the cast value likely contributed to increased contact tip wear in the biased direction, and the increase in the helix value resulted in simultaneous wear around the contact tip hole surface rather than in a specific direction. As a result, the increased cast and helix values for the E-wire resulted in greater wear during 60 min of welding.

3.4. Amount of Spatter Adhered to the Nozzle Based on the Copper Plating Method

Spattering refers to the phenomenon of fusion in which tiny droplets of molten metal are ejected and scattered around the welding area. Generally, all spatter generated during welding is collected to measure the spatter generation rate. However, in this study, which involved long and extended welding, collecting all of the spatter was impossible. Instead, the spatter adhered to the nozzle and was collected at 30 min intervals, as shown in Figure 13. The spatter was weighed, and the results are summarized in Table 5. Twelve grams of spatter adhered to the nozzle of the C-wire were 12.6 g (C-wire #2). Additionally, in C-wire #1, where the arc was unstable, a large amount of spatter (11.8 g) was observed after 48.5 min of welding. During 60 min of welding with E-wire, the amount of spatter was observed to be approximately half that of C-wire #2. The reduced spatter generation for the E-wire compared with the C-wire can be attributed to differences in arc stability and coating adhesion. As discussed earlier, the superior coating adhesion of the E-wire minimizes variation in wire feeding and arc fluctuation, which are primary contributors to spatter generation. In contrast, weaker coating adhesion in the C-wire leads to increased spatter due to irregular arc behavior. The higher spatter generation for the C-wire than that for the E-wire indicated reduced arc stability. An excessive amount of spatter adhering to the nozzle can interfere with the welding shielding flow, and spatter lodged in the contact tip hole may obstruct the wire feed.

The comparative analysis between the C-wire and E-wire revealed significant differences in welding performance. The E-wire demonstrated a more stable current/voltage profile and lower spatter generation rates, indicating improved arc stability. This is attributed to the E-wire’s superior coating adhesion and uniformity, which minimized fluctuations in wire feeding. Furthermore, despite the excellent coating uniformity and adhesion of the E-wire, the observed wear rate suggests that the casting and helix values, as well as the morphological changes in the coiled wire, had a significant impact on contact tip performance. These results provide practical implications for automated welding and WAAM processes, where arc stability is critical. While adopting electroplated wires is essential for improving arc stability, selecting wires with minimal variation in casting and helix values is equally vital to mitigate wire deflection. While previous studies were limited to examining contact tip wear during continuous welding [3,4,6,7,25], this study comprehensively evaluated welding quality under conditions where wear occurred.

However, this study is limited to specific welding conditions and consumable component configurations. Future research should explore a broader range of welding parameters and evaluate the long-term effects of wear under various operational stress conditions.

4. Conclusions

This study evaluated the welding characteristics during long-duration welding using an AWS A5.18 ER70S-3 solid wire with copper surfaces plated using chemical (C-wire) and electroplating (E-wire) methods.

(1): The surface of the copper plating on the E-wire was smoother and more homogeneous than that on the C-wire, and the adhesion of the plating on the E-wire was superior to that on the C-wire.
(2): Continuous welding was performed twice using the C-wire and E-wire for 60 min. The welding current and voltage were measured, and the standard deviations were calculated to evaluate arc stability. The E-wire exhibited better arc stability than the C-wire during 60 min of continuous welding, as confirmed by its lower standard deviation. In C-wire #2, E-wire #1, and E-wire #2, the welding voltage remained stable for 60 min, whereas the welding current decreased because of the wear on the contact tip. In the first continuous welding session with the C-wire, in which the plating adhesion was relatively poor, welding was interrupted at 48.5 min owing to arc instability, and electrical erosion was observed.
(3): Although the copper-plated surface of the E-wire was smoother than that of the C-wire, the contact tip wear was higher in the E-wire than in the C-wire. The increased contact tip wear rate during welding with the E-wire occurred because the rate of change in the cast helix values before and after welding was greater for the E-wire than for the C-wire. These variations in cast and helix sizes contributed to a higher wear rate on the contact tip.
(4): The weight of the spatter that adhered to the nozzle was measured to compare the welding spatter generation rates of the C- and E-wires. After 60 min of welding, the spatter weight of E-wire was approximately half that of C-wire. This lower amount of spatter indicated that the E-wire had better arc stability than the C-wire.

Solid wires are selected and used in welding operations based on the mechanical properties required for the weld joints. Furthermore, in cases where welding components are produced continuously or GMA welding is constantly performed, such as in wire-arc additive manufacturing, the copper-plating method of the solid wire and the form in which the wire is spooled should be considered. This would aid in managing the replacement cycle of consumable welding parts such as contact tips.

Author Contributions

Conceptualization, J.Y. and D.-Y.K.; methodology, D.-Y.K.; software, J.Y.; validation, D.-Y.K.; formal analysis, J.Y. and D.-Y.K.; investigation, J.Y; resource, D.-Y.K.; data curation, D.-Y.K.; writing—original draft preparation, D.-Y.K.; writing—review and editing, J.Y.; visualization, D.-Y.K.; supervision, J.Y.; project administration, J.Y.; funding acquisition, J.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the 2024 Ministry of Trade, Industry and Energy and the Korea Planning and Evaluation Institute of Industrial Technology (KEIT) grant funding (Development of electric furnace-based low-carbon emission steel wire and entry-level welding wire for automobiles that can secure a tensile strength of 1.2 GPa or higher in welds for 1.5 GPa grade ultra-high strength steel, RS-2024-00425265, Ministry of Trade, Industry and Energy).

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Appearance and specifications of the welding workability evaluation system.

Figure 2. Schematic of the welding current and voltage measurement.

Figure 3. CT results of solid wire contact condition inside the contact tip during wire feeding.

Figure 4. Surface analysis results of the solid wire according to the plating method; drawing direction: (a) C-wire; (b) E-wire; transverse direction; (c) C-wire; (d) E-wire.

Figure 5. Analysis of the copper surface homogeneity of the solid wire based on the plating method: (a) C-wire; (b) E-wire.

Figure 6. Results of coating adhesion: (a) C-wire; (b) E-wire.

Figure 7. Arc stability evaluation for C-wire during 1 h of welding (average current/voltage and standard deviation): (a) C-wire #1; (b) C-wire #2.

Figure 8. Actual welding current/voltage waveform of C-wire (10 kHz, 10 s): (a) stable welding section (point a); (b) unstable welding section (point b).

Figure 9. Analysis of the contact tip and wire after 48.5 min of welding with C-wire #1: (a) the contact tip inside; (b) surface of C-wire after welding.

Figure 10. Arc stability evaluation for the E-wire during 1 h of welding (average current/voltage and standard deviation): (a) C-wire #1; (b) C-wire #2.

Figure 11. Weld appearance during continuous welding: (a) C-wire #1; (b) C-wire #2; (c) E-wire #1; (d) E-wire #2.

Figure 12. Appearance of the contact tip end during continuous welding.

Figure 13. Nozzle spatter adhesion state by welding time for each solid wire during continuous welding.

Table 1. Chemical composition and mechanical properties of the welding wire.

Marking	Plating Method	Chemical Composition [wt.%]					Mechanical Properties
Marking	Plating Method	C	Si	Mn	P	S	TS [MPa]	YS [MPa]	EL [%]
C-wire	Chemical	0.07	0.65	1.14	0.015	0.010	440	560	28
E-wire	Electro	0.07	0.65	1.14	0.015	0.010	440	560	28

Table 2. Chemical composition and mechanical properties of the contact tip.

Contact Tip	UNS No.	Chemical Composition [wt.%]				Hardness (HV)	Strengthening Method	Applicable Electrode
Contact Tip	UNS No.	Cu	Cr	Zr	P	Hardness (HV)	Strengthening Method	Applicable Electrode
Cu–P	C12200 (ASTM B280)	Min. 99.9	-	-	0.015–0.040	115–140	Work hardening	Arc welding

Table 3. Contact tip wear rate according to welding time during continuous welding.

Welding Time (min)		0	30	48.5	60
C-wire	#1	0%	5.9%	12.3%	-
C-wire	#2	0%	11.1%	-	17.3%
E-wire	#1	0%	13.6%	-	23.5%
E-wire	#2	0%	14.9%	-	26.6%

Table 4. Size variations of the cast and helix for each solid wire.

		Cast			Helix
		Start Point	End Point	Variation Rate	Start Point	End Point	Variation Rate
C-wire	#1	530 mm	510 mm (48.5 min)	3.8%	7.0 mm	10.0 mm (48.5 min)	42%
C-wire	#2	550 mm	520 mm	5.5%	7.0 mm	12.0 mm	71%
E-wire	#1	710 mm	630 mm	11.3%	6.0 mm	24.0 mm	300%
E-wire	#2	800 mm	670 mm	16.3%	9.0 mm	20.0 mm	122%

Table 5. Weight of spatter adhered to the nozzle by welding time for each solid wire during continuous welding.

Welding Time (min)		30	48.5	60
C-wire	#1	4.8 g	11.8 g	-
C-wire	#2	5.1 g	-	12.6 g
E-wire	#1	2.9 g	-	6.2 g
E-wire	#2	2.6 g	-	5.5 g

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Kim, D.-Y.; Yu, J. Evaluation of Continuous GMA Welding Characteristics Based on the Copper-Plating Method of Solid Wire Surfaces. Metals 2024, 14, 1300. https://doi.org/10.3390/met14111300

AMA Style

Kim D-Y, Yu J. Evaluation of Continuous GMA Welding Characteristics Based on the Copper-Plating Method of Solid Wire Surfaces. Metals. 2024; 14(11):1300. https://doi.org/10.3390/met14111300

Chicago/Turabian Style

Kim, Dong-Yoon, and Jiyoung Yu. 2024. "Evaluation of Continuous GMA Welding Characteristics Based on the Copper-Plating Method of Solid Wire Surfaces" Metals 14, no. 11: 1300. https://doi.org/10.3390/met14111300

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