Metal Transfer Process Research Articles

Characterisation of 4043 aluminium alloy deposits obtained by wire and arc additive manufacturing using a Cold Metal Transfer process

ABSTRACT4043 aluminium deposits were elaborated using a 3D print device equipped with a Cold Metal Transfer welding source. Two sets of process parameters leading to different average powers were compared in order to establish the relations between the powers and energies produced and the geometrical characteristics of the deposits. The effects of the travel speed and layer superposition on the transfer mechanisms as well as on the geometrical characteristics of the deposits were discussed for both sets of parameters. Finally, the formed microstructures were analysed and the porosity defects were quantified and discussed with regard to the heat input characteristics and the solidification conditions.

The Joining Behavior of Titanium and Q235 Steel Joined by Cold Metal Transfer Joining Technology.

Cold metal transfer process is applied to join titanium and Q235 steel with copper filler metal. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) analysis, micro-hardness tests, and tensile strength test were performed to investigate the joining mechanism and strength of joints. The results show that the stacking order of two base metals affected the joining modes and strength. For top Q235 steel to bottom Ti-TA2 lapped joint, there was no distinct interface reaction layer between the steel base metal and the weld metal; dispersed TiFe2 intermetalics (IMCs) IMCs between the steel base metal and the Ti base metal greatly improved the strength of joint; the tensile force of the joint could reach up to 93% that of steel-steel joint using the same welding parameters. Additionally, the joints were fractured in dimple mode at the steel base metal. For top Ti-TA2 to bottom Q235 steel lapped joint, the increasing volume fraction of Ti-Cu IMCs at the Ti-Cu weld metal interface contributed to the strength of joint degradation. The joints under tensile loading are initiated at the Ti-Cu weld metal interface between the weld metal and Ti base metal, then propagated to weld metal, finally fractured with brittle mode.

Dynamic control of current and voltage waveforms and droplet transfer for ultrasonic-wave-assisted underwater wet welding

Ultrasonic vibration can change the dynamic behavior of the bubble and improve the process stability in underwater wet welding (UWW); thus, it has been attempted to profitably control metal transfer process. Arc signals about welding current and arc voltage together with the high-speed imaging detected in conventional UWW and ultrasonic-wave-assisted UWW (U-UWW) were used as information source for determining the droplet transfer mode. The results show that the change in the characteristics of bubble motion affects the droplet transfer process in U-UWW. During the short-circuiting transfer process in small arc voltage, the frequency of arc extinction and the peak of short-circuiting current are both decreased. During the droplet repelled transfer process in middle arc voltage, the droplet repulsive phenomenon is weakened, and the transfer frequency is increased from 7.9 Hz to 10.5 Hz at 34 V. Meanwhile, the droplet diameter is reduced and its transfer stability is improved. During the droplet repelled transfer process in high arc voltage, the frequency and duration time of arc extinction are both reduced. The underlying difference of droplet transfer process between conventional UWW and U-UWW was investigated by the two aspects including ultrasonic wave effect and dynamic bubble effect.

Comparison of microstructure, dilution and wear behavior of Stellite 21 hardfacing on H13 steel using cold metal transfer and plasma transferred arc welding processes

A comparative study of the Stellite 21 hardfacing on H13 steel produced by cold metal transfer (CMT) process and conventional plasma transferred arc welding (PTAW) process was carried out. The lower heat input of the CMT process resulted in finer microstructure and lesser dilution in the Stellite 21 coating than the PTAW process. The volumetric dilution values showed much scatter across the thickness of the PTAW coating than CMT. The effect of lower dilution and finer structure of the CMT coating resulted in a marginal increase in the microhardness. The room temperature (RT) and high temperature (600 °C) wear performance of the coatings were studied using a ball-on-disc tribometer using alumina ball. The wear tracks were analyzed using an optical profilometer and the volume loss was calculated. The CMT deposited coating showed better wear performance than PTAW coating. X-ray diffraction (studies of the room temperature wear tracks showed the transformation of γ-fcc phase in the as-deposited coating to ε-hcp phase after the wear. The volume percentage of the ε-hcp was observed higher for CMT deposited coating than the PTAW coatings, which can be attributed to lower dilution and finer microstructure of the former.

Metal transfer process and properties of double-wire double pulsed gas metal arc welding

Metal transfer processes during double-wire double pulsed gas metal arc welding (DP-GMAW) were observed in both the double pulse synchronous (DPS) and double pulse alternating (DPA) phases using a high-speed digital camera. Meanwhile, the corresponding waveforms were acquired. The results showed that metal transfer occurred as one drop per pulse (ODPP) during both the strong and weak pulse periods, irrespective of phase. In the DPA phase, ODPP was achieved more easily compared with the DPS phase and the metal transfer stability was improved. The droplet offset distance was shorter in the DPA phase. Moreover, the desirable fish-scale appearance was more evident on surface of the weld bead created in the DPA phase. Finally, penetration achieved in the DPA phase was significantly deeper, and fluctuations in the penetration were clearly observed in longitudinal section of the weld bead.

CMT Additive Manufacturing of a High Strength Steel Alloy for Application in Crane Construction

This work investigates the feasibility of manufacturing a near net shape structural part directly on a subassembly for application in crane construction without post-machining. Single- and multi-pass welding experiments, using the Cold Metal Transfer process (CMT), were executed to identify and verify suitable process parameters. The obtained parameters were then used to manufacture a wall structure and an optical measurement of the resulting geometry was performed. Mechanical properties of the all-weld metal in the as-built condition in different directions were determined. The results for tensile testing showed similar values to the filler material specifications and fracture toughness matched literature values, but a decrease of impact toughness was obtained. Although mechanical testing showed no significant anisotropy, hardness measurements showed the influence of the local temperature profile. Finally, strategies to manufacture a complex structural part were investigated. It was possible to establish a stable process to manufacture a section of the specified geometry in a first attempt. However, results indicate that there is still further work necessary to optimize this process and to investigate the influences on the mechanical properties of the final component.

Microstructure and mechanical properties of Inconel 625 fabricated by wire-arc additive manufacturing

In the present study Inconel 625 alloy fabricated using Cold Metal Transfer (CMT) Wire Arc Additive Manufacturing (WAAM) has been investigated. The microstructure and mechanical properties of the fabricated Inconel625 alloy, and the influence of torch travel speed on the properties of the manufactured specimens were researched. Microstructural studies revealed variation in microstructure in different layers of the specimen, with the bottom layer consisting of fine primary cellular grains. Mechanical properties that include hardness and tensile properties showed that with the increase in the travel speed, average micro-hardness of the manufactured specimens slightly improved from 248 HV to 253 HV. The ultimate tensile strength (UTS) increased from 647 MPa to 687 MPa, while yield strength (YS) increased from 376 MPa to 400 MPa. Results showed that the mechanical performance of the manufactured components by CMT-WAAM method was better than the mechanical properties of Inconel 625 alloy casting parts except UTS, which demonstrated that the Inconel 625 alloys can be fabricated by cold metal transfer process.

Effect of cold metal transfer process parameters on microstructural evolution and mechanical properties of AISI 316L tailor welded blanks

Annealed austenitic stainless steel AISI 316L sheets of 1.6-mm and 2-mm thickness respectively was successfully joined by cold metal transfer (CMT) process at two different heat inputs of 0.125 to 0.236 kJ/mm. The process parameters such as welding current and welding speed were optimized to get defect free joints with full penetration depth. The geometry of the weld bead and microstructure of AISI 316L tailor welded blanks using ER308L filler wire are evaluated. Weld metal microstructure inspection by optical microscopy (OM) revealed that higher heat input used to melt the material led to equiaxed grains in the center of weld metal (WM). Due to the lower heat input, the microstructure at the heat-affected zone (HAZ) was similar to base metal (BM). Tailor welded blank’s (TWBs) were formed by designing L9 orthogonal array for 1.6 mm, 2 mm, and dissimilar thickness joint (1.6 mm and 2 mm) wherein the joints exhibited higher tensile strength and hardness as compared to base metal. The increase in tensile strength is corroborated to the increase in δ-ferrite and content of the alloying elements and the grain size in the WM. The microstructure refinement and the δ-ferrite presence contributed to the increase in hardness at the WM compared to HAZ and BM. Bend test revealed quality and soundness of the TWBs with no cracks or openings. The X-ray diffraction plots exhibited an increase in ferrite in WM and the ferrite number has been quantified at an average of 6.36 FN for TWBs and less than 0.5 FN for BM using Fischer Feritscope, which results in better mechanical properties. Fractography examinations indicated that samples failed as a result of the presence of dimples and microvoids resulting in ductile mode fracture at the welded joints.

The effect of oxidation concentration on the adhesion between flexible substrate and metal layer in metal transfer process using UV curable polymer

There has been a recent trend towards the application of transfer processes to produce an electric circuit on a flexible polymer substrate. However, adhesion between the circuit layer and the target substrate in the transfer process is typically insufficient due to non-conformal contact between two layers or low-surface energy of the target substrate. To solve this problem, ultraviolet (UV) curable resin was proposed as an adhesive layer between the circuit layer and the polymer substrate. This study experimentally analyzed the effect of oxidation concentration on the adhesion between a substrate and metal layer in metal transfer process using UV curable polymer. We also demonstrated that controlling the degree of cure of acrylate UV-curable resin, which varies depending on the oxygen concentration of the atmosphere, was shown to be an effective method to improve adhesion to the polymer substrate and prevent metal patterns from being damaged in the transfer process by adjusting the oxygen concentration under atmospheric conditions. As a feasibility study on the transfer process for actual electronic devices, a metal pattern for RTD (resistance temperature detector) was transferred on a polymer film and characterized with the electrical resistance of the pattern.

Stability analysis of the Cold Metal Transfer (CMT) brazing process for galvanized steel plates with ZnAl4 filler metal

In order to achieve lower CO2 emissions and lower fuel consumption, modern motor vehicle industries have been reducing automotive weight with an increasing degree in the past years by replacing steel structures with brazed and welded components of steel and lightweight metals. In this context, the combination of galvanized steel and aluminum admits considerable application potential. Joints of the two cited different types of materials can be produced by partial brazing, through the Cold Metal Transfer (CMT) process with addition of zinc-based wire alloys. However, stability analysis for this process is still not well understood. Most papers focus on metallurgical characteristics such as intermetallic phase formation and joint strength. In order to assess stability, bead on plate samples made of ZnAl4 deposits on an automotive DX56D + Z140 galvanized steel was statistically correlated to current and voltage oscillograms as well as high-speed images, after variation of the IBoost parameter from 30 to 150 A. Short-circuit and arc burning times were acquired and used to compute the Vilarinho Regularity Index for Short-Circuit Transfer (IVsc), which is based on variation coefficients. The lower the IVsc, the more stable is the metal transfer. The index was used to assess bead homogeneity. The results pointed that bead homogeneity was found only for IBoost values below 97 A. However, stability was reached for IBoost levels of 97 A (with homogeneous bead) and 150 A (without homogeneous bead). This means that to determine homogeneity, the metal transfer stability, determined through IVsc, is an indicator, but other factors such as current level and its effects over the melt pool must also be considered.

Microstructure and mechanical behaviour of CMT-welded Mg/Al dissimilar joint using Inconel 625 as filler metal

ABSTRACTMg/Al dissimilar lap joint was produced by modified cold metal transfer process using Ni-based alloy wire Inconel 625 as filler metal. The characteristics of microstructure and mechanical behaviour of the joint were investigated. Microstructural analysis shows that the weld interface near Mg substrate consists of six types of areas: Mg2Al3-based area, Mg17Al12-based area, Al solid solution-based area, fusion zone-based area, Mg + Mg17Al12 eutectic area, and mixed area. With the characteristic of quasi-cleavage fracture, the tensile-shear load of the lap joint reached to 1.28 kN. The failure occurred primarily at the Mg2Al3-based area within the weld interface near Mg substrate. However, the harmful effect of the Mg2Al3 intermetallics on the strength of welded joint is limited.

Crystal Structures of the Periplasmic Metallochaperone AztD

High efficiency zinc import through ATP binding cassette (ABC) transporters is critical for the survival of many bacteria in zinc limited conditions. These systems are especially important for human pathogens due to severe zinc depletion at the site of infection as a result of “nutritional immunity”. Thus, bacterial ABC transporters for zinc are promising targets for the development of novel antibiotics. These systems are composed of a transmembrane permease, cytoplasmic ATPase and periplasmic or lipoprotein solute binding protein (SBP). The latter is required to bind zinc with high affinity and specificity and deliver it to the membrane permease for import into the cytoplasm. Recent data also indicates the participation of other periplasmic zinc-binding proteins in metal import through ABC transporters in some species. We have recently identified a zinc ABC transporter operon (aztABCD) in Paracoccus denitrificans that encodes a periplasmic metallochaperone (AztD) capable of transferring zinc to the associated SBP (AztC) through a specific, associative mechanism. The process can be followed in vitro using the significant increase of tryptophan fluorescence in AztC upon zinc binding. The aztABCD operon is highly conserved in several human pathogens, including the carbapenem-resistant Enterobacteriaceae (CRE) species Citrobacter koseri. We have solved the crystal structures of P. denitrificans and C. koseri AztD using single wavelength anomalous diffraction (SAD). These proteins adopt a beta-propeller fold that has never before been associated with metal transfer functions. Two highly conserved zinc binding sites were identified. Fluorescence zinc transfer assays with mutant AztD constructs indicate that only one of these sites transfers zinc to AztC. Protein-protein docking of AztC and AztD structures identify interaction interfaces and residue contacts essential for metal transfer that were again confirmed by mutagenesis. These data provide structural data on a completely new family of periplasmic metallochaperones as well as detailed mechanistic information on the process of metal transfer from AztD to AztC. As such, this work may be valuable in the rational design of small molecule inhibitors of metal transfer as antibiotics in multiple drug resistant bacteria such as the CRE. Support or Funding Information Funded by the National Institute of General Medical Science of the National Institutes of Health under award number R01GM122819. Docking of AztC (magenta) and AztD (green) showing the transient zinc transfer intermediate. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pulsed laser enhanced metal transfer of aluminum alloy in GMAW

Pulsed laser enhanced metal transfer of gas metal arc welding (GMAW) is a recent modification of conventional GMAW that applies a relatively low-power pulsed laser to the droplet. Previously current-independent metal transfer of carbon steel, in free-flight or short-circuiting mode, was achieved by utilizing single-side pulsed laser irradiation on the droplet. However, there are few studies on laser enhanced aluminum alloy metal transfer of GMAW due to the high reflectivity of aluminum alloy. In addition, the low melting point of aluminum alloy makes it possible to cut off the welding wire (irradiate on the wire) directly by pulsed laser with high energy density, instead of irradiating on the solid-liquid interface of the droplet. Hence, the laser-enhanced aluminum alloy metal transfer process is studied in this paper. The results demonstrate that when the pulsed laser irradiated the solid-liquid interface of the droplet, the laser was found to lead to a significant increase in the stability of welding process as an additional detaching force and change the transfer mode and flight path of the droplet. Both the short-circuiting (SC) transfer and the spray transfer processes were promoted by changing the stress state of the droplet, and the transfer frequency was effectively increased. Moreover, when the pulsed laser irradiated the welding wire, the welding wire was cut off and the arc climbed to the laser incident point. The cut wire-droplet (W-D) changed into a molten droplet by the heating of the arc and entered into the molten pool. A new spray transfer balance formed at the incident point and the restriction that the laser must impinge on the solid-liquid (S-L) interface of the droplet was released.

Wire arc additive manufacturing of hot work tool steel with CMT process

This study presents investigations on the additive manufacturing of hot work steel with the energy-reduced gas metal arc welding (GMAW) process, which is a cold metal transfer (CMT) process. The paper analyses the influence of arc energy and the thermal field on the resulting mechanical properties and microstructure of the material. The investigations were carried out with hot work tool steel X37CrMoV 5-1, which is used for the manufacturing of plastic moulds, hot extrusion dies, and forging dies. The results show that this steel can be used to generate 3D metal components or structures with high reproducibility, near-net-shaped geometry, absence of cracks, and a deposition rate of up to 3.6 kg/h. The variation of the wire feed speed and the welding speed enables the production of weld beads of width up to 9.4 mm. The mechanical properties of the generated structures can be adapted by the dominant thermal field, which in turn is influenced by the bypass temperature and the electric arc energy. A determining factor to describe the main variables of the welding process is represented by energy per unit length EL. If the bypass temperature is above the martensite start temperature (Ms), there is a homogeneous hardness level along the height of the additively manufactured structure height as long as the energy produced by the welding arc is enough to keep the temperature of all layers above Ms.

Wire + Arc Additive Manufacture of 17-4 PH stainless steel: Effect of different processing conditions on microstructure, hardness, and tensile strength

Wire + Arc Additive Manufacture (WAAM) is receiving increasing attention as it offers a way to fabricate meter scale parts, with relatively low capital cost, lower material wastage and logistical advantages. A wide range of metallic alloys could be manufactured using this process. Martensitic grade precipitation-hardening stainless steel 17-4 PH offers excellent combination of high strength and corrosion resistance. Hence, it is important to investigate the behaviour of this alloy in WAAM. In the present work, the effect of different process variables such as shielding gas, deposition path and post-fabrication heat treatment, on microstructure and mechanical properties were studied. A number of specimens were manufactured by WAAM using the Fronius Cold Metal Transfer (CMT) process under different controlled processing conditions. These specimens were subsequently characterized by optical and electron microscopy and mechanical properties in terms of tensile strength and hardness. It was found that using shielding gases that result in higher heat input reduces the amount of retained austenite in the as-deposited microstructure. It has been demonstrated that the required tensile properties can be achieved by applying post-deposition heat treatment. However, it is suggested that direct aging in as deposited condition resulted in formation of harmful intermetallic phases which embrittles the deposit.

Effects of pulse phase difference on metal transfer process and weld formation in the integrated circular triple-electrode GMAW

The pulse synergic control on three arcs in the integrated circular triple-electrode GMAW was proposed to reduce arc interference. The research focused on the effects of pulse phase difference on metal transfer process and weld formation. In the aspect of metal transfer mode, it was found that one droplet per pulse accounted for a higher proportion at pulse phase difference of 120°, followed by pulse phase difference of 180°. However, complete one droplet per pulse hardly occurred at pulse phase difference of 0°, and short-circuiting transfer and one droplet multiple pulses became main transfer mode. In the aspect of weld formation, there were no distinct differences among weld widths and weld reinforcements under three pulse phase differences of 0°, 120°, and 180°. Nevertheless, the weld depths under three pulse phase differences successively varied from minimum to maximum. Moreover, the special cross-section appearance of “twin peaks” was formed at pulse phase difference of 120°. There were two main reasons for this phenomenon, i.e., arc force and droplet impact.

Effect of Arc Length Correction on Weld Bead Geometry and Mechanical Properties of AISI 316L Weldments by Cold Metal Transfer (CMT) Process

Abstract Cold Metal Transfer (CMT) joining process is a clean and economical process in arc welding, which has higher productivity and good quality when comparing with traditional arc welding processes. The joining process has the characteristics like low heat input and low distortion while welding sheet metals. The influence of correction in arc length on the weld bead geometry of AISI 316L using ER 316L filler wire by a single variable is investigated in this research. The results depict that the effect is non-linear on the joining process. By optimizing the arc length correction full depth of penetration was achieved with low heat input, reduced bead width and top reinforcement. Also the uniaxial test and micro-vickers hardness test results reveal that there was improvement in tensile strength and hardness value. The tensile strength for the best joint was 569 MPa and Vickers hardness value of 210 HV. It was observed that the joints exhibited better strength compared to the base metal for 10% arc length correction.

Processing Behavior of Electrodes Made with Addition of Nanopowder

The study analyzes the processing behavior of welding electrodes made with addition of nanopowder, and compares them to standard welding electrodes (without addition of nanopowder). The effect of nanopowder of complex composition on the electrode metal transfer process is analyzed as well.

Weld overlay coating of Inconel 617 M on type 316 L stainless steel by cold metal transfer process

A study of microstructure and volumetric dilution of Cold Metal Transfer (CMT) clad of Nickel based super alloy, Inconel 617M on type 316L stainless steel (SS) substrate was carried out. Overlay coatings were deposited at three different current inputs (80, 90 and 100 A) to synergetic CMT welding set while the wire feed rate and pulse frequency were pre-programmed. The ability of CMT to produce very low dilution and low heat input with the minimal heat affected zone (HAZ), when compared to conventional Tungsten Inert Gas welding (TIG) process was successfully demonstrated. Detailed microstructural evaluation of the cross sections revealed porosity and crack free Inconel 617M overlay with complete fusion, making a metallurgical bonding at the interface. Transverse micro Vickers hardness evaluation from clad to substrate showed the absence of significant HAZ for overlay produced by CMT. Calculation of percentage volumetric dilution, based on elemental Energy Dispersive Spectroscopy (EDS) of Fe-K counts, revealed that the cladding deposited at 100 A current exhibited low dilution value of 6.3% at 100 μm away from the interface while clad produced by TIG show significantly higher dilution value of ~50% at 100 μm from interface. Electron Backscattered Diffraction (EBSD) studies revealed morphology similar to epitaxial growth, with same crystallographic orientation of grains across the interface for CMT overlaid coatings.

Correlations between Microstructure Characteristics and Mechanical Properties in 5183 Aluminium Alloy Fabricated by Wire-Arc Additive Manufacturing with Different Arc Modes.

The effect of arc modes on the microstructure and tensile properties of 5183 aluminium alloy fabricated by cold metal transfer (CMT) processes has been thoroughly investigated. Heat inputs of CMT processes with three arc modes, i.e., CMT, CMT advance (CMT+A), and CMT pulse (CMT+P), were quantified, and their influence on the formation of pores were investigated. The highest tensile strength was found from samples built by the CMT+A process. This agrees well with their smallest average pore sizes. Average tensile strengths of CMT+A arc mode-built samples were 296.9 MPa and 291.8 MPa along the horizontal and vertical directions, respectively. The difference of tensile strength along the horizontal and vertical directions of the CMT+P and CMT samples was mainly caused by the pores at the interfaces between each deposited layer. The successfully built large 5183 aluminium parts by the CMT+A arc mode further proves that this arc mode is a suitable mode for manufacturing of 5183 aluminium alloy.