mm outer diameter. The nominal chemical composition (wt-%) provided by the manufacturer is shown in Table 1 (Ref. 5). Welding Processes Two different versions of gas metal arc welding (GMAW) were used to clad. The first version was conventional GMAW, consisting of an Invision 456P power source, an XR-M wire feeder, and a conventional welding gun. The welding conditions are shown in Table 2. The second version was a controlled-short-circuiting (CSC) type GMAW process called GMAWCSC, consisting of an Invision 456P power source, a CSC process controller, and a special welding gun hooked up to the controller. The process controller coordinates the feeding and speed of the wire electrode with the level of welding current delivered by the power source (Ref. 6). Briefly, the welding process has two primary phases: the arc phase during which heat is generated to melt the base metal, and the short-circuit phase during which the filler metal droplet is deposited when the welding wire makes contact with the weld pool (Ref. 6). The controller monitors the voltage between the electrode and the workpiece to determine which phase the process is in at any given time. The controller clears the short by retracting the wire to the preset arc length level. Once the arc is established again, the controller begins feeding the wire toward the weld pool, and the cycle repeats. GMAW-CSC was originally developed and called “CSC-MIG” by Miller Electric Manufacturing Co. and subsequently manufactured by Jetline Engineering, Irvine, Calif. The waveforms of the welding current in GMAW-CSC can be tailored in great detail in order to optimize the welding process and reduce spatter. Examples of the operating parameters WELDING RESEARCH that can be specified include: 1) current levels and durations (for the start and mid periods) of the arc phase and those of the short-circuit phase, 2) the wire down speed, the delay before wire down, the wire up speed and the delay before wire up, 3) the arc length, and 4) the penetration delay. The welding conditions are shown in Table 3. The design and selection of the welding parameters were based on the experience of the authors in using the GMAWCSC process in the past few years. As compared to conventional GMAW, GMAW-CSC has been reported to reduce heat input and spatter (Refs. 7–9). Reducing heat input is desirable because it can help reduce dilution of the cladding by the base metal. Reducing spatter is also desirable to maximize deposit efficiency. The waveforms of the welding current and arc voltage were recorded using a computer data acquisition system together with LabView software. The data-sampling rate for each signal was 15,000 Hz. The heat input per unit length of the weld Q was calculated using the following equation (Ref. 8): (1) t �� ������ Q = (I �� E)dt 0 ������ / (t ��U) where I is the current, E is the voltage, t is the welding time, and U is the travel speed. 3D Printer A cladding may need to be deposited on a designated area on a component that requires highwear resistance or where the damaged cladding requires repairing. In such a situation, the pattern of motion of the GMAW welding gun relative to the workpiece may affect the quality of the resultant cladding. To study the effect of the motion pattern, a 3D printer can be useful, especially when a much more expensive robot or 3-axis CNC machine is not available. So, a low-cost open-source 3D printer was built as shown in Fig. 1, similar to that developed by Anzalone et al. (Ref. 10). Essentially, the platform that supports the workpiece can move the workpiece horizontally according to the specific motion pattern programmed by the computer, and it can also move vertically to DECEMBER 2016 / WELDING JOURNAL 453-s Fig. 2 — PolyTung NiBWC tubular wire. A — Transverse cross section; B — particles removed from inside wire; C — identification of particles by EDS analysis. A B C
Welding Journal | December 2016
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