A B welding crack-sensitive steels in the energy industry, components with sensitivity to heat in the heavy fabrication industry, and components requiring precise bead placement and controlled base metal dilution such as those found in the aerospace industry. A few nonproprietary applications are presented in the following paragraphs. EWI applied RWF-GMAW to the assembly illustrated in Fig. 5A. Both parts were made from crack-sensitive steel. Part B was inserted into Part A and held in place with a circumferential weld made in a narrow joint configuration. The partial penetration weld was required to have complete fusion with the root of the joint, complete sidewall fusion, no weld metal or heat-affected zone (HAZ) cracking, and withstand a minimum specified torque. The weld was to be made during final assembly, so the maximum temperature at the underside surface was limited to 100°C to prevent damage to other components. In addition to RWF-GMAW, EWI evaluated other arc welding processes as well as laser beam welding. Jetline Engineering’s Controlled Short Circuit (CSC) system was the RWF-GMAW equipment used for this evaluation because it produced welds that met the specified requirements. As shown in the macrograph in Fig. 5B, the CSC weld had complete fusion with the sidewalls and root of the joint, plus no HAZ or weld metal cracking. The top surface of the assembly was surface ground following welding, so complete fill wasn’t required. Components made from materials such as titanium and nickel-based alloys are often candidates for additive manufacturing due to high material cost and long lead times on materials. The RWF-GMAW process has been 72 WELDING JOURNAL / APRIL 2015 evaluated as an additive manufacturing method because of its low heat input and precise bead placement characteristics. The deposition rates achievable with RWF-GMAW can be significantly higher than those achieved with legacy additive manufacturing processes as well. Referring to Figs. 6 and 7, near net shape buildups were produced with RWF-GMAW using Ti 6-4 ELI (ERTi- 23) wire. Both buildups were made out-of-chamber on Ti 6-4 plate that was positioned in the horizontal plane. The buildup shown in Fig. 6 was 12 in. long, 3 in. tall, and made with the CMT process using a single bead per layer approach. Approximately 25 passes were required to produce the 3- in.-tall buildup. The buildup shown in Fig. 7 was 12 in. long and made using both Jetline’s CSC and Fronius’s CMT processes. The ¾-in.-wide × 1-in.-tall section was produced in the flat position using the CSC process and a 3 pass per layer approach. The 1-in.-wide overhang was made in the horizontal position using the CMT process and a single bead per layer approach. In addition, other machines that perform RWF-GMAW include the microMIG by SKS Welding Systems, Kaiserslautern, Germany, which is marketed in the U.S., and the Active Wire Feed Process by Panasonic, Osaka, Japan, but the company is not marketing equipment for this in the United States. Numerous applications in many industries require narrow surfaces to be built up or repaired. The legacy processes for these applications include gas tungsten arc welding (GTAW) and laser beam welding (LBW). The RWF-GMAW process has been evaluated for the buildup or repair of narrow surfaces for several reasons. When welding wire is used with GTAW and LBW, the torch and wire feed mechanism are not coaxial, making the process difficult to automate. The RWF-GMAW process is readily automated because the wire is fed coaxially through the torch. In addition, RWF-GMAW is capable of much lower heat input than GTAW, making it a candidate for welding Fig. 5 — A — Illustration of the carbon steel assembly; B — a macrograph of the joint welded with the CSC system. Fig. 6 — Ti 6-4 near net shaped buildup produced with the CMT process.
Welding Journal | April 2015
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