Productivity Enhancements for GMAW of Titanium Carrie Davis and Michael E. Wells Naval Surface Warfare Center, Carderock Division

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1 Productivity Enhancements for GMAW of Titanium Carrie Davis and Michael E. Wells Naval Surface Warfare Center, Carderock Division While titanium has been used extensively in seawater cooling systems on US Navy surface ships, increased use of the material is limited by high material and fabrication costs. Welding costs in titanium are driven by labor intensive precautions relating to cleanliness and shielding required for sound welds and the productivity limitations of the gas tungsten arc welding (GTAW) process. Gas metal arc welding (GMAW) offers productivity benefits over conventional GTAW, but it is not used because it has historically been associated with lower weld quality from arc turbulence and exposure of the droplets to impurities in the arc atmosphere. This effort is focused on enhancing the titanium GMAW process to allow broader use of titanium within the Navy and establishing GMAW as a viable alternative to GTAW for titanium use. The research associated with this effort includes optimizing pulse waveforms, determining the effect of gas composition on bead shape, and evaluating commercially available products for GMAW.

2 Titanium 2008 Las Vegas, NV Productivity Enhancements for GMAW of Titanium Carrie E. Davis and Michael E. Wells Naval a Surface Warfare aecenter, te,cadeoc Carderock Division so West Bethesda, MD 24 September 2008

3 Technical Issue High fabrication costs relative to steel and aluminum limit Navy applications Welding Cost Drivers: Specialized gas shielding Low deposition rates Labor intensive joint designs and preparation procedures NGSS Titanium Pipe Welding Facility 2

4 Objective Optimize the gas metal arc process to reduce titanium welding costs to a level equivalent to stainless steels and Cu-Ni alloys. Evaluating new welding products. Studying workmanship issues. Developing recommended practices. ONR Goal Weld large titanium structures (both shipyard and shipboard) at reduced cost. 3

5 Outline Evaluation of Japanese Welding Wire Property Plates Welding Setup Welding Parameters Chemistries Mechanical Properties Contact Tip Life Study Productivity Issue Burn Back Approach Results 4

6 Daido G-coat G-Coat is an oxide coating on the surface of the welding wire. Claimed benefits: Excellent arc stability in inert shielding gas Good wire feedability Smooth and uniform surface weld bead Low spatter Provides good mechanical properties in the welded joints as compared to base metal 5

7 Surface Roughness Japanese Domestic The Japanese wire is noticeably smoother than the Domestic wire. The Domestic wire has a rippled texture to the surface. 6

8 Property Plates 7

9 Welding Setup Wire Feeder Trailing Shield Torch 8

10 Weldment Procedure Ti-CP Gr. 2 plate, 0.5-inch thick Japanese Domestic ERTi inch diameter wire, Current A A Japanese 1.2-mm diameter wire Voltage V V First Side: Flat position, single Travel V, 60º included angle, Speed 92ipm ipm 9.2 inch land Heat Input 30 kj 30 kj Second Side: Flat position, back Wire Feed machined 0.5-inch ball mill Speed 350 ipm 350 ipm groove into the root of the first pass Torch Gas 100% He 120 cfh 100% He 120 cfh Standard joint preparation and interpass cleaning procedures Trailing Gas 100% Ar 100 cfh 100% Ar 100 cfh Complete shielding; torch, Backing 100% Ar 100% Ar trailing and backing gas Gas 100 cfh 100 cfh 9

11 Property Plate Weldments Domestic Japanese Welder s Notes: The [Japanese] wire fed much easier than the [domestic] wire. It had better arc characteristics, ti less spatter, and produced d a higher amperage with all welding parameters untouched from the [domestic] wire. 10

12 Independent Laboratory Wire Chemistry Results Oxygen Nitrogen Carbon Hydrogen Iron Japanese Cert 0.11 <0.015 < <0.12 Japanese Japanese Redo Domestic Cert Domestic Domestic Redo Specification (AWS( A5.16 ERTi-2) max 0.03 max max 0.12 max Both wires meet AWS A5.16 ERTi-2 specifications according to the supplier generated certification sheets. 11

13 Japanese Manufacturer Wire Chemistry Results Surface Coating? Oxygen Included 0.12 Heat# 8G023 Included Removed 0.04 Included 0.11 Heat# 5G021 Included 0.11 Removed 0.02 Specification (AWS A5.16 ERTi-2) Samples from the wire used in this project were returned to the manufacturer for chemical testing. Testing shows the Japanese wire does meet AWS A5.16 ERTi-2 specifications with the coating intact. 12

14 Weldment and Base Plate Chemistry Element Japanese Domestic Base Plate Specification Oxygen max Nitrogen max Carbon max Hydrogen max Iron max Weldments made with both wires and the base plate meet ASTM B265-06b requirements for Ti-CP, Grade 2. 13

15 Mechanical Properties All mechanical testing was conducted to AWS B4.0. All wrap around bend tests were satisfactory to at 2T. All-Weld Tensile Testing: Tensile Strength th (ksi) Yield Strength (0.2%) (ksi) Elongation Japanese Average % Domestic Average % Specification (ASTM B265-06b) 50 min % Both weldments meet ASTM B265-06b strength specifications. RT Charpy Impact Toughness Testing: (for info only) Impact Toughness (ft-lbs) % Shear Japanese Average Domestic Average

16 Material Hardness Welding Weld Base HAZ Wire Metal Metal Domestic Japanese

17 Weld Microstructures Japanese Domestic Both weldments have similar weld microstructures. 16

18 Property Plates Summary The Japanese wire fed easier, had better arc characteristics, less spatter, and produced a higher amperage with all else being equal. The tensile and yield strengths of the Japanese wire weldment are an average of 6.1-ksi and 4.5-ksi higher than the Domestic wire weldment, respectively. The Japanese wire weldment had lower RT Charpy Impact Toughness. The hardness data and weld microstructure are comparable. 17

19 Contact Tip Life Study 18

20 Contact Tip Life Issue Productivity in titanium welding is limited by the contact tip life. A major issue of contact tip life is burn back. What is burn back? Fusing of the electrode wire to the current contact tube by sudden lengthening of the arc in any form of automatic or semiautomatic metal-arc welding using a bare electrode. Source: 19

21 Burn Back Images a) New tip b) Wire welds to the contact tip c) More wire feeds the burn back causing weld metal to build on the contact tip d) Melted contact tip a) b) c) d) 20

22 Spatter in the Contact Tip 21

23 Contact Tip Life Approach Bead on plate welds were made with each wire based on arc times. At the completion of a specific arc time, the contact tip was changed and saved. Comparable arc time contact tips were made for each wire to compare the erosion of the contact tip from wire feeding wear. 22

24 Wire Arc Times 23

25 Contact Tip Erosion Maximum Tip Opening vs. Arc Time 4 Maximum Tip Opening (mm) Japanese Domestic MTO Arc Time (min) 24 Domestic wire could not produce >16-min comparable tips. Significant arc time improvements with the Japanese wire.

26 Contact Tip Life The results show a 9x increase in arc time using the Japanese welding wire. The domestic wire was the limiting factor due to burn back issues. There were no burn backs with the Japanese wire. The Japanese wire ran out to minutes without t cleaning and was stopped only because the torch gas was expended. To produce the ~16 and ~25 minute domestic arc times, the tips were cleaned during the welding process. 25

27 Summary Demonstrated as good or better weldment properties using the Japanese welding wire. Demonstrated significant improvement in contact tip life using the Japanese welding wire. 26

28 Questions? 27