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.

Titanium 2008 Las Vegas, NVg ,

Productivity Enhancements for GMAW of Titanium

Carrie E. Davis and Michael E. WellsNaval Surface Warfare Center, Carderock Divisiona a Su ace a a e Ce te , Ca de oc s o

West Bethesda, MD

24 September 2008

Technical Issue

High fabrication costs relative to steel andHigh fabrication costs relative to steel and aluminum limit Navy applications

• Welding Cost Drivers:S i li d hi ldi– Specialized gas shielding

– Low deposition rates Labor intensive joint designs– Labor intensive joint designs and preparation procedures

NGSS Titanium Pipe Welding Facility

2

p g y

Objective

• Optimize the gas metal arc process to reduceOptimize the gas metal arc process to reduce titanium welding costs to a level equivalent to stainless steels and Cu-Ni alloys.y– Evaluating new welding products.– Studying workmanship issuesStudying workmanship issues.– Developing recommended practices.

• ONR Goal– Weld large titanium structures (both

3

g (shipyard and shipboard) at reduced cost.

Outline

Evaluation of Japanese Welding Wire

• Property Plates– Welding Setup

– Welding Parameters

– Chemistries

– Mechanical Properties

• Contact Tip Life Study– Productivity Issue

– Burn Back

A h

4

– Approach

– Results

Daido G-coat

• G-Coat is an oxide coating on the surface ofG Coat is an oxide coating on the surface of the welding wire.

• Claimed benefits:• Claimed benefits:– Excellent arc stability in inert shielding gas– Good wire feedabilityGood wire feedability– Smooth and uniform surface weld bead– Low spatter– Provides good mechanical properties in the

welded joints as compared to base metal

5

Surface Roughness

Japanese Domestic

6

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

Property Plates

7

Welding Setup

Wire Feeder

Trailing Shield

8Torch

Weldment Procedure

• Ti-CP Gr. 2 plate, 0.5-inch thick Japanese Domestic

• ERTi 0.045-inch diameter wire, Japanese 1.2-mm diameter wire

• First Side: Flat position, single

Current 155-180 A 146-160 AVoltage 28.2-29.5 V 29.5-30.8 VTravel 9 2 ipm 9 2 ipmp , g

V, 60º included angle, 0.125-inch land

• Second Side: Flat position, back

Speed 9.2 ipm 9.2 ipm

Heat Input 30 kJ 30 kJWire Feed 350 i 350 ip ,

machined 0.5-inch ball mill groove into the root of the first pass

Speed 350 ipm 350 ipm

Torch Gas 100% He120 cfh

100% He120 cfh

• Standard joint preparation and interpass cleaning procedures

• Complete shielding; torch,

Trailing Gas

100% Ar100 cfh

100% Ar100 cfh

Backing 100% Ar 100% Ar

9

p g; ,trailing and backing gas

Backing Gas

100% Ar100 cfh

100% Ar100 cfh

Property Plate Weldments

Domestic

JapanesepWelder’s Notes:The [Japanese] wire fed much easier than the [domestic] wire. It had better arc h t i ti l tt d d d

10

characteristics, less spatter, and produced a higher amperage with all welding parameters untouched from the [domestic] wire.

Independent Laboratory Wire Chemistry Resultsy

Oxygen Nitrogen Carbon Hydrogen IronJapanese Cert 0.11 <0.015 <0.03 0.006 <0.12

Japanese 0.029 0.003 0.009 0.0037 0.033Japanese Redo 0 042 0 005 0 024 0 0024 0 034Japanese Redo 0.042 0.005 0.024 0.0024 0.034

Domestic Cert 0.095 0.0041 0.0114 0.0043 0.041

Domestic 0.067 0.002 0.009 0.0032 0.040

Domestic Redo 0.091 0.005 0.016 0.0020 0.037

Specification (AWS A5.16 ERTi-2)

0.08-0.16

0.015 max

0.03 max

0.008 max

0.12 max( )

Both wires meet AWS A5.16 ERTi-2 specifications according to the supplier generated certification sheets.

11

according to the supplier generated certification sheets.

Japanese Manufacturer Wire Chemistry Resultsy

Surface Oxygen Samples from theCoating?Oxygen

Heat# Included 0.12

Included 0 12

Samples from the wire used in this project were returned to the

8G023 Included 0.12

Removed 0.04

Included 0.11

manufacturer for chemical testing.

Heat# 5G021 Included 0.11

Removed 0.02

Testing shows the Japanese wire does meet AWS A5 16 ERTi 2Removed 0.02

Specification (AWS A5.16 ERTi-2) 0.08-0.16

meet AWS A5.16 ERTi-2 specifications with the coating intact.

12

Weldment and Base Plate Chemistryy

Element Japanese Domestic Base Plate SpecificationElement Japanese Domestic Base Plate SpecificationOxygen 0.136 0.147 0.171 0.25 maxNitrogen 0 008 0 009 0 010 0 03 maxNitrogen 0.008 0.009 0.010 0.03 maxCarbon 0.014 0.017 0.020 0.08 maxHydrogen 0.0020 0.0023 0.0004 0.015 maxHydrogen 0.0020 0.0023 0.0004 0.015 maxIron 0.066 0.063 0.079 0.30 max

Weldments made with both wires and the base plate meet ASTM B265-06b

13

prequirements for Ti-CP, Grade 2.

Mechanical Properties

• All mechanical testing was conducted to AWS B4.0.• All wrap around bend tests were satisfactory to at 2T

p

All wrap around bend tests were satisfactory to at 2T. • All-Weld Tensile Testing:

Tensile St th (k i)

Yield Strength (0 2%) (k i) ElongationStrength (ksi) (0.2%) (ksi) Elongation

Japanese Average 71.6 56.1 31%Domestic Average 65.5 51.6 37%

Specification (ASTM B265-06b) 50 min 40-65 20%

Both weldments meet ASTM B265-06b strength specifications.

• RT Charpy Impact Toughness Testing: (for info only)Impact Toughness (ft-lbs) % Shear

14

Japanese Average 62.3 56.6Domestic Average 105.3 100

Material Hardness

Welding Weld HAZ Base Wire Metal HAZ Metal

Domestic 83.0 89.5 87.0Japanese 85 6 90 7 88 5

15

Japanese 85.6 90.7 88.5

Weld Microstructures

Japanese Domestic

16Both weldments have similar weld microstructures.

Property Plates Summary

• The Japanese wire fed easier, had better arc characteristics less spatter and produced acharacteristics, less spatter, and produced a higher amperage with all else being equal.

• The tensile and yield strengths of the• 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 gwire weldment, respectively.

• The Japanese wire weldment had lower RT pCharpy Impact Toughness.

• The hardness data and weld microstructure

17are comparable.

Contact Tip Life Study

18

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• Fusing of the electrode wire to the current contact tube by sudden lengthening of the arc in any form of automatic or semiarc in any form of automatic or semi-automatic metal-arc welding using a bare electrode

19

electrode.Source: www.mesteel.com/dictionary/b.htm

Burn Back Images

a) New tipb) Wire welds to the contact tipc) More wire feeds the burn back causing weld

metal to build on the contact tipmetal to build on the contact tipd) Melted contact tip

20a) b) c) d)

Spatter in the Contact Tip

21

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

Wire Arc Times

23

Contact Tip Erosion

Maximum Tip Opening vs. Arc Time

4

3.5

g (m

m)

MTO2.5

3

Tip

Ope

ning

Japanese

D ti

2Max

imum

Domestic

1.50 15 30 45 60 75 90 105 120 135 150

Arc Time (min)

24Domestic wire could not produce >16-min comparable tips.Significant arc time improvements with the Japanese wire.

Contact Tip Life

• The results show a 9x increase in arc time using the gJapanese welding wire.

• The domestic wire was the limiting factor due to burn b k iback issues.

• There were no burn backs with the Japanese wire.Th J i t t 146 5 i t ith t• The Japanese wire ran out to 146.5 minutes without cleaning and was stopped only because the torch gas was expended.was expended.

• To produce the ~16 and ~25 minute domestic arc times, the tips were cleaned during the welding

25

process.

Summary

Demonstrated as good or better gweldment properties using the Japanese welding wire. Demonstrated significant improvement in contact tip life using the Japanese welding wire.

26

Questions?

27