FILLER METAL SELECTION
Titanium welding wire is covered by AWS A5.16-70 Specification ("Titanium and Titanium-Alloy Bare Welding Rods and Electrodes"). Selected wire compositions are given in Table 23.

It is generally good practice to select a filler metal matching the properties and composition of the titanium base metal grade. However, for both commercially pure grades and alloys, selecting a weld wire one strength level below the base metal is also done (i.e., use TIMETAL 35A wire to weld TIMETAL 50A). Special situations may require a different grade of filler wire to give desired combination of joint properties. For instance, several options are available for use with TIMETAL 6-4. The low interstitial grade is useful where high weld ductility, such as is required in cryogenic applications, is needed.

WELDING PARAMETERS
Guidelines parameters for machine welding titanium are given in Table 24. These guidelines were developed on automatic equipment with backup bar, trailing shield and hold-down shoes. Parameters for manual welding are similar under similar welding conditions. If slower welding speeds are desirable, amperage must be reduced proportionately. Generally speaking, the lowest heat input consistent with good weld properties is desirable in welding titanium. It is good practice to weld test samples to optimize parameters for a particular welding application before committing material and manpower to the job.

WELDING TECHNIQUE
In addition to clean joints and weld wire, proper parameters, and proper inert gas shielding, welder technique requires attention when titanium is being welded. Improper technique can be a source of weld contamination.

Before starting an arc in welding titanium, it is good practice to prepurge torch, trailing shield and backup shield to be sure all air is removed. Whenever possible, high frequency arc starting should be used. Scratch starting with tungsten electrodes is a source of tungsten inclusions in titanium welds. On extinguishing the arc, the use of current downslope and a contactor, controlled by a single foot pedal, is encouraged. Torch shielding should be continued until the weld metal cools below 800 degrees F. Secondary and backup shielding should also be continued. A straw or blue color on the weld is indicative of premature removal of shielding gas.

Preheating is not generally needed for titanium shop welds. However, if the presence of moisture is suspected, due to low temperature, high humidity, or wet work area, preheating may be necessary. Gas torch heating (slightly oxidizing flame) of weld surfaces to about 150 degrees F. is generally sufficient to remove moisture.

The arc length for welding titanium without filler metal should be about equal to the electrode diameter. If filler metal is added, maximum arc length should be about 1-1/2 times the electrode diameter. Filler wire should be fed into the weld zone at the junction of the weld joint and arc cone. Wire should be fed smoothly and continuously into the puddle. An intermittent dipping technique causes turbulence and may result in contamination of the hot end of the wire on removal from the shield. The contaminants are then transferred to the weld puddle on the next dip. Whenever the weld wire is removed from the inert gas shielding, the end should be clipped back about 1/2- inch to remove contaminated metal.

Interpass temperatures should be kept low enough, such that additional shielding is not required. Cleaning between passes is not necessary if the weld bead remains bright and silvery. Straw or light blue weld discoloration can be removed by wire brushing with a clean stainless steel wire brush. Contaminated weld beads, as evidenced by a dark blue, gray or white powdery color, must be completely removed by grinding. The joint must then be carefully prepared and cleaned before welding again.