How to weld titanium and its alloys successfully

Adequate shielding using inert gas is essential if repeatable, high quality joints are to be made in titanium and its alloys, says Huntingdon Fusion Techniques.

It will come as no surprise to a fabricator with experience in handling titanium that special consideration needs to be taken during preparation and welding.

Titanium and its alloys are reactive and can become contaminated by atmosphere gases.

Adequate shielding using inert gas is essential if repeatable, high quality joints are to be made.

For many years it was believed that titanium welding could only be performed satisfactorily in sealed chambers equipped with glove ports and viewing ports and filled with high purity inert gas such as argon.

A better understanding of the mechanism of metal/gas interaction has shown that provided adequate local shielding is provided and maintained during welding the use of sealed chambers is not necessary.

This understanding has afforded possibilities for welding large titanium fabrications and significantly extended the application areas for the metal and its alloys into major structural forms, especially in the aerospace industry.

The primary requirement then is to provide a protective gas atmosphere to the joint area during welding and subsequent cooling.

* Basic guidelines - use purge gas correctly - the pure gas should be 99.999% pure - even 99.995% gas can lead to some yellow-straw discoloration.

If the colour begins to mottle, or if it exhibits any hint of blue, the gas isn't pure enough, or it is not being applied it correctly.

Start the gas flow several seconds before starting to weld.

If you have enough shielding and the argon is being dispersed evenly over the part, you should see a uniform colour.

* After welding - protective gas flow is still needed until the metal has cooled below about 250 deg C to prevent discolouration.

* Good 'housekeeping' - use high-purity gas.

Clean all work areas.

Wear cotton gloves after cleaning the parts thoroughly.

Allow to cool before removing gas coverage.

Huntingdon Fusion Techniques (HFT) has 'spearheaded' innovative technology in providing quality gas coverage.

It continues to manufacture flexible enclosures but also produces weld purge monitors and trailing shields.

Additionally the company markets a wide range of expandable pipe stoppers for use in sealing tubular components during gas purging.

* Flexible enclosures - the principle advantage of flexible enclosures over the more traditional solid metal versions is significantly lower manufacturing cost but benefits also include the flexibility of minimal weight and the ability to move and store when not in use.

Previous HFT enclosures have been circular in section but developments in manufacturing technology now afford opportunities to produce square and rectangular enclosures.

Rectangular cross sections and the opportunity to produce to a length to suit the customer's requirements are expected to make the new additions attractive to a wider range of end-users.

Whereas circular enclosures can be expensive on purge time and purge gas, the rectilinear concept offers users the opportunity to match the shape to meet specific requirements.

Currently the company is able to manufacture these enclosures up to 2m long and 1m x 1m in section.

* Purge monitors - the Argweld monitor is believed to be the world's first instrument designed specifically for measuring oxygen levels in any purge gas during the welding of titanium and its alloys.

It shows oxygen levels down to 10 ppm using an alphanumeric display and incorporates an impressive array of features which include automatic fault finding diagnostics, data acquisition software, and push-button operated menu.

* Trailing shields - careful attention to design and construction by HFT has led to the development of a range of gas shielding accessories which meet the requirements of high quality gas coverage during welding.

The devices will accommodate any make of GTAW (gas tungsten arc welding - TIG) or PAW (plasma-arc welding) torch and are available to provide gas coverage on flat, internal or external radii.

* Pipe stoppers - expandable industrial grade nylon stoppers are widely used to seal pipes so that good gas coverage is maintained.

They are available from 12 to 160mm (0.5 to 6in) diameter.

References for further reading are as follows.

* 'Recommended Practices for Gas Tungsten Arc Welding of Titanium Pipe and Tubing' - American Welding Society - NSI/AWS D10.6/D10.6M:2000.

* 'Specification for Fusion Welding for Aerospace Applications - American Welding Society - ANSI/AWS D17.1:2001.

* 'Guide for the Fusion Welding of Titanium and Titanium Alloys' - American Welding Society - ANSI/AWS G2.4/G2.4M:2007.

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