Page 42: of Maritime Reporter Magazine (September 2018)

WELDING TECHNOLOGY

NASA Welding Technologies

Could Revolutionize Workboat Fabrication

Solliid-Stat te e Solid-State Welding Processes Being Developed for NASA Manufacturing Pro- gr ra am m ms s C Co g g grams Could Signi? cantly Reduce Workboat Fabrication Costs

BY JEFF DING

Whether it is for a tug boat, cargo ves- weld process takes place in the plastic to thicker-section plate material and

Thermal Stir Welding sel, or an offshore supply ship, much phase below the melting point of the ma- Before the introduction of the TSW higher strength heat resistant alloys (i.e. of the American workboat fabrication terials being joined. This precludes any process, it should be pointed out that titanium, steels, Inconels, etc.) where industry is located along the Southern possibility of solidi? cation defects. The FSW is a joining technology that is ex- there is a mismatch between the stir pa-

Coast of the U.S. But a visit to any one bene? ts include the ability to join mate- rameters required to sustain frictional panding in its application to space struc- of the workboat facilities in that area (or rials that are dif? cult to fusion weld, for tures as a solid-state joining method with heating and the stir parameters desired any other in the country) would reveal example 2XXX and 7XXX aluminum joint properties superior to fusion weld- for the hot working regimes of the alloy. antiquated and archaic fabrication pro- alloys, magnesium, and copper. Solid- ing joints. FSW methods are primarily Not to say that TSW’ing would not be cesses used 70 years ago. The workboat state welding processes can use purpose- associated with high-strength aluminum bene? cial for welding aluminum. It is manufacturing process is very expen- designed equipment or modi? ed exist- alloys such as the Al-Li alloys used to capable of welding all aluminum alloys sive, labor intensive, and has not really ing machine tool technology, and they manufacture cryogenic tanks, supporting whether it is thin sheets or thicker sec- changed since World War II. Perhaps it is are also suitable for automation and are structures, and rocket fuselage compo- tioned aluminum, all in a single pass.

time to go back to the drawing board and adaptable for robot use. The development of the TSW process nents. There is high interest in expanding redesign the workboat manufacturing Other advantages are as follows: FSW joining methods to higher-strength has led to the fabrication of a full-scale process from the ground up so that new and higher-temperature alloys to include machine, shown in Figure 2. It was used solid-state welding processes and other • Low distortion and shrinkage, even rocket engine components and other to support previous work funded by the aerospace technologies being developed in long welds. high-temperature materials applications Defense Advanced Research Projects at NASA’s Marshall Space Flight Center • Excellent mechanical properties in for space. However high frictional forc-

Agency (DARPA) and Of? ce of Naval (MSFC) can be utilized to reduce costs fatigue, tensile, and bend tests. es and high stir welding temperatures Research (ONR). Deliverables for this and decrease manufacturing schedules. • Single pass welds. project was to successfully demonstrate make this a dif? cult challenge.

Although NASA welding development • No arc or fumes. NASA has developed an innovative the single pass joining of .500-in-thick focuses on the aerospace discipline, • No porosity. variation of the FSW process called (25.2-mm-thick) commercially pure many applications exist for these same • No spatter. Thermal Stir Welding (TSW), a process (CP) titanium and Ti 6-4 ELI. solid-state weld processes in the mari- • Ability to operate in all positions. Since the TSW process de-couples the that introduces additional heat to the time industry. • Energy ef? ciency. workpiece independent of the frictional stirring, heating and forging functions of

Solid-state welding technologies at • One stir tool can typically be used heating between the stir tool and the the FSW’ing process and allows inde-

NASA’s MSFC have made signi? cant for up to 1,000 m (3,280 ft) of weld metal. A description of the TSW process pendent control of each process element, advances is support of NASA aerospace length in 6XXX series aluminum al- appears in Figure 1 and it shows the novel and very unique applications/ca- manufacturing applications. In addition loys. differences between the FSW and TSW pabilities can be attained using the TSW ? to conventional friction stir welding (C- • No ller wire required. processes. In FSW, the stirring RPM of process over the FSW process. Since the

FSW) and self-reacting friction stir weld- • No gas shielding for welding alumi- TSW process con? guration uses non- the stir tool, the heating from the shoul- ing (SR-FSW), both of which are used in num. der rubbing on the surface of the weld rotating containment plates (instead of

Space Launch System (SLS) cryotank • Some tolerance to imperfect weld joint, and the compressive forging force a rotating shoulder in the FSW process) manufacturing, MSFC is also develop- preparations; thin oxide layers can from the shoulder cannot be decoupled. to apply forging loads to the plasticized ing the ultrasonic stir weld (USW) and be accepted. weld nugget, it is possible to form the

TSW decouples the three process ele- the thermal stir weld (TSW) processes. • No grinding, brushing, or pickling ments and allows independent control of upper and lower containments plates to

These two processes are superior to required in mass production. a speci? c, unique geometry. This was each. The stir tool RPM is independent-

FSW in that the heating, stirring, and • Ability to weld aluminum and cop- ly controlled as well as the compressive done in the referenced work completed forging elements are decoupled to allow per of >75 mm (3 inches) thickness forging loads from the upper and lower for DARPA/ONR. One of the deliver- independent control of each element. in one pass. ables was a hexagonally shaped struc- containment plates. The heating is inde-

This allows for greater process control. • Once welding parameters are estab- pendently controlled using an induction ture which represented a sub-scale gun

The process advantages of all three solid lished, very, very few weld repairs coil. Because of the independent control turret sub-component. Figure 3 shows 1 state processes (FSW, USW, and TSW) required. of the process elements/parameters, the one of the angled welds while Figure 4 result from the fact that the solid-state real bene? t of TSW is especially biased shows the completed part. Note that the 42 Maritime Reporter & Engineering News • SEPTEMBER 2018

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