Page 46: of Maritime Reporter Magazine (September 2018)

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NASA has developed an innovative variation of the FSW process called Thermal Stir Welding (TSW), a process that introduces additional heat to the workpiece independent of the frictional heating between the stir tool and the metal. al force of the containment plate have decreased friction forces in the X axis, ure 6 shows integrally stiffened Isogrid of its structural pattern – the stiffening been de-coupled for greater process con- decreased shear forces in the X axis, in- and Orthogrid structures. Both Isogrid ribs use a square or rectangular waf? e trol. It is different than TSW and FSW in creased travel rates, and increased stir and Orthogrid structures contain inte- pattern rather than triangular. Both self- that ultrasonic energy is integrated into tool life. grated stiffeners that characteristically stiffened con? gurations are used where the rotating stir tool and the non-rotat- have exceptional strength-to-weight or low weight, stiffness, strength and dam- ing containment plate. Figure 1 shows stiffness-to-weight ratios for many ap- age tolerance are important.Isogrid and Orthogrid

Structures a schematic of the process and Figure plications besides aerospace propellant 5 shows the USW prototype located at Manufacture of Space Launch System tanks. Isogrid is able to withstand both Using NASA Technologies for

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MSFC. The bene? ts of using the USW (SLS) rocket hardware, primarily cryo- compressive and bending loads, mak- process include single pass welds in genic tank structures, takes advantage of ing it ideal for space and aerospace ap- Applying aerospace technologies to aluminum and heat resistant alloys, the superior strength and rigidity found plications. Orthogrid has similar bene? ts maritime applications would de? nitely decreased plunge forces in the Z axis, in Isogrid and Orthogrid structures. Fig- to Isogrid, however it differs in terms be a challenge. A “bottoms-up” ap-

Figure 5. USW Prototype system at MSFC.

46 Maritime Reporter & Engineering News • SEPTEMBER 2018

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