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It appears that they have an
effective way to weld titanium plates together without excessive weaknesses. A seventeen foot clean weld was
demonstrated. Titanium has been long
sought after for ship building but the metal is possibly the most difficult when
it comes to working with it.
This sounds like it has now become
possible to fabricate a hull as a predictable price and some security on
delivery. This will also make aircraft
fabrication a lot easier I am sure.
I suspect that the next challenge
is to bring the whole cost envelope down to where building the hulls can truly
commence.
Future Titanium
Navy
APRIL 04, 2012
An Office of Naval Research (ONR)-funded project will produce a
full-size ship hull section made entirely with marine grade titanium using a
welding innovation that could help bring titanium into future Navy ship
construction, officials announced April 3.
The contractor team building this section recently completed the
industry’s longest friction-stir titanium alloy welds and aims to complete the
ship hull section this summer. Friction stir welds more than 17 feet long
joined the titanium alloy plates for the section’s deck.
“This fast, effective friction stir weld technique is now an affordable manufacturing process that takes advantage of titanium’s properties,” said Kelly Cooper, the program officer managing the project for ONR’s Sea Warfare and Weapons Department.
What it means for the Navy
Titanium metal and its alloys are desirable materials for ship hulls
and other structures because of their high strength, light weight and
corrosion-resistance. If constructed in titanium, Navy ships would have lighter
weight for the same size—allowing for a bigger payload—and virtually no
corrosion. But because titanium costs up to nine times more than steel and is
technically difficult and expensive to manufacture into marine vessel hulls, it
has been avoided by the shipbuilding industry. But perhaps not for much longer.
Researchers at the University
of New Orleans School
Since antiquity, blacksmiths have joined iron or steel parts together by heating them in a forge, placing them on an anvil and striking the two pieces repeatedly with a heavy hammer. After several repetitions of heating and striking, the two pieces were “hammer forged” or “forge welded” together.
Friction stir welding joins metals using the heat of friction produced by a spinning pin tool pressed down on both pieces of metal at their common joint. Friction heating produced by the high-speed rotation causes both metal pieces to heat up to a “plastic” condition, but not to melt. As the tool passes down the common joint line, the heated, plasticized metal from both pieces is kneaded together in the rotating tool’s wake, forming the weld between them.
How it was accomplished
Friction stir welding works well for most aluminum alloys. Titanium,
however, is difficult to join by the same process because of the high
temperatures required, and pin tool materials that erode and react with
titanium, weakening the weld.
The researchers overcame that problem by using new titanium friction stir welding methods developed by Florida-based Keystone Synergistic Enterprises Inc. with funding from both ONR and the Air Force.
To fabricate the ship hull structure, more than 70 feet of welded linear joints were made—the longest known welds in titanium made with the friction stir process. This friction stir welding achievement showed a noticeable improvement from previous similar processes. It was made at a high linear speed—indicating reduced manufacturing time; showed excellent weld penetration—indicating a secure connection; and had no distortion of the titanium adjoining the weld.
Experts attribute the success to an effective design of the pin tool, process parameters that emphasized pin tool life and exact duplication of the process steps from facility to facility and machine to machine.
(1) Existing weld sizing criteria are excessively conservative for
construction of lightweight shipboard structures, particularly for applications
in ship hulls made of titanium and its alloys. A set of new criteria for
titanium ship construction is being developed by taking advantage of recent
analytical developments presented in this paper. Through both experimental
testing and analytical based interpretation of test data, the new weld sizing
criteria can be used for sizing welds for meeting both static and fatigue
strength requirements
(2) Although residual stresses are of a high magnitude in welded titanium components, welding-induced distortions may not be of as much a concern as anticipated. Further investigation is underway on additional joint types and plate thicknesses
(3) The highly localized residual stress features in titanium weldments is due to titanium material’s low thermal diffusivity. It is seen, on one hand, as a culprit in slowing down welding speed, and on the other, as being beneficial for reducing the propensity to developing buckling distortion in thermal cutting and welding. With this in mind, it now seems that welding-fabricated structural forms can now be viewed as a viable alternative to expensive extrusions which have been shown to be cost-prohibitive for ship hull applications
Future Naval Force May Sail With the Strength of Titanium
Office of Naval Research
Corporate Strategic Communications
875 N. Randolph St., #1225-D
Office: (703) 696-5031
Fax: (703) 696-5940
For Immediate Release: April 3, 2012
The contractor team building this section recently completed the
industry’s longest friction-stir titanium alloy welds and aims to complete the
ship hull section this summer. Friction stir welds more than 17 feet long
joined the titanium alloy plates for the section’s deck.
“This fast, effective friction stir weld technique is now an affordable
manufacturing process that takes advantage of titanium’s properties,” said
Kelly Cooper, the program officer managing the project for ONR’s Sea
Warfare and Weapons Department.
What it means for the Navy
Titanium metal and its alloys are desirable materials for ship hulls
and other structures because of their high strength, light weight and
corrosion-resistance. If constructed in titanium, Navy ships would have lighter
weight for the same size—allowing for a bigger payload—and virtually no
corrosion. But because titanium costs up to nine times more than steel and is
technically difficult and expensive to manufacture into marine vessel hulls, it
has been avoided by the shipbuilding industry. But perhaps not for much longer.
Researchers at the University
of New Orleans School
Since antiquity, blacksmiths have joined iron or steel parts together
by heating them in a forge, placing them on an anvil and striking the two
pieces repeatedly with a heavy hammer. After several repetitions of heating and
striking, the two pieces were “hammer forged” or “forge welded” together.
Friction stir welding joins metals using the heat of friction produced
by a spinning pin tool pressed down on both pieces of metal at their common
joint. Friction heating produced by the high-speed rotation causes both metal
pieces to heat up to a “plastic” condition, but not to melt. As the tool
passes down the common joint line, the heated, plasticized metal from both
pieces is kneaded together in the rotating tool’s wake, forming the weld
between them.
How it was accomplished
Friction stir welding works well for most aluminum alloys. Titanium,
however, is difficult to join by the same process because of the high temperatures
required, and pin tool materials that erode and react with titanium, weakening
the weld.
The researchers overcame that problem by using new titanium friction
stir welding methods developed by Florida-based Keystone Synergistic
Enterprises Inc. with funding from both ONR and the Air Force. The processes
were scaled up and transferred to the National
Center for Advanced Manufacturing
(NCAM), which is a partnership between the University
of New Orleans , NASA and the state of Louisiana
To fabricate the ship hull structure, more than 70 feet of welded
linear joints were made—the longest known welds in titanium made with the
friction stir process. This friction stir welding achievement showed a
noticeable improvement from previous similar processes. It was made at a high
linear speed—indicating reduced manufacturing time; showed excellent weld
penetration—indicating a secure connection; and had no distortion of the
titanium adjoining the weld.
Experts attribute the success to an effective design of the pin tool,
process parameters that emphasized pin tool life and exact duplication of the
process steps from facility to facility and machine to machine.
ONR funds collaborative projects investigating novel shipbuilding
materials and improved processes for titanium friction stir welding—especially
its affordability—as part of the Sea Base Enabler Innovative
Naval Prototype program.
About the Office of Naval Research
The Department of the Navy’s Office of Naval Research (ONR) provides
the science and technology necessary to maintain the Navy and Marine Corps’
technological advantage. Through its affiliates, ONR is a leader in science and
technology with engagement in 50 states, 70 countries, 1,035 institutions of
higher learning and 914 industry partners. ONR employs approximately 1,400
people, comprising uniformed, civilian and contract personnel, with additional
employees at the Naval Research Lab in Washington, D.C.
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