FTI's Split Sleeve Cold
Expansion™ system is a cost effective solution to
problems associated with fatigue cracks in holes in metal
structures. Split Sleeve Cold Expansion is accomplished
by pulling a tapered mandrel, pre-fitted with a lubricated
split sleeve, through a hole in aluminum, steel or titanium.
The function of the disposable split sleeve is to reduce
mandrel pull force, ensure correct radial expansion of
the hole, preclude damage to the hole, and allow one-sided
processing.
The process works by imparting
beneficial compressive residual stress around the hole.
The action of drawing the mandrel through the starting
hole causes a radial plastic flow of material and results
in an annular zone of residual compressive stresses
that extend up to one diameter beyond the edge of the
hole as shown below.
The sleeve allows for one-sided processing and shields
the hole from frictional forces generated by the high
interference of the expansion mandrel. The residual
stresses created by cold expansion significantly increase
fatigue life by reducing the stress intensity factor
and crack growth life by reducing the applied stress
ratio at the hole. The magnitude of the peak residual
compressive circumferential stress is about equal to
the compressive yield stress for the material. The compressive
stress zone spans one radius to one diameter from the
edge of the hole, for diameters up to 1/2 inch for most
materials. A balancing zone of tensile stresses lies
beyond the circumferential compressive stress zone.
Split Sleeve Cold Expansion is used on every commercial
and military aircraft in the world because it improves
the fatigue life of the structure and provides long-term
operation and maintenance cost savings.
FTI has adapted basic Split Sleeve Cold Expansion technology
to FTI processes - ForceTec®Rivetless Nut plate
system, ForceMate® Bushing Installation system,
BushLoc® Hole Repair and Resizing system, TukLoc
Blind Fastening system and our line of Expanded Fittings.
• In most cases, at least 3:1 fatigue life improvement
• Arrests small crack growth
• Cost effective alternative to redesign
• Adds no weight to structure
• Simple, one-sided operation
• Works on all common aerospace materials
• Applicable in both production and rework
• Can be automated
Step 1. After verifying the starting hole size,
slip the pre-lubricated split sleeve onto the mandrel,
which is attached to the hydraulic puller unit.
Step 2.Insert the mandrel
and sleeve through the hole with the nosecap held firmly
against the work piece.
Step 3. Activate the
puller unit. The mandrel is drawn through the sleeve and
the hole. The combined thickness of the sleeve and the
mandrel major diameter radially expand the hole. The lubricated
sleeve reduces the pull force required, protects the hole,
and allows the mandrel to exert radial forces through
the entire thickness of the material.
Step 4. Remove and discard
sleeve
Step 5. Ream hole to
final size. Use pin-end of combination gage to confirm
size.
Cold Expansion to Size:
Same as standard Split Sleeve Cold Expansion
but eliminates final reaming process. Cold Expansion
to Size is material dependent, and tooling is designed
according to the properties of the material. By knowing
how different material react to the radial stresses
of Split Sleeve Cold Expansion, we can predict the final
hole size. Cold Expansion to Size is ideal for production
work, but has also been used in rework situations. Also,
Cold Expansion to Size works well when incorporated
in automated drilling/fastener insertion systems.
Countersink Cold Expansion:
Tooling designed to simultaneously cold expand the countersink
and straight portion of the hole. Countersink Cold Expansion
is applicable in both production and rework
The Split Sleeve Cold Expansion uses the same PowerPak
and puller as the other processes.
The Split Sleeve Cold Expansion
tooling system includes:
Cutting Tools
Mandrel
Split Sleeves
Combination Gage
Mandrel Gage
Nosecap
Puller
Power Pak
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