TM 1-1500-204-23-11
care not to apply inish system in
requires less compaction time than the plain weave
fastener hole or countersink area.
fabric. After the dry cloth has been impregnated with
resin, the plies cut, and the plies lat ply collated,
it is debulked using a double vacuum bag debulking
7-11. DOUBLE VACUUM DEBULK PROCESS. The
tool (see igure 3-6). If the tool is not available, a
DVD wet layup process is similar to the standard wet
rigid box can be manufactured locally according to
layup process in that it is performed by the repair
igure 3-7 and paragraph 7-11c. This repair procedure
technician to prepare patches for a part, and can be
is not necessarily applicable to a particular weapon
utilized for contoured areas and substructure detail
system. Refer to the system speciic technical manual
manufacture. Unlike the standard wet layup process,
for instructions on the iber, resin, number of bleeder
it provides a technique for removing entrapped air
plies, and processing parameters. The applicability of
that causes porosity in wet layup laminates. The DVD
this repair depends upon additional factors such as
process also provides better control of resin content
loading conditions and laminate thickness. Consult
and better iber wetting. These characteristics of the
the system speciic technical manual or engineering
DVD process result in increased mechanical properties
for further guidance.
for the laminate. As a result, DVD wet layup laminates
are not limited to lightly-loaded structures.
(1) Facilities, Equipment and Materials. The
following equipment and materials are required: Tem-
a. DVD Wet Layup Process. In this technique a
perature/vacuum controller, Double vacuum debulk
rigid box is placed over the vacuum bag (inner
tool or locally manufactured rigid box, Scribe, Base
vacuum bag) containing the wet layup laminate and
Plate. This plate will be used below during the
heat blanket. The outer vacuum bag is placed over
layup of the DVD Tool Schematic (See igure 3-6).
the box and vacuum applied. This second vacuum
It should be made from at least 0.5 inch thick alu-
bag and rigid box relieve the compaction pressure
minum. (Local procurement), Heat Blanket, Vacuum
on the laminate induced by the initial vacuum bag,
Bag Repair Materials Kit, Fabric (See System Spe-
while maintaining vacuum on the inner bag. With
ciic Technical Manual), Adhesive, Liquid (See System
vacuum applied to both bags, the laminate is heated
Speciic Technical Manual), Aluminum Sheet Stock,
to the debulk temperature and held for a speciied
0.063 inches or thicker (Local Procurement), Marker,
time. This allows gases to be removed without being
Flash breaker Tape, Mylar, Squeegee.
trapped by the compressing (inner) vacuum bag. Next,
compaction of the laminate is accomplished by venting
(2) Material Preparation.
the outer vacuum bag to the atmosphere so that only
the inner vacuum is applied to the repair patch.
Following debulking and compaction, the laminate is
(a) Fabricate templates for each ply of the
removed from the debulking tool and formed to a
patch using Mylar ilm. Mark the ply
tool or part surface. A vacuum bag is then applied
orientation, ply number, and orientation
over the laminate (and heat blanket if applicable) and
marks on each template to facilitate
vacuum applied. Heat is then applied to cure the
layup. See paragraph 5-6.
laminate using an oven or heat blanket. The resin
used in this technique must have a fairly long pot
(b) Cut two sheets of porous release ilm so
life due to the use of heat and the time required
they extend 1 inch past each edge of the
to perform the process. Laminating resins need to
largest ply of the patch.
have a minimum of a 4-hour pot life and 200 F cure
temperature. These requirements are necessary to
(c) Cut the required number and type of
allow for the debulking and compacting cycle times and
iberglass plies to be used as bleeder
temperatures. Unique process procedures need to be
plies per table 7-6; cut them so they
developed for each resin system used by either the
extend 1 inch past the largest ply of the
resin manufacturer or system speciic authority. Two
patch.
fabrics are typically used for repair, 8 harness satin
weave and plain weave. These fabrics vary in weight
(d) Cut a single piece of the required repair
and thickness (see paragraph 4-3, igure 4-6 and igure
fabric, large enough to it all the repair
4-9). Since these fabrics differ, different amounts of
plies.
resin per square foot are required to impregnate the
fabrics. Also, the number of bleeder plies is speciic to
(e) Cut one ply of non-porous release ilm
the fabric type in order to obtain the correct resin ratio
so it is at least 1/2 inch past the edge
and laminate thickness. Another process variation is
of the porous release ilm. Perforate the
the compaction time. The compaction time is the
non-porous release ilm with a scribe on
period after venting of the outer box, when only one
approximately 2 inch centers.
vacuum is applied to the laminate. An 8 harness fabric
7-105
