Demolding Your Composite Part

Your part is done, now what? What do you do first when
taking the part out of the mold? Do you remove the peel ply while the
part is in the mold or leave it and remove it later? What kind of wedges
or tools are needed to remove the part without destroying the part or
the mold at the same time? The following will help answer all these questions and more as we dive into demolding your composite part.

The Demold Process Starts Before Plycut

of demolding occurs within the tooling design, layup, and the tool’s
preparation processes. With these three keys taken care of before the
part’s layup, all that is needed is cut protective gloves, safety
glasses, a brass scraper or small fiberglass shim, and possibly a rubber

Demold in Functional Tool Design

crafting and designing a part and layup mold, the parts demold process
should be one of the top 5 criteria in tool design. Keep the layup mold
as simple as possible. Suppose it is known that negative draft angles
or sharp radii will be a factor in the part design. In that case, using a
multi-segmented mold may be in order or use of secondary bonding of 2
composite pieces instead of complicating a tooling system. In short, the
design should simplify the demold process until there is a comfortable
experience established in demold AND tool design.

Demold in Layup

also can be aided in layup through ply design. For instance, laying up
into a bowl-like part. Demold tabs are easily added to the top of the
bowl with sacrificial material and are widely useful in aiding the
demold process. These tabs can be made from the extra plies in the layup
or fiberglass just lying around. Place these plies in an excess area
beyond the part’s final trim line, and there will be no remnant of it
left in the final part. It will aid the demold process tremendously as
the part will pop out with ease each time.

quality check of prepped mold surfaces for a proper application of mold
release will be needed, along with a useful tool design and layup
processes. It is ideal for keeping a record of tooling prep for any
given tool with information such as what release is placed onto it, how
it was applied, and the time and date in which it was applied.

the demold process, practice makes perfect. The above criteria will
mitigate any chances of human error. Experience with each material
system helps with stripping parts as each is a little different.

Reference Safety 101, Demold and Mold Prep Safety

use cut-resistant gloves as most composites’ edges are sharper than
most knife blades in any given home. It does not take much to need
stitches. Always wear proper eye protection as chips and resin bleed out
can be expected, and pieces may fly out and into the eyes.

the composite is out of the oven, autoclave, or air cure, let the part
cool to a temperature that allows for demold. There is no use in burning
oneself on a hot tool. Besides, a cool tool will be easier to strip
from a mold surface than a hot one.

is best practice to get peel ply and any other taping/resin damming
surfaces off the composite laminate. Getting these materials off is
easier with a part placed stationary on the mold surface rather than
when it is stripped from the mold surface. Doing so also mitigates the
chance of being cut by a part’s edge before deburring.

any non-marking shim between the tool surface and the part. The sharper
the edge, the more likely it will get between them very quickly. The
use of a rubber mallet may come in handy when initially creating
separation between the part and tool surface. It is crucial to have a
shim that is composite, brass, or non-marking. Most metal shims will
leave marks on most tooling surfaces. Once the shim is placed, wiggle
shim up/down, creating a fulcrum, and lift the part from the tooling
surface. With this process, be mindful of draft angles and the
possibility of fiber damage within the laminate. Do not use excessive
force. If the part does not easily come up from hand pressure, place
additional shims into the area until the part frees from the mold. Note:
Once the shim is placed in the laminate, an air gun may be used to
create additional separation from the mold and can be used to remove
laminate from the mold surface.

the part is out of the mold, place it out of the immediate traffic area
or immediately deflash part edges. Once deflashed, wrapping parts
completely or around edges with bubble wrap will mitigate the chances of
damage. The best practice is keeping parts wrapped in bubble wrap when
not in use, and while being transported or stored.

after demolding, it is vital to clean the tool using alcohol if the
mold release is compatible. Always reference respective technical
datasheets for application of mold release. Check the material
specification for information regarding mold releases as some will come
off with alcohol application. Once the mold is clean, apply at least 2-3
coats of respective release. Place a tag onto the mold surface for
knowing the details.