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OH NO! What To Do When Your Part Sticks In The Mold?

Apr 7th 2021

There are various reasons as to why a part may stick to a layup mold. Most often, the mold release that was used may not have been applied adequately, or the wrong mold release was used. Bad batches of mold release may also cause these problems. Regardless, if the part is stuck, the following actions and tools may help recover the mold surface and possibly the part.

It is important to keep realistic expectations when it is stuck in or on the mold. It can be a frustrating and non-ideal situation that, depending on the material, can easily result in a scrap part, a scrap tool, or both. The mold surface is of utmost importance even if the part is scrap by the process.

Tools Needed for part extraction:

Proper stripping tools should always be used when prying parts away from their mold surface. Most mold surfaces are very easy to scratch. Non-marring tools are a must-have in all stripping processes. Many kinds of metal scrapers will scratch softer metal tools and gel-coated tooling surfaces. The use of a flathead screwdriver is not advised.

  1. Fiberglass / Carbon Fiber Shims
    • Fiberglass shims are often used as a pry bar to drive between the two stuck surfaces. Carbon Fiber also makes a good shim material as it is stiffer, and more leverage can be applied to it without the shim bending. A sharpened shim is a useful tool in creating any space between surfaces.
  2. Rubber mallet
  3. Mold release
    • If air hose access is available, it may help separate the part from the mold
  4. Brass Scraper

Look for an area where any leverage could be placed upon the part's surface to pry against the mold surface. Ideally, this would be in a thicker area where the force applied would not delaminate the plies or crack the part. Grab a shim and rubber mallet, keeping mold release and air hose nearby. Depending on how much the part will move from the mold surface, it can give an idea of how thin a shim to use. The important part of this is finding something thin enough to get in between the two parts. Using a rubber mallet, drive the shim between the two pieces as far as it will go without digging into the mold surface. It should create some separation between the two surfaces. If any separation is created, pour some mold release into the cavity, and use the air hose to drive any additional separation. It may cause small pieces of the part that are stuck to free from the mold surface. With the initial separation created, repeat the process around the part's perimeter, building the shims up in any area to increase the separation. The separation will likely occur little by little. Eventually, one of two events will occur. The part will eventually give way from the tool surface, or the part will crack under the force given by the shims. Be wary of applying force to sharp or steep angles in the part/tool surface in which the part may buckle in the mold, causing delamination. Patience is key throughout the process. During the stripping process, a rush could cause a part to crack, delaminate, or be scrapped entirely beyond repair.

Usually, the tool surface resin or metal tools have a harder surface than the composite part. If the tool design is adequately completed, the part will crack before any permanent deformation occurs to the tooling surface.

As the part releases from the mold surface, it is likely that pieces of the original part will be stuck to the mold. The part's mold side surface will likely have imperfections and laminate resin/fabric bonded to the mold surface. For these pieces left on the tool, use a brass scraper or composite scrapper and rubber mallet to remove the high spots and remnant pieces as part of tool cleaning and prep. It is also likely that these pieces do not merely chip off the tool, in which hand sanding the areas down to the original tool should occur. Special care and precision should be practiced not to damage the tool surface. The use of hand sanding with a block is useful along with flat parts of the tool. Be sure not to angle the tool in such a way that drives the paper into the tool. For female radii along the tool, roll a piece of sandpaper in the areas that have remaining pieces and sand them away.

If separation cannot be achieved, likely mold release was not applied, or the wrong type may have been used. Depending on the tool's economic impact, scrapping the part and tool should be the last option.

If there was any tool prep completed with mold release, the above process should work. If the part still does not come out of the mold, the scrap part will still need to be taken from the mold surface. If the part is broken, use fiberglass shims to create space to jar any pieces from the mold surface; once this has been done, lightly sand to remove the remaining pieces. Sand all pieces out of the mold surface using care to mitigate damage to the tool surface.