Bracing materials range from wood to metal tubes/squares and should be designed to provide added mold stiffness and strength. A word of caution: Keep tab thicknesses to a minimum so as not to transfer any shock (thermal or mechanical) onto the mold surface. Cracked/broken tabs are easily repaired while in production. Gel coat repairs on molds, caused from external damage, will require the molds to be pulled from production.
Composite Mold Maintenance
Mold maintenance typically consists of:
- Training employees on demolding and mold maintenance.
- Cleaning off excess material and debris, blowing off and/or wiping down dust.
- Inspecting for mold damage or defects. (Small damage areas may be clayed to maintain schedules.)
- Performing preventative maintenance. Paste wax or reapply mold release as needed.
- Recording and tracking mold use and maintenance data, along with any needed repairs.
- Covering mold for storage, preferably not outside.
Mold sealers and releases take many forms and are often neglected. Today, most FRP composite manufacturers use “semi-permanent” type mold releases. In higher volume production operations, most manufacturers have standard maintenance that includes an accurate accounting of the number of cycles that a mold has experienced, especially in “low draft angle” molds. You should discuss best practices with your mold release manufacturer, but one best practice to live by is the 80 percent rule: For instance, if production discovers that 30 parts can be pulled from a mold before sticking, then reapply mold release after the 24th pull.
Running the mold until failure or repairing every part becomes expensive and limits product quality, so it should be avoided! Having a preventive maintenance system in place and training personnel is key. Proper demolding procedures and training will significantly improve FRP mold longevity, lower repair time and ensure employee safety.
Mold Making Innovations
Controlled shrink tooling materials include older, but still popular ATH filled systems (generally limited to 18 to 25 percent glass fiber by weight). Newer unfilled systems allow a much higher glass fiber content (40 percent glass fiber by weight), and the latest, infused versions allow up to 70 percent glass or carbon fiber content, along with the inclusion of well-consolidated core materials.
Many of these higher fiber content materials are finding a home in both traditional composite markets, as well as in the prepreg, 350 F cure temp markets and the thermoforming area (where temperatures in excess of 400 F are common). Thermal shock-resistant tooling gel coats are highly suggested for these applications.