As stated earlier, the production manufacturing process of the final parts significantly influences plug and mold-making decisions. Traditional open molding molds usually provide the lowest cost entry because you only need to build a single mold – generally called the A-side – which gets you to part production faster. Closed molding processes can offer improved back side surfaces, especially when a rigid counter-mold (RTM or light RTM) is built off of the A-side mold.
RTM offers many benefits, including improved dimensional control (part thickness), better resin-to-fiber ratio, reduced void content, cleaner working conditions and reduced emissions during part production. However, there are significant additional costs in making two molds instead of one. Further, the required flange detail, vacuum seals and various ports for resin and vacuum also increase the costs and time associated with building RTM and light RTM counter-molds. Those costs generally are negated by process and production improvements.
Another closed molding option is vacuum infusion processing (VIP). VIP has the lowest entry point costs for closed molding, but it is likely the most expensive process in the long term because VIP is inherently tied to a plethora of disposable materials, such as film, peel ply, resin feed lines, vacuum feed lines and sealant tape. However, VIP only requires building one mold. In addition, the process is very forgiving in laminate and core modifications as the film allows for those modifications.
The guidance above certainly doesn’t cover all the complexities of mold design and plug production. Every mold-building project is nuanced and presents different challenges. It’s important that composite manufacturers keep up to date on new technologies and materials that can lower costs and increase capabilities. Check out our column in the next issue for information on some of the latest advancements in mold making.
Disclaimer: Opinions, statements and technical information within the Best Practices column are that of the authors. ACMA makes no warranty of any kind, expressed or implied, with respect to information in the column, including fitness for a particular purpose. Persons using the information within the column assume all risk and liability for any losses, damages, claims or expenses resulting from such use.
The Composites Certification Program offers training books for various manufacturing processes, including opening molding, VIP and light RTM. Certifications also are available that enable composites professionals to demonstrate knowledge in these areas. Find out more at cct.acmanet.org.