For tooling, an environmentally-friendly gel coat is followed by fiberglass or carbon fiber laminates. Once the laminate is in place, the part is bagged with a manifold in place. After the bag is sealed, the laminate is wetted out with the low VOC vinyl ester or epoxy, depending on the design. “Every void in the laminate is filled. The ability to keep the resin within the bag traps the emissions, preventing them from going airborne,” says Kennedy. While the company makes a few tools using epoxy resin systems that require an oven, most often, parts made with the environmentally-friendly vinyl ester resin are air cured unless higher service temperatures are required.
“We started using closed mold infusion as many of our customers are chasing weight reduction. But it’s a double win when you’re reducing the resin required by the part and limiting the volatiles released into the atmosphere,” adds Kennedy.
Marine Concepts is also studying the feasibility of applying additive manufacturing technology to mold building for yachts and large boats. Printing molds directly, rather than making a pattern from which the mold is then made, would eliminate the cost to manufacture the pattern and facilitate the use of more sustainable materials for the mold. “The idea is to bypass the pattern stage to make a mold that is strong enough for the boat builder to use 40 to 60 times,” says Kennedy.
For MCDC’s first dive into additive manufacturing, the company teamed with CNC and machining specialist Thermwood Corporation and White River Marine Group to test a large boat hull pattern. The 3D-printed pattern was completed using near net shape additive manufacturing.
The boat hull pattern was made in six sections – four major sections with walls approximately 1.5 inches thick and a printed transom and bow. These were pinned and bonded together before being machined as a single piece. The pattern was printed slightly oversized and then trimmed to final net size and shape. The print, assembly and trim process for the pattern required less than 10 days to complete – 30 hours to print and 50 hours to machine. After coating and finishing, the 3,000-pound pattern was used to produce a production-capable fiberglass mold for the boat hull.
Now MCDC is working with Cincinnati Inc., a build-to-order machine tool manufacturer, to use additive manufacturing for the production of patterns for the molds of boat hatches. The molds will then be used in a light resin transfer molding process to produce the final hatches. “Our goal here is to test the ability of the material – carbon fiber and acrylonitrile butadiene styrene – to handle the complex geometries the mold requires,” says Kennedy. “In the long term, we plan to go direct to tooling for these hatches with minimal milling, reducing the disposal of excess material.” The new technology will be jointly presented at IBEX 2019 in early October.