The printed sections of this test mould are made of carbon fibre reinforced ABS from Techmer PM. ABS was chosen because of its physical properties and relatively low cost compared to other reinforced thermoplastics.
The story so far
Thermwood has already 3D printed a full size pleasure boat master pattern which has been used to produce multiple production boat hull moulds. While this demonstrated the value of additive manufacturing small boat tooling, much larger vessels, yachts for example, require a different approach. In these instances, since only a single mould is needed, it is desirable to print the mould itself rather than print a plug or pattern from which multiple production moulds can be made.
To demonstrate to the industry how this might work, Thermwood printed a 10ft section from a 51ft long yacht hull mould. This rather unique mould design was specifically developed for additive manufacturing. It is printed in sections, each about 5ft tall. These printed sections are then bound together both chemically and mechanically using high strength polymer cables into two mould halves. The two mould halves then bolt together to form a complete female mould for the yacht hull.
There are several interesting aspects to this design. First, each mould section has a moulded in rocker. When the mould is fully assembled, it rests on the floor on these rockers. At this point, the mould can be rolled over to tilt about 45° to either side, kind of like a giant rocking chair. This allows for easier access during the layup process. A set of moulded wedges are clamped to the rockers to hold the mould in the desired position. Once the hull has been laid up and fully cured, the mould is rolled to level and the printed wedges are clamped to both sides, holding them level. Then the two mould sides can be un-bolted and slid apart to release the finished boat hull.
The test pieces Thermwood printed show that this approach will work in practice. The printed sections of this test mould are made of carbon fibre reinforced ABS from Techmer PM. ABS was chosen because of its physical properties and relatively low cost compared to other reinforced thermoplastics.
Certain thermosets will work directly on the ABS moulded surface using just traditional mould release practices. However, other thermoset materials are based on solvents that can chemically attack the ABS polymer. To prevent this, Thermwood has experimented with several protective coatings including traditional mould gel coats. While virtually all coatings tested worked at room temperature, large thermoset moulds often experience some heat as a result of the exothermic reaction that occurs during the thermoset curing process. Thermwood tested each of the coatings at 200°F and found that some worked at both room and elevated temperature, while others that worked at room temperature did not work well at the elevated temperature.
While it appears that this approach will work today for certain thermosets, the ideal would be to develop a low cost polymer that is chemically resistant to the other thermoset solvents and eliminate the need for a protective coating.
The fine details
These demonstration pieces were printed and trimmed on Thermwood’s 10 x 10ft LSAM MT, the smallest and lowest cost additive manufacturing system currently available from Thermwood. The entire mould section, made of four printed pieces, weighs 4,012lbs and required 65.5 hours to print. The initial idea was to use this as the centrepiece of Thermwood’s additive manufacturing tradeshow presentation, however, with the cancellation of tradeshows, it has become more of a showpiece for visitors and prospective customers at Thermwood.
The bottom line
This demonstration shows that, if you need a really large part, you don’t necessarily need a really large machine. With a little imagination and some creative engineering, really large structures can be made, even on smaller, lower cost additive manufacturing systems. While the LSAM MT is not all that small, it does fit the needs of a lot of companies who would like to make larger parts but can’t quite handle Thermwood’s really large systems.
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