Thermwood & Purdue Compression Mold Parts Using Printed Tooling
Thermwood and Purdue’s Composite Manufacturing & Simulation Center have been working together to develop and test methods of using 3D printed composite molds for the compression molding of thermoset parts. They have just announced that they have successfully been able to compression mold test parts using 3D printed composite tooling.

The test part, a half scale thrust reverser blocker door for a jet engine, was designed at Purdue and is approximately 10” x 13” x 2” in size. The two-part matched compression mold for the part was 3D printed using Techmer PM 25% carbon fiber reinforced PESU at Thermwood, using its LSAM large scale additive manufacturing system.

The mold halves were then machined to final size and shape on the same system. The completed tool was next taken to Purdue’s Composite Manufacturing & Simulation Center, in West Lafayette Indiana, where it was mounted to their 250-ton compression press. Parts were then molded from Dow’s new Vorafuse prepreg platelet material system with over 50% carbon fiber volume fraction.

Both halves of the mold were printed at the same time. When using Thermwood’s “continuous cooling” printprocess, the polymer cooling determines the cycle time for each layer, allowing both halves to be printed in the same time it would take to print one half (since both parts could be printed in the layer cooling time available).

Machining, however, must be done in the traditional manner, one part at a time, although there is an advantage to machining printed parts. Since the part is printed to near net shape, the overall amount of material that must be removed is significantly less than if the tool was machined from a solid block.

The team determined that using printed composite molds in a compression press does require a significantly different approach than a tool for the same part machined from a block of metal. The tool must be internally heated since the polymer composite doesn’t transmit heat as well as metal.

A special heat control allows the temperature of various areas of the tool to be controlled independently, helping address the challenge of balancing the thermal characteristics of the thermoplastic composite mold with the processing temperature requirements of the thermoset material being processed.

Also, the outside of the mold must be reinforced so that the composite polymer used for the mold itself is under only compression loads and not tension during the molding operation, since forces developed during molding are greater than the tensile strength of the composite polymers used for the mold. This approach has successfully withstood molding pressure of 1,500 PSI during initial testing and the team believes even higher pressures are possible.

The speed and relatively low cost of printed compression tools has the potential to significantly modify current industry practices. Printed tools are ideal for prototyping and can potentially avoid problems with long lead time, expensive production tools by validating the design before a final version is built.

Potential applications in the auto industry include prototyping and production tool verification. Because of high volume requirements for auto production, it is unlikely that these tools would function adequately for full production use, but actual useful production life is still unknown.

In aerospace, parts tend to be much larger and production volumes much lower, so it is possible that printed compression molds could find actual production use for larger, lower volume aerospace components, perhaps replacing open face tools and autoclaves for certain parts.

For more information, contact Duane Marrett, Thermwood Corporation, 904 Buffaloville Rd., Dale, IN 47523, 800-533-6901, E-mail: duane.marrett@thermwood.com, Web: www.thermwood.com.