Machine manufacturer Thermwood has achieved a milestone in the development of 3D printed composite molds for compression molding. The company, working in collaboration with Purdue’s Composite Manufacturing & Simulation Center, has successfully compression molded tests parts using 3D printed composite tooling. The project marks a step ahead for the use of 3D printed molds for compression molding thermoset parts.
The successful test part was a half-scale thrust reverser blocker door for a jet engine which was designed by a team at Purdue. The scaled down part—measuring 10 x 13 x 2 inches—was created using a two-piece compression mold 3D printed by Thermwood using Techmer PM 25% carbon fiber-reinforced PESU and its Large Scale Additive Manufacturing system (LSAM).
The LSAM system 3D printed both halves of the compression mold and finished them by machining the parts to their final dimensions. The halves were printed simultaneously and completed within just over 2.5 hours. This speed was achieved thanks to Thermwood’s “continuous cooling” process which allowed for both halves to be printed at once within the layer cooling time. In other words, both halves were printed in the same time it would take to print a single half.
The subsequent machining was more traditional—the tooling halves had to be machined individually—though because the mold was printed to near net shape, the machining was minimal. According to Thermwood, the machining process took roughly 27 hours.
When the tooling was complete, it was delivered to Purdue’s Composite Manufacturing & Simulation Center where it was mounted to its 250 ton compression press. The final component was molded from Dow’s Vorafuse prepreg platelet material system with over 50% carbon fiber volume fraction.
Second try’s a charm
The successful run was, as one would expect, not the first try. As Thermwood explains, the first attempt at compression molding failed. This failure enabled the partners to adjust certain steps of the process to account for the mechanical and thermal conductivity of the polymer printing material. The second try was a much greater success, resulting in acceptable parts.
One of the adjustments that proved to be critical was integrating cartridge heaters into the tooling. Compared to metal tools, polymer tools do not conduct heat effectively, meaning they must be heated internally for the compression press. Thermwood developed a method to bore deep holes into the printed composite tool (using the LSAM’s trim head), which meant that heating cartridges could be inserted.
The team also integrated special heat controls to help balance the thermal characteristics of the thermoplastic composite mold to match the processing temperature requirements of the molded thermoset.
In order to successfully compression mold the part, the outside of the mold also had to be reinforced so that the composite polymer was only subjected to compression loads and not tension. By reinforcing the mold, Thermwood and Purdue were able to put the mold under pressures of 1,500 PSI during initial testing without negative effect.
AM and compression molding
The success of the joint project between Thermwood and Purdue has led the partners to believe that additive manufacturing could become an important manufacturing technique for compression molding applications.
“The speed and relatively low cost of printed compression tools has the potential to significantly modify current industry practices,” Thermwood wrote on its blog. “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.”
The partners will continue to work on smoothing out kinks in the process and tool design to further demonstrate the viability of the approach. In the near future, the technique could be used in the automotive industry for prototyping and production tool verification. In the aerospace industry, printed compression molds could be used for production applications for large-scale, low-volume parts. At this stage, it is unclear whether the composite 3D printed molds would be suitable for volume production.