While 3D printing is definitely shaking up the way many products are manufactured, it will likely never be a permanent replacement for other technologies like injection molding, which is most often used in large volume plastic manufacturing. However, 3D printing can be combined with injection molding to save on both cost and time – this is achieved by 3D printing the molds rather than tooling them. The other good thing about 3D printed injection molds is their design flexibility – they can be easily modified by engineers and designers. Recently, Formlabs teamed up with injection molding machine manufacturer Galomb to print molds for several small parts on a Form 2, which were then fabricated with Galomb’s Model-B100 Injection Molder.
The companies then tested and demonstrated how viable the 3D printed injection molds were. Formlabs researchers detailed the project in a white paper, titled “Injection Molding from 3D Printed Molds,” which you can get for free here.
The abstract reads, “This white paper describes the production of small injection molded thermoplastic parts that were created with 3D-printed molds produced on a Form 2 printer and injected using a Galomb Model-B100 Injection Molder. Two mold designs were tested in Clear Resin: one of a large butterfly and one that produces four smaller butterflies in one shot. A third mold of a USB device enclosure was tested in High Temp resin. These molds were 3D printed by Formlabs and the injection molded parts were produced by Galomb Inc and Formlabs in a variety of materials.”
The team used Formlabs’ Clear Resin and High Temp Resin, the latter of which has been used before to make pewter casting molds, to print molds of the Formlabs butterfly logo and a USB device enclosure on the Form 2. SLA 3D printing creates chemically bonded pieces, so SLA functional molds have a higher quality than FDM molds. Galomb then tested the molds with 25 shots of thermoplastic LDPE, which has a low melt temperature. The white paper details that after the shots were injected, there was no noticeable surface deterioration of the molds.
The actual process, detailed above, seems pretty simple, but there are some issues that can crop up when you’re 3D printing injection molds. First of all, there are multiple factors that go into determining whether 3D printed molds will even hold up under the injection molding process, such as part geometry, the melt temperature of the injection material, and cooling and cycle time. While the LDPE material adhered to the resin molds in this experiment with no problem, other plastics may need a mold release agent applied to help with extraction, so the mold doesn’t deteriorate.
If the mold is opened too early and there is too much residual heat, the success of the mold may be compromised. When using molds printed with Clear Resin, higher melt temperature plastics can cause thermal shock, which will fracture the surface of the mold. Also, when the resin mold warps during the cooling phase after multiple shots, some shots exhibit flash – when the injected plastic is forced out between the two halves of the mold – at the split line.
To learn about the steps you can take to solve some of these common issues, as well as learn some helpful design guidelines for creating your own 3D printed injection molds, you can request a free copy of the Formlabs white paper here.
Discuss this and other 3D printing topics at 3DPrintBoard.com, or share your thoughts below.[Images: Formlabs]
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