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Bottom view of the parts produced by both conventional mould tool (left) and AM mould tool (right)

In injection molding, parts are cooled by building channels throughout them. Those channels are typically straight lines, which can result in uneven cooling. Much more even, efficient cooling can be achieved with conformal cooling channels, which conform to the shape of the part. However, these types of channels are difficult to produce by conventional methods, making 3D printing an appealing alternative for the creation of injection molding tools. In a paper entitled “Conformal cooling by SLM to improve injection moulding,” a group of researchers use Selective Laser Melting to build conformal cooling channels in injection molding tools.

Specifically, the study aims to produce tooling for a support for pipette tips used in the medical industry. The main problem with conventional production of the part, the researchers explain, is a long cycle time, related to cooling difficulties on the thickest areas of the part.

“Furthermore, the high quantity of ejector pins on the core side creates additional problems since minimum distances must be kept from cooling channels,” the researchers continue. “To evaluate the impact of conformal cooling, numerical simulations were performed, providing excellent prospects concerning cycle time reduction.”

The plastic part they created for the study was a support for pipette tips, a rectangle with 12×8 housings for the tips, divided by thin walls. The part was designed to be stacked, with stronger outer storage walls. Trials were carried out with conventional manufacturing techniques, and certain thick spots at the intersection of the inner walls and the outer walls caused hot spots, where the material cooled slowly. This in turn caused sink marks and warping on the inner walls.

The researchers then re-engineered the mold to be produced with additive manufacturing, using a LaserCusing machine from Concept Laser. The two goals with the re-engineering were the reduction of cycle time and the prevention of warping. Using conformal cooling channels enabled them to reduce the cooling time from 35.5 seconds to 18 seconds.

“The second but not less important goal is to reduce temperature difference in order to prevent warpage,” the researchers state. Numerical results show that, with this design approach, temperature difference is significantly lower. The comparison between several nodal temperatures on different areas of the part shows that the highest temperature difference is now 10.6ºC.”

Overall cycle time had a significant reduction of 34.2%. The researchers also looked at the economic feasibility of producing injection mold tooling through 3D printing, and found that SLM costs as well as lead time were higher. However, manufacturing costs could be optimized if the cavity and core inserts were built in a single process. The researchers also foresee several other benefits to using additive manufacturing for the 3D printing of injection molding tools, including energy savings, scrap reduction, productivity and overall efficiency.

This study is not the first to confirm the effectiveness of using 3D printing to produce injection molding tools. Injection molding is an effective manufacturing technology in itself, but it has room for improvement, and additive manufacturing – rather than replacing injection molding completely – can improve it in a way that makes it even more efficient.

Authors of the paper include N. Reis, F.M. Barreiros, and J.C. Vasco.

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