Conformal cooling is prevalent in moldmaking. A primary driver of conformal cooling is the ability of a cooling circuit to follow the contour of the plastic molding cavity surface, yielding consistent cooling. Another driver is getting water into places that conventional milling and drilling will not allow. However, both benefits require creativity when it comes to creating complex contours, avoiding dead spots and promoting turbulent flow.
Conformal cooling also remains the top application of additive manufacturing in moldmaking—conformally-cooled 3D-printed mold inserts or additive tooling. Many mold builders have adopted additive tooling to differentiate their mold performance from the competition, but many designers hold onto the subtractive mindset, so the cooling circuits still look very conventional despite eliminating cross-drilled waterline plugs. Here is where additive tooling shines, as it enables limitless design constraints. However, conformal cooling is a delicate balance of creativity and convention. Conventional mold design standards are still important for maintaining design discipline to create highly-efficient cooling circuits.
For example, to maintain consistent cooling across the mold surface, keep cooling circuits consistently spaced apart. It is important to note that cold spots are possible in a mold, which, just like hot spots, can negatively impact molding performance. Consistency is key.
Things start to get interesting when working with circuit profiles because numerous options are available to promote more surface area and turbulent flow. Some profiles have internal grooves to maximize surface area while others have spiraling ramps that promote turbulent flow.
Most of these designs do not consider the build process and create features requiring supports that can restrict the cooling circuit flow or create sharp corners where concentrated stress could cause cracking. Elliptical or elongated cooling circuits are the best option for maximizing flow, achieving optimal thermal transfer and squeezing in between narrow steel sections that need the most cooling .
A controversial cooling circuit design is splitting circuits into several smaller channels and feeding them with a larger circuit from the mold. For example, a great way to minimize the number of circuits in a mold is to use a large inlet (¼-inch or ⅜-inch NPT waterline) that you break off into multiple waterlines and then rejoin at the exit.
However, with this design a circuit can get blocked and go undiscovered until the molder is producing bad parts. When you use a single circuit, you can easily monitor the in-and-out for flow and quickly identify any issues.
Another consideration when using multiple lines is the DMLS powder getting in the lines after a build. Multiple lines make it difficult to determine if all the powder evacuates prior to heat treatment. If the powder gets stuck in the circuit, shops must then scrap the insert. You can mitigate the risk of splitting waterlines internally by limiting the split section to less than one-third of the overall circuit length. This rule of thumb helps to maintain the larger flow and then splits the circuit only in the critical location required, enabling the powder to evacuate without the risk of a blockage.
Once you have an optimal circuit design, conduct a cooling simulation study to confirm effectiveness and then run FEA analysis to confirm the insert’s integrity and sufficient steel conditions for injection pressures. Taking this approach to circuit design identifies the most appropriate solution for the mold design before building the inserts.