The Shape of Cooling
An engineer who designs a mold to be made by traditional processes is working with two goals constantly in mind: that it be optimally functional and readily manufacturable. Frequently, reaching the second goal involves compromising the first.
In satisfying cooling requirements, the mold designer-constrained by needing to drill straight channels-chooses routes that circulate the greatest amounts of fluid as close to the mold surface as possible. But in this case, even the best solution is seldom the ideal solution: straight channels don’t always evenly cool curved surfaces in an efficient way. There can be potential hot spots, which can cause warped or distorted parts and also prolong cooling times. And since cooling times are a substantial portion of the molding cycle (up to 70 percent), those hot spots can seriously reduce production efficiency. That’s why more and more moldmakers are taking a serious look at how to manufacture channels that conform to the surface of the mold and go where they are most needed. The method of choice-because it is simple and lets engineers tap into the full potential of design-driven manufacturing-is direct metal laser-sintering (DMLS).
DMLS Makes Design-Driven Manufacturing Easy
DMLS frees the moldmaker to dispense with manufacturability issues and focus solely on creating channels that follow the optimum cooling path, no matter how it twists and turns along the mold surface. Here’s why: DMLS is an additive manufacturing process, not a cutting, drilling or grinding one. It builds parts from the bottom up, using data directly from a 3-D CAD model to guide the process. First the laser sintering system lays down a thin layer of powdered metal and melts a portion of it based on a cross-section taken from the model. It then spreads a layer on top of that one and sinters another cross-section, and another and so on, until the part is complete.
And except for surface finishing and a few other secondary operations, the part truly is complete. DMLS can grow a mold and its cooling channels at the same time, in one layer-by-layer operation. It’s not always faster than traditional manufacturing, but it can eliminate the need for drilling, EDM and other finishing work. And most importantly, it opens new frontiers for design. When conventional manufacturing reaches its limits, conformal cooling or DMLS turns complexity into simplicity.
Because the channels are not bound by manufacturing restrictions, and because DMLS can build parts with incredibly complex geometries, there is almost no limit to the path of a channel or its shape. Some engineers opt for channels with elliptical cross-sections to get greater heat transfer near the mold surface. Others put in ribs at points where they want to induce turbulence, increasing the Reynolds number of the flow. Always, the drive for optimized cooling guides design decisions.