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When cooling a plastic part, the fastest way is not a straight line!

May 23, 2018

The general public might be forgiven if they thought the plastic injection molding process is all about heat.  After all, you need a lot of heat to melt plastic resign, so it can be molded into any size or shape part you need, right?

What the GP doesn’t often think about is cooling, which is equally as important:  the cooling process is when the actual plastic part is created when it hardens into its final shape.  The cooling process affects cycle time, which affects efficiency, which, ultimately, affects profits.

Almost all injection mold dies are made with cooling channels that have been drilled from a block of solid steel, which later becomes the mold.  Cold water courses through these channels to cool the core, pulling heat away from the plastic part.  The conventional way to create these channels is by drilling a straight-line hole, and this is fine with a majority of simple-shaped plastic parts.  But when there is a complex shape to be molded these straight-line channels don’t draw away the heat as efficiently.

The answer to this problem is something called “conformal cooling.”  Conformal cooling utilizes non- straight-line channels which can “conform” to the contours of any shape.  These free-form channels draw away heat much more effectively than straight-line channels for irregularly-shaped parts which significantly reduces cycle times.

But drilling conformal channels the conventional way is challenging, if not impossible.  Enter metal 3D printing.  3D printing can produce metal molds — and cavities, such as holes — in any shape desired. Now metal 3D printing takes longer than conventional methods, and is thus more expensive, but these costs can be recouped due to the vastly improved cycle times and product quality of the end-product plastic part.  The conformal cooling channels are not only designed to closely follow the contours of the finished plastic part, they also stay close to the mold’s internal walls for greater cooling efficiency.

So what are the hard numbers related to conformal cooling vs. straight-line cooling? Simply put, the 3D printed molds performed significantly better than conventional straight-line molds, reducing cooling time by about 60%.  What’s more, conformal cooling improved product quality.

So apparently the fastest way to increased profits is not a straight-line, after all!



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