One custom, compliant heat exchanger, coming best up!
[Thane Hunt] needed to find a way to make a variety of different heat-seal patterns on a fluid heat exchanger made from polyolefin film, and didn’t want all the lead time and expense of a conventional sealing press machined from a steel plate. Pattern prototyping implied that the typical method would not allow sufficient iteration speed and chose to take a CNC approach. Now, who can think of a common tool, capable of positioning in the X-Y plane, with a drivable Z axis and a controlled heat source? Of course, nowadays the answer is the common-or-garden FDM 3D printer. As luck would have it, [Thane] had an older device to experiment with, so with a little bit of nozzle sanding, and a sheet of rubber on the bed, it was good to go!
Custom seal path made in Onshape
Now, heat sealing is typically done in a heated press, with a former tool, which holds the material in place and gives a flat, even seal. certainly this CNC method isn’t going to achieve ideal results, but for proof-of-concept, it is just fine. A sacrificial nozzle was located (but as [Thane] admits, a length of M6 would do, in a pinch) and sanded flat, and parallel to the bed, to give a 3mm diameter contact patch. A silicone rubber sheet was placed on the bed, and the polyolefin film on top. The silicone helped to hold the bottom sheet in place, and gives some Z-axis compliancy to avoid overloading the motor driver. Ideally, the printer would have been modified even more to relocation this compliancy into the Z axis or the effector end, but that was much more work. With some smart 3D modelling, Cura was manipulated to generate the desired g-code (a series of Z axis plunges along a path) and a customized heated indenter was born!
This isn’t the first such use of a 3D printer we’ve seen, here’s an earlier failure, and like everything, there’s much more than one way to do it – here’s a method of making inflatable bladders with a defocused CO2 laser.
(warning! two minutes of a 3D printer head-banging into the bed!)