Some of the most impactful display graphics owe much of their appeal to the painstaking process of distortion printing. This article uses an actual job to describe the demanding workflow.
Heat transfers to the mold each time a sheet is formed. The mold becomes so hot after a small number of cycles (the forming and cooling of each sheet) that it will no longer adequately cool the plastic sheets that form on it. Not only is the plastic’s cooling time affected, but image location on the tool—its registration—also becomes uncontrollable. We use many inches of continuous 0.25-in. copper tubing in a serpentine pattern on the inner surface of the mold to prevent this build-up of heat. We insert thin wire segments into the vac-holes to prevent them from clogging during the next step.
We use a spray-metal process, much like blowing hot solder off of the tip of a soldering iron, to cover the copper tubing completely, thereby permanently bonding it to the casting in the thermally conductive metal. Once in production, temperature-controlled water will be circulated through the copper to cool the tool—just like the way antifreeze cools a car engine. The thin wire segments are then removed from the vac-holes, opening them up through the spray-metal inner layer of the casting.
The last step in mold fabrication is construction of the vacuum chamber beneath the casting. A 3-in.-deep box, sized to match the casting’s length and width, is constructed using thick lumber sidewalls and a birch-plywood-bottom panel. A 1.5-in.-diameter hole is drilled through the bottom panel and matching pipe-flange attached panel’s outside, creating a vacuum port. Two brass couplers are attached to a sidewall, to which the two ends of the coolant tube are plumbed. These are the coolant’s inlet and outlet. Internal joints are sealed with silicone, and then the casting is sealed and screwed to the completed vacuum box. In the final step, we check the vacuum box and the coolant line for leaks.
Did you enjoy this article? Click here to subscribe to the magazine.