Most Replex mirrors are made with a thermoforming process called free blowing. Free blowing uses heat and differential air pressure to manipulate plastic into specific shapes that will eventually become mirrors.
Before work begins, an intellectual collaboration takes place to decide what kind of tooling will be designed and built, depending on the customer’s needs and the specifications of the product.
With thermoforming—like much of the work that takes place at Replex—it is imperative to maintain pristine surface quality. Any minor speck or particle could result in a blemish that would be dramatically magnified when the mirror is finished.
Free Blowing: Shaping without Touching
We start with substrate, which is a sheet of raw material made of either acrylic or polycarbonate. The substrate is gripped around the perimeter, heated, and then subjected to a pressure differential. This pressure differential is created either by pulling a vacuum or injecting compressed air on one side of the heated substrate and atmospheric pressure on the other side. This stretches the substrate and causes it to form a bubble.
Nothing solid ever touches the bubble.
The growth of the bubble is continuously monitored from the very beginning by optical sensors. This allows us to control the bubble’s growth accurately and precisely without ever contacting it. Any contact could create the risk of contaminating the pristine surface of the material.
When the substrate cools, the bubble maintains its shape and the process is complete.
Although free blowing is the preferred method used to create round, spherical shapes, it is a singularly focused protocol that does come with limitations. Free blowing does not excel at making certain shapes, such as the unique ellipsoidal shapes of some truck mirrors or the parabolic shapes of solar concentrator mirrors. Free blowing is a specialty method that does one thing very well: spherically shaped domes.