The mirror manufacturing process starts with the delivery of clear, flat plastic sheets. The choice of supplier is very important, because only a handful of them are capable of producing mirror-grade substrate. Good mirrors can’t be made from standard-quality substrate. Once a manufacturer has the necessary raw materials, the five-step process of manufacturing can begin
1.) Thermoforming: This step requires plastic to be heated to a softened — not melted — condition. Then, an air-pressure differential is applied across it to stretch the plastic like an inflated balloon. This creates a stretched, spherical shape. The process control instruments precisely control the growth of that stretch by bouncing light off of it and then looking for reflections. Once the correct shape is achieved, the plastic is cooled to room temperature, where the polymer freezes and holds the shape. Making convex mirrors and domes fundamentally is the art of precision bubble blowing!
2.) Metallization: Once the appropriate curvature is achieved, the clear dome is made reflective through a process called vacuum metallization (also called vacuum deposition, vacuum evaporation or physical vapor deposition). In this step, the parts are placed into a vacuum chamber, which is pumped until it is void of virtually all air. The residual pressure in the chamber reaches one ten-millionth of an atmosphere — almost zero.
Once the air is out of the chamber and the incredibly low pressure is achieved, metal (typically aluminum or chrome or even occasionally 24-kt. gold) is heated and evaporated. The metal then physically travels across space from the source to the product. This is achieved by heating the metal from a solid to a liquid to a gas. It then re-condenses on the plastic part in an extremely thin, uniform coating of approximately 200 nanometers, making it reflective. To avoid holes in the mirror, this process must be perfectly clean, free of any dust or dirt.
3.) Protection: The metal layer, which is on the back side of the plastic, is so thin that any abuse or mechanical contact could result in damage. It can be protected with the application of a protective back coating over the metal to shield it both mechanically and chemically. Mirrors that are failing typical show gray or black spots in the mirror where they are no longer reflective. This is often due to water seeping in and attacking the metal. The paint application protects against that corrosive effect. Here again, a robot can apply the paint perfectly. The mirror must then bake in an oven. Baking provides a chemical cure of the paint, providing an extremely tight bond.
4.) Trimming: Trimming is most accurate when done with computer numerically controlled (CNC) cutting operations. This allows manufacturers to trim to the perfect dimensions.
5.) Shipping: When the product is finished, inspected and cleared for sale, it is shipped directly to the customer.
Strong manufacturing processes involve a combination of cutting-edge technology — much of which can be developed and innovated by the manufacturer — and tried-and-true craftsmanship. Experienced craftsmen who are trained on technologically advanced machines produce mirrors, lenses and domes that achieve a remarkable degree of durability and longevity.