Photochemical machining (PCM) uses light and chemicals to etch images or cutouts on thin metal sheets. CAD software is used to create the design, which is transferred onto a laminate film. The metal is cleaned and laminated before being exposed to UV light and acid, creating the finished image.
Photochemical machining (PCM) involves creating etched images or designed cutouts using a computer process that exposes thin sheets of metal to light and various chemicals. Industries can use PC milling on virtually any type of sheet metal, including aluminum, brass or copper, as well as nickel and silver. Photochemical processing techniques can be used to produce delicate electronic components, medical implants or highly complex engravings. Rudimentary chemical etching with citric acid dates back thousands of years.
Engineers typically create the desired image using computer-aided design software, commonly called CAD drawing software. When used to cut particular parts, technicians replicate this pattern in columns and rows forming multiple images on a screen. The computer transfers the image onto a Mylar®-based laminate film with a silver emulsion coating. Before the photochemical processing, the chosen metal undergoes an accurate cleaning process, which guarantees adhesion to the photographic film. After being cleaned with a diluted solution, the sheet undergoes a water rinse and heat drying process.
When machining a complete metal cutout, technicians laminate, or sandwich, the piece of metal between two pieces of photo tool film. Only one side of the metal needs to be covered with foil when engraving or engraving. Technicians roll the metal using a dry roll or wet dip method. They use cameras during this process to ensure proper alignment of the metal and film. The laminate and phototool match identically in size.
The roll method involves passing the metal through a roll where the machine inserts the sheet between two pieces of laminate. Lamination requires contamination-free environments and the elimination of any air bubbles. The wet dip method involves dipping the metal in a liquid film and firing the plate in an oven to harden the film. The photochemical process continues by exposing the laminated metal to high intensity ultraviolet light, curing the image on the phototool.
After exposure, technicians expose the laminated metal to the developer solution, which removes any undeveloped laminate. Via a conveyor belt, the rolled metal enters a lined chamber with spray nozzles located above and below the conveyor. Hot etching acid sprays the metal from one or both sides, depending on the desired design. The acid dissolves unlaminated metal without leaving sharp edges or affecting the quality of the metal. This stage of the photochemical machining process creates the finished image formed on the CAD drawing.
The part now undergoes a water rinse and exposure to a stripping solution which removes any remaining laminate. The sheet goes through a final water rinse followed by a warm air dry. Technicians can use microscopes for a final inspection as a means of quality control.
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