Photochemical machining also known as PCM is a process that involves various important steps. Every step is an important condition for the next. Even though various companies that specialise in producing parts that use the photo chemical machining (PCM) process in Australia will usually be unique, the basic operations are typically similar.
Once a material is cut to a sheet size that is required it will be chemically cleaned to remove foreign debris, oil, grease, dust or any other types of contaminants to ensure the photoresist will be able to adhere to the surface of this metal. In the past, the more common types of cleaning techniques used on metal sheets associated with the PCM industry would involve solvent degreasing using solvents like trichloroethylene. However, the hazards to the environment soon became apparent and in the late part of the 80’s a company known as PEI was the very first of the PCM manufacturers that featured a facility that was solvent-free.
Currently, the majority of the metals are now cleaned with the use of mild soaps. This involves feeding the sheets of the metals through a 4-chamber or stage conveyor spray-machine. Each of the stages or chambers contains various concentrations of the cleaning agents including a 3-stage rinsing process after they have been cleaned. The rinsing process uses a high-pressure rinsing technique inside 2 of the chamber with the use of standard city water while the final rinse involves DI (Deionised) water. This last rinse makes sure that the metal is ready for the PCM process.
The following step involves applying the photoresist. This technique involves a dry-film photoresist that is rolled over the metal sheets that uses a lamination hot-roll system that sensitises the metal. This stage of the process the sheets of metal are processed within a safelight environment.
Developing the Photo Tool
Photochemical etching makes use of Mylar film to create a “working tool” compared to the “hard” tools that are used with metal stamping. Photo-tools can be created using a fully-dimensional drawing or a CAD file that features detailed dimensions. This process involves a tooling engineer that redraws the part. When the image is ready, it will be arrayed over the metal, and the image is used with a “laser photo-plotter” and then created onto the Mylar film.
In the area of printing the image is then transferred onto the sheets of metal in the way of activating a polymer in the photoresist. This is when the metal is placed between the photo tool (pieces of film), and this panel is then exposed to a UV light. Once printed onto the sheet it is moved to what is known as the wet-process area where it is developed.
Every sheet that has undergone a coating and exposure has to go now into the developing conveyorised system. Unexposed areas of the photoresist are then rinsed with an alkaline solution that exposes the metal that is bare that leaves resist on the areas that need protection from an etchant. This process produces a durable and adherent image on either side of the sheet of metal that will be equipped for the process of etching.