In the world of material processing, the photo chemical machining process has become a popular means of creating intricate designs in metals. Also called chemical milling or photo etching, it is a subtractive manufacturing method that uses photoresist and chemical etchants to produce thin, flat metal parts with precise dimensions.
In this process, a metal is coated with a light-sensitive film called photoresist and exposed to a high-resolution image of the desired pattern. The unexposed areas of the photoresist can be washed away, leaving the metal surface open for etching. The exposed areas remain protected by the photoresist layer and remain unetched. With the use of chemical etchants, the metal is then etched where the photoresist has been removed.
The photo chemical machining process has numerous advantages, including high accuracy, repeatability, and the ability to create complex designs. It leaves no detectable thermal or mechanical damage, has negligible undercutting, and requires no additional post-processing. Moreover, this process has no burrs, the edge quality is excellent, and there is no significant material loss, resulting in a net-shape product.
At the heart of the photo chemical machining process is the photoresist, which is applied directly to the surface of the metal to be etched. This photoresist is a light-sensitive polymer that will harden when exposed to UV radiation. The resist can be either positive or negative.
In positive photoresist, the areas exposed to UV radiation become polymerized, and these areas remain on the surface of the metal. The unexposed areas are removed, allowing the underlying metal to be removed by etching. Negative photoresists work oppositely. The areas exposed to UV radiation are removed, leaving a protective layer of photoresist over the metal to be etched.
The photoresist is typically applied in a thin layer, around 5-50µm, and is coated uniformly over the surface of the metal. The resist is usually applied using either the spin-coating process or the spray-coating technique. The metal substrate is then exposed to an image to be etched. The image is projected onto the surface of the photoresist, usually by using a mask or photomask.
Once the photoresist is developed, it leaves a pattern of the metal exposed through a photographic process. The exposed metal is now ready for etching. Chemical etching is a process that entails immersing the metal in a solution that dissolves it at a precise rate. This solution is usually an acid or alkali solution that causes a chemical reaction with the exposed metal surface that dissolves it.
Precisely controlling the etchant solution’s composition and temperature during the process ensures high etching accuracy and repeatability. The etch rate can be varied to attain varying depths to suit the final product’s design requirements.
With the etchant solution selectively attacking exposed metal regions, the unexposed or still-protected areas of metal are left unscathed. As a result, intricate designs with precisely shaped features can be created.
Once the etching process is completed, the remaining photoresist is removed. At this point, the metal product can undergo additional processing in a secondary phase to further refine its surface, add additional features, or improve its mechanical properties.
In summary, the photo chemical machining process is an established manufacturing process with many advantages like high accuracy, repeatability, and versatility in creating precise, intricate parts from various metals. The process starts with the application of a photoresist onto the surface of the metal, followed by exposure with high precision images and etching of the metal substrate. The photoresist is then stripped off, leaving behind the intricate pattern in the metal. With modern technology, the photo chemical machining process has become increasingly efficient, making it a top choice for many applications.