Chemical milling produces complex parts from hundreds of alloys in sheet or flat form and without imparting physical stresses on the materials or altering their ductility, hardness, grain structure, temper, or magnetic properties. This makes the process especially well suited for parts made from thin foils and brittle metals. Applications for chemical milling, also known as chemical etching or photochemical machining (PCM), include connectors, antennas, EMI/RFI shields, springs, and fine-resolution screens. PCM typically produces parts from 12 × 18-in. metal sheets, with part sizes ranging from a single component occupying an entire sheet to several thousand pieces per sheet. Certain materials allow machining parts up to 24 × 38 in.

The process works like this: Upon receiving sketches, drawings, or electronic files, engineers use CAD to make a pattern of repeated part designs. They laser-plot the pattern onto photographic film, creating what's called a photo tool, which can contain from one to several thousand images, depending on part size. Exposing the film to light transfers the images to a photosensitive, etchant-resistant polymer called photoresist, which coats the sheet of material. Spraying the sheet with a heated etching solution dissolves the metal not covered by photoresist, which leaves the completed parts.

PCM provides one of the fastest methods from print to part. In most cases, production orders take only two to three weeks. Prototype orders typically take a single day, giving engineering teams the flexibility to test and validate designs quickly. In fact, there is a seamless transitions between prototype and production runs because the process economically manufacturers both small and large quantities. This contrasts traditional methods, where one process handles prototypes and another handles production parts.

PCM also produces features to tolerances not typical to traditional manufacturing methods. For example, a rule-of-thumb for feature tolerances is ± 10% of the metal thickness. PCM handles step-etching part numbers and logos in metal surfaces to ± 0.0005-in. the depth of the step etch.

Lastly, photo tools cost around $250, which is considerably less expensive than laser-cutting set-up and engineering fees and the hard-tooling costs associated with stamping. Also, photo tools can be produced in few hours.