Thomas Vacca
Director of Engineering

Panel Photochemical Etching

We received a quote request from one of our largest customers for a high-volume thin-gauge part, and the feature sizes appear to be challenging to stamp within our comfort level. The tool will require very tiny punches and small die cavities, causing us concern over breakage, costly downtime and excessive maintenance. Do you have any advice for us before we turn down this request for low-volume prototypes?

When facing what seems to be a component-design nightmare, stampers might consider photochemical etching, also known as photochemical machining. Panel photochemical etching is an inexpensive way to fabricate a medium quantity of parts for evaluation prior to building a production stamping tool. The beauty of this process: It can create fine features for complex parts, small or large. Tooling costs are a fraction of the cost of hard tooling, and stampers can make design changes to the parts quickly on the fly. As the process employs optically based tooling, part complexity does not drive higher tool cost as it does with conventional stamping.  

Processing chemically etched sheet metal employs techniques common to those used in circuit-board manufacturing.  Both sides of the sheet are coated with photoresist and placed between two pieces of patterned film or glass. The metal is then exposed to ultraviolet light, and when the material is developed the unexposed resist is removed to create the bare metal areas that etching will remove. After etching, the remaining resist is removed and the finished part cleaned and dried.

The process is burr- and stress-free, so it does not introduce distortion into the part. It can create multitudes of tiny holes and features all at the same time, rather than punching progressively one segment at a time as with stamping. The temper of the material does not affect the process, while temper can significantly affect stamping-tool design. 

Potential feature sizes and tolerancing with photochemical etching depend largely on the raw-material stock thickness. For convenience, ratios can be used for preliminary design: Hole diameter can be 1.2 times sheet thickness or larger, and distance between features can be 1.0 times sheet thickness or greater.  The tolerance on some features can be as low as ±5 micro-in., depending on feature size and material thickness. Etching a feature from only one side can produce a razor-sharp edge, flow channels or a half-edge thickness connection for easy manual part removal, and text can be added for part identification.