Right First Time – Photochemical Machining of Stainless Steels via Control of Ferric Chloride Chemistry

The etching of stainless steels is a mainstay of photochemical machining (PCM) commerce worldwide. However, as a class of materials designed to be corrosion-resistant, stainless steels are not easy to etch. This paper discusses the complex nature of ferric chloride etchant used to etch stainless steels and the control of its chemistry. In particular, the effects of changes in etchant concentration and temperature, free hydrochloric acid, dissolved by-products and spray pressure and distribution are analysed with respect to achieving a viable etch rate and an acceptable surface finish in a range of commercial stainless steels.