Page 19 - PCMI Journal December 2020

Manufacturing Bespoke Aesthetic and Functional Surfaces via Photochemical Machining, Electrolytic Photoetching and Electrolytic Photopolishing Presented by: David M. Allen, Emeritus Professor of Microengineering, Cranfield University, UK
Visual contrast enhancement of graphics and text
Figure 3 illustrates the high contrast obtained in a micro-text etched with ferric
chloride into a polished, hard-rolled AISI 302 stainless steel disc. The 0.1 mm thick disc is 20 mm in diameter and the height of the 20-line text “RESEARCH IS A GAMBLE” (Figure 4) is 5 mm [3]. Thus, each letter is only 110 μm (≈4 mil) high but Dr Charles E. K. Mees’ humorous text is remarkably clear and easily legible when viewed through a x10 hand lens.
Figure 3. Visual contrast between etched characters and a reflective, rolled metal surface can be remarkably good even on microscopic text only 110 μm high [3].
It has been noted that varying ferric chloride and HCl concentrations affects the resultant surface finish of etched AISI 304 stainless steel. Allen has shown (Figure 5) that smoother etched surfaces are achieved at higher concentrations of ferric chloride and at HCl concentrations around 0.3-0.4% by weight [2]. Varying ferric chloride concentration and etch temperature also affects surface finish [2] as shown in Figure 6. These results were later confirmed by Visser and Weissinger (Figure 7) [4a].
Issue 136 December 2020 PCMI Journal 19