Page 22 - 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
Figure 7. Surface roughness as a function of ferric chloride concentration at an etchant temperature of 50°C [4a].
As independent studies by Abel [5] and Visser [4b] have shown that surface finishes of etched stainless steels do not depend on metal grain size, then to increase the surface roughness in the half-etch it is recommended to:
• lower the concentration of ferric chloride and/or
• lower the etchant temperature and to reduce the surface roughness to:
• increase the concentration of ferric chloride and/or
• increase the etchant temperature.
It is therefore possible to produce bespoke etched surfaces in stainless steel components with different Ra at different depths of etch, if required, using a different phototool set for each depth [6].
Half-etch fold-lines
The half-etch is also used in folding or bending sheet metal parts to create a third
dimension, especially in the forming of functional box-like structures. Figure 8a shows an aesthetic application; a 2019 Christmas decoration that incorporates both visual contrast and horizontal and vertical fold-lines for a folded 3-D fabrication (Figure 8b). These figures do not show two additional ID etched features on the back of the part; the name of the company that made the part and the year of fabrication.
Issue 136 December 2020 PCMI Journal 22