Page 17 - PCMI Journal December 2020

Manufacturing bespoke aesthetic and functional surfaces via photochemical machining, electrolytic photoetching and electrolytic photopolishing
Manufacturing Bespoke Aesthetic and Functional Surfaces via Photochemical Machining,
teEclehcntriqoluyetisc Photoetching and Electrolytic Photopolishing
David M. Allen
Presented by: David M. Allen, Emeritus Professor of Microengineering, Cranfield University, UK
Emeritus Professor of Microengineering, Cranfield University, UK (Presented at the Virtual PCMI Conference on Monday 19th October 2020)
Abstract
This paper reviews an aspect of photoetching that is rarely discussed. There is an
increasing need in manufacturing and micromachining applications to produce specific types of surfaces for either aesthetic or functional requirements including:
• non-directional, light-scattering, matt surface finishes for visual contrast enhancement in a half-etch,
• smooth surface finishes for optical reflection, laminar flow in microfluidic devices and particle filtration applications,
• very rough textured surfaces for abrasive applications and
• textured surfaces to reduce friction and wear for tribological requirements.
Examples of the above bespoke surfaces and their methods of fabrication using photochemical machining, electrolytic photoetching and electrolytic photopolishing are discussed.
Introduction
PCM is usually associated with the fabrication of metal components of a specific shape
and form. However, this paper considers a further aspect of photofabrication; that of producing bespoke surface finishes and surface textures. The term “bespoke”, implies “specific surface parameters requested by the customer”; in other words, a “tailored surface” to fit the customer demand.
We often take surfaces for granted but they can provide additional special properties to parts that are now becoming increasingly sophisticated, requiring extremely tight control in part manufacture to meet new, tighter specifications particularly in microengineering applications.
Examples of half-etch structures include:
• Visual contrast enhancement of graphics and text (including logos and machine-
readable ID and bar codes)
• Surfaces for quantitative contrast analysis
• Fold lines
• Multi-depth (step) etching
• Functional channels and pipes for fluid flow.
In PCM we are usually concerned with undercut (affecting dimensional control) and depth of etch (affecting metal thickness). We aim to achieve a high etch factor (depth of etch divided by undercut) by minimising undercut. This paper concentrates on control of depth of etch and surface finish in the “half-etch”.
Stainless steel half-etch applications
It must be realised that an etched surface finish on stainless steel is rough initially, due
to the presence of an etch-resistant chromium-rich oxide layer on the metal surface. As more
Issue 136 December 2020 PCMI Journal 17