Page 15 - PCMI Journal July 2018

David Allen | Emeritus Professor | Cranfield University | UK Photochemical Machining: Where has it come from, and where is it going?
Photochemical Machining: Where has it come from and where is it going?
Emeritus Professor David Allen, Cranfield University, UK
Abstract
The history and development of the photochemical machining (PCM) process is described together with predicted process developments that should lead to a more robust and versatile rapid manufacturing process for the future.
Introduction
Photochemical machining is generating a tremendous interest in production engineering circles due to its versatility, low cost [Tsang] and high resolution [Allen, 2016] and is playing an increasingly prominent part in the commercial world of miniaturisation in the twenty-first century [Micrometal].
Wikipedia (accessed 2017) states: “Photochemical machining (PCM), also known as photochemical
milling or photo etching, is a chemical milling process used to fabricate sheet metal components using a photoresist and etchants to corrosively machine away selected areas. This process emerged in the 1960s as an offshoot of the printed circuit board industry.”
However, I believe this statement is questionable and historical evidence suggests that it is incorrect. This paper aims to show that PCM is derived from photoengraving processes and not printed circuit board (PCB) production. It also explains why the PCM process is receiving considerable success as a rapid turnaround manufacturing process, especially in the fast-expanding field of microengineering, and looks forward to the implementation of the latest process developments that will extend the PCM process capability further for future products.
History
In the fifteenth century, a vinegar-based etchant was used in conjunction with a linseed oil paint acting as a maskant to decorate iron plate armour. Other maskants, or resists, were developed from waxes, resins and other natural products such that, a century later, the technique was being used for intaglio print-making by etching into iron or copper plates through a wax ‘ground’ cut with a needle-point. Intaglio printmaking was derived from observations that the contrast of an etched or engraved pattern on metal could be increased by filling the pattern with an ink or dye, enabling the craftsman to view the progress of the work in hand more readily. This concept was then exploited commercially as a method of printing by transferring the ink onto paper to form a reversed image.
The entire world thirsts for knowledge and the expression “Knowledge is power” has been attributed to Sir Francis Bacon (1561-1626).
Issue 131 July 2018 PCMI Journal 14