Electrochemical Manufacturing to Support Industry 4.0 – Spark Assisted Chemical Engraving (SACE)
Authors: Hof Lucas Abia , Wüthrich Rolf 
Published: February 2020

Manufacturing industry is facing new challenges as there is a growing demand for mass-personalized products at low cost. A new kind of processes need to be developed. This new revolution was recognized recently by industry and in Germany the key word industry 4.0 [1] was introduced to characterize this “fourth industrial revolution” for the entire manufacturing value chain. A major hurdle to overcome for successful production of mass personalized products are setup and tooling costs.
According to recent studies (made by the Universities of Michigan and Cincinnati for the World Economic Forum) hybrid technologies, including electrochemical technologies, are promising to address these manufacturing challenges [2]. Among the established electrochemical technologies can be cited electrochemical (discharge) machining, electro-deposition/-forming and electropolishing e.g. as post-process for metal additive manufactured (AM) parts. None is yet used for mass personalisation, where the custom products are no longer an assembly of individual parts (i.e. modular design), but they are fully personalized, i.e. the shapes of the parts change too.
Suitable manufacturing processes for personalized batch-size-1 production must be highly flexible and have little overhead, particularly for the tooling. Hybrid technologies are very promising as these processes require little to no specialized tooling and can handle virtually any shape, including inner surfaces.
At the same time, glass, existing for millions of years in its natural form, has fascinated and attracted much interest from both the academic and industrial world. The application of glass science to the improvement of industrial tools occurred only in the past century, with a few exceptions. Glass has been employed in many forms to fabricate glazing and containers for centuries while it is now entering new applications that are appearing in micro and even nanotechnology like fibers, displays and Micro-Electro-Mechanical-System (MEMS) devices [3]. Many qualities make glass attractive since it is transparent, chemically inert, environmentally friendly and its mechanical strength and thermal properties. In fact, no other materials being mass-produced have shown such qualities over so many centuries. Nowadays glass offers recycling opportunities and allows for tailoring new and dedicated applications. Moreover, glass is radio frequency (RF) transparent, making it an excellent material for sensor and energy transmission devices. Another advantage of using glass in microfluidic MEMS devices [4] is its relatively high heat resistance, which makes these devices suitable for high temperature microfluidic systems [5] and sterilization by autoclaving.
However, glass is a hard to machine material, due to its hardness and brittleness. Machining high-aspect ratio structures is still challenging due to long machining times, high machining costs and poor surface quality [6]. Hybrid methods like Spark Assisted Chemical Engraving (SACE) [7] perform well to machine high aspect ratio and smooth surface structures on glass. These assets of SACE technology combined with its relative high machining speeds compared to chemical methods and low-cost compared to femto-laser technologies make SACE perfectly suitable for rapid prototyping of micro-scale glass devices.
In this thermochemical process, a voltage is applied between tool- and counter-electrode dipped in an alkaline solution (typical NaOH or KOH). At high voltages (around 30 V), the bubbles evolving around the tool electrode coalesce into a gas film and discharges occur from the tool to the electrolyte through it. Glass machining becomes possible due to thermally promoted etching (breaking of the Si-O-Si bond) [7].
In the present communication, it is shown how electrochemical processes can be used to design new high precision manufacturing processes for industry 4.0. In particular hybrid machining by SACE technology is discussed for hard-to-machine materials like glass. Some other examples are highlighted as well in the field of post-processing technologies for metal AM parts and fabrication of high-precision complex metal structures based on 3D printed high resolution polymer models.
[1] Deloitte, “Industry 4.0. Challenges and solutions for the digital transformation and use of exponential technologies”, Deloitte, pp. 1–30, 2015.
[2] J. Ni, J. Lee “Emerging and Disruptive Technologies for the Future of Manufacturing” Case study no.7 World Economic Forum Global Agenda Council on the Future of Manufacturing
[3] E. Le Bourhis, “Glass, Mechanics and Technology.”, Wiley-VCH, 2014.
[4] G. M. Whitesides, “The origins and the future of microfluidics.”, Nature, vol. 442, no. 7101, pp. 368–373, 2006.
[5] D. Sinton, “Energy: the microfluidic frontier.”, Lab Chip, vol. 14, no. 17, 2014.
[6] L. Hof, J. D. Abou Ziki, “Micro-hole drilling on glass substrates – a review”, Micromachines, vol. 8, no.53, 2017.
[7] R. Wüthrich and J. D. Abou Ziki, “Micromachining Using Electrochemical Discharge Phenomenon.”,
Elsevier, 2015.

Figure 1