How to integrate glass machining in Industry 4.0?

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 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.

Among the established electrochemical technologies can be cited electrochemical (discharge) machining, electro-deposition/-forming and electropolishing. 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 (for example drill bits and clamps required to hold the workpiece in place during drilling). Hybrid technologies are very promising as these processes require little to no specialized tooling and can handle virtually any shape.

Hard-to-machine materials like glass and ceramics are challenging to integrate into industry 4.0, as there are only few efficient versatile technologies available to fulfil its machining requirements.

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. For long, glass was considered a ‘fourth state of matter’ before the realization of its ‘liquid-like’ structure. Glass appears on cooling down a liquid continuously until its viscosity becomes so high that it freezes to a glassy state. This happens at some range of temperatures that depends on thermal history, letting glass be a mysterious material, since the way it is prepared may change its properties.

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. 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 transparent, making it an excellent material for sensor and energy transmission devices. Another advantage of using glass in microfluidic MEMS devices is its relatively high heat resistance, which makes these devices suitable for high temperature microfluidic systems and sterilization by autoclaving.

Key in the new manufacturing paradigm ‘Industry 4.0’ is the fabrication of ultra-customized parts. Therefore it seems promising to consider glass as fabrication material. Glass can be transformed into very complex, unique shapes on demand by e.g. glassblowing techniques. In this sense, manufacturing of customized parts can be achieved. Nevertheless glassblowing techniques are very labour intensive and difficult to control by high degree of automation. Scaling down to the sub-millimeter and micron domain for glass features enabling customized MEMS devices of glass, other versatile technologies are needed. Unfortunately glass is a hard to machine material, due to its hardness and brittleness. In particular machining high-aspect ratio structures is still challenging due to long machining times, high machining costs and poor surface quality. Hybrid methods like Spark Assisted Chemical Engraving (SACE) 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.

Main requirement for fabrication of ultra-customized parts (batch-size 1) in any material, here glass, is the use of versatile machining methods which are cost-effective and precise. One has to keep in mind that not only the machining technology itself must be versatile, but in fact the complete process from the drawing of the part until the fabrication of the finished product. If one considers for example conventional CNC- milling technology, one can right away see a problem: the tooling. Since high forces are exerted on the work-piece to be machined, the required tooling has to be adequately engineered with sufficient precision, stiffness and mechanical strength, making it an expensive approach for batch-size 1 production of parts.

Even worse are technologies requiring highly specialized tooling such as for example injection molding or chemical processes needing masks. Such processes are excellent and unbeatable when it comes to mass production, but not suited for batch-size one production.

Considering both the machining requirements for glass micro-machining and the necessity for low-cost tooling, SACE appears a promising candidate among the available micromachining and manufacturing approaches. The ability to make use of low-cost tooling is due to its low forces exerted on the work-piece to be machined (typical in the sub-Newton range).

This technology has the potential to integrate glass machining in the Industry 4.0 approach.

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