Whether for aerospace components, prototypes in automotive manufacturing or chemical engineering, conventional industrial manufacturing processes come up against their limits wherever small component lots contributing high value are concerned. In situations like this, 3D printing enables considerable cost savings as well as new design options. In future, 3M will be offering precisely that for fully fluorinated polymers such as polytetrafluorethylene (PTFE).
The industry has been striving for years to manufacture components in ever bigger lots. Optimised production processes involve very high start-up costs for tools and require complex steps to be programmed. These costs are recovered very quickly, however, owing to the scale effects which result from the manufacture of hundreds of thousands or even millions of the same component. The most common processes are thermal ones in which metals or plastics are fluidised and cast in prefabricated moulds. They are often subtractively machined afterwards. Special tools such as drills or milling heads remove material until the desired geometries are achieved.
Limits of conventional manufacturing
These conventional manufacturing processes require a lead time, for example for ordering tools and programming the machining operations. Furthermore, design engineers are obliged to ensure that components can be manufactured using conventional methods. More complex components with several functions therefore generally consist of various individual parts that must be assembled afterwards. This in turn creates sealing points.
Non-melt-processable materials necessitate subtractive machining from blanks. This produces considerable quantities of unusable production waste – which is very uneconomical when expensive materials are a must. A further disadvantage is that moulded PTFE parts manufactured in the conventional way are almost always solid, thereby increasing the component weight. This is detrimental for aerospace or automotive engineering, where every additional gram counts.
Small lot sizes
In contrast to established large-scale manufacturing, the trend in Industry 4.0 is moving towards economical production of very small lots. Additive manufacturing is an important link in a digital engineering chain. In future, it will be possible to manufacture lightweight, ready-to-install, multifunctional moulded parts from CAD data in a single step, avoiding tool costs and long lead times.
In additive manufacturing without tools, the parts are printed in 3D. Based on digital design data, each component is built up layer by layer through the deposition of material. Unlike in the private sector, additive manufacturing processes are already widely accepted in numerous industrial applications. The first factory to use exclusively additive processes opened this year in Germany. Serial parts are already being printed for aerospace engines, while the automotive industry is shortening the development times for prototypes with the help of 3D printing technology.
PTFE for extreme requirements
In view of the above, this manufacturing process is highly attractive for the family of fully fluorinated polymers such as PTFE, which are almost universally chemically resistant. Their operating temperature range exceeds 500 °C, covering temperatures from -250 to +260 °C. PTFE is practically non-flammable. Its long-chain structure and high density lead to very good sealing properties. The electrical properties are equally good. PTFE and other fully fluorinated materials can be used when all other alternatives fail to meet the requirements. They add considerable value, for example as reliable and durable seals or linings. Fuel systems involving high temperatures as well as corrosion protection or sealing applications in processing plants utilising aggressive chemicals are just two of the typical applications.
Industrial users and drivers of additive manufacturing technologies are at the same time important purchasers of PTFE products. However, it has not been possible to process PTFE using conventional additive processes in the past. 3M has now developed a technology for manufacturing PTFE parts without tools on a conventional 3D printer. Out of the various processes investigated, it was stereolithography that proved to be most promising for processing PTFE. In the process developed by 3M the fully fluorinated polymer (in this case PTFE) is printed with the aid of a binding agent to form a so-called hydrogel. The binding agent is photosensitive, hardens under UV radiation and is thermally removed after printing. 3M currently prints moulded parts up to 35 x 30 x 55 mm in size with the 3D laboratory printer.
Density of printed moulded parts
Many properties of the components manufactured on the 3D laboratory printer exhibit a comparable profile to conventional PTFE moulded parts. Some properties may even be superior. Examinations of moulded parts around 1.4 mm thick show components manufactured without tools reaching density values of 2.12 to 2.17 g/cm³. These values are comparable to those of conventionally manufactured moulded parts. Neither pores nor cavities are discernible in scanning electron microscope images of printed and conventional moulded parts. Printed moulded parts offer the same virtually universal chemical resistance as their conventional counterparts.
PTFE processing by means of additive manufacturing opens up new options for fast and inexpensive production of very small series or even one-offs. Manufacturers can thus design complex shapes, reduce weights and advance the integration of functions, to name but a few of the benefits. Above all else, manufacturers and users will in future save time because they will be able to print moulded parts directly from the CAD data, for example in order to manufacture PTFE prototypes or spare parts.
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