High accelerations and up to 80 °C: Reliable linear bearings for 3D printers

Founded in 2012, Kühling&Kühling sells its customers flexible and easily scalable 3D manufacturing solutions. For the realisation of the first series-produced 3D printer, the Kiel-based solution expert was looking for an energy chain for safe cable routing and a suitable liner bearing solution. The demands of a 3D printer on the bearing technology are high: the high performance of the machines requires moving components that can withstand high accelerations over a long period of time without any problems and with as little maintenance as possible. In addition, the dynamic inner workings also result in enormous temperatures of up to 80 °C, for which the right materials had to be found. Finally, the built-in parts also had to fulfil the high requirements in terms of quietness.

The company Kühling&Kühling, based in Kiel, has been one of them since 2012. The two founders, mechatronics engineers Jonas and Simon Kühling, specialise in open source hardware development and production in the field of 3D printers. After one and a half years of development, the first product, the "RepRap Industrial", has been in series production since the end of 2013. It is a cost-effective solution for reliable and high-quality rapid prototyping, especially for heavy-duty continuous use

The system is constantly being further developed and has just received a fundamental update and various improvements with version "v1.1.0". All materials that meet certain basic specifications can be processed, ranging from high-strength thermoplastics and fibre-filled plastics to rubber-elastic materials. Printers that are available for domestic use or modelling only allow the use of a very limited range of printing materials. A so-called "bio-plastic" is predominantly used here, which is based on maize and generally cannot withstand the technical requirements of industrial use. This is because this plastic already fails at temperatures above 45 °C - the temperature limits in industry are significantly higher. Compared to other 3D printers for industrial use, the "RepRap Industrial" is particularly recommended due to its price. This is around 25 to 30 per cent lower than comparable systems. The success proves Kühling&Kühling right: the number of units is continuously increasing and has quadrupled within a year.

All materials that meet certain basic specifications can be processed, ranging from high-strength thermoplastics and fibre-filled plastics to rubber-elastic materials.

Simon Kühling remembers the search for a suitable supplier: "When we started developing the system, we initially thought of classic ball bearings. These have several disadvantages. Firstly, they are too expensive at a unit price of around 12 euros, and secondly, they stop working at an operating temperature of 65 °C. At this point, the seals start to fail. Then the seals start to fail and the lubrication wears out." This led to linear plain bearings with plastic sliding surfaces. "For cost reasons, we initially tested Asian products," says Simon Kühling. "However, these in no way fulfil our requirements, not to mention a fast and long-term delivery capability."

For the cable routing, the Kiel-based specialist opted for our energy chain from the E2 microseries, which takes up very little installation space and was developed for particularly dynamic applications. In addition, dryspin® spindle guides, drylin® R linear plain bearings and linear plain films made of iglidur® E7 were used as a linear bearing solution in the 3D printer generation. Unlike conventional recirculating ball bushings, the linear bearings made of the iglidur® material proved to be a cost-effective and at the same time high-performance solution.
They fulfil the high requirements for noise emissions, travel acceleration and continuous temperature resistance. In addition, the lifetime lubrication-free linear plain bearings are maintenance-free and therefore have particularly low wear and a long service life. 
Thanks to the precise positioning of the bearing elements, even during fast movements, and the absence of vibration, customers can also achieve optimum production results with their 3D printers.

The linear and drive technology "drylin®" from igus® offers designers of 3D printers various components - always completely lubrication-free and available in 24 hours and with no minimum order quantity. Another advantage of using linear plain bearings made of high-performance plastics is their quiet running; there is no mechanical rolling noise as with metal or ceramic balls.

A total of twelve igus®bearing products are used in the "RepRap Industrial": steel shafts and linear guide adapters with sliding foils made of "iglidur®" high-performance plastics to guide the respective axis, as well as lead screws and plastic threaded nuts as axis drives. The linear plain bearings are identical in design to recirculating ball bushings, economical and easy to install. They also dampen vibrations. This is all the more important as 3D printing does not generate large forces, but rapid accelerations do occur. The axis has to be light for this.

Kühling&Kühling's 3D printer also uses products from the second major business division at igus®, plastic energy chains. The chains from the "E2 micro" family used here are characterised by their extremely space-saving design, low weight and particularly smooth rolling movements. The smooth contours of the plastic-energy chain also protect the inserted cables.

The online catalogue from igus® has already given us a good overview of the range and the products that are suitable for us. However, the personal consultation helped us a lot to choose the right one from the mass of options."

In addition, there was a constant dialogue about the limits and possibilities of individual components and possible new developments. The latter applied, for example, in the area of sliding foils. The currently presented "iglidur® E7" sliding film was specially developed for linear movements. Its particular strength is its high service life and low wear rate on shafts made of steel, chrome-plated steel and all types of stainless steel. The operating temperature ranges from -30 to + 80°C. The "E7" is available as a sliding foil for diameters of 10 to 50 mm and can be combined with all linear housings from the "drylin® R" series.