Flexible and wear-resistant with minimal frictional losses – those were the requirements presented to Freudenberg Sealing Technologies for the development of a new seal for use in cobots.
Today’s industry can no longer get around the use of cobots. These flexible, fast machines work hand in hand with people in many activities. One of the key requirements is that they must be adaptable enough for use in different work environments, and not just handle a range of tasks.
One manufacturer was looking for a sealing solution to protect all its cobots’ joints from dust, spraying water and other contamination reliably and over the long haul. Simple PTFE rings have been used to this point so efficiency, energy consumption and the robotic arms’ speed of motion are not overly compromised. However, the rings were not able to guarantee the required IP54 protection class. High travel speeds and the forces generated in the robot arm also create an environment with temperatures as high as 60°C. A seal not only has to withstand these temperatures long-term – extremely low material elongation is important as well, to guarantee functionality in each operating mode and at all temperatures.
The development partner turned to Freudenberg Sealing Technologies, the company says, due to its “outstanding reputation and development expertise”. As a first step, the sealing experts presented a u-ring made of polyurethane (PU). But in practical tests, the frictional forces proved to be too great due to its relatively large surface. Those forces were not supposed to exceed one newton meter. This extremely low value made it necessary to significantly reduce the radial forces and at the same time also of contact stresses on the dynamic seal lip.
It was decided that the overall geometry to a z-profile had to be changed and a second groove was integrated into the design. This greatly reduced the contact pressure and met the requirement for a moment of friction of less than one newton meter. In the practical test, however, the level of wear was still too high. This was mainly due to the cobots’ lightweight, largely aluminium construction. The surface of the material is relatively rough due to the methods used during its processing and its basic characteristics. As a solution, Freudenberg developed a three-component solid film lubricant coating with high carbon content. The coating made it possible to further reduce the amount of wear.
With a Shore hardness of 92, the material in question, 92 AU 21101, is very soft and flexible. Nonetheless, its tensile strength is 59 MPa, putting it significantly above the required minimum level of 50 MPa. At minimal elongation, components made of 92 AU 21101 can be relied on in temperatures ranging from -50°C to +110°C. Their conformity with RoHS, 2015/863/EU and 2011/65/EU is unrestricted and valid.
In response to changes in the cobot’s design, the seal geometry had to be completely reworked once again. For the final version, Freudenberg selected a z-geometry with a further optimised dynamic seal lip. A static area with a groove was constructed externally. Thanks to the systematic use of FEA (finite element analysis) calculations for the lip thickness and a later simulation, it was possible to achieve significant savings as unnecessary process steps were eliminated.
The implementation with the help of Freudenberg Xpress® as a service provider offered fast responses and short development times throughout the process. Freudenberg Xpress® produces affordable, high-value CNC-turned sealing solutions. It not only manufactures prototypes – it handles small production runs and one-offs economically and quickly as well.
Product Developer Alexander May summed up the advantages of combining in-house development expertise with the services of Freudenberg Xpress®: “We can react and deliver the product quickly. That is not just a real advantage that our customers appreciate during periods of global bottlenecks. We arrive personally on site in short order and work directly on the specific challenges worldwide, which always results in positive feedback. In a world of highly automated mass production, we are active in an area that many other manufacturers do not find attractive: one-off products and short production runs. When this is combined with our knowhow and the same quality standards as with large-scale series production in the millions of units, it is a door opener.”
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