PTFE (Polytetrafluoroethylene) rings have been used to this point so efficiency, energy consumption and the robotic arms’s 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 (140 °F). A seal not only has to withstand these temperatures long-term – low material elongation is important as well, to guarantee functionality in each operating mode and at all temperatures.
As a first step, Freudenberg 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 1 newton meter. This low value made it necessary to reduce the radial forces and at the same time also of contact stresses on the dynamic seal lip.
So in the next step, the sealing experts changed the overall geometry to a z-profile and integrated a second groove. This reduced the contact pressure and met the requirement for a moment of friction of less than 1 newton metre. In the practical test, however, the level of wear was still far too high. This was mainly due to the cobots’s 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 soft and flexible. Nonetheless, its tensile strength is 59 MPa, putting it 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 unconditionally valid.
In response to changes in the cobot’s design, the seal geometry had to be 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 calculations for the lip thickness and a later simulation, it was possible to achieve 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 computer numerical control turned sealing solutions. It not only manufactures prototypes – it handles small production runs and one-offs economically and quickly as well. Here, it applies the same standards that it uses for large-scale production. It has established processes for quality assurance and lab testing, along with on-site service in much of the world. This enables Freudenberg to design, simulate and deliver solutions in the event of requirement modifications within two weeks.
Creating a new best practice, the robot manufacturer has decided to integrate partners such as Freudenberg into the development process for its products at an early stage. Their collective experience makes it possible to consider additional parameters in advance, which leads to shorter development times and fewer correction cycles. The product is also ready for the market sooner.
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 know-how and the same quality standards as with large-scale series production in the millions of units, it is a door opener.”
