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Freudenberg offers new sealing solution for cobots

Product developers at Freudenberg Sealing Technologies, Steve Cowell and Alexander May, discuss how the company tackles cobot challenges through innovative sealing solutions by refining materials and design, and in turn, ensuring efficiency and reliability.

Key Highlights:

Cobots have become an essential part of modern industry: In many activities, the agile and fast machines now work hand in hand with humans. Unlike traditional industrial robots, which are often isolated in cages or behind safety barriers, cobots are equipped with advanced safety features so they can operate in close proximity to people without posing a significant risk. They are also multifunctional: A robot working on welding tasks today, for instance, might be reassigned to a packaging line the following week. This places high demands on the application profiles of these popular production assistants. 

Guarding against dust, water splashes and other contaminants 

This was behind the manufacturer’s search for a sealing solution that could offer reliable and long-lasting protection against dust, water splashes and other soiling for all of the cobots’ joints.

For obvious reasons, such protection is an important factor in the machinery’s efficiency: Wear and tear on the delicate joints increases maintenance costs, lowers precision and, in the worst case, results in unplanned production downtime. So far, simple PTFE rings had been employed to prevent major restrictions on the robots’ efficiency, energy consumption and movement speed. These sufficed in their previous area of application – but were inadequate for guaranteeing the IP54 protection class required in the new application areas.

FST

In addition, the high traversing speeds and forces experienced by the robot arm generate environments with temperatures reaching up to 60 °C, conditions which the seal must withstand permanently. More than that, it must also exhibit extremely low material elongation to maintain its functionality across all operational states and at all temperatures. 

Thanks to its development expertise, Freudenberg Sealing Technologies (FST) was selected by the development partner. The initial design presented by the sealing specialists was a polyurethane (PU) groove ring. However, practical tests revealed that the relatively large contact surfaces caused excessively high friction forces. These forces were required to remain below the threshold of 1 Nm and are therefore extremely low, necessitating a significant reduction in both the radial forces and the contact stresses on the dynamic sealing lip. This again highlighted the advantage of having an experienced development partner, one that is not only well-versed in its own technologies but also has a precise understanding of the customer’s practical requirements. 

Significant reduction in contact pressure 

Consequently, the next step was to change the entire seal geometry to a Z-profile and add a second groove. This made it possible to greatly reduce the contact pressure, which had a positive effect on the frictional forces. 

FST

The selected material, 92 AU 21101 with a Shore hardness of 92, was developed internally by Freudenberg Sealing Technologies and is very soft and flexible. Nevertheless, it offers a high tensile strength of 59 MPa. This makes it ideal for scenarios that require a combination of flexibility and strength. 92 AU 21101 is also distinguished by its remarkably low material elongation, making it suitable for use at different temperatures and operational conditions. It can even resist extreme temperatures from -50 °C to +110 °C in practical use. Another advantage is its high chemical resistance: 92 AU 21101 can withstand a wide range of substances, making it the ideal choice for use in challenging environments. It also complies with the RoHS, 2015/863/EU and 2011/65/EU conformity standards, ensuring that it is free from harmful substances and meets environmental sustainability requirements. 

Although this met the requirement for a frictional force of less than 1 Nm, the wear was still much too high during practical testing. The main reason for this was the lightweight construction of the cobots, which are made mostly of aluminium. Due to the processing methods in its manufacture and its inherent properties, the material has a relatively high surface roughness, which quickly overwhelms even the most high-quality seals under the persistent stress. 

As a solution, Freudenberg worked with a long-time partner to develop a three-component bonded coating. Its three components are a binder, a solid lubricant rich in carbon and additives designed to improve specific properties. The high carbon content of the solid lubricant gives the coating its exceptional sliding capabilities and reduces friction. Carbon is known for its low friction and high resistance to wear. That is why this type of bonded coating is especially suited for applications that require a low-friction surface to minimise wear and enhance efficiency. This coating resolved the issue of excessive wear.  

Development expertise paired with express service 

A design change in the cobot necessitated a complete overhaul of the seal geometry during the development process. For this final version, Freudenberg chose a Z-geometry for the seal with an additionally optimised, dynamic sealing lip; the static area with the groove was positioned externally. Thanks to the consistent use of FEM calculations for the lip thickness and the subsequent simulation, it was possible to achieve significant savings by avoiding unnecessary steps. 

FST

By using Freudenberg Xpress for the execution, fast response and short development times were ensured throughout the process. Freudenberg was able to design, simulate and deliver solutions for changing requirements within two weeks. With CNC-turned seals, the company could produce not only prototypes but also small batches or individual items quickly and cost-effectively. Here Freudenberg applies the same standards that it uses for large-scale manufacturing. This includes fixed processes for quality assurance and laboratory testing along with extensive on-site services in many parts of the world. 

As a future best practice, the robot manufacturer plans to involve partners like Freudenberg very early in its own product development processes. The shared wealth of experience makes it possible to consider a much broader range of parameters, ultimately leading to shorter development times, fewer correction loops and quicker market launches. Thanks to Freudenberg’s development expertise, the cobots can now be used in a significantly broader range of applications. This high level of flexibility not only enhances user satisfaction, it also opens up new market segments.  

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