European workwear brand STRAUSS understands the importance of good personal protective equipment (PPE) and each of its products is designed to keep its clients safe on the job, whether it’s protective goggles, ear defenders, hard hats, chemically resistant gloves, or knee pads. In its mission to protect workers from occupational hazards and injuries, the company recently partnered with German additive manufacturing specialist OECHSLER to investigate the benefits of 3D printing knee pads.
Spoiler alert: the joint project proved to be a success, and STRAUSS is now selling the 3D printed PPE under the Master Grid 6D collection, offering greater durability, comfort, and damping properties. In this article, we’re diving into the STRAUSS knee pad use case, which showcases OECHSLER’s deep knowledge of lattice 3D printing as well as AM’s ability to unlock higher-performance designs and tap into new benefits for a myriad of consumer products.
The need for knee pads
As the largest joints in the human body, knees work hard for us. They bear our weight, provide balance and stability, and enable us to walk, run, jump, sit, kneel, you name it. But knees are also prone to strain and injury, particularly for those whose occupations put extra strain on the legs and knees.
For that reason, knee pads have become an integral part of personal PPE for tilers, landscapers, roofers, plumbers, and other workers in physically demanding or hazardous jobs. And they have many proven benefits: knee pads help to reduce impacts on your knees, as well as absorb shock and protect them from any sharp objects. For people who spend time kneeling or squatting, they can reduce the risk of long-term conditions like osteoarthritis and protect from fractures or other knee injuries.
Traditionally, knee pads are made from foam or a combination of plastic, foam, and fabric. Some can be wrapped over the wearer’s pants, while others are designed to slip into knee pockets on workwear pants. While effective and certainly better than no protection at all, the benefits of traditional knee pads do have limits. For one, they are prone to wear. After repeated use, foam starts to compress, which provides less impact protection. For another, traditional foam knee pads are not tailored to the different pressures a knee undergoes while working.
With an eye consistently on the future of workwear, STRAUSS saw a unique opportunity to improve the knee pad using 3D printing and a lattice design framework.
Optimized protection and ergonomic comfort
OECHSLER was the ideal partner to bring the ergonomic 3D printed knee pads to life. The company, which specializes in polymer production methods, has worked with numerous clients to develop and manufacture consumer products like backpacks, footwear, bike saddles, automotive seating, and protective gear, all of which leverage the benefits of lattice design and industrial 3D printing.
Working in close collaboration with STRAUSS, the OECHSLER team knew it could realize a knee pad design optimized for performance and comfort. Achieving this design involved a few key steps. First, the companies had to find the optimal lattice structure based on the needs of the wearer. Then, they had to find the right material for the job, which would meet industry standards for workwear. Finally, they had to bring the PPE item into production.
To begin, OECHSLER’s engineers evaluated several different lattice designs to determine the best lattice pattern and cell alignment for protective equipment. The main mission was to provide a superior balance of damping properties and energy recovery. In the end, a custom hexagonal lattice pattern was chosen because of its consistent ability to absorb loads and withstand pressure. The unique lattice is called the Master Grid 6D design and it has been used for the knee pads as well as other 3D printed workwear products released by STRAUSS.
In designing the knee pads, OECHSLER and STRAUSS also took into consideration the different types of pressure and strain a worker’s knees could undergo on the job. Using body mapping technology, the partners were able to achieve a pressure distribution of 70% energy absorption and 30% restoring force when kneeling. On top of that, they integrated a continuous external lattice to prevent sharp objects, like nails or pieces of wood, from piercing the wearer’s knees.
In terms of dimensions, the 3D printed knee pad is designed to match STRAUSS’ traditional knee pads. This was to ensure that the pads could be worn with certified STRAUSS workwear pants and fit easily into the knee pockets. The teams, therefore, generated a lattice within the constraints of the existing knee pad design. Using a DfAM approach, the knee pads were also optimized for printability, as well as pre- and post-processing in order to facilitate production scalability.
The right material fit
Material choice was another important factor, and OECHSLER led extensive testing at its AM facility to find a material that would meet the needs of labor-intensive occupations. In the end, Carbon EPU 41 was selected due to its good abrasion resistance, washability, and bending load test results. For instance, after undergoing 50,000 bending load cycles, the 3D printed EPU 41 knee pads showed no sign of crack propagation.
Carbon EPU 41, an elastomer polyurethane resin, also offers good tear resistance and energy return. Other material properties, including biocompatibility, breathability, water resistance, and temperature resistance (from -10 to 70 degrees Celsius), also made the material a clear choice for the workwear application. In the end, the combination of the Master Grid 6D lattice and Carbon EPU 41 resulted in a knee pad that is more durable and has less volume loss compared to traditional foam knee pads.
Before bringing its printed knee pads to market, STRAUSS also invited several craftspeople to test them out in working conditions. The feedback was more than promising: the newly redesigned knee pads were commended for their excellent absorption as well as comfort and wearability (since they can be easily positioned into STRAUSS workwear trousers). The knee pads have been certified to DIN EN 14404, as well as ISO 14404 and ISO 20347 workwear standards.
“With our technology partner OECHSLER we are able to step into a totally new world of workwear,” the STRAUSS design team said. “A world of products that is asking for maximum safety requirements and individuality. The 3D printing technology enables us to design the highest level of comfort, stability, and protection in a sustainable and long-lasting way. It helps us to translate valuable customer feedback rapidly into our development process and fulfill their demands on high-end workwear products.”
From product development to production
With the E.S. Knee Pad Master Grid 6D design complete, STRAUSS and OECHSLER were ready to move into production. Thanks to OECHSLER’s extensive additive manufacturing capability, the transition from product design to production was a seamless one. For those that aren’t already familiar with the German company’s capacity: OECHSLER operates a technology-independent high-volume production facility that houses 150 3D printers and can turn out over 2 million parts per year. It has worked with several high-profile brands to bring their products from concept to production in a cost and time-effective way.
STRAUSS’ knee pads are made at OECHSLER’s Additive Manufacturing Hub in Germany using Carbon’s AM solution (comprising 3D printing as well as pre- and post-processing). With both companies based in Germany, this also means that the knee pad production is local, minimizing transport costs and emissions.
And the knee pads aren’t the only 3D printed product STRAUSS is now selling: the companies also developed a pair of work shoes that integrate the custom Master Grid 6D lattice design in their midsole. The lattice functions similarly to the knee pad, providing stability and relieving pressure on the foot.
OECHSLER sums up the partnership saying: “STRAUSS has successfully launched high-quality solutions for workwear, taking advantage of OECHSLER’s expertise in developing and manufacturing additively manufactured applications. Designed for work environments and leveraging the benefits of 3D printing, we put ergonomics and the wearer‘s comfort first— unprecedented product quality and material strength ensuring longer product life cycles.”