Sustainability meets innovation

3D printing, also known as additive manufacturing, is becoming increasingly important in all sectors, including medicine and sport. In these areas in particular, there is a great desire for individualized products such as shoe soles for running shoes, shin guards, prostheses or orthoses. However, individual adaptations require a high degree of flexibility in production. At the same time, the service life of the products is limited. "For example, most people replace their running shoes or sneakers every year, often due to fashion trends and not for technical reasons. This results in a considerable amount of waste," says Dr.-Ing. Tobias Rosnitschek, Academic Council at the Chair of Design Engineering and CAD at the University of Bayreuth. However, there are still no satisfactory recycling strategies for material flows within additive manufacturing processes. This is where the MonoMat project comes in.

The aim of the project is to manufacture high-quality, individualized polymer products from a single material, as single-origin products are much easier to recycle. "This is possible by using different lattice structures in 3D printing, which allow us to easily manufacture different hardnesses and strengths. By individually adapting the unit cell - i.e. the smallest repeating unit of a lattice - the products can be personalized without incurring additional costs in development or production," says Professor Stephan Tremmel, Head of the Department of Engineering Design and CAD and coordinator of the MonoMat project.

The researchers in the MonoMat project have developed a cascade of different 3D printing processes and conventional manufacturing processes that can significantly reduce the amount of waste and new material. First, additive manufacturing is used to create an individualized medical device that must have outstanding material quality. If the medical device can no longer be used, the material is mechanically shredded. Using a different 3D printing process, it is then used in sports or lifestyle applications, where the quality requirements for the raw material are lower. The material is recycled until it has worn out. It can then be reused as a filler in mass production, for example. "With this cascade, the material can be used in the first life as an orthosis or shoe sole, for example, and in the second to ninth life perhaps as a backpack pad, before being used in the tenth life as a filler in injection molding for sunglasses," explains Rosnitschek.

At the invitation of the Federal Ministry of Economics and Climate Protection (BMWK), Prof. Dr.-Ing. Stephan Tremmel presented the main features and results of the MonoMat project at the 5th Lightweighting Summit at HANNOVER MESSE. The Lightweighting Summit is organized annually by the BMWK and is dedicated to the topic of lightweight construction. At the Lightweighting Summit, Rosnitschek showed how different 3D printing processes and recycling states of the material can nevertheless lead to the same effective properties in the product, using the example of a backpack in which the pads were each manufactured using different processes.