Could Multi-Material 3D Printing be the next step for AM?

Multi-material 3D printing is an innovative additive manufacturing technique that enables the creation of objects with different materials and properties. By adding more complexity to a part, multi-material 3D printing can significantly improve the performance and functionality of parts. The technology thus opens up entirely new design and production possibilities – and enables the creation of objects that would otherwise be impossible. Currently, multi-material 3D printing is possible with a range of plastics, polymers, and even silicones, making it an ideal solution for manufacturing realistic, full-color prototypes and concept models. In this tutorial, we will explore the benefits of multi-material 3D printing, the currently available processes, as well as the most common use cases and applications.

One of the main advantages of multi-material 3D printing is that complex parts with different material properties can be created in a single printing process. This differs from individual parts that must be assembled to obtain a part with different material properties. Multi-material 3D printing can therefore reduce the number of steps required to manufacture an object, which leads to a faster product development cycle. Designers and manufacturers can also benefit from multi-material 3D printing, as the combination of different material properties (such as translucency and rigidity) within a part can take design validation and functional testing to a new level. Another advantage of using different materials in 3D printing is the ability to create color gradations. By mixing materials in different ratios, various color combinations and color tones can be achieved without post-painting – this saves time in post-processing.

In multi-material 3D printing, different materials can be used in a single 3D printed object. While multi-material 3D printing is currently capable of processing materials such as thermoplastics and polymers, the combination of different metals or ceramics is not yet possible at this time. Today, companies such as Stratasys and 3D Systems offer multi-material 3D printing solutions for prototyping and modeling. For example, Stratasys' Connex multi-material system offers the following printing options:

With this option, you can simultaneously produce multiple parts made from different materials - and thus with different properties - in a single build. The "Mixed Build Chamber" option may be an ideal solution for companies that require high-volume prototyping.

Multi-material 3D printers can print parts with different properties in certain areas. By combining materials within a single part, the need to assemble separate parts is eliminated.

By mixing two or more materials, digital materials are used to create an object with improved properties and appearance that cannot be achieved if a part is 3D printed in a single material.

Material jetting is currently the most frequently used technology for multi-material 3D printing. In material jetting, print heads deposit droplets of a photosensitive material (or a mixture of materials or different materials through different print heads) that cure under ultraviolet (UV) light. The component is then created layer by layer using this process. Stratasys and 3D Systems are the leading manufacturers of multi-material 3D printers based on material jetting technology. For example, the Connex™ 3D printing system from Stratasys works with two or three different plastic materials during the 3D printing process. This results in the finished part simultaneously having different properties (such as rigidity and flexibility).

Currently, the most widely used material options for 3D multi-material printing are acrylate-based photopolymer resins and composites made from rigid plastics and elastomers. For example, 3D Systems introduced a new large-format multi-material ProJet MJP 5600 3D printer last year, which works with a range of synthetic resins and their combinations to create fully assembled prototypes and complex geometries with multiple material properties. Although the materials can vary in mechanical properties, progress in 3D printing materials means that engineering composites are also available. One of the latest innovations in multi-material 3D printing is silicon 3D printing, a technology developed by ACEO®, a subsidiary of Wacker Chemie AG. ACEO®'s innovative silicone technology enables the production of silicone parts with different colors, shore hardnesses, and properties. A useful application of this is the production of silicones that have insulating and conductive properties, as these can be used to create a composite part with integrated electrical conductivity.

The possibilities of multi-material 3D printing are endless, with a broad range of applications in the consumer, medical and other industries. Currently, multi-material 3D printing is mainly used in product development. For example, the swimwear company Speedo has used the technology to manufacture items such as goggles and other swimming equipment as part of the product development cycle. Other products, such as functional prototypes of seals, tires and shoe soles, are also possible with 3D multi-material printing. With this technology, the design and function of the product can be tested and verified before it goes into production. Since multi-material 3D printing can combine translucent and opaque materials, the medical industry has adopted the technology to create realistic anatomical models for training purposes as well as patient-specific models for preoperative planning and training. The technology also enables the creation of translucent parts with internal colored structures that can be used for visualizing fluid flows or testing medical devices. Mechanical engineers in the automotive, aerospace and other industries can use multi-material 3D printing to create functional prototypes with the appearance of the end product (colors, labels, etc.). Furthermore, multi-material 3D printing enables the manufacturing of molds for short injection molding and tooling series without assembly effort. An interesting aspect of advanced multi-material 3D printing is the ability to create parts with integrated functions, which is particularly useful for electronic devices. Nano Dimension Ltd. has recently achieved a breakthrough in the development of multi-material 3D printing inks. Conductive and dielectric inks can now be used simultaneously to manufacture electrically functional parts, circuits and antennas.

While multi-material 3D printing is currently used primarily for prototyping, it nevertheless offers enormous potential for manufacturing parts from different materials and a combination of mechanical properties. Research is therefore ongoing into how the existing challenges for multi-material 3D printing of functional parts can be overcome. The difficulty lies in developing a scalable and repeatable production process that can deliver high-quality end parts from multiple materials. This is particularly challenging for metals and ceramics, as when two materials with, for example, different melting temperatures and other material properties are melted together, there are significant physical limitations. However, Belgium-based company Aerosint claims to have developed a unique multi-material powder bed process to produce end parts with metals in sight. The technology, which works with polymers, controls the distribution of two different types of powders at the voxel level, which are then co-sintered.

Another fascinating research area is multi-material bioprinting, which could have revolutionary impacts on fields such as tissue engineering, regenerative medicine, and biosensing. Today, however, multi-material 3D printing offers tremendous opportunities for product development and validation testing, as the technology enables the creation of realistic 3D-printed models and prototypes with different properties. Ultimately, the next step for multi-material 3D printing will be to successfully implement the transition to the production of end parts with integrated functions and improved mechanical properties. This area of development, which is already experiencing significant research activity, will expand the potential of additive manufacturing to new horizons.