Rethinking foam—Carbon’s lattice innovation

December 6, 2017

Almost 80 years ago, Dr. Otto Bayer discovered polyurethane foam chemistry. Following a gradual start to market adoption, foam applications became common across industry verticals such as automotive, packaging, construction, electronics, bedding, and furniture. The most recent revolutionary innovation in the world of foam was memory foam, developed by NASA in the 1970s. In the last 50 years, substantive innovation in the foam sector has moved slowly. Innovations in the areas of comfort, performance, and safety associated with foam have been evolutionary at best.

This article will discuss how Carbon can make a sizable impact in the foam sector, driven by our elastomer lattice innovations that leverage proprietary programmable resins and software capabilities. Carbon’s advancements represent breakthroughs in manufacturability and material characteristics, and are poised to change the game for foam.

Carbon’s ability to 3D manufacture finely tuned lattices will fundamentally enhance human experience around the combination of comfort, performance, and safety of foam applications—products we all touch and feel every day.

 

CARBON’S LATTICE SOLUTION

Unprecedented in 3D Manufacturing, Carbon’s technology makes it possible to produce lattice geometries with functional elastomeric materials, opening up a wide range of product possibilities. Product designers working with lattices require software tools to optimize the ideal lattice parameters in their design—such as unit cell type, shape, and strut size—to achieve the desired mechanical response and manufacturability of the part.

Carbon’s solution is able to remove the guesswork from the design process, leveraging our exhaustive lattice library where each unique combination of lattice parameters is combined with base materials, resulting in a unique metamaterial with a well understood simulated mechanical response.

Instead of the trial-and-error process associated with conventional lattice prototyping tools, Carbon’s simplified approach requires only the submission of the desired mechanical response for parts and other design constraints, such as weight and size. Using Carbon’s validated library of metamaterials, the software tool outputs a lattice structure that meets the mechanical loading requirements of the part, and checks for manufacturability. Additionally, the tool allows distribution of different mechanical properties within the same part, enabling multiple functional zones (Figure 1).

 
Figure 1: Carbon’s lattice solution workflow showing inputs and output

 

STATUS QUO WITH FOAM AND CARBON’S DIFFERENTIATION 

 

COMFORT

While the term comfort might seem subjective, over the years, ergonomic researchers have developed a structured approach to quantifying comfort, with the help of blind tests and statistical tools. Of the many types of materials deployed to enhance product comfort, foam is one of the most versatile and widely used choices for products. For many applications, such as seats and headsets, foam enables a wide range of performance characteristics based on factors such as composition, placement, and thickness.

Despite the broad adoption of this material, all conventional approaches to foam design and experimentation still share the same significant limitation, which is that compression force applied to foam increases linearly (Figure 2), resulting in severe design constraints.

 

Figure 2: Linear relationship between load and compression for foam

 

To address this limitation, closed-cell elastomeric foams have been developed, enabling a more non-linear load-compression response (Figure 3). With this approach, the central plateau helps deliver an almost constant load within the same piece of foam, resulting in a product that can be used comfortably across a broader set of users.

 

Figure 3: Schematic compressive stress-strain response of closed-cell elastomeric foams¹

 

However, this increase in compression performance comes at a sizable cost: these closed-cell foams lack breathability, and as a result, demonstrate the thermal profile of an insulator. For users interacting with these foams, the closed-cell approach results in discomfort due to heat, caused by lack of airflow.

Carbon’s lattice innovation, in contrast to the insulating closed-cell approach, delivers an open-lattice cell structure for improved airflow and breathability. In addition, Carbon further improves comfort performance by providing a tunable load-compression profile.

 

Figure 4: Nine Carbon example lattice structures (metamaterials) with unique load-compression behaviors compared to the linear load-compression profile for foam

 

Figure 4 shows load-compression behaviors for nine different lattice structures and metamaterials from Carbon’s library, highlighting a wide range of available lattice behaviors.

These nine lattices represent only a small set of available possibilities; product development teams often collaborate with Carbon to identify material options for specific load-compression curves depending on the application. Leveraging our software capabilities, teams can tune the lattices for the desired comfort profile, delivering specific outcomes in mechanical and thermal characteristics.

As a result of this tunability, Carbon lattices outperform closed-cell elastomeric foam, delivering a wider stress-strain “band” within the flat plateau region, and superior performance on compression response and control (see Figures 3 and 4). Additionally, this solution provides the capability for digital control throughout the load-compression curve, making it possible to precisely define the transition points between linear elasticity, the plateau, and densification. In contrast, elastomeric foams do not allow for tunability and controllability, resulting in product development teams wasting cycles on trial and error, and optimization processes for every new application.

With Carbon’s technological capabilities, lattices can successfully displace foam in multiple applications including headsets, seats, headphones, and orthopedic pads, to name a few. 

 

SAFETY

Expanded Polystyrene (EPS) foam is used in safety applications such as helmets and car seats because it can absorb impact energy and protect humans. With Carbon’s tunable lattices, product development teams are able not only to create monolithic parts, but also to create designs that can absorb impact energy.

Traditionally, safety products require costly assembly of multiple foam parts to create varying functional performance zones within a single product. Using Carbon’s tunable lattice solution, designers can now 3D manufacture a single monolithic part produced from the same material with a design that delivers multiple functional performance zones. This approach enables products with improved safety performance and eliminates multiple foam interfaces, traditionally a site of part failures. Additionally, designers are exploring high-impact applications in sporting equipment such as helmets and pads, customized with Carbon lattices based on individual athlete physiological data (Figure 6).

Figure 6: Example applications that could benefit from improved and tunable impact absorption offered by Carbon lattices

 

PERFORMANCE

Another critical area in which Carbon’s lattice innovations are challenging conventions is performance. Foam’s ability to meet performance specifications makes it a natural fit for sports applications, such as football protection pads and shoe midsoles, for which it helps with cushioning and energy return. The most common foam used in sneaker midsoles is a closed-cell foam called EVA (ethylene vinyl acetate). Historically a single EVA foam structure has been used to make the entire midsole. In 1993, Saucony was the first athletic shoe company to create a dual density-molded midsole by combining different foams for areas of stability and cushioning, creating a de facto industry standard.² However, adidas and Carbon have substantially evolved this standard with the launch of the Futurecraft 4D shoe—unleashing a new era of athletic performance.

Using Carbon’s technology, engineers can, for the first time, 3D manufacture multiple unique functional zones within the same monolithic part and tune the mechanical properties within each of these functional zones separately. Prior to working with Carbon, adidas had been seeking a platform that would enable the company to tune cushioning properties throughout the shoe, and ultimately mass-manufacture a bespoke line of athletic footwear. With decades of experience and data derived from midsole design, adidas aspired to create something that would free them from the limitations of traditional footwear manufacturing. Traditional foam-based production methods cannot deliver complex, high-performance monolithic designs, and typically require the assembly of multiple parts to create varying performance zones within a single midsole.

Together, Carbon and adidas have pushed the functional performance of footwear to a new level with the launch of Futurecraft 4D. The shoe delivers precisely tuned functional zones within the midsole (Figure 7). The midsoles have different lattice structures in the heel and forefoot, to account for different cushioning needs for these parts of the foot while running. Carbon’s technology addressed adidas’ complex performance design requirements in a single high-performance monolithic midsole. In the long run, adidas and Carbon aspire to enable bespoke performance products tailored to individual athlete physiological data, on demand—thereby displacing foam as the primary performance platform for athletic needs.

 

 

Figure 7: An adidas Futurecraft 4D midsole printed on a Carbon printer, demonstrating varying lattice structures along the midsole

 

CONCLUSION

With Carbon, product development teams previously constrained by the properties of foam now have access to new materials, design freedom, and manufacturing capabilities, enabling them to rethink old benchmarks of comfort, safety, and performance. Applications such as bike seats, shoe midsoles, car seats, helmets, orthopedic pads, and headsets serve as starting points for product development teams considering Carbon’s technology to design and 3D manufacture new parts and products. Additionally, Carbon’s ability to print tunable lattices on a variety of resin materials represents an important opportunity for product development teams who are actively seeking materials to replace foam in their products and to improve the end-user experience.

To learn more about Carbon’s lattice solution and how our lattice library of metamaterials could help you to make differentiated products and lead to a paradigm shift in comfort, safety, and performance for your industry, please email us at sales@carbon3d.com.

 

____________________________________________________________________________

Carbon’s lattice solution and metamaterials described in this solution brief are currently available by working with a Carbon Technical Partner. They are dedicated resources provided by Carbon as part of a standard subscription agreement.

¹Lorna J. Gibson and Michael F. Ashby. Cellular solids – Structure and properties (second edition). Cambridge University Press, 2001; ISBN 0-521-49911-9

²https://www.sneakerfreaker.com/articles/material-matters-eva-foam/