Rethinking foam—the Carbon lattice innovation

In contrast, Carbon advancements illustrate how breakthroughs in manufacturability and material characteristics continue to change the game for foam. This article provides new insights into how Carbon, through the Carbon Design Engine, uses elastomer lattice innovations that leverage programmable resins and software capabilities to provide superior protection, cushioning, and comfort when compared to traditional foam.

Carbon can digitally generate, simulate, and manufacture finely tuned lattices driven by clinical and individual data. This opens the possibility of enhancing the human experience around improved performance, safety, and comfort.

THE CARBON LATTICE SOLUTION

Product designers and engineers 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. The Carbon DLS process enables the production of lattice geometries with functional elastomeric materials, opening up a wide range of product possibilities.

The Carbon Design Engine removes the guesswork from the design process. This solution leverages our exhaustive lattice library, where each unique combination of lattice parameters is combined with base materials and the customer’s desired mechanical response. The result is a unique metamaterial with a well-understood, simulated mechanical response (Figure 1).

Rethinking Foam Figure 1 Figure 1: The Carbon Design Engine generating and simulating more than 1,000 lattice design options.

 

In addition, the Carbon end-to-end solution can incorporate individualized data from various users, such as professional athletes and active individuals who agree that fit and comfort are top priorities. Carbon enables companies to then manufacture products tailored to each individual, with customization that can be produced at scale.

In contrast to the trial-and-error process associated with conventional lattice prototyping tools, this simplified method from Carbon only requires submitting the desired mechanical response for parts and other design constraints, such as weight and size. Using the Carbon validated library of meta-materials, 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 2).

 

Rethinking Foam Figure 2 Figure 2: The Carbon lattice solution’s workflow, showing input and output.

 

FROM FOAM TO LATTICE—THE CARBON DIFFERENCE
PERFORMANCE

A critical area in which Carbon lattice innovations are challenging convention 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 became the first athletic shoe company to create a dual density-molded midsole by combining different foams to improve stability and cushioning, thereby creating a new industry standard.1 However, adidas and Carbon have substantially surpassed Saucony’s benchmark with the launch of the Futurecraft 4D and the AlphaEdge 4D shoes—unleashing a new era of athletic performance.

Prior to partnering with Carbon, adidas desired 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. Using Carbon technology, engineers can, for the first time, digitally manufacture multiple unique functional zones within the same monolithic part and tune the mechanical properties within each of these functional zones separately.

Together, Carbon and adidas have pushed the functional performance of footwear to a new level with the original launch of Futurecraft 4D, and the more recent launch of the AlphaEdge 4D. The shoes deliver precisely tuned functional zones within the midsole (Figure 3). 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 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 3: An adidas 4D midsole digitally manufactured on a Carbon printer, demonstrating varying lattice structures along the midsole, and the midsole in final shoe product context.

 

SAFETY

Expanded Polystyrene (EPS) foam is used in safety applications such as helmets and car seats because it can absorb impact energy and offer protection. Maximizing impact absorption requires a single safety product to have varying functional performance zones, which results in a costly assembly of multiple foam parts. However, using Carbon tunable lattices, a highly damping elastomer, and real on-field data, Riddell and Carbon are changing how impact absorbing protective gear is designed and manufactured. The result is the next generation of head protection: the SpeedFlex Precision Diamond helmet model.

Riddell’s new Diamond helmet platform features a 3D printed, impact absorbing lattice helmet liner that is digitally manufactured using the Carbon DLS process. Using Riddell’s Precision-Fit head scanning and helmet-fitting process, the Carbon Design Engine creates a customized helmet liner contoured precisely to the athlete’s head. Driven by Riddell’s proprietary database of over five million impacts, the Design Engine then leverages physical simulation and optimization techniques to tune structures and further manage both linear and rotational impact energies. Each Riddell helmet liner is made up of more than 140,000 individual struts, carefully orchestrated into varying patterns that bear specific functionalities for attenuating impact forces while providing excellent comfort and fit. The final result is a Carbon DLS-printed, custom fit, impact absorbing helmet liner designed to advance the state-of-the-art in head protection (Figure 4).

 

Rethinking Foam Figure 4 Figure 4: Helmet foam liners are an example of an application that could benefit from improved and tunable impact absorption offered by the Carbon Design Engine. Pictured above is the Riddell Speedflex Precision Diamond helmet and one of its side lattice liners.

 

With Carbon tunable lattices, product development teams can create not only monolithic parts but also designs that can absorb impact energy. Designers can now digitally manufacture a single monolithic part produced from the same material with a design that delivers multiple functional performance zones. This approach enables the development of products with improved safety performance and eliminates multiple foam interfaces, which are traditionally a site of part failures.

 

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 popular 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 the compression force applied to foam increases linearly (Figure 5), resulting in severe design constraints.

 

Rethinking Foam Figure 5 Figure 5: Linear relationship between load and compression for foam.

 

To address this limitation, engineers have developed closed-cell elastomeric foams, which allow for a more non-linear load-compression response (Figure 6). With this, 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.

 

Rethinking Foam Figure 6 Figure 6: Schematic compressive stress-strain response of closed-cell elastomeric foams.2

 

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 causes discomfort due to heat, caused by lack of airflow.

The Carbon lattice innovation, in contrast to the insulating closed-cell approach, delivers an open-lattice cell structure for improved airflow and breathability. Carbon further improves comfort performance by providing a tunable load-compression profile. Figure 7 shows load-compression behaviors for nine different lattice structures and meta-materials from the Carbon library that highlight a wide range of available lattice behaviors.

Rethinking Foam Figure 7 Figure 7: Nine Carbon example lattice structures (meta-materials) with unique load-compression behaviors compared to the linear load-compression profile for foam.

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 by delivering a wider stress-strain “band” within the flat plateau region and superior performance in compression response and control (see Figures 5 and 7). 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 necessitating optimization processes for every new application.

Through Carbon, lattices can successfully displace foam in multiple applications including headsets, seats, headphones, and orthopedic pads, among others.

CONCLUSION

With Carbon, product development teams previously constrained by the shortcomings of foam now have access to new materials, design freedom, and manufacturing capabilities, all of which afford them the opportunity to rethink old benchmarks of comfort, safety, and performance. Applications such as bike seats, shoe midsoles, car seats, helmet liners, orthopedic pads, and headsets serve as starting points for product development teams considering Carbon technology to design and digitally manufacture new parts and products. Additionally, Carbon offers the ability to manufacture tunable lattices with a variety of resin materials. These resins represent 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 the Carbon lattice solution and how our lattice library of meta-materials could help you make differentiated products and lead to a paradigm shift in comfort, safety, and performance for your industry, please email us at sales@carbon3d.com.

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The Carbon lattice solution and meta-materials 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/