3D Printable Flexible materials

 
Flexible geometry printed in-house using ALT LLC's printing system.

Flexible geometry printed in-house using ALT LLC's printing system.

The Expanding World of Flexible 3D Printing Materials: A Comprehensive Guide

We print with many different soft materials at ALT LLC. Flexible 3D printing materials have unlocked a new dimension in additive manufacturing, empowering the creation of parts that can bend, stretch, and compress without fracturing. This versatility has paved the way for innovations across numerous sectors, from consumer goods and wearable technology to automotive components and medical devices that demand both elasticity and resilience.

Understanding the Spectrum of Flexibility

At the core of flexible 3D printing are thermoplastic elastomers (TPEs), a class of polymers that blend the processability of thermoplastics with the rubber-like qualities of elastomers. These materials can endure significant deformation and rebound to their original form, making them perfect for applications that require shock absorption, vibration dampening, and impact resistance. While TPE is a broad category, several distinct types of flexible filaments have emerged, each with unique characteristics.

Common Types of Flexible Filaments

Thermoplastic Polyurethane (TPU): As the most prevalent flexible filament in 3D printing, TPU strikes an excellent balance between flexibility and strength. It is celebrated for its high abrasion and chemical resistance, making it durable for end-use parts. TPU is generally easier to print than softer TPEs and is available in a wide range of hardness levels.

Thermoplastic Elastomer (TPE): While TPE is the overarching category, it also refers to a specific, typically softer and more elastic filament. Its rubber-like texture makes it ideal for applications demanding significant flexibility, such as toys and wearable items. However, its softness can present challenges during printing, often requiring slower speeds and specialized extruder setups.

Thermoplastic Copolyester (TPC): TPC is an engineering-grade flexible filament known for its durability, good chemical resistance, and thermal stability. It is generally less flexible than TPU but offers a great balance of flexibility and rigidity, making it suitable for parts like protective enclosures.

Soft PLA: A variant of the popular polylactic acid, Soft PLA offers a rubber-like flexibility and is biodegradable. With a Shore hardness typically around 92A, it provides a good degree of flexibility while being relatively easy to print.

Thermoplastic Polyamide (TPA): TPA is a chemical co-polymer that blends the flexibility of TPE with the smoothness of nylon. This results in a filament that is both highly flexible and durable, capable of withstanding repeated bending and stress.

We also print various biopolymers that are very flexible and can be printed using an auger tool with much lower stiffness. Filaments in general are limited in the softness as it becomes difficult to feed the filament through the system and work with Automated Materials Systems (AMS) such as on Bambu labs printers.

Key Material Properties and How They're Measured

The performance of a flexible material is defined by several key mechanical properties:

  • Shore Hardness: This is a critical measure of a material's resistance to indentation, indicating its softness or hardness. For flexible filaments, it's typically measured on the Shore A scale, with lower numbers signifying greater flexibility. For instance, a very soft filament might have a Shore hardness of 60A, while a semi-flexible one could be 95A.

  • Elongation at Break: This value, expressed as a percentage, reveals how much a material can stretch before it snaps. Highly flexible materials can exhibit elongation at break values ranging from 300% to over 700%.

  • Tensile Strength: This metric quantifies the maximum stress a material can handle while being stretched before it breaks. Flexible materials generally have lower tensile strength than rigid plastics but compensate with their superior elasticity.

Leading Flexible Filaments on the Market

Several brands have distinguished themselves in the flexible filament market:

  • NinjaTek: A prominent name, NinjaTek offers a range of flexible filaments, including the popular NinjaFlex (TPU) with a Shore hardness of 85A, known for its excellent flexibility and reliability.

  • Polymaker: Known for its innovative materials, Polymaker's PolyFlex line offers TPU filaments praised for their printability and consistency.

  • eSun: A popular brand offering a variety of filaments, eSun provides TPE and TPU options that are a favorite among hobbyists and professionals alike.

  • Fillamentum: This manufacturer offers a range of Flexfill TPU in different hardness levels, as well as TPE filaments that are safe for food-contact applications.

  • Recreus: The creator of Filaflex, one of the earliest elastic filaments, Recreus continues to innovate with options like recycled and even electrically conductive TPU.

Other notable brands include MatterHackers, ColorFabb, and SainSmart, each providing unique formulations to meet specific application needs.

A World of Applications

The unique properties of flexible materials have opened the door to a vast array of applications across diverse industries:

  • Consumer Goods: From protective phone cases and watch bands to ergonomic grips for tools and squeezable toys, flexibility enhances user experience and product durability.

  • Automotive and Industrial: In these sectors, flexible filaments are used to create custom gaskets, seals, vibration-dampening mounts, and protective components that can withstand harsh environments.

  • Medical and Healthcare: The ability to create soft, biocompatible parts makes flexible materials invaluable for producing patient-specific prosthetic liners, orthopedic insoles, and realistic anatomical models for surgical planning.

  • Wearable Technology and Footwear: The comfort and conformability of flexible materials are essential for wearable sensors, fitness trackers, and customized, high-performance footwear components.

  • Robotics: Soft robotics heavily relies on flexible materials to create grippers and other components that can interact safely and delicately with objects and humans.

Mastering the Art of Printing with Flexible Filaments

Achieving successful prints with flexible materials requires some adjustments to the printing process:

  • Print Speed: Slower print speeds, typically in the range of 15-30 mm/s, are crucial to prevent the filament from buckling or jamming in the extruder.

  • Extruder Type: Direct drive extruders are highly recommended as the shorter path from the drive gear to the hotend provides better control over the filament. While Bowden extruders can be used with semi-flexible materials, they are more prone to issues with softer filaments.

  • Retraction Settings: Minimizing or even disabling retraction is often necessary to prevent the elastic filament from stretching and causing clogs.

  • Bed Adhesion: A heated bed set to 40-60°C can improve adhesion. While many flexible filaments adhere well to standard build surfaces like glass or PEI, using a glue stick or painter's tape can provide extra security.

  • Filament Path: Ensuring a smooth and unconstrained path for the filament from the spool to the extruder is important to prevent any added tension that could lead to feeding issues.

Advantages and Challenges

Advantages:

  • Impact Resistance and Durability: Flexible parts can absorb significant impact and withstand repeated stress without breaking.

  • Vibration Dampening: The elastomeric properties make these materials excellent for reducing noise and vibration.

  • Design Freedom: Additive manufacturing with flexible materials allows for the creation of complex geometries and integrated flexible features like living hinges.

Challenges:

  • Printing Difficulty: The inherent elasticity of the material makes it more challenging to print than rigid filaments, often leading to issues like stringing and clogging.

  • Slower Print Times: The need for slow and steady extrusion results in longer print durations.

  • Hygroscopic Nature: Many flexible filaments can absorb moisture from the air, which can affect print quality. Proper storage in a dry environment with desiccants is recommended.

The Future of Flexible Materials

The development of flexible 3D printing materials is a dynamic field. Ongoing research is focused on creating bio-compatible flexible materials for advanced medical applications, conductive filaments for integrated electronics, and new formulations that are even easier to print without sacrificing performance. As these materials continue to evolve, they will undoubtedly fuel further innovation and expand the boundaries of what is possible with 3D printing.