Thermoset Extruder on Cosine AM1 3d Printer
What ARE 2k Thermosets?
Cosine has developed a new 3d printing technology where two component liquids are extruded out of a mixing nozzle and immediately begin to react to form covalent bonds and a solid part with isotropic properties. These thermosets do not require additional activation energy in order to produce parts, there is no need for a heated bed, no need for a heated chamber environment and no need for a heated extrusion system. Because there is no heat, there are no thermal expansion issues, no warping! Thermosets fill the gaps in the market where current thermoplastic AM technology falls short!
The main method of extrusion is where two resin components are pumped from their storage containers to the tool head, where they are passively mixed in a disposable extrusion nozzle. The mixture then under goes a chemical reaction where the extruded material will begin to gel and cure within a time frame of 2-60 seconds. Subsequent material extruded on top of the previous layers bond covalently, creating isotropic end-use parts. The ability to control the mixture ratio of the extrusion material allows for an operator to change in real-time: reaction kinetics, rheological characteristics, cross linking and rates of deposition. The “printability” of the material can be tailored for specific attributes (strength, surface finish, mechanical properties, etc.) of the final part.
THERMOPLASTIC vs THermoset
The fundamentals of traditional thermoplastic extrusion rely on thermal energy. To create the bonded layers of an FDM polymer print, liquid melted plastic is extruded at its specific melt point and an entanglement of polymer chains are formed between adjacent layers, creating the structure of the overall part, commonly referred to as layer adhesion. Common thermoplastic materials (ABS, PETG, PLA, etc.) require extrusion temperatures of 200°C and above in order successfully produce 3D printed parts, and issues of warping and interlayer adhesion become apparent when produced in environments below specified thresholds of heat. A common problem of thermally-driven, large-scale AM is that in order to create larger and larger parts, it requires scaling of the amount of thermal energy and thermal management combined with necessary scaling of spatial and thermal gradients to lock extruded material in place after deposition.
Thermoset printing utilizes liquid resin as the polymer extrusion material instead of traditional solid plastic formulation. The mixing of the resins can be adapted in real-time during the printing operation, allowing the operator to adjust the extrusion mixture in order to target specific mechanical properties. With the ability of an operator to directly tune the composition of the extrusion material, the polymers structure can create cross-linked networks. Produced parts can be even be tailored to be strong, clear, pigmented, flexible, electromagnetically active or any combination of these properties listed. Ambient cure extrusion also helps to eliminate the internal stresses and warping that typically hinder other methods of FDM in large parts. Thermosets can be used to create printed parts with strong inter-layer covalent bonds that show improved strength, chemical resistance, thermal stability and overall work-to-failure test figures when compared to similar parts created using FDM methods.
When comparing the production of parts using traditional AM methods, thermoset materials cure ambiently and does not require any melting of filament/pellet material, making thermoset processes less energy intensive, especially when applied towards large scale production. Thermoset extrusion can be adapted by increasing the extrusion nozzle diameter and flow rate, the only limiting factor found for how fast parts can be produced is the physical and motion limitations of the machine platform being used. With faster printing speeds being a main goal in the AM community, thermoset methods of production have demonstrated being at least 10x faster than what is offered by current thermoplastic AM technology. Thermoset materials have been seen outperforming thermoplastics in durability and chemical resistance.
HOW DOES THIS AFFECT THE 3D PRINTING INDUSTRY?
With the ability to create parts at greater speeds when compared to traditional AM methods, the goal of the community has always been trying to achieve greater print speeds in order to shorten lead time on parts. As previously stated, thermal management scaling is what hinders large-scale FDM from growing to the same capacity that thermosets are capable of. Since thermoset extruders do not require thermal energy nor water-cooling, the overall tool head can be lighter and move with less mass, translating to quicker rapids, and an increase in accuracy. Additionally, increasing print speeds provides a floorplan for current additive manufacturing production technology to be made more efficient and increase cost effectiveness.
Example of thermoset print, with the mix ratio producing a flexible final part after curing.
Parts created using thermoset methods tend to show higher work-to-failure when compared to similar test pieces created out of thermoplastic materials (ABS, Nylon and TPU). The failure observed with parts created using 2k thermosets were seen experiencing cohesive at the crosslinking between the layers, while FDM parts experienced delamination failures. Not only is thermoset extrusion faster, the parts created are also stronger than parts created using thermoplastics due to the increase of interlayer bonding in thermoset AM. Thermoset printing also allows for multi-mechanical property prints simply by adjusting the mix ratio of the extrusion material, which is currently unachievable using traditional thermoplastics without changing the filament/pellet material being used.
WHAT IS COSINE ADDITIVE DOING WITH THIS TECHNOLOGY?
Cosine has internally developed a print head that utilizing passive mixing at the extruder in order to deposit the material to build the parts. Mounted at the rear of the Cosine AM line of machines is a material loading system that takes feedstock and pressurizes the resin that is then delivered via paint line hosing. The printer’s pumps are designed to allow an operator to control the real-time material mixing, thus allowing for the creation of parts with variable mechanical properties without the need to change the extrusion material.
The two-part resin is chemically cured without the need of additional activation energy, and the layers are bonded covalently creating very strong isotropic parts. Using Cosine’s advanced linear motor motion system, thermoset printing can take advantage of the full speed speed (1000mm/s+) that our AM line of machines are capable of. Cosine has also developed its own thermoset extruder that enables operators to easily print parts. The material loading system can also be used with almost any compatible resin material, so the operator can have full control over the chemical and mechanical properties of parts they wish to produce.
