BigRep PA6/66 Filament is an unfilled polyamide 6/66 copolymer feedstock for large-format material extrusion. The product is supplied as a 2.85 mm diameter mono-filament with a dry density of approximately 1.13 g/cm³; common spool configurations are 2.5 kg and 4.5 kg. The copolymer architecture modifies crystallization relative to PA6 homopolymer: the 6/66 sequence lowers the crystalline melting point to a broad interval near 185 °C to 210 °C, reduces crystallinity, and moderates post-crystallization shrinkage in slow-cooled thick-section builds. Tensile property characterization is performed according to ISO 527-2, flexural stiffness according to ISO 178, and notched impact according to ISO 179-1/1eA. The material is intended for industrial jigs, fixtures, soft-jaw tooling, thermoforming aids, and short-run production parts on large-format fused filament fabrication machines with active chamber heating and polyamide-capable bed adhesion. Regulatory compliance documentation, including REACH and RoHS conformity certificates, should be obtained from the manufacturer for the specific lot before deployment.

What extrusion conditions govern interlayer fusion in PA6/66 on large-format platforms?

Interlayer fusion is controlled by melt temperature, chamber temperature, layer height, and hot-end residence time. The supplier processing window typically specifies a nozzle set point of 260 °C to 290 °C, a build plate at 90 °C to 110 °C, and a chamber temperature of 60 °C to 80 °C where a heated enclosure is available. A 0.8 mm or 1.0 mm nozzle with layer heights between 0.3 mm and 0.4 mm and print speeds of 30 mm/s to 70 mm/s maintains the previously deposited surface above the dry glass transition temperature of approximately 50 °C. At melt temperatures below 260 °C, shear viscosity rises sufficiently to cause under-extrusion and incomplete wetting at the weld interface. At temperatures above 290 °C, chain scission and yellowing are observed when hot-end residence time exceeds 30 min. At a 0.35 mm layer height, 1.0 mm bead width, and 35 mm/s print speed, the volumetric throughput is approximately 12.25 mm³/s, which exceeds the continuous melting capacity of many small hot ends and justifies the use of high-flow large-format extruders. The extrusion multiplier should be calibrated with a single-wall flow test before production because batch-to-batch melt volume-flow rate variation is controlled but not eliminated. Auxiliary cooling fans should be disabled or limited to 30 % duty cycle; premature surface solidification reduces interfacial molecular interdiffusion.

On large-format systems with horizontal axes exceeding 1 m, edge lift and mid-part delamination are the dominant failure modes. PA6/66 exhibits total volumetric shrinkage from melt to solid on the order of 10 % to 14 %. A heated chamber at 60 °C to 80 °C reduces cooling rate and permits stress relaxation. For open platforms without active chamber heating, warping is controlled with a sacrificial raft having 10 mm to 12 mm offset and by keeping first-layer speed below 25 mm/s. The bed surface should be a polyamide-specific adhesive or polyamide sheet; standard PETG adhesive films do not provide adequate bond above 90 °C. The chamber should be cooled below 40 °C before part removal to limit dimensional springback in long axes.

Moisture absorption is the principal process-control variable. Nylon 6/66 reaches an equilibrium moisture content of approximately 2.5 % to 3.5 % by mass at 23 °C and 50 % relative humidity when assessed according to ISO 62. If undried filament enters the melt zone, water volatilizes into steam voids that cause intra-bead porosity, filament diameter swell, and reduced interlayer tensile strength. Drying at 80 °C for 4 h to 6 h in a forced-air desiccant dryer, or in a vacuum oven under reduced pressure, is mandatory after environmental exposure exceeding 24 h. The target residual moisture before extrusion is below 0.15 % by mass as measured by Karl Fischer titration according to ISO 15512. Open spools should be stored in sealed containers with molecular sieve desiccant or under a dew point below -20 °C; re-drying after 8 h of open handling is standard practice. On production-scale large-format printers with direct-drive extruders, inconsistent feed and drive-gear grinding are observed when undried filament is processed; the failure mode is traced to moisture-induced softening and diameter swell at the feeding zone.

When PA6/66 replaces PA12 in fixtures, soft jaws, and thermoforming bucks

For load-bearing assembly fixtures and soft jaws, PA6/66 is selected over PA12 when higher compressive modulus and better creep resistance at 50 °C to 80 °C are required. In the dry state, conditioned PA6/66 printed specimens tested according to ISO 527-2 at 23 °C commonly show tensile strength of 40 MPa to 55 MPa, tensile modulus of 1.5 GPa to 2.3 GPa, and elongation at break of 10 % to 30 %, with XY-oriented specimens generating the higher values. PA12 printed on similar large-format equipment usually shows tensile modulus near 1.3 GPa to 1.6 GPa and a lower heat deflection temperature, which reduces its suitability for heated jig environments. However, PA6/66 absorbs more moisture than PA12; conditioned tensile modulus and glass transition therefore shift downward in humid air, and holes or mating features should be compensated after moisture-conditioned dimensional characterization according to ISO 62.

The tabulated values are not specification limits; they represent typical published ranges for printed coupons and are influenced by raster angle, porosity, and moisture conditioning. Lot-specific batch certificates should be consulted before tolerance analysis.

Tensile Anisotropy and Notch Sensitivity in Thick-Section Large-Format PA6/66 Prints

Tensile anisotropy in PA6/66 prints is introduced by the raster path, the weld boundaries between adjacent beads, and residual cooling stress. For XY-oriented coupons printed with 0/90° raster and tested according to ISO 527-2, the tensile modulus commonly reaches 70 % to 90 % of dry injection-molded PA6/66 reference data. The z-direction tensile strength is substantially lower; values below 20 MPa are observed in coupons printed with layer heights greater than 0.4 mm or with chamber temperatures below 60 °C because incomplete interlayer diffusion leaves elongated micro-voids at the weld plane. Notched impact tests according to ISO 179-1/1eA on z-oriented specimens frequently fall 40 % to 60 % below XY-oriented values, and the fracture surface shows flat interlayer separation rather than ductile tearing. For structural inserts, compression limiters should be inserted into printed bosses, and through-thickness bolting should not rely on the z-axis tensile capacity of the printed wall.

Published fatigue data for large-format FFF PA6/66 under cyclic loading are sparse. In fused filament fabrication, fatigue life is dominated by the weld-line root radius between adjacent beads, which acts as a notch population. Under fully reversed bending, printed nylon parts may initiate crack growth from surface porosity and show a lower endurance ratio than injection-molded equivalents. For rotating jig components, a conservative design limit of 25 % of the monotonic yield strength is used when no component-level cycle data are available. Creep deflection at 60 °C and 5 MPa sustained load is measurable; continued load-bearing use should be validated with an instrumented static fixture for 100 h or more.

Chemical resistance follows polyamide behaviour. The material is resistant to aliphatic hydrocarbons, mineral oils, hydraulic fluids, and dilute alkaline cleaners, but it is attacked by strong mineral acids, phenol, cresols, and some chlorinated solvents. Stress cracking risk is elevated when loaded parts are exposed to methanol, glycol ethers, or zinc chloride solutions; compatibility testing according to ISO 22088-3 or ASTM D543 is required before production use. In applications where printed parts contact brake fluid or coolant, the service temperature must be derated because absorbed fluid plasticizes the polyamide and lowers its heat deflection temperature. Unfilled PA6/66 is electrically insulating and does not require the hardened steel nozzle specified for carbon-fiber-filled polyamides, but it offers lower stiffness and lower thermal conductivity than fiber-reinforced grades. Dielectric properties are not stable in humid environments because absorbed moisture increases surface conductivity and dissipation factor.

Threshold Service Temperatures in Dry and Conditioned States

Short-term use in thermoforming molds and paint-shop fixtures is limited by heat deflection temperature and moisture content. Under the 1.8 MPa load of ISO 75-2/A, dry large-format PA6/66 specimens often exhibit heat deflection temperatures of 70 °C to 95 °C; under the lower 0.45 MPa load of ISO 75-2/B, values of 150 °C to 180 °C are typical. These values drop after conditioning to 50 % RH because water plasticizes the amorphous phase. A tool that survives 180 °C in the dry state may begin to creep at 120 °C after moisture conditioning. For thermoforming applications with surface temperatures above 100 °C, annealed PA6/66 builds with 0.3 mm layer height and high chamber temperature have been evaluated, but published data for this specific configuration is limited. A 4 h to 8 h thermal soak test under target load is recommended before committing to production tooling.

Compared with unfilled PETG and PLA on the same large-format platform, PA6/66 provides higher heat deflection temperature and better fatigue resistance in moving components, but it requires more stringent drying and bed adhesion control. Compared with PA12, PA6/66 provides higher stiffness and hardness but lower dimensional stability in humid air. Compared with carbon-fiber-filled PA6 grades, this unfilled material exhibits lower melt viscosity at equivalent melt temperatures, lower abrasiveness at the nozzle, and higher elongation at break, but lower tensile modulus and lower heat deflection temperature. For a flatness-critical thermoforming mold, post-print annealing at 100 °C for 4 h in a circulating oven with the part clamped between aluminium plates can reduce internal stress, but published data for this specific configuration is limited.