Large-format PETG filament is applied on automotive assembly lines as a fabrication stock for locating fixtures, go/no-go gauges, and end-of-arm robot grippers. The material is extruded through a 0.6 mm or 1.0 mm hardened steel nozzle at a melt temperature between 235°C and 245°C. Layer height is set to 0.2 mm for critical locating faces and increased to 0.4 mm for non-critical mass sections. Printed fixture bodies are reinforced at bolted interfaces with wall thicknesses of 5 mm or greater to reduce creep. In production environments where ambient temperature exceeds 30°C, polycarbonate or fibre-reinforced ABS is substituted. Published data for PETG fixture performance under cyclic clamp loads is limited. ASTM D638-14 tensile values for BigRep PETG are often cited as 45–48 MPa along the XY plane. The Z-plane interlaminar tensile value is approximately 50–70% of XY, requiring orientation of critical pins perpendicular to the tensile load. For large parts printed on a large-format FFF platform, a 50 mm brim is used to prevent edge lift.

The base PETG compound is tumble-blended with 2–4 wt% pigment masterbatch before extrusion on a twin-screw line. Pigment loading above 4 wt% raises melt viscosity enough to require a nozzle setpoint increase of 5–10°C. Batch-to-batch filament diameter variance of ±0.05 mm changes volumetric throughput; operators using 2.85 mm filament and 0.6 mm nozzles calibrate the feed rate multiplier per lot. Melt flow rate is measured per ISO 1133-1:2022 at 250°C under 2.16 kg. The dominant processing conflict is between interlayer fusion and surface finish. At 235°C, melt viscosity is high enough to reduce layer fusion and increase notch sensitivity. At 245°C, die swell and stringing increase. The practical window for this material on large-format extruders is therefore held within ±5°C around 240°C. A 100 mm single-wall spiral print is used to confirm melt consistency; acceptable wall width is 0.60–0.65 mm at 0.2 mm layer height. Failure modes observed on automotive assembly lines are corner cracking at heat-set inserts, Z-layer splitting under clamp preload, and creep at M8 bolt bosses.

What Limits Continuous Service Temperature in Under-Hood Fixtures?

Continuous immersion in ethylene glycol–water coolant at 80°C is not supported. The heat deflection temperature of the unreinforced material under 0.455 MPa is approximately 68°C per ASTM D648-07. The Vicat softening point is reported near 79°C under ISO 306 method B50. These values define a practical continuous service ceiling of 55–60°C in mechanically loaded fixtures. Short-term excursions to 70°C for 15 minutes may not cause dimensional collapse, but mating surface tolerances typically shift by 0.3–0.5%.

Coolant exposure also affects interlayer adhesion. The interface between layers is the weakest zone; ethylene glycol migration at 50°C can reduce interlaminar shear by up to 25% depending on print direction. For parts that must survive cooling system pressure tests at 1.5 bar, a post-print annealing cycle at 60°C for 2 hours in a circulating air oven is recommended. Annealing reduces residual stresses but can induce Z-axis shrinkage of 0.2–0.8%. Compensation for drilled hole locations must be validated on a production-scale dummy build. REACH 1907/2006 requires documentation of SVHC content in the filament; downstream automotive suppliers retain batch-level SDS and RoHS 2011/65/EU Annex II declarations.

Under-hood fixtures that encounter hot oil mist, brake fluid, or power steering fluid are not recommended. Published data for BigRep PETG in continuous hot coolant immersion is limited. The usual industrial test consists of a 300 mm gauge block immersed in 50°C 50:50 water–ethylene glycol for 7 days. Dimensional change greater than 0.5% or visible whitening at layer boundaries triggers replacement with a higher-temperature material.

Vacuum Forming Pattern Compensation and Thermal Cycling

In vacuum forming tooling development, the printed PETG master pattern is dimensionally compensated before machining. A pattern is typically designed with 0.5–1.0% shrinkage allowance when forming HIPS or ABS sheet, but published data for PETG-on-PETG forming is limited. The pattern surface is sealed with a two-part epoxy sanding sealer to close layer grooves before polishing to Ra 0.8 µm. Without sealing, formed parts replicate layer ridges. Tool surface temperature is kept below 65°C during forming cycles; above this, pattern softening and edge definition loss occur. In pilot runs, a 4 mm PETG sheet is heated to 150–160°C, draped over the PETG pattern, and cooled under vacuum at -0.8 bar. The tool is inspected for compressive set after each cycle. Internal ribs printed with 20% gyroid infill and 3 perimeter walls reduce print time while resisting vacuum load. Large pattern bodies are printed in segments and solvent-welded with dichloromethane or bonded with two-component epoxy. The bond seam is located away from high-draw areas. Failure mode observed on production-scale forming lines is edge chipping at the pattern perimeter where vacuum holes are drilled. Chamfering the hole entry to 1 mm radius mitigates crack propagation.

Thermal cycling on vacuum formers is asymmetric: the upper surface sees sheet heat, while the core remains cooler. This creates a through-thickness temperature gradient of 15–25°C. Repeated cycling can cause delamination in printed patterns with fewer than 3 perimeter walls. Pattern life is extended by printing with 30% infill and 5 perimeters in the first 10 mm of pattern height. The remaining upper volume is filled at 15–20% gyroid. Drilling vacuum holes with a 2 mm drill at 1200 rpm, with sacrificial scrap backing the exit side, reduces breakout.

Prototype guides, lane dividers, and drop chute housings for dry-food packaging lines are printed in BigRep PETG when stainless-steel fabrication is too slow for trial runs. The choice is confined to low-moisture or indirect contact duties because the filament supplier does not typically certify the printed article for direct fatty food contact under EU 10/2011. A specific FDA 21 CFR 177.1315 compliance statement for the final printed part is not automatically transferred from the base resin. A cleaning protocol for incidental product contact is based on 70% isopropyl alcohol or quaternary ammonium solution at 22°C. Steam sanitation at 121°C is outside the capability of the polymer; heat deflection temperature falls below autoclave condition. In dry cereal handling, the part must be smooth to prevent microbial harborage. For FFF PETG, layer grooves are sealed with FDA-compliant epoxy if direct food contact is required. The epoxy is cured at 23°C for 24 hours and then washed with 0.1 M sodium hydroxide to remove amine blush. Published data for the migration of PETG oligomers from FFF parts under repeated 70% ethanol exposure is limited. Downstream users often run cleanability verification per ISO 14159. The acceptance criterion is no visible residue after 10 wash-and-dry cycles and no surface roughness increase above Ra 1.6 µm.

When Quaternary Ammonium Disinfectants Contact Non-Invasive Medical Device Housings

Devices deployed in hospital usability tests are printed with BigRep PETG for non-invasive housings, diagnostic equipment shields, and training models. The material is not validated for long-term implantation or mucosal contact. The practical boundary is an external housing wiped with bleach-free disinfectant. Quaternary ammonium compounds at 0.1–0.5% concentration in water cause minimal visible change after 24-hour immersion at 23°C, based on published general PETG chemical resistance data. Alcohols such as 70% ethanol may induce environmental stress cracking if printed parts carry high residual stress from non-uniform cooling. Stress relief at 60°C for 1 hour per 10 mm wall thickness is used before disinfectant exposure. A 50 mm diameter disk printed with 0.2 mm layers and tested per ASTM D543-20 is used to screen disinfectant compatibility. The acceptance criterion is no visible cracking and less than 1.0% mass change after 24 hours at 23°C. In clinical usability tests, the printed housing is reinforced with brass heat-set inserts at M3 and M4 sizes. Insert boss outside diameter is at least 2.5 times the insert diameter to prevent hoop stress cracks. If the device is used in a room with 60% relative humidity, the filament spool is dried for 4 hours at 65°C before extrusion. The printed parts are then conditioned at 23°C and 50% RH for 48 hours before dimensional inspection.

When an outdoor enclosure must move from CAD to field trial in 48 hours, BigRep PETG is often selected over ASA for its lower warp tendency and simpler print sequence. The material withstands rain and UV better than PLA but is not a replacement for ASA or polycarbonate in 10-year outdoor exposure. Published data for unfilled PETG weathering reports tensile retention of approximately 80% after 2000 hours of QUV-B exposure. Direct comparison to BigRep PETG requires verification on a spool-specific basis. For outdoor use, the enclosure is printed with 30% infill and sealed with a polyurethane topcoat. The topcoat is applied at 60–80 µm dry film thickness. All cable glands and mounting holes are sealed with silicone RTV. Continuous service in direct sunlight at ambient temperatures above 40°C causes heat build-up on dark-coloured surfaces; surface temperature can reach 65°C, approaching the heat deflection temperature. Use of white or light grey material is specified for solar load. The lid-to-body interface is designed with a 3 mm overlap and a 50A durometer silicone gasket compressed to 25%. Thermal cycling between -20°C and 50°C causes differential expansion; PETG has a coefficient of linear thermal expansion of approximately 70–80 µm/m·K. A 500 mm long enclosure therefore expands 0.35–0.40 mm over that 70°C range. Mounting holes are slotted by at least 0.5 mm to accommodate this movement. Printed enclosure parts are tested for water ingress according to IEC 60529 IPX5 or IPX6 depending on mounting orientation. In IPX5 spray tests, failure occurs at layer bond lines before the bulk material if layer adhesion is compromised by moisture.