Hexcel HexPEKK EM is a polyetherketoneketone (PEKK) powder feedstock formulated for selective laser sintering (SLS) on high-temperature CO₂ laser powder-bed fusion platforms. The grade designation EM identifies a conductive filler system that moves the consolidated part from the electrically insulating behavior of unfilled PEKK into the static-dissipative and shielding-capable regime. The product is supplied as a free-flowing powder for use in the HexAM additive-manufacturing workflow, with part properties measured after SLS coalescence rather than on injection-molded test plaques. PEKK belongs to the polyaryletherketone family; the 2:1 ketone-to-ether ratio yields a semicrystalline morphology with a glass transition in the 160–170 °C range and a peak melt temperature near 300–315 °C as measured by differential scanning calorimetry according to ISO 11357-3:2018. In SLS, the material is processed on machines with heated build chambers capable of maintaining part-bed temperatures close to the crystallization onset, using 10.6 µm CO₂ laser energy to selectively melt powder layers. The principal differentiator from unfilled HexPEKK 100 is the controlled bulk electrical response, which is intended for avionics housings, electronics assemblies, and aircraft interior components requiring electrostatic discharge control or electromagnetic interference attenuation. The EM filler is dispersed at a size scale below the nominal SLS layer thickness, allowing the powder to flow through recoating blades and preserving a finer as-built surface than typical discontinuous carbon-fiber-filled polyaryletherketone powders.

The powder is not supplied as a one-parameter material. It requires combination with machine-specific laser power, scan speed, hatch spacing, and part-bed temperature settings. These settings are normally delivered as a validated parameter library for a specific high-temperature SLS platform rather than as a universal data sheet because the thermal history at the powder-bed surface controls crystallinity and interlayer diffusion. Hexcel supplies the material under the HexPEKK EM grade designation, with particle-size distribution and bulk density controlled to SLS requirements. Laser diffraction according to ISO 13320-1:2020 is the applicable method for powder particle-size verification; PEKK SLS feedstocks typically show a D50 near 50–60 µm and a bulk density near 0.40–0.50 g/cm³. Powder with excessive fines below 10 µm reduces flow and can form agglomerates in the recoating system, while oversize particles above 150 µm create layer defects and local porosity.

What powder-conditioning and thermal-threshold controls govern HexPEKK EM processing?

Powder conditioning precedes any machine parameter adjustment. At relative humidity above 60%, absorbed moisture on the powder surface reduces flowability and can generate porosity during laser consolidation; PEKK powders are therefore dried before use, with residual moisture held below 0.1 wt% and hopper purge gas maintained at a dew point below −40 °C. The SLS build chamber is purged with nitrogen to hold oxygen below 1.0 vol% to limit thermo-oxidative degradation. High-temperature SLS platforms must preserve part-bed temperature uniformity within ±3 °C across the build envelope because local deviations alter crystallinity and produce Z-direction curl. Layer thickness is selected in the 0.10–0.15 mm range; beam diameter, scan spacing, laser power, and scan speed are adjusted on a machine-OEM parameter library so that the applied energy density produces complete layer-to-layer coalescence without excessive melt-pool spread. Cooling after build is conducted under nitrogen at controlled rates that balance dimensional stability against excessive crystallinity; rates in the 0.5–2.0 °C/min interval are typical for PEKK SLS and must be validated for the EM filler system. Observed production-scale failure modes include powder caking in feed hoppers after moisture intrusion and part-bed edge-temperature drops of more than 5 °C that raise scrap rate. A machine with insufficient part-bed temperature capacity cannot process PEKK at the required thermal setpoint; attempts to compensate by raising laser energy density usually produce surface oxidation, porosity, and part growth rather than cohesive interlayer strength.

The consolidated HexPEKK EM part exhibits a semi-crystalline PEKK property profile modified by the conductive filler. Representative values reported for conductive PEKK SLS grades fall in the following ranges: density 1.29–1.33 g/cm³ by ASTM D792-20, XY tensile strength 80–95 MPa by ASTM D638-14, XY tensile modulus 3.8–4.5 GPa, XY elongation at break 2.5–4.0%, flexural strength 120–145 MPa by ASTM D790-17, flexural modulus 3.5–4.5 GPa, and heat deflection temperature at 0.45 MPa of 160–175 °C by ISO 75-2:2013. Z-direction properties are generally 15–30% lower than XY properties because of interlayer adhesion limits; this anisotropy is not a defect but a design input that must be carried through finite-element analysis. Surface resistivity is commonly measured on printed plaques after surface machining or cleaning with isopropanol, because powder residue or release agents can create a non-conductive skin. Values for the EM grade are specified in the static-dissipative range, typically 10⁵–10⁹ Ω/square under ASTM D257-14; electromagnetic shielding effectiveness is frequency-dependent and is measured using ASTM D4935-18 coupons or coaxial flanges. Published data for HexPEKK EM-specific shielding curves is limited, so application-specific verification must use the exact wall thickness, joint geometry, and post-processing sequence intended for production. The filler system also changes the Poisson’s ratio and fracture response relative to unfilled PEKK; Mode I fracture toughness and critical strain energy release rate should be evaluated under ASTM D5045-14 if the part contains snap-fits or press-fit inserts.

When electromagnetic attenuation and ESD compliance are required in flight-qualified hardware

HexPEKK EM is positioned for components in which an unfilled PEKK would require secondary conductive coatings or metal shielding enclosures. In avionics chassis covers, connector housings, and antenna ground planes, the additive process can consolidate mounting bosses, cable strain reliefs, and shielding surfaces in a single build. The conductive filler system provides volume conductivity that reduces static charge accumulation; surface resistivity is evaluated according to ASTM D257-14, and charge-decay performance is assessed with instrumented charged-plate monitors or IEC 61340-2-3:2016 for the assembled part. Shielding effectiveness requirements are derived from the system-level electromagnetic compatibility specification; a 20–40 dB attenuation range is often requested over 1–10 GHz, but the part geometry and the presence of gaps or joints control the final result. Hexcel HexPEKK EM-specific shielding data should be generated on fused coupons with the production wall thickness and seam design rather than extrapolated from flat plaques. The conductive network can be disrupted by aggressive post-machining or by sanding, which can tear filler-rich surfaces and increase surface resistivity; therefore, machined surfaces should be checked on each build lot with a surface-resistance meter. The material is not a replacement for a metal shield when high shielding effectiveness above 60 dB is required across a broadband range. For ESD-safe interior panels, the critical performance parameter is usually the resistance-to-ground from the printed panel to the aircraft ground network; joints, fasteners, and gaskets must be considered separately because the printed part alone does not guarantee system-level continuity. In connector housings, dimensional change after chemical exposure must be below the clearance allowed for insert retention; a 14-day fluid immersion per ASTM D543-21 is therefore applied to representative hex-shaped housings before mating force measurements.

Comparison with unfilled PEKK and discontinuous carbon-fiber PEKK SLS powders

Unfilled HexPEKK 100 and similar unfilled PEKK SLS powders provide the highest elongation and are electrically insulating; they require conductive coatings for ESD-safe applications. Discontinuous carbon-fiber-filled PEKK grades raise tensile and flexural modulus but introduce greater anisotropy, rougher as-built surfaces, and lower elongation because of fiber alignment in the recoating direction. HexPEKK EM uses a conductive filler system formulated at a size scale below the nominal SLS layer thickness to preserve a finer surface and lower melt-viscosity penalty than fiber-filled grades while adding static-dissipative response. Table 1 summarizes the positioning of the three powder classes using publicly available PEKK SLS property envelopes and test methods. The ranges are not substitutions for the supplier certificate of analysis.

Chemical compatibility screening for HexPEKK EM follows aerospace fluids exposure rather than generic immersion only. PEKK resins are generally resistant to phosphate-ester hydraulic fluids and hydrocarbon fuels; however, the conductive filler may alter surface wetting and should be tested using ASTM D543-21 immersion coupons under 14-day exposure at 60 °C. Collected volatile condensable material data for unfilled PEKK have been reported below 0.1% CVCM under ASTM E595-15, but HexPEKK EM-specific outgassing data is limited and must be requested from the supplier for space applications. The flame, smoke, and toxicity profile of the material is evaluated on finished printed parts because surface porosity and residual powder affect performance; candidate test methods include ASTM E662-21a or FAR 25.853 for smoke density and vertical burn. The EM filler system may reduce the limiting oxygen index relative to unfilled PEKK; therefore, thickness-specific qualification is required. The product is not cleared for direct food-contact use unless a separate FDA 21 CFR 177.2415 or equivalent migration study establishes compliance for the filled formulation. In addition, the use of aggressive solvents such as methylene chloride for vapor polishing should be avoided because solvent penetration can swell the conductive network and alter surface resistivity; if surface smoothing is required, mechanical abrasion followed by controlled reconditioning is preferred.

Support removal, post-machining, and recoating anisotropy impose production constraints

SLS does not require sacrificial support structures in the same sense as vat photopolymerization; the powder bed supports overhangs, but non-fused powder must be removed from internal channels, blind holes, and honeycomb-type features using compressed air, low-frequency vibration, or water-jet cleaning if permitted by the qualification. Post-machining of HexPEKK EM produces a discontinuous conductive network at machined surfaces; reaming or tapping holes can remove conductive filler-rich surface layers and alter resistivity. Batch-to-batch variation in filler dispersion can produce local surface-resistivity differences of up to one decade; therefore, quality control should include conductivity coupons from each build. Recycling of used powder must follow the machine OEM’s refresh rate; excessive recycle ratios reduce elongation and shift melt flow because of repeated thermal exposure. The powder bed temperature that yields optimum surface finish may differ from the temperature that maximizes XY tensile strength, so the process window is a compromise that should be locked by design of experiments rather than by single-variable changes. Parts requiring dimensional stability after humid aging should be conditioned at 23 °C and 50% RH for 48 h before final inspection; machinists should expect edge breakout when drilling thin walls below 0.8 mm and should use sharp polycrystalline diamond tooling. Internal threads in printed holes often require threaded inserts or helicoils because tapped PEKK does not provide metal-like thread durability; insert installation should be preceded by surface-resistance checks to ensure the conductive path remains intact. X-ray computed tomography according to ASTM E1570-21 can be used for internal porosity inspection; porosity below 2% is typical after optimized SLS, but local pores at recoating edges may be higher and must be considered for pressure-containing parts.