PEEK Machining in Kokomo, IN: Unfilled, Glass-Filled, and Carbon-Filled Grades for EV and Powertrain Applications

Unfilled PEEK (natural, ivory-colored) is the baseline grade — polyether ether ketone homopolymer without additives. It delivers tensile strength of approximately 100 MPa, flexural modulus of 580,000 PSI, continuous service temperature of 250°C, and essentially zero moisture absorption (0.1 percent at saturation). Its purity makes it the choice for applications where leachables matter: food processing equipment, pharmaceutical fluid handling components, and medical implant accessories where extracted particles must meet biocompatibility standards per ISO 10993. In Kokomo's EV supply chain, unfilled PEEK is specified for cell holder spacers and insulating standoffs within battery modules where dimensional stability over a -40°C to 150°C thermal cycle is required without introducing filler particles that could compromise cell chemistry. Glass-filled PEEK — typically 30 percent short glass fiber by weight, branded as Victrex PEEK 450GL30 or equivalent — improves stiffness and reduces thermal expansion at the cost of some impact toughness and electrical insulation. Flexural modulus increases from 580,000 PSI to approximately 1,400,000 PSI, and the coefficient of thermal expansion drops from 47 ppm/°C (unfilled) to 20 ppm/°C, critical when PEEK components are assembled adjacent to aluminum or steel structures that constrain thermal growth. Bearing cages, pump impellers, and connector housings in transmission fluid environments are natural 30GF PEEK applications — the glass fiber improves creep resistance under sustained load at 150°C where unfilled PEEK would deflect measurably over a long service period. Carbon-filled PEEK — 30 percent short carbon fiber — pushes performance further: tensile strength to 200 MPa, flexural modulus to 2,500,000 PSI, and thermal expansion to 15-18 ppm/°C, approaching that of aluminum. The carbon fibers also increase thermal conductivity (from 0.25 to approximately 1.0 W/m·K) and make the material electrically conductive — important to note when electrical isolation is required. Carbon-filled PEEK is the choice for structural load-bearing brackets, wear pads, and thrust washers in powertrains where maximum stiffness and wear resistance justify the material's premium cost over glass-filled grades.

PEEK machines more like aluminum than like most plastics, and shops already equipped for precision aluminum work in Kokomo's powertrain supply chain adapt readily. Unfilled PEEK turns and mills cleanly at spindle speeds of 3,000-8,000 RPM with standard uncoated carbide tooling, producing burr-free edges and surface finishes of Ra 32-63 microinch routinely. The key parameter is chip evacuation: PEEK generates long, stringy chips in turning operations that must be broken by appropriate tool geometry or interrupted by peck drilling and pecking passes to prevent chip recutting that degrades surface finish. Glass-filled and carbon-filled PEEK are more abrasive — the filler particles wear cutting edges faster than unfilled PEEK, requiring PVD-coated carbide or diamond-coated tooling for production runs. Surface finish with worn tooling deteriorates quickly, so tool life monitoring and replacement intervals must be established from sample runs before committing to production. Carbon-filled PEEK in particular generates electrically conductive dust that requires dedicated vacuum extraction and periodic machine cleaning to prevent contamination of spindle bearings and linear guides. Tolerance capability for CNC-machined PEEK depends heavily on thermal management. PEEK has a coefficient of thermal expansion approximately 2.5 times higher than steel, so bore diameters and profile dimensions change measurably between the shop floor temperature and the part's operating temperature. For Kokomo automotive programs requiring PEEK bearing cages or seal carriers held to ±0.001 inch at 23°C, the design engineer must account for thermal growth at 150°C service temperature — a 1-inch diameter unfilled PEEK bore will grow approximately 0.003 inch when heated from 23°C to 150°C. Coordinating with the machining shop on in-process temperature control and post-machining conditioning (24-hour temperature soak at 23°C before final inspection) ensures dimensional acceptance criteria are met.

One of PEEK's most compelling attributes for Kokomo's transmission and EV applications is its chemical resistance profile. Unfilled and filled PEEK grades are rated for continuous exposure to: ATF (automatic transmission fluid) at 150°C, engine oils, brake fluids, and most industrial hydraulic fluids. They resist dilute acids and bases that would attack polyamide (nylon) or acetal components and are unaffected by the phosphate ester and glycol-based coolants used in EV thermal management systems. This resistance is why PEEK seal carriers and valve seats in transmission hydraulic circuits can be specified for the life of the vehicle without fluid-compatibility qualification that cheaper polymers require annually. For EV battery module applications near Samsung SDI programs, PEEK components adjacent to lithium-ion cells must be evaluated for compatibility with electrolyte vapor (lithium hexafluorophosphate in ethylene carbonate/dimethyl carbonate) — a requirement beyond standard automotive fluid compatibility. Published data shows unfilled PEEK maintains dimensional stability and tensile strength within 5 percent after 1,000 hours immersion in standard LiPF6 electrolyte at 60°C, making it one of the few structural polymers qualified for direct contact with battery module internals. Qualification testing for PEEK components entering Kokomo automotive production programs typically requires PPAP Level 3 documentation: dimensional report on 30 production parts, material certification to the applicable grade specification (Victrex, Solvay, or equivalent), and functional validation in the assembly. For components in contact with transmission fluid at temperature, a 500-hour fluid immersion test per ASTM D543 with dimensional re-check confirms retention of tolerances within print limits.

PEEK stock — rod, plate, and tube in unfilled, 30GF, and 30CF grades — is available from regional plastic distribution centers in Indianapolis that carry Victrex, Ketron, and Sustapeek brands. Standard rod diameters from 0.5 inch to 6 inch in unfilled and 30GF grades typically carry two-to-three-week delivery; 30CF and specialty grades (bearing-grade PEEK with PTFE and graphite) may require four-to-six-week lead times. Large-section plate for complex machined components — 2-inch or thicker PEEK plate — may require eight-plus weeks if not in regional stock. For Kokomo programs with tight launch timelines, ordering PEEK stock to arrive before design finalization and having machining capacity committed in advance avoids the combination of material and capacity lead times that can add two to four weeks to a first-article delivery. ManufacturingBase surfaces regional plastic machining shops with verified PEEK experience, reducing the risk of sourcing a shop unfamiliar with the material's thermal and machining behavior.

PEEK is not always the right answer. Polyphenylene sulfide (PPS) offers similar chemical resistance at 40 percent lower cost with a 220°C service temperature, making it preferred for applications that do not reach PEEK's performance ceiling. Polyimide (PI) and PEKK (polyether ketone ketone) extend the temperature range above PEEK — PI to 300°C+ for short-term exposure — at even higher cost. For Kokomo buyers, the practical decision matrix is: use PPS where temperatures stay below 200°C and cost is the primary driver; specify unfilled PEEK where electrical insulation, biocompatibility, or electrolyte resistance is required; choose 30GF PEEK for loaded structural applications above 150°C; and reserve 30CF PEEK for maximum stiffness and wear resistance applications where cost is secondary. In EV battery module design, some Tier 1 suppliers have standardized on PEEK for all polymeric structural components within the module to simplify the material qualification process — one polymer, one set of fluid compatibility data, one supplier qualification file. The cost premium over engineering-grade nylon or PPS is justified by the reduction in qualification engineering hours and the elimination of fleet liability risk from an under-specified polymer component in a high-voltage assembly.