PAI CNC Machining

PAI, or polyamide-imide, is a high-performance amorphous thermoplastic known for its exceptional strength, rigidity, and thermal stability. It offers continuous service temperature around 250°C, excellent wear resistance, low friction, and good chemical resistance. Its mechanical properties are among the highest of any machinable thermoplastic, particularly in terms of creep resistance and dimensional stability under load. These characteristics make PAI a common choice for high-temperature bearings, bushings, wear rings, valve seats, and precision components in aerospace, industrial equipment, and semiconductor applications where PEEK's temperature limit is insufficient and PI's brittleness is a concern.

Unfilled PAI is the standard grade for general-purpose parts requiring high strength and thermal stability. Glass-filled PAI offers higher stiffness and lower thermal expansion, making it suitable for structural components. Graphite-filled and PTFE-filled PAI grades provide improved wear resistance and lower friction for bearing and sliding applications. PAI is commonly supplied under the trade name Torlon, but it is also available as generic polyamide-imide stock. The grade and filler type should be specified on the drawing because machinability and wear behavior differ between filled and unfilled versions.

PAI machines better than PI and roughly comparably to PEEK, but with its own characteristics. It is hard and rigid, producing chips rather than dust, and it holds dimensions well during machining. The main challenges are its notch sensitivity and its tendency to crack under stress if tooling is dull or clamping force is excessive. Glass-filled PAI is more abrasive and will wear tooling faster than the unfilled grade. Sharp carbide tooling, rigid setups, and moderate cutting parameters are standard. Overall, PAI is considered machinable for a high-performance thermoplastic, though it rewards careful process planning.

Standard machining holds ±0.02 to ±0.05mm. Precision work holds ±0.01mm on critical features. PAI's low thermal expansion and excellent creep resistance make it more predictable than most plastics for tight-tolerance work. The main risks are edge chipping and cracking, particularly on thin walls or sharp internal corners. Stress-relief annealing before finish machining is advisable for parts with tight tolerances or complex geometry, because machining-induced stress can cause slow cracking or dimensional drift after the part is put into service.

Yes, for most precision parts. PAI stock carries internal stress from the manufacturing process, and machining removes material unevenly, which can cause warping or cracking. Annealing the stock before machining, and sometimes between roughing and finishing, reduces this risk. The same applies to finished parts that will see elevated temperatures in service: stress relief improves dimensional stability and reduces the chance of stress cracking. Because PAI is often used in applications where failure is expensive, the annealing step is not one to skip.

As-machined PAI has a smooth surface with visible tool marks, typically Ra 1.6 to 3.2μm. Bead blasting produces a uniform matte finish. Polishing can achieve a higher gloss where appearance or low friction matters. Because PAI is usually specified for functional rather than decorative reasons, coatings are uncommon, though conformal coatings can be applied where additional electrical insulation or environmental protection is needed. PAI's natural color ranges from amber to dark brown depending on the grade and filler.

Aerospace: bushings, wear rings, and structural components in high-temperature zones. Industrial: bearings, seals, and valve seats in pumps and compressors. Semiconductor: wafer handling components and insulators requiring high-temperature resistance. Automotive: thrust washers and transmission components where high-temperature wear resistance is needed. PAI is often chosen where PEEK's temperature limit is insufficient or where its creep resistance and dimensional stability under load are the deciding factors.

PAI offers higher continuous service temperature than PEEK, roughly 250°C versus 260°C for PEEK, with better creep resistance and dimensional stability under load. It is also more expensive and more difficult to machine than PEEK because of its rigidity and notch sensitivity. Compared to PI, PAI is tougher and less brittle, making it easier to machine and less prone to cracking, though PI offers slightly higher temperature capability and lower outgassing. For applications requiring high strength and thermal stability with better toughness than PI, PAI is often the practical choice.

Milling up to 650 × 550 × 450mm. Turning up to 600mm diameter and 1,500mm length. PAI stock is typically available in smaller sections than commodity plastics, so very large parts may require assembly or may fall outside standard stock availability. Because PAI is brittle and expensive, large parts also carry higher risk during machining and handling, so the geometry and stock size should be reviewed during quoting.

Material test reports with grade identification and lot traceability. Dimensional inspection reports. Certificates of conformance. For aerospace applications, thermal and flammability test data is provided. For semiconductor applications, outgassing data and purity certificates are available on request. If stress-relief annealing is performed, the heat treatment record is included. Because PAI is often specified for critical applications, the material certificate and the processing record are usually reviewed as part of the customer's qualification process.