PSU CNC Machining

PSU, or polysulfone, is an amorphous high-performance thermoplastic known for its good balance of thermal stability, mechanical strength, and hydrolytic resistance. It offers continuous service temperature around 150°C, excellent dimensional stability, good electrical insulation, and transparency in its natural amber form. PSU is resistant to hot water and steam, though less so than PPSU, and it tolerates repeated sterilization cycles. These properties make PSU a common choice for medical device components, food processing equipment, electrical insulators, plumbing parts, and membrane housings in water treatment.

Unfilled PSU is the standard grade for most machined parts, offering the best balance of toughness and machinability. Glass-filled PSU offers higher stiffness and lower thermal expansion, making it suitable for structural components, though the reinforced grade is more abrasive to tooling. PSU is supplied as rod and plate for machining, and the grade should be specified on the drawing because filled and unfilled versions have different machining behavior. PSU is commonly known under trade names such as Udel, but it is also available as generic polysulfone stock.

PSU machines well for a high-performance thermoplastic, roughly comparably to PPSU and more easily than PEEK. It cuts cleanly with sharp carbide tooling and produces manageable chips. The main challenges are its notch sensitivity and its tendency to stress crack if clamping force is excessive or if residual stress is left in the material. Glass-filled PSU is more abrasive and will wear tooling faster. Overall, PSU is considered moderately machinable, and the process is closer to machining PPSU than to machining PEEK.

Standard machining holds ±0.02 to ±0.05mm. Precision work holds ±0.01mm on critical features. PSU's low moisture absorption and good dimensional stability make it predictable for tight-tolerance work. The limiting factor is usually residual stress and clamping distortion, particularly on thin-wall sections. Stress-relief annealing before finish machining is advisable for parts with tight tolerances or complex geometry.

Yes, for parts with tight tolerances or thin sections. PSU stock carries internal stress from the extrusion process, and machining removes material unevenly, which can cause warping or stress cracking after machining. Annealing the stock before machining, and sometimes between roughing and finishing, reduces this risk. The same applies to finished parts that will be exposed to elevated temperatures or repeated sterilization: stress relief improves dimensional stability and reduces the chance of environmental stress cracking.

PSU is compatible with steam autoclaving, ethylene oxide, and gamma radiation sterilization, though its resistance to repeated steam cycles is lower than that of PPSU. For applications requiring several thousand autoclave cycles, PPSU is the better choice. For applications with fewer sterilization cycles or with other sterilization methods, PSU is adequate and less expensive. If your part will be sterilized by a specific method, confirm this at quoting so the grade and the machining process are aligned with the sterilization cycle.

As-machined PSU 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 matters. Because PSU is often used in medical and food applications, the surface must be cleanable and free of features that trap contaminants, so the finish specification often includes a cleanliness requirement rather than just a roughness number. PSU's natural color is transparent amber; it can be supplied in opaque colors for specific applications.

Medical: device housings, sterilization trays, and instrument components that see repeated sterilization. Food processing: components that contact hot food or are cleaned with hot water and steam. Electrical: insulators, connector bodies, and standoffs. Water treatment: membrane housings and components that see hot water and chemical exposure. Industrial: pump and valve components in hot water or steam service. PSU is often chosen where PPSU's higher cost is not justified by the number of sterilization cycles or the severity of the environment.

PSU is less expensive than PPSU and PEEK, with lower continuous service temperature than both, around 150°C. PPSU offers better hydrolytic stability and resistance to repeated steam sterilization, making it the better choice for reusable medical instruments. PEEK offers higher temperature capability, roughly 260°C, and better chemical resistance, but at significantly higher cost and with more difficult machining. For applications up to roughly 150°C with moderate sterilization requirements, PSU is often the cost-effective choice.

Milling up to 650 × 550 × 450mm. Turning up to 600mm diameter and 1,500mm length. PSU stock is available in a range of plate and rod sizes, though very large sections may be limited by stock availability. Because PSU is notch-sensitive and prone to stress cracking, large parts benefit from stress-relief annealing and careful fixture design to avoid point loading during machining.

Material test reports with grade identification and lot traceability. Dimensional inspection reports. Certificates of conformance. For medical applications, biocompatibility and sterilization compatibility documentation is available on request. For food contact applications, FDA and EU food contact compliance certificates are provided where applicable. For water treatment applications, NSF or equivalent compliance documentation is available on request. If stress-relief annealing is performed, the heat treatment record is included.