A Practical Guide to PSU Material and CNC Machining

Polysulfone (PSU) is a high-performance engineering thermoplastic prized for its exceptional thermal stability, mechanical strength, and resistance to hydrolysis and chemicals. These properties make it ideal for demanding applications in medical devices, aerospace components, and precision industrial equipment—especially when parts must endure repeated sterilization, long-term loads, or exposure to aggressive environments.

For low-volume production, complex geometries, or rapid prototyping, CNC machining of PSU rods and sheets has become the go-to method—offering high dimensional accuracy without the need for expensive molds. This guide provides a practical, step-by-step overview of working with PSU in CNC operations, from material selection to post-processing.

1. Why Choose PSU for CNC Machining?

PSU stands out among engineering plastics for CNC applications due to:

• High heat resistance: Continuous use up to 150°C; withstands steam autoclaving (121–135°C).
• Excellent dimensional stability: Low moisture absorption (<0.4%) and minimal warpage during machining.
• Good mechanical properties: High tensile strength (~70 MPa) and rigidity, even at elevated temperatures.
• Inherent flame retardancy and compliance with medical/food-contact standards (e.g., USP Class VI, FDA).

Unlike metals, PSU is lightweight and electrically insulating; unlike commodity plastics, it maintains performance under stress and heat—making it perfect for structural, load-bearing CNC-machined components.

2. Selecting the Right PSU Semi-Finished Product

CNC machining starts with quality raw material. PSU is typically supplied as extruded rods, plates, or tubes, which serve as blanks for milling, turning, or drilling.

Key considerations when selecting stock:

• Extruded vs. compression-molded: Extruded PSU offers better consistency for standard sizes; compression-molded may be used for thick plates but can have higher internal stress.
• Pre-drying is critical: PSU must be dried at 120–140°C for 4–6 hours before machining to prevent surface defects (e.g., splay, bubbles).
• Low internal stress: Choose suppliers that control cooling rates during extrusion to minimize residual stress—this reduces deformation during and after machining.

Tip: Always verify that your PSU stock is specifically rated for mechanical machining—not all grades are optimized for this.

3. CNC Machining Best Practices for PSU

PSU machines well but requires attention to thermal and mechanical sensitivity. Follow these guidelines for reliable results:

3.1 Tooling and Cutting Parameters

Use sharp carbide tools with polished flutes to reduce friction and heat buildup.

• Cutting speed: Keep relatively low (e.g., 80–150 m/min for milling).
• Feed rate: Use moderate to high feed to avoid rubbing and localized melting.
• Depth of cut: Prefer multiple light passes over deep cuts to manage heat and stress.

3.2 Cooling and Chip Removal

• Air cooling is preferred; avoid water-based coolants unless absolutely necessary (PSU absorbs minimal moisture, but coolant residue can affect biocompatibility).
• Ensure efficient chip evacuation—long PSU chips can re-weld to the part if not removed promptly.

3.3 Design for Machinability

Avoid sharp corners: PSU is notch-sensitive. Use generous radii (≥0.5 mm) or chamfers on edges and internal corners to prevent stress cracking.

• Minimize thin walls: While PSU can be machined thin, sections <1.5 mm may flex or vibrate during cutting, affecting tolerance.
• Account for slight springback: Though low, elastic recovery can affect press-fit features.

3.4 Post-Machining Stress Relief (Annealing)

Machining introduces localized stresses that can lead to delayed cracking or dimensional drift. Stress-relief annealing is strongly recommended:

• Heat to 160–170°C (10–20°C below PSU’s Tg of ~185°C).
• Hold for 2–4 hours, then cool slowly in the oven (≤10°C/hour).

This step significantly improves long-term stability—critical for medical or aerospace parts.

4. Typical CNC-Machined PSU Applications

Thanks to its balance of performance and machinability, PSU is commonly used in:

• Medical: Surgical instrument handles, endoscope housings, reusable sterilization trays, fluid manifolds.
• Industrial: High-temperature electrical insulators, sensor mounts, pump components, semiconductor wafer carriers.
• Aerospace: Non-structural interior brackets requiring flame resistance and low smoke emission.

These applications benefit from CNC’s ability to produce complex, tight-tolerance parts without compromising PSU’s inherent advantages.

5. Partnering with a Reliable PSU Supplier

Success in PSU CNC machining begins with consistent, high-quality semi-finished stock. Shengwen Technology specializes in producing PSU rods and sheets engineered specifically for precision machining, featuring:

• Uniform molecular orientation and low internal stress
• Factory-controlled pre-drying to eliminate moisture-related defects
• Tight dimensional tolerances and smooth surface finish
• Custom sizes and technical support for challenging applications

Whether you’re developing a prototype or scaling low-volume production, Shengwen provides the material foundation for reliable, high-performance PSU components.

Contact Shengwen today for free samples, material data sheets, or expert advice on optimizing your PSU CNC machining process.

Conclusion

CNC machining unlocks the full potential of PSU for high-value, low-volume applications where precision, reliability, and performance under stress are non-negotiable. By understanding PSU’s material behavior and applying best practices—from stock selection to post-annealing—you can consistently produce parts that meet the most stringent medical and industrial standards. With the right material partner, PSU becomes not just a plastic, but a strategic engineering solution.