Wexmar handles Monel 400 and K500 CNC machining for pump shafts, valve stems, fasteners, fittings and marine hardware. Both are nickel-copper alloys with strong resistance to seawater, brines, hydrofluoric acid and many alkalis. Monel 400 (UNS N04400) is strengthened only by cold work. Monel K500 (UNS N05500) adds aluminum and titanium so it can be age hardened to roughly two to three times the yield strength of 400. We turn, mill and Swiss-machine both grades at our shop in Canastota, NY.
Monel machinability ratings
Approximate ratings on the AISI 1212 = 100 scale are about 20 for Monel 400 and about 15 for aged K500. Monel 400 is gummy and work hardens, so it smears and forms built-up edge if the tool is not sharp. Aged K500 is harder and more abrasive, which shifts the problem from smearing toward edge wear and heat.
Both grades have low thermal conductivity compared with steel, so heat builds at the tool instead of leaving with the chip. Surface speeds are set well below those used on 304 stainless, and inserts are indexed on a schedule rather than run until they fail. Cold-drawn Monel 400 bar is noticeably firmer than annealed bar, and we check the material condition on the mill cert before programming speeds and feeds, since the same part can cut quite differently from one heat lot to the next.
Tolerances and surface finish
For precision Monel parts we typically hold plus or minus 0.0005 in. on turned diameters and plus or minus 0.001 in. on milled features. Typical finishes run 63 Ra as machined, with 32 Ra on seal and bearing diameters. Long K500 pump shafts need close attention to straightness and runout, which we control with steady support during turning and verify during inspection. These values are typical, not guaranteed.
Machining gotchas for Monel 400 and K500
Monel 400
Sharp, positive-rake carbide with a polished rake face resists buildup. Feeds must stay heavy enough to cut under the work-hardened skin left by the previous pass. Chips are long and tough, so chipbreaker selection and peck drilling matter. Parts must be cleaned thoroughly of cutting fluid before any heat treatment, since sulfur and lead contamination can embrittle nickel alloys at temperature.
Monel K500
Aged K500 cuts more predictably with tough coated carbide grades, lower surface speed and flood coolant. Some programs rough in the annealed condition, age through qualified outside processors and finish afterward, because aging can cause slight size change. Burrs on both grades are ductile and tenacious, so chamfers and deburr passes are programmed into the cycle rather than left to the bench.
Heat treat and finish options
Monel 400 is not age hardenable; stress relief after heavy machining is available through qualified outside processors. K500 is age hardened, sometimes after a solution anneal, through qualified outside processors, with hardness reported on the processor cert. Most Monel parts ship bare because of the alloy's native corrosion resistance, but cleaning, pickling or plating can be arranged through qualified outside processors when specified.
Common Monel parts and Wexmar processes
- Pump shafts and propeller shafts: CNC turning on Mazak lathes, with centerless grinding in-house for OD work
- Valve stems, seats and trim: lathes with live tooling and Y-axis
- Bolts, nuts, pins and small fittings up to 32 mm diameter: Swiss-type machines with bar feeders
- Manifold blocks and instrument bodies: 4-axis horizontal machining centers
- Wear rings and bushings for seawater pumps: CNC lathes
Cost index versus 6061 aluminum
| Material | Approx. machinability (1212 = 100) | Cost index vs 6061 | Notes |
|---|---|---|---|
| Monel 400 | ~20 | 5.0 | Gummy, cold-work strengthened |
| Monel K500 (aged) | ~15 | 6.0 | Age hardened, abrasive |
| Inconel 625 | ~15 | 7.0 | Higher temperature service |
| Hastelloy C276 | ~12 | 9.0 | Severe chemical service |
| CP titanium Grade 2 | ~35 | 4.0 | Seawater alternative |
| 316 stainless | ~36 | 2.5 | Lower cost, less resistant |
| 6061-T6 aluminum | ~180 | 1.0 | Cost index baseline |
These values are typical and illustrative for a comparable part; actual quotes depend on geometry, quantity, tolerances and mill pricing.
Applications and industries
Monel parts serve pump and fluid power manufacturers, marine and seawater systems, chemical processing, instrumentation and defense build-to-print programs. Material certs and heat-lot traceability are available on request. See the industries we serve, or compare Inconel 625 for higher temperature service.
Getting a quote
For Monel machining services, upload a drawing for an instant estimate or call (315) 400-2654. A human estimator confirms every quote, including grade, condition and any aging requirement.