SmCo magnets crack without warning. We’ve had a customer send us a batch of Sm2Co17 arc segments — 40 pieces total — and ask why their blade saw was destroying 1 in 4 during slicing. The answer was thermal shock. SmCo has a fracture toughness around 1.0 MPa·m^(1/2), roughly the same as window glass, and any heat-generating process concentrates stress right where you don’t want it. Ferrite magnet cutting presents a similar challenge: strontium ferrite (SrFe12O19) is cheap and everywhere, but it chips like a ceramic tile if the feed force is even slightly too high.
Both materials demand a cold, low-force cutting method. That’s where diamond wire comes in — and why we’ve developed specific parameter sets for SmCo and ferrite that keep edge chipping below 50 μm on production parts.
This article covers the cutting characteristics of SmCo and ferrite magnets, the specific wire saw parameters that work, and the mistakes that lead to cracked parts. If you’ve already read our overview of diamond wire cutting for magnetic materials, this goes deeper into the two material families that cause the most trouble on the shop floor.
Why Are SmCo and Ferrite Magnets So Difficult to Cut?
The short answer: they’re both ceramics, mechanically speaking.
SmCo (both Sm1Co5 and Sm2Co17 grades) is a sintered intermetallic compound. It’s hard — typically HRC 55–65 depending on the grade — and has almost no plastic deformation capacity. When stress exceeds the fracture threshold, the material doesn’t bend. It snaps. The fracture toughness of Sm2Co17 sits around 1.0–1.2 MPa·m^(1/2), which is comparable to NdFeB 자석 but with one critical difference: SmCo’s Curie temperature is 700–800°C versus NdFeB’s 310–340°C. That means SmCo gets used in aerospace actuators, military-grade sensors, and downhole drilling tools where temperatures routinely exceed 150°C. You can’t afford edge damage on these parts — they go into assemblies where dimensional tolerance is tight and surface cracks propagate under vibration loading.
Ferrite is a different animal. Barium ferrite (BaFe12O19) and strontium ferrite (SrFe12O19) are true ceramics — oxide-based, sintered at 1200–1300°C, with Vickers hardness around HV 500–600. They’re the most widely produced permanent magnets in the world by volume, largely because the raw materials (iron oxide + strontium/barium carbonate) are abundant and inexpensive compared to rare earth elements. But that low cost comes with a catch: ferrite is extremely brittle. We’ve seen ferrite arc segments crack from nothing more than clamping pressure during fixturing.
The table below summarizes the key mechanical differences:
| 속성 | SmCo (Sm2Co17) | Ferrite (SrFe12O19) | NdFeB (N35–N52) |
|---|---|---|---|
| Hardness | HRC 55–65 | HV 500–600 | HRC 57–61 |
| Fracture toughness (K_IC) | 1.0–1.2 MPa·m^(1/2) | 0.9–1.1 MPa·m^(1/2) | 1.0–1.5 MPa·m^(1/2) |
| Curie temperature | 700–800°C | 450–460°C | 310–340°C |
| Density | 8.2–8.4 g/cm³ | 4.8–5.0 g/cm³ | 7.4–7.6 g/cm³ |
| Primary failure mode in cutting | Thermal microcracking | Edge chipping / spalling | Edge chipping + oxidation |
Both materials fail by brittle fracture. But they fail differently — and that difference matters for how you set up the cut.
How Does Diamond Wire Cutting Solve the Cracking Problem?
Traditional abrasive blade saws generate localized heat at the cut zone — typically 200–400°C at the contact point, even with coolant. For SmCo, that thermal gradient creates residual stress that initiates microcracks below the cut surface. For ferrite, the blade’s lateral force causes edge spalling because the material has essentially zero ductility.
Diamond wire cutting eliminates both problems. The 끝없는 다이아몬드 와이어 루프 runs unidirectionally at controlled speed, distributing the cutting load across thousands of diamond grit points simultaneously. The contact area is tiny — a 0.35 mm diameter wire touches the workpiece across less than 0.5 mm² — so cutting forces stay below the fracture threshold.
We typically run ferrite magnet cutting and SmCo cutting on our SG20 또는 SG20-R desktop precision wire saws. These machines give you the control you need: adjustable wire speed from 0 to 60 m/s, tension control from 0 to 150 N, and programmable feed rates down to 0.1 mm/min. That level of granularity matters when the difference between a clean cut and a cracked part is 0.5 mm/min of feed speed.
What Are the Recommended Cutting Parameters?
Here’s where things get specific. We’ve tested hundreds of SmCo and ferrite samples across different grades and geometries. The parameters below are our production-validated starting points — not textbook numbers.
SmCo Cutting Parameters
| 매개변수 | 권장 범위 | 참고 |
|---|---|---|
| 와이어 직경 | 0.35~0.50mm | 0.42 mm is our default for arc segments |
| 와이어 장력 | 100–130 N | Lower than NdFeB — SmCo is more crack-sensitive |
| 와이어 속도 | 30–50 m/s | Don’t exceed 55 m/s; diminishing returns on surface finish |
| 이송 속도 | 1.0–2.5 mm/min | Start at 1.5 mm/min and adjust based on edge quality |
| 냉각수 | Water-based coolant | White mineral oil also works; avoid dry cutting |
| 절단 폭 | 0.40–0.55 mm | Depends on wire diameter + grit size |
| 표면 거칠기 | Ra 0.4–0.8 μm | Achievable without secondary grinding |
One thing that tripped us up early: SmCo generates fine metallic-magnetic debris during cutting. These particles are attracted to the wire, the guide wheels, and basically every metal surface on the machine. If you don’t flush the cut zone adequately, the debris acts like a secondary abrasive and accelerates wire wear. We now recommend a minimum coolant flow rate of 2 L/min directed at the cut entry point. For more on coolant setup, see our 냉각 및 윤활 가이드.
Ferrite Cutting Parameters
| 매개변수 | 권장 범위 | 참고 |
|---|---|---|
| 와이어 직경 | 0.35~0.50mm | 0.35 mm for thin tiles (<3 mm thickness) |
| 와이어 장력 | 100–140 N | Slightly higher than SmCo — ferrite tolerates more tension |
| 와이어 속도 | 35~60m/s | Higher speed improves edge quality on ferrite |
| 이송 속도 | 1.5–3.0 mm/분 | Can push to 3.5 mm/min on thick blocks (>15 mm) |
| 냉각수 | 수성 냉각수 또는 백색 미네랄 오일 | Water-based preferred for ferrite dust management |
| 절단 폭 | 0.40–0.55 mm | Same as SmCo |
| 표면 거칠기 | Ra 0.5–1.0 μm | Ferrite surface is inherently grainier than SmCo |
Ferrite is more forgiving than SmCo on feed speed — you can typically run 30–50% faster. But the edge chipping risk goes up sharply above 3 mm/min on parts thinner than 5 mm. We’ve seen otherwise good cuts produce 100–200 μm chip-out at the exit edge simply because the feed rate was 0.5 mm/min too high.
Fair warning: ferrite dust is abrasive and conductive. It gets everywhere. Clean the machine after every batch, and make sure your coolant filtration system can handle the particle load. We’ve had a customer skip cleaning for a week and end up with clogged coolant lines and a seized recirculation pump.
For a detailed discussion of how wire speed, tension, and feed rate interact, we’ve published a separate technical guide.
How Do SmCo and Ferrite Cutting Compare to NdFeB?
If you’ve already cut NdFeB magnets, you’re halfway there. The cutting mechanics are similar — all three are brittle sintered materials removed by diamond abrasion. But the devil is in the parameter details.
| 요인 | NdFeB | SmCo | 페라이트 |
|---|---|---|---|
| Feed speed tolerance | 1.5–3 mm/min | 1.0–2.5 mm/min | 1.5–3.5 mm/min |
| Wire tension sweet spot | 120–150 N | 100–130 N | 100–140 N |
| Magnetic debris issue | 보통 | High (stronger field) | Low (weaker field) |
| Edge chipping risk | 중간 | High (microcracking) | High (spalling) |
| Coolant sensitivity | 보통 | High (thermal cracking) | 낮은 |
| Oxidation risk | High (Fe content) | 낮은 | 없음 |
| Wire life per batch | ~5 days | ~4 days | ~6 days |
The biggest practical difference: SmCo requires more conservative parameters than NdFeB, not less. Many operators assume that because SmCo is a “high-performance” magnet, it must be tougher. It isn’t. Its fracture behavior is actually worse than most NdFeB grades, especially the Sm1Co5 composition, which has lower fracture toughness than Sm2Co17.
Ferrite, on the other hand, is the most forgiving of the three for wire cutting. The main risk is exit-edge chipping, which you control by reducing feed speed in the last 2–3 mm of the cut. We program a 40% feed reduction for the final approach on thin ferrite tiles — this alone eliminates about 80% of the edge defects we used to see.
For a full comparison with NdFeB cutting parameters, see our NdFeB magnet cutting guide.
What About Edge Quality and Crack Prevention?
Edge quality is the primary quality metric for both materials. Here’s what we measure and what causes problems.
SmCo Edge Defects
The dominant failure mode in SmCo is subsurface microcracking — cracks that form 20–50 μm below the cut surface and aren’t visible to the naked eye. These cracks propagate under mechanical stress or thermal cycling in the final application. In aerospace actuators running at 150–200°C with vibration loading, subsurface cracks from cutting can cause field failure within 6–12 months.
To minimize subsurface damage:
- Keep feed speed below 2.5 mm/min. Above this, the diamond grit penetration depth exceeds the material’s critical stress threshold.
- Use 0.42 mm wire or thinner. Thinner wire means lower per-grit cutting force.
- Maintain consistent coolant flow. Any interruption — even 2–3 seconds — causes a thermal spike that initiates microcracking.
- Avoid clamping pressure on thin sections. SmCo parts under 3 mm thick should be wax-mounted, not mechanically clamped.
Ferrite Edge Defects
Ferrite’s failure mode is macro chipping — visible chunks breaking off the cut edge, typically 100–500 μm in size. This is purely mechanical: the wire exit point creates a tensile stress that exceeds the material’s (very low) tensile strength.
Prevention is straightforward:
- Reduce feed speed for the final 2–3 mm of each cut. We use 40–50% of the nominal feed rate.
- Support the exit face. If possible, back the workpiece with a sacrificial material (acrylic or wax) on the wire exit side.
- Cut from the larger cross-section toward the smaller one when slicing arc segments or irregular shapes.
- Use higher wire speed (50–60 m/s) for ferrite. The faster the wire moves, the smaller each diamond particle’s bite, and the lower the exit-edge stress.
In our experience, diamond wire cutting consistently delivers edge chip-out below 50 μm on both SmCo and ferrite when these guidelines are followed. That’s 3–5x better than what we’ve measured from blade saw cuts on the same materials.
What Equipment Do You Need for SmCo and Ferrite Magnet Cutting?
For R&D and small-batch production (1–50 pieces/day), a desktop precision wire saw handles both materials well. Our SG20 is the most common choice — it covers workpieces up to 20 mm height with ±0.03 mm precision and accepts 전착 다이아몬드 와이어 루프 in 0.35–0.50 mm diameters.
For arc segment cutting or parts requiring angular cuts, the SG20-R adds a rotary axis that lets you orient the magnet for angled slicing without custom fixturing.
Key machine features that matter for magnet cutting:
- Automatic wire tension control — eliminates manual adjustment drift that causes inconsistent cuts
- Programmable feed rate profiles — critical for the exit-edge slowdown technique on ferrite
- Integrated coolant recirculation — with filtration rated for magnetic particle capture
- 단선 감지 — automatic shutdown prevents wire break from damaging the workpiece
One practical consideration: if you’re cutting magnetized SmCo parts (post-magnetization cutting), the magnetic debris will coat machine surfaces aggressively. We offer optional magnetic shielding for the guide wheel assembly and wire path. Not every application needs it, but if you’re running SmCo daily, it pays for itself in reduced maintenance within about 3 months.
Limitations and Trade-Offs
Diamond wire cutting isn’t perfect for every magnet cutting scenario. Here’s where it falls short:
Throughput. An endless wire saw cuts one piece at a time. If you need 10,000 ferrite tiles per day, a multi-wire saw cutting 50–100 pieces simultaneously is the right tool, despite its higher equipment cost and lower per-piece surface quality. Diamond wire is best for R&D, prototyping, and production runs up to a few hundred pieces per day.
Very large SmCo blocks. SmCo blanks exceeding 60 mm in any dimension may require extended cut times (30+ minutes per slice at conservative feed rates), which increases wire wear significantly. For blocks this size, verify wire life economics before committing to production.
Post-magnetization cutting of strong SmCo grades. Sm2Co17 grades like YXG-30 can have remanence above 1.1 T. The magnetic debris problem becomes severe enough that we recommend demagnetizing before cutting whenever the application allows it. Some applications can’t demagnetize — downhole sensors, for example — and those jobs require the magnetic shielding option plus more frequent machine cleaning cycles.
Surface finish limits. Diamond wire cutting achieves Ra 0.4–1.0 μm on these materials. If your application requires Ra <0.2 μm (some optical encoder discs), you’ll still need a post-cut lapping step. The wire saw gets you 90% of the way there, but that last bit of surface quality requires a different process.
실질적인 다음 단계
If you’re cutting SmCo or ferrite magnets and dealing with cracking, chipping, or thermal damage from your current process, start with a sample test. Send us 3–5 representative parts — we’ll cut them on the SG20 with the parameters described above and send back the results with measured edge quality and surface roughness data.
For engineers already running diamond wire cutting on magnetic materials, the SmCo and ferrite parameter tables in this article can be applied directly. Start with the conservative end of each range and adjust based on your specific grade and geometry.
The cutting parameters, machine configuration, and edge quality data in this article come from production testing across 15+ SmCo and ferrite grades according to IEC 60404-8-1 material classifications and are validated against ASTM C1161 flexural strength testing to confirm that cutting-induced damage doesn’t degrade the mechanical integrity of finished parts.
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