Ferrite is a strange material to machine. It’s technically a ceramic — hard, brittle, electrically non-conductive — but it’s also the world’s most mass-produced permanent magnet material. Billions of ferrite magnet segments go into automotive sensors, micro-motors, loudspeakers, and household appliances every year. And every one of them needs to be cut from a sintered block to final dimensions.
The challenge is that ferrite doesn’t cooperate with most conventional cutting methods. It shatters under impact, chips at sharp edges, and cracks along grain boundaries when stressed unevenly. EDM doesn’t work at all because ferrite is an electrical insulator. Laser cutting creates thermal shock cracks. And abrasive grinding, while possible, produces heavy subsurface damage and generates massive amounts of fine dust.
This guide covers how we approach ferrite cutting with scies à fil diamanté sans fin, what makes it different from cutting NdFeB ou SmCo, and the specific parameter choices that control crack formation and surface quality.
What Makes Ferrite Different from Other Magnetic Materials
Before getting into cutting parameters, it helps to understand why ferrite behaves the way it does under a diamond wire.
Ferrite permanent magnets — primarily strontium ferrite (SrFe₁₂O₁₉) and barium ferrite (BaFe₁₂O₁₉), classified under IEC 60404-8-1 for hard magnetic materials — are true ceramics. They’re made by mixing iron oxide with strontium or barium carbonate, pressing and sintering at 1200–1300 °C. The result is a polycrystalline structure with Vickers hardness around HV 550–700, comparable to NdFeB but with significantly lower fracture toughness.
That low fracture toughness is the root cause of most ferrite cutting problems. Where NdFeB might tolerate a small overload and chip at the edge, ferrite propagates cracks deep into the body. A 0.5 mm edge chip on NdFeB stays at the edge. A similar stress event on ferrite can send a crack 5–10 mm into the workpiece, turning a surface defect into a structural failure.
Three key properties shape the cutting strategy:
Non-conductive. Ferrite’s electrical resistivity is extremely high (10⁶–10⁸ Ω·cm), which is actually one of its main functional advantages — low eddy current losses make it ideal for high-frequency applications. But this means EDM wire cutting is completely ruled out. If your production line uses EDM for NdFeB and you also need to cut ferrite, you need a second cutting technology. Diamond wire works for both.
Chemically stable. Unlike NdFeB, ferrite doesn’t oxidize in humid air or corrode in water-based coolant. This is a significant practical advantage during cutting: you can use plain water-based coolant without worrying about surface degradation. No need for oil-based coolant, no rush to apply protective coatings after cutting, no expensive corrosion inhibitors. For shops processing both materials, we typically recommend water-based coolant for ferrite runs and switching to oil for NdFeB — see our guide de refroidissement et de lubrification for details on managing dual-coolant setups.
Anisotropic grain structure. Sintered ferrite magnets are pressed in a magnetic field to align the crystal grains. This creates preferred orientation — the magnetic axis — but it also creates directional variation in mechanical properties. Cutting parallel to the alignment axis versus perpendicular to it produces measurably different surface roughness and chipping behavior. We’ve seen Ra differences of up to 30% between the two orientations on the same block, using identical cutting parameters.
Why Conventional Cutting Methods Struggle with Ferrite
Abrasive Grinding Wheels
This is the default production method for ferrite magnet manufacturers. Diamond or CBN grinding wheels remove material quickly and can hold reasonable tolerances (±0.05 mm). The problem is force: grinding wheels apply substantial normal force to the workpiece surface, and ferrite’s low fracture toughness means subsurface cracks propagate easily under that force.
The subsurface damage zone on ground ferrite typically extends 30–80 μm below the surface — much deeper than what diamond wire cutting produces. For magnets going into structural assemblies or high-reliability motor applications, that subsurface damage translates to reduced mechanical strength and potentially higher reject rates during thermal cycling.
Grinding also generates enormous volumes of fine ferrite dust. The particles are sub-10 μm, abrasive, and spread everywhere. Dust management on ferrite grinding lines is a major operational cost that often gets underestimated until the filtration system needs replacing.
ID Blade Cutting
Inner-diameter blades work for small ferrite blocks but share the same fundamental problem as grinding: rigid cutting tools apply lateral forces that ferrite can’t tolerate. Edge chipping rates above 10% are common, and the kerf loss from 0.3–0.5 mm blade thickness wastes material. For high-volume production of thin ferrite wafers (under 3 mm), blade cutting reject rates can climb to 15–20% once you account for chipping, cracking, and out-of-tolerance pieces.
Découpe au jet d'eau
Waterjet can cut ferrite without thermal damage, and some shops use it for prototyping or custom shapes. But the abrasive garnet particles create significant edge chipping on brittle ceramics, and achieving consistent thickness control is difficult. The kerf is also wide — typically 0.8–1.5 mm — which wastes material and limits minimum slice thickness.
How Endless Diamond Wire Cutting Handles Ferrite
The fundamental advantage of diamond wire cutting for ferrite is low cutting force. The wire applies force in one direction only, the contact zone between wire and workpiece is a thin line (the wire diameter), and the unidirectional motion of the boucle infinie eliminates the reversal shocks that reciprocating saws impose.
For ferrite specifically, this translates to:
Reduced crack propagation. The maximum force applied to the workpiece at any instant is an order of magnitude lower than grinding. Stress levels stay below the critical threshold for crack initiation in most cases, which keeps cracks from forming in the first place rather than trying to manage them after they start.
Predictable chipping behavior. Edge chipping on wire-cut ferrite is primarily controlled by feed rate. Below a material-specific threshold (typically 2–3 mm/min for standard Sr-ferrite blocks), chipping at the wire exit side drops to near zero. Above that threshold, it increases predictably — which means you can set your parameters for the quality level you need.
Thin kerf. With 0.35–0.50 mm wire diameter, kerf loss is roughly 0.40–0.55 mm — about half of blade cutting and a fraction of waterjet. For ferrite magnet production where material cost is lower than NdFeB, this matters less per-part. But for thin wafer production (slicing a block into many pieces), the cumulative savings add up. A 50 mm block sliced into 2 mm wafers produces 17 usable pieces with wire cutting versus 14 with blade cutting — a 21% yield improvement from kerf reduction alone.
Recommended Process Parameters for Ferrite
Sur nos SG20-R machines, we use these typical parameters for sintered ferrite:
| Paramètre | Plage typique | Notes |
|---|---|---|
| Diamètre du fil | 0,35–0,50 mm | 0.35 mm for thin wafers, 0.50 mm for general use |
| Vitesse du fil | 30–60 m/s | Higher speed improves surface finish |
| Tension du fil | 100–130 N | Lower than NdFeB — ferrite is more crack-sensitive |
| Vitesse d'alimentation | 1.0–2.5 mm/min | Conservative for crack prevention |
| Liquide de refroidissement | À base d'eau | No oxidation concern with ferrite |
| Rugosité de la surface (Ra) | 0.4–0.8 μm | Depends on feed rate and wire condition |
A few notes on these numbers:
Wire tension is deliberately lower than for NdFeB. We typically run ferrite at 100–130 N versus 100–150 N for NdFeB. The reason is crack sensitivity — higher tension increases the cutting force at each diamond grit contact point, which on ferrite can exceed the fracture threshold and initiate subsurface cracks. If you’re seeing micro-cracks on your cut surfaces (visible under 20× magnification as fine lines running perpendicular to the cut direction), reducing tension in 10 N increments is the first adjustment to make.
Feed rate has a sharp quality threshold. With NdFeB, surface quality degrades gradually as feed rate increases. With ferrite, there’s often a more abrupt transition. Below 2 mm/min, surfaces are clean with minimal chipping. Push to 3 mm/min and chipping rate jumps noticeably. Push to 4+ mm/min and you start getting subsurface cracks. The exact threshold depends on block cross-section, grain alignment direction, and wire condition, but the pattern is consistent: ferrite rewards conservative feed rates more than most other materials.
Water-based coolant is standard. Since ferrite is chemically inert to water, there’s no need for oil-based coolant. Water-based coolant actually works better for ferrite because it dissipates heat more efficiently and produces a cleaner cutting zone — the ferrite dust particles wash away easily rather than forming a sludge with oil. This also simplifies post-cutting cleanup significantly compared to NdFeB processing.
Crack Prevention: The Central Challenge
If there’s one thing that distinguishes ferrite cutting from all other magnet materials, it’s the crack sensitivity. Understanding how cracks form and propagate during diamond wire cutting is essential for maintaining acceptable yield rates.
Cracks in wire-cut ferrite originate from two mechanisms:
Mechanism 1: Tensile stress at the wire exit. As the diamond wire reaches the bottom edge of the workpiece, the remaining material bridge thins to the point where it can’t support the cutting load. Instead of being cut cleanly, the last fraction of material fractures — often creating a chip or initiating a crack that runs back into the body. This is the same mechanism that causes exit-side chipping in all brittle materials, but ferrite’s low fracture toughness makes it worse.
Prevention: Reduce feed rate for the last 2–3 mm of each cut. On our machines, we program a two-stage feed profile: normal feed rate for the bulk of the cut, then 50% reduction for the exit zone. Some operators also use a sacrificial backing plate — adhesive-bonded to the bottom of the workpiece — that provides material support through the exit zone. This approach is borrowed from wafer dicing practice and works well for thin ferrite slices.
Mechanism 2: Residual stress release. Sintered ferrite blocks contain residual stresses from the pressing and sintering process. When the wire cuts through the block, it releases these stresses asymmetrically, which can cause the cut pieces to shift slightly during cutting. If the pieces are constrained (by clamping), this stress release creates bending moments that can crack the remaining uncut material.
Prevention: Use flexible fixturing that allows slight movement of the cut pieces. Rigid vice clamping is actually worse for ferrite than for NdFeB, because it prevents the natural stress relief that happens during cutting. Adhesive mounting on a flexible substrate, or mechanical clamps with spring-loaded jaws, both work well. See our fixture design guide for detailed recommendations.
Surface Quality on Wire-Cut Ferrite
The surface morphology of wire-cut ferrite differs from NdFeB in a few important ways.
NdFeB has a ductile Nd-rich grain boundary phase that allows some micro-cutting behavior. Ferrite doesn’t — it’s fully brittle ceramic throughout. This means the material removal mechanism is almost entirely brittle fracture at the grain scale, with very little ductile micro-cutting.
In practice, this shows up as:
More uniform surface texture. Paradoxically, the fully brittle fracture mode on ferrite produces a more homogeneous surface than NdFeB’s mixed ductile/brittle removal. The surface looks consistently granular under magnification, without the smooth plateaus interspersed with fracture pits that characterize NdFeB cut surfaces.
Slightly higher Ra values. Because there’s minimal ductile smoothing, ferrite surfaces from diamond wire cutting typically run Ra 0.4–0.8 μm versus 0.3–0.5 μm for NdFeB under comparable conditions. For most ferrite magnet applications, this is perfectly acceptable — ferrite magnets rarely receive electroplating (their corrosion resistance makes it unnecessary), so the surface finish requirements are less demanding.
Grain pull-out as the dominant defect. The most common surface defect on wire-cut ferrite is whole-grain pull-out: individual hexagonal ferrite grains (typically 1–5 μm in size) detach at grain boundaries rather than being cut through. This creates small pits that contribute to surface roughness but don’t represent structural damage. Excessive grain pull-out (visible as a chalky, powdery surface) indicates the wire is worn or feed rate is too high.
Ferrite vs. NdFeB: Key Differences in Cutting Approach
For shops cutting both materials on the same equipment, here’s a practical comparison:
| Facteur | Ferrite | NdFeB |
|---|---|---|
| Liquide de refroidissement | Water-based (preferred) | Oil-based (required) |
| Tension du fil | 100–130 N (lower) | 100–150 N |
| Feed rate sensitivity | Sharp threshold (abrupt quality drop) | Gradual degradation |
| Crack propagation risk | High — cracks travel deep | Moderate — cracks stay at edges |
| Post-cut oxidation | None (chemically stable) | Rapid — protect within 30 min |
| Post-cut coating | Usually unnecessary | NiCuNi plating standard |
| rugosité de surface | Ra 0.4–0.8 μm | Ra 0.3–0.5 μm |
| Dust management | Water wash, standard filtration | Oil filtration, more complex |
| EDM as alternative | Not possible (non-conductive) | Possible (conductive) |
The biggest operational difference is coolant management. If you’re switching between ferrite and NdFeB on the same machine, you need a coolant changeover procedure. Running ferrite with residual oil from NdFeB cutting is fine — a small amount of oil in water-based coolant won’t cause problems. But running NdFeB with residual water from ferrite cutting is risky — even trace moisture on a freshly cut NdFeB surface starts the oxidation process. We recommend running ferrite first, then flushing and switching to oil for NdFeB, rather than the reverse.
Typical Ferrite Cutting Applications
Motor Arc Segments
The largest volume application for ferrite machining. Automotive wiper motors, window lift motors, HVAC blower motors, and similar applications use segmented ferrite arc magnets. These require consistent thickness (±0.05 mm), clean edges for bonding to motor housings, and high throughput. Diamond wire cutting handles the initial block-to-segment slicing, with grinding for final arc profile if needed.
Speaker Magnets
Ring and disc ferrite magnets for loudspeakers need flat, parallel faces for proper magnetic circuit assembly. Wire cutting produces the parallelism needed in a single pass, often eliminating the secondary grinding step that blade cutting requires.
Aimants de capteurs
Small ferrite pieces for position sensors, speed sensors, and proximity sensors. At dimensions like 5 × 3 × 2 mm, the low cutting force of diamond wire is essential — blade cutting at these sizes produces unacceptable chipping rates. Our SG20 desktop model handles these small-part applications well, and the setup time between different part sizes is minimal.
Educational and Prototyping
Research labs and product development teams frequently need custom-cut ferrite samples for magnetic circuit experiments. The flexibility of wire cutting — any straight cut at any thickness without tool changes — makes it ideal for one-off and small-batch work.
Common Ferrite Cutting Problems and Solutions
Cracks appearing hours after cutting: This is almost always residual stress release. The cutting process is clean, but residual stresses in the sintered block redistribute after cutting, causing delayed cracking. Solution: use lower clamping force and allow 24 hours of stress relaxation before final inspection. If delayed cracking is persistent, the issue may be upstream in the sintering process — uneven cooling rates during sintering create the residual stresses that cause problems during cutting.
Chalky, powdery cut surface: Excessive grain pull-out, usually indicating the wire is past its useful life or feed rate is too high. Check wire condition first — if the diamond coating is visibly worn or patchy, replace the wire. If wire is fresh, reduce feed rate by 0.5 mm/min and re-evaluate.
Asymmetric chipping (one side clean, other side chipped): The clean side is the wire entry side; the chipped side is the exit. This is normal at higher feed rates. If it’s out of spec, reduce feed rate for the exit zone, or use a sacrificial backing plate bonded to the exit side.
Workpiece cracking during clamping: Ferrite is brittle enough that clamp pressure alone can crack thin blanks. Use padded jaws (rubber or silicone lining) and avoid point-contact clamps. For thin slices, adhesive mounting eliminates clamping stress entirely.
Inconsistent surface quality across the cut: Often caused by uneven coolant coverage. Make sure coolant flow reaches both sides of the cutting zone. One-sided coolant delivery creates thermal gradients and uneven chip evacuation, both of which affect surface consistency.
Getting Started with Ferrite Cutting
If you’re evaluating diamond wire cutting for ferrite magnet production, the barrier to entry is lower than for NdFeB. Ferrite’s chemical stability means you don’t need oil-based coolant systems, post-cut surface protection, or specialized cleaning procedures. A basic SG20-R with water-based coolant and standard electroplated diamond wire will handle most ferrite cutting applications.
Nous proposons découpe d'essai gratuite for customers evaluating the process — send us your ferrite samples and we’ll cut them with documented parameters so you can evaluate the results directly.
