Sintered NdFeB Magnets Manufacturing Process Flow
Step 1: Ingredient Weighting
Sintered NdFeB magnets’ raw materials include PrNd metal, iron, BFe alloy, DyFe alloy, terbium, cobalt, aluminum, copper, gallium, NbFe alloy, etc. Total rare earth elements content is 28-35wt%, iron content is 60-70wt%, boron content is 0.8-1.2wt%, the balance are other doping elements and/or substitute elements. Sintered NdFeB magnet grades are determined by the basic ingredients.
Step 2: Melting & Strip Casting
The weighed raw materials are placed in the crucible of a vacuum melting furnace. After heated and melted, thin and uniform NdFeB magnet alloy sheets (thickness 200-400μm) are rapidly solidified and formed by strip casting.
Step 3: Hydrogen Decrepitation
Rare earth elements have hydrogen absorption effect. NdFeB magnet alloy sheets are placed in a vacuum tube rotary furnace. As hydrogen gas is filled, rare earth-rich phase in the grain boundary of NdFeB magnet alloy absorbs hydrogen gas. After hydrogen absorption saturated, the rare earth-rich phase turns to hydrogen desorption by the furnace being continuously evacuated. During the hydrogen absorption and desorption loop, NdFeB magnet alloy sheets are cracked into coarse powders (mean size <2mm) due to stress concentration effect.
Step 4: Jet Milling
NdFeB magnet alloy coarse powders are further cracked into fine powders (mean size 2-5μm) by high-speed nitrogen gas flow in a jet milling equipment.
Step 5: Aligning & Pressing
NdFeB magnet alloy fine powders are weighed and placed in a pressing mold. The powders rotate and are aligned under applied magnetic field, subsequently they are pressed into green compacts.
Step 6: Sintering & Annealing
NdFeB magnet green compacts are placed in a vacuum sintering furnace. The green compacts are almost densified after sintering (1000-1100°C). Followed by annealing (two stages 850-950°C and 400-600°C), NdFeB magnet blanks are finished.
Step 7: Material Testing
NdFeB magnet blanks’ appearance, density and demagnetization curve are inspected by sampling.
Step 8: Machining
After material testing passed, NdFeB magnet blanks are machined as per required dimensions. Machining methods including grinding, wire cutting, slicing, drilling, etc.
Step 9: Surface Treatment
NdFeB magnet materials are vulnerable to corrosion in a humid and/or corrosive environment. Their surfaces are treated with various coatings to protect them from corrosion. Most regular coatings are zinc and nickel coatings.
Step 10: Product Inspection
Sintered NdFeB magnet finished products’ coating appearance, dimensions, magnetic properties are inspected by sampling.
Step 11: Magnetizing
After product inspection passed, all NdFeB magnets are magnetized to saturation.
Step 12: Packing & Shipping
Finished NdFeB magnets are packed and shipped to customers.