Production method of compact
The method including: applying a graphite-based lubricant to a cavity surface of a die; forming a first graphite-based powder layer by disposing graphite-based powder that does not contain a binder on a cavity surface of a lower punch, forming a magnet powder body by putting magnet powder on the first graphite-based powder layer, and forming a second graphite-based powder layer by disposing graphite-based powder that does not contain a binder on the magnet powder body; and producing a compact by performing press forming using the lower punch and a upper punch while heating the magnet powder body surrounded by the graphite-based lubricant applied to the cavity surface of the die, the first graphite-based powder layer, and the second graphite-based powder layer, and releasing the compact from a forming die.
1. A production method of a compact in which a forming die is constituted by a die, an upper punch and a lower punch, and the upper punch and the lower punch slide inside the die, and the forming die defines a cavity with the die, the upper punch and the lower punch,
the production method comprising:
spraying a graphite-based lubricant comprising a solvent to a cavity surface of the die which faces the cavity;
forming a first graphite-based powder layer by disposing graphite-based powder that does not contain a binder on a cavity surface of the lower punch which faces the cavity, forming a magnet powder body by putting magnet powder on the first graphite-based powder layer, the graphite-based powder that does not contain a binder being disposed on a cavity surface of the upper punch which faces the cavity, and forming a second graphite-based powder layer by disposing graphite-based powder that does not contain a binder on the magnet powder body; and
producing a compact by performing press forming using the lower punch and the upper punch while heating the magnet powder body surrounded by the graphite-based lubricant applied to the cavity surface of the die, the first graphite-based powder layer, and the second graphite-based powder layer, and releasing the compact from the forming die.
2. The production method of a compact according to claim 1 , wherein
when the first graphite-based powder layer is formed by disposing the graphite-based powder that does not contain the binder on the cavity surface of the lower punch which faces the cavity, the magnet powder body is formed by putting the magnet powder on the first graphite-based powder layer, and the second graphite-based powder layer is formed by disposing the graphite-based powder that does not contain the binder on the magnet powder body, a pressure during the press forming is set to 50 MPa or higher.
3. The production method of a compact according to claim 1 , wherein
the first graphite-based powder layer and the second graphite-based powder layer are formed of only the graphite-based powder.
4. The production method of a compact according to claim 1 , wherein
the graphite-based lubricant comprises graphite powder dispersed in water.
5. The production method of a compact according to claim 1 , wherein
a film thickness of the graphite-based lubricant is 10 μm or greater.
6. The production method of a compact according to claim 1 , wherein
a sintered body is produced by performing press forming on the compact in a predetermined temperature atmosphere in sintering and densifying processes, and a rare-earth magnet is produced by performing hot working on the sintered body so as to provide magnetic anisotropy to the sintered body.
7. The production method of a compact according to claim 1 , wherein
the compact has an Nd—Fe—B-based main phase with a nanocrystalline structure and a grain boundary phase of an Nd—X alloy, where X is a metal element, the grain boundary phase being present around the main phase.
8. The production method of a compact according to claim 7 , wherein
the Nd—X alloy constituting the boundary phase is any one type of Nd—Co, Nd—Fe, Nd—Ga, Nd—Co—Fe, and Nd—Co—Fe—Ga or is a mixture of at least two of Nd—Co, Nd—Fe, Nd—Ga, Nd—Co—Fe, and Nd—Co—Fe—Ga, and
the Nd—X alloy is in an Nd-rich state.
9. The production method of a compact according to claim 3 , wherein
the graphite-based lubricant comprises graphite powder dispersed in water.
10. The production method of a compact according to claim 1 , wherein the second graphite-based powder layer does not adhere to the upper punch.
11. The production method of a compact according to claim 1 , wherein the magnet powder is covered by the second graphite-based powder layer prior to press forming.
12. The production method of a compact according to claim 1 ,
wherein the compact has an upper surface formed by the upper punch, a lower surface formed by the lower punch, and side surfaces formed by the die, and
wherein a layer of the graphite-based lubricant in which the solvent has been volatilized during press forming is formed at the side surfaces of the compact and layers of the graphite-based powder that does not contain a binder are formed at the upper and lower surfaces of the compact.