Metal injection molding methods and feedstocks
View Patent ↗Metal injection molding methods and feedstocks. Metal injection molding methods include forming a feedstock, molding the feedstock into a molded article, substantially removing a lubricant, a thermoplastic, and an aromatic binder from the molded article, and sintering the molded article into a metal article. In some examples, metal injection molding methods include oxygen reduction methods. In some examples, metal injection molding methods include densification methods. Metal injection molding feedstocks include a lubricant, a thermoplastic, and aromatic binder, and a metal powder.
1. A method for forming a metal article comprising:
forming a feedstock by mixing together a lubricant, an aromatic binder, a thermoplastic, and a metal powder;
molding the feedstock into a molded article by maintaining the feedstock at a temperature between 150 and 200° F., pressurizing the feedstock to a pressure of not more than 1000 psi to inject the feedstock into a mold, and maintaining the mold at a temperature not more than 120° F.;
substantially removing the aromatic binder from the molded article; and
sintering the molded article to form the metal article by heating the molded article.
2. The method of claim 1 , wherein:
the feedstock is pressurized to between 400 and 500 psi to inject the feedstock into a mold, and
the mold is maintained at a temperature between 50 and 90° F.
3. The method of claim 1 , wherein forming a feedstock comprises mixing together 3-6 vol. % of the lubricant, 8-12 vol. % of the thermoplastic, 28-38 vol. % of the aromatic binder, and 44-69 vol. % of the metal powder.
4. The method of claim 3 , wherein:
the lubricant is stearic acid;
the aromatic binder is naphthalene;
the thermoplastic is polystyrene; and
the metal powder is titanium, a titanium alloy, titanium hydride, a titanium matrix composite, or combinations thereof.
5. The method of claim 4 , wherein:
substantially removing the aromatic binder from the molded article includes immersing the molded article into an ethanol bath at ambient temperature; and
sintering the molded article to form the metal article includes heating the molded article to at least 2450° F.
6. The method of claim 1 , wherein the lubricant includes stearic acid.
7. The method of claim 1 , wherein the aromatic binder includes naphthalene.
8. The method of claim 1 , wherein the thermoplastic includes polystyrene.
9. The method of claim 1 , wherein the metal powder includes titanium, a titanium alloy, titanium hydride, or a titanium matrix composite, or combinations thereof.
10. The method of claim 1 , wherein:
the lubricant includes stearic acid;
the aromatic binder includes naphthalene;
the thermoplastic includes polystyrene; and
the metal powder includes titanium, a titanium alloy, titanium hydride, or a titanium matrix composite, or combinations thereof.
11. The method of claim 1 , wherein removing the aromatic binder from the molded article includes immersing the molded article into an alcohol bath.
12. The method of claim 11 , wherein the alcohol bath is ethanol.
13. The method of claim 11 , wherein immersing the molded article into the alcohol bath occurs at ambient temperature.
14. The method of claim 1 , wherein forming a feedstock includes mixing together not more than 10 vol. % of a lubricant, 6-15 vol. % of a thermoplastic, 20-40 vol. % of an aromatic binder, and 35-74 vol. % of a metal powder.
15. The method of claim 1 , further comprising:
enclosing the molded article in a container with a deoxidizing agent in an inert gas environment substantially free of air; and
heating the container containing the molded article and the deoxidizing agent to between 1600 and 1800° F.
16. The method of claim 15 , wherein the molded article is enclosed with an amount of the deoxidizing agent equal to 1-10% of the weight of the molded article.
17. The method of claim 15 , wherein the deoxidizing agent includes calcium metal.
18. The method of claim 15 , wherein forming a feedstock includes mixing together not more than 10 vol. % of a lubricant, 6-15 vol. % of a thermoplastic, 20-40 vol. % of an aromatic binder, and 35-74 vol. % of a metal powder.
19. The method of claim 1 , further comprising granulating the feedstock.
20. The method of claim 1 , wherein the thermoplastic includes one or more of ethylene vinyl acetate, polyethylene, and butadiene.
21. The method of claim 1 , wherein the metal powder includes copper, stainless steel, titanium, tantalum, or cobalt or combinations thereof.
22. The method of claim 1 , wherein forming a feedstock includes mixing together a lubricant, an aromatic binder, a thermoplastic, and a metal powder until the viscosity of the resulting mixture becomes substantially constant.