National Research Council of Canada

Abdelouahab Ziani

Sylvain Pelletier

Paul-Emile Mongeon

A method of lubricating the wall surfaces of a die cavity used in powder metallurgy involves spraying the wall surfaces with tribocharged particles of a lubricant material. The method is carried out by means of an apparatus centered about a plug member which has a three-dimensional shape conforming generally to that of the article to be formed. The plug member is slightly smaller than the article so that when the plug member is inserted into the die cavity there is a small, but uniform, gap created between the outer wall surfaces of the plug member and the walls of the die cavity. The plug member is secured to a closing plate which can be inserted into the die cavity so as to be sealed therewith. The closing plate is provided with vent holes and the plug member has a plurality of spaced apart tubes extending therethrough, which tubes exit at one or more of the wall surfaces of the plug member. The lubricant material is fed using an inert gas under pressure through tubing which tribocharged the lubricant particles and the tribocharged particles are sprayed from the tubes in the plug member into the gap so that they are electrostatically attracted to the walls of the die cavity and adhere thereto. Any excess gas and lubricant exits the gap through the vent holes in the closing plate. A uniform thin coating of lubricant is created on the walls of the die cavity. The green density of the article formed in the die is greater, and the ejection force required to remove the formed article from the die cavity is less, than with existing methods and apparatus.

Die wall lubrication method and apparatus

This invention relates to a method for producing sintered parts of aluminum or aluminum alloy with improved mechanical properties using batch degassing, die compaction and liquid phase sintering. The batch degassing consists of holding a prealloyed aluminum powder at a temperature of about 350.degree. to about 450.degree. C. in a stainless steel autoclave in which the pressure is reduced to less than 5.times.10.sup.-6 torr. Once the desired pressure is reached the powder is cooled down within the autoclave while still under vacuum. The resulting powder is then compacted at a pressure of 20 to 50 tsi at between room temperature and about 250.degree. C., but preferably at a warm temperature of about 65.degree. C. The final densification is completed by liquid phase sintering in argon atmosphere at 625.degree. C. This method allows the production of sintered compacts characterized by a density close to 97% of theoretical, which makes it possible to eliminate the need for a hot working step.

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St. Thomas, Canada

Abdelouahab Ziani