Strong and precise compact produced by giving high plastic energy to powder

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In the sintering of powder metallurgy, the vacancy left in the green compact causes the form change and lowers the strength. If the compact has no vacancy, the above problems will diminish. This study aims to produce perfect compact of no vacancy by giving high plastic energy to powder. New methods were designed, and the followings were clarified.1. Compress and Twist CompactingCommercially pure aluminum powder was compressed and twisted by the apparatus with two dies. The one die is fixed and the other rotates, and these dies pull against strongly each other. So, the powder set between the dies gets high pressure and severe twist. The followings were found: (1) The charge efficiency became high value of 95% at the die pressure of 600 MPa. (2) The tensile strength of the compact with no twist was only 2 MPa when the die pressure was 312 MPa. The strength increased according as the rotation of die, and became 22 MPa, which was 10 times bigger, at the rotation of 4PI radian (Sliding travel about 60 mm).2. Friction-aided Backward Extrusion Powder can not be extruded backward if the friction between the powder and dies is so large. At this time, if the container die is moved backward, the powder will be extruded from the narrow space between the container die and a punch by the aid of outward friction force between.the powder and the container die. This method showed the followings: (1) To give a form to the powder, the lowest punch pressure needed about 300 MPa irrespective of compacting condition. (2) The tensile strength became high value of 144 MPa which was comparable to that of a rolling sheet. (3) The reason why the powder was compacted well was confirmed by the microscopic analysis.