Patent Application
20090257904
The invention relates to a device and method for pressing a powder metal compact having a transverse feature by use of radially extending punches, which punches are radially removable upon release of punch compacting pressure.
The prior art shows a device for pressing metal powder compacts to be sintered which comprises a split die having a cylindrical cross section, each die cooperatively engaged in a horizontal plane, the horizontal plane being perpendicular to the direction of their longitudinal axis. This device further comprises punches that are movable toward each other in a direction that is perpendicular to the horizontal plane, each of which is associated with the split die and is adapted for pressing one of the metal powder compacts. The axes of movement of the punches is vertical. The powdered metal material is fed to the upper die when the punch associated therewith is lifted from the die. Suitable means are provided for moving the punches one towards and away from the other in order to compress the powdered material to press the compact and to eject the compact.
The device of the kind described does not, however, permit pressing of compacts with transverse features which otherwise could not be removed from the compacts from the dies solely by axial displacement of the punches and the dies. For instance, with a device of this kind it is not possible to press compacts having a recessed transverse feature.
Representative of the art is U.S. Pat. No. 3,752,622 which discloses a device for moulding compacts with undercut compacts to be sintered by compaction of powdered material. A two compact die forms the chamber in which the compact is moulded. A pair of opposed punches pass through the die to compact the powdered material. The two compacts of the die are held firmly in contact with one another during the stroke of the punches by an annular collar with inclined surface engaging oppositely inclined surfaces on the die. After the material has been compacted, the two compacts of the die are separated in such a direction as not to interfere with the undercut portions of the compacts. After the die has opened, one of the punches retracts while the other continues its stroke to move the compact from between the two compacts of the die.
What is needed is a device and method for pressing a powder metal compact having a transverse feature by use of radially extending punches, which punches are radially removable upon release of punch compacting pressure. The present invention meets this need.
The primary aspect of the invention is to provide a device and method for pressing a powder metal compact having a transverse feature by use of radially extending punches, which punches are radially removable upon release of punch compacting pressure.
Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.
The invention comprises a method of pressing a powder metal compact comprising partially filling a die cavity with powder metal, engaging a second die with the first die, extending radially inwardly punches for forming a transverse feature in the compact, filling the die cavity with powder metal, compressing the powder metal with a punch, relieving pressure on the compact, withdrawing the radially inwardly punches so as to allow axial movement of the compact, withdrawing the second die, and ejecting the compact from the die while simultaneously filling the die cavity.
The accompanying drawings, which are incorporated in and form a compact of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention.
Upper die 20 comprises radially moveable punches 21. “Radial” is determined with respect to the direction of movement of punches 11-14. Punches 11, 12, 13, 14 may each be moved vertically to compress the powder to form a compact. Punches 12, 13 and 14 each provide the means by which various elevation surfaces are formed into the compressed “green” compact.
Radially moveable punches 21 are then moved radially inward until they contact the outer surface of punch 12. Punches 21 may be moved by a variety of means, but the preferred method is hydraulically. The remainder of the cavity is then filled with powder to a level substantially equal with the top surface 19 of die 20. Feeder shoe 15 is then withdrawn, and in doing so the upper surface of the powder material is trimmed of excess powder. This results in the proper amount of powder in the die cavity, ready for compaction.
During final compaction punch 11 moves vertically toward punches 22 and 21. This is to avoid damaging portions 21 by imposing an otherwise unsupported bending moment. Hence, punch 11 compresses one end of the compact in part against portions 21, and punch 22 compacts the opposite end of the compact in part against punch 21.
Feeder shoe 15 is shown withdrawn to surface 17.
Punches 21 are moveably connected to upper die 20. Punch 22 holds compact 100 stationary while punches 21 are withdrawn.
The “green” compressed compact is then processed using known sintering methods which are not described herein but are well known in the art.
Although a form of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the sequence, construction and relation of parts without departing from the spirit and scope of the invention described herein.
