Student Information    

2.  Compaction

Upon completion of the design phase and typically, after the manufacture and testing of prototype parts, a production run is started.  Initially, the powder is compacted to place neighboring particles in intimate contact through particle deformation, to squeeze dry lubricant to the die walls for easier part ejection (and to increase tooling life), and to increase the density of the loosely packed powder.  The compaction cycle (Figure 6) is described in the following steps:

Figure 6: Pressing cycle for a single level part: Source "Powder Metallurgy Design Solutions", 1999, MPIF.

1.      A controlled amount of powder is gravity fed into the die carried by the powder feedshoe.

2.      The upper and lower punches move toward each other and apply a predetermined amount of pressure to  the loose powder, creating a compact that conforms to the shape and size of the die and punches.

3.      The top punch is withdrawn from the die and the bottom punch moves up, ejecting the part from the die.  At this stage, the compact is known as a “green” part or body.

4.      The bottom punch drops down to the bottom fill position, the powder feedshoe moves toward the die cavity, pushing the newly pressed part out of the way, and fills the die with powder for pressing of the next part.

The pressures used to compact the parts can range from a low of 10 st/in˛* to as high as 60 st/in² (138 to 827 MPa) or greater.  The desired density and part size are the determining factors.  In addition, the powder is usually kept at room temperature, although the die and punches are heated by friction as a result of the pressing operation. (*st/in² = short tons per square inch)

The majority of PM parts are consolidated in the manner cited.  Other specialized methods are also used and will be discussed subsequently.