Powder Metal Injection Molding

Powder Injection Molding of Metal and Ceramic Parts

“…The most popular method is to use a reciprocating screw, horizontal, hydraulic or electric machine in which a screw stirs the feedstock inside the barrel while it is melting. After melting the feedstock the screw acts as a plunger to generate the pressure to fill the die (Stevenson, 2009). Conventional screw-type injection molding machines consist of a clamping unit, injection unit and control system.…”

“…Due to the size of molded parts, injection molding machines used for PIM are in the lower range, with clamp force typically less than 100 tons, 18 to 25 mm screws and shot size of less than 30 cm 3 (Stevenson, 2009). However, the main important difference when dealing with injection molding of any powdered part is that many of the components of the molding machine are subject to a more intense wear, particularly screws, non-return valves, cylinders and molds (Rosato & Rosato, 1995).…”

“…Ratios between 1.2 and 1.8 are considered acceptable and a ratio of 1.6 is considered to be optimal for the removal of air between granules. It is also important to mention that when calculating the barrel capacity of the injection unit, the barrel rating must be scaled up to take into account the higher density of the PIM feedstock (Stevenson, 2009). …”

“…Since harder screws are more brittle, lower torque limits during startup are used to prevent screw breakage in PIM. The solid feedstock pellets cause the most abrasive wear in the feed section of the screw, thus the feedstock should be melted as early as possible in the injection cycle (Stevenson, 2009). …”