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PMT

PMT is an injection molding process that can produce precision mold cavities at high volumes
with high repeatability.

Powdered metal technology (PMT) involves metal powders being mixed with a binder that is granulated
to feed into an injection molding machine. A mold is designed and built to create the cavity part for the
injection mold. Green parts are molded and after a multistep process to separate the binder from the
metal, cavities are ready for any post molding work. These parts—typically made from H-13 tool
steel—can be heat treated, after which PMT cavities can be machined like any other cavity from
hardened tool steel. Machining processes such as EDM, grinding, etc., are no issue, which allows
for engineering changes, if necessary. And since PMT cavities are produced from a mold, engineering
changes can be made to the mold that produces the PMT cavities, and new PMT cavities can be
molded and machined for new part revisions. This technology can enhance the capabilities of any
moldmaker and help reduce the cost and increase the delivery for high cavitation injection molds.
Since this process allows for PMT cavity duplication from a master mold, the greatest advantage
is the guarantee that all cavities are precisely the same, regardless of volume or date of manufacture.
Other key features of PMT include:
• Cavities are H-13 tool steel, with other steels available depending upon the application
• Can be heat treated to standard Rockwell hardnesses
• Can achieve surface finishes of up to Rmax 2
• Cavities can be coated for corrosion resistance (TiN, nickel plate)
• Short pull ahead times for duplicate cavities, including spares

From a moldmaker and end user standpoint, PMT allows them to produce higher cavitation molds
that may have been too difficult or too costly with making cavities conventionally. PMT offers an
excellent economy of scale, suitable for high cavitation molds—typically 16 cavities and higher.
Since a master mold must be designed and manufactured to create the PMT insert, the cost of
this mold must be taken into account when producing cavities. The cost of the mold can be
amortized into the piece price of the individual PMT cavities or the mold can be paid for separately,
lowering the individual PMT cavity piece price. A moldmaker has to consider the cost and benefit
for the PMT technology based on cavitation. This is best for higher cavitation molds since the
higher the number of cavities, the lower the cost to produce each cavity. Depending upon the
size and configuration of the cavity detail to be produced, feature tolerances of up to 15 microns
are achievable. In addition to repeatability of the cavities, high cavity definition can be achieved
with PMT—fine details and sharp corners are easily produced. This is possible because the
impression of the master mold for the PMT cavity takes the green part shrinkage into account.
The part features in the master mold will be larger than those in the finished part, making them
easier to machine. Also, the mold impression will be opposite of the finished parts. A recess in
the final cavity is produced by a standing feature in the mold. This external, standing feature can
be machined with sharp corners. This will translate into a sharp corner feature in the finished
cavity, unlike conventional machining on a cavity, which can be limited based on machine
cutter radius or EDM overburn.
Figure 1 shows a magnified view of cavity detail in a PMT cavity insert. Also using PMT, if a
special design for the cavity is needed for the mold design, these cavities can be produced
with unique shapes that would be difficult or impossible to produce with other metalworking
processes. However, not all cavities can be made using PMT


 

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