Remington’s InjectAlloy® parts start as very fine metal powders, typically less than 20
microns in diameter, which are mixed in precise proportions with expendable thermoplastic
binders. The combination of metal powder and polymer is then pelletized and fed into
conventional injection molding machines. Under heat and pressure, the feedstock flows
into and assumes the shape of the mold cavity. After removal from the mold, parts are
subjected to thermal processing to remove the binders and are finally high-temperature
sintered to achieve the required metallurgical properties.
Typical properties of Injection Molded Alloys
SELECTED PROPERTY DATA
A variety of metal alloys can be made with the MIM Process. Remington works primarily with
compositions of low alloy steels, soft magnetic materials, stainless steels and tungsten
heavy alloys.Since final density is typically 95 to 98% of wrought metal, excellent
mechanical and magnetic properties can be achieved. The properties included in Table 1 are
not guaranteed minimums, but are typical values provided as an indication of the expected
range for design consideration. For minimum property data, please refer to MPIF Standard 35:
Materials Standards for Metal Injection Molded Parts.
PART PARAMETERS
As with any process, there are limits of applicability. The following paragraphs will help
to establish the general characteristics of MIM parts. These guidelines are not absolute,
and are influenced by a number of factors related to part design.
SIZE RANGE:
Metal injection molding is best suited for relatively small to medium size parts. On a
volume basis, parts should typically be smaller than a tennis ball, with the process being
most cost effective when parts are smaller than a golf ball. Irregularly shaped parts can
be produced with a major axis of up to about 4 inches (102mm) in length. The lower limit
of the size range is determined only by the limitations of the injection molding process
itself. Parts as small as 0.25 X 0.10 X 0.05 inches (6.4 X 2.5 X 1.3mm) are feasible.
The upper limit of part size is established by processing economics, not technical
limitations.
WALL THICKNESS:
The cross-section or wall-thickness is what ultimately determines whether it is feasible
to produce a particular InjectAlloy® part. The part thickness must be kept relatively low
to facilitate efficient binder removal. The practical range of section thickness is from
0.03 inch (0.75 mm) to 0.22 inch (5.6 mm). Parts can be molded with thinner cross-sections,
but are limited with regard to flow length. MIM parts are sensitive to the relationship of
cross-section to length, and it is difficult to form long, tubular parts with thin walls.
WEIGHT:
Parts can be made which weigh from 0.1 to 150 grams or more. However, InjectAlloy® parts
are most cost-effective in the range of 1 to 50 grams per part, which reflect size and
wallthickness considerations.
