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Compounding
Similar to plastic injection molding, a molten polymer (called
binder) plus ceramic or metal powder paste is injected into
a mold. The part is removed when the polymer cools. The
binder material is removed by either solvent extraction
or controlled heating to above the volatilization temperatures.
The volume (cubic inches) of the part is restricted to small
components, and material properties such as yield strength
are lowered.
Metal Injection Molding (MIM) is fine metal powders
mixed with plastic binders. Some of the different methods
that can be used to compact the powder include:
*Cold
isostatic pressing (CIP)
*Hot
isostatic pressing (HIP)
*Forging
*Rolling
*Extrusion
*Injection
Molding
*Pressureless
compaction.
This mixture is injected into molds similar to those used
in conventional plastic injection molding. Metal injection
molding is a technology that combines metal powder technology
with capabilities of plastic injection molding. It allows
complex shapes to be created by "reassembling" powder into
a solid part through injection molding. Compounding of these
metal powders with "binders" creates the feedstock. MIM
is a viable alternative to the material limitations of plastic
injection molding. This process is best applied to complex
shaped, high performance components, where manufacturing
cost is a key consideration.
Ceramic
Injection Molding (CIM) is very well suitable for
high volume production of complex design with tight tolerances
like bonding capillaries is needed. It is an effective way
of manufacturing complex precision components with highest
degree of repeatability, and reproducibility.
CIM process is a combination of powder, injection molding,
and sintering technologies. To obtain the necessary chemical
and physical properties, powders are selected by size and
shape and complemented with additives. Every particle of
the powder is coated with an inorganic binder, which transports
the powder for molding and gives the final form rigidity.
Molding
Once the feedstock is compounded it is ready for molding.
A
standard injection-molding machine is employed utilizing
standard injection tooling. At this stage the molded a part
contains both the binder and powder.
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Debinding
The
determining characteristics of binder selection depends on
applications economics, tolerance requirements, and geometrical
size of the part. Because of different binder systems selected
for the application, different debinding technologies are
required. The different debinding technologies are catalytic,
thermal or solvent.
After molding, the MIM part is debound and sintered at temperatures
from 600 degrees F to 2,200 F or higher to fuse the fine powdered
particles into a solid shape that retains all of the mold's
features. Temperature depends on which process and actual
materials you are working with. During this process, the molded
part shrinks close to 20 percent. Sintering follows the process
of compacting and shaping the powdered material. Sintering
is the process of heating the material to a temperature below
the melting temperature but high enough to allow bonding or
fusion of the individual particles. Continuous sintering furnaces
are used for most production.
Advanced sintering techniques are dramatically widening the
design process for a broad range of engineered parts. Sintering
is an important process for compressed powdered metal shapes,
called the green compacts. After compaction, the density and
strength of the material are low. Sintering, then, increases
both properties of the material.
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Metal
and Ceramic Powder Injection Molding
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Honeywell's
PowderFlo Technologies technology exceeds traditional
metal injection molding with the capability to produce
larger, thicker components, usually associated with
investment casting. In commercial applications PowderFlo
has been used to fabricate automotive oxygen sensors
and racing spark plugs.
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The
PowderFlo technology utilizes a water based binder system
instead of a solvent-based binder system. Honeywell's
PowderFlo is more environmentally sound, eliminates
time consuming debinding processing steps, and makes
possible larger, thicker, and more complex shapes than
currently available.
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Unlike the
manual or CNC grinding technology, the finished product
using the MIM or CIM process is molded net to
shape. No need to do grinding or major external finishing process
becuase of the superior surface finishing accomplished by the
processes.
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