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Manufacturing Processes |
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DHI currently utilizes the
following manufacturing methods:
- Investment Casting
- CNC Machining
- Electrical Discharge Machining
- Thermal (Flame) Spraying
- Hard Facing
- Grinding
- Lapping
- Etching and Coloring Metals
- Heat Treat
- Electroless Nickel Plating
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Investment Casting Process
Design for Investment Casting
As with most casting processes, best results from investment
casting are achieved when uniform wall thickness are
used. Gradual transition from thick to thin sections
is desirable. In addition, fillets should always be
utilized. Moreover, thermal contraction should be considered
which usually causes distortion. |
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Rapid Prototyping
- Stereolithography provides fast and accurate
part prototypes, cuts time to market, and
can reduce direct development costs.
- Pro E® software allows the direct production
of stereolithography cavities.
- A prototype is worth a thousand words!
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Pattern Production
The process begins with production of an expendable pattern.
This pattern is usually made by injecting wax into an aluminum
die.
Assemble Clusters
Patterns are fastened by the gates to one or more runners.
The runners are attached to the pouring cup. Both are usually
made of wax. Patterns, runners and pouring cup comprise the
cluster or tree, which is needed to produce the ceramic mold.
Shell Molding
| The cluster is rinsed in a pattern wash/etching
solution. This removes any mold release residue from
the pattern. The cluster is then dipped into a primary
slurry/binder. The cluster is manipulated so that the
patterns receive a complete and even coat of binder.
The cluster is then stuccoed with a primary refractory
grain, this |
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| gives us our face coat. After drying,
this primary coating process is repeated as necessary.
The primary coats determine detail and surface finish.
After completion of the primary coats the cluster is
ready for the secondary or back up coats. This is done
in the same manner as the primary coats except the binder
composition and viscosity is different and the stucco
grain size is coarser. The secondary/back up coating
process is repeated as necessary until the shell is
strong enough to hold molten metal. After completing
the back up coats the cluster is then given a seal coat
by dipping it back into the slurry. The shell, after
drying, is now ready for de-waxing. |
Ceramic Shell Dewaxing
The coated cluster is placed in a high temperature furnace
or steam autoclave. This melts out the patterns, gates, runners
and pouring cup - creating a ceramic shell containing cavities
of the casting shape desired with passages leading to them.
Ceramic Shell Firing
The molds must be fired to burn out the last traces of pattern
material and remove any moisture, bring the shell to fired
strength and aid in fluidity for thin sections.
Casting
Molten Metal is poured into the fired shell at temperatures
between 1300°F - 2950°F depending on the type
of alloy. Pouring temperatures are maintained as cool
as possible. |
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Mold Removal
After the poured metal has cooled, the mold material is removed
from the casting cluster using high pressure water, vibratory
or shot blast methods.
Casting Cut Off and Clean-Up/Finishing
The individual castings are removed from the cluster.
Remaining gates are removed by grinding. Generally,
the castings are sand blasted for a smoother finish. |
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Post Processing
- Surface Finish (Threading, Turning, Milling, Drilling,
Boring, Reaming)
- Heat Treating
- Welding (MIG, TIG & ARC)
- Blasting (Sand, Glass & Bead)
- Straightening
- Painting
- Polishing (Satin & High Gloss), Hand Buffing,
Degreasing
- Corrosion-resistant Coatings
- Plating (to all MIL specifications)
- Black Oxide, Pickling
- Impregnation
- Assembly
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Advantages to Investment Casting
- Cost Reduction
- Close Dimensional Tolerances
- Weight Reduction
- Design Flexibility (most shapes can be cast)
- Reduces or Eliminates Machining
- Superior Surface Finish (125 rms)
- Alloy Selection for Difficult or Impossible to
Machine Parts
- Production Runs Can Be Small or Large
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