Cast Prototyping and Precise Cast Prototyping, and the PCPro Technique
Cast Prototyping and Precise Cast Prototyping, and the PCPro Technique
Researchers have developed a new rapid-prototyping technique that
blends traditional casting methods with CNC milling which allows faster
prototyping; the best thing is that it happens in a single machine. The
technique is christened as “Precise Cast Prototyping†or PCPro and
was developed by researchers at the Fraunhofer Institute For Material
and Beam Technology, Dresden, Germany. Half of the mold is machine
using CNC machining, then silicon or polyurethane material is poured
into fill half the mold, this will be the lower half to render the
shape of one half of the part, while the part still in the CNC mill.
When the material is cured and hardened, the upper side of the
component is milled. The process is targeted at components with simple
geometry such as housings whose one side can be fairly easily machined
on aluminum or epoxy mold half and the other complicated half is on the
opposite side where it can be milled into the soft plastic.
Cost Saving: The technique is touted to be an enormously cost effective
as only one half of the tool is made and that too for low pressure
casting. There are no runners; gate, venting and parting lines to be
taken care of and besides these can be manufactured by toolmakers with
lesser experience. Another advantage is that one half casting allows
the air bubbles to escape freely; this translates into a more dense
part and better surface finish. Since the casting is machined again it
allows features such as threads and undercuts to be incorporated. The
casting method shapes the outer surface of the component while
precision CNC milling renders the inner contours. The fact that he
casting can be milled allows for parts with totally different dimension
to be manufactured from the same mold. This is because the second half
of the mold exists only as a CAD/CAM model and tool path programming.
Geometrical changes can be altered by just changing the parameters.
Time saving: Since the outer surface of the component are not machined
the process saves a lot of time .Moreover the inner dimensions gain
closer tolerances compared to prototypes manufactured by vacuum
casting. The reason for this is that the finishing takes palce after
the curing and shrinkage in conventional prototyping while in casting
it’s done before the casting shrinks. CNC allows for achieving of
tighter tolerances compared to casting technologies. Besides all the
machining is done in a single setting so there is no chance of
non-alignment of the outer and inner features. The PCPro technique
manufactures a prototype in just 6 steps, while the vacuum method takes
15 steps. A potentially major application of PCPro is to make housings
for cell phones and similar electronic products; this is because of the
technique’s ability to deliver flawless, close tolerance free-form
surfaces. The machine for the process is a blend of casting and milling
machine and is designed and patented by Fraunhofer. However it has to
be said that highly complex features are difficult to manufacture by
this method.
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