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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Tags: mold, geometry, contours, outer surface, cad cam, surface finish, air bubbles