Wednesday, October 29, 2008

The PCPro Technique

prototyping

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. This technique become public when it was invented and named Precise Cast Prototyping by a group of researchers in Germany at the Institute for Material and Beam Technology. 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 Rapid Prototype 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 Rapid Prototype advantage is that one half casting allows the air bubbles to escape freely; this translates into a more dense part and better surface finish. Threads and undercuts can actually be incorporated into the casting becacuse you can machine the casting again. The casting method shapes the outer surface of the component while precision CNC milling renders the inner contours. Whats nice about being able to mill these castings if that you can use the same mold for parts with totally different dimensions. 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 .Even with measured against vacuum casting, some of these prototypes will have inner dimensions with closer tolerances. 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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