The PCPro Technique
Researchers have developed a new 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 Prototyping 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. 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 .Furthermore, some of the inner dimensions will have even closer tolerances even when compared to those prototypes that are 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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Prototype Injection Molding, Thermoplastic Injection Molding, and information on Injection Molds
Approximately 30% of all plastic products in the world are produced by an injection molding Rapid Prototyping process. Within this another 30% are produced using a custom injection molding Rapid Prototyping technology. You can count many different steps in the injection process but a normal injection molding process usually has 6 steps. The first step is the clamping of the mould, the clamping unit makes for one of the three units of the molding machine. The other two being the injection unit and the mold, once the clamping unit holds on to the mold, the molten plastic is injected into the mold by the injection unit. Very timy pellets of the plastic material are fed into the hopper. These are then allowed into a cylinder where they are heated into a molten state and injected into the mold. The steps that follow are referred to as dwelling phase. Prototyping basically involves making sure all the cavities in the mold are fully filled. The next step is that the mold is allowed to cool but its important to do this as the clamping is still intact. Finally the mold is opened and the component is ejected out. The biggest advantage of plastic injection molding is the cost factor of the produced parts, especially when you need large number of parts. The disadvantage is the cost of manufacturing the molds; a simple injection mold can cost you $3000 while the bigger complex ones can run into several hundreds of thousands.
Rapid Prototyping: Rapid Prototyping is the process of automated manufacturing of physical components using solid freeform fabrication. They are used in a wide range of applications, everything from medical to fine art. Rapid Prototyping machine works by taking virtual models from software and then converting it into extremely thin, horizontal cross-sections and then goes onto create each of the cross-section in physical space in a cyclic manner until the model is completed. Rapid Prototyping is a WYSIWYG process in which the virtual model bears identical resemblance to the finished physical model. Additional fabrications allows the machine to lay down layers of sheet, liquid or powder material and build up a series of cross-sections These layers are finally automatically fused together to render the final product. The main advantage of rapid prototyping is the ability to create any shape no matter how complex the geometry is. The commonly used data interface between the machine and the software is the STL format. It works by approximating the geometry of a part using triangular facets, smaller the facets higher will be the surface quality. The word “rapid” is used relative top conventional methods which take days to construct a model depending upon its complexity. Rapid prototyping can create the model within a few hours, though it is highly dependent of the type of machines and the size of the model. There have been several new technologies available for rapid prototyping including Fused Deposition Modeling, Selective laser sintering, 3D printing, and Electron Beam Melting.
Prototyping Injection Molding is a specialized method of combining traditional plastic injection molding. CAM software are able to combine rapid tooling and plastic injection molding in order to quickly create small quantities of any thermoplastic part.
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