Lo Stampaggio ad iniezione plastica | A ugelli multipli (Costampaggio) | Assistito da Gas

#materialstechnology #design #stefanopasotti ========================================================== * It is one of the most widely used processes in plastics processing. Ideal for the mass production of large-scale products. It produces identical pieces on a large scale. Therefore, it is not suitable for the production of prototypes or one-off pieces. Why? Because a steel mold is required, which is quite expensive. Obviously, the cost varies depending on the size of the object and the complexity of the mold. Making a mold requires numerical control machining, an operation that removes material. But let's proceed in order: there are three types of plastic injection molding: what we'll call classic, gas-assisted injection molding, and co-molding, also known as multi-nozzle plastic injection molding. All three have one thing in common: the mold. What is a mold? A mold is a product made up of two or more parts and reproduces the negative of our object. Furthermore, inside a mold, we'll find not only the negative shape, but also other details, such as, in most cases, cylinders that serve to push the piece out of the mold, and these we'll call ejectors. In addition, we have a point from which the plastic is injected, which we'll call the injection point. The mold must also be designed slightly larger than the object we've envisioned, because it must allow for the elastic shrinkage of the material. Essentially, when it changes from a liquid to a solid state, the atoms come together. Molds must also provide for what's called a draft angle, meaning that even if we have perfectly straight walls, they must actually have a slight, even imperceptible, inclination toward the mold opening to facilitate extraction. Furthermore, a mold must avoid undercuts, meaning: when we design an object, it must be designed so that it can be easily removed from the mold. Therefore, there must be recesses that block this process. Now, the plastic we use comes in the form of small pellets or flakes that are inserted into a container that gravity-fed into a heated worm screw to melt and uniform the plastic. And essentially, what this screw does: it pushes the plastic steadily into a nozzle. And let's say that these points apply to all types. Let's get specific "Traditional" plastic injection molding involves everything we've discussed so far. Before inserting the plastic into our mold, we need to consider the air inside, as it could cause problems. Here, we have two solutions: either we remove the air and mold under vacuum, or we plan for strategically positioned air pockets. Once this is done, we push the plastic steadily and at high pressure into the mold, which will fill it completely. The mold remains closed until the plastic has completely solidified. Once solidified, the mold opens, and thanks to the ejectors, which are almost always small cylinders, the piece comes out and the mold closes for the next piece. The piece extracted could be a semi-finished product or a finished product. This depends on how the piece was designed. Why do I say this? Because if we look at Lego bricks, they come out already finished, unlike the Pnton chair, where we have a semi-finished product, because we have to refine the edges and cut the plastic injection point. In fact, when we look at a plastic injection-molded object in general, we understand that this process has been used because we can see the mold parting lines, the exit slide marks, and the plastic injection points. The type of plastic used can be made of many different pigments, can reproduce metallic effects, or have a wide variety of colors. This process can take just a few seconds, or over a minute, and this depends exclusively on the size of the mold and, consequently, the object we want to create. As I said, it is a very expensive process, and to reduce costs, we can design more than one piece inside a mold so that they are printed simultaneously. Thermoplastics that can be recycled are often used, always by combining them with new plastics, because recycling them causes them to lose some of their internal characteristics. Then we have what is called co-molding, or multi-nozzle molding.