Vacuum forming

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Vacuum forming is a casting process .

advantages

The vacuum forming process is characterized by the use of a vacuum to stabilize the casting mold . In contrast to other methods, the drafts of the cast workpieces, which are intended to make it easier to lift the casting mold from the model, can largely be dispensed with here. Another advantage of the process is a high level of dimensional accuracy with an equally high surface quality. The form burr on the dividing planes and on the core marks is also small. All castable metals and alloys known today can be cast , whereby the maximum castable weight only depends on the casting system, not on the process. With the vacuum casting process, tolerance deviations of a maximum of 0.3 to 0.6 percent are possible.

execution

A permanent model is used as a template , with which the lost mold is made from quartz sand . The solidification of the molding sand takes place by applying a negative pressure of around 0.3 to 0.6 bar inside the casting mold. To do this, the model is provided with small nozzle bores so that a film 0.05 to 0.1 mm thick is deep-drawn, i.e. H. can be pulled over the model half. Before deep drawing, the film is heated for a few seconds using a heating coil so that it can be plastically deformed. During the deep-drawing, the film is true to the contour and lies close to the model.

The free-flowing, binder-free quartz sand is then poured onto this contour. After the pouring pool and the feeder have been formed, the molding box is covered with another film. The molding sand is compressed by the negative pressure between the two foils, which causes frictional forces to develop between the sand grains, so that the movement between the sand grains is inhibited. Then you can subtract the created shape from the model. Both sides, i.e. the upper and lower box, are shaped in this way and, after being folded, form the mold cavity, which is then poured out. The negative pressure between the two foils in the upper and lower box is maintained until the cast part has completely solidified after casting. The vacuum is only switched off when the finished cast part is removed. The quartz sand is then reusable. This process is used to manufacture small to large series.

Vac-u-shape

Around 1961 Mattel developed the Vac-u-form and later the Vac-u-maker as a toy. In the 1990s, this concept was adopted by ToyMax.

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