Positive form mold

Arrays of distributed pillars can be manufactured using a patented technology that was invented at the Fraunhofer IKTS, Germany ° .This process consists of copying a soft mold from a positive form of the final structure, filling the mold with a slip loaded with the calcined piezoceramic powder and subsequent firing of the element in PbO-controlled atmosphere. 

If the sheet is formed over the male or positive mold and the inner surface of the thermoformed part touches and replicates, the mold is called positive forming (Figure 10.2a). In other way, if the thermoformed part is in the cavities of a female or negative mold and the outer surface of the part replicates, the mold is called negative forming (Figure 10.2b)... 

Machine with the forming mold. Mold is tilted in stacking position... 

The positive type mold closure has a long shearing surface between the male and female segments of the mold. This surface is formed when the mold segments are in close proximity to each other. The gap between the male and female segments is maintained closely, thus no flash is formed. The amount of material charged into the mold is carefully controlled because excess material would prevent mold closure. Insufficient charge results in a short shot, that is, an incomplete part will form. 

The final result of my endeavors and the subject of this book is the machine shown in figure 1. It uses a 120 volt heating element and is capable of forming 12 x 15 sheets of plastic up to l/4 thick and uses both positive and negative molds. The machine shown in figure 1 is using an air venturi pump for the vacuum source, but the it is set up to easily operate with an electric vacuum pump if you so choose. The machine is built on wheels so it can be easily moved from place to place and anotlier nice feature is the adjustable platen table making it possible to form molds of different sizes. 

Mechanical Properties and Structural Performance. As a result of the manufacturing process, some cellular plastics have an elongated cell shape and thus exhibit anisotropy in mechanical, thermal, and expansion properties (35,36). Efforts are underway to develop manufacturing techniques that reduce such anisotropy and its effects. In general, higher strengths occur for the paraHel-to-rise direction than in the perpendicular-to-rise orientation. Properties of these materials show variabiUty due to specimen form and position in the bulk material and to uncertainty in the axes with respect to direction of foam rise. Expanded and molded bead products exhibit Httie anisotropy. 

A special attribute of these processes is the abiHty to pre-position reinforcement, inserts, and core materials for stiffening ribs. Gel coatings can be apphed to the mold surface to eliminate post-mold finishing. Because both surfaces of the part are formed in a mold to close tolerances, accurate assemblies are possible, which is a requirement for many automotive or tmck body appHcations. 

Positive mold A projecting mold over which the product is formed, usually referred to as a male mold. 

In pressure forming, positive pressure is employed to assist the sheet-contents into the mold. The major advantage is a decreased cooling time for pressure forming. Crystalline PS, high-density PE, and oriented PP are used in this procedure. 

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