Prototype Rotational Molds

Rotational molding is well suited for prototype production of large parts such as boats, camper tops, missile containers, gasoline tanks, toys, and similar items. Almost any thermoplastic can be used for rotoforming. However, the greatest number of parts is made from polyethylene of both high and low density. 

Equipment. The eqnipment used in rotational molding is simple many variations are available. The most common type is the so-called carousel type (Fig. 1). This machine consists of a heating station or oven, a cooling station (frequently an enclosed chamber), and a loading and imloading station. A carousel has three to six spindles or arms where the mold or molds are moimted. Most carousels have the freedom to revolve in a complete circle. The spindles are moimted on a central hub and driven by variable motor drives. New control systems allow each arm to operate independently in movement and control of oven temperature and time. Microprocessors are incorporated in the control system. Computer simulation software can be utilized in prototyping and manufacturing. 

Molds from aluminum (aluminum casting and CNC-milled) or sheet steel are used today for rotational molds. Electroplated molding has established itself for special rotational molds for PVC plastisols. There are also a couple of other materials that can be used in prototype production. 

Due to the high temperature loads when producing rotomolded plastic parts, it is almost impossible to use cheap prototype molds. A rotational mold has to have a certain thermal conductivity and has to constantly withstand changes in heating and cooling. 

Figure 1.176 shows a carbon fiber prototype mold for a 400-liter fuel tank with a simplified frame and screwed form flanges. The attachment of required fixtures like a fuel-level sensor, threaded fittings, inserts, etc. enables the rotation of prototypes in production-based design. 

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