Rotational Molding is a method for manufacturing hollow plastic products. It is best known for the manufacture of storage containers, but designers all over the world are starting to realise that it can be used to make many different types of plastic parts.
Some of the sectors that it services include medical products, consumer products, agricultural and garden equipment, automotive and transportation components, toys, leisure craft and sporting equipment, furniture, materials handling articles, and highly aesthetic point-of-sale products.

The principle of rotational moulding of plastics is relatively straightforward. Indeed, the simplicity of the process is a key to its success because it allows the molder to exercise close control over, dimensions and properties. Basically, rotational molding consists of :

Introducing a known amount of plastic in powder, granular, or liquid form into a hollow, shell-like mold. The mold is heated and simultaneously rotated about two principle axis so that the plastic enclosed in the mold adheres to, and forms a layer against the mold surface. The mold rotation continues during the cooling phase so that the plastic retains the desired shape as it solidifies. When the plastic is sufficiently rigid, the mold rotation is stopped to allow the removal of the plastic product from the mold.

Rotational Molding is an atmospheric pressure process that produces nearly stress-free parts. The fact that there are no stresses on the melt as it is shaped is a major advantage that rotational molding has over all other manufacturing methods for plastic parts. Also, as there are no forces on the plastic melt during forming. Rotational molds can have thin walls and are relatively inexpensive to fabricate.
For simple parts, mold delivery times can be a few days or weeks. Modern, multi-armed machines allow multiple molds of different size and shape to be run at the same time. With proper mold design, complex parts that are difficult or impossible to mold by any other method, such as double-walled containers, can be rotationally molded. With correct process control, the wall thickness of rotationally molded parts is quite uniform, unlike structural blow molding or twin-sheet thermoforming. And unlike these competitive processes, rotational molding has no pinch-off seams or weld lines that must be post-mold trimmed or otherwise finished.

The Main Attractions :

    A hollow part can be made in one piece with no weld lines or joints
    The molded part is essentially stress-free
    The molds are relatively inexpensive The lead time for the manufacture of a mold is relatively short
    Wall thickness can be quite uniform (compared with other free surface molding methods such as blow        molding)
    Wall thickness distribution can be altered without modifying the mold
    Short production runs can be economically viable