Computer Controlled Rotational Moulding of liquid polymers for the manufacturing of elastomeric prosthetic interface liners.

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Interface Liners play an important role in the comfort and health for prosthetic leg users. They fit over the residual limb and go between the limb and the socket (the socket is the shell that encases the limb and connects the user to the prosthesis. The liner is a protective cover made of a flexible, cushioning material. (typically silicone, polyurethane or co-polymer) Worn over the residual limb, it reduces movement and chafing between the skin and the socket. Liners are designed with specific characteristics to work with different suspension systems. Current manufacturing methods utilise a cavity moulding technique where liquid not polymerised resin is gravity fed or pressure injected in a fixed volume cavity. The established liner manufacturers offer a considerable liner range with different sizes to accommodate for the diversity within the western amputee population. After curing of the liquid material, the moulds are separated and the product removed from the cavity. This process has a high quality consistency but the manufacturing of moulds is complex and expensive and therefore driving up the product costs. In addition, multiple cavities are needed when more than one material behaviour is required such as hard and soft areas. An exciting and innovative manufacturing technique is the liquid rotational moulding process aiming at using standard injection-moulding polymer grades normally used in the manufacturing of interface liners. In this process, the 2 component polymer is injected into a single mould rotating around two axes. Rotational moulding in two axes has the advantage of producing hollow products. Previously, the inherent difficulty was in the production of objects with uniform thickness since the speed of the two primary axes are fixed and cannot be varied independently to take into account the changes in material properties such as its density and viscosity. With the advent of computers, it is now possible to control the thickness of the object accurately. This is made possible by creating an intelligent software which takes in the viscosity and density time variation of the polymer and using the flat plate withdrawal theory, computes the new speed for each axis. The relationship between rotational moulding parameters and polymeric material properties for a room temperature vulcanisation (RTV) silicone rubber system to produce liners is the focus of this project. In addition, the single rotational mould approach will deliver, beside, off the shelf products a truly personalised capability for the manufacturing of bespoke multi material/behavioural liners.