Over moulding is a two stage special injection moulding process for producing multicomponent parts from two or more polymers with multidaylight principle.

Recent Advancements in Over moulding are: Horizontal mould rotation and Over moulding with a single injection unit.

A novel development in Over moulding is the 'Horizontal mould rotation' technique. Existing systems rotate the moulds on an axis perpendicular to the machine platens. But in this new technique, the mould is rotated horizontally with a rotating device, about an axis parallel to the platens.

Compared to traditional vertical turn table Over moulding, this new technique possesses the following advantages :

		Smaller moulds and machines can be used
		Mounting is simple for different moulds
		Reduced clamping forces
		Subsequent assembly is eliminated
		Possibility of combining materials that do no weld together
		Decreased production costs
		Less floor space
		Need for two machines is eliminated

Process Principle

In Over moulding, injection takes place in two phases. The first shot is injected into a cavity in the area of a front parting line. After the cycle is complete, during mould opening, the part formed remains on the side of the moving centre plate and can be transferred to second parting line by a 180° rotation of the centre plate. Thus the part is facing the opposite direction. Here, the second material is injected in to the cavity, to produce the two -component part. At the same time, another first shot is being injected at the front parting line. When the mould opens, the part is demoulded before centre plate rotates further.

Applications

Car lamp lenses, Large surface area parts (e.g. for automotive industry) and various housings for personal care and medical parts.

Few examples of applications are :

		Car Rear light - Reduction of five percentage is achieved in machine related production costs.
		Closure with sealing ring - Reduction in clamping forces, 350 tonnes instead of 600 tonnes.
		Over Moulding with a single injection unit - Over moulding can now be done with a single injection unit with some modification in mono sandwich process.

The conventional Over moulding machines have two separate injection units with special moulds. Mono sandwich machine has one injection unit with extruders. The injection units are separately controllable with a specially designed common nozzle for the purposes of sandwich process. The advantage of simplifying the machine technology is cost savings. A mono sandwich machine costs only 25% more than the standard machine but an over moulding machine with two injection unit costs about 60% more than a standard machine.

		Overmoulding mould: The mould is core back mould in which the space for the second component is created by retraction of movable cores.
		Changeover valve: The valve is placed inside the mould in the runner system that can release different runners as necessary.
		Mono sandwich m/c : Has one injection unit (main) and additional extruder with metering unit.

The metered melt from auxiliary unit flows into the injection cylinder (main unit) and it displaces material for the second component that has already been plasticized. Thus melts are layered in injection cylinder in succession i.e. one after the other to form the first and second component.

The layering of two melts does not lead to mixing between the two layers because the melts are highly viscous and exhibits only laminar flow. There is no transverse flow and the polymer particles only follow their line of flow.

When the melt has been layered, first of all, the volume of the first component is injected. The changeover valve is positioned accordingly which allows the melt to be filled in space provided for it. Then injection stops intermittently allows the valve to switch over within the mould. The melt to form the second component is injected next, as in conventional overmoulding. The changeover between the two components is so sharp during moulding, so that overmoulding of the component is possible.