Ever wondered, while holding your toothbrush in the morning, as to how it would have been manufactured, wherein the grip is made up of softer (rubber like plastic) material & the base material is comparatively rigid plastic? Of course, the process is Injection moulding, but with a slight difference.

It is basically an Over moulding. At its simplest, this method is used for cosmetic reasons - to allow the creation of single plastic part from 2 different plastics.

An over-moulded part is made in 2 distinct operations. First, the base or 'pre-mould' is made in a conventional injection moulding machine. Once the batch is complete, these parts are loaded either by hand or robot into a 2nd mould tool (in a 2nd machine) where the 2nd outer material is over-moulded over the base. The outer material bonds to base chiefly by mechanical means (designed-in lugs/ recesses in base), and to a lesser extent by a chemical bond, due to the sheer heat of the 2nd polymer. This over-moulding process allows designers to create a strong structural product with excellent ergonomics for the user.

In some cases, when an exceptionally strong bond is a critical functional requirement, the mechanical properties of each plastic can be leveraged to enhance useability. With multi component moulding we can achieve all this and still avoid misalignment and ensure a highly durable product (e.g. AC vents in Passenger cars, Waterproof connectors).
Particularly, in case of automotive or engineering components, the factors critical for design are :
1)Cost 2)Time-to-market

These become all the more important when multistep processes are involved. In such cases, the manufacturer has to work within the constraints of Production time, Component variation, labour intensity, Complexity of tooling/ machinery, Volume requirements and regulated specs (IP, Intrinsic Safety etc.) as s/ he selects the optimal method of Production.

2 shot moulding (or 2k moulding) uses a specialised machine that has an extra injection barrel so that the 2 separate polymers can be injected simultaneously into specially designed moulds. Usually Moulds are designed with 2 identical cores on the moving side of the tool and different cavities on the fixed side. The part that has been moulded with the 1st shot material stays on its core as the tool opens and the whole tool half rotates 180°. This moulding now becomes part of the 2nd cavity once the tool is closed. The 2nd material now covers this part to create the finished 2 shot part. This is ejected as the tool opens and the cycle continues.

As 2 shot moulding is made in one cycle, the polymers bond chemically: the heat from the 1st shot is retained, the part uncured, when the 2nd shot is injected. This translates to high repeatability and consistency of parts: one tool, one machine, making it a fully controlled & cost effective process. The chemical bond created by 2-shot moulding means IP67 rating can be more easily achieved. Added value benefits include the ability to produce components that are both hard and soft or clear and opaque at the same time. So, for example: windows, buttons and seals can be created as integrated elements, making this application quite popular for FMCG, Medical, Electrical, Personal care & Sanitary products as well, from an otherwise conventional injection moulded part.

In case of AC vent for car, a housing made out of ABS combined with PP fins (in white) means the finished item is not only strong but also elegant. The outer housing of ABS acts as an absolute fitted part within the instrument panel with delicate PP fins within, adding to grippability. The resultant tactility aids easy adjusting of air flow in a car.

FANUC Roboshot offers 2 shot or 2k Moulding (launched 2014) for such critical moulding requirements.

Key features

• Integrated 2nd Injection Unit by additional servo axis control.
• Accurate rotary table positioning by FANUC’s precision CNC.
• Allows rotary table setting on ROBOSHOT operation screen.

Latest launch - 3k moulding

This year FANUC introduced the latest concept in Multi component moulding with our cutting edge 3 Component moulding machine (2nd Injection Unit on Vertical plane, 3rd Injection Unit on Non Operator side).

This classic combination of Additional horizontal and vertical arrangement of the injection units fulfils the majority of requirements with regard to Multi-component Injection moulding.

Authored by Manish Sharma. The author is National Head of Plastics at FANUC India and can be reached at manish.sharma@fanucindia.com