A mould tool is the ‘central’ part of the moulding process, without it a product could not be produced. Whether the product is a simple plug, or a complex engineering part, a mould tool is critical in the moulding process.
The tool design not only provides the shape for the product, but can determine the quality and efficiency of the injection moulding process and of the final part. A mould tool for plastic injection moulding is typically made of metal, usually steel or aluminium. The core and cavity design of the tool provides the product profile, but there are many other aspects of the tool that are vital for the correct mould flow and creation of the end product.
Mould tools provide a channel for the molten plastic to travel from the injection cylinder, or barrel, to the mould cavity(s). It has venting inside which allows the trapped air to escape and prevent voids or air bubbles from forming, which would cause poor surface finish on the product.
It allows the moulding to cool until set, typically by controlling the temperature using water (or oil) that circulates through channels internally through the mould tool, similar to a motor engine coolant system. The cooling aspect is very important because if plastic material sets at the incorrect speed distortions and stress marks may occur. Finally, after the moulding has cooled, ejectors are used to push the moulding from the tool after it has opened, completing the product production.
Below is an image of a mould tool, with its various components numbered, and their functions explained:
1. Location Ring – This fits in a location hole on the fixed half platen of the injection moulding machine to ensure correct alignment of the tool and the machine.
2. Fixed Half Clamp Plate – Fits the fixed half of the mould tool to the platen of the injection moulding machine and provides the framework for the cavity to be mounted on.
3. Pillars & Bushes – Precision ground alignment pillars that ensure the fixed and moving halves of a tool lines up with one another.
4. Sprue Bush – This is the part of the tool where the molten plastic is first injected into the cavity. The sprue bush can be a hot or cold tip. A cold tip sprue bush is less costly to make but uses more plastic during moulding. A hot tip uses less plastic and can give greater moulding flexibility.
5. Fixed Half Cavity Plate – Usually contains the plastic moulding cavity or female half. This gives the plastic product half of its final shape.
6. Slides – This is not standard to all tooling, but, these hold part of the form of the plastic part and are used to create under cuts and details that cannot be moulded with simple open and shut tooling.
7. Moving Half Core Plate – Usually contains the other half of the plastic product shape, known as a Core or male half. The molten plastic is injected into the core and cavity, then sets hard into the final shape.The parts that lead to the core and cavity are 1) the runner, which allow the passage of molten plastic, these can be hot or cold, with hot runner systems being more expensive but providing greater flexibility and less wastage; 2) the gate, which is the point between the runner and the core and cavity, this is designed so the plastic will be thinner at this section, so that a natural week point is formed allowing for easy removal of the runner from the final plastic product.
8. Ejector Set – Plate and Pins – The ejector set is the plate that holds the ejector pins in the correct place and the pins which push the moulding out of the mould once it is set and the mould is open.
9. Risers – Provide space for the ejector plate to move.
10. Moving Half Clamp Plate – Moving half clamp plate fits the moving half of the tool to the injection moulding machine plate and provides the framework for the core to be mounted on.
At Bowles & Walker we provide support from design right through to production, building great working relationships with our customers. We will always be able to advise the best way to create your tooling so that moulding will be as cost effective and efficient as possible. For more information about our services please call us on 01953 885294 or email info@bowles-walker.com. We would be happy to work with you on your journey to create products, reduce costs and support UK manufacturers.
