Injection molding is a manufacturing process that allows for parts to be produced in large volumes. It works by injecting molten materials into a mold. It is typically used as a mass production process to manufacture thousands of identical items. Injection molding materials include metals, glasses, elastomers and confections, although it is most commonly used with thermoplastic and thermosetting polymers.
How does it Work?
The first stage of injection moulding is to create the mould itself. Most moulds are made from metal, usually aluminium or steel, and precision machined to match the features of the product they are to produce.
Once the mould has been created by the mould-maker, the material for the part is fed into a heated barrel and mixed using a helical shaped screw. Heating bands melt the material in the barrel and the molten metal or molten plastic material is then fed into the mould cavity where it cools and hardens, matching the shape of the mould. The cooling time can be reduced through the use of cooling lines that circulate water or oil from an external temperature controller. Mould tools are mounted on plate moulds (or ‘platens’), which open once the material has solidified so that ejector pins can eject the part from the mould.
Separate materials can be combined in one part in a type of injection moulding called a two-shot mould. This technique can be used to add a soft touch to plastic products, add colours to a part or produce items with different performance characteristics.
Moulds can be made of single or multiple cavities. Multiple cavity moulds can have identical parts in each cavity or can be unique to create parts of different geometries. Aluminium moulds are not best suited to high volume production or parts with narrow dimensional tolerances since they have inferior mechanical properties and can be prone to wear, deformation and damage due to the injection and clamping forces. While steel moulds are more durable they are also more expensive than aluminium moulds.
The injection moulding process requires careful design, including the shape and features of the part, the materials for the part and the mould and the properties of the moulding machine. As a result, there are various considerations that need to be taken into account when injection moulding.
Injection Moulding Considerations
There are a number of considerations to bear in mind before undertaking injection moulding:
1. Financial
The entry cost for injection moulding manufacture can be high – given the cost of the machinery and the moulds themselves.
2. Production Quantity
It is important to determine how many parts you wish to manufacture so as to decide whether injection moulding is the most cost-effective production method.
3. Design Factors
Minimizing the number of parts and simplifying the geometry of your items will make injection molding easier, thus Having experienced product developing engineers seems important. They can do their utmost to optimize the prats design with their expertise. In addition, the design of the mold tool is important to prevent defects during production.
4. Production Considerations
Minimising the cycle time will aid production as will using machines with hot runner moulds and well thought-out tooling. Such small changes and use of hot runner systems can equal production savings for your parts. There will also be cost savings from minimising assembly requirements, especially if you are producing many thousands of even millions of parts.
How Can I Reduce Mould Costs?
Injection moulding can be an expensive process, but there are several ways in which you can reduce mould costs, including:
- Eliminate undercuts
- Remove unnecessary features
- Use a core cavity approach
- Reduce cosmetic finishes
- Design parts that self-mate
- Modify and re-use existing moulds
- Monitor DFM analysis
- Use a multi cavity or family type of mould
- Consider your part sizes