How does Injection Moulding work?
26th June 2023
The injection moulding process involves heating & injecting plastic material under pressure into a closed metal mould machine. The plastic then cools and hardens into the shape desired inside the mould. This then means that the injection moulding machine can open to allow the moulds to be removed for inspection, delivery or more operations.
The manufacturing process for Injection moulding is most suitable for mass production of products with high-precision detail and complex shapes. The process of injection moulding is split into 6 key stages:
•Stage 1 : Clamping - This where the mould is clamped together to create the part.
•Stage 2. Injection - The molten plastic is then injected into the mould cavity
•Stage 3. Dwelling - The injection process is then paused and pressure is applied to make sure all of the mould cavities are filled.
•Stage 4. Cooling - The part is then cooled before the mould is opened to give the plastic time to harden and become the part (This is for steel moulds only).
•Stage 5. Mould opening - The mould is then opened to allow the part to be removed.
•Stage 6. Removal of product - Finally the ejector pins are used to remove the part from the mould and into a loading bin.
There are two types of metals used to create Injection moulding moulds these are aluminium and steel.
Aluminium moulds are able to transfer heat more efficiently than the steel moulds as they do not require cooling channel. Therefore, aluminium moulds are used for rapid injection moulding as this process saves time on cooling and is a quicker process to produce the part. Aluminium tooling is also quicker to CNC which means that Aluminium moulds are usually cheaper.
Steel moulds have more durability and strength than aluminium parts. Therefore if you are manufacturing products in high volumes with fine details it is most cost effective to use Steel moulds. However, steel moulds require cooling channels to prevent defects and warping. Steel moulds are more expensive than aluminium parts and they are more difficult to modify if you would need to make changes to the design.
What products have been Injection Moulded?
There are many times of Injection Moulded products. Medical product (syringes), Electrical products (casing), Automotive (inner car handle), kitchenware (plastic cutlery), children’s toys (Lego) and food grade packaging (water bottles).
Advantages and Disadvantages of Injection Moulding?
Injection Moulding Advantages :
Lightweight – The Injection moulding process uses a lot less plastic than rotational moulding, this makes injection moulded parts a lot more lightweight compared to rotational moulded parts.
Faster Production Time - Injection moulding uses high pressure which increase production time, therefore injection moulded parts are quicker to produced and distribute.
More Complex Designs – The high pressures used in injection moulding ensures that plastic fills every part of the mould, therefore injection moulding creates more complex designs with ease.
Excess Plastic can be reused – Injection moulding’s excess plastic can be reused to create other plastic parts.
Injection Moulding Disadvantages :
More Expensive Tooling – Injection moulding requires stronger and more expensive moulds due to the process using high pressures.
Less Durability – The injection moulded process usually creates weaker and less durable parts, especially in outdoor conditions.
Limited Part Size – Injection moulding capacity requirements are small, therefore initial cost of tooling and injection moulding a large part is very expensive
What is Pad Printing?
Pad printing is a simple and affordable way to adding colour and text to plastic injection molded parts. It works using a large pad with a raised design that picks up the paint and then applies it to the Injection moulded part. Heat is used for the printing machine to transfer the image from the printing plate to the plastic part.
Pad printing is applied to the part once it has been injection moulded. This process is perfect for printing logos onto products and can print on any surface whether it is small, awkward or uneven. It is a more expensive method as it is a secondary process rather than embossing or recessing the design into the part. However, it produces a high quality finish and prevents injection moulding issues such as undercuts and thin areas.
If you have an idea you would like our help with designing for manufacture, please don’t hesitate to get in contact with us. We would love to help!
For more information about the Injection Moulding Process there are a few links below :
https://richfieldsplastics.com/blog/what-is-pad-printing/
If you need more information about how to design for injection moulding please don’t hesitate to get in touch.