In the modern plastic processing industry, TPO injection molding is emerging as an efficient and widely used manufacturing process, showcasing its unique value across various sectors including automotive, construction, and home appliances. TPO, or thermoplastic polyolefin, is a material that combines plasticity and elasticity, offering excellent weather resistance, impact resistance, and recyclability.
TPO injection molding is a manufacturing method in which TPO material is heated and melted using an injection molding machine and then injected into a mold, cooling and solidifying into the desired product. This process combines the reprocessable meltability of thermoplastic materials with the elasticity of rubber, making it suitable for mass production of plastic parts with complex structures and precise dimensions.
TPO injection molding mainly includes the following four stages:
TPO granules are added to the hopper of the injection molding machine and heated to a molten state by the heating device. The main components of TPO are a mixture of polypropylene (PP) and rubber elastomers (such as EPDM), which form a homogeneous melt with fluidity when heated, ready for the next stage.
The molten TPO material is pushed to the front end of the injection cylinder by a screw and quickly injected into the closed mold cavity under high pressure. The mold is usually made of metal and is precisely processed according to the product's design shape. This stage requires careful control of injection speed, pressure, and time to prevent defects such as shrinkage marks, bubbles, or flow lines in the finished product.
After the TPO melt fills the mold, continuous pressure (holding pressure) is applied to compensate for the volume change due to material cooling shrinkage. Then, the mold begins to cool, and the molten material gradually solidifies into shape. The fast cooling rate of TPO material helps improve production efficiency.
Once the TPO product has cooled to a certain temperature and reached the set hardness, the mold opens, and the product is ejected by the ejection mechanism, completing the entire injection molding process.
TPO possesses both rubber and plastic properties, which are reflected in the following characteristics during the injection molding process:
Wide processing temperature range: TPO has a relatively low melting point, generally between 180–240°C, which allows it to be processed on various injection molding equipment;
Good fluidity: Helps in filling parts with complex shapes;
Moderate shrinkage rate: Proper control can achieve dimensionally stable finished products;
Non-corrosive to molds: Extends mold life and reduces maintenance costs.
