Office Chair Injection Molding Process

The injection molding process for office chairs primarily employs injection molding technology, completing the shaping of plastic components through steps such as heating, injection, pressure holding and cooling, and demolding.

1. Raw Material Preparation and Heating

Common plastic materials used in office chair injection molding include PP (polypropylene), ABS (acrylonitrile-butadiene-styrene copolymer), PS (polystyrene), PC (polycarbonate), and PMMA (polymethyl methacrylate), among others. These plastic pellets are fed into the hopper of the injection molding machine and then enter the heating barrel. Inside the heating barrel, a rotating screw serves two purposes: first, it mixes the plastic pellets through rotation to ensure uniform heating; second, it pushes the plastic forward to form a continuous molten state. The heating temperature needs to be adjusted according to the type of plastic. For example, the melting temperature of PP is approximately 160-230℃, while PC requires a higher temperature (220-320℃).

2. Injection and Pressure Holding

When the molten plastic is pushed to the front end of the heating barrel, the injection unit injects it into the closed metal mold cavity under high pressure (typically 100-200 MPa). The precision of the mold, the quality of the steel (such as H13 steel), and the design of the cooling system directly affect product quality. For example, the mold tolerance needs to be controlled within ±0.02 mm, and the product dimensional tolerance is ±0.05 mm. After injection, a pressure holding stage is required, where continuous pressure is applied to compensate for the shrinkage of the plastic during cooling, preventing internal voids or surface depressions.

3. Cooling and Demolding

The mold is designed with cooling channels to control the temperature through circulating cooling water or oil, accelerating the solidification of the plastic. The cooling time needs to be optimized according to the thickness of the component and the type of plastic. For example, thin-walled seats require shorter cooling times to improve efficiency, while thick-walled components need extended cooling to prevent deformation. Once the plastic is fully solidified, the mold opens, and mechanical components such as ejector pins push out the molded part. Sufficient draft angles (usually 1°-2°) need to be reserved during design to prevent ejection marks or scratches.

4. Key Process Optimization

• Gate Location and Cooling Sequence: For large thin-walled seats, the gate location needs to be optimized to avoid uneven melt flow leading to warping; the cooling sequence should match the gate direction to ensure uniform shrinkage.
• Mold Structure: Circular holes can be designed in the cavity to reduce contact area for auxiliary venting, while improving cooling uniformity and structural strength.
• Demolding Design: Complex components require side cores or angled lifters to ensure smooth demolding without damaging the surface.

By strictly controlling parameters and process details, injection molding can efficiently produce office chair plastic components with complex structures and precise dimensions.