The plastic base of the office chair is mainly manufactured through a one-piece injection molding process. The core steps include raw material mixing, high-temperature melting, high-pressure injection, cooling and shaping, and demolding and finishing, to ensure structural strength and mass production efficiency.
1. Raw Material Preparation: Precise Proportioning of Engineering Plastics The mainstream materials are reinforced nylon (PA6+GF) or modified PP. Depending on the load-bearing requirements, 20%–30% glass fiber or mineral fillers are added to improve impact resistance and creep resistance.
Raw materials must be pre-dried to prevent moisture from vaporizing at high temperatures, which could lead to bubbles or strength defects in the product.
2. Injection Molding: High-Pressure Injection into Precision Molds Molten plastic is heated to 240–280℃ in an injection molding machine and injected into the closed mold cavity at high pressure (approximately 80–150MPa) and high speed by a screw.
The mold is precision-machined using CNC to ensure that the symmetry error of the five-star base is ≤0.2mm, guaranteeing balanced stress distribution.
3.Cooling and Shaping: Controlling Shrinkage and Internal Stress The mold has built-in cooling channels, circulating coolant to ensure uniform solidification of the plastic within 60–90 seconds, preventing warping or internal stress concentration caused by uneven cooling.
Advanced processes utilize gas-assisted molding technology, injecting inert gas into thick-walled areas to create a hollow structure, achieving lightweight while maintaining rigidity.
4. Demolding and Removal: Structural Design Facilitates Smooth Separation After the mold opens, the ejector system pushes the finished product out. The draft angle (≥1.5°) and reinforcing rib radius design on the base effectively reduce adhesion forces, preventing jamming or edge damage.
Some complex structures utilize a slider core-pulling mechanism for lateral demolding, ensuring the integrity of details.
5.Post-processing and quality inspection: Ensuring factory quality. After removal, the edges are trimmed and deburred, and gate residue is removed. Some high-end models undergo surface texturing or painting treatment.
Random samples from each batch undergo static pressure testing (≥1136kg) and drop testing. Only those meeting international safety standards such as BIFMA are allowed to leave the factory.