Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Injection molding is a high-volume manufacturing process used to produce precise, identical parts by injecting molten material—most commonly thermoplastic polymers—into a custom-shaped mold. It's widely applied in industries like automotive, consumer goods, and electronics for items ranging from bottle caps and toys to complex gears and car body panels. 

 The process is efficient for mass production due to its speed (cycles often under 1 minute) and minimal waste, though it requires significant upfront investment in tooling.

How It Works: Step-by-Step Process

The process follows a cyclical sequence, often called the "injection molding cycle," which repeats for each part. Here's a breakdown for the most common thermoplastic materials:

1.Clamping and Material Preparation: The mold halves are clamped shut under high pressure. Raw plastic pellets are fed into the hopper and enter the heated barrel (typically 200–300°C). A reciprocating screw rotates to shear and melt the material, reducing its viscosity for flow. This "plasticizing" phase homogenizes the melt and builds up a "shot" volume at the screw's tip.

2.Injection: Once ready, the screw acts as a plunger, forcing the molten plastic (at pressures up to 20,000 psi) through the nozzle into the mold's sprue, runners, and gates. The cavity fills rapidly—often in under 1 second—to about 95–98% capacity using velocity control, then switches to pressure control to avoid defects.

3.Packing and Holding: Additional pressure is applied to pack the mold fully, compensating for material shrinkage as it cools (thermoplastics can shrink 0.5–2%). This phase lasts until the gate freezes (solidifies), sealing the part inside.

4.Cooling: Coolant (water or oil) circulates through the mold's channels to solidify the plastic, typically taking 10–60 seconds depending on part thickness and material. This ensures dimensional stability and prevents warping.

5.Ejection and Reset: The mold opens, and ejector pins push the cooled part out. The screw retracts to prepare the next shot, the mold closes, and the cycle repeats (up to thousands of times per hour in high-volume setups).

Materials Used

Thermoplastics (e.g., nylon, polyethylene, ABS) dominate due to their recyclability and ease of melting/reuse. Thermosets, metals (die-casting), elastomers, and even chocolates or glasses can be used, selected based on factors like strength, melting point, and cost. Pellets are pre-dried to avoid defects from moisture.

Designs must account for shrinkage, draft angles (for easy ejection), and tolerances (as tight as ±0.001 inches). Common defects like sink marks or warpage are mitigated through precise parameter tuning. Overall, injection molding excels in scalability but shines brightest for runs exceeding 10,000 units.