how to injection mould plastic and produce kinds of products

Injection molding is a widely used manufacturing process for producing plastic parts in large volumes.

Here’s a step-by-step guide to the process, including key critical steps:

1. Design and Material Selection

Product Design: Start with a 3D design of the part (using CAD software like Solid Works or Auto，CAD).

Plastic Material Choice: Select a polymer based on the part’s requirements (strength, temperature resistance, flexibility, cost, etc.). Common options include:

Thermoplastics (most common): PP, PE, ABS, PC, PET.

2. Mold Design and Fabrication

The mold is the core of the process, typically made of hardened steel (for high-volume production)

Key mold features:

Cavities: The hollow shape that forms the part (single or multi-cavity for mass production).

Gating system: Channels that deliver molten plastic to the cavity (e.g., sprue, runner, gate). Gates control flow rate and location (e.g., edge gates, sub-gates).

Cooling system: Water channels within the mold to cool molten plastic quickly and uniformly (critical for cycle time and part quality).

Ejection system: Pins, plates, or sleeves to push the cooled part out of the mold.

3. Preparing the Plastic Material

Drying: Many hygroscopic plastics PC, ABS) absorb moisture from the air, which causes bubbles or streaks in the final part. Dry them in a dehumidifying dryer at specific temperatures (e.g., 80–120°C for ABS) for 2–4 hours.

Colorants/Additives: Mix in pigments, fillers (glass fiber), or stabilizers (UV resistance) as needed. Pre-com pounded materials (already colored) simplify this step.

4. Injection Molding Machine Setup

Injection molding machines consist of an injection unit (melts plastic) and a clamping unit (holds and opens the mold). Setup steps:

Mount the mold: Secure the mold halves to the clamping unit (fixed and moving platens). Align carefully to avoid damage.

Set temperatures: Heat the barrel (injection unit) in zones to match the plastic’s melting point (e.g., 180–230°C for PP, 230–300°C for ABS). The nozzle (connects to the mold) is also heated.

Clamping force: Adjust the clamping unit to apply enough force to keep the mold closed during injection (prevents "flash"—plastic leaking between mold halves). Calculated based on part area and material pressure.

5. The Injection Molding Cycle

A single cycle produces one or more parts and includes 4 main stages:

a. Plasticizing (Melting)

Granular plastic is fed into the barrel via a hopper.

A rotating screw pushes the plastic forward, heating it via friction and barrel heaters until it melts into a viscous fluid (melt).

The screw retracts slightly to accumulate a measured volume of melt (shot size) at the front of the barrel.

b. Injection

The screw moves forward rapidly, forcing the molten plastic through the nozzle and into the mold’s gating system, filling the cavity.

Key parameters:

Injection pressure: Ensures the mold fills completely (varies by material; e.g., 700–1500 bar).

Injection speed: Controls how fast the cavity fills (too slow = cold spots; too fast = turbulence/air traps).

c.Packing & Holding

Once the cavity is full, the screw maintains pressure (holding pressure) to "pack" additional plastic into the mold, compensating for shrinkage as the plastic cools.

Reduces sink marks and ensures dimensional accuracy.

d. Cooling

The mold’s cooling system circulates water to remove heat, solidifying the plastic.

e. Ejection

After cooling, the clamping unit opens the mold.

Ejection pins push the solidified part out of the cavity.

The cycle repeats (typically 10–60seconds, depending on part size, structure,weight, performance and so on).