The essence of plastic injection molding is an injection mold (which is used) to reproduce high-precision, multi-complex plastic components on a mass basis. High pressure is used to inject the molten plastic in a mold cavity where it is left to cool, solidify, and ejected. A typical injection mold is made out of two major halves: the fixed part (fixed half also known as the stationary half) and the moving part (moving half also known as the moving half) that come together to form the entire cavity.

I. Main Structural Components (by Function)

Module	Key Components	Function Description
1. Forming System	Cavity, Core, Inserts	Directly shapes the part’s external/internal surfaces and dimensions.
2. Runner System	Sprue, Runners, Gate, Cold Slug Well	Guides molten plastic from nozzle → cavity. Gate type affects flow and appearance.
3. Guiding System	Guide Pins, Guide Bushings	Ensures precise alignment during mold closing (accuracy ≤ 0.02 mm).
4. Ejection System	Ejector Pins, Ejector Plate, Lifters, Slides	Forces the cooled part out of the mold. Slides for side actions (undercuts).
5. Cooling System	Cooling Channels (straight, baffled, fountain)	Controls mold temperature (40–120°C) for rapid, uniform cooling.
6. Venting System	Vent Slots, Parting Line Clearance, Vent Plugs	Expels trapped air/gas to prevent burn marks, voids, or short shots.
7. Support System	Support Pillars, Spacer Blocks	Withstands injection pressure (100–200 MPa) to prevent plate deflection.
8. Mold Base	Fixed Clamping Plate, Moving Clamping Plate, A/B Plates	Standard mold base (e.g., LKM, DME, FUTABA) provides mounting foundation.

II. Typical Mold Cross-Section (Text Diagram)

[Injection Nozzle]
     ↓
[Sprue Bushing] → [Locating Ring]
     ↓
[Fixed Plate (A Plate)]
   ┌────────────────┐
   │  Cavity Insert │ ← Forms outer surface
   │  Cooling Lines │
   └────────────────┘
[Parting Line (PL)]
   ┌────────────────┐
   │   Core Insert  │ ← Forms inner surface
   │ Ejector Pins   │
   └────────────────┘
[Movable Plate (B Plate)]
     ↓
[Support Pillars, Ejector Plate]
     ↓
[Movable Clamping Plate]
     ↓
[Ejector Mechanism] → Connected to machine ejector rods

III. Key Component Details1. Runner System Design

Component	Design Tips
Sprue	Taper 1:50–1:100, Ra 0.4 surface finish
Runners	Round/trapezoidal, short length, smooth corners
Gate Types	Pin gate (auto-cut), Submarine gate (scarless), Fan gate (large parts)

2. Ejection Mechanisms

Type	Application
Pin Ejection	Flat/simple parts
Angle Pin + Slide	Side holes, undercuts
Air/Hydraulic Core Pull	Deep ribs, thin walls
Double Ejection	Complex release sequence

3. Cooling Optimization

Channel diameter: Ø6–Ø12 mm
Distance from cavity: 10–15 mm
Use baffles or fountain wells for even cooling
Temperature variation: ±2°C

IV. Molding Cycle (Standard Two-Plate Mold)

Mold Close: Moving platen advances → guide pins align → parting line seals
Injection: Melt fills cavity (0.1–3 sec)
Packing: Compensates shrinkage (2–10 sec)
Cooling: Part solidifies (10–60 sec)
Mold Open: Moving platen retracts; part stays on moving side
Ejection: Pins push part out → return pins reset
Part Removal: Robot or manual → apply release agent → next cycle

V. Mold Classifications

Type	Features
Two-Plate Mold	Simple, single parting line
Three-Plate Mold	Dual parting lines, auto gate cut
Hot Runner Mold	No runner waste, faster cycles
Stack Mold	Dual cavities, doubles output
IML/IMD Mold	In-mold labeling/decorating

VI. Recommended Mold Steels

Area	Steel Grade	Hardness (HRC)	Lifespan (shots)
Cavity/Core	P20, 718H	30–36	300K–500K
Mirror/High Precision	NAK80, S136	38–42	500K–1M
High Wear	H13, SKD61	48–52	1M+
Mold Base	S50C, 1045	Pre-hardened	—

VII. Design Guidelines

Draft Angle: 1°–2° (external), 0.5°–1° (internal)
Uniform Wall Thickness: 1.5–3.0 mm to avoid sink marks
Fillet Radius: R ≥ 0.5 mm to reduce stress
Venting: Parting line gap 0.02–0.04 mm or vent grooves
Ejector Placement: On ribs or non-cosmetic areas

Summary:
Injection mold design is a precision engineering process integrating part design → mold structure → process parameters → material selection. Optimized design achieves:

High efficiency (cycle < 30s)
High quality (tolerance ±0.05 mm)

Injection Mold Structure

plastic mold