Take a Comprehensive Look at Injection Molds

Take a Comprehensive Look at Injection Mold

Injection molds are the core process equipment in injection molding, determining the shape, dimensional accuracy, surface quality, and production efficiency of plastic parts. To produce high-quality, low-cost, mass-producible plastic components, comprehensive control is essential throughout the entire process—from mold design and manufacturing to trial runs, maintenance, and lifecycle management. Starting with fundamental concepts, this article systematically covers injection mold types, structures, materials and manufacturing, design essentials, trial runs and maintenance, common faults and troubleshooting approaches, as well as industry trends—helping you build a comprehensive mold knowledge system.

Injection Molds

I. What Are Injection Molds? Why Are They Important?

An injection mold (Mold/Die) is a steel tool that injects molten plastic, cools it, and shapes it into the final part. Mold quality directly impacts:

Product appearance and dimensional accuracy;

Production cycle time and unit cost;

Post-processing workload (e.g., grinding, painting, machining);

Production stability and defect rate.

A well-designed mold can withstand hundreds of thousands to millions of injection cycles. Poor design or subpar machining, however, leads to frequent repairs or disrupts entire production lines.

II. Primary Mold Types

Common mold types by structure and application include:

Two-plate mold: Most common, with gates at the parting line. Simple structure, suitable for single injection parts.

Three-plate mold: Features a separate gate block, facilitating gate removal and automation.

Hot runner mold: Heated runners reduce scrap and processing steps, ideal for high-volume production and cosmetic parts.

Cold Runner Mold: Low cost and simple structure, but generates more scrap.

Multi-cavity Mold: Produces multiple identical cavities from a single mold, increasing production capacity.

Family Mold: Different cavities within the same mold form distinct parts, suitable for integrated assemblies or matching components.

Stack Mold: Doubles output by stacking cavities vertically, saving mold space.

Two-shot/Overmold: Produces dual-color or soft-hard composite parts in a single cycle.

Insert Molding: Embeds metal inserts or other components before molding.

Special Auxiliary Process Molds: Utilizes gas-assisted, liquid-assisted, foam, or melt-core technologies to meet specific structural or material requirements.

III. Mold Composition and Key Components

A typical injection mold primarily consists of two major parts: the mold base and the core (cavity). Key components include:

Cavity and Core

Gate, Runner, Sprue Bushing

Guide Pillar/Bushings

Ejector Pins and Ejector Plate

Locating Rings and Dowel Pins

Sliders/Lifters

Cooling Channels

Vents

Hot Runner System (Heater, Manifold) — For hot runner molds

Breaking, Distributing, and Ejection Mechanisms

IV. Mold Materials and Surface Treatment

Mold materials must balance strength, wear resistance, hardenability, and machinability. Common materials:

P20, 718, 2738, H13: Often used for standard injection molds; H13 is frequently used in high-temperature, high-pressure environments.

S136, 420, 8407: Corrosion-resistant steels commonly used for polished molds or mirror-finished parts.

Surface Treatments: Nitriding, hard chrome plating, electroplating, PVD coating, etc., enhance wear resistance, corrosion resistance, and surface finish.

V. Overview of Mold Manufacturing Processes

The manufacturing process typically includes: Product Analysis → Mold Design (CAD/CAE) → Machining (rough machining → heat treatment → finish machining) → EDM → grinding/polishing → assembly → trial molding (trial production) → adjustment and delivery.

Common machining equipment: CNC machining centers, wire EDM, precision grinding machines, polishing equipment. Heat treatment and finish machining are critical steps for ensuring mold longevity and precision.