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Types of Injection Molds: Complete Classification & Differences



Introduction

Injection molds are the core tooling for plastic manufacturing. All thermoplastic and thermoset parts, including Bakelite bushes, electrical insulators and precision structural components, are produced by injection molds. Understanding mold types and their characteristics helps engineers and buyers select the correct mold solution for different product requirements.
In the plastic molding industry, injection molds are mainly classified by structure, molding process, precision standard and cavity design. This article explains all mainstream injection mold types in detail.


Classification by Mold Structure


1.1 Two-Plate Mold (Single parting line)

The two-plate mold is the most common and basic mold structure. It consists of a fixed plate and a moving plate with only one parting surface. After injection, the product and runner stay on the moving half and are ejected by pins.
Features: Simple structure, low cost, easy maintenance, fast cycle time.
Applications: Simple bushes, gaskets, standard insulating parts and general plastic components.


1.2 Three-Plate Mold (Double parting line)

A three-plate mold includes an additional runner plate, creating two parting lines. It automatically separates products from runners during mold opening, achieving clean and burr-free products without manual trimming.
Features: High automation, excellent surface quality, no runner marks, complex structure and higher cost.
Applications: High-precision electrical parts, appearance-critical components and mass-production plastic parts.


1.3 Slide Mold (Side core pulling mold)

Designed for products with undercuts, side holes and grooves. The slide mechanism moves sideways to release the undercut structure before ejection.
Applications: Special-shaped insulating parts, complex structural components and electrical accessories with side features.


1.4 Lifter Mold (Angled pin mold)

Lifter molds are used for small internal undercuts and narrow grooves. The angled pin mechanism occupies less space and works faster than slides.

Applications: Micro precision Bakelite parts, small insulating clips and ultra-thin precision components.



2. Classification by Molding Material & Process


2.1 Thermoplastic Injection Mold

Used for POM, PA, ABS, PP and other ordinary plastics. Equipped with cooling water channels. The molding principle is “hot barrel + cold mold” for fast cooling and solidification.
Features: Long mold lifespan, fast mass production, suitable for general plastic products.


2.2 Thermoset Injection Mold (Bakelite / Phenolic / UF Mold)

Specially designed for thermoset materials such as phenolic resin (Bakelite) and urea-formaldehyde resin (UF). Equipped with electric heating systems, the mold works constantly at 160–200℃ to complete chemical cross-linking and curing inside the cavity.
Features: High temperature resistance, high venting requirement, ultra-stable dimensional accuracy, excellent hardness and wear resistance of finished parts.

Applications: Gas spring Bakelite bushes, electrical insulation parts, high-temperature resistant precision components.



3. Classification by Precision Grade


3.1 Standard Injection Mold

Suitable for ordinary products with loose tolerance requirements, common appearance and non-precision assembly usage.


3.2 Precision Injection Mold

Manufactured with high-precision CNC machining and mirror polishing. Tolerance can be controlled within ±0.01mm. Ideal for high-precision assembly and dynamic moving parts.

Typical applications: Gas spring guide bushes, high-end electrical insulating parts and precision mechanical components.



4. Classification by Cavity Quantity


4.1 Single-Cavity Mold

Produces one part per cycle. Easy adjustment, high yield rate, suitable for new product sampling and small-batch precision production.


4.2 Multi-Cavity Mold

Produces 2, 4, 8 or more parts per cycle. Highly efficient for mass production and greatly reduces unit cost.



5. Special Process Mold Types


  • Double-color injection mold: For dual-color or soft-hard combined plastic parts

  • Insert injection mold: For parts embedded with metal terminals or inserts

  • Compression mold: Traditional mold for thermoset compression molding



Conclusion


Injection molds can be classified by structure (two-plate, three-plate, slide, lifter), material type (thermoplastic and thermoset), precision grade and cavity quantity. For high-end gas spring bushes and electrical insulation components,high-precision thermoset multi-cavity molds are the best solution for stable quality and mass production.

Hitech(HK) International Limited specializes in precision thermoset mold development and Bakelite injection molding. We provide custom molds for precision bushes, insulating parts and special-shaped thermoset components with high precision and tight tolerance.