What Type of Mold is Used in Injection Molding?

In the injection molding industry, molds serve as the core carrier for production. Molten plastic forms the final appearance, dimensions and structure of finished parts inside the mold cavity. Many procurement and R&D engineers often wonder which category of injection mold to select for newproject development. Different mold types vary greatly in cost, service life, production efficiency and part precision. Improper mold selection may lead to wasted costs, insufficient production capacity or failure to meet design specifications. Drawing on realworld injectionmolding project experience, this article sorts out common mold classifications, their features and applicable scenarios, helping customers make quick and appropriate mold selections.

1. Classification by Number of Cavities

1. Singlecavity Mold (1outof1)

A mold containing only one product cavity, producing one component per molding cycle.

• Advantages: Simple structure, short lead time for mold making, convenient debugging, stable dimensional performance, easy product modification. Suitable for highly complex parts with strict dimensional tolerances.
• Disadvantages: Low production output, higher unit molding cost, not ideal for ultrahighvolume mass production.
• Applications: Lowvolume prototyping, complex custom parts, large plastic housings, medical components and sample development.

2. Multicavity Mold (multiout, 1×2 / 1×4 / 1×8 / 1×16, etc.)

One mold equipped with two or more identical cavities, producing multiple identical parts in one moldopeningclosing cycle.

• Advantages: Multiplied productivity and reduced perunit processing cost for highvolume standardized components.
• Disadvantages: Higher mold investment; higher requirements for mold workmanship and molding process. Balanced filling and pressure across all cavities must be ensured; otherwise inconsistent dimensions or appearance will occur among parts. Modification costs are higher.
• Applications: Bottle caps, small fittings, dailyuse goods and small consumerelectronic components for mass production.

3. Family Mold (multiple dissimilar cavities)

One mold containing cavities for several different parts, producing multiple distinct components in a single injection cycle.

• Advantages: Lower total mold investment for a set of matching small components within one project.
• Disadvantages: Imbalanced filling caused by varying part volume and weight. Modification to one cavity will affect the whole mold set. Not suitable for longterm highvolume mass production.
• Applications: Prototype samples and lowvolume matched assemblies.

2. Classification by Gating System: Coldrunner vs Hotrunner Molds

1. Coldrunner Mold

The conventional generalpurpose injection mold. Molten plastic flows through runners and gates into cavities. Solid runner sprues and gates are generated with every production cycle.

• Advantages: Low mold cost, easy maintenance, compatible with most plastic grades and low technical barriers for operation.
• Disadvantages: Waste sprue material is generated; recycling is restricted for certain materials. Higher material loss for multicavity molds and slightly longer cycle time. Gate marks may appear on largesize parts.
• Applications: Most ordinary plastic products for medium and lowvolume projects.

2. Hotrunner Mold

Heating assemblies are installed inside the runner system to keep plastic molten permanently within runners. No solid sprue waste is produced, and melt feeds directly into cavities. It is divided into singlepoint hotrunner and multipoint hotrunner types.

• Advantages: Zero sprue waste and material savings; shortened molding cycle and improved productivity; optimized filling performance with reduced weld lines for largesize or multicavity parts; cleaner gate appearance.
• Disadvantages: Considerably higher mold cost; a dedicated hotrunner temperature controller is required; higher maintenance knowhow demanded from operators; incompatible with some heatsensitive plastics.
• Applications: Highvolume mass production, cosmeticgrade appearance parts, large housings and precision multicavity products such as automotive and homeappliance components.

3. Specialpurpose Molds for Special Molding Processes

1. Overmolding Mold

Used for overmolding process: rigid substrate is injected first, then TPE or soft elastomer is overmolded onto the hardplastic surface. It can be implemented via twoset sequential molds or an integrated rotary overmolding mold.

• Features: Precise positioning is required to guarantee bonding interfaces between hard and soft materials; strict moldtemperature control directly determines overmolding adhesion performance.
• Typical products: Tool handles, antislip grips and waterproof sealing components.

2. Twocolor Injection Mold

Rotarytable mold matched with twocolor injection machines. The mold rotates in position to inject two different colors or materials sequentially for integrated oneshot forming.

• Features: High investment for both mold and equipment; high production efficiency and seamless integrated visual effect.
• Applications: Consumerelectronic housings and cosmetic packaging shells.

3. Gasassisted Injection Mold

Special molds fitted with gaspin ports. Highpressure gas is injected during molding to create hollow internal structures inside parts.

• Advantages: Reduced wall thickness, minimized sink marks and weight reduction of finished parts.
• Applications: Thickwall handles and large decorative components.

4. Classification by Mold Steel & Servicelife Grade

1. Prototype / Lowvolume Soft Mold

Fabricated from prehardened steel such as P20 and 718H, without quenching treatment.

• Service life: Tens of thousands of shots.
• Features: Low mold cost and short leadtime. Used for structural verification and smallbatch pilot production, not for longterm mass production.

2. Massproduction Hard Mold

Adopting quenchedandtempered steel grades including S136, H13 and NAK80.

• Service life: Hundreds of thousands up to over one million shots. Good wearresistance, corrosionresistance and polishing performance. Ideal for cosmeticgrade appearance parts and longterm export massorder projects.

Selection tip: Prefer S136 for mirrorfinish appearance parts; 718H for general structural components; H13 for highwearresistance requirements.

5. Quick Guidelines for Selecting Suitable Injection Molds

• Production volume: Choose singlecavity soft molds for lowvolume prototyping; consider multicavity molds for highvolume orders and evaluate hotrunner feasibility.
• Surface quality: Hardgrade mold steel is recommended for cosmeticgrade parts; hotrunner can be adopted when necessary to minimize gate marks.
• Process requirements: Overmolding dedicated molds for softgrip applications; rotary twocolor molds for dualmaterial / dualcolor visual effects.
• Budget constraints: Coldrunner is costeffective for limited budgets; hotrunner can offset extra mold cost via material savings when output volume is sufficiently large.

Conclusion

There is no universallybest injection mold — only the most suitable one. Singlecavity / multicavity, coldrunner / hotrunner, soft mold / hard mold and specialprocess molds shall be comprehensively evaluated according to production quantity, cosmetic requirements, material properties and project budget. Reasonable mold planning in earlystage development helps avoid costrelated, qualityrelated and capacityrelated risks in laterphase manufacturing.