Injection molding is the workhorse of mass plastics manufacturing — from tiny connectors to automotive housings. But "injection molding machine" is not one single machine. Depending on how it is driven, how the clamp opens, what material it runs, and how its hydraulic system is built, machines fall into very different categories. Knowing these categories helps you pick the right equipment — and set the right expectations — for your project.

Below, machines are classified along seven dimensions. For each dimension, we also note what is most commonly used in practice.

1Classification by Drive System

Hydraulic · All-Electric · Hybrid

The drive system is the "heart" that powers clamping and injection. There are three main types:

• Hydraulic injection molding machines — powered by hydraulic oil, like a high-torque gasoline engine. They deliver strong clamping and injection forces and remain the traditional mainstream, especially for large parts.
• All-electric injection molding machines — driven entirely by servo motors, like a clean and quiet Tesla. They offer high precision, energy efficiency, fast response and a clean workshop environment, making them popular for medical, optical and precision electronics molding.
• Hybrid (oil-electric composite) machines — a combination of both, offering high efficiency and good economy. They balance the power of hydraulics with the precision of servo electrics.

2Classification by Clamp Opening Direction

Horizontal · Vertical

This classification looks at how the clamping unit opens and closes the mold:

• Horizontal machines — the mold opens and closes horizontally. This is the dominant layout in modern production: parts drop out by gravity, automation and conveyors integrate easily, and operation is convenient.
• Vertical machines — the mold opens and closes vertically. Inserts can be placed and held in position by gravity, making vertical machines ideal for insert molding (e.g., electrical plugs, cable connectors) and compact cell layouts.

3Classification by Suitable Raw Materials

Thermoplastic · Thermoset · Powder (MIM/CIM)

Different plastics behave very differently when heated, so machines are built to match:

• Thermoplastic injection molding machines — for thermoplastics that soften when heated and re-harden when cooled, and can be remelted and reprocessed. This is by far the largest machine category.
• Thermoset injection molding machines — often called "Bakelite machines", for thermosetting materials that cure permanently once heated; they cannot be remelted.
• Powder injection molding machines — for metal, ceramic or alloy powders mixed with binders (the MIM / CIM processes), producing dense metal or ceramic parts after sintering.

4Classification by Hydraulic Circuit

Single · Dual · Triple Circuit

Inside the hydraulic system, machines differ in how many independent oil circuits they use:

• Single-circuit machines — one hydraulic circuit serves all functions, like a driver who focuses only on driving.
• Dual-circuit machines — two circuits, like a driver who also drinks water on the road: some functions can run independently for better efficiency.
• Triple-circuit machines — three independent circuits, like a driver who drives, drinks and sings at the same time: the highest level of parallel operation.

5Classification by Oil Circuit Control

Open-Loop · Closed-Loop

This dimension is about control precision of the hydraulic system:

• Open-loop machines — the system executes commands without feedback, like flooring the gas pedal to "110 km/h" without cruise control: actual speed fluctuates and stability is limited.
• Closed-loop machines — sensors continuously feed actual pressure, speed and position back to the controller, which auto-corrects — like a car's cruise control automatically adjusting fuel to hold a steady speed.

6Classification by Clamping Structure

Toggle · Direct-Hydraulic · Two-Platen

The clamping unit is where the mold is held shut against injection pressure. Three structures dominate:

• Toggle-type (knee-lever) machines — a mechanical linkage amplifies the hydraulic force to lock the mold. Fast cycles and lower energy use make toggles very widespread.
• Direct-hydraulic machines — the hydraulic cylinder clamps the mold directly. Full-surface clamp force, precise control, and easy mold-height adjustment.
• Composite direct-hydraulic (two-platen) machines — a simplified, two-platen design combining mechanical locking with hydraulic clamping; popular for large machines because it shortens the tie-bar length and reduces machine footprint.

7Classification by Injection (Plasticizing) Structure

Single-Color · Multi-Color

Finally, machines differ by how many sets of injection units plasticize and shoot material:

• Single-color machines — one injection unit, producing one material or color per shot. This covers the vast majority of everyday plastic parts.
• Multi-color machines — multiple injection units, enabling two-shot / multi-material molding: hard-soft combinations (e.g., TPE grips), multi-color buttons, lenses and seals — all molded in one cycle without secondary assembly.

8Summary: All 7 Dimensions at a Glance

The table below pulls everything together — the machine types in each classification dimension, and what dominates in actual industrial use.

Takeaways for Part Designers & Buyers

• Know your material first. Thermoplastic, thermoset or powder (MIM) determines the machine family outright.
• Match the machine to the part geometry. Insert molding leans vertical; most everything else runs horizontal.
• Precision needs closed-loop. Tight-tolerance parts benefit from closed-loop hydraulic control or all-electric drives.
• Hybrid drives are the current sweet spot — efficiency and economy in one package, which is why adoption keeps rising.
• Multi-color/multi-material saves assembly. If your part combines hard and soft materials, two-shot molding on a multi-color machine may beat secondary assembly on cost and quality.