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Differences between hydraulic and electric machines in injection molding process

2025/10/03 By le zhan

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Hydraulic and electric injection molding machines offer distinct process conditions for injection molding. Their differences lie in their mechanical design, with oil pumps and valves versus servo motors and ball screws. Still, the real impact extends to cycle time, repeatability, energy consumption, and part quality. This helps you understand which injection molding machine is best suited for your process, allowing you to make an informed choice based on these differences.

Differences in mechanical design also impact the injection molding process.

The fundamental difference that drives most downstream injection molding process variability lies in the mechanical design of each injection molding machine, resulting in different ways of generating motion and force. In hydraulic injection molding machines, a hydraulic pump pressurizes oil, which is delivered through valves to the hydraulic cylinders that control injection, screw rotation, and mold clamping. In contrast, electric injection molding machines use servo motors and mechanical transmissions (ball screws, linear guides) to convert rotary motion into linear motion of the injection and clamping axes.

When it comes to force transmission and clamping the platens, hydraulic systems provide strong, continuous force and virtually unlimited clamping capacity, making them suitable for very large molds and high-tonnage injection molding machines. Hydraulic systems generally provide smooth, high-force motion and strong overload tolerance. While electric injection molding machines offer increased peak clamping force through mechanical advantage and multi-motor designs, servo-driven lead screws or direct drive mechanisms typically generate the clamping force, and motor torque and gearbox design limit it at the maximum end. Therefore, electric systems excel at medium to high tonnages, where servo drives and mechanical transmissions can provide precise and repeatable clamping force.

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During the injection process, hydraulic systems enable fast and efficient injection, as they can withstand sudden pressure demands. The oil’s compressibility and large reservoir capacity help buffer transient pressure demands. Electric drives provide fast, precise position and velocity profiles with minimal variability in stroke-to-stroke motion. Electric drives provide superior control for complex contour injections, where precise positioning and acceleration are crucial. Therefore, if your injection molding process requires extremely high tonnage or long dwell times, a hydraulic injection molding machine is a suitable option. If your process requires high precision, repeatability, and fine motion control, an electric injection molding machine is a suitable option.

The injection molding process control and repeatability differ.

Electric injection molding machines are designed around high-resolution position encoders and deterministic servo drives, naturally supporting closed-loop position, speed, and torque control. This native servo control enables precise multi-step injection profiles, accurate position transfer for two-shot or insert molding, and fast, repeatable response to setpoint changes.

In injection molding, electric injection molding excels at position-based injection and drive-controlled multi-step speed/pressure profiles. Because servo motors predictively execute commands and provide instant feedback, process parameters such as injection stroke, screw position, and mold opening and closing are highly repeatable. In contrast, hydraulic molding machines rely on proportional valves or servovalves to regulate flow and pressure. While today’s hydraulic systems can achieve closed-loop pressure and speed control, they typically have slower bandwidth and are more sensitive to oil temperature and valve hysteresis.

All electric injection molding machine

Electric injection molding machines also enable very tight cavity pressure feedback loops, allowing for the sampling and adjustment of injection or holding pressure within a cycle at high frequency. This reduces cycle-to-cycle variation, resulting in an injection molding process with improved dimensional consistency and reduced warpage. Hydraulic systems can also utilize cavity pressure sensing. Manufacturers often use them for high-pressure, long-holding parts because the hydraulic system’s inherent force capacity allows for extended hold phases.

Cycle Time, Productivity, and Energy Efficiency

Electric injection molding machines offer significant advantages in cycle time, productivity, and energy efficiency. They eliminate hydraulic losses and, in some designs, enable the recovery of regenerative energy. Electric motors provide rapid axis motion with tightly controlled acceleration and deceleration. This translates to faster injection response, faster mold opening and closing speeds, and generally shorter non-productive time between shots. In contrast, hydraulic injection molding machines can reach or even exceed peak speeds under heavy loads, but this requires pump acceleration and valve adjustments, which can extend certain phases. For injection molding processes with very short fill phases and critical repeatability, such as high-speed thin-wall production, electric motors generally offer faster effective cycle times with less variability.

Hydraulic injection molding machines can also be prone to energy waste during the injection molding process. Hydraulic pumps may run continuously or cycle frequently, generating heat losses that the plant’s cooling system must remove. Electric injection molding machines only consume power when their axes are moving. In many production modes, electric machines can consume significantly less energy per cycle.

Material Properties and Product Quality Differences

Material selection, molding dynamics, and machine characteristics interact to determine the quality of the part. The injection molding process must control shear, temperature, pressure, and cooling to achieve the desired mechanical properties and aesthetics; choosing a hydraulic or electric injection molding machine influences how these controls are implemented.

In thin-wall packaging and consumer goods, thin-walled parts (with a wall thickness of 0.4-1.0 mm) require extremely fast injection speeds and strict shot-to-shot repeatability. Therefore, the fast response and precise speed control of electric machines make them the preferred platform for high-cavitation, thin-wall packaging molds, where balanced and consistent filling prevents underfill and flash.

For optical and aesthetic parts, electric injection molding machines can program complex injection/holding profiles, achieving cavity pressure control, and are more capable of meeting these stringent injection molding process requirements than many hydraulic systems. Then there are thick-walled and structural parts. For very thick parts that require high, long-lasting hold pressures and suppress shrinkage and sink, a hydraulic injection molding machine may be more suitable. The hydraulic system’s ability to maintain high pressure and hold pressure for extended periods can help address internal voiding and sinkage issues.

Select Based on Product and Process

The differences between hydraulic and electric injection molding processes determine part production reliability, production costs, and which product categories are profitable. Hydraulic injection molding machines remain the workhorse for large-tonnage applications and those requiring high, sustained pressure and long hold times. In contrast, electric injection molding machines offer superior motion control, energy efficiency, and repeatability. These advantages make them the preferred choice for thin-wall packaging, high-cavity consumer parts, optical and cosmetic parts, and processes requiring synchronized multi-axis motion.

 

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