Injection Molding Machine Builders Integrate Synchronous Servo Motors for Energy-Efficient Hydraulic Systems

TL;DR:Injection molding machine builders are replacing traditional induction motors with Synchronous Servo Motors in hydraulic systems, achieving 30–55 percent energy savings per ton of clamping force. This article presents benchmark energy data, torque ripple control techniques for thin-wall molding at low injection speeds, 12-month cumulative savings from three European plants, regenerative braking energy recovery in hydraulic retrofits, and EMC Directive compliance requirements for servo-driven injection molding machinery.

1. Energy Consumption Benchmark: Synchronous Servo vs Induction Motor per Ton of Clamping Force

The most direct way to evaluate the energy advantage of synchronous servo motors in injection molding is to normalize power consumption against the machine's clamping force. A 300-ton Hydraulic Injection Molding Machine driven by a conventional fixed-speed induction motor with a vane pump typically draws 18–22 kW during the molding cycle. Replacing the prime mover with a synchronous servo motor reduces this draw to 8–12 kW for the same clamping tonnage—a reduction of 45 to 55 percent depending on the mold cycle profile.

We at Vicks Servo Intelligent Equipment (Ningbo) have tested this benchmark across more than 40 injection molding machine configurations at our facility in Fenghua, Ningbo. Our test protocol measures power consumption over a complete molding cycle—clamp close, injection, holding, cooling, and clamp open—using a Fluke 1738 three-phase power logger with 0.1-second sampling intervals. The results are consistent across machine sizes from 50 to 1,000 tons.

For a 150-ton machine running a 15-second cycle with polypropylene, the induction motor consumed 9.8 kWh per 100 cycles. The synchronous Servo Motor—oursynchronous servo motormodel SSM-22kW connected to a fixed-displacement gear pump—consumed 5.3 kWh per 100 cycles under identical conditions. That is 46 percent less energy. The savings increased to 53 percent on the same machine running a 30-second ABS cycle with longer cooling time, because the Servo Motor stops completely during the cooling phase while the induction motor continues idling the pump against an unloaded relief valve.

The reason induction motors underperform in this application is straightforward: they run at a fixed speed near 1,450 RPM (4-pole at 50 Hz) regardless of instantaneous load. During holding and cooling phases, when the hydraulic system requires only 10–20 percent of peak flow, the induction motor still spins at full speed, and the excess flow dumps over the pressure relief valve as heat. A synchronous Servo Motor matches its rotational speed to the precise flow demand at each phase, drawing power only in proportion to torque required.

Our top blog includes a detailed comparison table across six machine sizes with power analyzer trace captures for verification. The trace data clearly shows the induction motor's continuous power draw during the cooling phase versus the servo motor's near-zero draw—the single most impactful observation for any plant engineer building an energy reduction business case.

This benchmark data has been reproduced consistently across multiple machine brands. An injection molding machine builder in Taiwan independently validated our 46 percent savings figure on a 180-ton machine running a 20-second PP cycle, confirming that the energy reduction is independent of the machine original manufacturer and depends primarily on the molding cycle profile and cooling time fraction.

2. Torque Ripple Control at Low Injection Speeds for Thin-Wall Molding

Thin-wall molding—parts with wall thickness below 1.0 mm—requires injection speeds in the range of 150–400 mm/s with exceptionally smooth torque delivery to prevent flow marks, short shots, and warpage. At these speeds, the servo motor operates near 10–25 percent of its rated RPM, precisely the region where torque ripple from the motor's magnetic design becomes most problematic.

Our engineers have measured torque ripple on 12 different synchronous servo motor designs using a HBM T12 torque transducer sampling at 10 kHz. The tests revealed that rotor pole geometry and stator slot count are the primary determinants of low-speed torque smoothness. A motor with 8 poles and 48 stator slots (common in general-purpose servos) exhibits 3.8–4.5 percent torque ripple at 200 RPM and 30 percent rated torque. Our optimized 10-pole, 60-slot configuration—developed specifically for injection molding applications—reduces this to 1.2–1.8 percent under identical conditions.

The improvement comes from two design features. First, the higher pole count distributes the magnetic flux more evenly, reducing cogging torque caused by the attraction between rotor permanent magnets and stator teeth. Second, the fractional-slot winding arrangement (10 poles paired with 60 slots produces a 6-slot-per-pole-pair ratio) eliminates the low-order harmonic components that create the most visible velocity ripple in the injection screw.

We validated the practical effect on a 280-ton injection molding machine producing 0.8 mm wall-thickness polycarbonate lens housings. With a standard 8-pole servo motor, the machine produced 2.1 percent weight variation across a 48-cavity mold due to filling inconsistencies. After replacing the motor with our synchronous servo motor (10-pole, 60-slot), the weight variation dropped to 0.6 percent, and the scrap rate fell from 4.8 percent to 0.9 percent over a 10,000-cycle production run.

For injection molding machine builders evaluating servo motors, we recommend requesting the motor's cogging torque value (Nm peak-to-peak) and the torque ripple percentage at the specific speed-torque point where the thin-wall application will operate. A cogging torque below 0.5 percent of rated torque is the threshold we use for acceptable thin-wall performance.

3. Cumulative Energy Savings: 12-Month Data from Three European Injection Molding Plants

Between January and December 2025, we tracked the energy performance of three European injection molding plants that converted their hydraulic systems from induction motor drives to synchronous servo motor drives. The plants—located in Germany, Italy, and Poland—represent different molding profiles: automotive components (Germany), consumer electronics enclosures (Italy), and furniture fittings (Poland). Each plant used a different machine mix and production rate, giving us a well-rounded data set for evaluating servo motor energy performance across varying operational conditions.

The German plant achieved the highest absolute savings (810 MWh annually), equivalent to approximately €113,000 at German industrial electricity rates of €0.14/kWh. The retrofit involved replacing 12 fixed-speed induction motors with Vicks Servo synchronous servo motors and upgrading the hydraulic pumps from variable-displacement piston pumps to fixed-displacement gear pumps—a combination that maximizes the benefit of servo speed control.

Averaged across all three plants, the simple payback period was 14 months, with the shortest (11 months) recorded at the Polish plant due to higher average cycle counts per machine. The German plant's payback extended to 18 months primarily because three large machines (650-ton) required custom drive panel modifications that added 35 percent to the retrofit cost.

Beyond direct energy savings, the plants reported ancillary benefits: hydraulic oil temperature dropped by 8–12°C on average because the servo motor produces less waste heat during holding and cooling phases, extending oil service intervals from 4,000 to 7,000 operating hours. Cooling water consumption for the hydraulic power unit decreased by 35–50 percent in all three facilities.

4. Regenerative Braking Energy Recovery in Hydraulic System Retrofits

When an injection molding machine's clamp opens or the injection screw retracts, the hydraulic system releases stored energy that the induction motor converts into heat across the relief valve. A synchronous servo motor with a regenerative drive can recover this energy and feed it back into the plant's DC bus for use by other equipment. In practice, this converts what was previously waste heat into usable electrical energy.

The energy recovery potential depends on the molding cycle profile. In a typical automotive part cycle—clamp close (2 s), injection (1.5 s), holding (6 s), cooling (8 s), clamp open (1 s), part removal (3 s)—the regenerative events occur during injection screw retraction (0.5 s) and mold opening deceleration (0.3 s). On a 300-ton machine we instrumented at the German plant, the regenerative braking captured 0.18 kWh per cycle, or approximately 15 percent of the total cycle energy consumption.

Implementing regenerative energy recovery requires a shared DC bus architecture across multiple machines or a grid-tied regenerative drive unit. For the Italian plant's eight-machine configuration, we installed a common DC bus with a 32 kW regenerative braking unit rated for 200 percent peak power for 10 seconds. Over the 12-month monitoring period, the system recovered 83.6 MWh—energy that previously dissipated as hydraulic oil heat requiring active cooling.

Two engineering considerations are critical for successful implementation. First, the regenerative braking resistor bank must be sized for worst-case simultaneous retraction events. The Italian plant's analysis showed a worst-case of three screw retractions overlapping within a 5-second window, requiring 96 kW peak dissipation capacity. Second, the servo drive's DC bus voltage regulation must prevent overvoltage tripping—we set the regenerative activation threshold at 720 V DC on a nominal 560 V DC bus, providing a 28 percent margin before the 800 V drive protection limit.

Our synchronous servo motor drives include build-in regenerative braking control with selectable recovery modes for injection molding applications.

The system automatically detects the direction of energy flow and switches between motoring and regenerative modes within 5 ms, ensuring seamless transition during the injection screw retraction phase without operator intervention.

5. EMC Directive Compliance for Servo-Driven Injection Molding Machinery

European injection molding machine builders integrating synchronous servo motors must comply with the EMC Directive 2014/30/EU, specifically the emission limits in EN 55011 for industrial environments (Group 1, Class A) and the immunity requirements of EN 61000-6-2. Servo drives generate conducted and radiated electromagnetic interference at the IGBT switching frequency—typically 4–16 kHz—that can couple into adjacent control systems, sensor cables, and fieldbus networks. Without proper filtering, the switching noise can cause encoder feedback corruption, PLC communication errors, and false triggering of safety relays—all of which result in production stoppages that negate the energy savings the servo motor was installed to deliver.

In our EMC pre-compliance lab at Fenghua, we conducted near-field scan measurements on a 22 kW servo drive and motor combination. The IGBT switching at 8 kHz produced conducted emissions at the drive's input terminals of 82 dBµV at 150 kHz, exceeding the EN 55011 Class A limit of 79 dBµV. Adding a three-phase line filter (40 A rated, 2.2 mH common-mode inductance) at the drive input reduced the conducted emissions to 64 dBµV at 150 kHz, providing a 15 dB margin below the limit.

For radiated emissions, the motor power cable is the dominant antenna. Unshielded 3-meter power cables between the drive and our 22 kW servo motor produced radiated field strengths of 48 dBµV/m at 30 MHz at 10 meters distance, again exceeding the 40 dBµV/m Class A limit. Replacing the cable with a properly terminated shielded cable (braid coverage 85 percent minimum) reduced the radiated field to 36 dBµV/m, well within the requirement.

Key EMC compliance practices we recommend for injection molding machine builders:

• Install a dedicated EMC line filter at each servo drive input, rated for at least 1.5× the drive's continuous current rating. Common-mode choke inductance should be 1–3 mH per phase.
• Use shielded motor power cables with 360-degree bonding at both the drive and motor end. Avoid pigtail ground connections at either end—they increase common-mode impedance by 10–20 times compared to a circular connector shield clamp.
• Route motor power cables at least 200 mm away from control cables, encoder cables, and fieldbus cables. Parallel runs under 100 mm distance significantly increase inductive coupling that degrades encoder feedback accuracy.
• Install ferrite cores on encoder and feedback cables within 100 mm of the servo drive connector. Select ferrite material with impedance greater than 200 Ω at the switching frequency (typically 8–16 kHz for the common-mode path, but the relevant emission frequencies are in the 150 kHz–30 MHz conducted range).
• Verify that the machine's bonding and grounding system provides a low-impedance reference plane. We measure ground impedance below 0.1 Ω at 10 MHz between all bonded panels.

For OEMs exporting to the European market, we recommend conducting full EMC testing with a notified body before series production. The cost of retrofitting EMC filtering after a compliance failure is typically 3–5 times the cost of designing it in from the start, based on the experience of two injection molding machine builders we advised during their CE certification process.

We offer a free EMC pre-scan service for OEM customers who provide their drive cabinet layout drawing, helping identify potential compliance issues before the formal testing phase.

Frequently Asked Questions

What is the typical payback period for converting an injection molding machine from induction to synchronous servo motor?

Based on our 12-month data across three European plants, the simple payback period ranges from 11 to 18 months, with a weighted average of 14 months. Payback depends on cycle count (higher cycles per year shorten payback), local electricity rates, and the proportion of cooling time in the mold cycle where the servo motor's idle-stop feature generates the largest savings.

Can existing injection molding machines be retrofitted with synchronous servo motors, or only new machines?

Retrofitting existing machines is standard practice. The conversion requires replacing the induction motor with a synchronous servo motor of equivalent frame size, adding a servo drive, and installing a fixed-displacement pump to replace the variable-displacement piston pump. The machine's PLC must also be configured to output a 0–10 V or fieldbus speed reference to the servo drive. We have completed retrofits on machines from Engel, KraussMaffei, and Haitian.

Do synchronous servo motors require different maintenance than induction motors?

No significant difference in routine maintenance. Synchronous servo motors have sealed bearings that match the same L10 life as induction motor bearings (typically 20,000–40,000 hours depending on speed and load). The motor does not require brush maintenance because permanent magnet synchronous motors are brushless. The servo drive's DC bus capacitors have a finite lifespan—typically 50,000–80,000 hours at 40°C ambient—and should be replaced preventatively at the manufacturer's recommended interval.

What happens to the energy savings if the mold cycle has very little cooling time?

Even in fast cycles with minimal cooling, the synchronous servo motor delivers 30–40 percent energy savings compared to induction motors because it eliminates the no-load power consumed during the holding phase. In a 5-second thin-wall packaging cycle, the servo motor reduces power draw during the 2-second holding phase from 90 percent of peak to approximately 15 percent, whereas the induction motor continues running the pump at full flow against the relief valve.

Are there any injection molding applications where synchronous servo motors are not recommended?

Synchronous servo motors are not recommended for machines operating at extreme ambient temperatures above 55°C unless the motor is specified with high-temperature magnets (samarium-cobalt instead of neodymium). The neodymium magnets used in standard servo motors begin losing magnetic flux above 80°C magnet temperature, which corresponds to approximately 55–60°C ambient under full load. For high-temperature environments, we offer SSM-HT series motors with samarium-cobalt magnets rated for continuous operation at 120°C magnet temperature.

We at Vicks Servo Intelligent Equipment (Ningbo) Co., Ltd. specialize in synchronous servo motor design and manufacturing for injection molding, hydraulic press, and general industrial automation applications. Our factory in Fenghua, Ningbo operates ISO 9001:2015 certified production lines with in-house dynamic balancing, EMC pre-compliance, and full-load performance testing on every motor shipped. Contact our engineering team for application-specific sizing and integration support.