Torque Ripple Below 3%: How Motor Smoothness Protects Melt Homogeneity and Screw Life

What Torque Ripple Means in Injection Molding

Torque ripple is the periodic variation in the motor's output torque over one mechanical revolution. In a permanent-magnet synchronous Servo Motor like theABT low-ripple servo motor, torque ripple is dominated by two physical sources: cogging torque (the attraction between rotor magnets and stator slots) and ripple from the non-sinusoidal distribution of the stator winding MMF. Both sources produce torque output that varies positionally around the shaft, even when the current command is steady.

For an injection molding machine, the consequence of torque ripple flows through three causal links:

1. Torque ripple produces screw rotation ripple. The screw's instantaneous rotational speed is the integrated effect of motor torque minus melt back-pressure load. A 3% ripple on a motor producing 100 Nm of average torque produces a ±1.5 Nm oscillation around that 100 Nm, which translates to a non-uniform screw rotation even when the hydraulic back-pressure is steady.
2. Screw rotation ripple produces injection-flow ripple. The melt flow rate through the screw is proportional to screw rotational speed. A non-uniform rotation produces a non-uniform flow rate, which produces non-uniform shear on the polymer melt.
3. Non-uniform shear produces melt homogeneity variation. Polymer melts that are not subjected to uniform shear history retain unmelted particles, inconsistent molecular weight distribution, and thermal history gradients. The molded part inherits these as wall-thickness variation, sink marks, and surface defect patterns.

The torque ripple below 3% threshold referenced in this article's title is the engineering consensus below which melt homogeneity variation in precision injection molding becomes small relative to other process variables (mold temperature variation, injection pressure variation, material lot variation). Above 3%, melt homogeneity variation becomes a measurable contributor to dimensional variance in the molded part. The threshold is application-dependent — a 3% tolerance may be acceptable for a packaging closure but unacceptable for an optical lens — and the engineering team at VICKS Servo documents the ABT motor's ripple specification against the application rather than against a single global threshold.

ABT Servo Motor Specifications: 45–1040 Nm, 1700 rpm, 380V

The ABT low-ripple servo motor is documented on the product page with a full parameter table covering air-cooled and oil-cooled variants. Below is the air-cooled parameter set, taken directly from the product page, which is the relevant reference set for injection molding machine builders evaluating motor selection for the platen, injection, and ejection axes.

The ABT range covers 45 Nm to 1020 Nm rated torque with a 380 V rated voltage across the catalog. The 1700 rpm rated speed is the most common reference point for injection molding machine builders, with 1500 rpm variants available for slower-torque applications and 2000 rpm variants for higher-speed applications. The torque constant (Nm/A) sits in the 2.75–3.37 range, which is the engineering signature of the ABT motor's magnetic circuit design.

For buyers sourcing a motor for a specific IMM application, the matching decision between motor torque and screw diameter is the first cut. As a rule of thumb from the engineering team: an injection molding machine with a screw diameter under 50 mm typically pairs with an ABT motor in the 45–84 Nm range (ABT1004–ABT1007); a 50–80 mm screw typically pairs with 84–247 Nm (ABT1007–ABT1320); a 80–120 mm screw typically pairs with 247–540 Nm (ABT1320–ABT1350); a 120 mm and above screw typically pairs with 540–1020 Nm (ABT1350 and above). The torque constant band of the catalog is consistent across the size range, which means the motor's current-to-torque scaling is predictable regardless of which ABT model is selected.

Motor Test Laboratory Methodology

The motor test laboratory page documents the testing infrastructure that backs the ABT motor's published specifications. For buyers evaluating Servo Motor torque ripple for a precision application, the test methodology matters as much as the published number. A motor rated at 2.8% ripple by one test method and 3.2% by another is the same motor with different reporting conventions, and the right method depends on which application the buyer is targeting.

Three test methods buyers should ask about

The engineering team at VICKS Servo uses three test methods for characterizing torque ripple, and the choice of method depends on the buyer's application requirements. Each method is appropriate for a different use case, and a motor supplier that quotes ripple without specifying the method has not given the buyer enough information to make a sourcing decision.

• Locked-rotor torque measurement: the motor is held at zero speed with a commanded current, and the torque output is measured at multiple angular positions. This method captures the cogging component of ripple, which is the dominant contribution at low speed. The locked-rotor method is the right one for buyers evaluating low-speed applications such as injection holding pressure.
• Constant-speed torque measurement: the motor is run at a constant commanded speed against a load machine, and the torque output is measured over multiple revolutions. This method captures the combined cogging and EMF harmonics at the operating speed. The constant-speed method is the right one for buyers evaluating mid-speed applications such as plasticizing.
• Dynamic torque measurement during cycle: the motor is run through a representative cycle profile (acceleration, hold, deceleration, dwell), and the torque output is measured at the cycle frequency. This method captures the dynamic response of the motor to the cycle load. The dynamic method is the right one for buyers evaluating full-cycle performance such as injection molding cycle time.

The motor test laboratory documentation covers the instrumentation for all three methods. Buyers who specify the ABT low-ripple servo motor for a precision application should request the test report for the specific model and method that matches the application.

Application Mapping: Injection Molding, CNC, Die Casting

The ABT motor range supports three primary application classes identified by Jacqueline Shu's engineering team at VICKS Servo. The application class determines which motor parameter takes priority in the selection process, and the same motor can serve multiple applications with different parameter trade-offs.

Injection molding machines (IMM)

For an injection molding machine, the ABT motor typically drives one of three axes: the plasticizing screw (low-speed, high-torque continuous duty), the injection plunger (high-speed, short-duration peak torque), or the ejector / platen (medium-speed, intermittent duty). The plasticizing axis is the most demanding for torque ripple, because the screw rotation directly drives polymer melt shear. The ABT motor's permanent-magnet synchronous design produces the smooth torque profile that the plasticizing axis requires.

CNC machine tools

For a CNC machine tool, the ABT motor typically drives the spindle or a feed axis. The spindle application requires high-speed operation (typically 3000+ rpm, above the ABT range's 2000 rpm ceiling for some applications) and low torque ripple at the spindle bearing interface. The feed axis requires smooth torque at low speeds for high-precision contouring. The ABT motor range covers the lower-power CNC feed axis applications.

Die-casting machines

For a die-casting machine, the ABT motor typically drives the injection plunger (high-torque, fast-cycle) or the die-clamp mechanism (high-torque, sustained-hold during solidification). The injection plunger application stresses torque ripple the same way an injection molding machine does — the melt stream into the die cavity is sensitive to flow-rate variation. The die-clamp application stresses sustained-torque hold, where the ABT motor's thermal capacity at rated torque matters more than ripple.

Selection Framework: 5 Specs Buyers Verify on Servo Motors for IMM

For a buyer placing an IMM motor order, the five specifications below are the engineering checklist that produces a defensible motor selection. Each specification ties directly to the ABT motor's published data sheet and to the test laboratory methodology discussed in section 3.

1. Rated torque at the operating speed. Verify that the rated torque at the screw's typical operating speed (typically 100–300 rpm for plasticizing) is sufficient for the melt shear rate required by the part's wall thickness and cycle time. The ABT parameter table lists rated torque at 1500, 1700, and 2000 rpm — interpolation to the operating speed is straightforward.
2. RMS current at the cycle load. Verify that the motor's continuous current rating is greater than the cycle's RMS current. The ABT rated current at each speed is the ceiling; the cycle's RMS current should sit at roughly 70–80% of the rated value for typical thermal margin.
3. Torque ripple specification at the operating method. Verify that the published ripple number references the test method relevant to the application. For IMM plasticizing, the locked-rotor or constant-speed method is the right one. The engineering team at VICKS Servo provides test reports against the three methods on request.
4. Encoder resolution and feedback type. Verify that the encoder resolution is appropriate for the positioning accuracy required. For precision IMM, 23-bit absolute encoders are the typical choice; for less demanding applications, 17-bit incremental encoders are sufficient.
5. IP rating and ambient temperature envelope. Verify that the IP rating and ambient temperature envelope match the IMM's installation environment. For typical factory floor installation, IP65 and 0–40 °C are the baseline; for washdown or outdoor installation, higher IP ratings are required.

Following this five-spec checklist, the engineering team at VICKS Servo can size an ABT motor against any IMM application in a single call. The output is a recommended motor model, a recommended Servo Drive model, and a recommended cable-and-connector set.

Maintenance and Screw Longevity: How Motor Smoothness Protects the Screw

The connection between Servo Motortorque ripple and screw life is mechanical, not electrical. Every motor torque ripple produces a corresponding screw torque fluctuation, which produces a corresponding screw bearing load fluctuation. The cumulative effect on screw bearing life is what makes motor smoothness a screw-protection lever, not just a melt-homogeneity lever.

How torque ripple becomes screw bearing wear

The screw bearing system is sized for continuous torque at the rated load. A torque ripple that produces ±1.5 Nm oscillation around a 100 Nm average load produces ±1.5% bearing-load variation at every revolution. Over thousands of cycles, the bearing accumulates impact loads at the same frequency as the torque ripple — which for a PMSM motor is typically at twice the electrical frequency (the dominant cogging harmonic).

The cumulative effect on bearing life is captured in the modified bearing-life equation that accounts for variable load. The typical result, for a motor at the ABT ripple specification operating at a typical IMM cycle, is that the bearing life is shortened by a small but measurable fraction compared to a motor at a lower ripple specification. For high-precision IMM running precision optical or medical parts, the bearing-life extension is a measurable contributor to the motor selection economics.

Maintenance intervals for the ABT motor in IMM service

The ABT motor's documented maintenance intervals for IMM service are:

• Encoder bearing: inspect annually, replace at typical 5-year service interval. The encoder is the most maintenance-sensitive component; the ABT motor's encoder is rated for the operating temperature and vibration envelope of IMM service.
• Main bearing: inspect annually for grease condition and bearing noise. The main bearing is rated for the load envelope documented in the ABT parameter table; deviation from the rated envelope produces accelerated wear.
• Resolver / encoder alignment: verify annually as part of the encoder-bearing inspection. The ABT motor's alignment is factory-set; field adjustment is not recommended.
• Cooling fan (air-cooled variants): inspect semi-annually for dust and bearing condition. The air-cooled ABT variants depend on the cooling fan for rated-torque operation; a degraded fan reduces the continuous-torque envelope.

The motor test laboratory provides the diagnostic instrumentation for the inspection tasks above. For buyers operating multiple ABT motors in a fleet, the engineering team at VICKS Servo provides a fleet-wide predictive-maintenance schedule that coordinates encoder-bearing, main-bearing, and cooling-fan inspections.

For broader regulatory and standards context, the relevant frameworks are IEC 60034 (Rotating electrical machines) for motor performance and testing, the NEMA MG 1 (Motors and Generators) standard for North American motor performance ratings, and the UL 1004 (Rotating Electrical Machines)safety standard. For buyers specifying Servo Motors for safety-critical applications, theIEEE 841 standard for severe-duty industrial motors applies. The European standards portal hosts the harmonized European motor standards that apply to CE-marked IMM equipment. For buyers operating in the automotive supply chain, ISO 9001 is the quality management baseline for the motor supplier.

Frequently Asked Questions: Servo Motor Torque Ripple and Melt Quality