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Diagnosing Inconsistent Shot Weights in an All Electric Injection Molding Machine

2025/06/11 By Topstar

All Electric injection molding machine 3-3

Unlike hydraulic machines, where pressure variations and fluid compressibility can cause inconsistencies, all electric injection molding machine utilize servo motors and precision ball screw mechanisms to meter polymers. However, even these energy-efficient injection molding machines can experience shot weight fluctuations due to mechanical, thermal, or control-related factors. So we need to diagnose and eliminate the root causes of shot weight inconsistencies through maintenance practices in terms of mechanical stiffness, servo control parameters, thermal stability, screw/barrel condition, sensors, etc., to maximize the performance and reliability of electric machines.

Mechanical Rigidity and Integrated Injection Seats

To assess whether mechanical clearance is causing shot weight variation, first visually inspect the injection unit for signs of frame bending or mounting bolt displacement. Then use a dial gauge to measure any lateral movement of the barrel or screw assembly when subjected to the nominal injection force. Even sub-millimeter deflection can alter the effective screw stroke, leading to shot size variation. Therefore, it is necessary to confirm the integrity of the injection seat and tighten or readjust the structure as needed to ensure that the mechanical foundation of the energy-efficient injection molding machine remains rock solid, which directly translates into repeatable shot metering. Additionally, Topstar’s all electric injection molding machine features a structurally integrated injection seat with high rigidity and a stable frame. This design minimizes deflection under high injection pressure and maintains perfect alignment between the servo-driven screw and the barrel.

Low-damping injection seat

Discrete intelligent drive for all electric injection molding machine for precise injection control

Discrete intelligent drives provide precise real-time motion control to maintain stable injection weight. They can assign control tasks directly to the servo drives of each axis, enabling local calculation of motion profiles. This architecture eliminates latency in the central controller and significantly reduces communication latency, ensuring that the injection screw follows its programmed trajectory with microsecond accuracy.

To diagnose control-related injection weight changes, check the drive log: Discrete intelligent drives record the torque, position, and speed of each axis at high resolution. Look for deviations in the acceleration and deceleration phases of the screw, as these may alter the metering volume. If differences occur, adjust the drive’s motion parameters, such as impact limits or profile tracking settings, which can fine-tune the transition between acceleration and steady-state speed. Properly configured discrete smart drives respond quickly when melting viscosity changes or backpressure spikes occur and instantly compensate to maintain shot weight accuracy.

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Thermal Stability and Temperature Uniformity

Temperature fluctuations in the barrel or mold can significantly affect polymer viscosity, directly affecting the amount of material delivered by the screw per cycle. On all electric injection molding machines, it is critical to keep the barrel area within ±1°C of the set point. Use infrared thermal imaging or embedded thermocouples to map temperature uniformity along the barrel’s length, particularly around the heating bands and cooling water channels. Identify any cold spots or hot zones due to heater overlap.

Next, verify the performance of the mold temperature controller by ensuring that the mold surface reaches the set point without overshoot and that the coolant flow is balanced across all cavities. When poor thermal management occurs, it often leads to phase change dynamics, which alter the melt density, resulting in slight shot weight drift. Finally, by stabilizing barrel and mold temperatures, you can lock in a consistent polymer viscosity profile, allowing your electric injection molding machine to meter the same shot weight every time.

Screw and Barrel Wear on All Electric Injection Molding Machine

Mechanical wear between the screw threads and the barrel bore is another common cause of inconsistent shot weights. Even doubling the nominal clearance can result in significant meltbackflow during the injection and holding phases. To diagnose this problem, remove the screw from the barrel for inspection: clean any polymer residue, then use a micrometer to measure the thread thickness at multiple axial points and compare the readings to the original design drawing. Similarly, measure the barrel’s ID with a bore micrometer to detect uneven wear or taper. If wear exceeds the wear limit, the barrel should be re-bored or the screw refurbished. Maintaining a tight screw-to-barrel clearance ensures volumetric efficiency, allowing every rotation of the servo motor to translate into a precise increment of molten resin pushed forward, thereby maintaining consistent shot weights on energy-efficient electric platforms.

plastic injection molding machine(1)

Sensor Health and Signal Integrity

Accurate shot-size metering also depends on reliable feedback from position and pressure sensors. On electric injection molding machines, linear encoders track screw positions with micron-level accuracy, while pressure sensors monitor injection and holding pressures in real-time. To diagnose sensor-driven inconsistencies, first, verify encoder performance by disconnecting the feedback loop and manually rotating the screw shaft to confirm that the reading matches the mechanical motion. For pressure sensors, calibrate them against a certified pressure gauge at multiple set points to ensure that they operate linearly over the entire pressure range of the machine. Loose wiring, connector corrosion, or electrical noise can introduce stray readings, causing the controller to misjudge the end of filling and change the injection weight. By confirming the health and signal integrity of the sensor, you can maintain the high-precision operation of the all electric injection molding machine.

Get consistent injection weight.

Inconsistent injection weight involves addressing multiple interrelated factors, including mechanical stiffness, servo control adjustments, thermal management, screw/barrel gaps, and data-driven troubleshooting. We can perform structural inspections, servo adjustments, and temperature uniformity checks to restore and maintain consistency for each injection gradually. At the same time, the high-rigidity integrated injection seat on Topstar’s all-electric injection molding machine also provides a solid mechanical foundation, and discrete intelligent drive and sensor feedback give the required accuracy and reliability.

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