Troubleshooting Methods for Stuttering or Jerky Slow-Speed Movements in Injection Molding Machines
Stutters and jitters occur when the equipment opens and closes the mold, ejects, and injects glue at low speed, which can easily cause scratches on the product and bumps on the mold. At the same time, the molding cycle will be lengthened. A hierarchical investigation from the perspective of oil circuit hydraulics, servo electronic control, mechanical structure, and parameter settings can alleviate low-speed operation abnormalities.
I. Inspection of the hydraulic circuit system (frequently occurring issue in servo models)
Hydraulic Oil and Filter Element Inspection
Deterioration of the hydraulic fluid, water ingress, contamination with impurities, or clogging of the suction/return filters can lead to intermittent oil flow and unstable oil pressure at low speeds, causing vibration. Change the hydraulic fluid regularly, clean or replace the complete set of filter elements, and remove accumulated sediment from the bottom of the oil tank.
Fuel system leaks and air intake issues
Slight leakage at hydraulic fittings and cylinder seals allows air to enter the lines, causing cavitation and resulting in noticeable hesitation during low-speed operation. Inspect all fittings and cylinders for oil leaks, tighten any loose lines, and bleed trapped air from the hydraulic system.
Wear of servo pumps and flow valves
Wear on the internal distribution plate of the servo pump and sticking of the solenoid valve spool cause intermittent flow output during low-speed operation. If the operating pressure curve shows excessive fluctuation, disassemble and inspect the valve components, and replace any parts showing severe wear.
II. Troubleshooting Servo Drive and Sensor Signals
Displacement sensor malfunction
Jitter occurs due to wear, loose mounting, or poor electrical contact in the mold-opening/closing and injection linear transducers, leading to intermittent position feedback signals and repeated servo output corrections. Secure the transducer mounting bracket, clean the sensing contacts, and promptly replace any damaged wiring or worn-out transducers.
Pressure sensor offset
Issues include sensor zero-point drift, distorted pressure feedback at low speeds, and stuttering caused by frequent motor speed adjustments. Calibrate the pressure sensor according to the standard procedures outlined in the equipment manual.
Abnormal heat dissipation in the servo drive
Dust accumulation in the electrical control cabinet and cooling fan failure caused the drive to overheat, triggering output limitations and resulting in unstable torque during low-speed operation. Clean the dust from the cabinet, service the cooling fan, and ensure proper ventilation and heat dissipation.
III. Inspection of the mechanical transmission structure
Insufficient lubrication or scoring of the tie bars
The four tie bars lack lubrication and exhibit surface scoring and scratches; sliding friction fluctuates at low speeds, causing vibration during mold opening and closing. Clean the tie bars to remove contaminants, apply specialized grease evenly, and polish the scored areas to restore the surface.
Wear and binding of guide sleeves and slide blocks
Uneven clearance due to wear on mold guide pillars and machine slide sleeves causes fluctuations in resistance during low-speed movement. Apply lubricant regularly and replace severely worn guide sleeves as needed.
Abnormalities in the mold adjustment mechanism or drive bearing clearance
Excessive clearance in the mold adjustment nut or wear on the plasticizing shaft bearings causes jerking and abnormal noise under low-speed load; disassemble the unit to adjust the clearance or replace the bearings.
IV. Optimization and Adjustment of Molding Process Parameters
Adaptation of gain parameters for the low-speed range
If the low-speed gain of the servo system is set too high, even slight variations in resistance can cause frequent, jerky oscillations; conversely, if the gain is too low, movement becomes sluggish and prone to sticking. Refer to the equipment manufacturer's parameter guidelines and slightly reduce the gain for the low-speed range.
Increase the low-speed buffer zone
Extend the cushioning stroke during the low-speed phases of mold opening/closing and ejection to avoid abrupt speed switching; lower the acceleration and deceleration rates in these low-speed phases to minimize vibration caused by sudden fluctuations in hydraulic pressure.
Match appropriate low-speed pressure
If the pressure setting for low-speed operation is too low, the system lacks the force to overcome mechanical resistance, making it prone to sticking or stuttering; the base pressure for low-speed operation should be increased slightly, while ensuring it does not become high enough to cause impact shocks.
V. Troubleshooting Additional Mold Resistance
Insufficient lubrication on mold guide pillars, binding of the ejector plate, or excessively tight fits for slides can increase operational loads, leading to jitter during low-speed movement. Regularly maintain sliding mold components and adjust the clearances for ejector pins and slides to reduce mechanical friction.
Provided that the oil lines are clean, sensor signals are normal, mechanical lubrication is adequate, and parameters are properly matched, issues such as stuttering and vibration during low-speed operation can be alleviated, resulting in smoother equipment performance.
