There are four main types of instability at high speeds: insufficient/fluctuating hydraulic energy, unstable control of injection valves, mechanical friction/clearance changes, and sudden changes in process and load.
1、 Hydraulic energy system (most common)
1. Insufficient or fluctuating accumulator pressure/nitrogen pressure
High speed relies on instantaneous large flow of energy storage devices; Low nitrogen pressure, aging of airbags, and leakage can lead to high-speed pressure drop and fluctuating speed.
2. Unstable oil supply and insufficient flow of hydraulic pump
Pump wear, internal leakage, insufficient oil suction, high oil temperature → system pressure fluctuations, inability to go up or drift at high speeds.
3. Oil temperature too high/too low
High oil temperature → thinning of oil, increased leakage, and poor rigidity; Low oil temperature → high viscosity, high resistance, slow response; All of them lead to poor high-speed repeatability.
4. Oil contamination and clogged filter element
Impurity stuck valve, clogged throttle hole, unstable damping → speed jump, intermittent fast and slow.
2、 Injection control and valve group
1. Wear, internal leakage, and jamming of high-speed proportional valves/plug-in valves
Valve core wear, poor sealing, impurities → unstable opening, flow pulsation, high-speed drift.
2. Second speed switching point/unstable signal
Wear, looseness, and signal jumping of encoder/displacement sensor; Switching positions too early/too late → High speed startup shock, large speed fluctuations.
3. Leakage and aging of seals inside the injection cylinder
Damaged piston seal → Internal leakage of high-pressure oil → High speed weakness, speed decreases with stroke, poor repeatability.
3、 Mechanical and Moving Parts
1. Punch/barrel wear and excessive clearance
Punch pull, barrel scratch, uneven clearance → fluctuating frictional resistance, speed fluctuation, high-speed drop.
2. Poor coaxiality of the injection rod and wear of the guide sleeve
Rod bending, loose guide sleeve → motion jamming, sudden change in resistance, unstable speed.
3. Poor or excessive lubrication of the punch
Insufficient lubrication → dry friction, high resistance; Excessive adhesion to aluminum and unstable resistance; All of them affect high-speed stability.
4、 Process and load factors
1. Temperature/mass fluctuation of molten metal
Low material temperature → high viscosity and resistance; High material temperature → low viscosity and resistance; Slag/oxidation → uneven resistance → high-speed speed changes accordingly.
2. Changes in mold temperature/cavity resistance
Low mold temperature → high filling resistance; High mold temperature → low resistance; Mold sticking and burrs in the cavity → sudden change in resistance → high-speed instability.
3. Changes in sprue/runner
Gate wear, aluminum adhesion, blockage → changes in filling resistance, high-speed fluctuations.
Quick investigation sequence (directly used on site)
1. Check the curve: whether the pressure/speed in the high-speed section drops or fluctuates → prioritize checking the nitrogen pressure in the accumulator and valve leakage.
2. Check hydraulic pressure: oil temperature, oil level, filter element, pump pressure, accumulator pressure/nitrogen pressure.
3. Check the valve group: whether the high-speed proportional valve and the second speed valve are overheating, making abnormal noises, or leaking; Calibrate valve parameters.
4. Check the machinery: wear, clearance, and strain of the punch/barrel; Coaxiality of injection rod and guide sleeve; Punch lubrication.
5. Check the process: material temperature, mold temperature, gate status, and aluminum liquid quality.
Summary in one sentence: High speed instability, 70% is hydraulic (accumulator/valve/oil temperature), 20% is mechanical (punch/barrel/coaxiality), and 10% is process load.
