I. Pre-fill Confirmation Steps: Execute a brief shot at 70% to 80% of the stroke, accurately marking the numbers of all cavities with slow filling, and verify that no other cavities are simultaneously exhibiting anomalous lag.
Calibrate the actual temperature of the hot runner nozzle for the corresponding cavity using a temperature monitoring instrument. This will affirm that there is no temperature drift causing under-temperature issues, thereby excluding hardware faults.
II. Prioritise Temperature Control Parameter Adjustment: Increase the set temperature of the hot runner orifice that corresponds to the slow-filling cavity by 3°C. Simultaneously elevate the temperature of the upstream manifold section by 2°C if the cavity's runner branch is extended.
Perform a brief shot and compare the length of the cavity's filling after the hot runner temperature has completely stabilised, which should take approximately 2 to 3 minutes.
If the improvement is not substantial, increase the nozzle temperature by an additional 2°C each time, ensuring that the material's allowable processing temperature limit is not exceeded, until the cavity's filling progress is significantly enhanced.
III. Targeted Modification of Injection Speed Parameters
Locate the filling section in the multi-stage injection speed settings of the injection moulding machine, where the melt is on the brink of entering the corresponding cavity runner. Increase the injection speed of that section by 10%.
Perform a brief shot to verify that the cavity's filling length has been further extended and that the cavity, which was previously filled routinely, has not developed any defects, such as flash or burning.
If the target is still not achieved, adjust the injection speed of that section by an additional 5% each time until the filling length of this cavity is within 5% of that of other cavities.
IV. Auxiliary Optimisation of Pressure Parameters
To supplement the flow driving force of the melt and overcome the remaining flow resistance of the cavity, increase the injection pressure corresponding to this filling section by 10%.
Confirm that the filling progress of this cavity is in alignment with that of other cavities and that the overall injection pressure does not exceed 85% of the equipment's rated maximum value by performing a brief shot.
V. Timing Adjustment for Needle Valve Hot Runner Systems
The needle valve gate's opening time for the cavity with delayed filling is advanced by 0.1 seconds, enabling the injection time of this cavity to be earlier than that of other cavities. This directly compensates for flow lag.
Verify the synchronisation of filling by performing a single brief shot. If there is still a deviation, advance the opening time by 0.05 seconds each time until the filling length deviation of all cavities is ≤2%.
VI. Final Verification and Curing
Continuously manufacture 20 moulds, ensuring that the weight deviation of the cavity with delayed filling from the other cavities is no greater than 1.5% by weighing each cavity individually.
Verify that all products are free of any defects, including flash, shrinkage marks, or missing material. To finalise the adjustment, curve all existing process parameters.
The production scenario of small-batch hot runner multi-cavity moulds is ideally suited to this set of steps. The adjustment process will not interfere with the normal filling status of other cavities and can quickly achieve synchronous filling of all cavities.
