I. Adjustment of the Temperature Control Parameter for the Hot Runner
Increase Nozzle Temperature: By 3-8°C, increase the set temperature of the hot runner nozzle that corresponds to the slow-filling cavity. This directly accelerates the melt flow rate in the cavity and reduces the local melt viscosity within the upper limit of the material's allowable processing temperature.
Zoned Temperature Gradient Compensation: In the event that the runner branch corresponding to this cavity is lengthy, the zone temperature of the upstream manifold should be increased by 2-5°C simultaneously to mitigate melt flow resistance within the runner and prevent an insufficient heating effect from nozzles alone.
Perform a brief injection to confirm the filling progress after the temperature has stabilised for 2-3 minutes following the adjustment. This prevents the misjudgment of the adjustment effect as a result of insufficient temperature.
II. Modification of the Injection Rate Parameter:
Targeted Enhancement of Segmented Injection Rate: To specifically accelerate the melt propulsion speed in the runner section of the cavity, increase the injection rate of the segment by 10%-20%. This will not affect the filling rhythm of other normal cavities.
To prevent the occurrence of secondary defects, such as flare and scorching, in cavities that are typically filled, it is important to optimise the injection speed exclusively for the filling range that corresponds to lagging cavities. This will prevent an overall speed increase.
III. Modification of the Injection Pressure Parameter
Local Filling Section Pressure Increase: By increasing the injection pressure within this filling range by 10% to 15%, the melt is provided with an additional flow propelling force, which overcomes the flow resistance of the cavity and expedites the filling process.
Ensure Adequate Pressure Reserve: To prevent equipment overburden and excessive melt shear heat degradation caused by excessive pressure, ensure that the overall injection pressure does not exceed 85% of the equipment's rated maximum value.
IV. Adjustment of Timing Control Parameters (Applicable to Needle Valve Hot Runners)
Early Gate Opening: By advancing the opening time of the needle valve gate related to cavities with slow filling by 0.1 to 0.2 seconds, the melt is able to enter the cavity earlier than in other cavities, thereby directly compensating for flow lag.
Fine-tuning the opening timing difference: To prevent the cavity from overtaking other cavities and causing new uneven filling, each adjustment should be controlled within 0.05 seconds. This will gradually reduce the filling time difference.
V. Closed Loop Verification of Adjustment
Perform 1-2 test shots following each parameter adjustment to confirm the advancement of cavity filling through the use of short-shot and weight measurement techniques.
Control the product weight deviation within 1.5% and ensure that the filling length difference between this cavity and other cavities is ≤2% through iterative adjustment. Afterward, establish the final process parameters.
The production scenario of small-batch hot runner multi-cavity moulds is fully compatible with this parameter adjustment scheme. Optimisation can be accomplished in as little as 30 minutes, ensuring that all cavities are filled in a synchronised manner, and the adjustment process will not interfere with the filling state of other cavities.
