COMPLETE PROCESSING PAGE OF INJECTION MOLDING MACHNE - 2

           Screw retraction before dosing (%)             

 * The speed of screw retraction before refill can be set here.  

Screw retraction after dosing (%)             

If  

* This speed setting determines the speed of screw retraction after refill (suck back speed). 

         Screw retraction after dosing (mm)             

* The end position of the screw after retraction is set here. 

Dosing stop (mm)                

 * The end position of the screw after dosing. This determines the shot weight of the screw after dosing. Dosing volume is a function of stroke in mm.

        Screw retraction before dosing (mm)             

 *The end position of the screw retraction before dosing is set here.

 Melt Cushion              

 * The position of the screw immediately after the completion of holding stage is displayed on the screen as melt cushion. 

 * Ensure that the melt cushion doesn't drop to zero as this may restrict the pressure transmitted during hold on stage. 

Switch over based on screw stroke  

* The position of the screw at which the injection phases ends and the hold on phase starts.  

 * Switchover stroke is usually set to occur after 95 - 99% of filling is over.  

* When the switchover is stroke based, ensure that the switchover time is set to a value slightly higher than the actual time taken by the screw to cross the switchover point. 

Switch over based on injection time  

 * If the switchover is set to occur in time based option, the injection phase ends and the holding phase starts after the set time is elapsed.  

 * When the switchover by time is selected, ensure that the switchover stroke is set to a value which can be reached within the set time. 

 Switch over based on injection pressure  

 * If the switchover is set to occur by monitoring pressure, the injection phase ends and the holding phase starts when the set pressure is achieved during injection. 

* When the switchover by pressure is selected, ensure that the switchover stroke & time is set to a value which can be reached before the pressure is reached. 

* Another setting called hold on release time is required to set to avoid the initial peak of injection pressure to be considered for switch over. This time has to be set to a value 0f around 1/3 of the total injection time.  

Stepped Dosing 

 * The screw rotation and back pressure can be programmed in 2 stages with one stroke dependent trigger point. 

 * Step 1 - Screw rotates with 28% speed and 6 bar back pressure until the screw position reaches 55.0 mm mark. 

* Step 2 - Screw rotates with 20% speed and 8 bar back pressure until the screw position reaches 83 mm mark.

 *The screw then retracts at 6% speed to 85 mm as per the suck back setting. 

 Note on switch over point setting 

 * Switch over from injection to hold on pressure can be triggered by either injection stroke or injection time or injection pressure. 

* The monitoring of the types of switch over point can be through  

Stroke  : For switch over by time. 

 Time  : For switch over by stroke.

  Pressure : For switch over by pressure 

 * It is important to select the monitoring parameter that is suitable for the type of switch over chosen, otherwise the monitored values may not read more than the trigger set point. 

* If a monitoring point is crossed, an appropriate error message is set and the machine will continue in its cycle until it reaches the base position

. 

Closed loop control of injection speed 

 Closed loop injection ensures that set injection speed is maintained, irrespective of fluctuations in processing conditions. The position cum velocity sensor senses the actual injection speed. The controller compares the actual and set value and takes corrective action if there is a deviation from the set point. 

CASE 1: If the actual velocity is LESS than the set velocity the controller will look for the actual pressure. If actual pressure is less than set pressure, the flow is increased to maintain the set velocity. 

CASE 2: If the actual velocity is MORE than the set velocity, the flow is decreased to maintain the set velocity. 

CASE 3: If the actual velocity is less than set velocity and if actual pressure attains the set pressure, the set pressure is increased by10 bar in two steps of 5 bar each. Even after the pressure correction, if the actual velocity has not yet attained the set velocity, the controller will maintain the last corrected flow & pressure till end of injection.  

During closed loop correction if actual pressure attains the set pressure controller will indicate a soft alarm  “INJECTION PRESURE OVER RUN”. It is an indication that the set injection pressure is too low; due to this pressure correction is taking place to maintain set velocity. This alarm does not stop the cycle, to avoid this   alarm appearing, set the pressure little higher than actual pressure, so that velocity correction takes place only based on flow. 

The velocity correction does not take place, 

 1. During Hold-on Phase.

 2. When actual injection time is above the set injection time.  

3. When the actual injection pressure attains the set Switch over Pressure, only when this PG is selected. 

 When the Switch Over based on Pressure is fitted on the machine, monitoring of pressure gets the overriding priority over other options such as Switch Over based on Stroke or Time, even when the PG 

Switch Over based on Pressure is not selected. When this  PG is not selected, set this pressure lower than actual injection pressure, so that the alarm ” No Holding Pressure Via, Time, Stroke or Pressure” does not set. 

Sufficient interlocks are provided for the velocity corrections, if the various number of Stepped Injection is used.