Specific Process Knowledge/Back-end processing/Polymer Injection Molder/Process

Process overview

Once a process is running satisfactory, the machine also has tool that can be used for monitoring a running process. These tools can be help to ensure desired sample quality and reproducibility. Press the second button from the top on the right column of buttons to get to the 'Cycle time analysis' screen:

The 'Cycle time analysis' screen provides an overview of the entire injection molding cycle.

• Mold Close to Part removal: In the left part of the screen the individual phases of the injection molding cycle is listed. Just to the right of these names there's a small box. If it's gray it means this step i current not active. If it's red it means this step is currently active (so in this example the sample is currently being ejected by the ejector pins and the sample is removed by the robot).

• Progress bars: A little further to the right (in the center of the screen), progress bars will indicate position and timing of each individual step in the cycle (both last cycle and current cycle). Note that the 'Part removal' step of Variotherm processes often takes quite a long time. This is because the 'Mold pause time' delay (mentioned in section '9. Ejection') used for reheating the mold is included in this step.

• Last and Current columns: In these columns it's possible to see how long time each phase takes in the currently active cycle. For comparison the corresponding time during the last cycle is also shown.

• Total time: In the bottom of the screen a progress bar will indicate progress for the currently running (yellow) and previous cycles (green). Please note that the time axis of the progress bars do not autoscale. Min and max time scale values must be entered manually (but since the total cycle time for both the current and last cycle is shown right above, it's very easy to enter a sensible value).

The injection molding machine also has tools for monitoring process parameters during and immediately after the injection phase. To ensure reproducible results it can be beneficial to monitor parameters that are tightly linked to sample quality/properties. This can be done using the 'Micrograph' tool:

The Micrograph tool can be used for monitoring process parameters during injection.

• Force build-up time: This setting defines how long time the machine has to build up the nozzle contact force. A value of 0,2-0,5 sec works fine for most applications

• Contact force: This parameter defines how hard the nozzle presses against the inlet port during injection and after/holding pressure. Please do not increase this value above 15 kN without contacting DTU Danchip as this may damage the nozzle tip or the mold inlet port! For polymers that undergo significant shear thinning (such as PP and PE) contact forces around 14 kN can be required (depends on injection speed) while lower contact forces (10 - 12 kN) will be sufficient for most other polymers.

• Delay time retraction: In some cases it may be desirable to maintain the inlet port at high temperature after injection and holdin/after pressure. In this case a delay can be entered here (usually 5 - 10 seconds is fine). Keep in mind that if the sum of 'Plasticizing delay time' described earlier and the 'Delay time retraction' on this page exceeds the cooling time, this will cause a delay in the injection molding cycle (thus increasing the effective cooling time).

There are also other possibilities for documenting and monitoring injection molding processes.