Specific Process Knowledge/Back-end processing/Polymer Injection Molder/Demolding: Difference between revisions

Latest revision as of 12:18, 7 August 2020

Demolding

Demolding is the process of opening the mold and thereby pulling the sample off the shim. Many of the previously mentioned parameters will influence the demolding process. Generally, the higher the mold temperature, the faster injection speed, the higher switchover/after pressure and the larger the structured area, the more difficult it can be to demold the sample. If the shim thickness is not optimal, polymer may also get in between the shim and the holding plate, making demolding almost impossible. A very critical parameter in easy demolding is designing the structures in a way, that makes them easier to demold (side walls of deep structures should not be completely vertical but have appropriate slip angles to aid in release and roughness of side walls can also severely impact the release properties).

The demolding settings are found on the 'Mold open' screen:

Parameters for opening the mold is found on the 'Mold Open' screen.

Opening profile: A constant speed can be set using the '=' button or the arrows. Alternatively individual points of the graph can be edited. If samples tend to break during demolding it might help lowering the opening speed. In general the speed should be low towards the end position (fully open position) to avoid violently slamming the mold against the end stop.

Mold stroke position: This value defines how far the mold opens. It should generally be avoided to open the mold all the way to the end position, since this causes the mold to bang violently into the end stop. If this happens (you hear a bang every time the mold reaches the open position) decrease the mold stroke position by a few millimeter (e.g. change the stroke from 235 mm to 232 mm). Remember that changing the opening stroke will also change sample take-off position, so remember to adjust the take off position (under robot settings) accordingly.

Sequence settings: These settings change how the robot is allowed to move around the mold. These settings should generally not be changed (be very careful if you do) to avoid crashing the robot into the mold.

@@ Line 1: / Line 1: @@
 == Demolding ==
-Demolding is the process of opening the mold and thereby pulling the sample off the shim. Many of the previously mentioned parameter will influence the demolding process. Generally, the higher mold temperature, faster injection speed and higher injection/after pressure, the more difficult it will be to demold the sample.
+Demolding is the process of opening the mold and thereby pulling the sample off the shim. Many of the previously mentioned parameters will influence the demolding process. Generally, the higher the mold temperature, the faster injection speed, the higher switchover/after pressure and the larger the structured area, the more difficult it can be to demold the sample. If the shim thickness is not optimal, polymer may also get in between the shim and the holding plate, making demolding almost impossible. A very critical parameter in easy demolding is designing the structures in a way, that makes them easier to demold (side walls of deep structures should not be completely vertical but have appropriate slip angles to aid in release and roughness of side walls can also severely impact the release properties).
-The dosing/plasticizing settings are found on the 'Plasticizing' screen:
+The demolding settings are found on the 'Mold open' screen:
 [[File:06-demold.png|600px|thumb|left|Parameters for opening the mold is found on the 'Mold Open' screen.]]
+<br><br>
-*'''Dosing speed''': Dosing speed is adjusted by pressing the left (green) ''''='''' sign and entering a value. Alternatively the up/down arrow can be used or the points of the green graph may be edited directly. It is recommended not to increase the speed above ~0,34 m/s. For sensitive polymers it may be necessary to lower the speed.
+*'''Opening profile''': A constant speed can be set using the '=' button or the arrows. Alternatively individual points of the graph can be edited. If samples tend to break during demolding it might help lowering the opening speed. In general the speed should be low towards the end position (fully open position) to avoid violently slamming the mold against the end stop.
-*'''Back pressure''': The back pressure is adjusted by pressing the right (red) ''''='''' sign and entering a value, using the arrows or editing the red curve points directly. During dosing the only thing that moves the screw backwards is polymer entering the cylinder and thus pushing the screw backwards. A back pressure is used to "press against" this motion. The higher the back pressure the harder 'kneading' of the polymer. Again, some sensitive polymers might require reduced back pressures to avoid thermal damage (decomposition) of the polymer. It is usually sufficient to keep the back pressure at 120 bars or below, but in some cases (e.g. when using pigments) a higher back pressure can give better mixing of pigment and polymer. But be aware of the risks involved regarding decomposition of the polymer.
+<br>
-*'''Shot volume''': This is the setpoint for the amount of polymer that is loaded into the heating cylinder. Note that this number is '''in no way''' linked to the amount of polymer injected into the mold cavity. This is defined on the "Switchover" screen mentioned earlier.
+*'''Mold stroke position''': This value defines how far the mold opens. It should generally be avoided to open the mold all the way to the end position, since this causes the mold to bang violently into the end stop. If this happens (you hear a bang every time the mold reaches the open position) decrease the mold stroke position by a few millimeter (e.g. change the stroke from 235 mm to 232 mm). Remember that changing the opening stroke will also change sample take-off position, so remember to adjust the take off position (under robot settings) accordingly.
-*'''Plasticizing time monitoring''': It is recommended to always keep this enabled (it '''must''' remain enabled if leaving the machine unattended) to make sure the machine stops in case of errors. Usually the maximum plasticizing time is set around 4-8 times the actual plasticizing time (which can be seen in the light blue field just above the setpoint). In this particular screenshot it shows 0,00 sec because no samples has been produced yet after the machine was started.
+<br>
-*'''Decompression''': To avoid problems with stress in the polymer melt it can be a good idea to enable decompression. A setpoint of 1 cm<sup>3</sup> works well for most cases. This means that after plasticizing the screw moves a little further backwards to provide space for the polymer melt to relax. This is particularly beneficial when running at high back pressure.
+*'''Sequence settings''': These settings change how the robot is allowed to move around the mold. These settings should generally not be changed (be very careful if you do) to avoid crashing the robot into the mold.