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

Revision as of 16:12, 25 January 2018

Switch-over type

The switch-over type is a very important setting. This setting defines when the injection-phase is done and thus when the machine will continue to the next phase of the injection molding cycle (after pressure / holding pressure). Since this setting defines when we consider injection is done it significantly affect the properties of the produced sample, in particular filling. The switch-over setting are found on the 'Switchover type' screen (which is a sub-icon of the 'Inject' icon):

Volume-dependent switchover: When a certain volume of polymer has been injected, injection is considered complete. Note that the volume entered (3,2 cm3 in this example) is not the volume injected, but the amount of polymer left after injection! This also means that if you change shot volume (the amount of polymer in the heating cylinder before injection) the amount of polymer the machine tries to inject will also change unless the switch-over point is adjusted accordingly. Volume dependent switchover is particularly well suited when you want to develop an injection molding process from scratch (so you can gradually find the point where the cavity is ~95% filled) or if you already know the exact volume of polymer required.
Time-dependent switchover: After a certain amount of time, injection is considered complete. Not used very often because it offers very little control over both injection volume and pressure.
Injection pressure-dependent switchover: Polymer is injected until a certain pressure is reached. Please note that the pressure in question is measured in the injection unit (heating cylinder). The pressure inside cavity is not know. Special molds with an integrated pressure transducer is required to determine the pressure inside the cavity (the most interesting, but unfortunately not available at DTU Danchip). This switchover mode is very easy to use and is not influenced by e.g. changes in shot volume. The selected switchover pressure (in this example 800 bar) is critical for replication. Very low switchover pressures can result in bad replication or even incomplete filling while too high pressure can cause the sample to stick so well to the shim, that it gets very difficult to demold.
External switchover: Injection continues until a signal is received from an external device (e.g. an external pressure transducer). Can not be used, since no external external device is available.
Parallel switchover: Injection is defined by a combination of parameters. Has never been used until now.

@@ Line 5: / Line 5: @@
 [[File:03-switchover.png|600px|thumb|left|On the 'Switchover type' screen it's possible to select between volume, time, pressure, external and parallel switchover]]
 <br>
-*The injection velocity can be adjusted in several ways. One can tap the ''''='''' sign to enter a constant velocity or alternatively use the up/down arrows to move the curve up and down. For more complicated injection speed profiles it is also possible to tap the curve to enter the graphical curve editor where the number and position of individual data points can be edited. This makes it possible to make custom injection speed profiles.
+*'''Volume-dependent switchover''': When a certain volume of polymer has been injected, injection is considered complete. Note that the volume entered (3,2 cm3 in this example) is not the volume injected, but the amount of polymer left after injection! This also means that if you change shot volume (the amount of polymer in the heating cylinder before injection) the amount of polymer the machine tries to inject will also change unless the switch-over point is adjusted accordingly. Volume dependent switchover is particularly well suited when you want to develop an injection molding process from scratch (so you can gradually find the point where the cavity is ~95% filled) or if you already know the exact volume of polymer required.
-*The 'Specific injection pressure limit' is an upper safety limit that can be set to protect the mold and/or shim (e.g. if using shims that are soft and thus prone to deformation). Note that '''this setting does not in any way ''set'' the injection pressure'''. It is only an upper safety limit that will not be exceeded.
+*'''Time-dependent switchover''': After a certain amount of time, injection is considered complete. Not used very often because it offers very little control over both injection volume and pressure.
-*The 'Minimum injection time' is usually set around 0-0,05 sec and 'Max. injection time' around 5-8 times the actual injection time. The actual injection time can be seen in the blueish/gray filed just over the max injection time setpoint (in this case it says 0.00 sec because no sample has been produced yet). Actual injection times are usually around 0,2 to 2 seconds so the 'Max. injection time' can typically be set to 1,0 - 15 seconds.
+*Injection pressure-dependent switchover: Polymer is injected until a certain pressure is reached. Please note that the pressure in question is measured in the injection unit (heating cylinder). The pressure inside cavity is not know. Special molds with an integrated pressure transducer is required to determine the pressure inside the cavity (the most interesting, but unfortunately not available at DTU Danchip). This switchover mode is very easy to use and is not influenced by e.g. changes in shot volume. The selected switchover pressure (in this example 800 bar) is critical for replication. Very low switchover pressures can result in bad replication or even incomplete filling while too high pressure can cause the sample to stick so well to the shim, that it gets very difficult to demold.
+*'''External switchover''': Injection continues until a signal is received from an external device (e.g. an external pressure transducer). Can not be used, since no external external device is available.
+*Parallel switchover: Injection is defined by a combination of parameters. Has never been used until now.