Dual-extrusion printing is an absolute treat and Polyvinyl Alcohol (PVA) as a support structure is truly worth a celebration! You can produce immensely detailed models with a ton of supports and not be concerned about removal. Just immerse your model in water and watch all your post-processing fear dissolve along with the supports. A sweet feeling indeed. And this is not even bringing in the fact that you create a 3D printed model with various colours and multiple different material properties.
Now, 3D printing in this manner does require some forethought. Purge towers and ooze shields are crucial to successful dual-extrusion prints. Both methods are techniques a 3D printer can use to prime the print nozzles for the next layer. On Ultimaker printers (along with many other 3D printers) two nozzles are employed to enable dual-extrusion. One nozzle prints one filament and the other nozzle prints the other filament. They are independent from each other and only one nozzle can be active at a time.
Inside Ultimaker Cura, a 3D printing slicing software, there are methods to prevent this leaked material from impacting the 3D print in a negative way. Stringing or blemishes can be some of the problems encountered. For more information on this check out Improving 3D Printed Models - Ultimaker Cura. The two Ultimaker Cura methods to produce the best models using dual-extrusion will be purge towers and ooze shields. The contents of the guide are seen below.
To re-establish, dual-extrusion printing is the process of 3D printing with multiple filaments in a single print and when it first arrived it ushered in vast new potentials. You could now print composite materials, produce with ease multicoloured components and have drastically advanced support structure options all at your fingertips. For more information check out the tutorial Ultimaker Dual-Extrusion 3D Printing Guide. There is also an Ultimaker Cura Overview Guide which is a great reference point if this is your first time encountering Cura and you want to hit the ground running.
Some of these settings talked about will be hidden settings in Cura. To be able to make them visible in the Print Settings Menu go to |Top Tool Bar > Settings > Configure Setting Visibility| then find the particular setting in the list and click on its Checkbox. As always if you have any questions, queries or things to add to this topic please let us know your thoughts!
Overview on Purge Towers and Ooze Shields
When 3D printing with two separate materials a purge towers or an ooze shield is required to prime the nozzles for the next layer. These techniques are an added complexity and expend filament, but their use guarantees an enhanced overall print quality. Furthermore, using both gives the best opportunity for your 3D prints to succeed. A purge tower and ooze shield have both been used in a 3D print that can be seen in the image below.
Without either a purge tower or an ooze shield, you will end up with stringy hair-like filament covering your desired component and have blemishes on the surface. This happens when the filament being printed is swapped to the other filament. When this happens the 3D printer will perform a retraction on the no longer used filament. Retraction is when the filament is wound backwards away from the extruding head. This is done to reduce the pressure inside the nozzle so that filament does not continue to come out of the nozzle tip. However there is still pressure inside the nozzle, perfection has not been reached in this regard, and it is common for material to continue to leak out of the tip of the nozzle. These leaks end up as stringy filaments on your model. These can cause errors in your print, require post-processing and possibly fail the 3D print entirely. Purge towers and ooze shields are available as an option in Ultimaker Cura and require only a couple of user-inputted parameters to give the best result.
Purge towers, also referred to as prime towers, are an additional print created on the build plate made to the height of the component desired. It is a hollow cylindrical object with layers of the first material and the other material forming a ring around it. Whenever a nozzle is swapped between the purge tower is built higher. If there is a layer which does not need a nozzle swap the purge tower is the last section to be printed on that layer. To ensure the prime tower is sturdy and capable of holding all the oozed material, the nozzle purges a small volume inside the tower. The tower acts as a waste bin and collects all excessive material. This is also utilised in the printing operation as a method to clean excess material off the nozzles as there is a surface for them to rub against. This cleans the nozzle before continuing the printing process.
Ooze shields are a one-layer wide wall that encases, but does not touch, the final model. This thin wall is made by alternating between both materials, layer by layer. It catches ooze from incoming nozzles before each layer is printed. Thus, the ooze shield is the first section printed for each and every layer. This acts as a barrier against the unwanted leaking material ending up on your final 3D printed model. The effective use of an ooze shield will save lots of post-processing.
Purge Tower Cura Settings
This will be a dive into all the setting Ultimaker Cura offers to adjust and use purge towers. All the settings available and a brief explanation can be seen below.
- Enable Prime Tower. Click the checkbox to enable the use of a prime tower.
- Prime Tower Size. This decides the width, in the X/Y direction, of the cylindrical prime tower. A larger footprint creates a more stable prime tower.
- Prime Tower Minimum Volume. This decides the volume of the prime tower. The volume must be enough for the nozzle to prime properly.
- Prime Tower Flow. The overall flow of the prime tower. This is set to 100% by default.
- Prime Tower Brim. Click the checkbox to create a brim base to the prime tower. Using this will improve stability.
- Prime Tower X/Y Position. The position of the prime tower as seen from the origin point in Ultimaker Cura. A good location is near the switching bay to reduce printing time.
Now, the prime tower will be made to the same size as your model. If your model is tall the prime tower also will be tall. In this scenario, it is liable to be toppled over by the print nozzle as it is wiping itself. Also, certain materials when cooled are inclined to curl upwards. This, if not accounted for correctly in the software, will cause the print nozzle to hurtle into the top edge of the purge tower and batter it down. Once the purge tower has fallen stringing and other negative effects on the model will occur. Furthermore, there is the possibility that the print can be held-up or failed as the purge tower can roll into the model being printed.
So the recommendations to get the best out of your prime tower have to do with increasing its stability. Start by increasing the Prime Tower Size from the default 20mm to 35mm. Next, always ensure the Prime Tower Brim setting is activated. All the stability and grip of the tower to the build platform comes from these two settings. Increasing these values will give dramatically more grip to the build platform for the prime tower.
Ooze Shield Cura Settings
This will be a dive into all the setting Ultimaker Cura offers to adjust and use purge towers. All the settings available and a brief explanation can be seen below.
- Enable Ooze Shield. Click the checkbox to enable the use of an ooze shield.
- Ooze Shield Angle. The maximum angle of the ooze shield can have. This is to prevent the shield from collapsing. A smaller angle will lead to more material being required.
- Ooze Shield Distance. The distance between the ooze shield and the model in the X/Y plane. This is used to prevent the ooze shield from merging undesirably with the model.
The ooze shield is a separately printed one-layer wide wall, which catches ooze from incoming nozzles before each layer is printed. An Ooze Shield Distance distance of 2mm away from the model and an Ooze Shield Angle of 60° will work well for most materials and 3D printing scenarios. Recently for models I want extra-crisp I increase the Ooze Shield Distance to 6mm.
If sure you curious as to what was being printed all will be revealed soon! Keep cosy.
