¶ Layer Separation
“Layer Separation” specifically means poor bonding issues between the 2 layers. We'll discuss the root of this issue and how to avoid this issue.
¶ 1. “Temperature”
Firstly, we'll start from the “temperature” to address the root.
FFF/FDM is a process of depositing fused filament and bonding the layers. In the inter-layer bonding process, when it is depositing a new layer, the nozzle and extruded filament reheat the previous layer, the right amount of heat makes the 2 layers a good bonding. When the heat is not enough, the bonding between 2 layers will be poor (extruded filament has relatively low viscosity, and previous layer cannot be felt a little), and generate voids between 2 layers. Thus, Z-strength decreases, or even worse layer separation happens.
- From figure - 1.1, we can see that the extruded filament deposited and formed the first layer, while its temp got lower down to around 130℃. When it is printing the 2nd layer, the extruded filament of 2nd layer and the nozzle reheat the formed first layer, this melt the first layer a little (viscosity increased), which makes the 2 layers a good bonding. (Figure 1.2 & 1.3)
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- For some engineering materials and high performance materials, it is necessary to maintain a proper chamber temp, this makes the model not collapse (if there's too much heat), as well as the previous layer not lose too much heat for a good bonding with the new layer. (Figure -1.4)
Therefore, good bonding performance depends on the right heat. So, how do we do the adjustment on the heat when we meet layer separation issue?
- The nozzle temp. Increase the nozzle temp to give the extruded filament more heat. It is recommended to increase 5℃ each time to address the right nozzle temp. Figure - 1.5 (Negative effects: if nozzle temp is too high, filament could be blocked in throat, little feature in the model might get collapse, etc.)
- Chamber temp. Increasing the chamber temp to avoid losing heat on previous layer. It is recommended to increase 2℃ for each temp to get the right setting. Figure - 1.6
- Filament cooling fan. Lower the rate of filament cooling fan to keep the extruded filament more heat. (Negative effects: little feature in the model or the layers might get collapse due to too much heat)
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2. Printing Speed & Flow
Similar to the effect of temp on layer separation issue, improper printing speed & flow settings also can lead to layer separation issue. and it happens with X&Y axis as well, not only limit to Z axis.
- Printing Speed - Z axis
When we only increase the printing speed without increasing right flow setting, the width of extruded filament gets smaller. Thus, the contact area between upper and lower layer becomes smaller, this makes the bonding not good enough, which leads to layer separation. Or, if there are no changes applied, but the width of extruded line is narrow, there is a gap between lines (X,Y or Z axis), then it is recommended to lower the printing speed for a try. Figure - 1.8
- Printing Speed - X&Y axis
When the inner wall printing speed is different from the speed of outer wall, the width of extruded lines of inner wall and outer wall will have a little difference (even through the slicing software might compensate and revise the flow based on different printing speed), which might lead to poor bonding between inner and outer wall. Make the printing speed of inner and outer wall the same is recommended to solve this issue. Figure - 1.9
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- Printing Speed & Flow
If printing speed and flow are increased, it is necessary to increase the nozzle temp for a bit to keep each unit of filament get equal amount of heat. Otherwise, layer separation issue might happen.
¶ 3. Z - movement
- Uneven movement of build-plate in Z axis
If the movement of build-plate in Z axis for each layer is uneven, layer separation issue might happen as well. It's necessary to check if the parts related to Z-movement are all tightened, such as Z driving motor assembly, driving belt, build-plate frame, screws, build-plate sheet, etc.
- Layer height
Generally, the thicker layer is easier to cause layer separation issue. The layer thickness should be at least 20% smaller compare with nozzle diameter. For example, if nozzle diameter is 0.4mm, the layer thickness shoud be no bigger than 0.32mm, otherwise good inter-layer bonding performance cannot be guaranteed. The range of proper layer thickness should be 0.1mm to 0.25mm, this gives the model good resolution and inter-layer bonding performance. Set the right layer thickness based on your needs.