What Is the Flow of 3D Printing and How Do You Adjust It?

While 3D printing, you have to consider multiple parameters to ensure a successful print. A slight mistake in any of the properties will not deliver an accurate result. With trial and error, you can fine-tune your settings and quickly churn out perfect 3D prints, but still, there is one parameter that is not well understood, and hardly any new users know about it.

We are talking about the flow of 3D printing, called the flow rate. Flow rate is often ignored and yet it is the most critical measurement to maximize print speed.

So here are some tips that will give you the power to better control your prints.

The Flow of 3D Printing

The flow of a 3D printer is the volume of filament passing through the extruder.

This value is automatically calculated by the 3D printer and depends on the steps per millimeter (steps/mm) that the extruder stepper motor takes. This also depends on the diameter of the filament and the diameter of the nozzle. All these factors combine to rule the 3D printer flow rate. 

In slicing software, the flow rate is also called an extrusion multiplier. By default, the multiplier is set to 1 or 100%. So, if a user adjusts the multiplier to 1.2 or 120%, the flow rate will increase by 20%. If the multiplier is set to 0.8 or 80%, the flow rate will be reduced by 20%.

High Flow Rate

The advantage of a high flow rate is that it increases the speed of 3D printing. The higher the flow rate, the faster the print. The disadvantages are that a high flow rate also increases the chances of oozing, stringing, under extrusion, extruder skipping, and it can result in nozzle clogging.

Low Flow Rate

A low flow rate is desirable when you have a larger-diameter filament and want to reduce the flow to ensure all intricate details are captured by the print. However, a low flow rate can cause under extrusion as well as gaps in the print.

How to Identify Flow Rate Issues

Flow rate issues always tend to cause two major problems: over extrusion and under extrusion. When these problems occur, it is most likely due to the wrong flow rate. The following are some of the major issues this can cause.

Nozzle Clogging

If your nozzle clogs frequently, you likely have too high of flow rate compared to the mechanical limitations of your printer.

Nozzle clogging is a common problem associated with high flow rates and can be addressed by slightly lowering the flow rate or properly calculating your volumetric flow rate.

Stringing

When the nozzle crosses an empty space, the extruder retracts the filament to stop the material from depositing, but if the flow rate is high the material still oozes, and this causes strings to appear in the print.

Dimensionally Inaccurate Parts

In a bit of a backwards twist, increasing the flow rate too high will result in underextrusion. This happens if you’re trying to push too much filament through the nozzle than your nozzle can melt. This causes increased backpressure and friction, eventually leading to your extruder skipping steps.

In our reviews we originally tested maximum flow rate as the point where the extruder started skipping. However, I found that some (especially Creality ones with cheap extruder gears) won’t skip until the system is underextruding to nearly 60% of the expected extrusion volume.

It’s best to test your maximum flow rate by marking your filament at 60-100mm from the extruder, pushing the same amount of filament through the system, and writing down the distance between your mark and the extruder extrance.

Then, subtract the amount left from the expected amount and divide that by the expected amount of extruded filament and you’ll have the amount of actual extrusion. (For example, if you have 1mm between the mark and the extruder on a 60mm extrusion, you’d calculate (60-1)/(60) or 98.33% extrusion aka 1.67% under extrusion – a perfectly reasonable amount.)

Gaps

If you find gaps in adjacent layers, then it is probable that the issue is caused by a low flow rate. Try adjusting the flow rate and check if the problem persists.

Missing Layers

If you find that the print is missing parts of layers, then not enough material is being extruded. This problem can be resolved by increasing the flow rate.

Holes

Sometimes prints have holes. These are due to a low or intermittent supply of material. This is an indication of a low flow rate, so adjusting to a higher flow rate will help eliminate the problem.

How to Adjust the Flow of 3D Printing

Now that we know what the flow of 3D printing is, how it impacts the prints, and how to solve related issues, this is how to adjust the flow to eliminate flow rate problems.

For demonstration purposes, we will consider Ultimaker Cura, a widely used slicer software, to explain the process.

Check Material Settings

Cura’s default parameters will not show you the flow rate/extrusion multiplier parameter. So the first thing you should always do is check the material settings and the parameters mentioned under it. You’ll be lucky if you find the “flow” parameter there.

Open Additional Settings

If you don’t find the flow parameter, then click on the small gear beside the material settings. This will open up a long list of settings available to be exported into your default list, which is visible on the main user interface. 

Find the Flow Parameter

Find the flow parameter on the list and tick it so it becomes visible. This will instantly show you the addition of this parameter on your screen.

You will also find more flow options that you can export to the default list, but it is not required when you are just getting started with this setting.

Modify the Percentage

The flow parameter can be modified in terms of percentage. The default value is 100%, but depending on the problems you face, you can modify the value to increase or decrease the flow rate. 

Adjust the Diameter of the Filament and Nozzle

As a general rule of thumb, you should always try to find the ideal combination of filament and nozzle diameter. Not all filaments can work with all nozzles. So, by staying within the ideal size range flow rate, issues can be reduced. This will lessen the pain of frequently adjusting the flow rate settings. 

If you are using a 1.75mm filament, then the recommended nozzle size is less than 0.4mm in diameter. Alternatively, if you are using a 3mm filament, then the recommended nozzle size is greater than 0.4mm in diameter. 

This avoids the nozzle getting clogged and thus eliminates the over or under extrusion problems, which are the most important issues concerning flow rate.

One Last Recommendation

After every filament change, the flow rate should be studied and modified if needed. This is because every filament has a different composition, and the density is also not always the same. So, ignoring this small check may cause a lot of issues going forward.

Meet our Guest Author

Christine Evans

“Christine Evans is the Director of Product Marketing & Content Strategy at Fictiv, an on-demand manufacturing company. Over the past six years, Christine has grown Fictiv’s popular Hardware Guide and Digital Manufacturing Resource Center, with over 2,000 teardowns, DFM guides, and mechanical design articles to help democratize access to manufacturing and hardware design knowledge.”