CEAD is at the forefront of advancing large format additive manufacturing (LFAM) technologies, with a strong focus on achieving greater accuracy while printing bigger objects. To achieve this, CEAD has developed a diverse range of pellet extruders with varying characteristics, allowing for a tailored LFAM solution that meets specific market needs.

As a result of these innovations, over 100 CEAD technology systems are currently used in facilities worldwide. But CEAD’s efforts to improve LFAM accuracy did not stop with the development of pellet extruders.

In fact, this paved the way for the creation of upgrades that address specific challenges in LFAM. One of the most significant upgrades is Dynamic Flow Control (DFC), which enables printing with greater precision control and higher quality output. Because of this, the DFC enables cleaner start/stops and thus enables travel moves.

In this article, we’ll delve into the benefits of DFC and how it can revolutionize large scale 3D printing in industrial settings. CEAD’s technical explanations are supplemented by examples from the practice, from both a commercial and research point of view.

These insights are provided by Kyle Rowe from US-based Haddy and Dominik Leubecher from the University of the Bundeswehr Munich. Haddy uses CEAD’s Flexbot’s in efficient and circular MicroFactories in the US to 3D print furniture. The renowned University of the Bundeswehr Munich uses a Flexbot for research purposes.

CEAD's DFC for more accurate 3D printing

Enhancing the precision of Large Format Additive Manufacturing

Large format additive manufacturing (LFAM) typically utilizes a pellet-based extrusion system (FGF) to create large scale prints. In this process, thermoplastic pellets are melted in the extruder, which contains a heated barrel and then extruded onto the workpiece through an extruder.

However, the screw within the extruder can pose several challenges that impact the accuracy and consistency of the final product. These inaccuracies are described in the following paragraphs.

1. Inconsistencies in pressure

The pressure inside the extruder may not always be consistent, which can lead to slight variations in the width of the extruded beads. This may create some minor cosmetic flaws, but it usually does not significantly affect the mechanical properties of the final print. This can occur for example when you interrupt the extrusion to make a travel move. This process is also referred to as start/stops.

2. Delay for screw adjustments

Because of the pressure inside the barrel, there may be a minor delay between the time when the screw is adjusted to influence output and the actual increase or decrease in extruded material. This effect is influenced by the length of the screw, the longer the screw, the greater the delay that occurs.

Although large format 3D printing typically uses continues toolpaths, it is possible to add additional starts and stops to the toolpath. However, without any finishing, such as milling, any start and stop points will be slightly visible on the final print due to the pressure on the melted material inside the barrel that forces any residue material out of the nozzle.

CEAD DFC attached to a Flexbot for 3D printing

3. Influence on the bead

When the screw is rotated, its shape forces melted material out of extruder’s nozzle. The more rotations the screw makes per minute (RPM), the higher the extruder’s output will be. However, the exact amount of extruder material is influenced by the position of the screw. The shape of the screw makes that there is a slight variation in extruded material.

These factors can result in slightly uneven bead widths and small variations in material pulses, making it more difficult to measure the mechanical properties of the printed object accurately. CEAD’s engineers were driven by these three inaccuracies described above to develop the Dynamic Flow Control (DFC). The DFC is an innovative upgrade for pellet extruders mounted on the Flexbot system, that addresses these challenges, resulting in higher quality, faster printing, and greater control over the printing process.

“The Dynamic Flow Control plays a critical role in a large-scale material extrusion system and is indispensable for the efficient processing and extrusion of thermoplastics. It enables precise control and maintenance of melt flow as the material moves through the extrusion system. With its help, it is possible to convey the viscous melt flow with high precision and constant speed.”

Dominik Leubecher, the University of Bundeswehr

“We have done a lot of material development in the past on other machines, and I will say by far the easiest machine for that work had the Dynamic Flow Control. In 3D printing, because we get such good consistency, your eye picks anything that is just slightly thinner or thicker. The Dynamic Flow Control helps to achieve that consistency that we are aiming for.”

Kyle Rowe, Haddy
CEAD's DFC for more accurate 3D printing
CEAD's DFC for more accurate 3D printing
CEAD's DFC for more accurate 3D printing

DFC: faster printing, greater control, and higher quality output

CEAD’s engineers designed and produced a solution for the complications listed above: Dynamic Flow Control. The DFC consists of a device on the extruder. This DFC consists of two gears that rotate downwards, moving melted pellets down the barrel.

The Dynamic Flow Control serves as a buffer and as an on/off switch inside the barrel. Usage of the DFC thus results in less accumulated pressure within the barrel. This significantly decreases the delay between adjustments to the RPM and actual output.

Not only causes the use of a DFC a smaller delay, but it also increases the material volume precision. The increased accuracy allows start/stops to be incorporated into a design. Two advantages of this are found in the benefits it provides for the design process. This allows travel moves in the toolpath, as well as printing two separate parts in one design.

The reason why we’re using Dynamic Flow Control is ultimately summed up in repeatability and consistency of the printed bead. You know the exact flow of the material, which is going to determine the width of your bead. And if that’s a consistent flow rate, then you get a consistent bead.”
Kyle Rowe, Haddy
The reason why we’re using Dynamic Flow Control is ultimately summed up in repeatability and consistency of the printed bead. You know the exact flow of the material, which is going to determine the width of your bead. And if that’s a consistent flow rate, then you get a consistent bead.”
Kyle Rowe, Haddy

More advantages of Dynamic Flow Control are elaborated in the following paragraphs.

The advantages of Dynamic Flow Control

The past paragraphs elaborated on the problems that lead to the development of the Dynamic Flow Control. However, the DFC provide more advantages for large scale additive manufacturing:

1. Precise control over the volume of plastic coming out of the nozzle. This increased accuracy leads to more control on the width and height of a bead.

“The DFC ensures more efficient use of the extrusion system by providing a constant and even flow of material. This reduces fluctuations and impurities in the extruded material and improves the overall performance of the system.”

Dominik Leubecher, the University of Bundeswehr

2. Adding start and stops to a 3D print. The DFC makes it possible to accurately incorporate multiple toolpaths in a design.

“The dynamics of additive manufacturing is rarely a process of equilibrium. It is usually in transition. The DFC offers more control when you start and stop for example. You have effectively decreased the length of your extruder when it comes to the kind of stored energy in the polymer. The DFC really helps by providing more control over the consistency in the bead width.” 

Kyle Rowe, Haddy

3. Since an extruder with DFC provides more control and accuracy, it enables producers and researchers to understand a new material faster. This speeds up the incorporation of other materials in the production process.

“It’s not to say that you can’t do well a single screw extruder that doesn’t have the Dynamic Flow Control, you definitely can. We used to print that way for a long time. But when you need to bring the material science more into that equation, the DFC helps to process a larger number of materials really well.”

Kyle Rowe, Haddy

“The use of a melt pump offers numerous advantages. Due to the improved control over the material flow, higher accuracy and reproducibility of the extruded products are achieved. Even complex geometries and filigree structures can be produced effortlessly.”

Dominik Leubecher, the University of Bundeswehr

“And for us it’ is more important to be able to just print a multitude of different materials. If carbon fiber filled ABS is the only thing that you are printing, great. I know that is a perfectly fine on a single screw extruder, we process many materials between filled polymers, different colors, clear polymers, and so I think that for us that is probably the big benefit.”

Kyle Rowe, Haddy
CEAD's DFC for more accurate 3D printing
CEAD's DFC for more accurate 3D printing

Considerations for Dynamic Flow Control

The use of Dynamic Flow Control comes with considerations:

  1. The Dynamic Flow Control is an addon to CEAD’s pellet extruders. Therefore, the investment for an extruder with DFC will always be higher than a standard extruder.
  2. Slicing your 3D model to gcode for an extruder using a DFC requires a different workflow. The slicer you are using has to support this process. The slicers that CEAD works with, such as Siemens NX, AI Build and the CEAD post processor, are all able to slice for extruders equipped with DFC. Our customer support engineers will help you get acquainted with this method.

Dynamic Flow Control for the Flexbot

The Dynamic Flow Controle module provides possibilities for those that want to take additive manufacturing to the next level. It enables the Flexbot to process a wide variety of materials with less effort and provides perfect control over the material flow.

While CEAD’s pellet extruders are integrated into existing robot arms, the DFC is only available as a Flexbot upgrade. It can’t be integrated on stand alone pellet extruders.

Are you looking into upgrading your manufacturing process? Contact our team to learn what the Flexbot can offer your company’s processes.

All in all, the use of a melt pump in a large-scale material extrusion system contributes to improved product quality, higher efficiency and expanded processing capabilities. Precise control of the material flow and process parameters can create sophisticated products.
Dominik Leubecher, the University of Bundeswehr