High-speed 3D printing

In recent months the concept of high-speed FFF 3D printing has become very popular thanks to the launch of the Hyper FFF kit for Raise3D's Pro3 series and, subsequently, the high-speed printing capabilities of some new models such as the Bambulab X1, the Ankermake M5 or the recently introduced Prusa MK4 and Creality K1.

These new printers promise print speeds up to five times faster without affecting part quality, but how much is reality and how much is marketing?

First of all, it is necessary to understand the limitations and problems that occur during high-speed printing.

Limitations of high-speed 3D printing

The concept of high-speed FFF 3D printing generally refers to desktop 3D printers. This is because these printers, due to their cost and compact construction, are more susceptible to vibrations due to movement and their heads, which are more compact than those of industrial equipment, are not prepared to extrude high volumetric flow rates. This is why the maximum speed that an FFF 3D printer can accept depends on three factors:

• The loss of precision and quality caused by the vibrations of the structure.
• The maximum volumetric flow rate that the printhead is capable of extruding.
• The thermal behaviour of the printing material.

Image 1: Industrial FFF 3D printer (left) and desktop FFF 3D printer (right). Source: Raise3D.

Vibrations and their effect on print quality

As spindle speeds and accelerations increase, so do the inertias transmitted to the structure and hence the vibrations. At low speeds, printer structures have sufficient capacity to absorb and damp vibrations, however, as speed and acceleration values increase, the risk of a resonance phenomenon increases. Once the structure enters into resonance, it will start to vibrate at a specific frequency characteristic of each printer.

This vibration is transmitted to the spindle during movement, with two consequences:

• Loss of positioning accuracy.
• The appearance of a wave pattern on the surface of the part.

Depending on the stiffness of the structure, the frequency and amplitude of vibration varies. More stable structures will have higher resonance frequencies and lower amplitudes, resulting in less loss of accuracy and a less visible effect on the surface of the part.

Image 2: Pattern marked on the surface of a part due to resonance. Source: simplify3D.com

The most common way of dealing with this problem on desktop FFF 3D printers was based on developing mechanically more stable structures, until Klipper, a free firmware alternative to Marlin, implemented a resonance compensation method based on the "Input Shaping" vibration control method. This software-based method means that, once the vibration frequency is known, a sequence of pulses is sent to the motors that cause the spindle to vibrate in an inverse pattern to the resonance, thus cancelling out the spindle vibrations during movement. This is similar to the approach used, for example, in noise-cancelling headphones or optical stabilisers.

Video 1: Example of vibration compensation using the input shaping method. Source: ACS Motion Control.

Extrusion volume flow rate limitations

Another important limitation in high-speed printing is the maximum capacity of a die to melt and extrude plastic. This concept, known as maximum volumetric speed, is a parameter specific to each hotend and varies according to the material used. The maximum volumetric speed is related to three variables:

• Nozzle diameter
• The layer height
• Maximum printing speed

According to the following ratio:

Therefore, for a given printer, the maximum printing speed is also limited by the maximum volumetric speed characteristic of its extruder according to the following ratio:

The most common maximum volumetric speed of a desktop printer when printing ABS is around 10 mm³/s, which implies that the theoretical maximum speed at which ABS could be successfully printed using the standard configuration based on a layer height of 0.2 mm and a nozzle of 0.4 mm would be only 125 mm/s. If we also use another common configuration such as a 0.6 mm nozzle and a 0.3 mm layer height, the maximum print speed would drop to 55 mm/s. Using higher speeds would imply a high risk of missing extrusion and delamination of layers.

Image 3: Volcano hotend, with a larger melting area compared to conventional hotends. Source: e3d-online.com

In order to increase the maximum volumetric speed, new hotend and nozzle designs have been developed. For example, E3D's Volcano hotends can increase the maximum volumetric speed by around 70%, while Bondtech's CHT nozzles can increase the maximum volumetric speed by 30% without the need to modify the hotend.

Video 2: Bondtech CHT nozzle vs. conventional V6 nozzle. Source: Bondtech.

Material properties

The last important point in high-speed printing is the material used. As discussed in the previous section, the maximum volumetric speed depends not only on the design of the hotend, but also on the material used. On a desktop printer, the maximum volumetric speed is achieved using PLA (around 15 mm³/s), while other materials such as ABS, ASA or PETg are limited to a maximum speed of 10 mm³/s. There are also some materials such as TPU or TPE, where exceeding volumetric speeds of 3-5 mm³/s can be difficult.

This is why the development of specific plastics for high-speed printing, in combination with new hotend designs, is essential to take full advantage of high-speed FFF 3D printing.

Image 4: Ordinary carbon fibre reinforced filament (left) versus Raise3D's Hypercore technology filament. Source: Raise3D.

High-speed implementations in commercial printers

As mentioned at the beginning, the interest in implementing high-speed FFF 3D printing systems on desktop printers originated with the popularisation of the free Klipper firmware, however, due to the nature of this project, it was only available within the maker environment. The first manufacturer to develop a professional high-speed system on its printers has been the renowned company Raise3D with the introduction of the Hyper FFF Kit for the Pro3 series.

Video 3: Comparison of Raise Pro3 with Hyper FFF vs. standard Raise Pro3. Source: Raise3D.

The Hyper FFF system is the first to offer a comprehensive approach that addresses all three of the above-mentioned constraints together:

Resonance compensation: The Hyper FFF firmware for the Pro3 series implements an input shaping resonance compensation system similar to the one used in Klipper. For the determination of the resonance frequencies in X and Y, the Hyper FFF kit includes a calibration head equipped with a high-precision accelerometer. This, combined with a highly stable structure optimised over the years since the N2 series, guarantees precise resonance compensation at any speed.

Maximum volumetric speed: The Raise3D Hyper FFF kit includes two new redesigned hotends to increase the maximum volumetric speed by up to 200% over the original hotend.

Materials adapted to high-speed printing: Raise3D has developed, in conjunction with the FFF kit, a new series of Hyperspeed filaments, which allow the maximum volumetric speed to be increased by up to 50% compared to standard materials. In addition, the new line of Hyper Core composite materials guarantees maximum mechanical properties in high-speed printing.

Image 5: Hyper FFF kit for Raise3D Pro3. Source: Raise3D.

This global approach allows real printing speeds 3 to 5 times faster than those of a standard desktop printer, without affecting either the aesthetic quality of the parts or their mechanical behaviour.

After Raise3D, several manufacturers have implemented high-speed FFF 3D printing systems in one way or another. Recently Prusa introduced the new Prusa MK4, which includes a high-speed printing system. This system, based on an implementation of the Klipper module in Marlin. This, together with the new hotend that provides a larger fusing area compared to the original V6, allows to increase the printing speed between 150 % and 200 %. Regarding the determination of resonance frequencies, the printer includes generic values determined by the manufacturer in the firmware. This, although it can be effective, is the least accurate method of calibration. According to the manufacturer, the MK4 includes a dedicated port for an accelerometer, although there is no confirmation as to whether this can be used for actual calibration in the future.

Image 6: Prusa MK4. Source: Prusa3d.com.

At the same time, some well-known Chinese manufacturers such as Creality, Ankermake or Bambulab have presented models aimed at the professional sector that include high-speed FFF 3D printing. These are printers that directly implement customised versions of Klipper. It is precisely these manufacturers that advertise higher speeds, offering maximum volumetric speeds of up to 32 mm³/s and printing speeds of up to 600 mm/s. Although the implementation of Klipper and the incorporation of new hotends guarantee higher printing speeds, the values given are not realistic and are merely a marketing strategy. First of all, well-known high-flow systems such as the E3D Volcano system are capable of delivering maximum volumetric speeds of 20 mm³/s with PLA under standard conditions (0.4 mm nozzle and 0.2 mm layer height). Only some special configurations such as the E3D Supervolcano hotends can guarantee similar values to those advertised. On the other hand, even if these printers could guarantee maximum volumetric speeds of 32 mm³/s, the maximum printing speed under standard conditions would be limited to 400 mm/s, according to the formula relating printing speed and maximum volumetric speed. This limit is far from the advertised values of 600 mm/s.

Image 7: Banner advertising a high-speed printer. Source: Creality.com.

Conclusion

High-speed FFF 3D printing is a revolution that promises to minimise one of the main handicaps of printing by increasing the productivity of this technology. However, it is a complex process that requires a comprehensive approach beyond resonance compensation. It also requires the development of hotends capable of guaranteeing high volumetric speeds together with new material formulations, in order to achieve high speeds without affecting the finishes and final properties of the part. This is especially critical in technical materials such as composites where, to date, only the Raise3D system includes technical materials optimised for high speed.

Regarding the maximum speeds that can be obtained today, the most realistic values in those printers with resonance compensation and optimised hotends are around 150 - 200 mm/s. These values are in line with those advertised for the Prusa Mk4, but far from the values advertised by other brands. In the case of using specific materials for high speed the increase could reach up to 250-300 mm/s. This does not mean that it is not possible to reach higher speeds without seeing the appearance of ghosting or ringing on the part, but the final properties and mechanical behaviour of the part will be compromised due to the appearance of defects or low adhesion between layers.