This is how a 3D printed piece of furniture is made from a biopolymer filled with wood fibres

How was the inertia of the screw extruder adjusted using the example of the demonstrator so that material discharging could be handled more accurately?
Lukas Belzer: The inertia of mass discharge is affected by several factors. First of all, the material specific design of extruder components, especially the screw, barrel and mold waiting room, plays an important role. Moreover, our extruders have high response dynamics due to the combination of highly dynamic servo motors and gears with low transmission ratio. Finally, our route planning software takes into account any remaining idle and can compensate for this by specifically controlling the extruder motor.

The screw extruder is directed by a robot with an articulated arm. Can you use a standard bot for this or should it be designed accordingly?
Belzer: For the system presented at the K 2022 trade fair, we decided to use a TX2 series articulated arm robot from Stäubli International. This robot combines long range, high movement dynamics and precise positioning. In addition to assembling the screw extruder, which is very light at about 10kg, the load capacity of 25kg also enables other peripheral devices, such as temperature controllers, to be attached in the bonding area, greatly improving layer adhesion.
The excellent cooperation with Stäubli enabled us to get deeply involved in the control of the system. This made it possible to seamlessly integrate the bot into the overall system, which in turn could be manipulated via traditional G-code.

What is the diameter of the hole at the exit of the extruder and is it necessary to adapt it to the component or material?
Belzer: The diameter of the nozzle used to make the stool is 3 mm. With this nozzle, strand widths from 3 mm to about 6 mm can be achieved. The nozzle can be changed in minutes, for example to a smaller diameter nozzle to produce detailed components, or to a larger diameter nozzle to maximize material extraction. Bandwidth ranges from 0.25mm to 6mm. Depending on the proportion and size of the processed fibers, larger nozzle diameters should be selected to avoid nozzle blockage.

To what degree is the build platform heated to process bioplastics?
Belzer: The build platform temperature of 65 °C proved sufficient to cure the used bioplastic. In combination with the structured surface of the build platform, it was possible to ensure good adhesion of the component during the manufacturing process.

Since the component occupies only a small part of the area, the heat is radiated into the installation space. How much is it heated and does this increase in temperature contribute to the quality of the ingredient?
Belzer: In addition to the sustainability of the processed materials, the responsible use of other resources, such as energy consumption during operation, was also important to us during the development of the system. For this reason, the building platform consists of eight individually controllable zones. When manufacturing smaller components, only the required areas of the build platform can be heated in a targeted manner. For the processing of technical plastics, an increase in the temperature of the installation space can be beneficial. When the entire construction platform is heated to 65°C, the construction area temperature of about 31°C is reached after a few minutes. The installation space temperature is currently limited to 40°C due to the robot’s operating conditions specified by the manufacturer.

Stool example: The base is made of two lignin-degradable plastics. One of them is very full of fir fibers. How high is the fiber content in the material and what is the proportion in the main body resulting from this?
Belzer: The Arboform LV4 material used has a fill level of up to 50% by weight. The mixing ratio between filled and unfilled material was usually 1:1 during the production of the core body, which means that the core body had a fill level of 25% by weight of fir fiber. However, the stools were also made without the addition of unfilled materials. These contain the full fiber content of Arboform LV4.

They state that the stiffness of Arboform LV4 is equivalent to that of fiberglass filler. How high should the bioplastic be filled with fiberglass to achieve the same stiffness?
Belzer: The hardness of Arboform LV4 is 6200 MPa. This corresponds, for example, to the stiffness of polyamide 6 with a fiberglass filling of between 15% and 20%.

Last but not least: what is the weight and dimensions of the stool and what is the printing time?
Belzer: Chair seat size is 360mm x 360mm with total height of furniture pieces 460mm. The finished bench weighs 3.07 kg and can currently be made in 120 minutes. By optimizing component cooling, production time can be further reduced in the future.