Hi everyone! Here are the GBX R&D updates from the past month:
Part Cooling Testing
After the initial promising results for part cooling last month, the design was further optimized and tested this month. Computational fluid dynamics (CFD) simulations were conducted on the air flow from the part cooling fan in relation to the extruder nozzle. Ideally, the airflow would be directed right below the nozzle where the printed part is located, and not directed toward the nozzle, which may cause issues with fluctuating nozzle temperatures or difficulty in heating to temperature.
CFD simulations were conducted with Simscale. Air velocity was calculated from a 40mm fan’s air output of 7.56 cubic feet per minute (CFM), and directed perpendicular to the fan. A CFD simulation was conducted on part revision 7 of the part cooling design, which is the design with which all previous part cooling testing was performed.
A CFD simulation of part cooling airflow for part revision 7 of the back extruder barrel cover.
The results show that the airflow was not directed anywhere near the nozzle, and would therefore not be cooling the printed part near where freshly extruded material would be deposited onto the printed part. Interestingly, the results from last month’s bridging testing showed that this part cooling design still provided a significant part cooling effect.
After multiple design iterations and simulations, part revision 9 was developed to address the issues in revision 7. Characteristics of revision 9’s design include:
- Split airflow pathways to direct airflow from two opposite sides of the extruder to reduce asymmetric part cooling effects on the printed part from having airflow from one direction
- Airflow outlet geometry optimized to direct airflow to right below the nozzle
- Geometry designed to minimize internal support structures when 3D printing this part. The only internal support structures are located at the air vent outlets and can be removed without necessitating dissolvable support.
A CFD simulation of part cooling airflow for part revision 9 of the back extruder barrel cover. The simulation is publicly hosted on Simscale here.
Revision 9 was installed on an in-house GBX, and bridging tests were repeated with the new design. The new revision increased the maximum bridging distance for a 1.75mm nozzle to 25mm, up from 12mm (no part cooling) and 16mm (part cooling with revision 7). Plotting against the corresponding infill percentages shows a decrease in minimum rectilinear infill percent of 6%, down from 12% (no part cooling) and 9% (part cooling with revision 7). For minimum full honeycomb infill percent, the new revision 9 achieved 16%, down from 30% (no part cooling) and 24% (part cooling with revision 7). Since revisions 7 and 9 both used the same 40mm fan, these improvements can be attributed to the direction of airflow.
Bridging improved enough that a new bridging test model was developed to test bridging distances up to 35mm. Bridging tests with a 0.8mm nozzle were printed and still need to be measured and compared against data from the previous part cooling design.
Graphs showing the sagging distance of the bridging line in relation to bridging distance, rectilinear infill percentage, and full honeycomb infill percentage for Ultrafuse rPET printed with a 1.75mm nozzle.
Single perimeter cones were also printed with a 1.75mm nozzle for no part cooling (left), part cooling with revision 7 (middle), and part cooling with revision 9 (right). The results show reduced heat build up for lower layer times for the revision 9 design.
GBX Firmware Bug Fix
In an effort to standardize the testing and release of firmware, Gigabot X 4.2.4 firmware updates are currently frozen for testing until October 16th 2021, which means they won’t accept any updates except for bug fixes. This past month, a bug was identified in the Viki screen where the extruder numbers changed from 0/1/2 to 1/2/3 during heat up. The corresponding bitmap was updated in the firmware to consistently label the extruders as 0/1/2. The change was logged in this Github commit.
A firmware version is officially released once it has undergone four months of testing on in-house machines, at which time it will be linked on the firmware section of the Knowledge Base. However, the most recent, unstable GBX firmware in testing is always available for download from Github-- just beware of potential bugs from new development.