Hi everyone! Here are the GBX R&D updates from the past month:
Material Testing: Techmer PM Electrafil ABS with 20% Carbon Fiber
This past month Techmer PM’s Electrafil ABS 1501 3DP pellets were tested on Gigabot X. The Electrafil ABS 1501 3DP pellets are filled with 20% carbon fiber, and they are formulated for use for large, high-strength models. This is because not only does the carbon fiber add strength, it also adds rigidity during printing, which prevents warping and shrinkage issues that are common issues for larger prints.
Previous testing with Electrafil PC, also filled with carbon fiber, resulted in inconsistent extrusion with a 0.8mm nozzle since the carbon fibers clogged the nozzle. Increasing the nozzle size to 1.75mm prevented any nozzle clogging issues. Therefore, the Electrafil ABS was printed with a 2.85mm nozzle to test how the carbon-fiber filled material behaved at an even larger nozzle size.
Some major takeaways from the testing:
- Bed temperature: 60C
- Extruder temperatures: 245C / 235C / 185C
- Bed adhesive: PVA Glue
- The printer hardware had no issues extruding the material at high extrusion rates. However, print speed was limited by issues with print quality and heat build up that occurred at higher speed.
- Proper drying has a significant impact on print quality and print surface quality
- Oozing and issues at the beginning of lines were present in prints without continuous line printing, otherwise known as vase mode. Occasionally a piece of material stuck up from the print, cooled, and collided with the nozzle during subsequent layers, resulting in a layer shift.
24:1 Compression Screw Extruder
The current GBX extruder can extrude up to about 0.8kg/hr of Ultrafuse rPET pellets. The limiting factor is the motor’s ability to provide enough torque to rotate the extruder screw, and higher extrusion rates cause motor skipping. To address larger-scale applications for pellet printing, a new extruder design was developed to operate at a higher extrusion rate. The new extruder has a longer compression screw with a 24:1 compression ratio. The motor was also upgraded to a larger one (Model 86HS98-5004Z). The extruder is currently installed on an in-house GBX and is undergoing testing.
Updated Hopper Gantry Parts
The  Hopper Gantry Endtruck and  Hopper Gantry Trolley [Printed] printed parts were updated to incorporate a couple design changes:
- A small shelf to align the rail rollers to the printed parts during assembly
- Additional holes for heat set inserts on the faces that interface with bellows. The heat set inserts can be used to fasten the bellows to the parts using screws, which is more secure than the current velcro and adhesive.
Part Cooling Design
One of the subtasks of re:3D’s NSF Phase II grant is to develop a part cooling solution for GBX. Previously, the design was being worked on by Michigan Tech University, but since the beginning of June, the project was handed back to re:3D to further the development started by MTU. Since then, the  GBX Extruder Barrel Cover Back was modified to take a 40mm fan that directed air below the nozzle.
After installing the updated part cooling design on an in-house Gigabot X, the fan wires were plugged into the Azteeg X3 board and powered through pin 17, which is set in the Marlin firmware. The part cooling fan and its speed is controlled in Simplify3D.
So far, the part cooling design passes basic testing, including fit on the machine and control through both Simplify3D and gcode commands. More rigorous testing on the effect of part cooling on printed parts is still needed. MTU’s previous work on the solution included design testing procedures to quantify part cooling effectiveness through test prints that test bridging, heat build up, and overall print quality.
Updating Customer GBXs With New Hardware
As R&D updates continue to be made to Gigabot X, re:3D has kept in contact with beta users and updated beta GBX units to incorporate essential hardware changes. One example is the hopper gantry, whose development arose from material feeding issues from the previous static hopper feeding system when used in combination with XL, XLT, and larger build volumes. The feeding issues resulted in frequent failures for prints with print times longer than several hours, since material would get stuck in the feed system and stop flowing into the extruder. The hopper gantry fixed this issue by allowing the hopper to move in the X and Y direction and follow the extruder during a print, effectively shortening the length of the feed tube and eliminating any slack or bends where material can accumulate and stop flowing.
Once the hopper gantry design was mostly finalized, hopper gantries were sent to Gigabot X customers in France, Korea, and Tennessee. The instructions for upgrading a GBX from the old static hopper hood frame to the new hopper gantry system can be found on re:3D’s website here.
The second hardware upgrade sent out to beta users was the Gigabot X pellet extruder. The pellet extruder has undergone multiple improvements, many of which enable more consistent extrusion and higher extrusion rates, both of which significantly impact the capability and print quality of the Gigabot X. As of July 2021, the updated pellet extruder includes the following changes:
- Updated extruder body with a larger inlet hole: the larger inlet hole allows more consistent flow of material into the pellet extruder
- Updated feed throat: The newer revisions of the feed throat interface with the larger inlet hole in the extruder body, as well as provide a smoother transition for material flow from the feed tube to the extruder.
- Larger motor with higher torque: this increases the maximum extrusion rate
- Extruder cover: The extruder cover provides wire management, a safety barrier for hot components, and a fan to cool the extruder motor during machine operation.
- Modular nozzles: The nozzle was updated to a two-component system, enabling it to accept standard M6 threaded nozzles. This makes maintenance much easier and reduces the number of times the nozzle adapter must be removed, preventing leaks.