Full Blue Racing Collaboration
Back in Michaelmas of 2022, we were approached by the Cambridge Formula Student team, Full Blue Racing, to see if we could be any help with their build. While they already utilise 3D printing themselves extensively and have their own CR10, they had multiple ideas for their intake manifold that required a more specialist printer, namely our BCN3D Sigmax R19.
The plenum is a component that splits airflow from a single intake into four separate channels, one for each cylinder of the engine. The aims for this part are to minimise the restriction to the airflow, which involves the part being large and streamlined, and hence have a very organic shape, and to be able to withstand all the vibrations of the car without cracking.
FBR were keen on using our Sigmax to print it, as its large size means that the component can be printed as a single part without any joins, increasing it's strength. It can then be wrapped in carbon fibre sheeting to give it a a high level of strength and rigidity.
This part also required the use of threaded inserts to connect the plenum to the throttle body, so smaller test pieces were made to practice inserting them and verify that the dimensions of the slot were correct before progressing on to the final full size print, which ended up taking 36 hours, by far the longest print I have ever set going!
The two photos to the left show the test prints made for the threaded inserts. As can be seen, some practice was required to insert them properly.
The three photos below show the plenum in various stages of printing. Supports were used on the underside, and quite a bit of stringing was observed, especially inside the print. However, this is easy to clean up afterwards. None-the less, the retraction settings need to be optimised for the Sigmax.
Another crucial part of the intake manifold is the injector holders. Four of these mount on the engine and allow the injectors to inject fuel directly into the air stream as it flows into the engine. These components need to withstand the heat of the engine, and so cannot simply be printed using PLA, which would risk melting. Instead, ColorFabb make a filament called HT which has a glass transition temperature of 100˚C, high enough to be mounted to the outside of the engine without issue.
This requires a printing temperature of 260˚C, and a bed temperature of 90˚C, much higher than the typical 200˚ C and 50˚C for PLA, and so needed a printer with an all-metal hot end and enclosure. Our BCN3D Sigmax should be able to fit this bill. Test parts were first done in PLA before altering the settings to print in ColorFabb HT. These parts take approximately 6 hours each to print. Unfortunately, the BCN3D struggled with the HT material, with the nozzle continually clogging due to the slow print speed. This led to the material clumping around the nozzle, and damaging one of the thermistors.
The upper two photos show the injector holders in the process of printing and the lower three photos show the completed injector holders. Note the issue with under-extrusion that appears in the upper half of the last photo. This is believed to be due to a blockage that formed in the nozzle. It is also possible to see the updated design in the right-most photo where the holder is strengthened to reduce the chance of cracking.
We then tried printing this material on Pistachio, one of our Ultimakers. Although this was defintely pushing the Ultimaker to it's limits, it did manage to successfully complete the prints. In total, 14 separate attempts needed to be made before 4 successful injector holders were produced:
PLA initial proof of concept
Two PLA with updated design on Mint Choc Chip
PLA with updated design on Honeycomb
HT on Mint Choc Chip (tolerances too tight so it cracked when the injector was inserted)
HT on Mint Choc Chip (updated tolerances but nozzle blocked half way through so didn’t extrude correctly)
HT on Mint Choc Chip (significant under extrusion)
HT on Pistachio (Layer shift halfway through and nozzle blocked)
HT on Pistachio (Broke lose from build plate)
HT on Pistachio (Put tape down. Still broke lose from build plate)
Four HT on Pistachio (Put lots of tape down and increased brim width) Success