Medusa Multi Material Printing

Medusa is our solution to many of the problems encountered with existing Multi Material FDM Printers. 

With traditional 2/2 (2 input 2 nozzle) systems (E3D Chimera) to control ooze, the second hotend must be cooled while not in use. This method of ooze control significantly increases print time and doesn’t eliminate ooze entirely resulting in poor overall print quality. For example, with 1 material change per layer, over 400 layers, this cooling / heating process could add hours to the print.   This method of ooze control is commonly used with a very wasteful wipe shield to catch oozing filament.  It seems, with traditional 2/2 systems, printing PLA and PETG – controlling ooze is very difficult. 

Similar to Medusa IDEX 2/2 systems use 2 hotends move independently of each other, parking the out of use hotend away from the print over a “waste bucket” to catch any ooze which falls from the hotend. When the secondary hotend moves into position, the relatively slow process of moving into position can result in ooze falling from the hotend, ultimately ending up on the printed object. As with traditional 2/2 systems, temperature is usually adjusted with each material change to reduce ooze. Again, over a 400 layer print this could increase print by hours, plus the 2-5 seconds (or more) per layer required for the hotend to move into position ready to print.

2/1 systems, use a single nozzle and heater-block with 2 or more input filaments. Compared to 2/2 systems, 2/1 Nozzle systems are easier to use and configure, however the ease of use comes at a massive ongoing material and print time cost. With 2/1 Systems, changing from one material to another requires the purging of waste material each time the material change occurs resulting in solid purge blocks often much larger and heavier than the object being printed. These purge blocks can take 60 seconds per layer to print, adding hours to a relatively small print. For example, a 100x100x100mm print with 10% infill can weigh around 180 grams and take 6 hours to print. If this was a multi material print, with a 2/1 nozzle system, the purge block required for this print could easily weigh 230 grams. That’s roughly 55% of the filament wasted while increasing print time by over 6 hours.

Our Medusa Multi Material System solves these problems. 

Unique to Medusa, by blocking the out of use nozzle, filament is prevented from oozing and creating a mess across the surface of the printed model. The secondary hotend is always at printing temperature – ready to use. Medusa material changes happen in the blink of an eye. As it’s a 2/2 system, no purge block is required, resulting in massive material savings. Put simply, the medusa is a 2/2 printing system without the time penalties incurred by traditional 2/2 or IDEX systems and without the time consuming, wasteful purge block incurred by 2/1 printing systems.

Challenges in designing Medusa

Designing Medusa was no simple task.  To date, this design has been revised and remade around 100 times.

We started with E3D V6 Hotends, but found the slot-mount neck too difficult to mount reliably within the space available.  Regular heat creep blockages occurred and we turned our attention to Slice Engineering Mosquito Magnum.

Originally, the Medusa featured a Pancake stepper motor to actuate the hotend switching.  We found these motors to have insufficient holding torque to reliably move each hotend to position.  Calculating torque, we found that in order to achieve the torque required, a stepper motor would need to be unreasonably large and heavy.  We then turned our attention to Servos.

We tested scores of Servos.  Most of them we too fragile when used in Hot Environments.  Either the electronics inside the servo failed, or the servo motors would overheat.  After destroying countless servos in our testing, eventually we found one specific make and model capable of handling the torture.

Another challenge we countered was the slight variability of the laser cut Hotend mounts and hotend assembly.  We found that from prototype to prototype, these slight variations resulted in failures of the blocker system.  If the blocker was out by just a tiny amount, the nozzles would interfere with the blockers as they rotate or fail to block the nozzles entirely.   We also found that these manufacturing variations would affect the geometry of the system, potentially resulting in hotends which would not reach a completely vertical position when engaged.   To counter this, we made our blockers and vertical position stops slotted and adjustable to accommodate manufacturing inaccuracies with the net effect of allowing customers to use a wider variety of nozzle shapes and sizes.

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