3D Printing FDM Multi-material adhesion experiment

Background

Most multi-material prints I've seen on Thingiverse or Printables involve using multiple colors of the same material for cosmetic effects - printing characters, making art, etc. 

While this is interesting, being able to print multiple types of filament in the same 3D print also enables using different materials for mechanical design reasons. Examples include adding a soft touch surface to a rigid mechanical part or flexible hinges to a rigid part. 

For this to work, the different materials must adhere together during printing. If there is no bonding during printing, mechanical interlocks could also be used. 

I'm planning on designing and making a part which good adhesion during printing is desired, so I conducted a quick experiment to test adhesion between various materials.

Method

I designed a small block- 25mm x 25mm with two solid bodies. Test block available on thingiverse here

I had 4 material combinations I wanted to test:

• PLA to TPU
• PETG to TPU
• Nylon to TPU
• PC to TPU

For this experiment, for all experiment trials conducted, the experiment material was the base, printed directly on the build plate, and the TPU was the top material. 

Equipment

• Prusa Research MK3S+ with MMU3
• Prusa Research smooth PEI build plate

Prusa Slicer really didn't like using TPU as a material option to print with the MMU, so you need to manually select this material profile in the filament tab.

PLA / TPU test block

All Test blocks

Results Table

Base Material	Top Material	Adhesion
PLA eSUN PLA+, Blue	TPU ANYCUBIC A11795 TPU, red	Very Good
PETG Prusament, Orange	TPU ANYCUBIC A11795 TPU, red	Good
Nylon https://www.lay3rs.nl/ Nylon, Black	TPU ANYCUBIC A11795 TPU, red	Very Poor
PC Blend Prusament PC Blend, Black	TPU ANYCUBIC A11795 TPU, red	Poor

Conclusions

This TPU appears to adhere well to both PLA and PETG. Qualitatively, PLA may be slightly better, but both seemed firmly adhered with this test piece.