Small Batch Prototyping for 3D Printed Parts

3D printing enables rapid prototyping but lacks production-ready qualities such as smooth surfaces, temperature resistance and food safety. These attributes however can easily be added by combining 3D printing with casting silicone and urethane plastic for small batch production runs.

As long as you don’t need hundret thounsands of parts, this method should get you up and running without paying a fortune for a silicone injection molding setup.

When selecting mold making materials for 3D printed parts, it is important to be clear about the intended material for mold and cast .

Some points to consider are:

  • Silicone such as Dragon Skin can be extremely difficult to stick to surfaces, except silicone itself. 
  • Urethane plastic such as Smooth Cast 310  is exotherm. This means it gets hot while it’s hardening.
  • Some 3D printing filaments are more temperature-sensitive than others.
  • Some 3D printing filaments are easier to post-process than others.

Having this in mind, the proper materials can be chosen basing on the desired material of the positive.

For PLA the following works nicely:

Final Positive Mold Seperate Seal Release
Urethane Plastic Silicone Monster Clay XTC-3D Ease Release 200 
Silicone Urethane Plastic Sculptex oil based clay  XTC-3D Universal Mold Release

Please note that urethane plastic is exotherm:

  • This requires a non-wax based clay to define the two-part mold. Otherwise the surface in contact with the clay will be full of air bubbles due to the melting wax-based clay.
  • Hot glue is not a good choice for the mold as the glue melts again and the mold leaks. Better use glue + Acryl or Wood + Screws (+ glue)

Applying multiple coats of XTC-3D with sanding (400…1500) in between is highly recommended.

Degasing the silicone and urethane before pouring significantly reduces trapped air bubbles and increases the chance of success.

Other useful items:

 

Amount Description Link
1 Medicine Cups to mix XTC-3D Amazon
1 Gloves Amazon
1 Mixing Cups for silicone and urethane plastic Amazon
1 Craft Sticks Amazon
1 Safety Glasses Amazon
1 Vacuum Chamber for degasing Amazon
1 Vacuum Pump for degasing Amazon
1 Clay Sculpting Tools Amazon
1 Hot Glue Gun Amazon
1 Durometer Amazon

Raspberry Pi Zero W Enclosure

The 3D model of the Raspberry Pi Zero W is hosted on Thingiverse. This page contains the bill of material, in case you want to build a similar setup.

This setup in combination with a regular 3B has been used for demonstrating “Real-Time” FFT of ADXL345 data via MQTT with Node-Red. The code and documentation can be found on Github.

Bill of Material

AmountDescriptionLink
1 Raspberry PI Zero W Amazon
1 Memory Card Amazon
1 Power supply Amazon
1 HDMI Adapter (optional but highly recommended) Amazon

Long Flight Time (1h), Aerial Photography Quad, 770mm 17inch

RC Groups

Centerboard

The center board has been glued with HK CA glue (HC-50-175). A small frame with screws through the four beam holder holes kept the sandwich layers aligned.
Note: Better do large areas with this glue outside as it generates a fume.
Using nylon spacers and screws, the top and bottom sandwich were assembled.

Beams

The beams were machined with a 1/32″ flat end mill and cut to length in the last run.
M3 nylon screws lock the beams and act as breaking point when crashing.

Electronics

To attach the electronics to the center board, I chose two different approaches. Components which will not be used in every flight have been attached using Velcro. The other components were glued directly to capton tape I put to the center board. The ESCs were wrapped in capton tape to prevent short circuits. I hope the heat dissipation is reasonably low with the 30A ESCs.

Sandwich Glue

  • HK CA glue (HC-50-175)
  • Loctite Vinyl, Fabric & Plastic Flexible Adhesive
  • HK 30min Slow Cure Epoxy
  • 3M General Purpose 45 Spray Adhesive

Sandwich Bend Test

  • 100x10mm x 1mm CFK, 3mm Fill, 1mm CFK

CFK 1mm, 3k plain weave carbon, orientation parallel (0°/90°) to centerline
Fill +/-45°

Bend test showed best adhesion and no separation up to 6kg for HK CA glue (HC-50-175). All other separated well below this (usually at around 3-4kg). However glueing is tricky for large areas such as the center board.

Endurance

During the first flights, the flight time was reasonably high at a bit over one hour with 1555 props.

Crashing

Arms folded away during the first crash (I’d love to call it unplanned rapid decent though :-)) and the M3 nylon screws broke as planned, preventing damages to the rest of the drone.

Flight Time

With this setup, flight times above one hour have been achieved, even including the 180g 3-axis gimbal and GoPro.

In the diagram below various test flights for a 15″ 5.5 and 17″ 6.0 propeller were aggregated to show the effect the prop choice has on flight time.

Update: I’ve updated the battery with a 6600mAh 6S and the quad flies a lot more stable now.

Previously the flight recorder showed motors occasionally maxing out during sharp moves or wind gusts.

I’ll do some test flights and check the flight time. First flight was 2500mAh for 15min

Bill of Material

Amount Description Link
6
rctimer 5010 360kv
NA
3
Multistar Lipo Pack XT90
Amazon
4
Flyduino KISS
Amazon
4
1760 Folding Props
Ebay
1
Flight Controller and Power Module
Hobbyking
1
GPS witd Compass
Amazon
1
Receiver
Amazon
1
Damping Balls
NA
1
Folding GPS Antenna Base/Black
Ebay
1
Lipo Voltage Checker
Amazon
1
FPV Camera
Amazon
1
VTX
Amazon
1
Telemetry Radio
Amazon
1
Skyfpv Video Switch
NA
1
OSD
Amazon
2
LC Filter
Amazon
1
FPV 3 Axis CNC Metal Brushless Gimbal With Controller For DJI Phantom GoPro 3 4
Banggood
1
GOPRO
Amazon
1
pigtail
Amazon
1
Silicone Wire
Amazon
1
FPV Antenna
Amazon
1
Transmitter
Amazon
1
Goggles
Amazon
2
Goggle Battery
Amazon