Better Grip: Part Two

A project log for Autonomous RC car

My attempt at robot Folkrace

Martin PålssonMartin Pålsson 07/22/2017 at 08:130 Comments

Printed all parts, including cast, in CPE. Did a first test with the singular mold and it worked. Printed a quad mold to get all tires done at once.

I used Xencast PX30 1kg kit

How to mold in polyurethane:

You need:

  1. Make a CAD model of your detail, complete with mold. Let the CAD program calculate the volume of your detail. 
  2. 3d-print necessary parts and mold. Sand the mold for a smooth finish. Clean everything. 
  3. Calculate how much resin + hardener you need. This is usually done by dividing the volume of the detail by the density of the resin. In the case of Xencast PX30 the resin + hardener should be mixed 50/50 by weight. Also, keep in mind that the real world is not a perfect place, put in a little bit excess resin and hardener for good measure.
  4. Optional: Apply Release Agent to the mold.
  5. Put your mixing cup on a scale and tare the weight. Pour as much resin as you need.
  6. Optional: If you don't want dull yellow-brown PU, this is a perfect time to add pigment to the resin! Mix them thoroughly.
  7. Add hardener to the mix.
  8. Mix the components thoroughly.
  9. Pour.
  10. Demould (pre-curing): Let the pour sit for approx 24 hours in 25 centigrade temperature. During this time the resin is merely beginning to take the shape of the mold. Do not rush the curing at this point.
  11. Curing: You can either let the pour sit for one week at 25 centigrades, or you can rush it in an oven.
  12. Rushing the cure: Let the pour sit in an oven at 80 centigrades for 2 hours.
  13. When the detail is cured it is safe to release it from the mould.
  14. Take note on what you can do better next time you mold, and share it with me =)

My quad mold with the lid behind it. The easiest way to spot the tires are the marks from the evacuation holes.