Starting extruder development

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This article is about developing a new extruder for Reprap, with the idea to show general development methods.


"Please make allowances for mistakes/poor grammar/stupidity, unfortunately I do not have time to write this page properly, but thought I must start or I will never have any chance of finishing."


The first thing in any design project is to decide and then record what you want the design to do. What it is REQUIRED to do to be a successfull design. This first step should result in a list of requirements. This list can be adjusted as you go, but if you don't have a clear set of requirements, it's often not clear that you've reached your design goals when you're done.

For the extruder I wrote this:

Building of a polymer melter and extruder, including electrical heating element, extrusion nozzle, thermal insulator and barrier such that mounting points are below 60 degrees celcius when extrusion nozzle is at 300 degrees. Drive mechanism to force solid polymer rod of upto 2mm diameter into extruder heater element with force of 50 newtons or that required to extrude at a rate of 50mm per second. Optional axis positioning drive.


Next important point in developing is do some research and experiments and think about what is going on.

After doing that I revised the requirements to add:

Heat control of polymer carrier with ability to heat between 150 and 350 celcius with a control resolution of 5 degrees celcius. Ability to extrude polymer feedstock of between 1.25 - 3.5mm. Easily changeable extrusion nozzles. Ability to extrude multiple polymer types.



Some rules

  1. 1) Do some research,
  2. 2) Do some basic calculations,
  3. 3) try to understand exactly what you are trying to do,
  4. 4) Ignore anyone elses advice unless it works for you,
  5. 5) Do some experiments,
  6. 6) Ask youself what is wrong with current designs,
  7. 7) Ask for help, but be ready to ignore or discard things that you do not feel work well,
  8. 8) Always think about what is the minimum you need to accomplish the task
  9. 9) ....... I am sure I will think of some more later.



Extruder specific


A polymer extruder is basically a heater (hot end) and a piston.


All heating is 100% efficient if what you want is heat, but what may not be efficient is getting heat where you want it.

The design of the hot end should be about reducing heat loss from the parts that do not contact the polymer and increasing heat transfer to the polymer.


T.B.C.


There are lots more things I wanted to add, but I forget them now and don't have time to think further.


I hope I will comeback and edit this at some time.

Further reading