Table of Contents
Design OverviewCurrently, there are a few major design considerations:
First is an auger screw, which will drive plastic pellets from a hopper through a heated barrel and nozzle. Should the auger screw fail, custom extrusion screw designs will be substituted.
Second is using a heated gear pump to melt and extrude plastic. Gear pumps are known for having consistent, continuous flow.
Third is to combine the first two into a complete system. The reason for this would be if the screw is giving inconsistent flow and the pump has insufficient power to drive molten plastic. Combining the two will solve both of those issues
As of the complete design review, the pump options have been discarded.
The print head was modeled and simulated using COMSOL Multiphysics. This is a preliminary analysis of a simplified version of the printer head components, and only includes the metals directly involved with heating. Temperatures are in Celsius.
Results show 35 pounds of force is needed to drive plastic through the screw, which will produce a torque selection for the motor. It is worth noting that the pressure is extremely high, which will lead to some reconsideration in design.
Drawings, Schematics, Flow Charts, Simulations
This particular screw design uses a length to diameter ratio of 20:1, and a compression ratio of 2:1, which is within the extrusion specifications for ULTEM 1000 thermoplastic. Because the length is constrained to 3D printer dimensions, the diameter and flight dimensions are extremely small.
Based on the previous design, this screw uses a L/D ratio of 16:1, to allow for more material on the rest of the features.
Cross Sectional view of the assembly. Colors are for clarity. In blue is the auger screw, yellow is a steel barrel, copper is a nozzle adaptor, bronze is the nozzle, and the red is the heat/insulation component. Drawings for parts are available below.
- Assembly Drawing
- Auger Barrel Drawing
- Auger Drawing
- Mounting Bracket Drawing
- Nozzle Adaptor Drawing
- Steel Barrel Drawing
Bill of Material (BOM)
The Bill of Materials will be continuously updated as more detailed information about part selection is made available through analysis.