P15551: High Temperature Pellet Based 3D Printer Head
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Detailed Design

Table of Contents

Design Overview

Currently, 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.

Prototyping, Simulation

Simulation of Temperature Distribution

Simulation of Temperature Distribution

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.

Engineering Analysis

Updated Screw Calculations

Updated Screw Calculations

Updated Screw Calculations

Updated Screw Calculations

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

Preliminary Screw Design

Preliminary Screw Design

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.

Updated Screw Design

Updated Screw Design

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 Section View for Assembly

Cross Section View for Assembly

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.

Rendered Cross Section

Rendered Cross Section

Updated Render of Full Assembly

Updated Render of Full Assembly

Drawings

Bill of Material (BOM)

Updated Bill of Materials

Updated Bill of Materials

The Bill of Materials will be continuously updated as more detailed information about part selection is made available through analysis.

Test Plans

Tentative Test Plan

Heater Cartridge Test Plan

Test Plan for Transportation of Pellets

Test Plan for Mass Flow Rate and Layer Resolution

Filabot Test Plan

Risk Assessment

Risk Assessment can be viewed here
Risk Progression

Risk Progression

Risks were assessed with risk progression analysis, and shows a trend of decreasing with time.

Design Reviews

Subsystems Design Review

Detailed Design Review

Final Detailed Design Review


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