Thermal Powder Mixing R&D and PID Heating Control - Formlabs

About This Project

During my time at Formlabs on the SLS team I was tasked with solving a vaguely defined problem: To ensure SLS powder is heated to a uniform temperature as it moves from one place in the 3D printer to another. 

Problem 

As seen in the figure to the right, the new SLS powder entering the trough is cooler. This obstructs the thermal uniformity significantly when printing and had to be addressed. 

Since most SLS 3D printing powders are insulative, achieving thermal uniformity is challenging.

Solutions

During my time at Formlabs, I led two R&D initiatives to try and solve this problem. I began with the heated transport concept, and then moved to exploring internal mixing of hot and cold powders within the 3D printer.

Heated Transport

Powder Mixing

Heated Transport Benchtop Validation

Overview

To test this solution, the following benchtop rig was built and used for testing. It automatically logs powder flowrate and exit temperature.

Electrical

To accurately heat the powder to the desired setpoint for SLS printing, I implemented a PID loop control for the heater.

Conclusions

This solution is not preferred. Most SLS powders are naturally insulative, meaning the center of powder in the tube could not effectively transfer heat. This led to powder exiting the tube with poor thermal uniformity and below the target setpoint temperature.

Pipe Cross Section

Powder Mixing Benchtop Apparatus

Overview

The powder mixing benchtop apparatus is another concept for increasing thermal uniformity. As seen in GIF to the right, different color SLS powders model the hot and cold powders for qualitative analysis

In-Printer Thermal Testing

From the R&D study, a metal version was designed and built to be tested in next gen printers to see how thermal uniformity would be improved. The parts were cut on a water-jet, and I used a break to form the helical pieces. 

Results