3D Printer Failure Analysis

During my junior year at Duke, I, along with a few classmates, identified and analyzed failure modes of the leadscrew on a FormLabs Form2 SLA printer. Our team chose to perform calculations and create an experimental setup to test the lead screw’s capabilities because of its integral role in operating the FormLabs Form 2 SLA Printer. The FormLabs Form 2 3D Printer is currently one of the most widely used SLA 3D Printers used in the United States.

Form 2 SLA Printer

Failure Modes

We ultimately settled upon performing in-depth calculations for failure of the lead screw in torsion, as bed-leveling issues that occur often in FormLabs printers and heavy 3d printed parts contribute to the build platform tilting relative to the lead screw and jamming, inducing failure due to torsion towards the powered end of the lead screw.

Failure Due to Shear Stress

Failure Due to Tensile Stress

Back-of-the-envelope Calculations

Finite Element Analysis

A finite element analysis was performed on the lead screw to simulate real loading conditions during printer jams or failed prints. During a jam, the 24V DC Motor continues to apply a torque about an effectively fixed rod, as such the torsional force was included. Additionally, as the build platform moves with respect to the printer and the fixed rod, the rod has been locked at both ends in place. Thus, the torque applied is the motor’s attempt to spin a rod that has been jammed against the build tray, which applies a pressure that acts perpendicular to the rod. In this case, failure means the device has been deformed outside of the tolerance of the device. This means that while the shaft may not literally fail or break, the lead screw is now out of device tolerance under plastic deformation and needs to be replaced for operation.

Max Displacement

Max Loading Stress

Regular Operational Displacement

Regular Operational Stress

Experimental Setup

Experimental Setup CAD Top View

To validate the theoretical calculations and the finite element analysis, we designed an experimental setup for quantifying the torsion accumulation in the region of the lead screw closest to the motor when the build platform tilts relative to the lead screw, jamming the screw.

Experimental Setup CAD Isometric View

Experimental Procedure

With the experimental setup constructed, the following test method can be executed.

Position the build platform below the resisting rod. Record the initial height relative to the top of the torque sensor.
Start recording the DAQ channels for the torque sensor and the rotary encoder.
Power the stepper motor such that the build platform moves away from the stepper motor using the native Form 2 control hardware and power supply, to preserve any motor control characteristics programmed by Formlabs, as these will be present in real-life usage.
(This step is a note, no action necessarily required): The build platform should move up, resisted by the resisting rod such that the build platform jams the lead screw. The lead screw should be effectively fixed at the top end of the z-tower.
Allow the motor to continue to run until it stalls, fails, or the lead screw breaks.
Stop data collection.
Record the following:
1. The angle of the build platform when jammed relative to horizontal
2. The distance of the build platform when jammed relative to the top of the torque sensor. (final relative height)
3. The maximum torque recorded by the torque sensor (from the recorded data)
4. The stall torque recorded by the torque sensor, if applicable (from the recorded data)
5. The rotation value of the rotary encoder (from the recorded data)
6. The rotation value of the encoder integrated in the torque sensor (from the recorded data)

Bill Of Materials

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