Quality assurance of 3D prints

Abstract

Low- and middle-income countries are facing a growing burden of non-communicable diseases that require surgical interventions. However, the lack of functioning medical equipment is hindering access to surgical care in these countries. 3D printing has the potential to provide a solution to this problem, but ensuring the quality of 3D-printed medical products remains a challenge.

The objectives of this master thesis are twofold.

1. To design a low-cost and easy-to-use test that can be used in low- and middle-income countries to ensure the quality of 3D-printed parts.

Method: First, the requirements for the test method were established. Existing test methods were reviewed, after which a test set-up was designed and built. The test set-up was subsequently validated by comparing it with a conventional Zwick/Roell test. PLA specimens were produced using an Ultimaker 2Go 3D printer according to the ASTM D790 standard. Three different batches of specimens were created, divided into two groups, and tested for their bending properties using both the homemade test set-up and the conventional Zwick/Roell test.

Results: The majority (8/9) of the results obtained from the homemade test set-up and the Zwick/Roell test exhibited no significant difference. However, the t-score for the Fmax measured for specimen batch 1 showed a significant difference between the two methods. All results measured with the homemade test set-up were higher than those measured with the Zwick/Roell test, indicating that the homemade system may have been incorrectly calibrated initially. Calibration of the load cell may therefore reduce this discrepancy.

Conclusion: Depending on the desired level of measurement accuracy, the homemade test set-up appears to be a viable alternative to the Zwick/Roell test.

2. To investigate the effect of temperature and relative humidity on the quality of fused deposition modelling (FDM) printed parts.

Method: The influence of temperatures of 20°C, 35°C, and 40°C combined with relative humidity levels of 50%, 70%, and 90% was investigated under nine environmental conditions. Two situations were studied: (1) storage of the print material 24 hours prior to and during printing, and (2) storage of the final print 24 hours prior to and during testing.

In Situation 1, PLA filament was stored under one of the environmental conditions before printing. Specimens were then printed under the same conditions using an Ultimaker 2Go printer inside an Espec humidity oven. For each condition, two batches of seven specimens were produced. After printing, specimens were stored at room temperature and approximately 40% relative humidity for a maximum of five days before being tested for bending properties using a Zwick/Roell test.

In Situation 2, specimens were printed similarly, after which the final printed parts were stored under one of the nine environmental conditions for 24 hours prior to testing. The specimens were then tested for their bending properties using a Zwick/Roell test.

Results: Fmax, maximum bending strength, and elastic modulus all decreased when specimens were printed or tested at increased temperature and relative humidity. Increased relative humidity appeared to have a particularly negative effect at higher temperatures. Furthermore, higher temperature and humidity resulted in under-extrusion, lower specimen weight, and poorer surface quality.

Conclusion: Increasing relative humidity and temperature during both the printing process and storage prior to testing negatively affects the bending properties of FDM-printed PLA specimens. The findings demonstrate the importance of environmental control for maintaining the quality of 3D-printed products and suggest that a low-cost quality assurance test may provide a practical solution for resource-limited settings.