Real-Time Imaging of Bonding in 3D-Printed Layers

Our research aims to improve layer bonding during 3D printing. We use a method called laser speckle imaging to visualize the bonding process in real time. These insights will guide the optimization of printing conditions, hopefully leading to enhanced material design and performance.

Currently, the layer bonding is studied using infrared imaging techniques that visualize this plastic surface temperatures. To study layer bonding with infrared imaging, it is assumed that the inner temperature and the surface temperature is equal. Also the complex relationship between temperature and the plastic fluidity has to be known.

We've adapted laser speckle imaging for the use of 3D printing and have shown how to easily obtain deeper understanding of the layer bonding. Our LSI approach measures the polar motion inside the plastic, visualizing the layer bonding without any assumptions. The technique is also non-invasive, easy to use, and has an excellent sensitivity.

The method shown in this research can be used to study 3D prints or patterns that are challenging. The results can be used to understand how the setting should be changed to improve the print's quality. Begin by placing the 3D printer on a steady surface to minimize vibrations.

Place the LSI instrument next to the printer so that the camera has a clear view of the printing area. Position the LSI slightly higher than the camera build plate and tilt it downward slightly to prevent view obstruction. Next, turn on the laser and bright field illumination.

And ensure that they are aligned with the imaging area. Start with a test print, making sure that the LSI camera is focused on the printing area. During the test print, optimally align the lighting and the digital camera and adjust the laser direction to illuminate the whole imaging area homogenously.

Adjust the diaphragm so that the speckle size is slightly larger than the pixel size. Select the parameters for the live LSI data analysis, being sure to choose the frequency that produces the best imaging contrast between molten and solidified plastic. Choose the frequency and length of image saving to prepare the LSI instrument to capture images.

Start by drawing the object using a 3D drawing software of choice, and export the object as a SDL file. Next, import the SDL file into the slicing software and choose the printing settings. Press the slice button in the slicing software to obtain the layers and travel path of the print head.

Save the resulting G code and send it to the 3D printer. Now stop the 3D printer and allow it to warm up. Start the LSI measurement when the plastic starts to extrude to prevent unnecessary data saving.

Once the 3D printer is done printing, stop the LSI measurement. Load the resulting data into an image viewing software. And visually inspect the printed object.

Print quality of the object appeared good with the surface showing layer lines. LSI imaging showed increased polymer motion in the recently printed layers. The experiment when repeated with the cooling fan, resulted in slower cooling of the plastic at 0%fan speed, causing poor visual print quality with irregular surface layer lines and blobs.

The overall designed geometry was imperfectly reproduced with the windows and holes being deformed. LSI imaging indicated increased polymer motion throughout the whole object. Advanced data analysis for the comparative welding zones of six fan speeds showed peak profile positions at which the polymers were most mobile.

The welding zone profiles for 40 to 100%cooling were nearly identical, while the zone for 0%cooling extended over the entire measured area.