Part quality monitoring in a stereolithographic additive manufacturing system

A method for printing a 3D part, the method comprising:

• providing a pool of polymerizable liquid in a vessel having a build window;
• positioning a downward-facing build platform in the pool of polymerizable liquid a distance of a thickness of a layer from a top surface of the build window;
• imparting ultraviolet energy through the build window to photocure the liquid and form a printed layer of the part adhered to the build platform;
• scanning at least a portion of the build window with monochromatic, polarized infrared or visible light along a plane of incidence, wherein the light includes polarized parallel to the plane of incidence (p-polarized) and includes light oriented perpendicular to the plane of incidence (s-polarized);
• measuring a change in intensity and polarity of the light to obtain information about the printed layer;
• raising the build platform to a height of a next layer to be printed;
• modifying the ultraviolet energy imparted into the next layer based upon the obtained information to print a next layer;
• and
• repeating the imparting, scanning, measuring, raising and modifying steps until the part is printed.

A method for 3D printing a part in a layer-wise manner, the method comprising:

• providing a pool of polymerizable liquid in a vessel having a build window;
• positioning a build platform in the pool of polymerizable liquid a distance of a thickness of a layer from a top surface of the build window, defining a build region;
• imparting ultraviolet energy into the build region through the build window to selectively solidify the polymerizable liquid in the build region and thereby form a printed layer of the part adhered to the build platform;
• utilizing an ellipsometric imaging system to scan at least a portion of the build window with monochromatic, polarized infrared or visible light along a plane of incidence, wherein the light includes polarized parallel to the plane of incidence (p-polarized) and includes light oriented perpendicular to the plane of incidence (s-polarized) and measure a change in intensity and polarity of the light to obtain information about the printed layer;
• raising the build platform a height of a next layer to be printed;
• modifying the ultraviolet energy imparted into the next layer based upon the obtained information to print a next layer;
• and
• repeating the imparting, scanning, measuring, raising and modifying steps until the part is printed.