Accurate Hydrographic Printing for 3D Objects

Objects that have been 3D printed can be beautiful, but generally they come out monochromatic because they’ve been printed in one of a handful of single-color materials. You can paint them, of course, but that would be impractical for mass production.

One solution is hydrographic printing, which uses PVA film suspended in water to “wrap” a pattern around a 3D object. This process is used to put repeating patterns on objects, and while it’s relatively inexpensive it is nearly impossible to align the image on the film to the object. That’s why most companies use single patterns on the films.

Researchers at Zhejiang University and Columbia University have solved that problem, coming up with what they call computational hydrographic printing, which allows precise alignment of the film with the 3D object. In a video demonstration (which you can view below) they are able to align a mask print onto a 3D printed mask, as well as using multiple processes to put the image of a cheetah onto a three-dimensional cat figure.

The hydrographic process involves placing a PVA film on top of a container of water, spraying it with an activator chemical, and then dipping the object onto the film. The film wraps the surface of the object. Previously, it was impossible to align the image and the object, and the films could sometimes tear.

Using the computational process, the object is held by a gripper at the end of a rod. A 3D vision system (Microsoft Kinect) measures the location and orientation of the object with respect to the film. The computational model the researchers came up with is used to simulate the color film distortion during the process and creates a “texture map” to guide the object onto the film.

The system relies on Kinect and KinectFusion to construct a point cloud of the 3D object already attached to the gripper, as well as obtaining the exact location of the film on the water using 3D markers on the sliding bar.

The result: a nearly perfect match between the image and the object, even when multiple “dips” are required to place several films on the item.

Source: Columbia University