Extrusion printing is a notoriously messy process. The same material properties that allow for bridging, overhangs and good adhesion lead to nozzle buildup and print errors. This is a particular problem with multi-material prints where the inactive nozzles often ooze material. The H-Series tool changer moves these inactive nozzles out of contact with the part, so the oozed material doesn’t contaminate the print. However, the unknown volume of lost material still presents a problem when that printhead is used for the next operation. Purge walls and prime pillars can help to prep the printhead before it is brought into contact with the part, however some of the lost material inevitably builds up on the outer surface of the nozzle and makes its way to the print. For this reason, we felt an effective and repeatable nozzle cleaning system was critical to the function of the H-Series machine. We prototyped many different configurations of wipers and brushes, both passive and active. The problem was always that the cleaning action got worse over time. Melted plastic would build up on the bristles, often transferring back onto the nozzle in the next pass. Flexible wipers had similar issues and often did not offer enough abrasive action to remove the melted plastic.
The H-Series cleaning system starts with the nozzle design. An extended cylindrical nose and non-stick plating provide a surface that is well-suited for automated cleaning. A solenoid driven pincer mechanism (shown in the image above) is used to close a pair of blades radially over the nose of the nozzle and scrape material axially away from the