Shortly before delivery comes the acceptance test. We filmed it: power up the machine, heat it, purge it, start a test print – and hold a ceramic part at the end. This article works through the steps and explains what happens at each one.
The machine
What you see is the KeraPrint in its tabletop version, which will later sit on a bench at the customer's site. The build volume is 220 mm in all three directions – enough for the ceramic components intended.
The pellet extruder is fully hardened: screw, nozzle and barrel are made of hardened steel, in this case even with a PCD diamond nozzle from Gühring. With abrasive compounds that is not a luxury but a prerequisite for tool life.
Switching on means confirming twice
Operate the main switch, press the reset button. The click signals that the safety relay has been reset – only now do the heaters and motors draw power when needed. Pressing the emergency stop interrupts it again.
Within the software, too, switching on heaters and motors has to be actively confirmed. For an industrial machine that is the right approach: a heater does not come on by accident.
The interface: Mainsail, extended
Anyone who has worked with Klipper and Mainsail will find their way around immediately – it is the same interface, which we have extended with our own functions. These include temperature monitoring, fan control in per cent, macros and a self-test that queries the status of the fans and the main processor unit. It also runs in the background, so it is clear whether the machine is working reliably.
The most important addition is the calibration window. On a pellet extruder the extrusion value has to be adjusted at every material change and for every different nozzle diameter, because compression and back pressure change. This comparatively involved step is one we want to take off the user's hands.
We are also beginning to integrate slicing: nozzle and material are stored, and simple geometries – a 50 mm cube with two walls and three top layers, say – can be generated directly at the machine. That is useful when commissioning a new material.
Preheating and purging
The material in this case is aluminium oxide from our material supplier PT+A. The machine heats to 125 degrees at the nozzle and the bed to 60 degrees. It then homes and moves to a position where the purged material is out of the way.
Purging is not an optional step on a pellet extruder. Because we melt a mass, and material sits at temperature too long during heating and cooling, a certain quantity has to be run out before printing starts. We choose the purge speed so that the volume flow matches the one in the part itself – a constant volume flow is the central goal in pellet printing.
And the residue? It can simply be shredded and fed back in.
Why there is tape on the print bed
With ceramics, bed adhesion is never the problem – rather the opposite. The material is paste-like and bonds almost too well with the build platform. The tape can be peeled off together with the part, which removes it safely. With a considerably more expensive material that is worth the effort.
Printing: deliberately slightly over-extruded
The first layer runs fast – that too serves a homogeneous mass flow from layer one onwards. Once the value is set correctly, it already looks clean.
With ceramic feedstocks we deliberately work just on the edge of over-extrusion. Very slight ridges should form, ones you can feel by hand. The aim is the densest possible part, because debinding and sintering are the critical subsequent steps – and they do not forgive voids.
You check this at the break: a broken part should show a homogeneous mass that fractures across the beads, almost as if cast. That is precisely the prerequisite for good sintering results.
Some figures for context
The printed part weighs around 60 grams and was finished in roughly 10 to 15 minutes with a 1 mm nozzle – without our being anywhere near the throughput limit. Around 200 to 250 grams per hour are possible with this extruder model. In terms of mass that is not comparable with a filament extruder.
It is not a highly complex geometry, and the slicer parameters are not yet perfect. But that is not what this system is about: it is designed to deposit a lot of material near net shape in a short time. For final accuracy the part can then be machined on a mill.
Removing it – carefully
After printing you set the purge residue aside and peel the part off via the tape, much as with plastic. Care is still needed: the material is still paste-like and can be deformed by hand pressure alone. Better to let it cool under light pressure first.
Chapters in the video
The video is in German; the chapter titles below link straight to the relevant passage.
- 0:00 · Intro – the machine at final acceptance
- 0:26 · KeraPrint Tabletop: build volume and extruder
- 1:05 · Power-on, reset and the safety chain
- 1:43 · Klipper and Mainsail with S2S extensions
- 2:22 · Calibrating the extrusion value in pellet printing
- 3:24 · Self-test, macros and integrated slicing
- 4:33 · Loading aluminium oxide, heating and homing
- 5:15 · Why there is tape on the print bed
- 6:22 · Purging at a constant volume flow
- 7:34 · Test print: a cylinder with two wall lines
- 8:14 · First layer and deliberate over-extrusion
- 9:06 · The fracture surface as a quality indicator
- 10:41 · Result: 60 g, 1 mm nozzle, throughput
- 11:40 · Removal, cooling and inspection
- 13:17 · Conclusion and a call for test geometries