As the project is being wrapped up, for next year’s minor students to continue on, we can reflect on the progress made and of course list the areas which in our eyes have the highest potential for improvement.
During the initial week of the project progress seemed slow, with a quick visit to a metal workshop to receive some guidance on welding processes and settings. Deciding on which axis system to use and acquiring the right parts took longer than expected, luckily there was a Prusa supplier about 20 minutes away by bike!
After printing a simple wall, simply by stacking bead upon bead of metal is an obvious start. Let’s face it though, it is not the most challenging of structures. To investigate the boundaries of the printer we have first printed an overhanging wall, basically a slanted wall, by offsetting the printerhead slightly per layer we managed to print a wall of similar quality to our vertical wall. The initiation and termination points of the welder were quite problematic resulting in a slightly tapered wall.
Having finished assembly and laid down several beads of metal on the plate a series of “scientific” tests were done to tune our setup. The variables include:
- Feed rate MIG welder
- Voltage setting of the MIG welder
- Travel rate of the torch
Results were rated qualitatively and after a day of testing a final setup was chosen which was deemed suitable for our purpose.
The MIG welder is set to feed wire at a rate of 4 [m/min]. The open circuit voltage level is set to 16.9 [V]. Travel rate of the torch will be 330 [mm/min]. Gas flow is set to 9 [L/min].
Using this setup beads were layered on top of each other to form a wall like shape resulting in a surprisingly consistent and strong structure. Grinding off the outer layer and polishing the smooth surface revealed a uniform formation with no visible lines between the layers of welds. A second wall was printed, to be analysed and destructively tested at the 3mE facilities.
The next step in the project will be to print hollow structure. More results to follow.
– The Metalprinters
Welding over a long period of time generates high amounts of heat (remember steel melts at around 1400 °C). In an earlier post about manual 3D printing it was mentioned that regular breaks must be taken in the welding process to avoid overheating of the both the welding apparatus and the print product. In order to prevent the plastic 3D printed parts on our machine from melting it was decided to re-manufacture critical components out of aluminium.
A heat shielded box will be used to protect the rest of the machine from the heat of the product and to contain most of the molten metal bits which fly around. The box is made by bending a 2 mm sheet of aluminium, it is then lined with slabs of light weight, heat resistant tiles. These tiles were thoroughly tested beforehand by welding right on top of them with varying power settings of the machine (note: for 3d printing only the lowest setting will be used). At low power settings the tiles could be picked up by hand immediately after welding. Damage occurred only when large pools of molten steel came in direct contact with the tiles when welding at with the highest power setting. To protect the MIG torch from sparks and molten metal a simple shield was fabricated from sheet aluminium, this was attached to the torch clamp.
Heat resistant tile after testing, it discolours at high heat but is damaged only when in direct contact with molten steel.
– The Metalprinters