Introduction: From a Microwave Oven to a Post-curing Chamber for 3D-printed Parts
Photopolymer 3D-printing has gained popularity over the years, and different manufacturers have developed resins and process for printing. However, virtually all of them could benefit from a post-curing step to make the printed parts stronger. There are two types of post-curing: heating and extra UV exposition. Both of them allow growing the polymer chains.
What we describe here is quick way to obtain a UV chamber, which can be easily updated with simultaneous heating. The idea is to use an old microwave oven replacing the magnetron by a blacklight.
Once you have the material, the whole project will take no more than one hour to be accomplished. Although the project is quite simple, ask for help to make the electric modification if you don’t know what you are going to do.
Step 1: Disconnect the Magnetron
Unplug the microwave oven, remove the cover, and disconnect the terminals from the microwave power transformer. You don’t need to remove the magnetron or any other part of the oven. By the way, keep the glass dish, because we can use it to allow spinning of the pieces while they are exposed to UV light, which will make more uniform the exposition.
Warning: Even after the oven is turned off, capacitors may remain charged and be dangerous if the terminals are touched. Therefore, don’t touch an exposed electrical contact if you are not sure that it is safe.
Step 2: Put the Lamp Holder
Put the lamp holder on the inner wall. In our case, we chose the perforated region of the wall for sake of simplicity. The holder should be fixed by using nut and bolt, and an additional hole should be provided allowing the passage of the wire.
Step 3: Connect the Lamp to the Magnetron Controller
Connect the wires from the lamp holder to the terminals of the electronic circuit that controls the magnetron. From now on, when the oven tries to turn the magnetron on, the UV lamp will be activated instead. If you wish to include a second UV lamp or a heater, just put them in parallel with the first lamp.
Step 4: Use Aluminum Foil As a Reflector
Use aluminum foil (from your kitchen) to cover as much as possible of the inner walls of the oven. The foil does not need to be form a perfectly flat surface, because the idea is to reflect the light and send it to different sides of the 3D-printed object.
Oops, that is the right time to clean the oven after all these years in the kitchen.
Step 5: Finish the Job by Putting the UV Lamp
Different UV lamps can be used. We used a 25-W blacklight, which emission spectrum is shown in the figure. There is a large band at 365 nm and a small band at 405 nm, which is the same wavelength of the LED from the 3D printer. The absorbance spectrum of the photopolymer resin manufactured by Wanhao shows great absorbance in this entire region.
In addition to the UV emission, the blacklight also heats the oven. For instance, after 10 min working, the inside temperature rises from 25 °C to about 40 °C, which helps enhancing the curing process.
Step 6: Use It!
You can control the exposition time as you would do with a regular microwave oven. Of course, this time should be optimized for each case.
1. If you don’t know about electronics, ask for help.
2. Don’t put the aluminum foil inside the oven until you are sure that the magnetron was fully deactivated.
3. Blacklight is a gas-discharge lamp, which usually doesn’t work in PWM mode. Therefore, always chose the full power mode (100% power) at the oven panel.
4. Pay attention to the emission light spectrum of the UV-lamp. Remember that UV light can cause injuries to the skin and eyes. If needed, cover the oven window with a UV-filter or an opaque plastic, metal, or paper foil.
5. Put the chamber close to a window to help dissipate the released organic vapors.