3.1 Craft ceramic and Laser 3D modeling
In the first step, we used Taiwan Miaoli Clay in a laser firing test. We fired the craft clay with a 20W laser.
Using a layered laser-firing method, we were able to achieve clay melt at a depth of about 2mm.
We cut the clay into a thin slice , and then added one new slice of clay on top of the already-fired layer. After completing several of these laser-firing processes, we cleaned the clay sample with water. After washing the clay, we were able to observe a vitrified [glass] tube in the clay. This observation confirmed that craft clay can be used in laser 3D modeling.
A Kiln firing system requires a lot of equipment, like a kiln, a gas tank, an electrical system, and a chimney. Because laser firing systems can be operated without kiln equipment and fossil fuels, they are much more cost-efficient.
3.2 Comparing kiln firing and laser-firing processes for ceramic
To test laser firing’s ability to infer corresponding kiln temperatures, we changed the clay and used a kiln firing tool (Orton Cone 014, Temperature cone).
The following table shows our results:
Comparing kiln firing and laser firing
We fired clay and glaze with a 20W laser at 1~20mm/sec.
Building off of observations from our kiln firing experience, we changed several glaze elements and observed the corresponding laser firing results.
After changing the laser speed and the ceramic component, we observed a melting effect on ceramic that was fired via laser. Each element of the ceramic had a different melting temperature and heating rate.
As shown in the Orton Cone 014 firing temperature chart, the kiln heating rate is 30°C/hr. In other words, in kiln firing, energy accumulation is based on the kiln’s heating rate. When enough energy is accumulated, the Orton Cone will melt or bend.
We used the laser to fire ceramic and the Orton Cone. The laser speed corresponded to the kiln’s firing temperature. With different laser speeds, the energy accumulation created a bending [wave] texture on the ceramic and the Orton Cone.
In our tests, the laser’s speed had a bigger impact on the final product than the laser’s power did.
By using a lens to concentrate the laser on a 0.2mm focus point, we achieved a rapid heating effect.
Based on the melting speed we observed in the ceramic, the laser’s heating rate is much higher than the heating rate of the kiln.
In the ceramic vitrification firing process, the kiln heated at a rate of 0.0416 °C/sec. The laser heated at a rate of 527.85 °C/sec. The laser’s heating rate is 12688.7 times faster than the kiln’s heating rate. According to these firing tests, kiln firing and laser firing create different results in the final ceramic product.
In laser heating, the glaze’s melting pattern is different than it is in kiln firing. To figure out the differences between these two techniques, we compared ceramics fired by kiln with laser-fired ceramics. By recording the melting pattern of the ceramic surface and the laser speed, we found that the laser has a comparatively high heating rate.
When we set the laser’s speed to 1mm~20mm/sec, we observed the following features:
According to kiln firing classifications, ceramic products are divided into blanks (body) and glazes.
The ceramic body’s melting temperature must be higher than the glaze by over 100°C. This temperature discrepancy allows the product to maintain its shape and form a smoothly-textured glaze on its surface.
1. In this study, we used a laser (20W, 1~20 mm/sec) to fire ceramic materials. The Iron oxide in the clay showed a reduction color when laser-fired as it did in kiln reduction firings.
2. We also used the laser to fire the same clay at different temperatures. We studied 1) room temperature clay, 2) clay fired at 800 °C, and 3) clay fired at 1230°C. At each temperature, the result when fired at a slow laser speed (1~2 mm/sec) was the same. From this we conclude that the result of laser-firing is similar to that of kiln firing. In this way, we can measure the craft clay and the glaze’s heat resistance.
3. When we changed the laser speed, the clay surface displayed a gradual change in texture. By recording the gradual change in texture, we observed the melting threshold of the clay.
At the same laser speed, an obvious wavy texture [a “melt & flow” texture] appeared on the ceramic surface of the clay at room temperature, the clay fired at 800 °C, and the clay fired at 1230 °C.
When compared, the kiln-fired and the laser-fired glaze and clay displayed different features.
The laser’s high heating rate made the glaze’s melt different than the kiln-fired melt.
With the laser’s speed set to 1mm~20mm/sec, we fired the ceramic and recorded its surface melt.
1. When a 20W laser was used, the clay displayed a green color. When kiln fired, it displayed a brown color.
Our clay contains 2.3% iron oxide. Based on this percentage, we predicted that the iron oxide colorants would cause the clay color to change. We also predicted that the glaze’s components would affect the laser firing result.
2. We observed an obvious wavy texture and melting texture on both the clay and the glaze when they were fired with lasers of different speeds at several different ranges.
3. When firing ceramic in a kiln, a potter adds clinker powder into the clay to reduce clay shrinkage.
For the above reasons, we believe that the obvious wavy texture and melting texture on the laser-fired ceramics are due to a difference in shrinkage rate. Each glaze has its own melting temperature.
For this reason, the obvious wavy texture appears on the surface of different ceramics with different glaze components that are fired at different laser speeds.
In our test samples (kiln firing with blank
s bodies sintering at 1230°C and glazes melting at 1230°C), the blank s bodies (kiln fired at 1230°C, sintered) displayed an obvious wavy texture when laser fired at 5 mm/sec.
The glazes (kiln fired at 1230°C, melted) displayed an obvious wavy texture when fired with a laser at 14 mm/sec.
3.3 Laser energy calculation and kiln firing comparison
In this test, we used 20W lasers at several different speeds. We then plugged our results into the following equation:
Power Density/ speed (mm/sec) = Ceramic firing energy value
The laser’s focal point radius was set to 0.2mm, and the laser’s speed ranged from 1~20 mm/sec.
The laser’s firing energy range is 159.1545709~ 7.957728546.
The power density of laser fired blanks (body 1250 °C sintered, kiln fired) is 53.05152364~31.83091418 (speed 3~5 mm/sec).
The power density of glazes (melted at 1230°C, kiln fired) is 19.89432136~15.91545709 (speed 8~10mm/sec).
According to data on kiln firing, ceramic products need a 250°C difference between blank (body) firing temperature and glaze firing temperature.
By calculating the energy and sample melting data of a 20W laser with a speed of 3~10 mm/sec, we were able to mimic the results of kiln firing at 1240~1000°C.
The laser’s firing energy rapidly attenuated as the laser’s speed increased. A low laser speed can therefore accurately predict the kiln firing temperature needed for a given piece of ceramic.
3.4 Using laser firing to form a reduction ceramic surface.
Laser firing is able to change the color of ceramic. To identify the reason for this, we conducted a firing test that compared glaze component changes in both kiln firing and laser firing. We studied a clay with 2.33% Fe2O3 and used glaze elements to form a clay-like component without Fe2O3. The laser firing melting energy was the same for both components.
We found that :
1)The clay containing 2.33% Fe2O3 displayed a green color when laser fired.
2)The glaze containing 0% Fe2O3 displayed a transparent color when laser fired.
3)The clay containing 2.33% Fe2O3 displayed a brown color when fired via kiln oxidation.
4)The glaze containing 3% Cu2CO3 displayed a green color when kiln fired.
5)The glaze containing 3% Cu2CO3 displayed a red color when laser fired.
Based on these observations, we concluded that laser firing can form a reduction firing effect in an oxidized environment. Using the data from this firing test, we obtained an invention patent [Taiwan, R.O.C Patent Number: I687394].
3.5 Laser firing Fe2O3 and the CuCO3 to from a conductive ceramic surface
According to the above laser firing test, laser firing can create a reduction firing effect on ceramic. Our next test uses laser reduction firing to make oxidized metal conductive.
We began with non-conductive oxidized metals Fe2O3 and CuCO3. We then used a laser to fire those oxidized metals. After being laser fired, they became conductive but were very fragile.
We tried firing the oxidized metals again, this time on a ceramic surface. After firing and cleaning the surface, we achieved a conductive metal surface [CuCO3 with 42Ω and Fe2O3 with 120Ω].