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DQ-Series laser available from Laser Resources

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article image Edge removal at thin film solar cells done through q-switched lasers

Rofin, partners of Laser Resources , have introduced the new DQ-Series.

Based on Q-Switch technology, the DQ-Series laser is available up to 850 Watts in power.

When compared to sandblasting and chemical etching processes, the DQ-Series laser produces consistent processing results, faster processing speeds, is more cost-efficient and eco-friendly.

ThyssenKrupp Tailored Blanks GmbH are adopting this new process to remove metallic coatings from a special steel alloy and have selected the DQ-series laser for the job.

Welding reinforced steel safely

ThyssenKrupp Tailored Blanks GmbH also find these q-switched lasers interesting, for coating removal on their new manganese boron steel tailored blanks.

Compared with conventional steel, the tensile strength of these steels, especially after a heat treatment, is much bigger which leads to reduced sheet metal thicknesses without reducing the strength of the structures.

The automotive industry has already been using those positive features to reduce weight (Which equals reduction of fuel consumption) and increase crash protection. But tailor welded blanks had not been used with this steel before because this new steel is coated by aluminium silicon.

This is necessary because those reinforced sheet metals can only reach a constant conversion at temperatures of more than 900°C. A zinc coating would vaporise at this temperature and the work piece would not be protected from scaling and corrosion.

Both, aluminium and silicon have disadvantageous effects when laser welding tailored blanks; they lead to a mixture between the basic material and the coating in the weld seam. The solution was the removal of the coating in the area of the weld seam. The only question was how.

When a car manufacturer requested tailored blanks of reinforced steel, ThyssenKrupp Tailored Blanks GmbH consulted Rofin’s laser specialists in Hamburg with this problem in October 2006. It was soon discovered that the removal of any kind of metallic coating from tailored blanks could be accomplished using q-switched lasers.

Now, the task was to qualify the special demands of the application in trials and tests. The linear sheet metals that had to be welded by butt joint, needed to be processed with a rate of feed of 10m/min and a removal width of 1 mm.

“We have been producing a small series of these reinforced work pieces via sandblast method so far. But our customers expect a delivery of 30,000 pieces per month from August 2007 on – the expenses for this method would become immense”, says Jörg Maas, Key Account Manager of ThyssenKrupp Tailored Blanks GmbH in Duisburg, Germany.

“Our tests with the lasers from Hamburg showed very positive results: all our demands, such as the required processing speed and the removal width, could be met, so we decided to purchase a DQ laser with 450 Watt power. Summarized you can say that we have found our commercial and technical optimum with this laser.”

Edge removal at thin film solar cells

Laser removal can be used in the manufacturing of solar cells. With a strong demand to find alternative energy solutions, the solar market has a strong growth rate. As a result, the development and production rate of solar cells is ever increasing.

The thin film solar cells are being produced more and are up to 100 times thinner than standard solar cells. These thin film solar cells are mostly applied directly onto a carrier (e.g. glass) by precipitation during the gas phase and can have the size of several square meters.

Depending on the producer, the removal of 10 to 20mm of the coating around the solar cell is necessary to protect the solar cells constantly from environmental impacts and to join a second protective glass pane or thermoplastic foil permanently with the carrier.

Sandblasting leaves a rough surface that makes it difficult to bond and hermetically seal both panes together. Furthermore, the sand disposal is troublesome and expensive because the recycling is labour intensive.

With a q-switched laser, the edge removal rates exceed speeds of 50 cm²/s and completely remove the conducting layers and the electrical insulation. In addition, the surfaces are well prepared for a better connection with the second protective glass layer.

Turn round into square – new fibre geometries available

A major advantage of solid state lasers is the ability to deliver the beam through a fibre optic. This makes the laser a flexible tool.

Round fibres are common and widely used. Most surface removal applications have fine tolerances that must be met on the geometry of the ablated area.

The new fibres offered by Rofin produce a square spot at the surface. The square beam geometry can process an area that is 51% larger per pulse, compared to a round beam and is the same diameter.

When an overlap process is required, the removal rate is much more efficient. For both the tailored blank and edge deletion applications, a square fibre was used to optimize the process and increase processing speeds.

Outlook

Whether it is the square or the round fibre for surface processing of tailored blanks or solar cells - there are several new applications under development: in flat screens, electric conducting layers have to be separated, so that the correct pixel lights up at the right time, paint and lacquers have to be removed and surfaces have to be activated – these are good opportunities for the new lasers.

Principle description:

Rofin’s q-switched lasers are based on the approved diode pumped technology. A special way of running those CW-lasers is the so called q-switch. Here, the resonator beam path is optically blocked by an active element (the q-switch).

A laser activated crystal stores the continuous applied pumping energy. When the optical barrier is removed, the beam path is opened, all the saved energy will be provided within a short pulse.

In the following, the beam path is closed again. This process is repeated continuously, whereas the pulse lengths can vary between 10 and 1000 ns. These short pulses can create top pulse performances that are more than a 1000 times higher than those of CW Laser powers. Frequencies from cw to 200,000Hz are possible.

The new DQ series:

The DQ series laser is available as Standard, Premium and Premium+ that differ in power and equipment. Standard is available with powers from 350 to 850 Watt and round fibre diameters of 600 µm.

The versions Premium (500 Watt, 600 µm fiber diameter) and Premium+ (800 Watt, 800 µm fiber diameter) are able to operate with round or square fibers. Additionally, both laser versions have an optical attenuator that supports a very fine and long-term stable parameter adjustment which leads to safe results even for sensitive applications, for example, selective removal of coating layers.

All three versions allow a second resonator in the same laser housing. This construction saves separated supply measures, doubles the capacity and facilitates the integration into already existing work stations. In both Premium variations there are separated triggers so two independent beam sources can be used.

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