A Coherent DC Series 1 kW laser provides the combination of performance, reliability, and cost required for this industrial process, and Coherent's support makes the integrator's job easier.
With over 100 years of experience in welding, machine tool manufacturer Arnold Ravensburg (Ravensburg, Germany) is an expert in this technology. The company was an early adopter of laser welding and has been building its own systems since 1985.
Because of its outstanding expertise, particularly in CO₂ lasers, companies around the world turn to Arnold Ravensburg to solve some of their most challenging welding challenges. They know the company will develop a customized solution—often incorporating the laser, beam delivery system, fixtures, and robotics for part handling—rather than imposing a "one-size-fits-all" approach to their customers' unique problems.
"The combination of performance stability and consistency, along with high operational reliability, makes Coherent's DC Series CO₂ lasers ideal for integrators, system builders, and end users."
– Hansjörg Klotz, Sales Director, Arnold Ravensburg
Application for sealing lamps
In 2023, a major lighting manufacturer approached Arnold Ravensburg to supply a system for sealing discharge arc lamps. Specifically, the cylindrical quartz glass envelope of the lamp bulb must be melted to form a seal with the internal ceramic structures supporting the anode and cathode. This seal must be continuous and hermetic, extending around the entire circumference of the bulb. This is necessary to retain the high-pressure gas mixture with which it will be filled in a later step. This seal must last throughout the entire lifetime of the bulb.
To do this, the glass must be melted in two places around the entire circumference of the bulb, forming a hermetic seal with the ceramic part inside. This allows the bulb to retain its gas filling throughout its entire service life.
The lamp manufacturer originally performed this sealing process with a flame. However, over the past 10 years, they have switched to laser processing. Laser sealing proved more repeatable, and the use of a pyrometer system for temperature measurement enabled better control of the process, resulting in higher consistency and yield.
Unfortunately, the original laser system supplier was experiencing quality and delivery issues. They were looking for a new supplier that could offer a faster, more consistent process and deliver on time.
The lighting manufacturer was already working with Arnold Ravensburg, so it made sense to entrust the company with this project. Especially since the only practical source for this application is a CO₂ laser, and Arnold Ravensburg is particularly familiar with this technology.
The CO₂ laser is necessary because the material of the bulb's envelope is transparent in the visible and near-infrared range. This means it can't easily be processed with shorter-wavelength lasers—their light simply passes through the material instead of being absorbed and heating it.
Choosing the right laser
While this application obviously required a CO₂ laser, Arnold Ravensburg first had to determine the specifics of the process. The optimal method involved continuously rotating the piston while simultaneously directing the laser energy to the desired location. This rapidly heats the piston. The material temperature is continuously monitored by a non-contact pyrometer, and when it reaches the correct value, the laser is turned off. The piston continues to rotate, and the molten glass flows to create the seal.
Arnold Ravensburg's engineers realized they couldn't perform both seals simultaneously due to potentially different process parameters. Therefore, the two seals are manufactured sequentially. The rate-limiting factor is the flow rate of the glass bulb material, which results in each weld taking approximately three minutes.
The process requires a laser power of about 800 W. Arnold Ravensburg chose the Coherent DC 010This is the 1 kW model from our DC series of sealed, high-power CO₂ lasers, which ranges up to 8 kW.
"Several factors led us to use the DC 010," explains Hansjörg Klotz, Sales Manager at Arnold Ravensburg. "Our end customers appreciate that the sealed slab discharge design offers much higher reliability than the fast-flow design used in other multi-kilowatt CO₂ lasers. It also offers lower operating costs, greater reliability, a longer lifetime, and a longer maintenance interval. Furthermore, because these lasers are sealed, there are no issues with contaminants entering the laser, which is always a concern in industrial environments. Finally, the output power of the DC series remains constant throughout the laser's lifetime, ensuring excellent process consistency."
A partnership for success
From the perspective of a machine builder like Arnold Ravensburg, Klotz cites ease of integration as a key advantage. "We've used Coherent's DC series lasers many times, and it's very easy to build a system around them. They offer a true industrial interface and integrate seamlessly into a fieldbus environment. Many of our customers use the Profibus protocol, especially in Germany, where Siemens controllers are almost universal, and the DC series supports this directly."
"Another factor is Coherent itself," reports Klotz. "We consider Coherent a partner, and it's always easy to get the support and information we need from them. For example, we sometimes need detailed data on the beam characteristics of a particular laser for optical calculations, and Coherent never hesitates to provide it."
"Furthermore, we have found that Coherent lasers exhibit excellent unit-to-unit consistency. This means that once we have designed an optic, we can build systems with the confidence that no significant custom adjustments will be required. The same applies to beam stability, which does not change after installation. This fits very well with our own design philosophy. Arnold Ravensburg's beam delivery systems are designed so that no optical readjustment is necessary when replacing a mirror. However, this assumes, of course, that the laser alignment itself remains stable.
"These lasers are workhorses that only require annual maintenance," says Klotz. "We can install them without worrying about performance issues or field failures. Using Coherent DC Series lasers in our systems no longer causes headaches for us or our customers. And that's why they keep coming back to us."