Multi-Laser Additive Manufacturing

Build speed and part size increases with multiple-laser AM systems

EOS additive

In a production setting, it is worth evaluating whether it is better to have a multiple laser system or several single laser systems. Photo courtesy of EOS.

The industry has become increasingly comfortable and confident with metal additive manufacturing (AM) and its ability to produce quality parts. As AM becomes more mainstream, OEMs are pushing the productivity boundaries of the technology by developing bigger and faster platforms. This push comes from shops looking to tighten lead times while increasing part size. In particular, the aerospace industry is looking to produce larger parts, while the automotive industry is looking to print as many parts as possible. One way that this is being done is through the addition of multiple lasers. Parts that were traditionally unable or uneconomical to be built with metal AM now can be produced cost-effectively.

"More lasers doesn’t automatically equal a higher rate of production, but when you are working on a larger build plate, a multi-laser approach can improve the effectiveness and efficiency in making single or several parts," said Ankit Saharan, manager R&D and applications development, EOS, Pflugerville, Texas. "At the end of the day, though, it’s about creating efficient energy delivery systems within machines, whether that’s with one or multiple lasers."

Laser power, speed of the laser, and layer thickness all play a part in the efficiency of AM systems. Increasing layer thickness will increase build speed, but may require a higher laser power to do so. However, the physics of the technology limit these factors, forcing machine builders to look to alternatives, specifically multiple lasers.

"Adding multiple lasers gives manufacturers more production flexibility," said Aaron LaLonde, director applications engineering, SLM Solutions NA Inc., Wixom, Mich. "With multiple lasers, the lasers can all be utilized to work on the same part at once, or they can work on separate parts at the same time, allowing shops to produce multiple parts simultaneously. Having multiple lasers allows manufacturers to adapt production flow to meet changing daily needs."

Single-laser systems still have a place in the market, but LaLonde conservatively estimates that more than half of the market either has or is looking to adopt multiplelaser systems.

ALIGNMENT ISSUES

Depending on the application, using a multi-laser system can add some challenges that are not found in traditional machines. When producing multiple parts on one build plate, it makes sense to have one laser working on a certain area of the parts while the other lasers work on other areas. However, with a larger part, multiple lasers may play in the same space, creating potential for alignment-related issues.

Saharan explained that proper alignment is critical for good part quality, making it important to ensure that one beam isn’t interfering with another. Manufacturers need to align work zones with respect to each laser. If work zones are not properly aligned, parts may be produced with surface marks or defects where material is unmelted, ultimately negating the benefits of engaging multiple lasers.

As the system size goes down and the number of lasers goes up, it becomes increasingly difficult to co-ordinate the lasers. However, proper overlap is also necessary. The experts agree that the system software makes it much less of a challenge, but it is still important to ensure that there are no voids or defects in this overlap region. There must be consistent and continuous material structure and properties when one laser is building and the system switches to another. Without this capability, there is no value in producing a large part using multiple lasers.

GAS FLOW

Multi-laser systems tend to produce condensate and particulate at a much higher rate than single-laser systems. Proper gas flow is needed to effectively remove these contaminants from the build platform to minimize the contamination risk to the powder bed. "From the beginning, proper gas flow needs to be established and controlled in order to evacuate that condensate," said LaLonde. "This is important for all types of systems but even more so when you have multiple lasers, because there is that much more condensate being produced. This will help keep the process clean and maintain a high quality of the material coming out the machine."

Material can potentially be redeposited in areas that haven’t been melted yet, so it is important to be aware of the exposure order of these parts from different lasers.

SLM additive manufacturing

SLM demonstration part in titanium showing the advantage of the use of multiple lasers, higher laser power, and thicker layers. Photo courtesy of SLM.

MISCONCEPTIONS

"Most people think more lasers means more productivity, which isn’t the complete picture," said Saharan. "It depends on the part you’re making in terms of the type of application you want to use. If you’re a service bureau that makes a wide variety of parts for different industries, you’re going to look to integrate multiple lasers so that you can cater to a wider market."

However, Saharan added, in a production setting it is worth evaluating whether it is better to have a multiple-laser system or several single-laser systems. AM technology has progressed significantly over the years to meet operational liability and quality demands for production-level jobs, but Saharan noted that there may be a benefit of having the redundancy of several single-laser machines rather than one multi-laser machine.

It also is important to distinguish among applications when looking at different multi-laser systems. Determining whether multiple lasers can be used for one large part with coverage overlap or are restricted to zones for multiple-part production is an important first step. Understanding where the lasers work, whether they overlap, how they overlap, how material properties are handled in the overlap, and scanning strategies will determine if a system will work for a shop’s requirements.

One of the biggest misconceptions LaLonde sees is that metal AM is not a proven or reliable method of production, and that couldn’t be further from the truth. Not all applications are suited for AM, but there are many areas where this technology is helping shops break into new application fields.

"We are demonstrating, day in and day out, that multi-laser AM is a viable option," said LaLonde. "We can provide machine and material data testing information to support using multi-laser systems, adopting thicker layers, and adding higher-power lasers to produce high-quality parts just as good, if not better than, a single-laser option."

INNOVATION

The size and value of the parts produced using AM continue to grow, making the quality and robustness of the machines crucial. The market is expanding, and machine builders are finding the balance between laser power, build chamber size, laser count, system cost, and reliable support. Investing in a high-end system makes sense only if a shop is confident that high-value parts can be produced with zero effect on quality.

The experts noted that the latest systems allow for different configurations of one, two, or four lasers at different levels of power, 400 or 1,000 W.

"That flexibility makes the machine much more complex, but at the same time opens up the process window to how you process a part," he explained.

Often left out of the conversation is the importance of material and software to AM innovation. Many manufacturers are looking to diversify material choices, moving away from conventional options to advanced alloys designed for AM. This segment represents the greatest area of opportunity for the industry. AM opens up the possibility to design parts using materials that could not be produced using any other method. More companies are looking to engineer new powders customized to the 3D printing process.

Software also plays a key role, defining the exact path the laser takes during the part build process, influencing surface finish, tensile strength, and build speed. Today’s software options offer users a large tool set and parameter control settings for greater freedom of optimization. Beyond that, machine manufacturers have adopted smart technology and connectivity to make monitoring build controls easy and adaptable. As the software technology matures, failures are decreasing and uptime is increasing, making multi-laser 3D printing a more efficient and reliable process overall.

EOS additive manufacturing

The EOS M 400-4 offers a large building volume of 400 by 400 by 400 mm combined with four 400-watt fibre lasers for up to four times higher productivity. Photo courtesy of EOS.

Associate Editor Lindsay Luminoso can be reached at lluminoso@canadianmetalworking.com.

EOS, www.eos.info

SLM Solutions Group, www.slm-solutions.com
About the Author
Canadian Metalworking / Canadian Fabricating & Welding

Lindsay Luminoso

Associate Editor

1154 Warden Avenue

Toronto, M1R 0A1 Canada

Lindsay Luminoso, associate editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. She worked as an associate editor/web editor, at Canadian Metalworking from 2014-2016 and was most recently an associate editor at Design Engineering.

Luminoso has a bachelor of arts from Carleton University, a bachelor of education from Ottawa University, and a graduate certificate in book, magazine, and digital publishing from Centennial College.