New frontiers in laser 3D printing

The primary driver behind growth in additive manufacturing (AM) and laser 3D printing is the design flexibility and freedom that the approach allows, although taking full advantage is not always a straightforward matter.

"Laser 3D printing is an innovative process, illustrative of the new technological advancements now being achieved within the field of manufacturing generally," contends Bo Gu of Bos Photonics. "However, AM does create new challenges. Knowledge of the materials and the manufacturing process itself becomes critical in achieving desired product design and part performance."

At SPIE Photonics West in January, the Laser 3D Manufacturing conference, co-chaired by Gu along with Hongqiang Chen of GE Research and Henry Helvajian from The Aerospace Corporation, included a session on Frontiers of Laser 3D Manufacturing at which some of the cutting edge developments in the field were discussed. The intention was to inform attendees about newly developed laser sources; new or improved process monitoring techniques; and the current state of materials development, especially regarding metal alloys, refractory alloys, and highly reflective metals. It also described current trends in the real-world application of these techniques, especially the latest uses in space systems and space manufacturing.

Recent progress in novel AM techniques has exploited developments in the laser systems involved, including the use of shorter wavelength lasers with green or ultraviolet emissions, and of shorter laser pulse widths from ultrafast sources. Using a laser beam with a wavelength in the visible or ultraviolet spectrum, as opposed to infrared emissions of around 1 micron, enables laser AM of highly reflective materials like copper, aluminum, gold, silver, platinum and iridium to be more effective and efficient, according to Bo Gu. Techniques for 3D printing of glass have also now opened the door to novel structures with both unconventional structures and tailored composition.

"Use of ultrafast lasers, along with optimized process parameters such as laser power, scan speed, hatching space, layer thickness, and patterning strategy, can lead to high density samples of a variety of materials, including refractory materials," he says. "Refractory alloys, with their extraordinary resistance to heat and wear and superior durability, are often the desired material for extreme-environment applications such as space craft, missiles, and hypersonic vehicles. Due to the difficulty and high cost associated with traditional manufacturing in complex shapes, their utilization has been hampered even in the most demanding applications. Laser 3D printing, on the other hand, has demonstrated a superior shape-producing capability that is unattainable with traditional manufacture. 3D printing of refractory metal alloys can greatly enhance the extreme environment performance of the parts and reduce the costs at the same time."

The aerospace industry presents one good example of an expanded application envelope for AM techniques, says Gu, in which new challenges have been set and then tackled.

Bo Gu is co-chair of the Laser 3D Manufacturing conference at Photonics West. Credit: Bos Photonics

"Laser 3D printing is transforming all segments of the aerospace industry, including commercial and military aircraft, space applications, as well as missiles systems," he notes. "Such transformation is due to the unique ability of AM to produce parts with complex designs, reduce manufacturing costs by improving material waste and allowing fewer tools and fixtures, and fabricate parts with premium materials with small production runs and short turnaround times. In addition the capability of AM to fabricate free-form designs makes it very suitable for the aerospace industry."

For metal parts, the main AM technologies in aerospace applications are directed energy deposition and powder bed fusion. However, as with all commercial materials and processes, variation in part quality and mechanical properties due to inadequate control of dimensions, microstructure, potential defects, surface roughness, and residual stress can result in designs that limit a part's use in high-value or mission-critical applications. This means that ensuring quality and consistency, and enabling more widespread use, requires robust quality control with stringent qualification and certification procedures.

"Unfortunately, few quality documents are publicly available, forcing aerospace companies and organizations to establish their own guidelines," says Gu. "Furthermore, where parts and systems require regulator certification, requirement interpretations are still evolving. These challenges to the control of part quality, dimension and mechanical properties are also quite common in laser 3D applications in other industries."

A lack of industry-wide standards features on Bo Gu's list of the common challenges currently being addressed by AM developers serving a range of end users. Others include production speeds and printing costs; inconsistencies in material properties; and the need for software that exactly matches the requirements of the technique. The rapid growth of the sector has also led to issues around copyright protection, the skill set of the workforce, and an industry ecosystem, which remains relatively disjointed, compared to other manufacturing sectors.

Tackling these challenges

The hurdles can all be tackled by industry-wide efforts and specific technical advances, comments Bo Gu. "Many current industrial 3D printers still lag behind traditional mechanized equipment in terms of speed and efficiency," said Gu. "This is particularly an obstacle for adoption in industries driven by mass serial production, such as automotive and consumer goods. In these industries, products need to be manufactured and delivered in as short a time frame as possible, in order to maintain production efficiency."

High printing costs have become a hurdle for AM in comparison with traditional manufacturing techniques, which have built up refined and extremely efficient processes over the years; and for some uses 3D printing may simply be too expensive for a few more years to come, as processes are simply not streamlined enough. The 3D printing platforms required by large companies can cost tens of thousands of dollars, and when they are used the process is slow and costly.

The time taken to 3D print depends on the number of layers that need to be printed and the speed of the printer itself, with even the best 3D printers able to build only between 5 and 60 centimeters per hour, according to Gu.

Limited raw materials and inconsistencies in material properties are another consequence of the relative youth of AM manufacturing, which lacks the decades of materials development which traditional manufacturing processes have undergone. "3D printing's own material development has just begun," says Gu. "While it can create items in a range of plastics and metals, the available selection of raw materials is not exhaustive, since not all metals or plastics can be temperature controlled enough to allow 3D printing. In addition the industry currently lacks a solid database of materials with proven printing parameters and defined specifications. As a result, it becomes challenging to achieve a consistent and repeatable 3D printing process."

Thriving and evolving

A lack of industry-wide standards, another issue connected to the history and development of this advancing market sector, is a further problem, not least because it introduces the potential for sub-standard products to ultimately enter the manufacturing chain and find their way to end users. Many manufacturers worry that their products, or the parts of those products being produced via 3D printing, will not be on a par with other manufacturing methods in terms of quality, strength and reliability. This creates a wariness of 3D printing technology generally, since the risks involved are judged to be too great compared with the benefits. Bo Gu says that this uncertainty will be removed as firmer standards are brought in across the AM sector, and that efforts to do so are now underway.

"Design and data preparation are still a bottleneck in this industry," he continues. "The need to transfer AM design data through multiple software solutions results in a time-intensive and error-prone design process. Although great progress is being made on the AM design and print preparation front, there is still room for improvement. Providing designers with the ability to modify 3D models within the CAD environment and to quickly iterate them without cumbersome data conversion will be key to making the design preparation challenges a thing of the past."

Post-processing is likely to remain a key aspect of AM techniques, since most 3D printed parts need some form of cleaning up to remove support material from the build and to smooth the surface to achieve the required finish. The amount of post-processing required depends on factors including the size of the part being produced, the intended application and the type of 3D printing technology used for production; and this is where optimizations are possible.

Intellectual property

3D printing is well known for bringing advanced manufacturing within easier reach of a greater number of individuals, but this has in turn made issues of copyright and intellectual property a substantial consideration. There is now an increased possibility for people to create fake and counterfeit products, and it will almost be impossible to tell the difference.

The structure of the industry itself is also a key factor, and Gu says that workforce elements are really critical right now. "There are not enough engineers, managers, executives who truly understand the technology well enough to work and develop a strategy to get what they need to get out of it," he says. "A lack of thorough understanding of the capabilities of 3D printing technologies can create many barriers to entry. Currently, there is still a knowledge gap in terms of what 3D printing technologies are, what their capabilities are and how they can be used. As a result, businesses which could benefit from the technology are unwilling to adopt it, as they struggle to develop a business case or use case for 3D printing."

Reorganizing the entire AM ecosystem so that it is less fragmented will remove the frequent obligation for solutions to be built from a number of individual small solutions and companies, a key step for AM processes to scale at the industrial level. The AM value chain, which begins from conception to production and post-processing of the product, needs to become more consolidated, according to Gu, who commented that the market is saturated with many different solutions, which ideally could be integrated to create a comprehensive offering, and simplify adoption of the technology. Companies looking to adopt AM are currently faced with the need to buy disparate solutions and then try to make them work together, a lack of integration in the value chain that creates inefficiencies in the workflow.

"As a young technology, laser 3D printing still has many challenges, even though the industry has made a quantum leap forward by developing better and faster systems, characterizing more materials and creating many automation solutions and expanding the list of approved standards over the last twenty years," concludes Gu. "Now we are seeing the growth of a new generation of AM professionals, and consolidation within the industry as companies are looking to partners in a bid to create comprehensive solutions. This is a thriving and evolving industry, which will continue to grow and evolve rapidly in the years to come. The best is yet to come."

Best kept secret in AM

Other discussions in the Laser 3D Manufacturing conference will include a presentation from Youping Gao of AM developers Castheon about the impact of the technique on the manufacture of components for use in hypersonic flight. The refractory alloys needed for such environments have extraordinary resistance to heat and wear with superior durability, and so are often a desired material for extreme applications such as spacecraft, missiles, and hypersonic vehicles. But the difficulty and high cost associated with manufacturing them in complex shapes has hampered their utilization.

Castheon is developing 3D printing-based processes suited to the additive manufacture of refractory metal alloys to enable superior materials properties. Credit: Castheon.

Castheon is developing manufacturing operations "suitable for AM of refractory metal alloys through 3D printing processes with superior materials properties, and envisages a significant leap in producing highly sophisticated geometries at lowered manufacturing cost," notes the company of its SPIE Photonics West presentation. "A case study of performance gain in sophisticated C-103 niobium engineered hardware will be presented."

The use of alternative laser wavelengths in AM operations, mentioned by Bo Gu as an example of recent technical progress, will be the topic discussed by Eliana Fu of Trumpf in a presentation on the use of green lasers in this sector — the "best kept secret in laser additive manufacturing," according to Fu. "Green Laser technology developed from the traditional laser cutting and welding sector, when applied to 3D printing, makes sense in terms of achieving results with better density, lower porosity, better surface finish, less spatter and improved productivity — depending on the part and parameters used, up to ten times faster than an infrared laser source with pure copper powder."

Tim Hayes is a freelance writer based in the UK. He was previously industry editor of optics.org and Optics & Laser Europe magazine. This article originally appeared in the 2022 SPIE Photonics West Show Daily.