Category Archives: Laser Materials Processing

Laser Additive Manufacturing’s Journey to Commercialization

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By Andrew Albritton

As seen in LIA TODAY

LASER ADDITIVE MANUFACTURING CHALLENGES

Laser Additive Manufacturing (LAM), as it pertains to powder based manufacturing, is a technique that utilizes the interaction of lasers and base materials to construct a product, rather than removing material from a pre-constructed block of material. LAM is quickly approaching the critical point of being more than a method to produce prototypes and small runs of one-off parts – it is poised to turn everything we know about mass production on its head. Professor Dr. Minlin Zhong, President-Elect of LIA and Director of the Laser Materials Processing Research Center at Tsinghua University, believes it surpasses all available alternative methods.  Prof. Dr. Zhong  says “LAM shows obvious advantages on freeform manufacturing, including free geometry, free structures, free strengthening mechanism, free microstructures, free performance and even free scale (from macro, to meso, to micro, to nano),”. Manufacturers who use LAM are able to reduce the waste of materials commonly associated with traditional subtractive manufacturing methods; decrease the weight of parts by cutting out filler materials; and have more control over material properties resulting in stronger, more complex, lighter, and more efficient parts. With such exceptional technology currently at our disposal, why hasn’t LAM been more widely adopted?

IT’S EXPENSIVE

One of the most commonly cited reasons is that the costs to produce parts through LAM are prohibitive. The key driver of these high costs is that the supply chain for metal powders is not yet optimized for LAM technology. Materials are expensive, custom made, or not readily available. The Metal Powder Industries Federation (MPIF) states in its 2017 PM Industry Roadmap that, “A better understanding of the precursor materials impact on the metal AM process is required. Traditionally, precursor materials have been existing thermal spray powders that have not been refined/tuned to the AM process limiting optimization.” LAM parts producers are often using metal powders that have not been designed for use in LAM processes, which frequently results in suboptimal products.

According to MPIF, as of 2017, there are approximately 12 suppliers of metals for Additive Manufacturing (AM) for the international market, most produce stainless steel, cobalt-chrome, and titanium, with a few supplying aluminum alloys, copper, super alloys, platinum, Inconel, tungsten, molybdenum, and tool steels. With so few suppliers and a sparse number of common material types, there is a bottleneck for providing quality affordable metal powders to the LAM industry. With companies expanding the selection of materials that can be laser processed, it is vital that the problem of material availability be resolved. For example, Nuburu has produced a “blue” laser which operates at the 450 nm wavelength, and is capable of processing gold, aluminum, brass, and copper.

SUPPLY AND DEMAND

What can be done to improve the supply chain and reduce the cost of LAM part production? The metal powder industry does not supply enough quality powder to support widespread adoption of LAM, while early adopters of LAM applications do not create enough demand to drive competition into the metal powder market to reduce prices. A first step to get these industries operating in unison will be the creation and mass adoption of standards, specifications, and best practices in regards to metal powders. By standardizing metal powder properties for best final product properties, metal powder suppliers would be able to build up an inventory without relying on custom special orders. Specifications on how surplus powder from a project can be reused could also help introduce addition cost savings to manufacturers.

STANDARDS FOR QUALITY CONTROL

Another hurdle for LAM is microstructural quality, uniformity, and repeatability. To become a replacement for more legacy manufacturing methods, LAM needs to produce parts consistently and continuously that are to specifications. With traditional subtractive manufacturing methods, there are several quality control points where product is inspected and defects are addressed prior to the next step, resulting in no wasted effort past the point of failure. With LAM, the part in question is created from the ground up; this determines the final product’s quality, microstructure, and mechanical properties simultaneously. The process is completed with either a perfect or defective final product. Paul Denney, Director of Advanced Process Development with IPG Photonics, states, “Unlike machining where you start with a “block” of material with known quality and properties, additive production of parts requires a combination of motion with the prediction of the microstructures, mechanical properties, and stresses. Because the properties are closely connected to how the material is deposited, this greatly complicates the development of processing procedures and parameters.”

What methods can be implemented into a given LAM process to help ensure quality of the final product? The first quality control concerns are addressed long before the process begins. Starting materials must be certified as appropriate for the application, the order of operations of the production device should be scrutinized to ensure that the final product will be to spec with minimal waste, and the machine itself must be operating at peak parameters. As the production of a LAM product can take an extended amount of time, any loss of power to the point of interaction can have detrimental effects to the end product and even the products in queue. Loss of power can be caused by an actual power failure, a dirty or damaged optic, or other origins. With the structural integrity of a LAM part resting critically on the success of every step of the process, it is imperative that the process is stringently optimized and the machine is operating at peak performance. Here is what Paul Denney has to say about the subject:

“Because of the additive manufacturing approach in bed based systems, even if defects can be detected and possibly ‘corrected’, any changes may not be possible. An example of this may be what is done if a ‘defect’ is flagged in a single part in a batch of parts being produced. One approach would be to stop the processing and ‘correct’ the defect. However, if this is done then the thermal history for all of the parts may be altered and all parts may now be out of the desired properties. Another approach would be to stop processing on the part with the defect, but this again would alter the heat load on the complete batch or the time between other parts being produced which may again alter the properties. So any monitoring system will need to detect changes prior to the formation of any defects while at the same time any corrections must be made within the acceptable parameter range.”

There is a thin line between success and failure: one small interruption can ruin an entire batch of product. What can be done to prevent this?

As Paul explained, this is not a single issue, LAM processes need both a method to detect defects and the ability to immediately respond to them. A starting point is to ensure that redundancies are incorporated into the build process so that if a common defect occurs at a certain stage, there are defined responses the system can take automatically to correct them. In the case of a laser lens issue, it may be beneficial to incorporate additional laser delivery systems to the process as a redundancy to pick up where a suboptimal device has failed in real time.

EVALUATING THE FINAL PRODUCT

In addition to inline defect detection, the industry as a whole will require a standardized best practice for evaluating finalized parts. For traditional manufacturing methods, a sample of the produced part pool is selected for evaluation via destructive and non-destructive tests to certify whether a set of parts are built to specifications. As many LAM-produced parts are complex and costly to produce, it seems wasteful to destroy a set of them to certify them. In the paper “Evaluation of 3d-Printed Parts by Means of High-Performance Computer Tomography” presented at ICALEO 2017, authors Lopez, Felgueiras, Grunert, Brückner, Riede, Seidel, Marquardt, Leyens, and Beyer reviewed the viability of X-ray Computer Tomography (CT) and 3d scanning as methods to detect inferior AM parts. The paper concludes that the CT method best fits the needs of the AM industry. According to Lopez et. al, “Computer tomography can quantify all complex structures in scope of the proposed demonstrator and delivered deviation values of the measured structure, providing a good base for comparison across demonstrators made by different methods, materials and dimensions. Porosity or defects down to 3 µm can be determined by the used CT system.” Currently, CT scanning a LAM part is a time consuming process, but with additional focus on improvement it could become an essential quality non-destructive control method for finalized parts to evaluate complex internal structures.

TOO MANY ALTERNATIVES

A third barrier to the spread of LAM is the multitude of alternative methods in the industry. As stated by Prof. Dr. Zhong, “Some conventional metal deposition technologies such as arc building-up welding, plasma building-up welding and electronic building-up welding can also fabricate metallic components in near shape. Their deposition rate and productivity may be high and the costs may be lower, but normally they are limited in fabricating complex geometry and accuracy.” Freeform manufacturing is where LAM excels, but despite its many advantages over alternative methods, it has an Achilles heel.

One advantage of alternative manufacturing methods is the speed at which a product can be produced. However, according to Paul Denney, this speed gap is closing faster every day.

“While higher laser powers allow for higher deposition rates but at the expense of lower resolution, some researchers are looking to maintain the resolution by combining multiple lasers into an additive deposition system. Research groups and equipment builders are investigating how best to handle multiple lasers in the same processing area. There are other areas that may be investigated including power distribution to improve the interaction between the power and laser beam to improve efficiency of the process and to minimize defects. This could improve the deposition rates while at the same time maintaining quality.”

Prof. Dr. Zhong hopes that soon LAM researchers will, “improve the materials diversity, increase the dimension (to square meters), increase the deposition rate and decrease costs. A hybrid approach to combine LAM with the conventional additive manufacturing methods may be a solution to achieve the above targets.” The concept of a hybrid production system that can combine multiple lasers with fast alternative methods where complexity is not a requirement could lend itself to faster build times.

THE LATE ADOPTERS

Earlier in the article, we touched on the final barrier to the wide spread success of LAM: industry standards. Current standard offerings from ASTM and ISO cover Design, Materials and Processes, Terminology, and Test Methods. Additionally, new processes are created frequently and new standards are being developed every year in an attempt to keep up. It is unclear how much of the industry has adopted these existing specifications. Until the entire market accepts a set of standards for all steps of the Additive Manufacturing process and supply chain, the evaluation of AM parts will remain a costly endeavor that will limit AM’s potential. MPIF expresses a bleak outlook on metal AM in its State of the PM Industry in North America – 2017 document: “Despite all the fanfare, true commercial long-run production still revolves around only three product classes: titanium medical implants, cobalt-chrome dental copings, and cobalt-chrome aircraft nozzles.” The truth of the matter remains that without a set of clearly defined standards, the LAM industry will continue to remain confined to early adopters like the Aerospace and Medical fields. With the benefits in intricacy and weight saving advantages LAM should have obvious opportunities in the automotive and electronics industries.

Markets are watching LAM for innovative uses before taking the plunge and embracing the technology. Currently, LAM may appear to have a bad Return on Investment (ROI) if producers only hope to replicate their existing products through LAM rather than innovating their parts to capitalize on its strengths. In the words of Paul Denney, “If AM is supposed to make big impact, companies are going to have to rethink their parts; determine how AM allows for changes in the design and possibly improve the performance. The benefits can come in many forms which could be a weight savings, a production savings, and/or a performance savings.” The industry needs to challenge its way of thinking about production to allow the benefits inherent to LAM to propel their production and parts to new levels of performance. Paul Denney provided the following illustration: “With the formation of properties ‘locally’ instead of in ‘bulk,’ it is possible to produce ‘gradient’ materials. The ‘gradient’ can come by changes to the properties of a given chemistry of material or by using materials with different chemistries. As an example: a bracket could be produced for a jet engine that has high temperature properties near the engine but as the bracket extends to an attachment point, the properties/chemistry can be altered to improve the fatigue properties.”

LAM has a bright future and many engineers and scientists are working to unlock its full potential. Once the barriers of the supply chain, dynamic quality control, speed of production, and process standardization have been resolved, it is highly likely the LAM will be a manufacturing method of choice.

 

ACKNOWLEDGEMENTS

Paul Denney, Director of Advanced Process Development with IPG Photonics and LIA’s Past President

Prof. Dr. Minlin Zhong, Director of Laser Materials Processing Research Center at Tsinghua University

and LIA’s President-Elect

 

References:

Lopez, E., Felgueiras, T., Grunert, C., Brückner, F., Riede, M., Seidel, A., Marquardt, A., Leyens, C., Beyer, E. (2018). Evaluation of 3D-printed parts by means of high-performance computer tomography. Journal of Laser Applications 30, 032307; https://doi.org/10.2351/1.5040644

Superhydrophobic and Superhydrophilic Functionalization of Engineering Surfaces by Laser Texturing

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By Suwas Nikumb, Peter Serles, and Evgueni Bordatchev

As seen in ICALEO 2017 and LIA TODAY

 

Nature is a bountiful source of inspiration to advance innovative surface functionalities, processes, and technologies for engineering materials. For example, the super-hydrophobic surface characteristic of the lotus leaf can be recreated by mimicking the microstructure and surface energy on stainless steels. This super-hydrophobic behavior, which causes water to roll off the lotus leaf while collecting dust particles, enables the self-cleaning of the leaf surface and is primarily due to the hierarchical conical structures, as well as the wax layer present on the leaf surface. A good understanding of the surface topography of the microstructures, water droplet contact angle, and surface chemical composition provides the important clues necessary for the creation of artificial super-hydrophobic or superhydrophilic surfaces and using state-of-the-art ultrafast laser ablation treatment.

Figure 1

Controlling the wettability of a material surface for superhydrophobic or superhydrophilic performance has been an interesting area where numerous different methods are being pursued. While many coatings and thin-films are able to achieve extremely high or low wettability, their endurance life, chemical compatibility, and large area scalability make them less attractive for manufacturing environments. Meanwhile, ultrafast pulsed lasers with several megahertz pulse repetition rates can tune the wettability of a surface without changing its chemical composition and offers higher endurance lives. This is accomplished by instant vaporization (laser ablation) of the material in specific micro-scale patterns thus creating structures that changes the way the surface topography interacts with water.

A superhydrophobic surface is characterized by its ability to repel water using structures that are akin to a bed of nails allowing the water droplet to rest only on the peaks using surface tension and therefore repel from the surface (see Fig.1). Contrarily, a superhydrophilic surface is characterized by its ability to attract and spread the water so features a series of channels that trap water and wick it away using micro-capillary forces. Such surface functionalization techniques have been developed at Canada’s National Research Council for stainless steel (304 SS) and Silicon Carbide (SiC) surfaces respectively to demonstrate the effectiveness of laser texturing technology for wettability control of common engineering surfaces. Fig.2 depicts superhydrophobic performance of a bouncing water droplet at ~5° tilt on 3×3 cm2 textured area.

Experimentally, a 10 W picosecond pulsed laser operating at 1 MHz frequency was focused to a tiny spot of 25 µm diameter. The samples were mounted on a CNC motion system equipped with argon gas protective environment. The optimization of laser structuring process included varying each of the laser parameters, e.g. power, frequency, feed rate, grid pitch, etc. and evaluating the water droplet contact angle using the standard drop-shape analysis method. For the 304 SS superhydrophobic surface, a laser beam fluence of 2.61 J/cm2 was used to promote narrower, shallower features by material redistribution rather than complete vaporization, while the SiC superhydrophilic surface was realized using a much higher fluence of 10.7 J/cm2 to create thicker and deeper channels for the water to impregnate. Both surfaces were machined using the five-axis CNC micromachining system to texture grid patterns, ensuring an even distribution of micro-structures.

Figure 2

 

The superhydrophobicity of 304 SS surface was highly dependent on post-processing conditions in order to tune the wettability. Specifically, the chemical nature of the surface was reactive for 14 days after laser processing due to high-power interaction with the material which excites the chemical state. The samples were thus stored in different environments and exhibited vastly different contact angles. Most notably, the sample which was submerged in deionized water showed hydrophilic tendencies while the sample kept in extremely dry (<8% relative humidity) air was highly superhydrophobic with a contact angle of 152º. Following this two week period, the sample attained stable chemical equilibrium and the wettability was unchanged regardless of environment.

Figure 3

The superhydrophilic SiC surface on the other hand was not as reactive and therefore showed a contact angle of 0º immediately after processing. As aforementioned this sample was intended to have wider and deeper channels to hold and wick the water away from the contact point. The micro-capillary forces that are responsible for spreading the water across the surface were strong enough even to counter gravity; Figure 3 shown below depicts a time-lapse of a 3×3 cm2 textured area placed vertically with the bottom edge in water. Within a 10-second span, the entire surface was wet by the micro-capillary forces pulling water vertically against the force of gravity.

The potential for laser texturing technologies spans many applications in manufacturing industries. Superhydrophobic surfaces have been proposed as a method to mitigate many fluid problems; by decreasing the interaction between a pipe wall and the fluid, the drag experienced by the fluid has been shown to decrease significantly in both laminar and turbulent flows. Thus far, only superhydrophobic coatings and thin-films have been tested for this application however they remain plagued by rapid wear and very short lifetimes. The robustness of the laser texturing process to achieve superhydrophobicity therefore presents exciting new opportunities. As well as water repellency of superhydrophobic surfaces, longer freezing times of water droplets and lower adhesion strength of ice to the surface are characteristics of these high contact angle surfaces and thus present an iceophobic surface property. This enables applications for machinery that operate in colder climates such as wind turbines and airplane wings and engines.

Applications for superhydrophilic surfaces are commonly based on the micro-capillary forces demonstrated as the rapid dispersion creates a thin film of water on the surface. This thin film allows for an increased rate of evaporation from the surface opening doors for anti-fogging applications or greatly increased rates of heat transfer. Other applications manipulate the thickness of the film formed which can provide antireflection ability for surfaces such as solar cells. Superhydrophilic textured surfaces also exhibit increased adhesion strength with the liquid due to the impregnation of the liquid into the surface, therefore providing applications for improvement in bonding strength of joints between different material surfaces.

The wettability control functionalization on engineering surfaces opens the door for new applications with both superhydrophobic and superhydrophilic surfaces. The robust nature of laser surface texturing technologies in combination with chemical compatibility and industrial scalability makes this method unique and most promising to deploy a wide range of functions in manufacturing products. While this technology has already provided solutions to several significant industrial tasks, many more applications are currently being explored at NRC.

 

More details on this topic can be found on YouTube: Combined Wettability Control (https://youtu.be/7IW2aC_rkjw), Super-hydrophobic Bouncing (https://youtu.be/b1vXDuvf3aQ), Super-hydrophilic Ceramic (https://youtu.be/9ZCcW4cOccw), along with other presentations on NRC’s micro/nano-machining capabilities. Further details on these studies can be found in: Superhydrophobic and superhydrophilic functionalized surfaces by picosecond laser texturing. Journal of Laser Applications 30, 032505 (2018); https://doi.org/10.2351/1.5040641

Recap: CO2 vs. fiber laser shootout by Cincinnati Incorporated

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In case you missed today’s CO2-vs.-fiber shootout by Cincinnati Incorporated using its 4,000-watt CL440 CO2 and CL940 fiber lasers to cut identical parts side by side, here’s a quick rundown.

Performed at the company’s Customer Productivity Center in Harrison, Ohio, about 20 miles west of Cincinnati, this demonstration by the longtime LIA exhibitor used their machines to fashion parts out of 20-gauge mild steel, 1/2-inch mild steel and 1/8-inch aluminum. Both systems have identical drive systems.

In broad terms, of course, fiber lasers — which have been carving out more and more market share — cut thinner materials faster, while CO2 performs better with materials thicker than 10 gauge.

The results:

Cincinnati Incorporated pits its CL940 fiber laser against its CL440 CO2 laser.

• 20-gauge mild steel (assisted by shop air): Fiber laser cut the part at 27 seconds at a rate of 2,160 inches per minute vs. 31 seconds for the CO2 laser run at 850 inches per minute. Estimated cost of the process is $6.90 per hour for fiber vs. $9.88 for CO2.
• ½-inch mild steel (oxygen): CO2 cut the part at about 79 seconds at a rate of 60 inches per minute vs. about 99 seconds for fiber run at 45 inches per minute. Estimated hourly operating cost is $6.52 for fiber vs. $10.33 for CO2.
• 1/8-inch aluminum (piercing with nitrogen, cutting with oxygen): Fiber cut the material at 56 seconds at 950 inches per minute (vs. 500 inches per minute if cutting with nitrogen).

Audience polling during the demonstration yielded an interesting look into laser purchasing habits:

• 32 percent said they had two to five lasers in their facility; 30 percent said one, 30 percent said none and 9 percent said more than five.
• 82 percent said they had not purchased a new laser within the past three years.
• 45 percent said they might consider automation with their next laser purchase, 40 percent said yes and 15 percent said no.
• 51 percent said they would be more likely to purchase a fiber laser, 30 percent a CO2 laser, 19 percent unsure.

The presentation is scheduled to be made available at Cincinnati’s website.

— Geoff Giordano

Powder-bed machine’s journey symbolizes N.J. firm’s path toward additive manufacturing

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Imperial Machine & Tool’s SLM280 machine on the exhibit floor at RAPID 2013 in Pittsburgh. Photo by Geoff Giordano

Imperial’s SLM 280 machine at its facility in June 2014. Photo courtesy of Imperial.

As RAPID 2014 wraps up today in Detroit, revisiting the journey of an SLM 280 powder-bed fusion machine purchased at last year’s event by Imperial Machine & Tool of Columbia, N.J., illustrates some of the motives driving U.S. manufacturers toward additive technology.

Imperial is heavily involved in advanced manufacturing — particularly for the Department of Defense — and has spun off a 3D printing operation in nearby Pennsylvania. The company’s purchase of the SLM 280 was part of the company’s $1 million investment in additive manufacturing, says Imperial President Christian M. Joest.

AM “is obviously going to be a game-changer for U.S. manufacturing,” Joest asserts. As a 70-year old company and third generation myself in this business, I’m always interested in longevity. I want to make sure the company’s around for another generation or two.”

Typically, he says, “the company is very forward-looking; we’re not your standard machine shop that’s looking to make 5 cents on every widget that comes through here. Rather, we’re a high-end builder of equipment and components that are challenging. Our focus now is probably slightly different than many others shops like us that would buy this (equipment). I’m not nearly as focused on trying to make a buck on my 3D printer right now as others would be. There are going to be others out there who bought a machine and they want it to pay for itself as soon as it can and keep it paying for itself. That is not my focus.”

Taking the long view Joest’s goal is to “develop this technology — be leaders in the technology development and everything that goes along with it, whether it be training or materials development. We want to hold the hands of our customers as we introduce this new technology so they don’t get bitten. And then everything will follow after that; a rising tide will start to float all boats. The more customers I can get to accept the technology … the better off we all will be.”

A longtime major player in advanced manufacturing techniques, Imperial has decades of experience in multi-axis machining, multi-step processes, rough machining and welding. “We do a lot of military work and a lot of very challenging tech work in unusual materials as well as unusual applications,” Joest explains. “I was always keeping an eye out on new technologies. Rather than just expand our current capabilities — we’re a successful company that generally stays pretty busy — I saw additive manufacturing as an opportunity for us to re-engage with our customers, to have new conversations with folks we’ve been talking to for many years. And for that it has been outstanding. We have engaged with every one of our existing customers, most of all of whom have welcomed this technology with open arms; of course, it’s early in the game.”

But can a well-established company changes gears adequately to get into the game? Joest says his company’s history is a significant advantage.

“We’re already Prime Contractors for the U.S. government. We already know what it takes to meet their contracting requirements. We already know what it takes to go through the quality process. It is not a big step for us; we’re not just an additive manufacturing company that does that and doesn’t know how to do anything else in the world. We’re a manufacturing company that now understands how to additively manufacture pieces and inject that into the production sequence.”

Of late, Imperial has been in conversations with the Navy not only on using AM to field spare parts but also how to set up AM operations. Developing new materials suitable for AM, particularly high-heat materials, is also a priority.

As other experts have noted, most recently at LIA’s sixth-annual Lasers for Manufacturing Workshop in Houston in March, Joest knows that AM’s advancement relies on far more than just the machines. It means powders for additive processes must keep pace — as must the skills required of a 21st-century workforce.

Acknowledging that “lasers are our weakness,” Joest fully expects to engage more at LIA events in the quest to help lead U.S. manufacturing to greater heights. “We will be trying to find out as much as we can about lasers and who the laser people are who can aid us in reaching some of our goals — one of which would require us to understand lasers very, very, very in-depth. I expect to need laser talent either that I’ve contracted for or that I hire.”

For those with the same motives, the fourth-annual Lasers for Manufacturing Event from Sept. 23-24 in Schaumburg, Ill., will be a perfect opportunity to network with top-tier laser equipment suppliers and practitioners in many industries. And for the first time, LIA is holding a Lasers for Manufacturing Summit on Sept. 22 at the LME venue to provide a more intimate AM overview to executives.

Geoff Giordano, veteran editor and art director for newspapers and magazines, has been an editor and reporter for LIA since 2009. Contact him with comments or suggestions at ggiordano@lia.org.

Non-Disruptive, Low Loss In-Line Laser Beam Monitoring System for Industrial Laser Processing

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By Michael Scaggs and Gilbert Haas

The BWA-MON (Beam Waist Analyzer MONitor) system is a “smart” focus head that provides “real-time” laser beam measurement, analysis and monitoring of low to very high power lasers in accordance with international standards ISO11146 and ISO13694 related to lasers without disrupting the laser beam in use and with minimal loss.

Prior to the genus of the BWA-MON, any measurement of a focused laser beam required a complete disruption of the beam; regardless of the application.  Laser manufacturers that develop or research lasers have to align the laser based upon arbitrary conditions, take it to an M-square measurement setup; make a measurement and if not desirable, go back and realign.  This process can take months to fully develop a system.  The BWA-MON aids the laser manufacturer by allowing them to adjust the laser in real time; so there is no need to remove the laser and test in another location and thereby greatly reduce development, setup and alignment time.  Continue reading →