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Investigating Properties of Virgin, Sieved, and Waste 316L Metallic Powder for SLM 3D Printing

We often see metal 3D printing used to make steel parts, so plenty of research is being done regarding the material properties. Researchers from VSB – Technical University of Ostrava in the Czech Republic published a paper, “Research of 316L Metallic Powder for Use in SLM 3D Printing,” about investigating Renishaw’s AISI 316L powder for use in Selective Laser Melting (SLM) technology.

“Understanding the SLM process is extremely challenging, not only because of the large number of thermal, mechanical and chemical phenomena that take place here, but also in terms of metallurgy. The presence of three states (solid, liquid, gaseous) complicates the ability to analyze and formulate a model formula for proper simulation and prediction of part performance when printed,” they explained. “Since the SLM process operates on a powder basis, this process is more complicated by another factor compared to the use of other bulk material. The properties of the used printing powder define to a large extent the quality of the finished part.”

Because the material can impact an SLM 3D printed part’s final properties, powder research should be done ahead of time for best results. Particle size, shape, flowability, morphology, and size distribution are key factors in making a homogeneous powder layer, and using gas atomization to produce spherical particles helps achieve high packing density; this can also be improved with small particles.

The researchers investigated three phases of metallic powder present in the SLM process – virgin powder (manufacturer-supplied), test powder that had been sieved 30 times, and waste powder “that had settled in the sieve and was no longer being processed and disposed of.” They used a non-magnetic austenitic stainless steel, alloyed with elements like nickel and chromium and containing a low percentage of carbon.

Scanning electron microscopy (SEM) was used to investigate the powder morphology, which “affects the application of metal powder by laser in terms of fluidity and packing density.” First, the shape of the powder particles was measured and evaluated, and then a visual quality evaluation was completed to look at the spherical quality and satellite (shape irregularity) content. The team found that many particles had satellites, but that this number increased in over-sized powder.

Fig. 1. SEM image of virgin powder 316L, magnification x180

“The measurement of virgin powder (Fig. 1) reveals that the production of powder by gas atomization is not perfect and the shape of some particles is not perfectly spherical,” the researchers wrote. “It is also possible to observe satellites (small particles glued to larger ones, Fig. 2), which are again a defect of the production method.”

Fig. 2. Satellite illustration, magnification x900

They found that the particle shape was “not always isometric,” and that cylindrical, elongated, and irregular shapes appeared alongside spherical particles in over-sized powders.

“Another interesting phenomenon was manifested in the sieved powder, where particles with a smoother and more spherical surface were observed than the original particles. This is most likely due to the melting and solidification process that is specific to AM,” they noted.

Fig. 3. Morphological defects – a) particle fusion; b) gas impurities; c) agglomeration – sintered particle;
d) dendritic particle structure; e) spherical particle; f) particles with a satellite

An optical method was used to measure powder porosity. The 316L powder was embedded in a resin, and was “1 mm layer abraded” post-curing before the particles were cut in half and polished with diamond paste. The images captured via microscope were loaded into analysis software, which determined that the total density of the powder was 99.785%.

“In general, pores must be closed from 3/4 of their circumference to be considered pores,” the team explained. “Particles that do not comply with this rule are automatically considered irregular particles.”

Fig. 4. An example of open pores that correspond to the rule (L), and pores that do not conform (R)

The researchers also measured the size of all individual pores and recorded which ones began at 5 µm, though they noted that due to potential image resolution issues, “pore sizes of about 5-8 μm should be taken with some uncertainty.”

Fig. 5. Pore size measurement of 316L metallic powder

A histogram showed that, in the metallic powder particles, the “15 µm pore size was most present,” and that the largest was 30 µm.

Table 3. Measured values of porosity of powder particles

Finally, they used an optical method to measure and examine grain size distribution of the virgin and sifted powder. Using 200x magnification, measurements were taken at five random locations, each of which had roughly 200 particles on which they performed static analysis. The results were processed with statistical software, which created cumulative curves to indicate how many particles were smaller or larger than a certain size.

“Of these, the quantiles d10, d50 and d90 were obtained, which express the cut-off limit within which the size falls to 10, 50, 90 % of the measured particles,” they wrote.

The average particle size only increases a little by repeatedly sieving the metallic powder, but because of irregular particles, agglomerated or molten particles larger than 45 μm, they fall through the mesh. Results show that <10 µm particles are reduced, while larger particles are increased, in the sift powder. But, the team notes that the powder is still usable.

“The sift powder showed an increase in particle volume and surface area while circularity decreased, indicating that virgin powder generally has a higher sphericity,” the team explained.

They found defects like agglomeration, gas impurities, and particulate fusions at all three stages, but since the powder is still usable, they concluded that SLM is both an economic and ecological technology. The researchers listed several measures to take in order to “achieve the best possible consolidation,” such as high purity, fine surface, low internal porosity, tight particle distribution, and as few surface pores and satellites as possible.

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3D Printing News Briefs: May 12, 2020 Nanofabrica, Voxeljet, Elementum, AMPOWER

We’re all business today in 3D Printing News Briefs – Nanofabrica has raised $4 million in funding, and voxeljet is expanding its presence in India. Elementum 3D has achieved an important industry certification. Finally, AMPOWER has released its 2020 report.

Nanofabrica Raises $4 Million in Funding

Tel Aviv startup Nanofabrica, which makes 3D printers for fabricating complex electronic and optical parts for semiconductors and medical devices, has raised $4 million in funding, and the round was led by Microsoft’s venture arm M12, which invests in enterprise software companies in Series A through C funding with a focus on infrastructure, applied AI, business applications, and security, and NextLeap Ventures, an investor group made of former Intel Corp employees. The startup says it will use the funding – it’s raised a total of $7 million so far – to expand its sales and continue its R&D work.

M12 partner Matthew Goldstein said, “Nanoscale, precision manufacturing is a growing need for R&D organizations, as well as production-scale manufacturing companies,” and that the technology allows for the “digital mass manufacturing of precision parts.”

voxeljet Grows Presence in India with Sale of VX4000

The VX4000 is voxeljet’s largest 3D printer and has a building volume of 8 cubic meters

Industrial 3D printing solutions provider voxeljet AG has expanded its Asian presence with the announcement that Indian steel casting experts Peekay Steel Castings Pvt Ltd is investing in its 4000 x 2000 x 1000 mm VX4000 3D printer – the company’s largest industrial system. Peekay Steel, which makes high-quality steel castings, will use the printer to expand into new business areas and better cater to its current clients’ increasing demands. The flexibility, size, and speed of the VX4000 will allow the company to continue supporting the foundry industry in its native India, but also give them the opportunity to build a new Knowledge Center centered around the large 3D printer that will provide open access to a training facility. The VX4000 will be set up at a new Bangalore location in the Airport City.

“We want to offer our customers an end-to-end solution and position ourselves as a supplier of high-quality, ready-to-install components in record times. With the VX4000, we are able to increase the flexibility of our production in order to be able to react quickly, even to complex projects,” said K.E. Shanavaz, Jt., Managing Director, Peekay Steel Castings (P) Ltd. “3D printing gives us a unique competitive advantage, especially when it comes to expanding our business areas. Since the beginning, we have emphasized the importance of co engineering with our customers, most of these are Fortune 500 companies, to optimize and customize the product design, to lend better functionality and a clear competitive advantage. A specialized Design Center aligned to the VX4000 will help add value for our customers.”

Elementum 3D Achieves Quality Management Certification

Colorado metal 3D printing materials company Elementum 3D announced that it has received the important ISO 9001:2015 certification. This is recognized as the worldwide standard for quality management practices and systems, and was issued to the company through the Denver-based ISO 9001 management certification firm Platinum Registration, Inc. The scope of its certification includes manufacturing prototype and production parts to customer specifications, designing and manufacturing advanced composites, metals, and superalloys, and developing new manufacturing processes.

“This is an important milestone for Elementum 3D. It’s a rigorous process to become ISO 9001 certified. Our staff worked very hard with Platinum Registration’s auditors to demonstrate we meet the requirements of the standard. Not only does that make us feel confident we’re the most efficient that we can be, it assures our customers that we have a completely transparent and robust management system; and that means we have reliable, repeatable, continuously improving business processes so that our customers receive the best value for their money,” said Dr. Jacob Nuechterlein, Elementum 3D President and Founder.

AMPOWER Releases 2020 Metal AM Report

Metal additive manufacturing consultancy AMPOWER has released its new 2020 report, containing analysis based on over 250 data sets of metal AM supplier and user surveys. If you purchased the previous AMPOWER Report, you can get the latest edition for free through the online portal, or you could subscribe to the report to start getting it; either way, the publication is chock-full of helpful information. For instance, a separate section analyzes the possible impact scenarios of the COVID-19 pandemic on the metal AM industry in both 2020 and 2021, and new contributions from the worlds of standards and startups are included from ASTM and AM Ventures, respectively. The report includes in-depth market data, and has also added new databases with over 700 entries, so readers can browse through a list of material, service, and systems suppliers; the new interactive cost calculator has been updated with the most recent productivity values.

“We hope the AMPOWER Report 2020 continues to support our customers in making the right decisions in these challenging times,” AMPOWER’s Matthias Schmidt-Lehr, Dr. Maximilian Munsch, and Dr. Eric Wycisk wrote in an email.

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SLM Solutions Webinar: “We Want to Give our Customers the Freedom to Innovate”

A new webinar series by 3D metal printer manufacturer SLM Solutions showcases its system’s ability to empower customers to grow in the ever-evolving additive manufacturing (AM) marketplace. For many 3D printing companies, webinars are turning into a fundamental tool to create awareness about new developments and to identify customer needs. For the German-based top metal 3D printing supplier, this new series of webinars can draw in users in search of cost-efficient, fast, and reliable Selective Laser Melting (SLM, DMLS, Powder Bed Fusion) 3D printers for part production, which is the core development at SLM Solutions.

During the hour-long educational talk through the advantages of true open architecture in AM, the Director of Industrialization Strategy for SLM Solutions Americas, Thomas Haymond, explores the company’s goal: building a system that grows with the user. By opening up the system’s architecture, SLM Solutions wants to prove that customers will never outgrow the machines and instead be able to adapt their businesses, reduce their learning curve, and innovate from day one. 

Defined by Haymond as a system that allows for full user access, where there are no closed doors, and essentially everything about the system and its inherent variables is fully discoverable, open-architecture systems are unquestionably important to the company. So, what are the key elements? Haymond defined four:

  1. Powder variety
  2. Open process parameters
  3. Freedom to control variables
  4. Customized development

Certainly, many metal 3D printing manufacturers offer open access to certain aspects of their systems, however, SLM Solutions claims that its product is different and unique because there are no additional requirements associated with it. 

“The initial variable of powder variability is an open architecture element we recognize and we will support you with. Empowering the user to understand this intricate knowledge expedites their evolution and turns them into power users of additive manufacturing technology,” asserted Haymond. “By providing the ability to utilize an unlimited variety of raw materials, opening the doors on all of our parameter configurations, and educating the customer on how to transform all facets of built strategy parameters, we are enabling them to apply the SLM technology in whatever direction they choose.”

Achieving a successful build is heavily dependant on the powder being used, which according to Haymond, is arguably one of the most important system-level variables. In fact, he considers that the first key element of an open architecture system is the ability to vary the raw material, emphasizing the importance of powder quality and variety. That is why SLM Solutions offers a wide assortment of materials, from the traditional to the rather exotic more advanced AM powders, as well as a few new aluminum alloys which they have yet to release.

“So, why is powder critical to success? Powder specifications are critical to succesfull builds. We understand that there is a need for material diversity as this industry is constantly growing and establishing new applications. In the old additive manufacturing world, it was about processing properties and performance; but in the metal additive manufacturing world, powder drives processing, drives properties and ultimately drives performance, something we call P4.”

One of the big perks of SLM Solutions systems is that they work with external powders. Haymond described that there are no fees, penalties, or stigma associated with sourcing raw materials for their SLM systems. However, he indicated that “while we do permit these external powder use we do so with a number of recommendations with respect to powder quality and powder specifications that are critical to building quality and success.”

When customers choose to source powder externally the company claims they will walk them through the three basic requirements, that is flowability, moisture content, and particle size distribution.

SLM Solutions manufacturing headquarters in Lübeck, Germany (Credit: SLM Solutions)

To encourage user development, SLM Solutions said they develop and provide parameters for each of its released materials. The open process parameters are the materials and parts in specific settings that can be varied and impact a user’s build quality. Haymond indicated that there is no need to actively edit any of these available parameter settings, but they are open in case a customer wishes to do alter them in pursuit of a specific development objective. 

“When you purchase one of our systems, you are guaranteed to have access to all build strategies that we have released. Furthermore, the software that we have developed around parameter modification and material development is a very detailed sweep that allows our customers to explore the intricacies of the build strategies that we have released. It is designed to provide the user with as much functionality, information, sensor feedback, and flexibility that is really possible. Both SLM solutions software, that is the Build Processor and the Material Development Module (MDM), facilitate the variation of every available parameter in a very user-friendly fashion, as we strive to provide the most comprehensive software for our customers.” 

Haymond suggested that this access essentially allows users to understand the logic behind the systems’ parameter structure, and learn how to create similar constructs for themselves in pursuit of their growth with SLM Solutions machines, and within the AM industry itself.

“Additionally, through providing this unparalleled level of access we are enabling significant cost and time savings for the development of new materials or the development of new exposure strategies for established materials.”

SLM Solutions machines (Credit: SLM Solutions)

There is no real limit to the number of combinations for a given material family. And SLM Solutions makes it unnecessary to edit the variables because the parameters they claim to provide for any given material are deemed to produce ideal mechanical and physical properties for a wide range of geometries. Yet, like in the previous two elements of open-architecture systems, the company believes that having the freedom to control variables will enhance the user’s experience, allowing them to innovate and grow with the system and technology. 

All the variables are modified with the Build Processor. Haymond explained that they “found many of our customers begin their path to custom development with the use of a new material not currently offered with an optimized parameter set.” So SLM has developed a unique tool within the built processor software, the MDM, which facilitates the automatic varying of individual parameters and will also automatically assign the matrix of parameters across the given build platform. Haymond proposes that users who have experienced a new material development will appreciate that they will no longer have to laboriously and tediously create each individual parameter set and type it in by hand and then assign it to the parts. Instead, the MDM software eliminates all this time consuming and error-prone activities.

“Essentially the MDM allows the user the ability to perform a systematic analysis of the part parameter variation. It is an incredibly useful tool, mostly focused around the editing of the basic parameters. The software is designed to utilize the user-specific rules to create matrices of every parameter setting. So once customers decide which parameters they wish to study and establish their relative boundary conditions the rule editor can be utilized to build the matrix.”

One of the primary tenants of open architecture philosophy means altering and modifying all parameter variables, which will eventually lead to customized development. That’s the goal for SLM Solutions: providing capability of complete customization gives the user freedom.

SLM Solutions machines at work (Credit: SLM Solutions)

As the AM world develops, SLM Solutions asserted that they will continue to develop and release material and process parameter combinations. Even more so, Haymond stated that the “needs of our customers can sometimes outpace our efforts, and rather than forcing our customers to wait for us we choose to empower them to continually strive for the rise of metal AM, using our machines as their vessels.”

“Essentially, it all boils down to providing the capability that the user needs to customize the development. We feel that we want to provide an open architecture to allow customers to grow because this is such a new industry with so much potential, and we are still in the infancy of its development, furthermore, without the flexibility of open architecture, you’ll be forever catching up to market trends. Instead, we want to empower our customers to be the trendsetters.”

High-quality SLM additive manufacturing machines have high costs, especially if parts aren’t optimized or designed for the process. SLM Solutions’ approach to creating true open architecture manufacturing systems expects to offer customers full access to every aspect of the system and its inherent variables, enabling them to optimize their systems. As discussed in the webinar, providing accessibility to control variables and parameters can take the users to new levels. 

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VELO3D Develops Process for 3D Printing Aluminum F357 on Sapphire Systems

California-headquartered digital manufacturing company VELO3D, which recently raised $28 million in a Series D funding round, just announced that it has developed a process for 3D printing parts out of foundry-grade Aluminum F357 on its Sapphire metal 3D printers. The commercial release of this capability is significant, because the material is traditionally manufactured with casting technology, but now it can be 3D printed in intricate, complex shapes that casting just can’t achieve.

“Aluminum F357 has already been certified for mission-critical applications—unlike some exotic alloys—so it was a logical addition to our materials portfolio. We will continue to add more compatible materials that enable customers to print parts they couldn’t before, yet with even better material properties than traditional manufacturing,” explained VELO3D Founder and CEO Benny Buller.

This aircraft-grade aluminum alloy, which is well-suited for laser powder bed fusion 3D printing, lets companies in the aerospace, defense, and military sectors 3D print parts that used to be made through casting. Specific components that VELO3D specializes in 3D printing with Aluminum F357 are for thin-walled heat transfer applications.

These photos of 3D printed components demonstrate various perspectives of the design freedom that VELO3D’s SupportFree capabilities offer when it comes to heat exchangers.

VELO3D worked with global advanced cooling solutions supplier PWR to develop the Sapphire metal 3D printing process for Aluminum F357. This was a smart partnership, as PWR has provided cooling solutions to several racing series, including Formula 1 and NASCAR, and customers in the aerospace, automotive, and military industries.

Matthew Bryson, General Manager for PWR, said, “We chose Aluminum F357 due to its ideal material properties to suit thermal performance, machining and weldability.

“Our ability to print free-form and lightweight structures for heat transfer applications with our Sapphire system from VELO3D will further enhance performance and packaging optimization opportunities for our product range and provide significant value to our customers.”

VELO3D’s patented SupportFree capability for metal 3D printing means that support structures for steep overhangs, low angles, and complex passageways are not required, allowing users to attain geometric freedom. The Sapphire metal 3D printing system is built with a semiconductor mindset to ensure repeatability in serial manufacturing, and paired with a con-contact recoater, its print process is able to fabricate the high aspect ratios and extremely thin wall structures needed for flight-critical applications.

Notice the ultra-thin features in the core (cross-section image). Such complexity is near-impossible to attain with existing AM technologies.

While other aluminum alloys, like AlSi10Mg, are used in metal 3D printing more often, Aluminum F357 is ideal for thin-walled AM applications due to shared characteristics with popular casting alloy A356, and because it can be anodized. SmarTech Analysis reports that aluminum alloys accounted for close to 10% of 3D printed metal content last year, which led to a 43% growth in shipments of aluminum powder. The lightweight material is obviously growing in AM popularity, as VELO3D wasn’t the only company this week to roll out the material – Optomec just announced the use of its LENS DED systems for 3D printing aluminum parts.

VELO3D’s Sapphire metal 3D printer is now compatible with Aluminum F357, INCONEL alloy 718, and Titanium64. If you’re interested in a 3D printed aluminum alloy prototype, contact the company. Last month, VELO3D also announced that a 1-meter tall Sapphire system would be available in Q4 2020 for industrial customers, like Knust-Godwin, interested in using LPBF technology to print tall parts without supports.

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Interview with Roscher Van Tonder on Simplified Manufacturing with Additive Manufacturing

Roscher Van Tonder

Managing Director and Founder of AMTC, Roscher Van Tonder takes us through an interesting topic on Simplified Manufacturing in 3D Printing and Additive Manufacturing. Currently based and operating in South Africa, Roscher is actively involved in the sector through consulting and printing as a service.

What is it that you do? 

The manufacturing world is changing and it is daunting to many companies out there, the rise of I4.0 has a lot of people unsure of what the correct direction is for the business relating to AM.

AMTC Pty Ltd goal is to supply a unique set of systems, strategies, additive manufacturing equipment, and materials to our customers and to cater for a wide range of industries ranging from, Aerospace, Automotive, Manufacturing industry, Mining, Oil & Gas, Metal Casting to the Defence industries.

Our scope is to assist companies to adopt AM by creating successful business cases with exceptional ROI. These business cases complement the current business workflow. We look at the business as a whole and we identify the core areas where the maximum benefit will be reached by implementing AM for sustainable successes.

AM-WorX addresses all the business areas to ensure total coverage and ensures maximum benefit to the bottom line.

The main stages of AM-WorX

  • An onsite audit (Gauge potential AMT scope)
  • Business readiness analyst (Current and lacking AM Experience/Gaps/Skills )
  • Market review ( current and potential new markets and opportunities)
  • Parts/Product review (Ascertain the printability of the product/parts)
  • Develop the new processes and skill framework for AMT integration

By aligning with some of the bleeding edge technology companies out there the result is a business case that shows a minimum potential revenue increase compared to current company revenue over the planning horizon by showing the 10x Value guarantee by unlockable the value of AMT in the business.

Can you also explain the Simplified Manufacturing line of thought concerning 3D printing and Additive Manufacturing?

Our slogan “simplified manufacturing” comes from the benefits that technology brings to the table.

Time Reduction of the new product to market.

Additive Manufacturing has been seen as an R&D tool, the last 2 years the change to the final product has taken shape. The company that gets the product out into the market the fastest has the leverage, the technology typically cuts these times by 40-60%.

Customization & Mass customization

The instant gratification culture created by online stores and the internet is spilling over to the manufacturing industry. The ability of a company to leverage mass customization will give them an advantage on their competition, Additive manufacturing is allowing companies to move away from minimum batch volumes and give the freedom to offer customized products on-demand as per customer preference in a short amount of time.

 

Various Products and models from Prototyping to Mass Customization

On Demand Manufacturing

One of the biggest benefits of Additive Manufacturing is that it enables on-demand manufacturing. The ability to manufacture parts at the point of need points to a shift from “make-to-stock” to a more sustainable “make-to-order” model for low-volume production of spare parts.

Lead Time reduction

Hydroforming is primarily used for low volume forming of sheet metal parts while thermoforming is mainly used for high volume forming of plastic sheets. The tooling used in these processes is typically produced by CNC machining of materials such as aluminum or wood which typically involves high costs and long lead times. Additive manufacturing makes it possible to substantially reduce the cost and lead time involved in making these tools while offering additional design freedom and reducing tooling weight.

Simplified Manufacturing process

Part consolidation

AM is uniquely capable of producing complex geometries that can’t be manufactured using legacy manufacturing. A mechanical assembly that would normally have many parts fabricated as separate components and then assembled can be additively manufactured as a single unit, even if the geometry is very complex. In addition to design simplification, there are other tangible benefits to using AM for part consolidation. This leads to lower overall project costs, less material, lower overall risk, better performance.

Tool-less manufacturing

We give users the ability to deliver end-use parts directly from CAD files, saving cost by cutting out tooling requirements. Benefits: Accuracy and repeatable production, High-speed printing production, Material flexibility, and versatility, improved time-to-market and part mass-customization, Low Total Cost of Operation (TCO) and low per part cost & scalable options to meet growing needs.

Manufacturing Process step reduction

The technology can reduce current legacy manufacturing processes by up to 70%. Cost-saving implications are extensive as well as risk reduction and resource savings to the company. For exaample, in an investment cast application AM can reduce the production steps from 7 steps to 3 steps.

What impact can Simplified manufacturing with 3D Printing have, especially on African economies?

We believe that Africa is sitting on an opportunity that could change the Africa continent forever. AM technology brings the ability for SMEs to not just compete but to lead supply of manufactured parts, become self-sufficient, by exporting final products that are created from our raw materials, creating sustainable economies throughout Africa. The danger is if we miss this opportunity Africa will probably never become a major player in the manufacturing world. Why should we be following if we can lead?

Are companies especially in supply chain ready or prepared for 3D printing?

The process of manufacturing, storing, and delivering spare parts is a time-consuming and laborious one for OEM, s and remote operations. Costly warehouse, transport & logistics, storage of spare parts in addition to time-intensive lead times and shipping are just some of the difficulties faced. I believe that some Multi-national companies are getting ready, however in South Africa only a handful are starting to look at AM. As Africans, we are very slow to change and adapt to “New” we don’t like change and have a mentality of “if it’s not broken why fix it” and this is hindering the widespread adoption of AM.

The change and adoption must come with a clear vision from top management that drives the vision, this is a new way of doing things potential changing the whole business model and logistics will be one of the hardest hits I believe. Savings of 30-60% on stock holding can be achieved with AM.

 

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Texas A&M: A Method for 3D Printing Porosity Free Martensitic Steels

While seeking a corrosion-resistant alloy for gun barrels in 1912, British researcher Harry Brearley, who is commonly regarded as the inventor of stainless steel, discovered a martensitic stainless steel alloy. Although several variants of steel exist today, this type particularly stands out from its steel cousins as stronger and more cost-effective to produce. The renowned metallurgist probably never thought that his breakthrough discovery would go beyond developing affordable cutlery to the masses, well into applications in the aerospace, medical, automotive, and defense industries. Now over 100 years later, it can also be used as a metal 3D printing material for complex designs.

However, for these and other applications, the metals have to be built into complex structures with minimal loss of strength and durability, which is why researchers from Texas A&M University, in collaboration with scientists in the Air Force Research Laboratory, have developed guidelines that allow 3D printing of martensitic steels into very sturdy, defect-free objects of nearly any shape.

Reported in the scientific journal Acta Materialia, the findings of their study suggest that the process optimization framework introduced is expected to allow the successful printing of new materials in an accelerated fashion and introduces the process parameters for building porosity-free parts.

Although the procedure developed was initially for martensitic steels, the researchers said they have made their guidelines general enough so that the same 3D printing pipeline can be used to build intricate objects from other metals and alloys as well.

“Strong and tough steels have tremendous applications but the strongest ones are usually expensive — the one exception being martensitic steels that are relatively inexpensive, costing less than a dollar per pound,” said Ibrahim Karaman, Chevron Professor and head of the Department of Materials Science and Engineering at Texas A&M. “We have developed a framework so that 3D printing of these hard steels is possible into any desired geometry and the final object will be virtually defect-free.”

A flowchart summarizing the framework, introduced in this study (Credit: An ultra-high strength martensitic steel fabricated using selective laser melting additive manufacturing: Densification, microstructure, and mechanical properties)

The high-strength, lightweight, and cost-effective martensite steels are formed when steels are heated to extremely high temperatures and then rapidly cooled. The sudden cooling unnaturally confines carbon atoms within iron crystals, giving martensitic steel its signature strength.

Texas A&M claimed that to have diverse applications, martensitic steels, particularly a recently discovered type of low-alloy, ultra-high-strength martensitic steel known as AF9628, need to be assembled into objects of different shapes and sizes depending on the particular application they will be used for, and that’s when additive manufacturing (AM) offers a practical solution.

Stainless steels can be used to 3D print complex designs that are normally impossible to fulfill. 3D printing methods initially used by the team to build complex items were direct metal laser sintering (DMLS) aka selective laser melting (SLM) and also known as Powder Bed Fusion. However, Texas A&M researchers detected that 3D printing martensitic steels using lasers can introduce unintended defects in the form of pores within the material. Moreover, they detected that there is currently no known work describing process-structure-property relationships for AF9628 in the context of AM, something they considered should be systematically studied, focusing on the effects of AM process parameters on the microstructural evolution and resulting mechanical properties of this new martensitic steel.

“Porosities are tiny holes that can sharply reduce the strength of the final 3D printed object, even if the raw material used for 3D printing is very strong,” Karaman said. “To find practical applications for the new martensitic steel, we needed to go back to the drawing board and investigate which laser settings could prevent these defects.”

In an effort to produce high strength parts with a high degree of control over geometry, the researchers presented the effects of the SLM parameters on the microstructure and mechanical properties of the new steel AF9628.

For their experiments, Karaman and his team first chose an existing mathematical model, called Eagar-Tsai, inspired from welding to predict the melt pool geometry, that is, how a single layer of martensitic steel powder would melt for different settings for laser speed and power. By comparing the type and number of defects they observed in a single track of melted powder with the model’s predictions, they were able to change their existing framework slightly so that subsequent predictions improved.

They claim that after a few of these iterations, their framework could correctly forecast, without needing additional experiments, if a new, untested set of laser settings would lead to defects in the martensitic steel.

Raiyan Seede, a graduate student in the College of Engineering at Texas A&M and the primary author of the study, explained that “testing the entire range of laser setting possibilities to evaluate which ones may lead to defects is extremely time-consuming, and at times, even impractical. By combining experiments and modeling, we were able to develop a simple, quick, step-by-step procedure that can be used to determine which setting would work best for 3D printing of martensitic steels.”

Seede also noted that although their guidelines were developed to ensure that martensitic steels can be printed devoid of deformities, their framework can be used to print with any other metal. He said this expanded application is because their framework can be adapted to match the observations from single-track experiments for any given metal.

“Although we started with a focus on 3D printing of martensitic steels, we have since created a more universal printing pipeline,” Karaman indicated. “Also, our guidelines simplify the art of 3D printing metals so that the final product is without porosities, which is an important development for all type of metal additive manufacturing industries that make parts as simple as screws to more complex ones like landing gears, gearboxes or turbines.”

Backscattered electron images of the etched cross-sections of AF9628 ultra-high strength martensitic steel as-printed cubes. The yellow dotted lines indicate melt pool boundaries (Credit: An ultra-high strength martensitic steel fabricated using selective laser melting additive manufacturing: Densification, microstructure, and mechanical properties)

This research, funded by the Army Research Office and the Air Force Research Laboratory, reports a successful methodology to determine optimal processing parameters, like laser power, laser scan speed, and hatch spacing, in selective laser melting AM in order to fabricate porosity-free parts.

The team of researchers effectively used it to fabricate fully dense samples over a wide range of process parameters, allowing the construction of an SLM processing map for the new martensitic steel alloy AF9628. Given the potential of this new high-performance steel, useful for machine tool components, structural components for aircraft gear, automotive parts, and even for ballistic armor plates, creating a new framework offers the potential to 3D print this new material much quicker, providing a powerful tool to many industries.

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International Researchers Analyze Corrosion Properties in 3D Printed AISI 316L Steel

Researchers from the Czech Republic and Poland continue the trend in exploring and expanding materials for 3D printing and additive manufacturing, releasing their findings in the recently published ‘Complex Corrosion Properties of AISI 316L Steel Prepared by 3D Printing Technology for Possible Implant Applications.’

Noting some of the benefits in 3D printing that are specific to this study, the authors mention one of the most important factors: with progressive technology like selective laser melting (SLM), industrial users can look forward to creating complex geometries that may not have been possible before—ultimately resulting in parts that offer better performance and functionality for a wide range of applications.

Many different types of 3D printing technology and materials are opening up a new world of options in the development of parts for aerospace, automotive, and more—but the medical industry has already been widely impacted—especially regarding medical models and medical devices like implants.

While extreme durability is often not required as much for prototypes, as 3D printing has become attractive to users for the fabrication of functional parts, there is often much to be considered—from software, hardware, and materials, to printing parameters that can have a significant effect on mechanical properties and overall quality of components. For medical devices such as implants, biocompatibility and safety for the patient are critical factors too.

Stainless steel and metal 3D printing have been increasing in popularity as users on all levels continue to refine the development and production of functional parts, as well as preventing serious issues like corrosion. As samples were created for this study, the main goal was to compare and analyze the properties of AISI 316L prepared by SLM and classical AISI 316L.

“Investigations were performed on the austenitic stainless steel AISI 316L prepared by the additive manufacturing process from atomized powder certified by Renishaw with an average particle size of 45 ± 15 μm,” explained the researchers.

Chemical composition of atomized AISI 316L powder according to Renishaw certification.

Parameters of SLM process.

Samples were fabricated in the shape of an ‘H,’ cleansed, and then soaked in acetone for five minutes. Middle sections of each sample were then removed to avoid overheating and the possibility of any changes to structure.

Samples for further testing.

All samples displayed porosity, with pore character proving to be ‘analogical for all samples,’ and microcracks apparent in the sharp edges. Very few pores displayed smooth edges, and in those cases, they were connected to gas trapped in the microstructure.

Microstructure of pores in detail, showing nonmelted round particles inside.

Chart of OCP evolution in 169 hours exposition for each sample.

“The corrosion rate obtained by potentiodynamic polarization method was deeply under the recommended limit. The reference sample demonstrated the most promising results of corrosion rate, especially after 169 h exposure,” concluded the researchers. “The highest values of corrosion rate were measured for the sample after 1050 °C heat treatment and after 1 h exposition in saline solution. The signs of corrosion came in the form of the selective dissolving of microstructural components, leaving cellular-like reliefs on the exposed surfaces rather than in the corrosion pits.”

“According to these results, SLM stainless steel AISI 316 shows promising properties for manufacturing medical instruments or implants, preferably for short term implantations. It was proven that heat treatment of SLM samples from AISI 316 increases their corrosion rate under the conditions of the human body. According to the results from this study, high temperature heat treatment should not be used for implants with long-term applications, wherein the amount of released ions from corroded material increases with time.”

What do you think of this news? Let us know your thoughts; join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘Complex Corrosion Properties of AISI 316L Steel Prepared by 3D Printing Technology for Possible Implant Applications’]

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German Manufacturers Heraeus AMLOY and TRUMPF Collaborate to 3D Print Industrial Amorphous Parts

Two German companies are collaborating to begin 3D printing industrial amorphous metals—also known as metallic glass and twice as strong as steel—offering greater elasticity and the potential to produce lightweight products. Heraeus AMLOY brings expertise in the production and processing of amorphous metals while TRUMPF introduces powerful experience in additive manufacturing.

Amorphous expansion sleeve
(Source: Heraeus AMLOY)

The overall goal in this partnership is to see amorphous parts take their place in standard production, as well as enjoying the many benefits offered by 3D printing, mainly in affordability and better performance in production. Another added bonus is that 3D printing offers engineers much greater latitude during 3D design and printing, not only meaning that they are able to work on-demand for parts but they can also create and make changes to prototypes or components quickly without a middleman.

Amorphous parts display isotropic behavior, evident in materials like glass or metal—meaning that properties are the same in every direction. Applications like aerospace and mechanical engineering will benefit especially with the use of amorphous metals in production, as well as the medical field due to biocompatibility.

“Amorphous metals hold potential for numerous industries. For example, they can be used in medical devices – one of the most important industries for additive manufacturing. That is why we believe this collaboration is such a great opportunity to make even more inroads into this key market with our industrial 3D printing systems,” says Klaus Parey, managing director TRUMPF Additive Manufacturing.

TruPrint 2000 – The new TruPrint 2000 3D printer from TRUMPF is the ideal choice for printing amorphous metals from Heraeus AMLOY. (Source: TRUMPF)

3D printing also leads to the potential for new applications with amorphous metals:

“3D printing of amorphous components in industry is still in its infancy. This new collaboration will help us speed up printing processes and improve surface quality, ultimately cutting costs for customers. This will make the technology more suitable for a wider range of applications, some of which will be completely new,” says Jürgen Wachter, head of the Heraeus AMLOY business unit.

It is easy to understand why the two companies see the benefit of using a 3D printer for amorphous metals as they are created via molten metal that cools rapidly. Fabrication can be performed on a large scale and at a lighter weight, reducing the use of materials and eliminating extra waste. Parts can also be created in one piece rather than numerous parts that must be assembled afterward.

Heraeus AMLOY is currently optimizing their amorphous alloys for use with TRUMPF’s TruPrint systems, especially the latest-generation TruPrint 2000 machine.

“Two 300-watt lasers scan the machine’s entire build chamber in parallel. Using a laser focal diameter of just 55 micrometers, users can carry out both low and high-volume production of amorphous parts with extremely high surface quality. The ‘Melt Pool Monitoring’ function automatically monitors the quality of the melt pool, so any errors in the process are spotted at an early stage,” state the companies in a press release sent to 3DPrint.com.

Customers already working with TRUMPF 3D printers can use them for processing of Heraeus AMLOY zirconium-based alloys. Together, the two companies hope to make copper and titanium alloys available to customers for 3D printing soon.

Metal 3D printing is being used around the world today in a variety of industries, to include aerospace, automotive, medical, and more. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

From left to right: The project team from Heraeus AMLOY and TRUMPF Additive Manufacturing: Hans-Jürgen Wachter (Head of Business Unit Heraeus AMLOY), André Kobelt (Chief Commercial and Technology Officer of Heraeus Holding), Moritz Stolpe (Heraeus AMLOY), Valeska Melde (Heraeus AMLOY), Arwed Kilian (TRUMPF Additive Manufacturing), Klaus Parey (Managing Director TRUMPF Additive Manufacturing), JanChristian Schauer (TRUMPF Additive Manufacturing). (Source: Heraeus AMLOY)

[Source / Images: Trumpf Media]

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Improving Foundry Production of Metal Sand Molds via 3D Printing

Saptarshee Mitra has recently published a doctoral thesis, ‘Experimental and numerical characterization of functional properties of sand molds produced by additive manufacturing (3D printing by jet binding) in a fast foundry.’ Delving into hybrid casting and improved methods for creating metal molds, Mitra analyzes varied printing parameters and their effects on mechanical properties.

Centered around improving production in foundries, the author investigates ways to create molds in a completely automated manner, taking advantage of some of the most classic benefits in 3D printing—from greater affordability and faster production time, to better quality in prototypes and parts.

“Besides, the absence of tooling costs makes this process particularly economical, and much complex geometry that cannot be manufactured using traditional sand casting can be reconsidered,” states Mitra. 3D printers are generally faster, easier to use and cheaper than other add-on technologies. It is also possible to make foundry sand molds of extremely small dimensions and very thin parts. Modern foundry industries gradually use this Hybrid Casting technology because they provide ease of sand molding with good surface finish.”

The goal of Mitra’s thesis is to create molds for metal casting with greater stiffness and permeability—ultimately, for use in both the aerospace and automotive industries—applications we have seen significantly impacted by AM processes from car parts to rocket engines, to the qualification of important end-use parts.

(a) Ancient Greece; bronze statue casting circa 450BC, (b) Iron works in early Europe: cast-iron cannons from England circa 1543 [4]

“Sand casting is the most widely used metal casting process in manufacturing, and almost all casting metals can casted in sand molds,” explained Mitra. “Sand castings can range in size from very small to extremely large. Some notable examples of items manufactured in modern industry by sand casting processes are engine blocks, machine tool bases, cylinder heads, pump housings, and valves.”

Metal casting requires:

  • Proper design
  • Suitable choice in material
  • Production of patterns for molds and cores
  • Selection of the casting process
  • Post-processing
  • Quality control

“Three-dimensional printing (3DP) of sand molds using binder jetting technology overcomes challenges faced in the traditional production method, e.g., limitations in terms of part complexity and size, production time and cost (which depends on the quantity and the part complexity, optimization in part design/design freedom for any castable alloys,” states Mitra.

Schematic representation of particle binder bonding and resin

Powder binder jetting process

A series of chemically bonded 3D printed samples were examined. While binder amounts were evaluated by Loss on ignition (LOI) experiments, mechanical strength was measured via standard 3-point bending tests. Permeability was measured by the air flow rate through the ‘samples at a given pressure.’

Mitra learned that molds could be stored extensively at room temperature, but permeability of samples did decrease as temperature was raised.

Printing recipe on ExOne 3D printer

3D printed 3PB test bars and permeability specimens

The author also noted that strength of the molds was ‘profoundly influenced’ by binder content, with increased amounts consequently increased mechanical strength.

“X-ray µ-CT images were used to compute the porosity, pore size, throat size and the permeability of the 3D printed specimens for different binder contents and grain sizes, using analytical and numerical methods,” concluded Mitra. “The permeability predicted in the steady-state was compared with experimental and analytical measurements for layered silica grain arrangement. A major advantage of using X-ray CT characterization is the nondestructive nature of the tests. The computed permeability can be used as input to numerical simulations of metal casting allowing the prediction of macroscopic defects.”

“The present findings represent a step forward towards improved prediction of mass transport properties of the 3DP sand molds. However, further characterization of permeability of such additively processed sand mold should be performed with varying average grain diameter, to check the convergence of the present model. Also, samples printed with other printing process parameters should be studied.”

Steps involved, (a) 3D printing of sand mold, (b) melting iron, (c) casting process
and (d) eroded molded with the respective positioning of thermocouples.

What do you think of this news? Let us know your thoughts; join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

[Source / Images: ‘Experimental and numerical characterization of functional properties of sand molds produced by additive manufacturing (3D printing by jet binding) in a fast foundry’]

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MELD Manufacturing Reaches Major Milestone with Metal 3D Printed Components

Virginia-based company MELD Manufacturing Corporation was launched in the spring of 2018 as a subsidiary of Aeroprobe Corporation, which produces instruments that provide and measure real-time air and flow data. Aeroprobe had been working with the Edison Welding Institute to develop Friction Stir Additive Manufacturing for printing functionally gradient metal components, and founded MELD to continue working on this novel technology.

That’s exactly what the company did. Even though its technology had already been in development for more than a decade, MELD continued making strides to its patented process of creating, and repairing, metal components out of off-the-shelf materials. Not long after its launch, MELD was in the news for winning the RAPID Innovation Award at RAPID + TCT 2018.

“The MELD technology is a revolution. To be recognized at RAPID by these industry leaders demonstrates just how much potential MELD has to change the way we think about manufacturing,” MELD Manufacturing Corporation’s CEO Nanci Hardwick said at the time. ” We want to see MELD adopted across industries, so it’s exciting to see genuine interest from such a diverse crowd.”

MELD Manufacturing Corporation CEO Nanci Hardwick and Production Manager David Smith with measuring tape extended to 1.85 meters (6 feet).

A few months later, the company was selected as a finalist for the global R&D 100 Awards, and is now celebrating a major milestone regarding the size of its metal 3D printed parts. Using off-the-shelf Aluminum 6061, MELD has 3D printed components that are larger than 1.4 meters (55 inches) in diameter; some of these components even have solid walls that are over 102 mm (4 inches) thick!

So, what makes this technology so unique? It can actually print fully dense parts without having to melt any metal. The innovative, solid-state process can be used to 3D print, coat, repair, and join metals and metal matrix composites. By avoiding melting, MELD also avoids issues like hot-cracking and porosity, and uses less energy to produce high-quality parts with full density and low residual stresses.

Large scale components made from off-the-shelf Aluminum 6061 material using the MELD process.

“MELD is uniquely open atmosphere, meaning no special chambers or vacuums are needed. This flexibility not only means less equipment and cost, but also that MELD is scalable and can make parts bigger, better, and faster than other processes,” the MELD website states.

“The combination of material freedom and scalability make MELD a revolution for a wide range of industries, including aerospace, defense, turbomachinery, and many others.”

Due to a decrease in domestic forges and mills, there’s an increased demand for large-scale metal parts, like the ones MELD is now creating, than foreign companies can readily supply. The current COVID-19 pandemic has not made these delays any better, either.

“Prior to the pandemic our customer told us that these parts, printed in a few days at MELD, would have taken them up to two years to get from their supply chain,” Dr. Chase Cox, MELD’s Director of Technology, said in a press release. “This global economic shutdown likely added 6 months or more to that 2-year lead time estimate. MELD represents an opportunity to re-establish domestic manufacturing capability at a critical time.”

MELD Manufacturing Corporation CEO Nanci Hardwick with a large-scale aluminum component built with the MELD process.

MELD’s material is widely used in industry applications, though it’s not compatible with other forms of metal additive manufacturing, and the large size of its 3D printed components is a good example of the advantages in scalability that this type of open-air 3D printer can provide. Large metal structures that are commonly fabricating with forging can now be 3D printed, on-demand, with MELD’s technology.

What do you think about this? Discuss this story, and other 3D printing topics, at 3DPrintBoard.com or share your thoughts in the Facebook comments below. 

(Images provided by MELD Corporation)

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