University of Pittsburgh Develops Depowdering Machine for Metal Printing

The University of Pittsburgh has developed a depowdering solution for metal 3D printers that could significantly reduce the cost of 3D printed metal parts. Lead by Professor Albert To, a team of undergraduates has made a gyroscope-based depowdering machine. Professor To is the leader of the AMRL, or ANSYS Additive Manufacturing Research Laboratory, at Pitt and also runs the MOST AM lab, which is a cutting edge lab that develops 3D printing simulation tools. To’s ANSYS AMRL teams decided to attempt a much more hands-on project, however, with this depowdering machine, the Pitt Depowdering Machine.

Why is depowdering important?

Post-processing accounts from anywhere from 30 to 60% of the cost of a metal 3D printed part. Far from a machine driven push-button process metal printing technologies such as Powder Bed Fusion require a high degree of manual labor. Files have to be prepared by hand, support strategies have to be thought up builds have to be nested and material has to be loaded. Once the build is done the parts have to be depowdered. This usually involves a brush and vacuum cleaner. Then parts will also have to be destressed, sawed off, tumbled and may require EDM, CNC, precipitation hardening, shot peening etc. All the while a human operator will be carrying the parts around a factory. The actual 3D printing metal process is still rather artisan even though we’re promising the world that we will make millions of car parts cost-effectively. To bridge this gulf automation will be necessary. Additive Industries is including post-processing steps in the machine others are making lines of machines aimed to reduce the cost. The cool thing about adding automated conveying, destressing, EDM wire, and other systems to an existing line is that these add ons can be used to reduce costs in existing lines and be used with machines from several vendors. All of metal 3D printing’s promises and promise will have to be fulfilled through the nuts and bolts of improving and creating industrial processes. Automated post-processing is a key element of that so Pitt’s machine is very timely to say the least.

Pitt Depowdering Machine

To tells 3DPrint.com,

“The depowdering machine employs a gyroscope design that can rotate the AM build 360 degrees in two orthogonal directions. There is a vibrator that is attached to the build and vibrates the build at a high frequency so that the powders are loosened up and come out from the build as the gyroscope is rotating through different angles. There is a funnel below the gyroscope that is used to collect all the powders coming out from the build. The machine is equipped with two sieves at the bottom of the funnel to sieve the powders to the right size for re-use.”

Such a device has the power to reduce a lot of carrying around and operator time. The speed at which one could depowder a build varies enormously but as per the team’s data they should have a huge productivity increase in terms of time over existing users.

“Typically, we put an AM build on the machine for 15-30 minutes depending on the size of the parts,” To said.

That’s not all, however: the machine may also be more efficient than existing processes.

“In one test, the machine shook out 5 more grams of powders after the technician did his best to depowder manually with the aid of a vibrator.”

A vibrator in a metal 3D printing context is a rotary or tub vibrator or a vibratory finisher which is a machine where parts are mixed in with media and then vibrated to de-clog and remove powder.

If the Pitt machine performs like this in continuous operation the savings could be significant.

To says,  “We are still evaluating whether to commercialize the machine and talking to other people about it at the moment.”

We would strongly encourage them to commercialize this machine. Any in line device that could really reduce the costs of 3D printed parts would make many more metal 3D printing applications possible.

 

Participate in SmarTech’s Metal Additive Manufacturing Survey

Industry analyst firm SmarTech has launched a market survey of the metal additive manufacturing supplier market in advance of its May release of its industry-leading report on metal powder-based additive manufacturing.  The purpose of the survey is to add background information to the firm’s reporting and analysis as well as provide basis for content that will be made available to readers.

The survey is broken out into four segments to account for the issues particular to materials, machines, software and service bureaus.  The questions for each survey take approximately 10 minutes to complete depending on the depth the respondents which to offer. All respondents will receive a formatted and cleaned version of the data output.

SmarTech’s report on metal additive manufacturing with metal powders is the industry standard for research reports of this nature.  Packed with forecasts and analytical insights the report is purchased by a who’s who of industry leaders, contenders and up and coming firms.

For companies looking to participate:

Hardware Suppliers Survey

Software Suppliers Survey

Materials Suppliers Survey

Service Bureaus Survey

Participants who complete the survey also receive a free copy of our Research Note,

Growing Pains: Will the Metal Additive Manufacturing Hardware Market Rebound in 2019? By Scott Dunham, Vice President of Research, SmarTech Analysis

“To use a poorly thought-out metaphor, a dark storm cloud rolled across the metal additive growth party during 2018’s fourth quarter. The result was the first quarterly decline in hardware revenues the market has seen since 2016, when GE Additive shook up the market with billion-dollar acquisitions, leaving customers waiting to see how the market would shake out. From SmarTech’s advisory market tracking services, the metal additive hardware market grew year over year in revenues generated from machine sales during the first three quarters of 2018 but contracted about 9 percent versus the prior year in the fourth quarter –typically the industry’s most important sales quarter. As a result, industry growth in hardware for the calendar year was just under 10 percent –an amount that almost seems paltry compared to the prior five years, and an amount that is likely to cause some executives, board members, and shareholders to raise questions…

3DPrint.com is an equity holder in SmarTech.

Singapore: Researchers Study Effects of Spatter in Large-Scale SLM Printing

Ahmad Anwar, thesis student at Nanyang Technological University in Singapore, explores undesired byproducts of 3D printing in ‘Large scale selective laser melting : study of the effects and removal of spatter by the inert gas flow.’ The topic of spatter is usually considered in regard to imperfections, but here Anwar explores such issues in connection with fabrication on the larger scale too—a necessary method that results in hardware of increasing sizes so that larger parts can be made.

Large scale selective laser sintering can be restricted by powder weight, along with other features such as the number of lasers, and powder bed area. For successful SLM printing, Anwar states that the study of spatter particles is necessary. Spatter is notable due to its size and darker color, and effect on 3D printed layers—along with inducing porosity. The goal of the research study was to find out more about effects of spatter on the manufactured parts, analyze how they impacted mechanical properties, and simulate the activity of spatter in 3D printing during inert gas flow.

Anwar also studied ‘suitable ejection profiles,’ as well as what performance would be like without any inert gas flow at all. The researchers used an SLM Solutions 280 HK machine for their experiments and chose argon as the gas of choice for exploring spatter.”

“With respect to the spatter particles on the powder bed, the mass and size distributions were characterized,” states Anwar. “The Stokes (Suk) number was then used as a parameter to observe the gas flow effectiveness in the spatter transport, which accounts for particles suspended in the gas flow. Image processing was also applied in order to immediately characterize the spatter distribution on the powder bed.”

The researchers set up a camera to monitor spatter and then processed them for comparison with the mass distribution characteristics. As Anwar explains, spatter usually occurs during any SLM printing process as such particles are ejected and often accumulating near processing regions or the powder bed. The volume of spatter is also dependent on energy output like:

  • Laser power
  • Scanning speed
  • Layer thickness
  • Hatch spacing

Schematic of spatter ejection from melt pool and its transport by the inert gas flow (green arrows) in the -x direction.

Higher energy input resulted in larger spatter, increased scattering, and greater jetting height. As the researchers experimented with methods to reduce the spatter, they pumped gas into the chamber:

“For the SLM Solutions machines, argon gas is pumped in from the right to the left side (in the negative x direction). There are two reasons for the introduction of the inert gas; Firstly, oxidation of the molten powder needs to be minimized as much as possible. Hence, scanning only starts when oxygen content is below 0.05%. Secondly, during the scanning itself, the flow of gas aids in the removal of unwanted spatter as a result of the ionized metal vapor and plasma plume that exert recoil pressure on the melt pool,” stated Anwar.

The researchers collected 15 samples of spatter, with each one measured and evaluated after being scooped from a deposit area near the outlet.

“The reasons why we chose to collect the spatter at that area are: (i) it is not possible to collect the spatter directly on the powder bed as it is mixed with fresh powder; (ii) it is not possible either to collect the powder blown out of the outlet, as one cannot completely clean the powder collector (gas filter) between runs; (iii) on the contrary, the region near the outlet where the powder is collected in our experience could be cleaned up several times per run, resulting in reliable results; (iv) finally, it can be safely assumed that the quantity of the powder collected near the outlet is proportional to the total quantity blown out of the powder bed and that its composition is similar,” states the author.

SEM images of A: Fresh powder; B: spatter collected near the outlet observed;
C: Single particle of spatter. D: Sample EDS result of single spatter

Simulations were performed to analyze how gas crossflow contributes to moving spatter away from laser-scanned regions. Argon gas was not substantially impressive in removing spatter to the outlet. The researchers also found that increasing gas flow velocity did not reduce the number of particles in the powder bed.

“Interest in large scale AM processes have generated much research on the issues hindering the development of larger machines, and it is no exception for SLM,” concluded the author. “The prospects of manufacturing larger parts for the aerospace and automotive industries are deemed to be very attractive.

“The results reported from the experimental and simulation studies of the spatter particle distribution on the powder bed could prove to be significantly and scientifically beneficial for the development of an optimized inert gas flow system. In the future, such improvements made to remove spatter particles over a larger powder bed area would realize the possibility of producing larger SLM machines capable of fabricating even larger parts than current standards.”

Almost as soon as we realized the miraculous potential of 3D printing and the infinite choices for innovation before us, it was time to start critiquing and improving—and just as the technology is based on a layer by layer approach, its continued progress has been made with one improvement mounting on another. Flaws in 3D printing must be addressed, however, as many parts are relied on for strength and functionality. The study of spatter is important in trying to reduce or eliminate any defects. In other studies, researchers have studied ejecta and its role in causing imperfections, other types of spatter, and have even set up high-speed cameras to study 3D printing in situ. Find out more about the impact of spatter in large scale selective laser melting here.

[Source / Images: ‘Large scale selective laser melting : study of the effects and removal of spatter by the inert gas flow’]

Powder accumulation on left side of SLM Solutions 500 HL build chamber

Design Guidelines for Direct Metal Laser Sintering, Selective Laser Melting, Laser Powder Bed Fusion

Perchance I came across an excellent document on the design guidelines for  Direct Metal Laser Sintering, also called DMLS, Selective Laser Melting, SLM, Laser Powder Bed Fusion and referred to as metal 3D printing. This document was made by UK based design consultancy Crucible Design. Crucible Design was founded in 1990 by Hugh Raymond and Mike Ayre who for the past 28 years have been tackling tough, complex advanced engineering and design projects. Whether working on cost reduction projects or bringing completely new products to market Crucible Design has carefully built up its reputation over the decades. I was so impressed with Crucible’s design guidelines for metal printing document that I asked CEO Mike Ayre if we could republish it here. I also asked him how he came to make it.

The main reason behind my work with metal 3D printing was the SAVING project, which was run by a consortium in 2011 and 2012. The consortium consisted of Exeter University, ourselves, Plunkett Associates, Delcam, EOS and Simpleware. The point of the project was to find ways to use additive manufacturing to reduce energy use. As the processes themselves are so energy intensive, we soon concluded that the only way to achieve the objective was through the use of the parts, not their manufacture. This is where the airline buckle project came from – reducing the weight of the plane to minimise fuel wastage.

The main problem with metal 3D printing was the same as all design approaches to additive manufacture: early promoters pushed the idea that there were no design limitations, and we ‘were only limited by our imagination’. In fact, this proved to be completely wrong, with 3D printing just having different limitations to conventional methods. In terms of metal printing, the main one is the need to machine out the support structures that are required for any downward facing horizontal surface (the kind of thing that can be washed away using and FDM machine). This requires any efficient design to adopt almost medieval approaches to design, with pointed arches and sloping surfaces that can be built without supports.

Why did you make the guide?

The main reason for making the guide was to inform designers of some of the basic rules and encourage a more creative approach to the use of 3D metal printing and additive manufacture in general. It has been good to see that, since it was written, there is a lot more discussion about appropriate design methods for additive manufacture.

Now the guide was published in 2015 which is eons in 3D printing land. However, the same process limitations and design rules persist. I’ve made design guidelines and design rules documents before and was super impressed with how clear and concise this one was.  I think that this is a very valuable resource to people in metal printing today either to learn about designing for metal 3D printing or to use as a teaching aid to help others. If you’re in a design project with a customer then this is also super helpful in trying to let them see that “complexity is free only in dreams.” I am absolutely certain that these images will be spread far and wide, do please credit Crucible Design for their hard work, be mindful that these images are still their copyright and reach out to them should you need any 3D printing design services done. The images below are all Crucible’s the comments are mine.

Below we can see how DMLS works. A layer of metal powder around 40 micron in diameter and round but not too round is deposited on a build platform and spread out by a recoater. This may be a roller or a knife blade type of recoater. The laser fuses the powder that will make up your part leaving the other loose powder behind. To keep your part from ripping itself apart due to thermal stress supports are needed which will be removed later.

 

While the build plates below seem very full and indeed parts can be stacked efficiently often single parts are built at a time and parts are not stacked. This has to do with the fact that much of the industry is not yet optimized for production and worry that layer skips or recoater bumps and other errors will disrupt a week long build four days in. Note the high amount of manual labor required here. Every one of the bottom column steps will require a person lifting a few kilos at least to a new station or machine. Not shown here is the manual removal of loose powder. In addition to EDM CNC or tumbling (sometimes for a week or more) may be used as well. Depending on the needed Ra and finish of the part many steps will be required including quality control steps such as CT scanning the part to make sure that there are no internal tears or holes.

Parts built in such a way as to make it easy for the recoater to hit them with any force and its best to mitigate part strength in such a way that when that does happen your build doesn’t fail.

Overhanging surfaces in DMLS can be very rough indeed this may require a lot of post-processing. Occluded holes could trap material inside or require supports that can not be removed while large holes could cause parts to tear themselves asunder.

Another thing to consider below is, can the final part withstand the removal of the suports? 

Designing supports that are easy to remove saves a lot of labor. Often a staff member with a flex or circular saw will be cutting away supports. Making sure that this person could do this without damaging the part reduces time and the need to rebuild a part.

Below are some simple support strategies for DMLS. Often a person with decades of experience can do this in their head. While there are some tools that build supports, support strategies for parts still require a lot of experience and thought. Often it will take days for a build and post processing to complete. If you then after four days find out your part has failed then you have to do another iteration. When making completely new geometries several part failures are common. If you have a type of geometry understood (acetabular cups, teeth) then you can print millions of them in many variations.

 

DNA Biosensing with 3D Printing

Biosensor Structure

3D printing is useful in how it makes tools for us humans. Tools are the gateway to innovation within our world. 3D Printing helps different industries because of cost reductions and material waste. We are going to look into a specific industry application and how it is leveraging 3D printing technology.

A biosensor is an analytical device, used for the detection of a chemical substance, that combines a biological component with a physicochemical detector. The sensitive biological element, e.g. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc., is a biologically derived material or biomimetic component that interacts, binds, or recognizes with the analyte under study.

How DNA Biosensors Work

We are particularly interested in DNA biosensors. DNA biosensors can theoretically be used for medical diagnostics, forensic science, agriculture, or even environmental clean-up efforts. No external monitoring is needed for DNA-based sensing devices. Typically these machines were very large and expensive devices that were only for research purposes. DNA biosensors are now becoming complicated mini-machines—consisting of sensing elements, micro lasers, and a signal generator.  This means that DIY construction of such a device will lead to better public health implications for makers. DNA biosensors function on the fact that two strands of DNA stick to each other through chemical attractive forces. Only an exact fit—that is, two strands that match up at every nucleotide position leads to a fluorescent signal that is then transmitted to a signal generator.

The field of biosensors has developed extensively and now has become one of the essential state of the art technologies in laboratory medicine. The idea of biosensors has revolutionized the concept of self-testing by the patient in many clinical conditions. Quick diagnosis and early prevention are critical for the control of disease status. Some commercial biosensors on the market include the following:

So why are 3D printers important in the field of biosensing? In terms of tool creation, it is vital for biotech companies and researchers to build new prototypes and mini machines for biosensing. In order to rapidly make advances within this type of technology, 3D printing is used to cut down costs, as well as iterate designs. This helps to streamline innovation and develop new methods to reduce the production of biosensors.

Researchers currently are working on the potential of adopting 3D printing technology for electrochemical DNA biosensing applications. Some groups have created helical-shaped stainless steel electrodes that are vital for biosensing. An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). This connection is vital for signal processing and seeing whether or not DNA can be identified within a biosensor.

These can be designed and 3D printed through the use of a selective laser melting (SLM) method, which fuses a fine metal powder on a printing stage with a high intensity laser beam, in a layer-by-layer manner. SLM is also called Laser Powder Bed Fusion and is similar to DMLS or Direct Metal Laser Sintering while commonly being called metal 3D printing. It is important to use metal printing for a biosensor because specific chemical and electrical reactions occur with the use of different metal groups.

SLM method

The future of biotech is oriented towards how devices can be made quickly and cheaply. With 3D printing, a maker who is curious has a lot of tools and the ability to make devices efficiently. This leads to projects and innovations when one is open to iterating and experimenting. More importantly one should learn how to create their own devices. Health care as a whole is leaning toward preventative measures. It is important to have tools that can diagnose complications that we are not aware of. It also is important due to the fact that healthcare will be more expensive as time continues. For underdeveloped nations, having access to open source solutions to biotechnology projects can lead to better maintenance of their citizens and their general health.

The future of health is reliant on different technologies, and 3D printing is a very essential part of the equation. With 3D printing, we are able to create tools that were previously only accessible to industry experts. Now a common consumer with an interest can create medical tools such as a biosensor to assist them in their own general health. What will we as makers do to help that?

Wolfmet 3D 3D Prints 100% Tungsten Using SLM Showcases Its Products at TCT Birmingham 2018

Wolfmet 3D is the commercialization of 3D Printing methods developed at M&I Metals to 3D print tungsten. The company is a service bureau that makes tungsten 3D printed components for industry. Tungsten is not completely new to 3D printing with us having written about a study looking into the parameters of 3D printed tungsten and looking at Philips subsidiary Smit Rontgen 3D printing tungsten.

Now, Wolfmet 3D will try to conquer the world with this very special very dense material that for our industry is very exotic. To introduce their product the Wolfmet3D team is exhibiting at the TCT show in Birmingham and we interviewed them about 3D printing tungsten. Curious about them? Check them out at stand G41.

What is Wolfmet 3D?

Wolfmet 3D is the revolutionary additive manufacturing process whereby we produce 3D printed parts via SLM. It allows us to make parts which would either be impossible or not economical using traditional subtractive techniques.

What are the applications for 3D printed tungsten?

Extensive! It really is a very exciting time. Medical and industrial imaging in many ways are at the forefront of recent developments, but we are making new advances all the time in other areas too. To give just one example, we are in discussions with clients interested in tungsten’s heat resistant properties, which opens up another field of possible applications.

Tungsten is a very heavy metal. We almost always think about lightweighting things using 3D printing. But your material is used to make things heavier?

As you indicate, tungsten has a very high density (approx. 60% denser than lead). In the applications we have discovered so far for Wolfmet 3D, it is valued for its radiation attenuation properties, derived from the density, and also its heat resistance. The weight is really incidental.

What do you see as future applications for 3D printing tungsten?

Future opportunities are perhaps only limited by our own imagination, so our specialists work in partnership with leading research institutes and universities to ensure we are at the forefront of new developments across the globe.

How is tungsten used in vibration damping?

Tungsten’s high density enables it to act as a vibration weight in various dynamic applications.

Why does one want to 3D print a collimator?

The collimator’s function in an imaging system is to focus beams of radiation (gamma or x-ray) onto a detector and to filter out stray beams which might distort the signal. The detector’s software converts the signals into a 3D image of the subject. Until the arrival of Wolfmet 3D, most collimators were made from lead. Lead has several disadvantages – it is toxic and has to be handled with care and it is relatively soft. Most importantly, from the point of view of imaging systems, its density is much lower than that of tungsten. As a result, lead collimators are much less effective in screening out stray beams and, therefore, give inferior image quality.

What is the DEPICT system?

The DEPICT system was developed by a consortium which included Kromek and the University of Liverpool. Its function is to measure the amount of radioactivity issuing from a thyroid cancer patient during radiation therapy. This enables the medical staff to personalise the dosage of each treatment according to the patient’s physique and metabolism. The DEPICT team acknowledged early on that a tungsten collimator would give much more accurate readings than a lead one and we are very proud to have worked with them on this project.

Do you see many more applications in MRI or imaging generally?

Yes absolutely, Wolfmet 3D helps to make the innovations of our clients possible. Wolfmet tungsten has been shown to be MRI compatible in terms of its magnetic properties. This, together with the advantages that using tungsten can bring, makes it an exciting prospect for the future.

Are imaging apertures also a good application for your technology?

“In principle, yes, if the design is complex, as is increasingly the case.”

Isn’t shrinkage a huge problem with tungsten?

There is no shrinkage with the SLM technology which we use. I believe that this is not always the case with other Additive Manufacturing methods.

What kind of part properties can you get with this material?

The density is typically 94 – 96%. We have a continuous improvement programme designed to optimise the physical properties.

What kind of alloys are available?

At present we offer 100% tungsten components but as this is such a rapidly developing market, we are of course looking at other options. We have clients who are interested in developing other tungsten-based materials, but I’m afraid that I am also prevented from saying more due to our confidentiality agreements.

 

TU Delft Researchers Develop Heat Accumulation Detection Procedure for SLM 3D Printing

Selective Laser Melting (SLM), a powder-based 3D printing technique also known as Laser Beam Melting or Laser Powder Bed Fusion, has been used to process metal in a variety of sectors, such as automotive, medical, and aerospace. Because this AM method offers excellent freedom of form, it’s a perfect enabling technology for designs that are topology optimized; this means they have a complex layout, but still offer a superior performance. But, SLM 3D printers don’t always realize the dimensional accuracies that are necessary for very precise components.

Because of laser-induced heat, SLM 3D printed layers go through stages of rapid heating-cooling, which can cause inaccuracies, such as unwanted mechanical properties and poor surface finish. If certain design features, like thin sections and overhangs, that can cause local heat accumulation could be detected earlier in the design stage, this issue could be avoided more easily. To do this, next generation topology optimization (TO) methods need to be developed.

A group of researchers from TU Delft recently published a paper, titled “Towards Design for Precision Additive Manufacturing: A Simplified Approach for Detecting Heat Accumulation,” focused on a simper heat accumulation detection procedure – very important for creating a TO scheme that can account for thermal 3D printing aspects.

“In order to address thermal aspects of AM into a TO framework, an appropriate AM process model is required. This becomes problematic because a high fidelity AM process model is computationally very expensive and integrating it within a gradient-based TO framework becomes even more cumbersome,” the researchers explained in the paper. “Therefore, in this research, a physics based yet highly simplified approach is proposed in order to identify zones of heat accumulation in a given design. The computational gain offered by the simplification, makes it feasible to integrate the heat accumulation detection scheme within a TO framework.”

Definition of overlapping cells for heat accumulation detection.

In addition to being used in a TO process, the team’s new procedure can also be used to independently analyze 3D printing designs, manual design improvements, and even determine the best build orientation.

Equivalence of a 3D body (A) to a simplified body (B) with equal thermal capacitance
and conductance.

Two simplifications made in this research can be used to help lower the computational cost that’s associated with the thermal analysis of 3D printable designs. The first, “motivated by the fact that the local geometry of only few previously molten layers” can significantly effect the new layer’s initial cooling rate, is to perform thermal analysis in the vicinity of the 3D printed layer being deposited.

The second is to use a steady, rather than transient, state thermal response to predict heat accumulation.

“For this purpose, a physics based conceptual understanding is developed which enables estimation of spatially averaged transient thermal behavior of a local geometry just from its steady state response,” the researchers wrote.

A structure’s topology can influence its internal heat flow; as such, different geometrical features in an AM design can obstruct or facilitate heat flow during the 3D printing process differently.

The researchers explained, “In this work we explore the possibility to approximately quantify, and hence compare, different geometries from the viewpoint of heat accumulation. For this purpose, first the concepts of thermal conductance and time constants are studied.”

Time constant maps obtained by the heat accumulation scheme using the concept of
overlapping cells.

Thermal conductance, equivalent to the reciprocal of thermal resistance, is a structure’s measure to conduct heat, while the time constant of the transient thermal response is studied to quantify the heating/cooling rate. The team also divided the design in their experiment into overlapping cells, so as to increase the possibility of detecting the heat accumulation zones.

High time constants were recorded close to overhang surfaces, and so the researchers discovered that heat accumulation for design features depends a lot on the nearby local geometry, and that “purely geometric design guidelines of prescribing a limiting overhang value might become insufficient for preventing problems associated with local heat accumulation.”

“The computational advantage offered by the proposed method enables development of a physics based topology optimization method which would be beneficial for designing precision AM components,” the researchers concluded. “Next step for this research is to combine the developed method with density based topology optimization by penalizing design features which are prone to heat accumulation during each iteration.”

Co-authors of the paper are Rajit Ranjan, Can Ayas, Matthijs Langelaar, and Fred van Keulen. The team will publish an additional paper on their heat accumulation detection method’s integration within a TO framework.

Discuss this research and other 3D printing topics at 3DPrintBoard.com or share your thoughts in the comments below.

New Study Shows that SLM 3D Printing Has High Potential for Fabricating Metallic Glass Components

Metallic glass, also known as amorphous metal, was first introduced in the early 1960s, and since then, it seems that everyone wants in on the action. The material is valued for its many exceptional properties, such as low stiffness, near-theoretical strength, high corrosion resistance, and large elastic strain limits. Bulk metallic glasses (BMG), which have characteristic specimen sizes in excess of 1 mm, have been explored successfully for for glass formers.

It’s not easy to produce metallic glasses with complex geometry, because the molten alloys must be cooled rapidly to move past the nucleation and growth of crystals, and most commonly used methods, such as melt spinning, casting, and powder metallurgy, are limited in both complex geometry and dimension. That’s why it’s so important to continue exploring and developing more novel processing routes for producing amorphous components.

A schematic illustration of SLM-YZ250 3D printer: (a) operating mode of the device; (b) processing scanning pattern.

A team of researchers from the University of Science and Technology Beijing have been investigating the use of selective laser melting (SLM, also called DMLS, Direct Metal Laser Sintering, Powder Bed Fusion, Laser Powder Bed Fusion) 3D printing to fabricate Fe-based metallic glass powder with unrestricted, complex geometry. This specific technology offers very high cooling rates, which is important for glass formation of most BMGs, and can apply various processing parameters involving laser energy density to melt the metal powder.

The researchers recently published a paper, titled “Fabrication and characterization of Fe-based metallic glasses by Selective Laser Melting,” in the Optics and Laser Technology journal. The paper details SLM’s high potential for 3D printing metallic glass components with complex geometries.

The abstract reads, “Fe-based metallic glasses (MGs) can be potential structural materials owing to an exceptional combination of strength, corrosion and wear resistance properties. However, many traditional methods are difficult to fabricate Fe-based MGs with complex geometry. In this study, a new metallurgical processing technology, selective laser melting (SLM), was employed to fabricate Fe-Cr-Mo-W-Mn-C-Si-B metallic glasses. The microstructure, thermal stability and mechanical properties of the as-fabricate samples processing with different laser energy density have been investigated by X-Ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and nano-hardness. Thanks to the high cooling rates of SLM, the crystalline phases in the gas-atomized powder almost completely disappeared and nearly fully amorphous structure parts were obtained after SLM processing. By choosing appropriate parameters, the size and quantity of the pores were reduced effectively and the relative density of the samples can reach values of over 96%. Although additional work is required to remove the residual porosity and avoid the formation of cracks during processing, the present results contribute to the development of Fe-based bulk metallic glasses parts with complex geometry via the SLM.”

(a) SEM secondary electron image of the gas-atomized powder; (b) SEM back-scattered image of the cross-section of the powder.

Fe-based BMGs are important for their unique combination of high physical, chemical, and mechanical properties, low affinity towards oxygen, and the fact that the raw material is less expensive than other commercial BMGs. So the researchers used a Fe-based metallic system Fe-Cr-Mn-Mo-W-B-C-Si with large glass forming ability (GFA) for the study, and used X-Ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) to investigate structural variations between the original powder and the SLM 3D printer parts.

Samples prepared with different laser energy density.

According to the powder’s morphology, the surfaces are very smooth, which results in good flowability. But, the team also observed that micro-pores were formed by trapped glass, and that crystallization did occur in a small amount of the powder, due to the fact that, as the researchers explained, “the cooling rate during gas atomization is not high enough to suppress crystallization.”

However, the crystalline phases in the gas-atomized powder disappeared after SLM 3D printing.

Samples were 3D printed with different laser energy densities, in order to investigate the metallic glasses’ mechanical properties and microstructural evolution. By choosing the appropriate parameters, the researchers were able to successfully 3D print high quality Fe-based metallic glasses.

“At present it is great challenge to produce large-scale glassy alloys in sophisticated geometries with the existing technologies. SLM technology, including heating the powder to melting in very short time and then the melting pool rapidly solidifying procedures, provides new opportunities for the creation of large, geometry freedom of metallic glass components,” the researchers explained. “From the results above, we noticed that although the as-received powder had partially crystallized, the powder experienced a quickly laser processing procedure with high cooling rates, leading to nearly fully amorphous structure. This phenomenon proves that under optimized SLM processing conditions, the nucleation and crystallization are inhibited, and amorphous structure can be acquired.”

They also noted that to improve the quality of the SLM 3D printed parts by decreasing micro-cracks and pores, further fine-tuning of the processing parameters is necessary.

A selection of the as-built parts.

The researchers concluded, “In addition, the preparation process of the powder system still needs to be optimized, and ensuring a fully amorphous structure powders can be obtained which eliminates crystallization in the SLM parts. The present results confirm that additive manufacturing by SLM represents an alternative processing method for the preparation of bulk metallic glass components without limitations in size and intricacy. The processing method and conditions are in principle available for a large variety of metallic glasses production.”

Co-authors of the paper include X.D. Nong, X.L. Zhou, and Y.X. Ren with the university’s State Key Laboratory for Advanced Metals and Materials.

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Using Two-Stage T6 Heat Treatment to Tailor the Mechanical Properties of 3D Printed Aluminum AlSi10Mg Alloys

Backscattered electrons images to observe oxidation regions of (a) T6 heat-treated, and not in (b) as-built, selective laser melting samples, (c) magnification of (a).

While many aluminum alloy components are still fabricated using traditional casting technologies, there’s been plenty of research and development into 3D printed aluminum alloys as well. For metallic 3D printing, the selective laser melting (SLM) method is typically used to produce Al alloys; however, AlSi10Mg alloys made with SLM technology must set up different post-printing treatments. This is due to a rapid cooling rate during the solidification process, which causes the microstructure and mechanical properties of the part to be vastly different from conventional cast or forged metal alloys.

Additionally, high heat transfer, high reflectivity to the laser beam, and easy oxidation to a tenacious oxide film make SLM-produced AI alloys more difficult than those of steel or titanium.

A pair of researchers recently published a paper, titled “T6 heat-treated AISi10Mg alloys additive-manufactured by selective laser melting,” in the Procedia Manufacturing journal about tailoring the mechanical properties of SLM-fabricated AlSi10Mg alloys with a two-stage T6 heat treatment.

The abstract reads, “A two-stage T6 heat treatment has been proposed to tailor mechanical properties of the selective laser melting fabricated AlSi10Mg alloy. The process included solid solution at 535 ºC and artificial aging at 158 ºC for 10 h. The densification, hardness and oxidation behavior have been investigated after T6 heat treatment. The results demonstrate that the hardness of the T6 heat-treated samples are lower than untreated ones. This is because a fine-grained recrystallization microstructure develops during solid solution. Oxides aggregation and dimple distribution occurred due to sufficient diffusion at the artificial aging of the second stage.”

Optical microscopy images of (a) as-built selective laser melting, and (b) magnification; (c) T6 heat-treated, and (d) magnification, samples perpendicular to building direction of selective laser melting.

The T6 heat treatment is most often used to increase the strength of Al-Si components with Cu and/or Mg in conventional manufacturing, which uses a high-temperature solution treatment to both dissolve larger intermetallic particles and homogenize the alloying elements. Then, lower temperature artificial aging is used to form fine precipitates.

New studies show that T6 heat treatment can actually cause cast alloys to soften, instead of harden, when they’re annealed at either 300 ºC or 530 ºC, which contrasts earlier research. In addition, SLM-fabricated AlSi12 post-solution had a 25% increase of ductility.

“However, most research so far focuses on how to increase the tensile strength during selective laser melting processing, only a few can refer to balancing plasticity and the resistance to facture by post heat treatment. Furthermore, only limited comprehensive work has currently been done to study heat treatment processes specific for selective laser melting-fabricated AlSi10Mg alloys, particularly on their influence on the mechanical properties,” the researchers wrote. “Thus, this raises the need to verify conventional T6 heat treatments when it comes to selective laser melting materials, and what would be the influence of these heat treatments on the specific mechanical properties of selective laser melting-produced AlSi10Mg alloys.”

Hardness measurement of as-built selective laser melting and T6 heat-treated samples.

The paper’s proposed thermal treatment uses a solid solution at 535 ºC and artificial aging at 158 ºC for 10 hours on  gas-atomized AlSi10Mg powder provided by Renishaw. Then, the researchers investigated the impact of their two-stage T6 heat treatment on both the mechanical and microstructural properties developed in SLM 3D printed samples.

The samples’ mechanical properties depend on the densification mechanism of the parts, and their microstructure during SLM processing.

“In AlSi10Mg alloys, the theoretical bulk density usually is 2.68 g/cm3. After the selective laser melting processing, the densification of the as-built samples was 96%. By contrast, after T6 heat treatment, the mean value of the densification of the samples is 96.52% and the maximum densification is 98.13%,” the researchers wrote.

These similar values are an indication that the two-stage T6 heat treatment had very little effect on the SLM 3D printed parts’ densification. Additionally, post-T6 heat treatment, the hardness of the as-fabricated sample in a building direction significantly decreased as well. Evidence also shows that the T6 heat treatment can spheroidize oxidation regions to even further enhance the mechanical properties of SLM 3D printed samples.

The researchers concluded, “This heat treatment aims to tune the mechanical behavior of selective laser melting-produced AlSi10Mg alloys. The effects of the T6-like heat treatment on the densification, hardness, and oxidation behavior have been investigated. Similar densification of 96% in the as-built samples and of 96.52% in the heattreated samples indicates that the T6 heat treatment has no importance to the densification. Decrease by about 20% in the hardness of heat-treated samples compared with the selective laser melting as-built samples. The T6 heat treatment can spheroidize oxidation regions and thereby form dimple structure. This finding can offer an intriguing insight into explore oxidation behavior and mechanical properties of selective laser melting-fabricated AlSi10Mg alloy using a two-stage heat treatment.”

Co-authors of the paper are Xianglong Yu with the CAS Key Laboratory of Mechanical Behavior and Design of Materials (LMBD) at the University of Science and Technology of China and Lianfeng Wang with Shanghai Aerospace Equipment Manufacturer.

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