The project to keep a 1944 P-51 Mustang flying was covered again, this time in 3D Metal Printing Magazine (Pg 23-33). Concept Laser worked with PADT to reverse engineer and print the exhaust manifold from a P-51 to keep it flying. Unlike the other article and video on the project, this reporter used this example as a great way to look at the readiness of military aircraft, and not just antique planes.
As PADT’s Rey Chu says ““This was a great exercise that’s suitable for numerous military applications and very relevant to the future use of 3D metal printing to maintain fleets in the field,” Chu says. “Maintaining spare-parts inventory has become a significant challenge, for example, to the Air Force. Additive manufacturing could be the solution.”
Mostly we make boxes. Pretty boxes but the bulk of what we 3D Print is some sort of plastic box that people stuff electronics in to. Most of the time we also don’t really know what customers do with the objects we make for them. But every once in a while you get involved in a project that really makes a difference. That could not be more true than two recent medical applications for 3D Printing that we worked on with Intermountain Healthcare (IHC) in Salt Lake City, Utah.
KSL, a local TV station, did a story on our IHC was deploying 3D Printing to produce better outcomes for their patients. You can view the story here.
PADT was fortunate enough to be part of two of the cases mentioned in the story. The first was a St George man who was feeling some pain in his back. He had a scan and they found 12 kidney stones. On top of that, his kidney was not in the right place and was distorted. PADT helped print a model of the scan so that the doctors could just get a real feel for what they were dealing with, and then plan the surgery.
The second situation really pulled at our heart strings. A 10 year old boy needs heart surgery and its a complicated problem. They need a model fast so we worked with Stratasy to quickly print an accurate model so tha the surgeons could come up with a plan. We still have not heard how it went, they are scheduling things, but the feedback from the team was that the 3D model was extremely helpful. We are talking life saving.
Both of these recent situations build on years of examples where we have worked the doctors and their technical assistance to convert scans of patients into usable 3D Models. If you are in the surgery or surgery planning space and want to learn more about how accurate 3D models printed directly from scan data can be used to improve patient outcome, contact PADT at firstname.lastname@example.org and we will connect you with our 3D Printing team.
Download all 5 parts of this series as a single PDF here.
This is part 2 of a 5-part series on the lessons we learned installing our first Metal 3D printer, a Concept Laser MLab Cusing R. Please read the first post if you haven’t already, where I listed all the different equipment (in addition to the 3D printer itself) one needs to run this process.
A reminder at the outset: these posts are meant to be informative only, to give you a sense of what questions you need to ask and get answers to. Specific requirements will vary by equipment and your site specific needs.
Most metal 3D printers, including the Concept Laser machines, are manufactured in Europe and have electrical requirements that differ from what most American machine shops are setup for (which is the scope of this section). If you have installed 230 V European equipment before and know what L-N and PE stand for and how they differ between European and American systems, you can skip this section. If not, read on.
There are two key items here one needs to be aware of: first of course is the fact that these pieces of equipment typically run on single-phase 230 V (3-phase 400V for the very large machines like Concept Laser’s XLine 2000R) as opposed to the standard 110V. Secondly, and this is easier to miss, European electrical connections have one “hot” line (L) for a single-phase, one Neutral line (N) and one Protected Earth (PE) – this is different from the US standard where you have 2 “hot” lines and 1 ground. The reason for these differences and how to address them electrically is beyond the scope of this post (or my understanding), but the main point is to have an electrician familiar with European codes review this early on. A dedicated custom transformer for all your European 230V equipment is one solution, and the one we employed here at PADT, as shown in Figure 1. (I rarely give shout-outs, but our experience with Fargo Electric on procuring a custom, affordable transformer was one of the best transactions I have ever had.)
2. Inert Gas
Laser melting of powder metals needs to be conducted in an inert atmosphere. Most suppliers recommend using Argon for Aluminum and Titanium alloys, but that Nitrogen is fine for the non-reactive alloys such as steel, Inconel and Cobalt-Chrome alloys. At PADT, we leveraged our existing nitrogen generator and added an additional line running to our metal 3D printer (Figure 2). Before doing this, you need to add up all the consumption rates for the machines (at their peaks) to make sure you don’t exceed the generator’s capabilities. It is a good idea to demarcate space for Argon cylinders should you need them at a later stage.
3. ESD Mats or Floors (for Reactive Metals)
As we will see in the next blog post in this series, avoiding charge dissipation into metal powder is a key safety requirement for operating metal 3D printers – this is achieved through a range of strategies like ESD (Electro Static Discharge) armbands, grounding ElgiloyHastelloy C4 wires etc. If you plan on running reactive metals and especially if you expect to have many operators, an ESD coated floor with ESD shoes or boot straps, along with an ESD meter (like the one Honeywell installed at their facility) is a good strategy. From personal experience with ESD boot straps, I know these can be fickle in passing an ESD meter test. Connecting the ESD meter to the entryway door so entry is only provided after passing the test is one way to ensure only those with functioning straps enter the workspace. For those without this strategy, grounded ESD mats and ESD armbands connected to the machine are also alternative strategies which I will discuss in more detail in the next post. From a facilities standpoint, if you do want to enable ESD coated floors, boot straps and ESD meters, you need to plan this early, which is why I have included it here.
Access to running water is essential for cleaning the wet separator (vacuum) that is used for sucking up fugitive powder – ideally the water source is near your liquid waste storage so you can clean out the wet separator and pour the powder-contaminated water into storage. Alternatively, you can also use a garden sprayer for smaller machines, like we do at PADT. Fill up the sprayer with water and use it to rinse out the wet separator right on top of the waste storage bin.
Another reason you need access to water is to passivate the filter. While not all OEMs recommend water passivation, Concept Laser does and we find it to be very user friendly, as I demonstrate in the video below (video starts 2:58 in, which is when I discuss filter passivation with water).
5. Access Control
It is important to restrict access to your metal AM laboratory through badge scanning or key pad entry to those who are trained on using the machine, and your building facilities team. It also helps to provide as much visibility through glass windows so that folks that are entering can study what activity is in progress before entering.
6. Structure & Ventilation
Here I move into the subjective (gray area) domain – I request anyone who has more specific information on these matters to kindly share them with me for inclusion in this post (with due credit). I have heard anecdotally that in some places the city has required the supplier to install blast walls and other explosion resistant infrastructure – yet others have not required such infrastructure (including ours). I am not well informed in this space and can only emphasize the need to have these discussions out in the open in the early stage of planning your facility and ask your city’s building safety person if the walls you have planned (or already have installed) are adequate or not – this is likely to be a function of the amount and reactivity of the powder you are handling, proximity to vulnerable areas, human occupancy and other concerns. With regard to ventilation, the more open the space the better (these machines can heat up a small, closed room) – at the same time the space needs to be sealed off from the elements including wind. I know this too is a subjective matter, so discussions with city representatives are the best way to go.
Fast, easy to use lightweighting for structural analysis is now only a few clicks away thanks to the introduction of Topology Optimization in ANSYS 18.
Engineers who use Finite Element Analysis (FEA) can reduce weight, materials, and cost without switching tools or environments. Along with this, Topology Optimization frees designers from constraints or preconceptions, helping to produce the best shape to fulfill their project’s requirements.
Topology Optimization also works hand-in-hand with Additive Manufacturing; a form of 3D printing where parts are designed, validated, and then produced by adding layers of material until the full piece is formed. Pairing the two simply allows users to carry out the trend of more efficient manufacturing through the entirety of their process.
Join PADT’s simulation support manager Ted Harris for a live presentation on the full
benefits of introducing Topology Optimization into your manufacturing process. This webinar will cover:
A brief introduction into the background of Topology Optimization and Additive Manufacturing, along with an overview of it’s capabilities
An explanation of the features available within this tool and a run through of it’s user interface and overall usage
An in-depth look at some of the intricacies involved with using the tool as well as the effectiveness of it’s design workflow
When I was asked to take part in a demonstration put on by one of our local communication companies, Cox Communications, showing off what a “smart home” looks like, I of course said yes. I love gadgets, and smart gadgets more. On top of that it was another chance to evangelise on the power of 3D Printing. And I got to hang out in a brand new luxury condo in Downtown Phoenix, a post kid lifestyle change that is very appealing. Plus we deal with customers designing and improving Internet of Things (IoT) devices all the time, and this is the perfect chance to see such products in action.
So I packed up one of our Makerbots, none of our Fortus machines fits in the back of my Prius, and headed downtown. The first thing that shocked me was that I had the printer, my iPhone, iPad, and laptop connected to their network in about one minute. The printer showed up on the Makerbot Print app on my iPad and I was printing a part in about three minutes.
The whole point of the demonstration was to show how the new high-speed Internet offering from Cox, Gigablast, can enable a true smart home. So I was focused on the speed of the connection to the Internet, which was fast. What I didn’t get till I connected was that the speed and bandwidth of the WiFi in the house was even more important.
When everything was connected, we had 55 devices on the local network talking to each other and the Internet. At one point I was downloading a large STL file to the printer while on a teleconference on my iPhone and my “roommate” was giving a violin lesson to one of his students in Canada.
Oh, and the roomba started to vacuum the floor. On the balcony someone was giving a golf lesson and a doctor was diagnosing a patient in the master bedroom. That was on top of the smart kitchen gadgets. And it all worked. Yes, it all worked.
I’m trying to convey shock and surprise because the reality is that nine times out of ten when I show up for some event, at a customer, or at a friends house and we try and connect things to the internet… it doesn’t work. If you are a technical guy you know that feeling when your vacation or visit for dinner turns into an IT house call. All I could think of was how awesome it was that everything worked and it was fast.
So I went to work printing little plastic Arizona style houses with COX on the roof. And then a reporter showed up. “3D Printing, interesting. Hmmmm… they are cool and all but really, what does that have to do with a smart house?” Damn reporters and their questions. I was still reveling in the fact that everything worked so well, I hadn’t taken to time to think about the “so what.”
Then I thought about it. 3D Printing in the home is just now starting to take off, and the reason why is actually high-speed internet connections. If you wanted a 3D Printer in your home in the past you needed the printer, a high end computer, and some good 3D modeling software on that computer. Basically you had to create whatever you wanted to make. Unless you are a trained engineer, that may not be so easy.
But with a well connected home you have access to places like Thingiverse and Grabcad to download stuff you want to print. And if you do want to create your own, you can go to Tinkercad or Onshape and use a free online 3D modeler to create your geometry. All over the web, even on a pad, phone (I don’t recommend trying to do modeling on a phone, but it does work), or on a basic computer. The files are stored in the cloud and downloaded directly to your printer. No muss, no fuss. All you need is a reliable and fast connection to the internet and in your home.
High speed internet and a smart 3D printer makes anyone a maker.
And when we had a three hour break, I went downstairs to a coffee shop on the ground floor of the condo and worked, while monitoring my builds using the camera in the smart 3D Printer.
Pretty cool when you step back and think about how far we have come from that first Stereolithography machine that PADT bought in 1994. We had to use floppy disks to get the data from our high-end Unix workstation to the machine. Now it sits on the web and can be monitored.
This may be what we have been waiting for when it comes to 3D Printers in the home moving beyond that technologists and makers.
I’ve been focused on my experience with the 3D printing in the smart home, but there was a lot more to look at. Check out these stories to learn more:
I also did a piece for the Phoenix Business Journal while I was at the event on “3 keys to success for smart home devices” based on what I learned while playing with the other devices in the smart home.
All and all a good day. Oh, and being a 10 minute walk from my favorite pub made the idea of living downtown not such a bad idea, which doesn’t have much to do with high speed internet, connected devices, or 3D Printing. But one of my goals was to check out post-child urban living…
Download all 5 parts of this series as a single PDF here.
What equipment does one need for metal 3D printing?
This is the first in a five-part series that brings together the different lessons we learned installing our first metal printer, a Concept Laser MLab Cusing R at PADT, shown in Figure 1. In this post I list the different equipment needed to enable metal 3D printing end-to-end, along with a brief explanation of its purpose. In subsequent posts, I deal with (2) Facilities, (3) Safety, (4) Environmental & (5) Housekeeping aspects of the technology. I hope this information adds to the conversation in a meaningful way and help those who are thinking about, or in the process of installing a metal 3D printer.
The specifics of some of this information will vary depending on the equipment and materials you handle, but my hope is the themes covered here give you a sense of what is involved in installing a metal 3D printer to aid in your preparation for doing the same and for having good discussions with your equipment supplier to ensure these are addressed at a minimum.
One way to look at classifying the equipment needed (beyond the obvious metal 3D printer!) is by its purpose, and I do so here by dividing it into two broad categories: Ancillary Equipment (necessary to the printing itself) and Post-Processing Equipment (focused on the part).
At the outset, it is crucial that the difference between reactive and non-reactive metal alloys be comprehended since a lot of the use of the equipment differs depending on what kind of metal alloy is being used. A previous blog post addressed these differences and these terms will be used in the following sections.
1. Ancillary Equipment
1.1 Wet Separator
The wet separator is essentially a vacuum cleaner that is designed to safely vacuum stray (“fugitive”) metal powders that cannot be cleaned up any other way. When dealing with powders, the typical recommendation is to first brush whatever you can into the overflow bin so you can reuse it. The next step is to try and wipe up powder with a moist lint-free cloth (to be covered in the housekeeping post). The wet separator has a water column that passivates the metal powder and renders it non-reactive to allow for easier disposal (to be covered in the environmental post). Wet separators require a significant amount of maintenance, particularly when dealing with reactive metals like Titanium and Aluminum alloys, where the supplier recommends the wet separator be cleaned out on a daily basis. At least one company has developed a kit to help with wet separator cleaning – which gives you an indication of how significant of an issue this is. Most suppliers provide a wet separator along with their equipment.
1.2 Glove Box
A glove box is a useful piece of equipment for dealing with reactive metals in particular. The glove box allows an operator to manage all the powder handling in the build chamber to be done in a closed environment. For non-reactive metals this is not a necessary piece of equipment but it is highly recommended for reactive metals. The glove box when used in concert with reactive metals will allow for inert gas flushing out of oxygen to low PPM levels prior to operator intervention, and also includes grounding connections for the box to the machine. The nice thing about having a glove box is it reduces the amount of time you need to have a respirator on by allowing you to add powder and unpack builds in a closed environment. The glove box may also be integrated into the machine itself – ours is a stand alone device on wheels that we roll over to the machine when we need it.
1.3 Powder Sieve
Unless you plan on disposing all the powder in each build after it is completed, you need a sieve to separate out the larger particles and contaminants from the powder you wish to reuse in subsequent builds. The sieves are also typically provided with the machine and can be enabled with inerting capability (as shown in Fig 4 on the left, or as shown on the right, come as a small desktop unit that can sieve about 3-5 lbs of powder at a time). While the sieve on the left may be used for reactive metal sieving, it is uncertain if one can safely use the desktop sieve for the same, even with grounding the table it sits on and the operator – this is a gray area and I am keen to hear thoughts on this from those that have the expertise/experience in this space.
1.4 Ultrasonic Cleaner
The purpose of the ultrasonic cleaner is to remove as much trapped powder as possible before the part and the build plate are subjected to any post-processing – this is to minimize the risk of trapped powder getting airborne during downstream processes – which cannot be completely eliminated (which is why PPE should be used all the way through till the final part is in hand after cleaning).
The Ultrasonic cleaner is used twice: first before the parts are removed from the build plate, and again after they are removed. Sometimes I will even use it a third time after all supports have been removed, if the part has internal p. I typically use the 40 kHz and 60 C temperature setting but have not sought to further optimize the parameters at this time.
2. Post-Processing Equipment
The purpose of the furnace is to relieve residual stresses built in the parts prior to removing them from the build plate. So this is the first step after the parts and the plate come out of the ultrasonic cleaner. We use a furnace that allows for nitrogen or argon flushing, and place our parts wrapped in stainless steel foil in a gas box. Instructions for heat treatment (time and temperature profile) are typically provided on the technical specifications that come with the material. Metals like stainless steel can be stress relieved in a nitrogen atmosphere but Inconels and Ti6Al4V for example require higher temperatures of between 800-1000 C and argon atmospheres – so you need to be setup for both gases if you are considering running more than 1 metal in your operation.
2.2 Support Removal
All parts are connected to the build plate by between 3-5mm of supports that need to be removed. This is a two step process: the first step involves removing the parts with supports off the build plate, and this is most commonly done with a table saw or a wire EDM. At PADT, we stumbled upon a third way to do this, using an oscillating hand tool and a carbide blade – which works well for small parts (<3″ in X-Y space). It is important to always wear gloves and a supplier recommended (N95 or higher) respirator while removing supports since there could be trapped powder in the supports that was not removed with the Ultrasonic cleaner. The second step is to use hand tools to pry out the supports from the part – this is why it is important to design supports that have weak mechanical connections to the part itself – ideally you can tear them off with hand tools like a perforated sheet of paper [Video below courtesy Bob Baker at PADT, Inc].
2.3 Die Grinder
A carbide die grinder is then used to grind away the support-model interface – for tiny parts, this can be achieved with a hand file as well for some parts but is easier to do with a die grinder. For large parts, this need can be eliminated by designing in regions that are to be machined later and aligning these regions with supported regions, so as to reduce the need for finishing on these surfaces.
2.4 Face Milling
This may come as a bit of a surprise, but you also need some way of replenishing the build plates after use so you can re-use the plates – this involves using a face milling technique to remove all the remnant supports on the build plate and take off a thin slice at the top of the build plate, while retaining flatness to within 100 microns (0.004″). Having this capability in-house will greatly speed-up your ability to start successive prints and reduce the need to keep large inventories of build plates [Video below courtesy Bob Baker at PADT, Inc].
2.5 Surface Finishing
A combination of techniques can be used for surface finishing. At a minimum, you must have the ability to do glass bead blasting – this is both for the printed parts, but also for the build plate itself – a bead blasted finish is recommended to improve the adhesion of the first layer of powder to the build plate.
2.6 Other Capabilities
The list above is what I would consider a minimum list of capabilities one needs to get started in metal 3D printing, but is not comprehensive and does not include facility, safety, environmental and housekeeping requirements which I will cover in future posts. Additional CNC equipment for machining metal AM parts, heat treatment and HIP, and superior surface finishing and cleaning techniques are often called upon for metal AM production, but these are highly dependent on application and part design, which is why I have left them out of the above list.
Move on to part 2 of this series where I discuss the facilities requirements for metal 3D printing (electrical, inert gas etc.). Did I miss anything or do you have a better way of doing the things described above? Please send your thoughts to email@example.com, citing this blog post, or connect with me on LinkedIn.
Acknowledgements: Garrett Garner at Concept Laser, Inc and Bob Baker at PADT, Inc. for their insight and expertise that helped us select and bring in the above capabilities at PADT.
Sometimes we run across some great exampls of industry and academia working together and like to share them as examples of win-win partnerships that can move technology forward and give studends a great oportunity. A current Capstone Design Project by students at ASU Polytechnique is a great example. It is also an early exmple of what can be done at the brand new Additive Manufacturing Center that was recently opened at the campus.
I’ll let ASU Mecanical Enginering Systems student Dean McBride tell you in his own words:
Orbital ATK in Chandler currently utilizes two Stratasys Dimension SST 1200es printers to prototype various parts with. These printers print on parts trays, which must be removed and re-inserted into the printer to start new prints. Wanting to increase process efficiency, Orbital had the desire of automating this 3D printing process during times when employees are not present to run the printers. After the idea was born, Orbital presented this project to ASU Polytechnic as a potential senior capstone design project. Shortly after, an ambitious team was assembled to take on the project.
Numerous iterations of the engineering design process took place, and the team finally arrived at a final solution. This solution is a Cartesian style robot, meaning the robot moves in linear motions, similar to the 1200es printer itself. The mechanical frame and structure of the robot have been mostly assembled at this point. Once assembly is achieved, the team will focus their efforts on the electrical system of the robot, as well as software coding of the micro-controller control system. The team will be working to fine tune all aspects of the system until early May when the school semester ends. The final goal of this project is to automate at least two complete print cycles without human interaction.
Here is a picture of the team with the robot they are building along side the Stratasys FDM printer they are automating.
What do you do when you want to replace the exhaust on a 1944 P-51D Mustang warbird and you also happen to be a pioneer in additive manufacturing? You work with Concept Laser and PADT to can and print a replacement stainless steel part. In “Metal Additive Manufacturing Keeps Legend Flying” Engineering.com details the project that involved blue light scanning and 3D Printing of new metal part in modern Stainless Steel, replacing the three-piece weldment with a single part.
They also did a fantastic video about the effort:
If you would like to learn how PADT can help you reverse engineering your legacy geometry and recreate it using Additive Manufacturing, contact us.
In a previous post, I laid out a structural classification of cellular structures in nature, proposing that they fall into 6 categories. I argued that it is not always apparent to a designer what the best unit cell choice for a given application is. While most mechanical engineers have a feel for what structure to use for high stiffness or energy absorption, we cannot easily address multi-objective problems or apply these to complex geometries with spatially varying requirements (and therefore locally optimum cellular designs). However, nature is full of examples where cellular structures possess multi-objective functionality: bone is one such well-known example. To be able to assign structure to a specific function requires us to connect the two, and to do that, we must identify all the functions in play. In this post, I attempt to do just that and develop a classification of the functions of cellular structures.
Any discussion of structure in nature has to contend with a range of drivers and constraints that are typically not part of an engineer’s concern. In my discussions with biologists (including my biochemist wife), I quickly run into justified skepticism about whether generalized models associating structure and function can address the diversity and nuance in nature – and I (tend to) agree. However, my attempt here is not to be biologically accurate – it is merely to construct something that is useful and relevant enough for an engineer to use in design. But we must begin with a few caveats to ensure our assessments consider the correct biological context.
1. Uniquely Biological Considerations
Before I attempt to propose a structure-function model, there are some legitimate concerns many have made in the literature that I wish to recap in the context of cellular structures. Three of these in particular are relevant to this discussion and I list them below.
1.1 Design for Growth
Engineers are familiar with “design for manufacturing” where design considers not just the final product but also aspects of its manufacturing, which often place constraints on said design. Nature’s “manufacturing” method involves (at the global level of structure), highly complex growth – these natural growth mechanisms have no parallel in most manufacturing processes. Take for example the flower stalk in Fig 1, which is from a Yucca tree that I found in a parking lot in Arizona.
At first glance, this looks like a good example of overlapping surfaces, one of the 6 categories of cellular structures I covered before. But when you pause for a moment and query the function of this packing of cells (WHY this shape, size, packing?), you realize there is a powerful growth motive for this design. A few weeks later when I returned to the parking lot, I found many of the Yucca stems simultaneously in various stages of bloom – and captured them in a collage shown in Fig 2. This is a staggering level of structural complexity, including integration with the environment (sunlight, temperature, pollinators) that is both wondrous and for an engineer, very humbling.
The lesson here is to recognize growth as a strong driver in every natural structure – the tricky part is determining when the design is constrained by growth as the primary force and when can growth be treated as incidental to achieving an optimum functional objective.
Even setting aside the growth driver mentioned previously, structure in nature is often serving multiple functions at once – and this is true of cellular structures as well. Consider the tessellation of “scutes” on the alligator. If you were tasked with designing armor for a structure, you may be tempted to mimic the alligator skin as shown in Fig. 3.
As you begin to study the skin, you see it is comprised of multiple scutes that have varying shape, size and cross-sections – see Fig 4 for a close-up.
The pattern varies spatially, but you notice some trends: there exists a pattern on the top but it is different from the sides and the bottom (not pictured here). The only way to make sense of this variation is to ask what functions do these scutes serve? Luckily for us, biologists have given this a great deal of thought and it turns out there are several: bio-protection, thermoregulation, fluid loss mitigation and unrestricted mobility are some of the functions discussed in the literature [1, 2]. So whereas you were initially concerned only with protection (armor), the alligator seeks to accomplish much more – this means the designer either needs to de-confound the various functional aspects spatially and/or expand the search to other examples of natural armor to develop a common principle that emerges independent of multi-functionality specific to each species.
1.3 Sub-Optimal Design
This is an aspect for which I have not found an example in the field of cellular structures (yet), so I will borrow a well-known (and somewhat controversial) example  to make this point, and that has to do with the giraffe’s Recurrent Laryngeal Nerve (RLN), which connects the Vagus Nerve to the larynx as shown in Figure 5, which it is argued, takes an unnecessarily long circuitous route to connect these two points.
We know that from a design standpoint, this is sub-optimal because we have an axiom that states the shortest distance between two points is a straight line. And therefore, the long detour the RLN makes in the giraffe’s neck must have some other evolutionary and/or developmental basis (fish do not have this detour) . However, in the case of other entities such as the cellular structures we are focusing on, the complexity of the underlying design principles makes it hard to identify cases where nature has found a sub-optimal design space for the function of interest to us, in favor of other pressing needs determined by selection. What is sufficient for the present moment is to appreciate that such cases may exist and to bear them in mind when studying structure in nature.
2. Classifying Functions
Given the above challenges, the engineer may well ask: why even consider natural form in making determinations involving the design of engineering structures? The biomimic responds by reminding us that nature has had 3.8 billion years to develop a “design guide” and we would be wise to learn from it. Importantly, natural and engineering structures both exist in the same environment and are subject to identical physics and further, are both often tasked with performing similar functions. In the context of cellular structures, we may thus ask: what are the functions of interest to engineers and designers that nature has addressed through cellular design? Through my reading [1-4], I have compiled the classification of functions in Figure 6, though this is likely to grow over time.
This broad classification into structural and transport may seem a little contrived, but it emerges from an analyst’s view of the world. There are two reasons why I propose this separation:
Structural functions involve the spatial allocation of materials in the construction of the cellular structures, while transport functions involve the structure AND some other entity and their interactions (fluid or light for example) – thus additional physics needs to be comprehended for transport functions
Secondly, structural performance needs to be comprehended independent of any transport function: a cellular structure must retain its integrity over the intended lifetime in addition to performing any additional function
Each of these functions is a fascinating case study in its own right and I highly recommend the site AskNature.org  as a way to learn more on a specific application, but this is beyond the scope of the current post. More relevant to our high-level discussion is that having listed the various reasons WHY cellular structures are found in nature, the next question is can we connect the structures described in the previous post to the functions tabulated above? This will be the attempt of my next post. Until then, as always, I welcome all inputs and comments, which you can send by messaging me on LinkedIn.
What types of cellular designs do we find in nature?
Cellular structures are an important area of research in Additive Manufacturing (AM), including work we are doing here at PADT. As I described in a previous blog post, the research landscape can be broadly classified into four categories: application, design, modeling and manufacturing. In the context of design, most of the work today is primarily driven by software that represent complex cellular structures efficiently as well as analysis tools that enable optimization of these structures in response to environmental conditions and some desired objective. In most of these software, the designer is given a choice of selecting a specific unit cell to construct the entity being designed. However, it is not always apparent what the best unit cell choice is, and this is where I think a biomimetic approach can add much value. As with most biomimetic approaches, the first step is to frame a question and observe nature as a student. And the first question I asked is the one described at the start of this post: what types of cellular designs do we find in the natural world around us? In this post, I summarize my findings.
In a previous post, I classified cellular structures into 4 categories. However, this only addressed “volumetric”structures where the objective of the cellular structure is to fill three-dimensional space. Since then, I have decided to frame things a bit differently based on my studies of cellular structures in nature and the mechanics around these structures. First is the need to allow for the discretization of surfaces as well: nature does this often (animal armor or the wings of a dragonfly, for example). Secondly, a simple but important distinction from a modeling standpoint is whether the cellular structure in question uses beam- or shell-type elements in its construction (or a combination of the two). This has led me to expand my 4 categories into 6, which I now present in Figure 1 below.
Setting aside the “why” of these structures for a future post, here I wish to only present these 6 strategies from a structural design standpoint.
Volumetric – Beam: These are cellular structures that fill space predominantly with beam-like elements. Two sub-categories may be further defined:
Honeycomb: Honeycombs are prismatic, 2-dimensional cellular designs extruded in the 3rd dimension, like the well-known hexagonal honeycomb shown in Fig 1. All cross-sections through the 3rd dimension are thus identical. Though the hexagonal honeycomb is most well known, the term applies to all designs that have this prismatic property, including square and triangular honeycombs.
Lattice and Open Cell Foam: Freeing up the prismatic requirement on the honeycomb brings us to a fully 3-dimensionallattice or open-cell foam. Lattice designs tend to embody higher stiffness levels while open cell foams enable energy absorption, which is why these may be further separated, as I have argued before. Nature tends to employ both strategies at different levels. One example of a predominantly lattice based strategy is the Venus flower basket sea sponge shown in Fig 1, trabecular bone is another example.
Volumetric – Shell:
Closed Cell Foam: Closed cell foams are open-cell foams with enclosed cells. This typically involves a membrane like structure that may be of varying thickness from the strut-like structures. Plant sections often reveal a closed cell foam, such as the douglas fir wood structure shown in Fig 1.
Periodic Surface: Periodic surfaces are fascinating mathematical structures that often have multiple orders of symmetry similar to crystalline groups (but on a macro-scale) that make them strong candidates for design of stiff engineering structures and for packing high surface areas in a given volume while promoting flow or exchange. In nature, these are less commonly observed, but seen for example in sea urchin skeletal plates.
Tessellation: Tessellation describes covering a surface with non-overlapping cells (as we do with tiles on a floor). Examples of tessellation in nature include the armored shells of several animals including the extinct glyptodon shown in Fig 1 and the pineapple and turtle shell shown in Fig 2 below.
Overlapping Surface: Overlapping surfaces are a variation on tessellation where the cells are allowed to overlap (as we do with tiles on a roof). The most obvious example of this in nature is scales – including those of the pangolin shown in Fig 1.
What about Function then?
This separation into 6 categories is driven from a designer’s and an analyst’s perspective – designers tend to think in volumes and surfaces and the analyst investigates how these are modeled (beam- and shell-elements are at the first level of classification used here). However, this is not sufficient since it ignores the function of the cellular design, which both designer and analyst need to also consider. In the case of tessellation on the skin of an alligator for example as shown in Fig 3, was it selected for protection, easy of motion or for controlling temperature and fluid loss?
In a future post, I will attempt to develop an approach to classifying cellular structures that derives not from its structure or mechanics as I have here, but from its function, with the ultimate goal of attempting to reconcile the two approaches. This is not a trivial undertaking since it involves de-confounding multiple functional requirements, accounting for growth (nature’s “design for manufacturing”) and unwrapping what is often termed as “evolutionary baggage,” where the optimum solution may have been sidestepped by natural selection in favor of other, more pressing needs. Despite these challenges, I believe some first-order themes can be discerned that can in turn be of use to the designer in selecting a particular design strategy for a specific application.
This is by no means the first attempt at a classification of cellular structures in nature and while the specific 6 part separation proposed in this post was developed by me, it combines ideas from a lot of previous work, and three of the best that I strongly recommend as further reading on this subject are listed below.
As always, I welcome all inputs and comments – if you have an example that does not fit into any of the 6 categories mentioned above, please let me know by messaging me on LinkedIn and I shall include it in the discussion with due credit. Thanks!
Thursday, March 2 is PADT’s annual SciTech Festival Open House, from 5-8pm (click HERE to register). This year, three student groups working on a range of projects will be present to showcase their work, all of which involved some level of 3D printing. Please bring friends and families to meet and discuss ideas with these students from our community.
Formula SAE Team (Arizona State University)
ASU’s Formula SAE team will be onsite with their 2016 car, demonstrating specifically how they used 3D printing to manufacture the functional intake manifolds on these cars. What is specifically interesting is how they have modified their manifold design to improve performance while leveraging the advantages of 3D printing, and also they have evaluated multiple materials and processes over the recent years (FDM, SLS).
Prosthetic Arm Project (BASIS Chandler)
Rahul Jayaraman will be back to discuss how he and 30 students at BASIS Chandler manufactured, assembled and delivered about 20 prosthetic hands to an organization that distributes these to children in need across the world. Rahul and PADT were featured in the news for this event.
Cellular Structures in Nature (BASIS Chandler)
A BASIS Chandler High School senior, Amy Zhang, just started her Senior Research Project with PADT, focusing on a project at the intersection of biology and 3D printing, investigating cellular structures that occur on surfaces in nature, like the wing of a dragonfly or the shell on a turtle or the encasing of a pineapple – all of which are comprised of cellular geometries. Using 3D scanning, image analysis and mathematical methods, Amy hopes to develop models for describing these structures that can then be used in developing design principles for 3D printing. You can learn more on Amy’s blog: http://shellcells.blogspot.com/
Attending AeroDef this year in Fort Worth? Make sure you register to tour Concept Laser on March 6th before AeroDef! You’ll hear an update on the GE acquisition and presentations on customer applications and machine safety. Registration ends February 24th, 2017, so don’t miss this opportunity!
Speed, superior quality monitoring, and an open architecture that enables innovation – that is what makes Concept Laser’s Direct Metal Laser Melting (DMLM) technology a leader in the metal additive manufacturing industry. Come and hear about how Concept Laser is investing to bring you innovation through new products and processes that will lead to revenue-generating opportunities for your business.
The Tour is March 6th from 8:30am to 11:30pm and includes round trip transportation from the conference and more.
What you will see on the tour:
Direct Metal Laser Melting
In-situ Quality Assurance
Best-in-class safety guidelines when interacting with reactive and non-reactive materials
It was my first time visiting New Orleans. I have heard many stories of how good the food is and how everyone is really nice there so I was excited to visit this city for a business trip. Stratasys Launch 2017! There was some buzz going on about some new FDM printers that Stratasys has been working on and I was really excited to see them and hear what sets them apart from the competition. Rey Chu (Co-Owner of PADT), Mario Vargas (Manager of 3D Printer Sales), Norman Stucker (Account Executive in Colorado), and I (James Barker, Application Engineer) represented PADT at this year’s Launch.
The city did not disappoint! I ate the best gumbo I’ve ever tried. Below is a picture of it with some Alligator Bourbon Balls. The gumbo is Alligator Sausage and Seafood. Sooooo Good!!
My last night in New Orleans, Stratasys rented out Mardi Gras World. That is where they build all the floats for Mardi Gras. They had a few dancers and people dressed up festive. I was able to get a picture of Rey in a Mardi Gras costume.
After dinner at Mardi Gras World, I took Rey and Mario down Bourbon Street one last time and then we went to Café Du Monde for their world famous Beignets. Everyone told me that if I come home without trying the Beignets, then the trip was a waste. They were great! I recommend them as well. Below is picture of Mario and me at the restaurant.
As you can see we had a fun business trip. The best part of it was the unveiling of the new FDM printers! Mario and I sat on the closest table to the stage and shared the table with Scott Crump (President of Stratasys and inventor of FDM technology back in 1988). These new printers are replacing some of Stratasys entry level and mid-level printers. What impressed me most is that they all can print PLA, ABS, and ASA materials with the F370 being able to print PC-ABS. You also can build parts in four different layer heights (.005, .007, .010, and .013”), all while utilizing new software called GrabCad Print.
GrabCad Print is exciting because you can now monitor all of you Stratasys FDM printers from this software and setup queues. What made me and many others clap during the unveiling is that with GrabCad Print you no longer have to export STL files! You can import your native CAD assemblies and either print them as an assembly or explode the assembly and print the parts separately.
Everyone wants a 3D Printer that can print parts faster, more accurately and is dependable. You get that with the family of systems! Speed has increased big time, they are twice as fast as the Dimension line of FDM printers. Stratasys has published the accuracy of these new printers to be ±.008” up to a 4 inch tall part and then every inch past 4 inches, you add another .002”. These machines are very dependable. They are replacing the Uprint (Uprint SE Plus is still current), Dimension, and Fortus 250 machines that have been workhorses. Many of our customers still have a Dimension from 2002 when they were first launched. In addition to the 43 existing patents that Stratasys has rolled into this phenomenal product, they have an additional 15 new patents that speaks volumes as to the innovation in these 3D printers.
Stratasys Launch was a blast for me. Seeing these new printers, parts that were printed from them, and understanding why these are the best FDM printers on the market was well worth my time! I look forward to helping you with learning more about them. Please contact me at firstname.lastname@example.org for more information. If you would like to hear my recorded webinar that has even more information about the new F170, F270, and F370, here is the link. Or you can download the brochure here.
I had a really great time designing the Metal 3D printed shift knob from my previous blog post. I was curious what the other benefits of the knob may be besides being cool to look at and show off. What better way than to use the simulation software that we use here at PADT every day!
One of the clear differences between my solid spherical knob and the Metal 3D printed version is surface area. Being that PADT is based in Tempe, AZ, some may say that we have “warm” summers down here. Couple the 120F days with a black car, and the interior can get very hot, at some points feeling like the sun itself has taken up residence inside the back seat. With modern A/C, this heat can be mitigated fairly quickly, only to attempt to shift into gear to be scalded by the shift knob!
I wanted to see what the rate of cooling for the two knobs would be in a basic situation with some basic assumptions. Using ANSYS transient thermal, I initialized the knobs to 150F, temperatures that can be quickly reached in parked cars here in AZ. I added a convection heat transfer boundary condition on the outer surface of each shift knob, assuming a film coefficient of 50 W/m^2C, and that the ambient temp in the car is at a cool 70F.
I ran the simulations for 5 minutes, and the results were in line with what I expected. As the 3D printed knob has more surface area for cooling, it’s final temperature was ~84F, compared to the solid spherical knob at a final temperature of 115F!