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…
Technology is always changing, and it is changing faster and in more ways. Even if your business is not a “technology” business, new ways of doing things, new business models, and new ways of communicating will impact your business. In “6 ways to adapt your business model to disruptive technology” I explore six simple things that you can do to not just avoid harm by, but to take advantage of disruptive technologies.
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.
We are very pleased to announce our new newsletter, the PADT Pulse. For a while now customers have been asking for a monthly update on what is going on without having to go through our blog. So we are taking the best of what we did in a given month and sharing it in this newsletter.
Not only does it have a recap of important activities, it summarizes our most popular blog posts, shares some outside news of interest, and keeps you up to date on our upcoming events. We hope you enjoy it.
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.
We here at PADT are proud to present the ease of use and productivity enhancements that have been added to ANSYS Mechanical in release 18.
With this new release, ANSYS Mechanical focuses on the introduction of a variety of improvements that help save the users time, such as smarter data organization and new hotkeys, along with additions that can help you to better visualize specific intricacies in your models.
This webinar is coming up soon
Join PADT’s Simulation Support & Application Engineer Doug Oatis for an overview of the current user friendly interfaces within ANSYS Mechanical, along with the numerous additions in this new release that help to improve efficiency tenfold, such as:
Pretension Beam Connection
A beam connection is a power idealization to connect parts without modeling the bolts. Now the beam connection can be pretensioned as well.
Register today to find out how you can use this highly requested feature and many others to improve your throughput and stay ahead of the curve!
A support request from one of our customers recently was for the ability to make Thermal Contact Conductance, which is sort of a reciprocal of thermal resistance at the contact interface, a parameter so it can be varied in a parametric study. Unfortunately, this property of contact regions is not exposed as a parameter in the ANSYS Mechanical window like many other quantities are.
Fortunately, with ANSYS there is almost always a way……in this case we use the capability of an APDL (ANSYS Parametric Design Language) command object within ANSYS Mechanical. This allows us to access additional functionality that isn’t exposed in the Mechanical menus. This is a rare occurrence in the recent versions of ANSYS, but I thought this was a good example to explain how it is done including verifying that it works.
A key capability is that user-defined parameters within a command object have a ‘magic’ set of parameter names. These names are ARG1, ARG2, ARG3, etc. Eric Miller of PADT explained their use in a good PADT Focus blog posting back in 2013
In this application, we want to be able to vary the value of thermal contact conductance. A low value means less heat will flow across the boundary between parts, while a high value means more heat will flow. The default value is a calculated high value of conductance, meaning there is little to no resistance to heat flow across the contact boundary.
In order to make this work, we need to know how the thermal contact conductance is applied. In fact, it is a property of the contact elements. A quick look at the ANSYS Help for the CONTA174 or similar contact elements shows that the 14th field in the Real Constants is the defined value of TCC, the thermal contact conductance. Real Constants are properties of elements that may need to be defined or may be optional values that can be defined. Knowing that TCC is the 14th field in the real constant set, we can now build our APDL command object.
This is what the command object looks like, including some explanatory comments. Everything after a “!” is a comment:
! Command object to parameterize thermal contact conductance
! by Ted Harris, PADT, Inc., 3/31/2017
! Note: This is just an example. It is up to the user to create and verify
! the concept for their own application.
! From the ANSYS help, we can see that real constant TCC is the 14th real constant for
! the 17X contact elements. Therefore, we can define an APDL parameter with the desired
! TCC value and then assign that parameter to the 14th real constant value.
! We use ARG1 in the Details view for this command snippet to define and enable the
! parameter to be used for TCC.
r,cid ! tells ANSYS we are defining real constants for this contact pair
! any values left blank will not be overwritten from defaults or those
! assigned by Mechanical. R command is used for values 1-6 of the real constants
rmore,,,,,, ! values 7-12 for this real constant set
rmore,,arg1 ! This assigned value of arg1 to 14th field of real constant
! Now repeat for target side to cover symmetric contact case
r,tid ! tells ANSYS we are defining real constants for this contact pair
! any values left blank will not be overwritten from defaults or those
! assigned by Mechanical. R command is used for values 1-6 of the real constants
rmore,,,,,, ! values 7-12 for this real constant set
rmore,,arg1 ! This assigned value of arg1 to 14th field of real constant
You may have noticed the ‘cid’ and ‘tid’ labels in the command object. These identify the integer ‘pointers’ for the contact and target element types, respectively. They also identify the contact and target real constant set number and material property number. So how do we know what values of integers are used by ‘cid’ and ‘tid’ for a given contact region? That’s part of the beauty of the command object: you don’t know the values of the cid and tid variables, but you alsp don’t need to know them. ANSYS automatically plugs in the correct integer values for each contact pair simply by us putting the magic ‘cid’ and ‘tid’ labels in the command snippet. The top of a command object within the contact branch will automatically contain these comments at the top, which explain it:
! Commands inserted into this file will be executed just after the contact region definition.
! The type number for the contact type is equal to the parameter “cid”.
! The type number for the target type is equal to the parameter “tid”.
! The real and mat number for the asymmetric contact pair is equal to the parameter “cid”.
! The real and mat number for the symmetric contact pair(if it exists)
! is equal to the parameter “tid”.
Next, we need to know how to implement this in ANSYS Mechanical. We start with a model of a ball valve assembly, using some simple geometry from one of our training classes. The idea is that hot water passes through the valve represented by a constant temperature of 125 F. There is a heat sink represented at the OD of the ends of the valve at a constant 74 degrees. There is also some convection on most of the outer surfaces carrying some heat away.
The ball valve and the valve housing are separate parts and contact is used to allow heat to flow from the hotter ball valve into the cooler valve assembly:
Here is the command snippet associated with that contact region. The ‘magic’ is the ARG1 parameter which is given an initial value in the Details view, BEFORE the P box is checked to make it a parameter. Wherever we need to define the value of TCC in the command object, we use the ARG1 parameter name, as shown here:
Next, we verify that it actually works as expected. Here I have setup a table of design points, with increasing values of TCC (ARG1). The output parameter that is tracked is the minimum temperature on the inner surface of the valve housing, where it makes contact with the ball. If conductance is low, little heat should flow so the housing remains cool. If the conductance is high, more heat should flow into the housing making it hotter. After solving all the design points in the Workbench window, we see that indeed that’s what happens:
And here is a log scale plot showing temperature rise with increasing TCC:
So, excluding the comments our command object is 6 lines long. With those six lines of text as well as knowledge of how to use the ARG1 parameter, we now have thermal contact conductance which varies as a parameter. This is a simple case and you will certainly want to test and verify for your own use. Hopefully this helps with explaining the process and how it is done, including verification.
How do competitors work together in a mutually beneficial way? In “How universities can be a needed catalyst and safe place for cooperation” I take a look at the important role Universities can play in enabling this type of cooperation. Based on our own experience in such partnerships, I talk about what Universities can do to take a leadership role in this area.
Please join Phoenix Analysis and Design Technologies in welcoming our new engineering services business development manager, John Williams. John will be an integral part of our growth in helping customers turn their innovations into real products through our advanced engineering capabilities, flexible project management skills and careful vendor selection process.
“With John joining our team, we’ll be able to take our engineering services business to the next level and expand on our offerings,” said Eric Miller, co-founder and principal at PADT. “His sales and business development experience at the national and international level makes him ideal to handle our diverse client portfolio and position us as a major player in this category.”
To help PADT improve its market position in engineering services and product development, Williams will help define long-term organizational goals, build customer relationships, identify new business opportunities, and maintain extensive knowledge of market conditions.
“PADT is a diverse and innovative company that presents a number of exciting opportunities,” said Williams. “I look forward to using my experience and reach to raise awareness of the great engineering expertise the company can provide. Once companies realize how PADT can help them solve tough problems and implement their designs, the word will spread that PADT really does make innovation work.”
Williams brings more than 16 years of sales experience to the position. He joins PADT from Bell Helicopter Textron Inc. in South Asia where he was the director of business development. Prior to working at Bell Helicopter, John was Regional Sales Director for Textron Aviation for South Asia. Prior to this, he was President of Williams Consulting Group (WCG) in Phoenix, AZ.
Before starting WCG, Williams spent 12 years with The Boeing Company where he was last responsible for implementing Boeing’s offset programs in India. He also played a key role in successfully winning several large orders for Boeing. Prior to this assignment, Williams was in International Contracts at Boeing Defense Systems where he successfully negotiated and closed several major Commercial and US FMS contracts with foreign governments.
Williams holds a Bachelor’s Degree in Economics from Northwestern College. He has numerous professional certifications including a Master’s Certificate in Global Leadership from Thunderbird, the American Graduate School of International Management; as well as certifications in various U.S. Federal Acquisition Programs.
In support of the ANSYS Startup Program, PADT is proud to introduce the PADT Startup Spotlight.
We here at PADT are firm believers in the opinion that today’s startup companies are tomorrow’s industry leaders and thus should be give every possible opportunity to thrive and succeed.
As a result we are offering full access to our promotional capabilities in order to help startup companies developing physical prototypes to grow and develop in a competitive environment.
We will look through those startups that have purchased the ANSYS Startup Package through PADT, and select one to feature and promote, that we believe clearly represents the drive and entrepreneurial spirit that is key in order to succeed in today’s day and age.
Presenting the first Startup Spotlight:
Since their inception in 2014, Velox Motorsports has always been focused on speed; whether that be the speed of the NASCAR teams they have worked with or the desire their customers have for speed, which drives their competitiveness and fuels the demand for their products.
They even show a passion for speed in the company’s name (Velox), which translates from Latin to “swift or speed”.
One of the cool new features in CFX 18 is the ability to actively review results while the calculation is running. It is supported for steady state and transient calculations, and now includes support for rotating reference frames as well.
What follows are some tutorial-esque steps to get you started.
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.