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/
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.
Although February is a short month, we have lots of activities scheduled to talk about new releases from both ANSYS and Stratasys as well as a STEM and Medtech event. Take a look for details below or visit the bottom of our home page to see the latest.
Arizona Science Bowl
ASU West Campus
PADT will be attending this great event for middle and high schools. Dr. Bhate will be speaking to the middle school students
Stratasys is introduce some new products and you are invited to attend online to learn how once again they will advance 3D Printing to the next level. PADT’s engineers will not just share information about these new systems, they will also explain what we thing is important about each machine and what its new advantages are.
ANSYS is rolling out a new version of their entire software platform, and we are offering seminars to help users understand what is new and cool. This first webinar will be focused on ANSYS Mechanical APDL and what is going on way deep under the hood.
Medtech has grown a lot in Arizona over the past couple of years, so the Tech Council is putting on an event for everyone involved to get together to network and learn. PADT will have a booth and will be talking about 3D Printing in medical devices. If you are at all involved in medical technology, you should attend.
ANSYS is rolling out a new version of their entire software platform, and we are offering seminars to help users understand what is new and cool. This second webinar will be focused on ANSYS HPC licensing and how that has changed.
Metal 3D Printing is one of the more exciting areas of additive manufacturing, and we are learning a lot about how to safely operate our new system. Our very own Dhruv Bhate, PhD shared those lessons learned in this new video:
The video stresses the importance of keeping an inert environment to keep part quality and to ensure a safe operating environment. Our Concept Laser Metal 3D Printer uses high powered lasers to melt metal powder one layer at a time to build 3D Parts. This process produces soot that is highly flammable.
Dhruv shows the process we use to break the part from the machine, clean the chamber of soot, and replace the filter that captures the soot.
To learn more about PADT and how we can help you with your 3D Printing, product development, or Numerical Simulation needs, please visit www.padtinc.com
Use this link to see all of our blog posts on Metal 3D Printing
On January 18th, ASU will officially Launch their Manufacturing Research and Innovation Hub, the Largest Additive Manufacturing research and teaching center in the Southwestern US. PADT is proud to have partnered with ASU as well as with Concept Laser and Honeywell to get this important piece of the local manufacturing ecosystem started and to keep it growing.
Located on the Polytechnic School at ASU in Mesa, Arizona, this facility is amazing. And you can see it for yourself, the public is invited to the launch on January 18th, 2017 at 9:00 am. ASU Polytechnic Dean Kyle Squires and the Director Ann McKenna will be speaking as will our very own Rey Chu, John Murray from Concept Laser, and Don Godfrey from Honeywell. Tours will follow. Learn more and register for this free event that will bring together the local 3D Printing community here.
You can also learn more by reading the official press release from Concept Laser that outlines what the center does and the partnerships that make it possible:
Concept Laser, Honeywell, and PADT Build Largest Additive Manufacturing Center in Southwest at Arizona State University
GRAPEVINE, Texas, January 11, 2017 – The Polytechnic School at Arizona State University (ASU) offers the only manufacturing engineering undergraduate degree in Arizona; it is also one of only 22 ABET accredited manufacturing engineering programs in the United States. By forming a partnership with Concept Laser, Honeywell Aerospace, and PADT, Inc. the largest additive manufacturing research facility in the Southwest is now on the Polytechnic campus. The 15,000 square foot center holds over $2 million of plastic, polymer, and 3D metal printing equipment.
The lab has a Concept Laser M2 cusing and Mlab cusing machine which are dedicated to 3D metal printing, also known as metal additive manufacturing. Unlike conventional metal fabrication techniques, additive manufacturing produces fully-dense metal parts by melting layer upon layer of ultra-fine metal powder. The Polytechnic School is using the machines for a wide range of research and development activities including materials development and prototyping complex mechanical and energy systems.
Don Godfrey, Engineering Fellow at Honeywell: “Honeywell is thrilled to be participating in the opening of the new additive manufacturing laboratory at the Arizona State University Polytechnic campus. For many years, we have worked with ASU seniors on their capstone projects with three of these projects this school year additive manufacturing focused. In addition to our own additive manufacturing operations, we have provided mentorship to students in the program and assisted in the procurement of one machine for the schools’ new lab. We look forward to growing our relationships with the university in developing brilliant minds to tackle and overcome industry challenges associated with aviation and additive manufacturing.”
John Murray, President and CEO of US-based subsidiary Concept Laser Inc: “Changing the future of metal additive manufacturing begins with educated teachers and curious students. The educational leadership that the ASU Polytechnic School provides to the Southwest region and the industry will certainly be impactful. Concept Laser is proud to be a partner in this initiative.”
Rey Chu, Principal, Manufacturing Technologies at PADT, Inc: This partnership is the next and obvious step in the progression of additive manufacturing in the Southwest. With Concept Laser’s outstanding technology, Honeywell’s leadership in applying additive manufacturing to practical Aerospace needs, PADT’s extensive network of customers and industry experience, and ASU’s proven ability to educate and work with industry, the effort will establish a strong foundation for the entire regional ecosystem.
Ann McKenna, Director of ASU’s Polytechnic School: “Partnering with these industry leaders provides us the capability to do additional research and enhance our education programs. With so few of these types of centers, this makes ASU more attractive among academic partners, federal agencies and corporations to advance additive manufacturing.
The ASU Polytechnic School will be hosting an open house to celebrate the launch of their Manufacturing Research and Innovation Hub on January 18, 2017 at 9am. There will be guided tours showcasing student projects. Honeywell, Concept Laser, and PADT will be in attendance. Please register your attendance at www.mrihlaunch.eventbrite.com.
About Concept Laser
Concept Laser GmbH is one of the world’s leading providers of machine and plant technology for the 3D printing of metal components. Founded by Frank Herzog in 2000, the patented LaserCUSING® process – powder-bed-based laser melting of metals – opens up new freedom to configuring components and also permits the tool-free, economic fabrication of highly complex parts in fairly small batch sizes.
Concept Laser serves various industries, ranging from medical, dental, aerospace, toolmaking and mold construction, automotive and jewelry. Concept Laser machines are compatible with a diverse set of powder materials, such as stainless steel and hot-work steels, aluminum and titanium alloys, as well as precious metals for jewelry and dental applications.
Concept Laser Inc. is headquartered in Grapevine, Texas and is a US-based wholly owned subsidiary of Concept Laser GmbH. For more information, visit our website at www.conceptlaserinc.com
LaserCUSING® is a registered trademark of Concept Laser.
About Phoenix Analysis and Design Technologies
Phoenix Analysis and Design Technologies, Inc. (PADT) is an engineering product and services company that focuses on helping customers who develop physical products by providing Numerical Simulation, Product Development, and 3D Printing solutions. PADT’s worldwide reputation for technical excellence and experienced staff is based on its proven record of building long term win-win partnerships with vendors and customers. Since its establishment in 1994, companies have relied on PADT because “We Make Innovation Work.” With over 80 employees, PADT services customers from its headquarters at the Arizona State University Research Park in Tempe, Arizona, and from offices in Torrance, California, Littleton, Colorado, Albuquerque, New Mexico, and Murray, Utah, as well as through staff members located around the country. More information on PADT can be found at www.PADTINC.com.
About Arizona State University
The Ira A. Fulton Schools of Engineering at Arizona State University include nearly 19,000 students and more than 300 faculty members who conduct nearly $100 million in research, spanning a broad range of engineering, construction and technology fields. Across the six schools contained within the Fulton Schools, 24 undergraduate and 32 graduate programs are offered on ASU’s Tempe and Polytechnic campuses and online. The schools’ educational programs emphasize problem solving, entrepreneurship, multidisciplinary interactions, social context and connections. Arizona State University includes more than 80,000 students and 1,600 tenured or tenure-track faculty on multiple campuses in metropolitan Phoenix as well as online. For more information, please visit www.asu.edu or asuonline.asu.edu.
Our 10-page article on “Modeling the Mechanical Behavior of Cellular Structures for Additive Manufacturing” was published in the Winter 2016 edition of the Metal AM magazine. This article represents a high-level summary of the different challenges and approaches in addressing the modeling specific aspects of cellular structures, along with some discussion of the design, manufacturing and implementation aspects associated with AM.
Click HERE for link to the entire magazine, our article starts on page 51. Digital editions are free to download. Swing by PADT in the new year to pick up a hard copy or look for it at our table when you visit us at trade shows.
To stay in touch with the latest developments at the intersection of AM and Cellular Structures, connect with me on LinkedIn, where I typically post 1-2 blog posts every month on this, or related subjects in Additive Manufacturing.
I have always had an issue with leaving well enough alone since the day I bought my Subaru. I have altered everything from the crank pulley to the exhaust, the wheels and tires to the steering wheel. I’ve even 3D printed parts for my roof rack to increase its functionality. One of the things that I have altered multiple times has been the shift knob. It’s something that I use every time and all the time when I am driving my car, as it is equipped with a good ol’ manual transmission, a feature that is unfortunately lost on most cars in this day and age.
I have had plastic shift knobs, a solid steel spherical shift knob, a black shift knob, a white shift knob, and of course some weird factory equipment shift knob that came with the car. What I have yet to have is a 3D printed shift knob. For this project, not any old plastic will do, so with the help of Concept Laser, I’m going straight for some glorious Remanium Star CL!
One of the great things about metal 3D printing is that during the design process, I was not bound by the traditional need for a staple of design engineering, Design For Manufacturing (DFM). The metal 3D printer uses a powder bed which is drawn over the build plate and then locally melted using high-energy fiber lasers. The build plate is then lowered, another layer of powder is drawn across the plate, and melted again. This process continues until the part is complete.
The design for the knob was based off my previously owned shift knobs, mainly the 50.8 mm diameter solid steel spherical knob. I then needed to decide how best to include features that would render traditional manufacturing techniques, especially for a one-off part, cost prohibitive, if not impossible. I used ANSYS Spaceclaim Direct Modeler as my design software, as I have become very familiar with it using it daily for simulation geometry preparation and cleanup, but I digress, my initial concept can be seen below:
I was quickly informed that, while this design was possible, the amount of small features and overhangs would require support structure that would make post-processing the part very tedious. Armed with some additional pointers on creating self supporting parts that are better suited for metal 3D printing, I came up with a new concept.
This design is much less complex, while still containing features that would be difficult to machine. However, with a material density of 0.0086 g/mm^3, I would be falling just short of total weight of 1 lb, my magic number. But what about really running away from DFM like it was the plague?
There we go!!! Much better, this design iteration is spec’d to come out at 1.04 lbs, and with that, it was time to let the sparks fly!
Here it is emerging as the metal powder that has not been melted during the process is brushed away.
The competed knob then underwent a bit of post processing and the final result is amazing! I haven’t been able to stop sharing images of it with friends and running it around the office to show my co-workers. However, one thing remains to make the knob functional… it must be tapped.
In order to do this, we need a good way to hold the knob in a vise. Lucky for us here at PADT, we have the ability to quickly design and print these parts. I came up with a design that we made using our PolyJet machine so we could have multiple material durometers in a single part. The part you need below utilizes softer material around the knob to cradle it and distribute the load of the vise onto the spherical lattice surface of the knob.
We quickly found out that the Remanium material was not able to be simply tapped. We attempted to bore the hole out in order to be able to press in an insert, and also found out the High Speed Steel (HSS) was not capable of machining the hole. Carbide however does the trick, and we bored the hole out in order to press in a brass insert, which was then tapped.
Finally, the shift knob is completed and installed!
How can the mechanical behavior of cellular structures (honeycombs, foams and lattices) be modeled?
This is the second in a two-part post on the modeling aspects of 3D printed cellular structures. If you haven’t already, please read the first part here, where I detail the challenges associated with modeling 3D printed cellular structures.
The literature on the 3D printing of cellular structures is vast, and growing. While the majority of the focus in this field is on the design and process aspects, there is a significant body of work on characterizing behavior for the purposes of developing analytical material models. I have found that these approaches fall into 3 different categories depending on the level of discretization at which the property is modeled: at the level of each material point, or at the level of the connecting member or finally, at the level of the cell. At the end of this article I have compiled some of the best references I could find for each of the 3 broad approaches.
1. Continuum Modeling
The most straightforward approach is to use bulk material properties to represent what is happening to the material at the cellular level [1-4]. This approach does away with the need for any cellular level characterization and in so doing, we do not have to worry about size or contact effects described in the previous post that are artifacts of having to characterize behavior at the cellular level. However, the assumption that the connecting struts/walls in a cellular structure behave the same way the bulk material does can particularly be erroneous for AM processes that can introduce significant size specific behavior and large anisotropy. It is important to keep in mind that factors that may not be significant at a bulk level (such as surface roughness, local microstructure or dimensional tolerances) can be very significant when the connecting member is under 1 mm thick, as is often the case.
The level of error introduced by a continuum assumption is likely to vary by process: processes like Fused Deposition Modeling (FDM) are already strongly anisotropic with highly geometry-specific meso-structures and an assumption like this will generate large errors as shown in Figure 1. On the other hand, it is possible that better results may be had for powder based fusion processes used for metal alloys, especially when the connecting members are large enough and the key property being solved for is mechanical stiffness (as opposed to fracture toughness or fatigue life).
2. Cell Level Homogenization
The most common approach in the literature is the use of homogenization – representing the effective property of the cellular structure without regard to the cellular geometry itself. This approach has significantly lower computational expense associated with its implementation. Additionally, it is relatively straightforward to develop a model by fitting a power law to experimental data [5-8] as shown in the equation below, relating the effective modulus E* to the bulk material property Es and their respective densities (ρ and ρs), by solving for the constants C and n.
While a homogenization approach is useful in generating comparative, qualitative data, it has some difficulties in being used as a reliable material model in analysis & simulation. This is first and foremost since the majority of the experiments do not consider size and contact effects. Secondly, even if these were considered, the homogenization of the cells only works for the specific cell in question (e.g. octet truss or hexagonal honeycomb) – so every new cell type needs to be re-characterized. Finally, the homogenization of these cells can lose insight into how structures behave in the transition region between different volume fractions, even if each cell type is calibrated at a range of volume fractions – this is likely to be exacerbated for failure modeling.
3. Member Modeling
The third approach involves describing behavior not at each material point or at the level of the cell, but at a level in-between: the connecting member (also referred to as strut or beam). This approach has been used by researchers [9-11] including us at PADT  by invoking beam theory to first describe what is happening at the level of the member and then use that information to build up to the level of the cells.
This approach, while promising, is beset with some challenges as well: it requires experimental characterization at the cellular level, which brings in the previously mentioned challenges. Additionally, from a computational standpoint, the validation of these models typically requires a modeling of the full cellular geometry, which can be prohibitively expensive. Finally, the theory involved in representing member level detail is more complex, makes assumptions of its own (e.g. modeling the “fixed” ends) and it is not proven adequately at this point if this is justified by a significant improvement in the model’s predictability compared to the above two approaches. This approach does have one significant promise: if we are able to accurately describe behavior at the level of a member, it is a first step towards a truly shape and size independent model that can bridge with ease between say, an octet truss and an auxetic structure, or different sizes of cells, as well as the transitions between them – thus enabling true freedom to the designer and analyst. It is for this reason that we are focusing on this approach.
Continuum models are easy to implement and for relatively isotropic processes and materials such as metal fusion, may be a good approximation of stiffness and deformation behavior. We know through our own experience that these models perform very poorly when the process is anisotropic (such as FDM), even when the bulk constitutive model incorporates the anisotropy.
Homogenization at the level of the cell is an intuitive improvement and the experimental insights gained are invaluable – comparison between cell type performances, or dependencies on member thickness & cell size etc. are worthy data points. However, caution needs to be exercised when developing models from them for use in analysis (simulation), though the relative ease of their computational implementation is a very powerful argument for pursuing this line of work.
Finally, the member level approach, while beset with challenges of its own, is a promising direction forward since it attempts to address behavior at a level that incorporates process and geometric detail. The approach we have taken at PADT is in line with this approach, but specifically seeks to bridge the continuum and cell level models by using cellular structure response to extract a point-wise material property. Our preliminary work has shown promise for cells of similar sizes and ongoing work, funded by America Makes, is looking to expand this into a larger, non-empirical model that can span cell types. If this is an area of interest to you, please connect with me on LinkedIn for updates. If you have questions or comments, please email us at email@example.com or drop me a message on LinkedIn.
Our work on 3D printed honeycomb modeling that started as a Capstone project with students from ASU in September 2015 (described in a previous blog post), was published in a peer-reviewed paper released last week in the proceedings of the SFF Symposium 2016. The full title of the paper is “A Validated Methodology for Predicting the Mechanical Behavior of ULTEM-9085 Honeycomb Structures Manufactured by Fused Deposition Modeling“. This was the precursor work that led to a us winning an 18-month award to pursue this work further with America Makes.
Download the whole paper at the link below:
Abstract ULTEM-9085 has established itself as the Additive Manufacturing (AM) polymer of choice for end-use applications such as ducts, housings, brackets and shrouds. The design freedom enabled by AM processes has allowed us to build structures with complex internal lattice structures to enhance part performance. While solutions exist for designing and manufacturing cellular structures, there are no reliable ways to predict their behavior that account for both the geometric and process complexity of these structures. In this work, we first show how the use of published values of elastic modulus for ULTEM-9085 honeycomb structures in FE simulation results in 40- 60% error in the predicted elastic response. We then develop a methodology that combines experimental, analytical and numerical techniques to predict elastic response within a 5% error. We believe our methodology is extendable to other processes, materials and geometries and discuss future work in this regard.
Building on the worldwide success of previous products in the family, PADT has just released the new SCA 3600, a large capacity cleaning system for removing the support material from Stratasys FDM parts. This new system adds capacity and capability over the existing benchtop SCA-1200HT System.
The SCA 3600 can dissolve support from all the SST-compatible materials you use – ABS, PC, and nylon. A “no heat” option provides agitation at room temperature for the removal of Polyjet SUP706 material as well. The SCA 3600’s versatility and efficient cleaning performance are built on the success of earlier models with all the features you have come to expect, in a larger and more capable model.
Since the launch of the original SCA-1200 in 2008, PADT has successfully manufactured and supported the SCA family of products for users worldwide. Common requests from desktop SCA users were for a larger system for bigger parts, the ability to clean many parts at the same time, and the option to remove supports from PolyJet parts. The SCA 3600 is the answer: Faster, larger, and more capable.
SCA 3600 Key Features are:
Removes soluble support from ABS, PC, and nylon 3D printed FDM parts
Removes soluble support from PolyJet 3D Printed parts
User-selectable temperature presets at 50, 60, 70, and 85°C and “No Heat” for PolyJet
Uses cleaning solutions from Stratasys
Unique spray nozzle optimizes flow coverage
230 VAC +/- 10%, 15A
Includes rolling cart for easy movement, filling, and draining.
Capacity: 27 gal / 102 L
Size: 42.8″ x 22.8″ x 36.5″/ 1,086 x 578 x 927 mm
16” x 16” x 14” / 406 x 406 x 356 mm removable large parts basket
Integral hinged lid and small part basket
Stainless steel tub and basket
Over temperature and water level alarms
Automatic halt of operation with alarms
Field replaceable sub-assemblies
Regulatory Compliance: CE/cTUVus/RoHS/WEEE
You can download our new brochure for both systems:
If you are interested in learning more or adding an SCA 3600 to your additive manufacturing lab, contact your Stratasys reseller.
Official copies of the press release can be found in HTML and PDF.
New 3D Printing Support Cleaning Apparatus Features Large Capacity for Stratasys FDM Systems
Offered Worldwide, the SCA 3600 is Big Enough to Handle Large 3D Printed Parts, Effortlessly Dissolving Support Material
TEMPE, Ariz., November 17, 2016 – Phoenix Analysis & Design Technologies, Inc. (PADT), the Southwest’s largest provider of simulation, product development, and rapid prototyping services and products, today introduced its new SCA3600 3D Printing Support Cleaning Apparatus (SCA). The systems are sold exclusively by Stratasys, Ltd. (SSYS) for use with its FORTUS line of 3D Printers. The hands-free support removal technology is a huge advantage to people who use Fused Deposition Modeling (FDM) systems for their 3D Printing.
“With more than 10,000 of our benchtop SCA units in the field, we gathered a wealth of knowledge on performance and reliability,” said Rey Chu, Co-owner and Principal of PADT. “We used that information to design and manufacture a system that cleans larger parts, or multiple small parts, while keeping the speed, easy maintenance and great user experience of the benchtop system.”
A powerful upgrade over PADT’s successful SCA-1200HT and SCA-1200 support removal products that have been in use around the world since 2008, the SCA 3600 features a simpler, more user-friendly design. The new versatile SCA offers temperature choices of 50, 60, 70 and 80 degrees Celsius, as well as no-heat, that readily cleans supports from all SST compatible materials – ABS, PC and Nylon. The SCA 3600 also features a large 16” x 16” x 14” parts basket, 3400 watts of heating for faster warm-up and a wheeled cart design for mobility.
The advantages of the system were highlighted by Sanja Wallace, Sr. Director of Product Marketing and Management at Stratasys, Ltd. when she commented, “the addition of the SCA 3600 as an accessory to our very successful FORTUS systems simplifies the support removal process with increased speed and capacity for multiple large parts.”
Once parts are printed, users simply remove them from their Stratasys FDM system, place them in the SCA 3600, set a cleaning cycle time and temperature, and then walk away. The device gently agitates the 3D printed parts in the heated cleaning solution, effortlessly dissolving away all of the support material. This process is more efficient and user friendly than those of other additive manufacturing systems using messy powders or support material that must be manually removed.
Phoenix Analysis and Design Technologies, Inc. (PADT) is an engineering product and services company that focuses on helping customers who develop physical products by providing Numerical Simulation, Product Development, and Rapid Prototyping solutions. PADT’s worldwide reputation for technical excellence and experienced staff is based on its proven record of building long term win-win partnerships with vendors and customers. Since its establishment in 1994, companies have relied on PADT because “We Make Innovation Work.” With over 80 employees, PADT services customers from its headquarters at the Arizona State University Research Park in Tempe, Arizona, and from offices in Torrance, California, Littleton, Colorado, Albuquerque, New Mexico, and Murray, Utah, as well as through staff members located around the country. More information on PADT can be found at http://www.PADTINC.com.
In the Fused Deposition Modeling (FDM) process, support structures are needed for features with overhang incline angle less than 45-degree from horizontal. Stratasys developed a series of support materials for different model materials: SR-30TM for ABS, SR-100TM for polycarbonate and SR-110TM for nylon. Also, they developed the Waterworks Soluble Concentrate, P400-SC, to be used to dissolve these support materials. In this blog post, I develop a theory for the chemical reaction how P400-SC Waterworks dissolves SR-30TM, SR-100TM and SR-110TM support materials. As part of this, I explain how PADT’s Support Cleaning Apparatus (SCA) tank, with its heating and unique circulation and agitation capabilities that are important for the support dissolving process.
We begin by looking at the composition of the different materials involved in the table below.
Polymer can swell and then dissolve into water as a consequence of abundant hydrophilic groups, like carboxyl group (-COOH), ether group (-O-), hydroxyl group (-OH) and so on in its molecular structure. Theoretically, SR-30TM and SR-100TM /SR-110TM Soluble Support Materials including a carboxyl group (-COOH) in their repeat unit are likely to be water soluble. However, they also have a hydrophobic ester group (-COO-) in their repeat unit, which counteracts the efficacy of the hydrophilic group on the long carbon chain. Thus, the key to making SR-30TM and SR-100TM /SR-110TM soluble, is to somehow get rid of the ester group.
Hydrolysis of ester in pure water is a slow process even the system is heated. Both acid and alkaline conditions can catalyze and speed up the process. Under the acid condition, the hydrolysis is a reversible process until it reaches an equilibrium state, whereas alkaline conditions promote a thorough hydrolysis with a stirring and heating system.
P400-SC Waterworks contains sodium carbonate, sodium hydroxide, sodium lauryl sulfate and sodium metasilicate. The last two constituents, with 1-5 wt% respectively, are auxiliaries in the P400-SC Waterworks. The remaining two react with carboxylic acid and ester group per the following chemical reaction:
where R is the remaining carbon chain apart from carboxyl group and R1, R2 represent the two-side segments of ester group. Ester hydrolysis is the main reaction we need, which ionizes the ester group and makes it water soluble with an increased polarity. These reactions would happen when SR-30TM or SR-100TM /SR-110TM supports are dropped into a tank with P400-SC Waterworks cleaning solution inside.
From the table above, we can see that ABS-M30TM and PC-10TM don’t have hydrophilic groups, which restrains their solubility into water. Nylon is semi-crystalline polymer and difficult to dissolve into water and most organic solvent, despite the presence of the hydrophilic group acylamino (-CONH-), which still results in a nice water-absorbing ability. All these model materials are common-use engineering plastic with nice chemical resistance (depending on their functional groups), they can be safe in the cleaning solution.
PADT’s Support Cleaning Apparatus (SCA)
The SCA tank offers an optimized environment with agitation and heating for the ester hydrolysis reaction. The tank has four preset temperature options (50 ℃, 60℃, 70℃, 85℃) for ABS-M30TM, PC-10TM, and FDMTM Nylon 12 model materials, due to their different thermal resistance. The innovative custom designed pump is key to cause the solution to effectively and efficiently dissolve and remove the support materials.