The Additive Manufacturing section of this blog is for PADT customers in particular, and users of 3D Printing in general. We hope you find it useful and entertaining.
Over time we will post information below. Feel free to use the search to find specific information. We also have some non-changing information on our resource page.
Posted on March 28, 2017, by: Dhruv Bhate, PhDWhat 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.
Design StrategiesIn 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-dimensional lattice 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.
ReferencesThis 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.
- Gibson, Ashby, Harley (2010), Cellular Materials in Nature and Medicine, Cambridge University Press; 1st edition
- Naleway, Porter, McKittrick, Meyers (2015), Structural Design Elements in Biological Materials: Application to Bioinspiration. Advanced Materials, 27(37), 5455-5476
- Pearce (1980), Structure in Nature is a Strategy for Design, The MIT Press; Reprint edition
Posted on March 3, 2017, by: Eric MillerWhile installing our new metal 3D Printer we learned a couple of important lessons on working with local inspectors. In "Installing a metal 3-D printer was a lesson on working with regulators" we share what we captured.
Posted on February 28, 2017, by: Dhruv Bhate, PhDThursday, 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. https://www.youtube.com/watch?v=FwRv7lwMBkE
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/
Posted on February 21, 2017, by: Eric MillerAttending AeroDef this year in Fort Worth? Make sure you register to tour Concept Laser on March 6th before AeroDef! You’ll hear an update on the GE acquisition and presentations on customer applications and machine safety. Registration ends February 24th, 2017, so don’t miss this opportunity! Register now: http://aerodefevent.com/sessions/concept-laser-tour/ Speed, superior quality monitoring, and an open architecture that enables innovation – that is what makes Concept Laser’s Direct Metal Laser Melting (DMLM) technology a leader in the metal additive manufacturing industry. Come and hear about how Concept Laser is investing to bring you innovation through new products and processes that will lead to revenue-generating opportunities for your business. The Tour is March 6th from 8:30am to 11:30pm and includes round trip transportation from the conference and more. What you will see on the tour:
- Direct Metal Laser Melting
- In-situ Quality Assurance
- Best-in-class safety guidelines when interacting with reactive and non-reactive materials
Posted on February 13, 2017, by: James BarkerIt 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 email@example.com 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.
Posted on February 9, 2017, by: Nathan HuberI had a really great time designing the Metal 3D printed shift knob from my previous blog post. I was curious what the other benefits of the knob may be besides being cool to look at and show off. What better way than to use the simulation software that we use here at PADT every day! One of the clear differences between my solid spherical knob and the Metal 3D printed version is surface area. Being that PADT is based in Tempe, AZ, some may say that we have "warm" summers down here. Couple the 120F days with a black car, and the interior can get very hot, at some points feeling like the sun itself has taken up residence inside the back seat. With modern A/C, this heat can be mitigated fairly quickly, only to attempt to shift into gear to be scalded by the shift knob! I wanted to see what the rate of cooling for the two knobs would be in a basic situation with some basic assumptions. Using ANSYS transient thermal, I initialized the knobs to 150F, temperatures that can be quickly reached in parked cars here in AZ. I added a convection heat transfer boundary condition on the outer surface of each shift knob, assuming a film coefficient of 50 W/m^2C, and that the ambient temp in the car is at a cool 70F. I ran the simulations for 5 minutes, and the results were in line with what I expected. As the 3D printed knob has more surface area for cooling, it's final temperature was ~84F, compared to the solid spherical knob at a final temperature of 115F!
Posted on February 8, 2017, by: Eric MillerDid you know that PADT does scanning of parts? No? You are not alone. We recently ran into several customers who were sending their scanning out of state and didn't know that they could have it done by PADT, someone who is already a trusted partner. So we thought it would be a good time to do an update on our Scanning services and provide some additional background on what it is.
Part Scanning 101The idea behind part scanning is that you want to take a part in the real world, and get an accurate model in a computer. To do this you somehow measure the part with a computer, getting a three dimensional representation of the parts surface. Today, there are six basic ways to do this:
PADT offers Structured Light and Cross Sectional ScanningAll of these methods create points in space. The more sophisticated the software, the more automatic the process of assembling the points to define the surfaces of the full object. These points are sometimes called a "point cloud." The Point cloud can them be turned in to a faceted representation of the object. For many people, this is all they need. This faceted representation can be rendered on a computer screen or 3D Printed. It can also be used with inspection software to determine the accuracy of the part relative to its original specification as well as variations across multiple copies of the same geometry. If users need more, like a full CAD model, that can be created from the point cloud using specialized software. PADT uses Geomagic DesignX. This tool not only creates usable geometry, but it can export in the customer's native CAD format. To do accurate part scanning you need:
- A precision scanning device
- Software to take the measured data and create an accurate point cloud. This includes repair and cleanup tools.
- Software to convert the point cloud into a usable 3D CAD model
- or, Software to conduct accurate inspection on the measured geometry.
Why does Part Scanning Take so Long and Cost So Much?When people ask for their first part scanning quote, they can often be surprised by the cost. The scanning process doesn't look that hard. And to be honest, the amount of time you actually spend scanning most parts is pretty short. The time is spent on the preparation, scanning hard-to-reach areas, the clean up, and then converting the data in to usable formats. If we are working with a light based scanner, we have to prepare the parts so that they reflect the light properly. Sometimes we have to cover the part with a find powder, sometimes we may even have to paint it. What we need is for the reflection and color of the part to not interfere with the scanning. If we are using cross sectional scanning, the part needs to be cast inside a rigid material, so the part we are scanning does not distort as we remove layers. In addition, if the part is not a solid light or dark color, it may need to be died to provide contrast for the camera. Both processes also require some study to determine the orientation of the part relative to the scanner and how the scanning process will take place. Once all this is worked out, the scanning often goes very fast. If there are nasty little parts that are hard to get to or that confuse the device, the engineer may have to modify things, do some special localized scanning, or even make castings that are then scanned. As is usual with technical processes, a very small portion of the surface being scanned may take up the vast majority of the scanning time. Once the scanning is done, the real hard work begins. Although software is much better than it was in the past, the resulting point cloud needs to be massaged and cleaned. Stray data is removed, and points from different scans need to be positioned and combined. Then everything must be checked. If a CAD solid model is needed, then the engineer must spend considerable time dealing with complex features and transition areas. As with the scanning, the bulk of the time spent creating a CAD model is spent on a relatively small percentage of the geometry. All of this adds up. Plus, to be honest, things rarely go as planned and unexpected issues arise that need to be dealt with.
Part Scanning Services at PADTNow we get to the important part of this post: hiring PADT to do your scanning. We added this capability to support our 3D Printing customers that wanted copies of physical parts. But as we looked at it, we found that we also had customers who needed inspection and reverse engineering of legacy parts. We studied the problem for some time and found the right tools and people to make it happen. Our primary scanner is a Zeiss Comet L3D 5M STructured light scanner. It used to be called a Steinbichler, till Zeiss bought them in 2015. Although it is portable and easy to manipulate, the Comet L3D 5M is highly accurate. It allows us to scan everything from small medical devices to the front end of acar, and to know that the resulting geometry will be accurate and usable. This is the best option for inspection and reverse engineering of high-precision parts. We also have a Geomagic Capture scanner. Although less accurate it is more portable and simpler to operate. It is ideal or taking to a customer and getting geometry for reverse engineering or part copying. If parts have internal features, and are made of plastic, we use our Cross Sectional Scanners. These high precision devices do a fantastic job and are really the best way to capture inside surfaces. Our customers love it to see how injection molded parts are coming out on well used molds. If anything else is needed, our experts can outsource to a niche supplier.
Want to do it Yourself?If you need to do your own scanning, no worries. PADT also sells all the tools we use inhouse to customers that need the capability internally.
Next StepsHopefully this posting has answered most of your questions and you are eager to try 3D Part Scanning. The best place to start is to get a quote from PADT. However, if you still have questions then feel free to contact us and fire away. We are passionate bout this capability and love talking about it. Either way, you can email firstname.lastname@example.org or call 480.813.4884 and ask to talk about Part Scanning. We also have some information on our website at www.padtinc.com/scanning.
Posted on January 31, 2017, by: Trevor Rubinoff
We here at PADT are excited to share information on the next big release from Stratasys, the global leader in 3D printing, additive solutions, materials and services.
The name Stratasys has always been synonymous with top of the line machines that meet even the most advanced rapid prototyping needs, and excel at every stage of the design prototyping process.
This new release is no exception.
Posted on January 31, 2017, by: Eric MillerTwo weeks ago we were part of a fantastic open house at the ASU Polytechnic campus for the grand opening of the Additive Manufacturing Research center, a part of the Manufacturing Research and Innovation Hub. What a great event it was where the Additive Manufacturing community in Arizona gathered in one place to celebrate this important piece in the local ecosystem. A piece that puts Arizona in the lead for the practical application of 3D Printing in industry. I could go on and on, but better writers by far have penned some great stories on the event and on the lab. ASU's article is here: New hub's $2 million in cutting-edge 3-D printing equipment will allow students to stay on forefront of rapidly growing sector And Hayley Ringle of the Phoenix Business Journal summed it all up, with some great insight into the impact on education and job growth in "See inside the Southwest’s largest 3D printing research facility at ASU" And last but not least, here are some pictures related to PADT that ASU provided:
Posted on January 23, 2017, by: Eric MillerMetal 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: https://youtu.be/0wQhXle6VEA 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
Press Release: Concept Laser, Honeywell, and PADT Build Largest Additive Manufacturing Center in Southwest at Arizona State University
Posted on January 11, 2017, by: Eric MillerOn 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:
Metal AM Magazine Article: Modeling the Mechanical Behaviour of Additively Manufactured Cellular Structures
Posted on December 19, 2016, by: Dhruv Bhate, PhDMetal AM Magazine publishes an article by PADT! 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.
Posted on December 8, 2016, by: Nathan HuberI 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!
Posted on December 5, 2016, by: Dhruv Bhate, PhDHow 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 ModelingThe 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 HomogenizationThe 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 ModelingThe 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.
ConclusionContinuum 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.
References (by Approach)
Bulk Property Models
 C. Neff, N. Hopkinson, N.B. Crane, "Selective Laser Sintering of Diamond Lattice Structures: Experimental Results and FEA Model Comparison," 2015 Solid Freeform Fabrication Symposium
 M. Jamshidinia, L. Wang, W. Tong, and R. Kovacevic. "The bio-compatible dental implant designed by using non-stochastic porosity produced by Electron Beam Melting®(EBM)," Journal of Materials Processing Technology214, no. 8 (2014): 1728-1739
 S. Park, D.W. Rosen, C.E. Duty, "Comparing Mechanical and Geometrical Properties of Lattice Structure Fabricated using Electron Beam Melting", 2014 Solid Freeform Fabrication Symposium
 D.M. Correa, T. Klatt, S. Cortes, M. Haberman, D. Kovar, C. Seepersad, "Negative stiffness honeycombs for recoverable shock isolation," Rapid Prototyping Journal, 2015, 21(2), pp.193-200.
Cell Homogenization Models
 C. Yan, L. Hao, A. Hussein, P. Young, and D. Raymont. "Advanced lightweight 316L stainless steel cellular lattice structures fabricated via selective laser melting," Materials & Design 55 (2014): 533-541.
 S. Didam, B. Eidel, A. Ohrndorf, H.‐J. Christ. "Mechanical Analysis of Metallic SLM‐Lattices on Small Scales: Finite Element Simulations versus Experiments," PAMM 15.1 (2015): 189-190.
 P. Zhang, J. Toman, Y. Yu, E. Biyikli, M. Kirca, M. Chmielus, and A.C. To. "Efficient design-optimization of variable-density hexagonal cellular structure by additive manufacturing: theory and validation," Journal of Manufacturing Science and Engineering 137, no. 2 (2015): 021004.
 M. Mazur, M. Leary, S. Sun, M. Vcelka, D. Shidid, M. Brandt. "Deformation and failure behaviour of Ti-6Al-4V lattice structures manufactured by selective laser melting (SLM)," The International Journal of Advanced Manufacturing Technology 84.5 (2016): 1391-1411.
Beam Theory Models
 R. Gümrük, R.A.W. Mines, "Compressive behaviour of stainless steel micro-lattice structures," International Journal of Mechanical Sciences 68 (2013): 125-139
 S. Ahmadi, G. Campoli, S. Amin Yavari, B. Sajadi, R. Wauthle, J. Schrooten, H. Weinans, A. Zadpoor, A. (2014), "Mechanical behavior of regular open-cell porous biomaterials made of diamond lattice unit cells," Journal of the Mechanical Behavior of Biomedical Materials, 34, 106-115.
 S. Zhang, S. Dilip, L. Yang, H. Miyanji, B. Stucker, "Property Evaluation of Metal Cellular Strut Structures via Powder Bed Fusion AM," 2015 Solid Freeform Fabrication Symposium
 D. Bhate, J. Van Soest, J. Reeher, D. Patel, D. Gibson, J. Gerbasi, and M. Finfrock, “A Validated Methodology for Predicting the Mechanical Behavior of ULTEM-9085 Honeycomb Structures Manufactured by Fused Deposition Modeling,” Proceedings of the 26th Annual International Solid Freeform Fabrication, 2016, pp. 2095-2106
Press Release: New 3D Printing Support Cleaning Apparatus Features Large Capacity for Stratasys FDM Systems
Posted on November 17, 2016, by: Eric MillerBuilding 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. A copy of the press release is below. At the same time, we are also launching a new website for support removal: www.padtinc.com/supportremoval. 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
- User-controlled timer
- Uses cleaning solutions from Stratasys
- Unique spray nozzle optimizes flow coverage
- 230 VAC +/- 10%, 15A
- Whisper-quiet operation
- 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