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:
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.
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.
- 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
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.
What do you get when you combine a motivated student leader, enthusiastic classmates, a worldwide online community, and the latest 3D Printing technology from Stratasys? You give children around the world a cool way to hold things again. That is what happened when high school student Rahul Jayaraman of Basis Chandler decided to take part in a project called Enabling The Future. They describe themselves as “A global network of passionate volunteers using 3D Printing to give the world a ‘helping hand'” by designing a wide variety of prosthetic hands for kids that can be printed and assembled by volunteers.
Local news station, KSAZ FOX 10 Phoenix stopped by PADT while we were printing three hands in our Stratasys FORTUS 450 to interview Rahul and talk to us about the project. It gives a great summary:
And Channel 3, KTVK, came to the assembly event at Basis Chandler:>
As did Channel 12, KPNX:
3D Printing is a fantastic technology for one simple reason, it enables almost anyone to manufacture parts. All you need is a good design. And that is where the people at Enabling the Future come in. Check out their website to see some great examples of how their volunteer work changes so many lives. Have a box of tissue handy if you watch the videos…
This is how the project works. A leader like Rahul takes the initiative to sign up for the project. He then chooses which of the many designs he wants to make. For this first go around, he picked a general design from Thingiverse called the Raptor Reloaded. Next they needed the hardware you could not 3D Print – screws springs, velcro, and bits and pieces that hold the design together. For this they needed to raise $25 per hand so Rahul was given the opportunity to learn how to raise money, a very useful skill.
PADT’s Dhruv Bhate and the rest of our 3D Printing team worked with Rahul to get the design just right and then 3D Print the hands. That will be done this week and this weekend the next phase will take place. Rahul and a large number of his classmates from Basis Chandler will get together at the school this weekend to put thirty or so hands together. They will then box them up and another volunteer group, www.HandChallenge.com, will ship them to kids in the developing world that need them.
Here is a video from Tom Fergus from Fox10 showing a closeup of the hand in action:
— Tom Fergus (@TomFergusFox10) October 14, 2016
We at PADT love projects like this because it is win-win-win. The students get a chance to run a complicated project by themselves, learning the skills they will need later in life to organize, manage, and finish a project. PADT wins because we can contribute to our chosen area of charity, STEM education, in a way that benefits others beyond a given school. And the big winners are the kids around the world that receive a new and cool way to grab hold of life.
We will have sample hands at our open house next Thursday: Nerdtoberfest as well as an update when we get feedback from the distribution of the hands.
Is PolyJet MED610 truly biocompatible? And what does that mean anyway?
A couple of months ago, our product development team contacted me to see if I could 3D print them a small bio-compatible masking device that was needed for temporary attachment to an invasive device prior to insertion for surgery. That led me to investigate all the different bio-compatible materials we did have access to at PADT on our FDM (Fused Deposition Modeling) and PolyJet machines. Given the tiny size and high detail required in the part, I decided to opt for PolyJet, which does offer the MED610 material that is claimed to be biocompatible. As it so happens, we have an Objet Eden 260V PolyJet machine that has been dedicated to running MED610 exclusively since it’s installation a year ago.
We printed the mask, followed all the post-processing instructions per supplier recommendations (more on that later) and delivered the parts for further testing. And that is when I asked myself the questions at the top of this post.
I set off on a quest to see what I could find. My first stop was the RAPID conference in (May 2016), where the supplier (Stratasys Inc.) had a well-staffed booth – but no one there knew much about MED610 apart from the fact that some orthodontists were using it. I did pick up one interesting insight: one of the engineers there hypothesized that MED610 was not very popular because it was cost-prohibitive since its proper use required machine dedication. I then went to the Stratasys Direct Manufacturing (a service bureau owned by Stratasys) booth, but it turned out they don’t even offer MED610 as a material option for service jobs – presumably because of the low demand for this material, consistent with our own observations.
So I took a step back and began searching for all I could find in the public domain on MED610 – and while it wasn’t much, here is the summary of my findings that I hope help anyone interested in this. I categorize it in three sources of information: claims made by the supplier, published work on in vitro studies and finally, some in vivo animal trials. But first, we must ask…
What does it mean for a Material to be Biocompatible?
A definition by Williams (The Williams Dictionary of Biomaterials, 1999) is in order: “Biocompatibility is the ability of a material to perform with an appropriate host response in a specific application.” So if PolyJet MED610 is to be called biocompatible, we must ask – what application do we have in mind? Fortunately, the supplier has a recommendation.
MED610 was launched by Objet in 2011 (Objet was acquired by Stratasys in 2012) as a biocompatible material, ideal for “applications requiring prolonged skin contact of more than 30 days and short-term mucosal-membrane contact of up to 24 hours“. Stratasys claims that parts printed according to Objet MED610 Use and Maintenance Terms were evaluated for biocompatibility in accordance with standard “DIN EN ISO 10993-1: 2009, Biological Evaluation of Medical Devices-Part 1: Evaluation and testing within a risk management process. This addresses cytotoxicity, genotoxicity, delayed hypersensitivity, and USP plastic Class VI, which includes the test for irritation, acute systemic toxicity and implantation”. Unfortunately, the actual data from the biocompatibility study conducted by Objet have not been made publicly available.
It is important to remember that Stratasys publishes a “Use and Maintenance Terms” document that details the steps needed not just to clean the part after printing, but also on the proper setup of the machine for ensuring best chances of meeting biocompatibility requirements. These are published online at this link and include a 3 hour soak in a 1-percent NaOH solution, a 30 min soak in IPA and multiple water jet rinses, among other steps. In other words, the claimed biocompatibility of MED610 is only valid if these instructions are followed. These steps are primarily driven by the need to completely remove supports and any support-residue, but it is not clear if this is needed if a part can be printed without supports. Given such strong process dependencies, it is only to be expected that Stratasys provide a disclaimer at the end of the document clarifying that the users of their machines are responsible for independently validating biocompatibility of any device they make with MED610.
The next question is: have there been any relevant published, independent studies that have used MED610? In my search, I could only find two instances, which I discuss below.
Primary Human Cells Response (In Vitro)
In a recent (January 2016) study published in the Journal of Medical and Biological Engineering, Schmelzer et al. studied the response of primary human cells to four 3D printed materials in vitro: ABS, PC, PLA and MED610 – the only such study I could find. All samples instead went through a 100% ethanol brief rinse and were washed 5 times with de-mineralized water – this seems like a less stringent process than what the supplier recommends (3 hour 1-percent NaOH solution soak, 30 minutes IPA soak and 10 times waterjet blasting) but was designed to be identical across all the materials tested.
There were some very interesting findings:
- Different cells had different responses:
- MED610 had the most negative impact on cell viability for keratinocytes (epidermal cells that produce keratin) – and the only material that showed statistically significant difference from the control.
- For bone marrow mesenchymal (stem) cells, a different effect was observed: direct culture on ABS and PC showed significant growth (7X compared to control) but MED610 and PLA showed no significant effect
- Surface Roughness influences cell attachment and proliferation:
- In agreement with other work, the authors showed that while rougher surfaces promote initial cell attachment, subsequent cell proliferation and overall cell numbers are higher on smoother surfaces. The MED610 samples had rougher surfaces than the FDM samples (possibly due to the use of the “matte” finish option) and could be one of the contributors to the observed negative effects on cell viability, along with the leached contents from the specimen.
Glaucoma Drainage Device (In Vivo, Rabbit studies)
A group of Australian researchers published a 2015 paper where they designed and used PolyJet MED610 to manufacture a Glaucoma Drainage Device (GDD). They selected PolyJet because of its ability to resolve very fine details that they needed for the device. Importantly, the purpose of this study was to assess the effect of different design parameters on the effectiveness of the device (relieving intraocular pressure). The device was implanted into rabbit eyeballs where it remained for up to 4 weeks.
The devices were printed on a Connex 350 PolyJet machine, after which the supports were removed from the devices with a water jet and “were repeatedly washed and inspected for consistency and integrity.” Tubes were attached with Silicone adhesive and the entire assembly was then “washed and sterilized with a hospital-grade hydrogen peroxide system before use”. The researchers did not examine the cellular and extracellular reactions in great detail, but did conclude that the reactions were similar between the MED610 device and the more standard polypropylene injection-molded device.
A short video recorded by some of the researchers as part of a Bioprinting course also provides some details into the 3D printing aspects of the work done.
In conclusion, the question I posed at the start of this post (Is PolyJet MED610 truly biocompatible?) is too simplistic. A process and a material together are not sufficient – there are procedures that need to be defined and controlled and further and more importantly, biocompatibility itself has to be viewed in the context of the application and the specific toxicity and interaction demands of that application. And that brings us to our key takeaways:
- MED610 is only recommended at best for applications requiring prolonged skin contact of more than 30 days and short-term mucosal-membrane contact of up to 24 hours and there is no data to dispute the suppliers claim that it is biocompatible in this context once all recommended procedures are implemented
- The work done by Australian researchers in using PolyJet MED610 for devoloping their Glaucoma Drainage Device in animal trials is perhaps the best example of how this material and the technology can be pushed further for evaluating designs and hypothesis in vivo when really fine features are needed. Stratasys’s FDM PC-ISO or ABS M30i materials, or other FDM extrusion capable materials like PLA, PCL and PLGA may be better options when the resolution allows – but this is a topic for a follow-on blog post.
- More in vitro work needs to be done to extend the work done by Schmelzer et al., which suggests that MED610 potentially has leachables that do impact cell viability negatively. Specifically, effects of surface finish (“matte” vs “gloss”) and sterilization on cell viability is a worthwhile follow-on step. In the interim, MED610 is expected to perform well for mucosal membrane contact under 24 hours (and why this is a great technology for dental guides and other temporary in-mouth placement).
If you have any thoughts on this matter or would like to collaborate with us and take advantage of our access to a PolyJet printer that is dedicated to MED610 or other bio-compatible FDM materials, as well as our extensive post-processing and design & analysis facilities, please connect with me on LinkedIn or send us a note at email@example.com and cite this blog post.
Thanks for reading!
- Stratasys Bio-compatible Materials Page: http://www.stratasys.com/materials/polyjet/bio-compatible
- PolyJet MED610 Data Sheets: http://www.stratasys.com/materials/material-safety-data-sheets/polyjet/dental-and-bio-compatible-materials
- Schmelzer, E., Over, P., Gridelli, B., & Gerlach, J. (2016). Response of Primary Human Bone Marrow Mesenchymal Stromal Cells and Dermal Keratinocytes to Thermal Printer Materials In Vitro. Journal of Medical and Biological Engineering, 36, 153-167.
- Ross C, Pandav S, Li Y, et al. Determination of Bleb Capsule Porosity With an Experimental Glaucoma Drainage Device and Measurement System. JAMA Ophthalmol.2015;133(5):549-554. doi:10.1001/jamaophthalmol.2015.30.
- Glaucoma case study in online course on Bioprinting, University of Woolongong, Future Learn, https://www.futurelearn.com/courses/bioprinting/3/steps/87168
Our loop around the Southwest with the new Stratasys J750 Full Color 3D Printer finished strong with a well attended gathering at ASU’s Skysong in Scottsdale. The event was so popular, Channel 10 did a story on it. Over 130 people signed up to learn more about this fantastic device, get caught up on latest industry trends, and talk with other users of Additive Manufacturing.
This event had a great mix of users from multiple industries as well as students and people wanting to just learn more about the technology.
The presentations were a big hit from every seminar, and Dhruv’s was especially popular in Arizona. You can download the presentations here:
Eric Miller’s Presentation on Design for 3D Printing:
Dhruv Bhate’s Overview of Additive Manufacturing:
James Barker and Mario Vargas’s Introduction of the Stratasys J750:
During the breaks and after the presentations, we had a chance to interact one-on-one with customers, show off parts, and answer questions. If you have any questions, please feel free to contact us at 480.813.4884 or firstname.lastname@example.org.
Lastly, we were visited by local TV channel 10, KSAZ who did a short but really informative segment on the show and the Stratasys J750:
The second stop on our trip around the Southwest for Stratasys’ new J750 Full Color 3D Printer was in fantastic downtown Salt Lake City. This device is reinventing 3D printing, and we are showing it off in person so people can see it up close along with holding incredible parts it makes in their hands.
Next stop if Phoenix – sign up here!
The 3D Printing community in Utah is very mature and the attendees were mostly very experienced users of many different additive manufacturing technologies. So we focused on real world applications for the J750 as well as other Stratasys systems.
We were fortunate enought to have a customer, Ultradent, present the fantastic ways that they use their FDM and Polyjet printers to make prototypes, tooling, and production parts.
As is usual in this type of an event, the discussion between and after presentations are the best part. People from Aerospace, sporting goods, medical devices, and consumer products swapped stories, suggestions, and tips.
It was also a family affair. with Jame Barker’s latest family addition was in attendence to help spread the word on the value of 3D Printing with Stratasys solutions:Beyond the little guy, the other hit of the afternoon was the J750. As seasoned additive manufacturing profesionals they see the incredible leap forward this machine represents – truly reinventing 3D Printing and opening up a huge range of oportunities.
Denver was the first stop on a trip around the Southwest for Stratasys’ new J750 Full Color 3D Printer. We are showing this machine that is reinventing 3D printing off in person so people can see the device up close and hold the incredible parts it makes in their hands.
The Denver event was hosted by St. Patrick’s Brewery in Littleton, right down the street from PADT’s Colorado Office. Several customers and PADT employees gave talks on how to better use 3D Printing, including a presentation from Mario Vargas on the new Stratasys J750.
On top of all of that, local radio station KDMT, Denver’s Money Talk 1690, did a live broadcast from the event. You can listen in here. Again, PADT employees and customers talked about 3D Printing as well as the new Stratasys J750.
We also made the local paper, check that out here.
According to some, the novelty of 3D printing has been wearing off — its mentioned in daily conversations, used on Grey’s Anatomy episodes, incorporated in high school and college classes. Most iPhone-wielding millennials know what it is and how it works. It’s not a “new thing” anymore, right?
Coming to Denver, Salt Lake City, and Phoenix — Phoenix Analysis & Design Technologies (PADT) invites you to be one of the first to meet the Stratasys J750 3D Printer: the latest introduction in the portfolio of PolyJet 3D Printers. The Stratasys J750 is the first-ever full-color, multi-material system, which finally addresses the frustration of designers who want realistic models but have to contend with inconsistent color results and rough finishes from current technology.
Ready to register now? Click here and jump right to it! Or keep reading . . .
Unlike other 3D printers currently in existence, the Stratasys J750 can operate with five different colors: cyan, magenta, yellow, black and white — all of the primary colors in the CMYK color process, just like day-to-day 2D full-color printers. The Stratasys J750 also achieves very fine layer thicknesses, enabling high surface quality and the creation of models and parts with very fine, delicate details, where current 3D printers usually result in relatively rough surface finishes.
What does this mean for those who use 3D printing? The Stratasys J750 not only delivers incredible realism but it’s also the most versatile 3D printer available. Designers and producers can say goodbye to the days of adopting multiple 3D-printing technologies and still resorting afterwards to extensive post-processing, such as sanding, painting and bonding.
Before the Stratasys J750, no single 3D printer could deliver full color, smooth surfaces and multiple materials. Now, however, you can print realistic prototypes, presentation models, Digital ABS injection molds, jigs, fixtures, educational and promotional pieces, production parts – or all of the above, with one system.
The Stratasys J750 even goes one step past versatile, simultaneously being the fastest, simplest, and easiest 3D printer to use. The printer includes several user-requested upgrades, such as server functionality, six-material capacity, and even three print modes that are suitable for different priorities: high speed, high mix and high quality. Additionally, where some 3D printing processes must run in a dedicated facility due to the possible hazard of the materials, chemicals and post-processing steps involved, the Stratasys J750 3D Printer uses a clean, easy process, with no hazardous chemicals to handle.
The Stratasys J750 is one choice among an ever-growing array of 3D printers in the marketplace. But its capabilities and versatility make it more than just a 3D printer; It’s a solution-maker.
In other words, Stratasys has just invented 3D printing. Again. PADT’s 3D Printing team can help you pick the best printer for your job and provide you with one-on-one engineering and prototype support.
If you’re at all interested in technology, you won’t want to miss this printer’s big coming-out day.
Check out times and locations below.
Saint Patrick’s Brewing Company
3:00 pm to 6:00 pm
Salt Lake – Wednesday, July 27th
Hilton Salt Lake City Center
3:00 pm to 6:00 pm
Phoenix – Friday, July 29th
2:00 pm to 5:00 pm
A few months ago, I did a post on the Technology Trends in Laser-based Metal Additive Manufacturing where I identified 5 key directions that technology was moving in. In this post, I want to do the same, but for a different technology that we also use on a regular basis at PADT: Fused Deposition Modeling (FDM).
1. New Materials with Improved Properties
Many companies have released and are continuously developing composite materials for FDM. Most involve carbon fibers and are discussed in this review. Arevo Labs and Mark Forged are two of many companies that offer composite materials for higher performance, the table below lists their current offerings (CF = Carbon Fiber, CNT = Carbon Nano Tubes). Virtual Foundry are also working on developing a metal rich filament (with about 89% metal, 11% binder polymer), which they claim can be used to make mostly-metal parts for non-functional purposes using existing FDM printers and a heat treatment to vaporize the binder. In short, while ABS and PLA dominate the market, there is a wide range of materials commercially available and this list is growing each year.
|Arevo Labs||CF, CNT in PAEK|
|CF in PEEK|
|Fiberglass in PARA|
|Mark Forged||Micro-CF in Nylon|
|Fiberglass (High Strength High Temperature)|
2. Improved Properties through Process Enhancements
Even with newer materials, a fundamental problem in FDM is the anisotropy of the parts and the fact that the build direction introduces weak interfaces. However, there are several efforts underway to improve the mechanical properties of FDM parts and this is an exciting space to follow with many approaches to this being taken. Some of these involve explicitly improving the interfacial strength: one of the ways this can be achieved is by pre-heating the base layer (as being investigated by Prof. Keng Hsu at the Arizona State University using lasers and presented at the RAPID 2016 conference). Another approach is being developed by a company called Essentium who combine microwave heating and CNT coated filaments as shown in the video below.
Taking a very different approach, Arevo labs has developed a 6-axis robotic FDM process that allows for conformal deposition of carbon fiber composites and uses an FEA solver to generate optimized toolpaths for improved properties.
3. Faster & Bigger
A lot of press has centered around FDM printers that make bigger parts and at higher deposition rates: one article discusses 4 of these companies that showcased their technologies at an Amsterdam trade show. Among the companies that showcased their technologies at RAPID was 3D Platform, that showed a $27,000 3D printer for FDM with a 1m x 1m x 0.5m printing platform. Some of the key questions for large form factor printers is if and how they deal with geometries needing supports and enabling higher temperature materials. Also, while FDM is well suited among the additive technologies for high throughput, large size prints, it does have competition in this space: Massivit is one company that in the video below shows the printing of a structure 5.6 feet tall in a mere 5 hours using what they call “Gel Dispensed Printing” that reduces the need for supports.
4. Bioprinting Applications
Micro-extrusion through syringes or specialized nozzles is one of the key ways bioprinting systems operate – but this is technically not “fused” deposition in that it may not involve thermal modification of the material during deposition. However, FDM technology is being used for making scaffolds for bio-printing with synthetic, biodegradable or bio-compatible polymers such as PCL and PLGA. The idea is these scaffolds then form the structure for seeding cells (or in some cases the cells are bioprinted as well onto the scaffold). This technology is growing fast and something we are also investigating at PADT – watch this space for more updates.
5. Material Modeling Improvements
Modeling FDM is an important part of being able to use simulation/analysis to design better processes and parts for functional use. This may not get a lot of press compared to the items above, but is a particular interest of mine and I believe is a critical piece of the puzzle going to true part production with FDM. I have written a few blog posts on the challenges, approaches and a micromechanics view of FDM printed structures and materials. The idea behind all of these is to represent FDM structures mathematically with valid and accurate models so that their behavior can be predicted and designs truly optimized. This space is also growing fast, the most recent paper I have come across in this space is from the University of Wisconsin-Madison that was published May 12, 2016.
Judging by media hype, metal 3D printing and 3D bioprinting are currently dominating the media spotlight – and for good reasons. But FDM has many things going for it: low cost of entry and manufacturing, user-friendliness and high market penetration. And the technology growth has no sign of abating: the most recent, 2016 Wohlers report assesses that there are over 300 manufacturers of FDM printers, though rumor on the street has it that there are over a thousand manufacturers coming up – in China alone. And as the 5 trends above show, FDM has a lot more to offer the world beyond being just the most rapidly scaling technology – and there are people working worldwide on these opportunities. When a process is as simple and elegant as extruding material from a hot nozzle, usable innovations will naturally follow.
Have you ever looked at the mechanical properties in an FDM material datasheet (one example shown below for Stratasys ULTEM-9085) and wondered why properties were prescribed in the non-traditional manner of XZ and ZX orientation? You may also have wondered, as I did, whatever happened to the XY orientation and why its values were not reported? The short (and unfortunate) answer is you may as well ignore the numbers in the datasheet. The longer answer follows in this blog post.
Mesostructure has a First Order Effect on FDM Properties
In the context of FDM, mesostructure is the term used to describe structural detail at the level of individual filaments. And as we show below, it is the most dominant effect in properties.
Consider this simple experiment we did a few months ago: we re-created the geometry used in the tensile test specimens reported in the datasheets and printed them on our Fortus 400mc 3D printer with ULTEM-9085. While we kept layer thickness identical throughout the experiment (0.010″), we modified the number of contours: from the default 1-contour to 10-contours, in 4 steps shown in the curves below. We used a 0.020″ value for both contour and raster widths. Each of these samples was tested mechanically on an INSTRON 8801 under tension at a displacement rate of 5mm/min.
As the figure below shows, the identical geometry had significantly different load-displacement response – as the number of contours grew, the sample grew stiffer. The calculated modulii were in the range of 180-240 kpsi. These values are lower than those reported in datasheets, but closer to published values in work done by Bagsik et al (211-303 kpsi); datasheets do not specify the meso-structure used to construct the part (number of contours, contour and raster widths etc.). Further, it is possible to modify process parameters to optimize for a certain outcome: for example, as suggested by the graph below, an all-contour design is likely to have the highest stiffness when loaded in tension.
Can we Borrow Ideas from Micromechanics Theory?
The above result is not surprising – the more interesting question is, could we have predicted it? While this is not a composite material, I wondered if I could, in my model, separate the contours that run along the boundary from the raster, and identify each as it’s own “material” with unique properties (Er and Ec). Doing this allows us to apply the Rule of Mixtures and derive an effective property. For the figure below, the effective modulus Eeff becomes:
Eeff = f.Ec + (1-f).Er
where f represents the cross-sectional area fraction of the contours.
With four data points in the curve above, I was able to use two of those data points to solve the above equation simultaneously and derive Er and Ec as follows:
Er = 182596 psi
Ec = 305776 psi
Now the question became: how predictive are these values of experimentally observed stiffness for other combinations of raster and contours? In a preliminary evaluation for two other cases, the results look promising.
So What About the Orientation in Datasheets?
Below is a typical image showing the different orientations data are typically attributed to. From our micromechanics argument above, the orientation is not the correct way to look at this data. The more pertinent question is: what is the mesostructure of the load-bearing cross-section? And the answer to the question I posed at the start, as to why the XY values are not typically reported, is apparent if you look at the image below closely and imagine the XZ and XY samples being tested under tension. You will see that from the perspective of the load-bearing cross-section, XY and XZ effectively have the similar (not the same) mesostructure at the load-bearing cross-sectional area, but with a different distribution of contours and rasters – these are NOT different orientations in the conventional X-Y-Z sense that we as users of 3D printers are familiar with.
The point of this preliminary work is not to propose a new way to model FDM structures using the Rule of Mixtures, but to emphasize the significance of the role of the mesostructure on mechanical properties. FDM mesostructure determines properties, and is not just an annoying second order effect. While property numbers from datasheets may serve as useful insights for qualitative, comparative purposes, the numbers are not extendable beyond the specific process conditions and geometry used in the testing. As such, any attempts to model FDM structure that do not account for the mesostructure are not valid, and unlikely to be accurate. To be fair to the creators of FDM datasheets, it is worth noting that the disclaimers at the bottom of these datasheets typically do inform the user that these numbers “should not be used for design specifications or quality control purposes.”
If you would like to learn more and discuss this, and other ideas in the modeling of FDM, tune in to my webinar on June 28, 2016 at 11am Eastern using the link here, or read more of my posts on this subject below. If you are reading this post after that date, drop us a line at email@example.com and cite this post, or connect with me directly on LinkedIn.
Thanks for reading!
Two related posts:
For several years now PADT has 3D Printed special thank you awards for the fantastic companies that sponsor the Arizona SciTech Festival. This year we decided to stick with the color of the Stratasys Connex3 but add some moving parts. This gear design spins around and was made as one part, we just wash the support material out of the gaps between parts.
This is a great example of going directly from a CAD model to a custom part. Each award has the recipient’s name printed on the smaller gear. Everything was designed in an hour or so and it took about another hour to add in the 30 or so names. We think these may be the best awards we have made so far.
Here is a video showing off how they spin:
Awards are kind of simple and fun. But the same technology is applied by PADT to help our customers design and build better medical devices, rockets, aircraft engines, computers, and pretty much any physical product you can think of. Give us a call at 1-800-293-PADT or email firstname.lastname@example.org to see how “We Make Innovation Work”
While much has been (justifiably) written about HP and XJet releasing new, potentially game-changing products at RAPID 2016, I wanted to write this post about some of the smaller, unexpected joys that I discovered. If I sound overly enthusiastic about the people and companies behind them, it is likely due to the fact that I wrote this on the flight back, staring out at the clouds and reflecting on what had been a wonderful trip: I own no locks, stocks or barrels in any of these companies.
1. Essentium Materials – Carbon Nanotubes and Microwaves to improve FDM mechanical properties
Over the past year, I have studied, written and made presentations about the challenges of developing models for describing Fused Deposition Modeling (FDM) given their complex and part-specific meso-structure. And while I worked on developing analytical and numerical techniques for extracting the best performance from parts in the presence of significant anisotropy, the team at Essentium has developed a process to coat FDM filaments with Carbon nanotubes and extrude them in the presence of microwave radiation. In the limited data they showed for test specimens constructed of unidirectional tool-paths, they demonstrated significant reduction in anisotropy and increase in strength for PLA. What I liked most about their work is how they are developing this solution on a foundation of understanding the contributions of both the meso-structure and inter-filament strength to overall part performance. Essentium was awarded the “RAPID Innovations award”, first among the 27 exhibitors that competed and are, in my opinion, addressing an important problem that is holding back greater expansion of FDM as a process in the production space.
2. Hyrel 3D – Maker meets Researcher meets The-Kid-in-All-of-Us
I only heard of Hyrel 3D a few days prior to RAPID, but neglected to verify if they were exhibiting at RAPID and was pleasantly surprised to see them there. Consider the options this 3D printer has that you would be hard pressed to find in several 3D printers combined: variable extrusion head temperatures (room temp to 450 C), sterile head options for biological materials, a 6W laser (yes, a laser), spindle tools, quad head dispensing with individual flow control and UV crosslinking options. Read that again slowly. This is true multiple degree-of-freedom material manipulation. What makes their products even more compelling is the direct involvement of the team and the community they are building up over time, particularly in academia, across the world, and the passion with which they engage their technology and its users.
3. Technic-Print: New Chemistry for Improved FDM Support Removal
If you manufacture FDM parts with soluble supports, keep reading. A chemist at Technic Inc. has developed a new solution that is claimed to be 400% faster than the current Sodium-Hydroxide solution we use to dissolve parts. Additionally, the solution is cited as being cleaner on the tank, leaving no residue, has a color indicator that changes the solution’s color from blue to clear. And finally, through an additional agent, the dissolved support material can be reclaimed as a clump and removed from the solution, leaving behind a solution that has a pH less than 9. Since PADT manufactures one of the most popular machines that are used to dissolve these supports that unbeknown to us, were used in the testing and development of the new solution, we had an enriching conversation with the lead chemist behind the solution. I was left wondering about the fundamental chemistry behind color changing, dissolution rates for supports and the reclaiming of support – and how these different features were optimized together to develop a usable end-solution.
4. Project Pan: Computationally Efficient Metal Powder Bed Fusion Simulation
I presented a literature review at AMUG (another Additive Manufacturing conference) last month, on the simulation of the laser-based powder bed fusion. At the time, I thought I had captured all the key players between the work being done at Lawrence Livermore National Labs by Wayne King’s group, the work of Brent Stucker at 3DSIM and the many academics using mostly commercially available software (mostly ANSYS) to simulate this problem. I learned at RAPID that I had neglected to include a company called “Project Pan” in my review. This team emerged from Prof. Pan Michaleris’s academic work. In 2012, he started a company that was acquired by Autodesk two months ago. In a series of 3 presentations at RAPID, Pan’s team demonstrated their simulation techniques (at a very high level) along with experimental validation work they had done with GE, Honeywell and others through America Makes and other efforts. What was most impressive about their work was both the speed of their computations and the fact that this team actually had complex part experimental validations to back up their simulation work. What most users of the powder bed fusion need is information on temperatures, stresses and distortion – and within time frames of a few hours ideally. It seems to me that Pan and his team took an approach that delivers exactly that information and little else using different numerical methods listed on their site (novel Hex8 elements, an element activation method and intelligent mesh refinement) that were likely developed by Pan over the years in his academic career and found the perfect application, first in welding simulation and then in the powder bed fusion process. With the recent Autodesk acquisition, it will be interesting to see how this rolls out commercially. Details of some of the numerical techniques used in the code can be found at their website, along with a list of related publications.
5. FDA Participation: Regulating through education and partnership
On a different note from the above, I was pleasantly surprised by the presence of the FDA, represented by Matthew Di Prima, PhD. He taught part of a workshop I attended on the first day, took the time to talk to everyone who had an interest and also gave a talk of his own in the conference sessions, describing the details of the recently released draft guidance from the FDA on 3D printing in medical applications. It was good to connect the regulatory agency to a person who clearly has the passion, knowledge, intelligence and commitment to make a difference in the Additive Manufacturing medical community. Yes, the barriers to entry in this space are high (ISO certifications, QSR systems, 510(k) & Pre-Market Approvals) but it seems clear that the FDA, at least as represented by Dr. Di Prima, are doing their best to be a transparent and willing partner.
What really makes a trip to a conference like RAPID worth it are the new ideas, connections and possibilities you come away with that you may not stumble upon during your day job – and on that account, RAPID 2016 did not disappoint. As a line in one of my favorite song’s goes:
“We’ll never know, unless we grow.
There’s too much world outside the door.”
– Fran Healy (Travis, “Turn”).
Over the past two academic semesters (2015/16), I had the opportunity to work closely with six senior-year undergraduate engineering students from the Arizona State University (ASU), as their industry adviser on an eProject (similar to a Capstone or Senior Design project). The area we wanted to explore with the students was in 3D printed lattice structures, and more specifically, address the material modeling aspects of these structures. PADT provided access to our 3D printing equipment and materials, ASU to their mechanical testing and characterization facilities and we both used ANSYS for simulation, as well as a weekly meeting with a whiteboard to discuss our ideas.
While there are several efforts ongoing in developing design and optimization software for lattice structures, there has been little progress in developing a robust, validated material model that accurately describes how these structures behave – this is what our eProject set out to do. The complex internal meso- and microstructure of these structures makes them particularly sensitive to process variables such as build orientation, layer thickness, deposition or fusion width etc., none of which are accounted for in models for lattice structures available today. As a result, the use of published values for bulk materials are not accurately predictive of true lattice structure behavior.
In this work, we combined analytical, experimental and numerical techniques to extract and validate material parameters that describe mechanical response of lattice structures. We demonstrated our approach on regular honeycomb structures of ULTEM-9085 material, made with the Fused Deposition Modeling (FDM) process. Our results showed that we were able to predict low strain responses within 5-10% error, compared to 40-60% error with the use of bulk properties.
This work is to be presented in full at the upcoming RAPID conference on May 18, 2016 (details at this link) and has also been accepted for full length paper submission to the SFF Symposium. We are also submitting a research proposal that builds on this work and extends it into more complex geometries, metals and failure modeling. If you are interested in the findings of this work and/or would like to collaborate, please meet us at RAPID or send us an email (email@example.com).
Many of you may have seen the recent launch of an Atlas V rocket from United Launch Alliance (ULA). We are honored to have lent our expertise to ULA’s 3D Printing efforts that resulted in the use of parts on that rocket made with additive manufacturing. We will be talking about that and other ways we help the Aerospace Industry at the 32nd Space Symposium this week in Colorado Springs Colorado. Please stop by!