Meet Ovid. He is a very simple character that we use to explain 3D Printing to kids. Explaining how 3D Printing works to anyone without a technical background can be tough. To help out PADT has created a collection of resources that shows how it is done, including a hands on model for younger kids, that feature Ovid as the object being printed.
Let’s start by getting technical. 3D Printing is a common term for a class of manufacturing methods referred to as Additive Manufacturing. In 3D Printing you take a computer model and you print it out to get a real world three dimensional object. The way we do it is that we slice the computer model into thin layers, then build up material in the 3D printer one layer at a time. Here is a simple GIF showing the most common process:
This is Fused Deposition Modeling, or FDM. If a classroom has a 3D Printer it is most likely an FDM printer.
The idea behind these resources is to show the process:
Start with a 3D Computer model
Build it one layer at a time
The materials below can be used by parents or teachers to explain things to kids, K-8. Please use freely and share!
This PowerPoint has slides that explain the 3D Printing process and the video is of the slides being presented, with our narration.
Our fun little plexiglass model of Ovid is an example of a manual 3D printing process. Students can stack up the layers to “3D Print” their own Ovid by hand, reinforcing the layered manufacturing process.
We did everything the same as a real 3D Printer, but instead of automatically stacking the layers, we cut each layer on a laser cutter and the students do the cutting.
Here is a video showing the laser cutting.
And this is a zip file containing the geometry we used to make Ovid in STEP, IGES, Parasolid, and SAT.
To put it all together we created a triangular rod with a base and height that are identical. Figure out the size you need once you have scaled the geometry for your version of Ovid. we glued the rod to a base.
Files for 3D Printing and Other Information
If you have access to a 3D Printer, you can print your own Ovid. Here is an STL and a Parasolid: Ovid-PADT-3D_Printing-1
We also have a video showing how the software for the printer slices the geometry and makes the tool path for each layer:
And to round things out, here is a few minutes of Ovid being made in one of our Stratasys FDM printers:
3-D Printing is having a significant impact on healthcare technology. In “3-D Printing Applications Changing Healthcare” PADT’s Dhruv Bhate gives real world examples of how this technology is enabling never-before-seen breakthroughs.
ULTEM-9085 is one of my favorite materials to 3D-print: one of the reasons is it is a high performance polymer that can and has been used for end part manufacturing (see my blog post about ULTEM in functional aerospace parts), but the other is because it is a demanding material to print, in ways that ABS, Polycarbonate and even Nylon are not. What makes it demanding is primarily that ULTEM supports are not soluble and need to be removed mechanically. An additional challenge comes from the fact that the support is best removed when the part is at a high temperature (175-195 C), which requires the use of gloves and reduces the user’s dexterity. For complex geometries with internal channels, this is particularly challenging and occasionally results in an inability to print a certain part in ULTEM-9085, which runs contrary to the design freedom this technology otherwise enables.
In this post, I accumulate what I have learned through working (and failing) on many an ULTEM-9085 job, as well as through discussions with other users, and share this here in terms of design and process guidelines. To demonstrate these guidelines, I use a recent geometry that we printed for the Arizona State University’s (ASU) SAE team for an engine intake manifold. These guidelines apply to the Stratasys Fortus platform (for Fused Deposition Modeling, or FDM) using the Insight software that accompanies these tools. The screen shots are from Insight 10.6, and a Fortus 400 was used to print the parts shown.
Summary of Guidelines:
Orient the part to eliminate supports in regions where you cannot remove them
Remove the supports as soon as the part comes out of the build chamber
Other observations: the interface of separation
1. Part Orientation
The single most important factor in simplifying support removal is part orientation. Most users of the FDM process know that part orientation determines the amount of support material consumed and also impacts the time to build the part. When working with ULTEM-9085, the additional challenge is that it is possible to design in supports that cannot be removed and will require you to scrap the job. This is especially true of internal features. While the automatic orientation feature in Insight allows you to minimize supports, it does not account for the difficulty of removing them. Thus when you are dealing with internal features, you may need to manually orient your part such that the internal features are aligned as close to the vertical as possible, and above the support angle (to be covered later).
As shown in Figure 1, for the intake manifold, I oriented the internal pipe structure close to the vertical and had to iterate a few times and verify that I had no support in the hard-to-reach areas. While I did have supports internally, they were limited to areas that were easy to access.
2. Box Supports
In a recent software upgrade, Insight added the ability to create box supports. The support structures consist of adjacent boxes instead of a continuous raster, which has the effect of allowing for easier separation of the support, though does slow down the build time. In my experience this support strategy does help with removal – the one parameter to consider here is the “Perforations” setting, though the default values were used for this part. The perforation is a layer of model material that is inserted into the support to make for easier breaking off of the support material. All cleavage surfaces in Fig. 3 are at perforation edges and you can see the building like construction with each floor distinguished by a layer of model material. When you have supports in hard to access regions, consider increasing the interval height so as to ensure you get separation at the model-support interface on the part before it occurs within the support on a perforation layer.
3. Optimize Process Parameters
While orientation will have the most significant impact on the support you need, another variable to be aware of is the “Self-Support Angle” parameter. This angle is measured from the horizontal, and represents the minimum angle of the part wall that will be built without supports. As a result, to reduce support requirements, you want this number to be as low as possible so that a greater volume of the part can be self-supported. Stratasys recommends default values, but these scale as a function of the contour width, and layer thickness, as shown in Fig. 4. The values bottom out at 40 degrees for the 0.013″ layer thickness and 43 degrees for the 0.010″ layer thickness. Thus, all other things being equal, you will be able to reduce the support needed by choosing a 0.013″ layer thickness and a 0.026″ or larger contour width. Note that both of these will impact your ability to resolve thin walls and fine features, so ensure you scan through all the tool-paths to validate that the geometry is accurately filled in.
4. Remove Supports Immediately
Supports are best removed when the model-support interface is hot. The best time to do this is right after you remove the parts from the print chamber, which is held at 195 C for ULTEM-9085. Ensure you have safety glasses on, work with thermal gloves and have a plier handy to pull out the support. In theory the parts can be re-heated again (175 C is a reasonable value for the oven), but Stratasys suggests that each re-heat cycle actually strengthens the interface, making it harder to remove. As a result, the best time to remove the supports is immediately out of the printer. Figure 5 shows the results of support removal for the intake manifold parts, including the build sheet.
5. Other Observations: the Interface of Separation
It helps to visualize what we are trying to do when we remove supports. There are two interfaces in question here, as shown in Figure 6. One is the model-support interface, the other is the support-box structure interface. We need separation at the model-support interface since removing the thin piece of interface material can prove challenging if the box supports have broken off (as happened for the piece below). What this means is as you remove support, you need to not just pull the supports but also add some peeling force that creates the separation. Once you create separation at the correct interface, you can pull the supports and should have proper cleavage.
One final point to keep in mind is that in some cases, eliminating internal supports may be impossible, as shown for a different part in Figure 7 below. The point is to eliminate the support in places you cannot reach with your pliers and get enough peeling force applied to. In the case below, I chose to have supports at the wide opening since I had adequate access to them. With practice, you will get a better sense of what supports can and cannot be removed and use that intuition to better shape your design and process layout decisions before you print.
Show your support for ASU’s Formula SAE team at their Facebook page and see a video about the endeavor here.
We thought we would open PADT’s doors to families and maybe a few people would stop by. Over 250 people did just that. What a great evening of smiling kids and adults enjoying the excitement of engineering. Exciting engineering? Yes, we know enough to not talk about quality system protocols, matrix inversions, and non-linear turbulence model convergence. We stuck to 3D Printing, elephants on skateboards, and 3D scanners. And we fed everyone pizza.
It was a great evening where everyone learned something. The focus was on exposing what engineers do, what PADT does, to people who may not be technical. Mostly kids but we also saw it as a way for engineers to show their family members and friends what engineering is about. The results far exceeded our expectation, mostly because of how great everyone who showed up was.
Some of the quotes from people who have emailed to thank us are:
“Thank you for opening up your office to me. What a cool place! Even though I have been familiar with and worked with 3D printing for 20+ years, it is always nice to see the new technology, products, and the output of the products. “
“… to see my son and all of the other kids so excited and amazed was truly awesome. Mason told me it was the best night of his life! And this morning his first words to me where thanking me for taking him to the event and when can we go back.”
“This is such a great opportunity for me to show my grandkids what I spent my life doing, and seeing them get so excited about it is wonderful”
The best part of the event for most of us here at PADT were the fantastic questions. As one of our engineers said “for 2 hours I was just lost in the joy of positive human interaction.” We do love what we do here, but it was nice to share it with other people.
At a recent Lunch-n-Learn organized by the Arizona Technology Council, I had the opportunity to speak for 10 minutes on 3D printing. I decided to focus my talk on trying to answer one question: how can I determine if 3D printing can benefit my business? In this blog post, I attempt to expand on the ideas I presented there.
While a full analysis of the Return-On-Investment would require a more rigorous and quantitative approach, I believe there are 5 key drivers that determine the value proposition for a company to invest in 3D printing, be it in the form of outsourced services or capital expenditure. If these drivers resonate with opportunities and challenges you see in your business, it is likely that 3D printing can benefit you.
1. Accelerating Product Development
3D printing has its origins in technologies that enabled Rapid Prototyping (RP), a field that continues to have a significant impact in product development and is one most people are familiar with. As shown in Figure 1, PADT’s own product development process involves using prototypes for alpha and beta development and for testing. RP is a cost- and time effective way of iterating upon design ideas to find ones that work, without investing in expensive tooling and long lead times. If you work in product development you are very likely already using RP in your design cycle. Some of the considerations then become:
Are you leveraging the complete range of materials including high temperature polymers (such as ULTEM), Nylons and metals for your prototyping work? Many of these materials can be used in functional tests and not just form and fit assessments.
Should you outsource your RP work to a service bureau or purchase the equipment to do it in-house? This will be determined by your RP needs and one possibility is to purchase lower-cost equipment for your most basic RP jobs (using ABS, for example) and outsource only those jobs requiring specialized materials like the ones mentioned above.
The video below contains several examples of prototypes made by PADT using a range of technologies over the past two decades.
2. Exploiting Design Freedom
Due to its additive nature, 3D printing allows for the manufacturing of intricate part geometries that are prohibitively expensive (or in some cases impossible) to manufacture with traditional means. If you work with parts and designs that have complex geometries, or are finding your designs constrained by the requirements of manufacturing, 3D printing can help. This design freedom can be leveraged for several different benefits, four of which I list below:
2.1 Internal Features
As a result of its layer-by-layer approach to manufacturing a part, 3D printing enables complex internal geometries that are cost prohibitive or even impossible to manufacture with traditional means. The exhaust gas probe in Fig. 2 was developed by RSC engineering in partnership with Concept Laser has 6 internal pipes surrounded by cooling channels and was printed as one part.
2.2 Strength-to-Weight Optimization
One of the reasons the aerospace industry has been a leader in the application of 3D printing is the fact that you are now able to manufacture complex geometries that emerge from a topology optimization solution and reduce component weight, as shown in the bracket manufactured by Airbus in Figure 3.
2.3 Assembly Consolidation
The ability to work in a significantly less constrained design space also allows the designer to integrate parts in an assembly thereby reducing assembly costs and sourcing headaches. The part below (also from Airbus) is a fuel assembly that integrated 10 parts into 1 printed part.
Nature provides several design cues, optimized through the process of evolution over millenia. Some of these include lattices and hierarchical structures. 3D printing makes it possible to translate more of these design concepts into engineering structures and parts for benefits of material usage minimization and property optimization. The titanium implant shown in Figure 5 exploits lattice designs to optimize the effective modulus in different locations to more closely represent the properties of an individuals bone in that region.
3. Simplifying the Supply Chain, Reducing Lead Times
One of the most significant impacts 3D printing has is on lead time reduction, and this is the reason why it is the preferred technology for “rapid” prototyping. Most users of 3D printing for end-part manufacturing identify a 70-90% reduction in lead time, primarily as a result of not requiring the manufacturing of tooling, reducing the need to identify one or more suppliers. Additionally, businesses can reduce their supplier management burden by in-sourcing the manufacturing of these parts. Finally, because of the reduced lead times, inventory levels can be significantly reduced. The US Air Force sees 3D printing as a key technology in improving their sustainability efforts to reduce the downtime associated with aircraft awaiting parts. Airbus recently also used 3D printing to print seat belt holders for their A310 – the original supplier was out of business and the cost and lead time to identify and re-tool a new supplier were far greater than 3D printed parts.
4. Reducing Costs for High Mix Low Volume Manufacturing
According to the 2015 Wohlers report, about 43% of the revenue generated in 3D printing comes from the manufacturing of functional, or end-use parts. When 3D printing is the process of choice for the actual manufacturing of end-use parts, it adds a direct cost to each unit manufactured (as opposed to an indirect R&D cost associated with developing the product). This cost, when compared to traditional means of manufacturing, is significantly lower for high mix low volume manufacturing (High Mix – LVM), and this is shown in Figure 6 for two extreme cases. At one extreme is mass customization, where each individual part has a unique geometry of construction (e.g. hearing aids, dental aligners) – in these cases, 3D printing is very likely to be the lowest cost manufacturing process. At the other end of the spectrum is High Volume Manufacturing (HVM) (e.g. semiconductor manufacturing, children’s toys), where the use of traditional methods lowers costs. The break-point lies somewhere in between and will vary by the the part being produced and the volumes anticipated. A unit cost assessment that includes the cost of labor, materials, equipment depreciation, facilities, floor space, tooling and other costs can aid with this determination.
5. Developing New Applications
Perhaps the most exciting aspect of 3D printing is how people all around the world are using it for new applications that go beyond improving upon conventional manufacturing techniques. Dr. Anthony Atala’s 2011 TED talk involved the demonstration of an early stage technique of depositing human kidney cells that could someday aid with kidney transplants (see Figure 7). Rarely does a week go by with some new 3D printing application making the news: space construction, 3D surgical guides, customized medicine to name a few. The elegant and intuitive method of building something layer-by-layer lends itself wonderfully to the imagination. And the ability to test and iterate rapidly with a 3D printer by your side allows for accelerating innovation at a rate unlike any manufacturing process that has come before it.
As I mentioned in the introduction, if you or your company have challenges and needs in one or more of the 5 areas above, it is unlikely to be a question of whether 3D printing can be of benefit to you (it will), but one of how you should best invest in it for maximum return. Further, it is likely that you will accrue a combination of benefits (such as assembly consolidation and supply simplification) across a range of parts, making this technology an attractive long term investment. At PADT, we offer 3D printing both as a service and also sell most of the printers we use on a daily basis and are thus well positioned to help you make this assessment, so contact us!
Metal Additive Manufacturing, or Metal 3D Printing, is a topic that generates a lot of interest, and even more questions. So we held a webinar on February 9th, 2016 to try and answer the most common questions we encounter. It was a huge success with over 150 people logging in to watch live. But many of you could not make it so we have put the slides and a recording of the webinar out there. Just go to this link to access the information.
The presentation answered the fllowing common questions:
Who are PADT and Concept Laser?
How does laser-based metal 3D printing work?
Are there other ways to 3D print in metal and how do they compare?
What are the different process steps involved?
How “good” are 3D printed metal parts?
What materials and machines do you offer?
Who uses this technology today?
What is the value proposition of metal 3D printing for me?
What can I do after this webinar?
As always, our technical team is available to answer any additional questions you may have. Just shoot an email to firstname.lastname@example.org or give us a call at 480.813.4884.
Most histories of Additive Manufacturing (3D printing) trace the origins of the technology back to Charles Hull’s 1984 patent, the same year production began on the first of the Back to the Future movies. Which is something of a shock when you see 3D printing dotting the Gartner Hype Cycle like it was invented in the post-Seinfeld era. But that is not what this post is about.
When I started working on Additive Manufacturing (AM), I was amazed at the number of times I was returning to text books and class notes I had used in graduate school a decade ago. This led me to reflect on how AM is helping bring back to the forefront disciplines that had somehow lost their cool factor – either by becoming part of the old normal, or because they contained ideas that were ahead of their time. I present three such areas of research that I state, with only some exaggeration, were waiting for AM to come along.
Topology Optimization: I remember many a design class where we would discuss topology optimization, look at fancy designs and end with a conversation that involved one of the more cynical students asking “All that’s fine, but how are you going to make that?”. Cue the elegant idea of building up a structure layer-by layer. AM is making it possible to manufacture parts with geometries that look like they came right out of a stress contour plot. And firms such as ANSYS, Autodesk and Altair, as well as universities and labs are all working to improve their capabilities at the intersection of topology optimization and additive manufacturing.
Lattice Structures: One of the first books I came across when I joined PADT was a copy of Cellular Solids by Lorna Gibson and M.F. Ashby. Prof. Gibson’s examples of these structures as they occur in nature demonstrate how they provide an economy of material usage for the task at hand. Traditionally, in engineering structures, cellular designs are limited to foams or consistent shapes like sandwich panels where the variation in cell geometry is limited – this is because manufacturing techniques do not normally lend themselves well to building complex, three dimensional structures like those found in nature. With AM technologies however, cell sizes and structures can be varied and densities modified depending on the design of the structure and the imposed loading conditions, making this an exciting area of research.
Metallurgy: As I read the preface to my “Metallurgy for the Non-Metallurgist” text book, I was surprised to note the author openly bemoan the decline of interest in metallurgy, and subsequently, fewer metallurgists in the field. And I guess it makes sense: materials science is today mostly concerned with much smaller scales than the classical metallurgist trained in. Well, lovers of columnar grain growth and precipitation hardening can now rejoice – metallurgy is at the very heart of AM technology today – most of the projected growth in AM is in metals. The science of powder metallurgy and the microstructure-property-process relationships of the metal AM technologies are vital building blocks to our understanding of metal 3D printing. Luckily for me, I happen to possess a book on powder metallurgy. And it too, is from 1984.
At PADT, we’re as big of a fan as anyone of the cool, trendy software and IT companies that run up billion dollar valuations in Silicon Valley and keep us all entertained and productive with their latest apps and platforms.
But as an engineering product and services company, we’re hardware geeks at heart and one of our favorite conferences is coming up quick. It’s the Aerospace, Aviation, Defense and Manufacturing (AADM) Conference hosted by the Arizona Technology Council and Arizona Commerce Authority on March 3 at the Hilton Scottsdale Resort.
Arizona has a rich history in this sector. TechAmerica’s 2014 Cyberstates Report ranks Arizona fourth nationwide for jobs in the space and defense systems manufacturing industry, employing more than 8,300 people. Industry giants such as Raytheon, Honeywell, Boeing, Lockheed Martin and General Dynamics all have a big presence here. Luke Air Force Base, Fort Huachuca and the Yuma Proving Ground all provide ideal places for testing and flying in our cloudless skies and more than 300 days of sunshine.
When you look at manufacturing, you’ll find thousands of varied companies located here that are propelling Arizona’s economy into the next era of growth. Industries leaders such as Intel, Microchip, and Frito Lay all have significant Arizona operations.
Now in its fifth year, this conference has become the gathering place for Arizona’s AADM industry. You’ll not only have a chance to hear what the big companies are up to, you’ll meet potential suppliers and customers during the interesting presentations and well-attended cocktail reception. And for as little as $750 you can get a booth space and two conference tickets – that’s a deal you won’t find in New York City! The traffic at our booth always keeps us hopping and give us the opportunity to capture great leads.
If you haven’t checked it out yet, get on it, check out the sponsorships and register now. And don’t forget to stop by the PADT booth. We’ll show you how we make innovation work!
Have an idea for a product and feel like you need a prototype.Tishin Donkersley from the Arizona Tech Beat asked me over to their offices to do a short interview and share some pointers on the subject. Take a look at the result here.
I talk about trends in the 3D Printing world that impact startups who have a need for prototypes, and share a few pointers on getting a prototype made.
While you are there, take a look around the sight. AZ Tech Beat is one of the best places to find out what is going on in the Arizona Tech Community as well as in tech in general. I especially like their gadget updates.
Metal 3D printing involves a combination of complex interacting phenomena at a range of length and time scales. In this blog post, I discuss three of these that lie at the core of the laser fusion of metals: phase changes, residual stresses and solidification structure (see Figure 1). I describe each phenomenon briefly and then why understanding it matters. In future posts I will dive deeper into each one of these areas and review what work is being done to advance our understanding of them.
Phase changes describe the transition from one phase to another, as shown in Figure 2. All phases are present in the process of laser fusion of metals. Metal in powder form (solid) is heated by means of a laser beam with spot sizes on the order of tens of microns. The powder then melts to form a melt pool (liquid) and then solidifies to form a portion of a layer of the final part (solid). During this process, there is visible gas and smoke, some of which ionizes to plasma.
The transition from powder to melt pool to solid part, as shown in Figure 3, is the essence of this process and understanding this is of vital importance. For example, if the laser fluence is too high, defects such as balling or discontinuous welds are possible and for low laser fluence, a full melt may not be obtained and thus lead to voids. Selecting the right laser, material and build parameters is thus essential to optimize the size and depth of the liquid melt pool, which in turn governs the density and structure of the final part. Finally, and this is more true of high power lasers, excessive gas and plasma generation can interfere with the incident laser fluence to reduce its effectiveness.
Residual stresses are stresses that exist in a structure after it reaches equilibrium with its environment. In the laser metal fusion process, residual stresses arise due to two related mechanisms [Mercelis & Kruth, 2006]:
Thermal Gradient: A steep temperature gradient develops during laser heating, with higher temperatures on the surface driving expansion against the cooler underlying layers and thereby introducing thermal stresses that could lead to plastic deformation.
Volume Shrinkage: Shrinkage in volume in the laser metal fusion process occurs due to several reasons: shrinkage from a powder to a liquid, shrinkage as the liquid itself cools, shrinkage during phase transition from liquid to solid and final shrinkage as the solid itself cools. These shrinkage events occur to a greater extent at the top layer, and reduce as one goes to lower layers.
After cooling, these two mechanisms together have the effect of creating compressive stresses on the top layers of the part, and tensile stresses on the bottom layers as shown in Figure 4. Since parts are held down by supports, these stresses could have the effect of peeling off supports from the build plate, or breaking off the supports from the part itself as shown in Figure 4. Thus, managing residual stresses is essential to ensuring a built part stays secured on the base plate and also for minimizing the amount of supports needed. A range of strategies are employed to mitigate residual stresses including laser rastering strategies, heated build plates and post-process thermal stress-relieving.
Solidification structure refers to the material structure of the resulting part that arises due to the solidification of the metal from a molten state, as is accomplished in the laser fusion of metals. It is well known that the structure of a metal alloy strongly influences its properties and further, that solidification process history has a strong influence on this structure, as does any post processing such as a thermal exposure. The wide range of materials and processing equipment in the laser metal fusion process makes it challenging to develop a cohesive theory on the nature of structure for these metals, but one approach is to study this on four length scales as shown in Figure 5. As an example, I have summarized the current understanding of each of these structures specifically for Ti-6Al-4V, which is one of the more popular alloys used in metal additive manufacturing. Of greatest interest are the macro-, meso- and microstructure, all of which influence mechanical properties of the final part. Understanding the nature of this structure, and correlating it to measured properties is a key step in certifying these materials and structures for end-use application.
Phase changes, residual stresses and solidification structure are three areas where an understanding of the fundamentals is crucial to solve problems and explore new opportunities that can accelerate the adoption of metal additive manufacturing. Over the past decade, most of this work has been, and continues to be, experimental in nature. However, in the last few years, progress has been made in deriving this understanding through simulation, but significant challenges remain, making this an exciting area of research in additive manufacturing to watch in the coming years.
Direct Laser Melting systems have made fantastic improvements in the last five years or so, making 3D Printing of metal parts a reality. The accuracy and strength of the finished parts rivals cast parts in the same material, but with the advantages of Freeform Fabrication. In fact, everywhere we go, people have questions about Metal 3D Printing.
So we decided to hold a webinar to answer those questions all at once. Our manufacturing team, lead by Dhruv Bhate, PhD, will share with you what we have learned while working to develop our own metal 3D Printing capability and while consulting with many of our customers as they acquired their own systems.
When: February 9, 2016
11:00 am MST / 10:00 am PST
If you would like to attend, or would like to receive a link to a recording of the event, please register here.
We look forward to sharing this exciting information with all of you.
In part 1 of this two-part post, I reviewed the challenges in the constitutive modeling of 3D printed parts using the Fused Deposition Modeling (FDM) process. In this second part, I discuss some of the approaches that may be used to enable analyses of FDM parts even in presence of these challenges. I present them below in increasing order of the detail captured by the model.
Conservative Value: The simplest method is to represent the material with an isotropic material model using the most conservative value of the 3 directions specified in the material datasheet, such as the one from Stratasys shown below for ULTEM-9085 showing the lower of the two modulii selected. The conservative value can be selected based on the desired risk assessment (e.g. lower modulus if maximum deflection is the key concern). This simplification brings with it a few problems:
The material property reported is only good for the specific build parameters, stacking and layer thickness used in the creation of the samples used to collect the data
This gives no insight into build orientation or processing conditions that can be improved and as such has limited value to an anlayst seeking to use simulation to improve part design and performance
Finally, in terms of failure prediction, the conservative value approach disregards inter-layer effects and defects described in the previous blog post and is not recommended to be used for this reason
Orthotropic Properties: A significant improvement from an isotropic assumption is to develop a constitutive model with orthotropic properties, which has properties defined in all three directions. Solid mechanicians will recognize the equation below as the compliance matrix representation of the Hooke’s Law for an orthortropic material, with the strain matrix on the left equal to the compliance matrix by the stress matrix on the right. The large compliance matrix in the middle is composed of three elastic modulii (E), Poisson’s ratios (v) and shear modulii (G) that need to be determined experimentally.
Good agreement between numerical and experimental results can be achieved using orthotropic properties when the structures being modeled are simple rectangular structures with uniaxial loading states. In addition to require extensive testing to collect this data set (as shown in this 2007 Master’s thesis), this approach does have a few limitations. Like the isotropic assumption, it is only valid for the specific set of build parameters that were used to manufacture the test samples from which the data was initially obtained. Additionally, since the model has no explicit sense of layers and inter-layer effects, it is unlikely to perform well at stresses leading up to failure, especially for complex loading conditions. This was shown in a 2010 paper that demonstrated these limitations in the analysis of a bracket that itself was built in three different orientations. The authors concluded however that there was good agreement at low loads and deflections for all build directions, and that the margin of error as load increased varied across the three build orientations.
Laminar Composite Theory: The FDM process results in structures that are very similar to laminar composites, with a stack of plies consisting of individual fibers/filaments laid down next to each other. The only difference is the absence of a matrix binder – in the FDM process, the filaments fuse with neighboring filaments to form a meso-structure. As shown in this 2014 project report, a laminar approach allows one to model different ply raster angles that are not possible with the orthotropic approach. This is exciting because it could expand insight into optimizing raster angles for optimum performance of a part, and in theory reduce the experimental datasets needed to develop models. At this time however, there is very limited data validating predicted values against experiments. ANSYS and other software that have been designed for composite modeling (see image below from ANSYS Composite PrepPost) can be used as starting points to explore this space.
Hybrid Tool-path Composite Representation: One of the limitations of the above approach is that it does not model any of the details within the layer. As we saw in part 1 of this post, each layer is composed of tool-paths that leave behind voids and curvature errors that could be significant in simulation, particularly in failure modeling. Perhaps the most promising approach to modeling FDM parts is to explicitly link tool-path information in the build software to the analysis software. Coupling this with existing composite simulation is another potential idea that would help reduce computational expense. This is an idea I have captured below in the schematic that shows one possible way this could be done, using ANSYS Composite PrepPost as an example platform.
Discussion: At the present moment, the orthotropic approach is perhaps the most appropriate method for modeling parts since it is allows some level of build orientation optimization, as well as for meaningful design comparisons and comparison to bulk properties one may expect from alternative technologies such as injection molding. However, as the application of FDM in end-use parts increases, the demands on simulation are also likely to increase, one of which will involve representing these materials more accurately than continuum solids.
Colorado is a major contributor to the space industry, and they are quickly adopting 3D Printing to keep costs down and get to space faster. In this article, “Colorado Companies Bringing Space Costs Down to Earth” the DBJ explores how automation and 3D Printing can have a big impact on cost and schedule. Many of the companies sighted in the article are PADT customers, and PADT’s very own Norman Stucker was quoted extensively for the article.
The recent explosion of interest in 3D printing has been fascinating to engineers like myself that have been using what we call Additive Manufacturing as a standard tool for over two decades. It is easy to dismiss the interest of the general public and the media as hype and trendiness. But doing so would be a mistake. It is a big deal, but not for the reasons that most people think. “Why is 3D Printing Such a Big Deal” explains what the real power is behind 3D Printing.
As our final contribution to the AZ Tech Council and PBJ’s TechFlash Column for year, we shared how “3-D Printing Hits Major Milestones in 2015.” The article give our picks for what was significant with Additive Manufacturing for the Materials, Medical, Manufacturing, Military, and Mainstream aspects of the business.
The 3-D industry had a typical year in 2015. Of course, when it comes to 3-D printing, “typical” means lots of change, growth and innovation. It’s always hard to tell which of the year’s innovations will have the biggest impact on the future, but that doesn’t take the fun out of forecasting.