September is here and it is a jam packed month of events, many of them related to BioMedical engineering. We are continuing with ANSYS webinars and talking about 3D Printing as well. See what we have below:
September 13: Salt Lake City, UT Manufacturing Promotes Innovation Summit
The UMA Summit is a day long event filled with networking, guest speakers and informative information. In between speakers network with our vendor booths and see the latest products and services available for the Manufacturing Industry. PADT will be there with lots of example of 3D Printing and ready to engage on how manufacturing really does drive innovation. Check out the event page for times and an agenda.
September 15: Scottsdale, AZ ANSYS Arizona Innovation Conference
ANSYS and PADT are pleased to announce that we be holding a user meeting in Scottsdale for the entire ANSYS use community. Join us for an informative conference on how to incorporate various productivity enhancement tools and techniques into your workflow for your engineering department. ANSYS Applications Engineers and local customers like Honeywell, Galtronics, On Semi, Ping, and Nammo Talley, will discuss design challenges and how simulation-driven product development can help engineers rapidly innovate new products. See the agenda and register here.
September 19: Phoenix, AZ Seminar: Medical Device Product Development for Startups – The Bitter Pill
We will be kicking off our Arizona Bioscience Week with this a free seminar at CEI in Phoenix with a sometimes brutally honest discussion on the reality of medical device product development.
No one wants to discourage a good idea, and entrepreneurs make it a long way before someone sits them down and explains how long and expensive the engineering of a medical device product is. In this one hour seminar PADT will share the hard and cold realities of the process, not to discourage people, but to give them the facts they need.
September 21-22: Minneapolis, MN Medical Design & Manufacturing Minneapolis
PADT Medical will have a booth with our partner Innosurg at this premier event for medical device development. For 22 years, Medical Design & Manufacturing Minneapolis has been the medtech innovation, communication, and solution epicenter of the Midwest. Now over 600 suppliers strong, and with more than 5,000 industry professionals in attendance, the event provides the solutions, education, and partnerships you simply won’t find anywhere else. Learn more here. And if you are attending, please stop by and say hello, we are in booth 1643.
September 21: Phoenix, AZ AZBio Awards
Join PADT and others for this annual event that recognizes those that contribute to the growing AZ BioTech community. The awards will be made by PADT’s 3D Printing team again this year. Stop by our table to say hello. Register here.
September 21 & 22: Phoenix, AZ White Hat Investor Conference
The West was won by innovators, investors, and prospectors who understood the value of discovery and accepted the challenge of investing in new frontiers. PADT will be joining others in the investment community to meet with and hear from companies (32 are signed up to present right now) in the Bioscience space and to also share ideas and network. Registration for this special event can be found here.
September 30: Albuquerque, NM New Mexico Tech Council: Experience IT NM Conference
Geek out on all things technology. The New Mexico Tech community will gather the best and the brightest entrepreneurs, technicians, hackers, and tech fans for presentations, talks, meet-ups, and parties; all to highlight the vibrant tech community in our city. The Conference takes place on the final day of a week of events, and will focus on HR, CRM, Manufacturing, and Creative concerns of the tech community with panels and presentations. PADT’s Eric Miller will be presenting in two “MakeIT” sessions.
We are pleased to announce the new Flownex Training Course for Flownex SE, the world’s best (we think) thermal-fluid modeling tool. The Flownex course is aimed at new users with a desire to quickly equip themselves in the basics of system modelling as well as enabling one to visually refresh one’s memory on the various capabilities and applications within the Flownex suite.
If you are not a user already but want to check this tool out by going through the training course, go to the login page and simply click “Don’t have an account?” and register. This will get you access and we will follow up with a temp key so you can try it out. This is actually the best way for you to get a feel for why we like this program so much.
Here is a list of the sessions:
Session 1: Background to Flownex
Session 2: Page navigation
Session 3: Boundary values
Session 4: Pumps & Fixed mass flow functionality
Session 5: Flow restrictions
Session 6: Exercise 1
Session 7: Designer functionality
Session 8: Heat Exchangers
Session 9: Containers
Session 10: Exercise 2
Session 11: Excel component
Session 12: Visualization
As always, If you have any questions or want to know more, reach out to us at email@example.com or 1.800.293.PADT.
This is a common question that we get, particularly those coming from APDL – how to get nodal and element IDs exposed in ANSYS Mechanical. Whether that’s for troubleshooting or information gathering, it was not available before. This video shows how an ANSYS developed extension accomplishes that pretty easily.
Updated (8/30/2016): Two corrections made following suggestions by Gilbert Peters: the first corrects the use of honeycomb structures in radiator grille applications as being for flow conditioning, the second corrects the use of the Maxwell stability criterion, replacing the space frame example with an octet truss.
Within the design element, the first step in implementing cellular structures in Additive Manufacturing (AM) is selecting the appropriate unit cell(s). The unit cell is selected based on the performance desired of it as well as the manufacturability of the cells. In this post, I wish to delve deeper into the different types of cellular structures and why the classification is important. This will set the stage for defining criteria for why certain unit cell designs are preferable over others, which I will attempt in future posts. This post will also explain in greater detail what a “lattice” structure, a term that is often erroneously used to describe all cellular solids, truly is.
Honeycombs are prismatic, 2-dimensional cellular designs extruded in the 3rd dimension, like the well-known hexagonal honeycomb shown in Figure 1. All cross-sections through the 3rd dimension are thus identical, making honeycombs somewhat easy to model. Though the hexagonal honeycomb is most well known, the term applies to all designs that have this prismatic property, including square and triangular honeycombs. Honeycombs have a strong anisotropy in the 3rd dimension – in fact, the modulus of regular hexagonal and triangular honeycombs is transversely isotropic – equal in all directions in the plane but very different out-of-plane.
1.2 Design Implications The 2D nature of honeycomb structures means that their use is beneficial when the environmental conditions are predictable and the honeycomb design can be oriented in such a way to extract maximum benefit. One such example is the crash structure in Figure 2 as well as a range of sandwich panels. Several automotive radiator grilles are also of a honeycomb design to condition the flow of air. In both cases, the direction of the environmental stimulus is known – in the former, the impact load, in the latter, airflow.
2. Open-Cell Foam
Freeing up the prismatic requirement on the honeycomb brings us to a fully 3-dimensionalopen-cell foam design as shown in one representation of a unit cell in Figure 3. Typically, open-cell foams are bending-dominated, distinguishing them from stretch-dominated lattices, which are discussed in more detail in a following section on lattices.
2.2 Design Implications Unlike the honeycomb, open cell foam designs are more useful when the environmental stimulus (stress, flow, heat) is not as predictable and unidirectional. The bending dominated mechanism of deformation make open-cell foams ideal for energy absorption – stretch dominated structures tend to be stiffer. As a result of this, applications that require energy absorption such as mattresses and crumple zones in complex structures. The interconnectivity of open-cell foams also makes them a candidate for applications requiring fluid flow through the structure.
3. Closed-Cell Foam
3.1 Definition As the name suggests, closed cell foams are open-cell foams with enclosed cells, such as the representation shown in Figure 6. This typically involves a membrane like structure that may be of varying thickness from the strut-like structures, though this is not necessary. Closed-cell foams arise from a lot of natural processes and are commonly found in nature. In man-made entities, they are commonly found in the food industry (bread, chocolate) and in engineering applications where the enclosed cell is filled with some fluid (like air in bubble wrap, foam for bicycle helmets and fragile packaging).
3.2 Design Implications
The primary benefit of closed cell foams is the ability to encapsulate a fluid of different properties for compressive resilience. From a structural standpoint, while the membrane is a load-bearing part of the structure under certain loads, the additional material and manufacturing burden can be hard to justify. Within the AM context, this is a key area of interest for those exploring 3D printing food products in particular but may also have value for biomimetic applications.
Lattices are in appearance very similar to open cell foams but differ in that lattice member deformation is stretch-dominated, as opposed to bending*. This is important since for the same material allocation, structures tend to be stiffer in tension and/or compression compared to bending – by contrast, bending dominated structures typically absorb more energy and are more compliant.
So the question is – when does an open cell foam become stretch dominated and therefore, a lattice? Fortunately, there is an app equation for that.
Maxwell’s Stability Criterion
Maxwell’s stability criterion involves the computation of a metric M for a lattice-like structure with b struts and j joints as follows:
In 2D structures: M = b – 2j + 3
In 3D structures: M = b – 3j + 6
Per Maxwell’s criterion, for our purposes here where the joints are locked (and not pinned), if M < 0, we get a structure that is bending dominated. If M >= 0, the structure is stretch dominated. The former constitutes an open-cell foam, the latter a lattice.
There are several approaches to establishing the appropriateness of a lattice design for a structural applications (connectivity, static and kinematic determinism etc.) and how they are applied to periodic structures and space frames. It is easy for one (including for this author) to confuse these ideas and their applicability. For the purposes of AM, Maxwell’s Stability Criterion for 3D structures is a sufficient condition for static determinancy. Further, for a periodic structure to be truly space-filling (as we need for AM applications), there is no simple rigid polyhedron that fits the bill – we need a combination of polyhedra (such as an octahedron and tetrahedron in the octet truss shown in the video below) to generate true space filling, and rigid structures. The 2001 papers by Deshpande, Ashby and Fleck illustrate these ideas in greater detail and are referenced at the end of this post.
Video: The octet truss is a classic stretch-dominated structure, with b = 36 struts, j = 14 joints and M = 0 [Attr. Lawrence Livermore National Labs]
4.2 Design Implications Lattices are the most common cellular solid studied in AM – this is primarily on account of their strong structural performance in applications where high stiffness-to-weight ratio is desired (such as aerospace), or where stiffness modulation is important (such as in medical implants). However, it is important to realize that there are other cellular representations that have a range of other benefits that lattice designs cannot provide.
Conclusion: Why this matters
It is a fair question to ask why this matters – is this all just semantics? I would like to argue that the above classification is vital since it represents the first stage of selecting a unit cell for a particular function. Generally speaking, the following guidelines apply:
Honeycomb structures for predictable, unidirectional loading or flow
Open cell foams where energy absorption and compliance is important
Closed cell foams for fluid-filled and hydrostatic applications
Lattice structures where stiffness and resistance to bending is critical
Finally, another reason it is important to retain the bigger picture on all cellular solids is it ensures that the discussion of what we can do with AM and cellular solids includes all the possibilities and is not limited to only stiffness driven lattice designs.
Note: This blog post is part of a series on “Additive Manufacturing of Cellular Solids” that I am writing over the coming year, diving deep into the fundamentals of this exciting and fast evolving topic. To ensure you get each post (~2 a month) or to give me feedback for improvement, please connect with me on LinkedIn.
 Ashby, “Materials Selection in Mechanical Design,” Fourth Edition, 2011
 Gibson & Ashby, “Cellular Solids: Structure & Properties,” Second Edition, 1997
 Gibson, Ashby & Harley, “Cellular Materials in Nature & Medicine,” First Edition, 2010
 Ashby, Evans, Fleck, Gibson, Hutchinson, Wadley, “Metal Foams: A Design Guide,” First Edition, 2000
 Deshpande, Ashby, Fleck, “Foam Topology Bending versus Stretching Dominated Architectures,” Acta Materialia 49, 2001
 Deshpande, Fleck, Ashby, “Effective properties of the octet-truss lattice material,” Journal of the Mechanics and Physics of Solids, 49, 2001
* We defer to reference  in distinguishing lattice structures as separate from foams – this is NOT the approach used in  and  where lattices are treated implicitly as a subset of open-cell foams. The distinction is useful from a structural perspective and as such is retained here.
After three years on the market and signs that sales were increasing year over year, we decided it was time to go through our popular training book “Introduction to the ANSYS Parametric
Design Language (APDL)” and make some updates and reformat it so that it can be published as a Kindle e-book. The new Second Edition includes two additonal chapters: APDL Math and Using APDL with ANSYS Mechanical. The fact that we continue to sell more of these useful books is a sign that APDL is still a vibrant and well used language, and that others out there find power in its simplicity and depth.
This book started life as a class that PADT taught for many years. Then over time people asked if they could buy the notes. And then they asked for a real book. The bulk of the content came from Jeff Strain with input from most of our technical staff. Much of the editing and new content was done by Susanna Young and Eric Miller.
Here is the Description from Amazon.com:
The definitive guide to the ANSYS Parametric Design Language (APDL), the command language for the ANSYS Mechanical APDL product from ANSYS, Inc. PADT has converted their popular “Introduction to APDL” class into a guide so that users can teach themselves the APDL language at their own pace. Its 14 chapters include reference information, examples, tips and hints, and eight workshops. Topics covered include:
– User Interfacing
– Program Flow
– Retrieving Database Information
– Arrays, Tables, and Strings
– Importing Data
– Writing Output to Files
– Menu Customization
– APDL Math
– Using APDL in ANSYS Mechanical
At only $75.00 it is an investment that will pay for itself quickly. Even if you are an ANSYS Mechanical user, you can still benefit from knowing APDL, allowing you to add code snippets to your models. We have put some images below and you can also learn more here or go straight to Amazon.com to purchase the paperback or Kindle versions.
ANSYS Mechanical allows you to specify settings for load steps one at a time. Most users don’t know that you can change settings for any combination of load steps using the selection of the load step graph. PADT’s Joe Woodward shows you how in this short but informative video.
I am writing this post after visiting the 27th SFF Symposium, a 3-day Additive Manufacturing (AM) conference held annually at the University of Texas at Austin. The SFF Symposium stands apart from other 3D printing conferences held in the US (such as AMUG, RAPID and Inside3D) in the fact that about 90% of the attendees and presenters are from academia. This year had 339 talks in 8 concurrent tracks and 54 posters, with an estimated 470 attendees from 20 countries – an overall 50% increase over the past year.
As one would expect from a predominantly academic conference, the talks were deeper in their content and tracks were more specialized. The track I presented in (Lattice Structures) had a total of 15 talks – 300 minutes of lattice talk, which pretty much made the conference for me!
In this post, I wish to summarize the research landscape in AM cellular solids at a high level: this classification dawned on me as I was listening to the talks over two days and taking in all the different work going on across several universities. My attempt in this post is to wrap my arms around the big picture and show how all these elements are needed to make cellular solids a routine design feature in production AM parts.
Classification of Cellular Solids
First, I feel the need to clarify a technicality that bothered me a wee bit at the conference: I prefer the term “cellular solids” to “lattices” since it is more inclusive of honeycomb and all foam-like structures, following Gibson and Ashby’s 1997 seminal text of the same name. Lattices are generally associated with “open-cell foam” type structures only – but there is a lot of room for honeycomb structures and close-cell foams, each having different advantages and behaviors, which get excluded when we use the term “lattice”.
The AM Cellular Solids Research Landscape
The 15 papers at the symposium, and indeed all my prior literature reviews and conference visits, suggested to me that all of the work in this space falls into one or more of four categories shown in Figure 2. For each of the four categories (design, analysis, manufacturing & implementation), I have listed below the current list of capabilities (not comprehensive), many of which were discussed in the talks at SFF. Further down I list the current challenges from my point of view, based on what I have learned studying this area over the past year.
Over the coming weeks I plan to publish a post with more detail on each of the four areas above, summarizing the commercial and academic research that is ongoing (to the best of my knowledge) in each area. For now, I provide below a brief elaboration of each area and highlight some important research questions.
1. Representation (Design)
This deals with how we incorporate cellular structures into our designs for all downstream activities. This involves two aspects: the selection of the specific cellular design (honeycomb or octet truss, for example) and its implementation in the CAD framework. For the former, a key question is: what is the optimum unit cell to select relative to performance requirements, manufacturability and other constraints? The second set of challenges arises from the CAD implementation: how does one allow for rapid iteration with minimal computational expense, how do cellular structures cover the space and merge with the external skin geometry seamlessly?
2. Optimization (Analysis)
Having tools to incorporate cellular designs is not enough – the next question is how to arrange these structures for optimum performance relative to specified requirements? The two most significant challenges in this area are performing the analysis at reasonable computational expense and the development of material models that accurately represent behavior at the cellular structure level, which may be significantly different from the bulk.
3. Realization (Manufacturing)
Manufacturing cellular structures is non-trivial, primarily due to the small size of the connecting members (struts, walls). The dimensions required are often in the order of a few hundred microns and lower, which tends to push the capabilities of the AM equipment under consideration. Additionally, in most cases, the cellular structure needs to be self-supporting and specifically for powder bed fusion, must allow for removal of trapped powder after completion of the build. One way to address this is to develop a map that identifies acceptable sizes of both the connecting members and the pores they enclose. For this, we need robust ways of monitoring quality of AM cellular solids by using in-situ and Non-Destructive techniques to guard against voids and other defects.
4. Application (Implementation)
Cellular solids have a range of potential applications. The well established ones include increasing stiffness-to-weight ratios, energy absorption and thermal performance. More recent applications include improving bone integration for implants and modulating stiffness to match biological distributions of material (biomimicry), as well as a host of ideas involving meta-materials. The key questions here include how do we ensure long term reliability of cellular structures in their use condition? How do we accurately identify and validate these conditions? How do we monitor quality in the field? And how do we ensure the entire life cycle of the product is cost-effective?
I wrote this post for two reasons: I love to classify information and couldn’t help myself after 5 hours of hearing and thinking about this area. But secondly, I hope it helps give all of us working in this space context to engage and communicate more seamlessly and see how our own work fits in the bigger picture.
A lot of us have a singular passion for the overlapping zone of AM and cellular solids and I can imagine in a few years we may well have a conference, an online journal or a forum of some sort just dedicated to this field – in fact, I’d love to assess interest in such an effort or an equivalent collaborative exercise. If this idea resonates with you, please connect with me on LinkedIn and drop me a note, or send us an email (firstname.lastname@example.org) and cite this blog post so it finds its way to me.
At PADT we provide help to many of our customers who have trouble with their ANSYS simulations. At the top level, though, there are some computer skills for Windows that we consider basics that every engineer should know. If these are skills you already have in your tool belt, fantastic! If not, hopefully this information will help you be more effective in your simulation tasks.
Also, since most of us have been or are currently being updated to Windows 10, I’m providing the instructions for Windows 10. Windows 7 is similar, though.
1. Run as Administrator
This allows us to run programs, a.k.a. “apps” with administrator privilege, even if our login credentials don’t allow this level of usage. This is the case for most users of engineering software. Certain components of ANSYS, including the CAD Configuration Manager and the Client ANSLIC_ADMIN Utility require changes to your computer that non-admin rights won’t allow. By running as administrator, we allow the program to make the needed changes.
To do this, click the Start Menu, then find the program (app) you need to run in the resulting list, such as the Client ANSLIC_ADMIN Utility, but one important thing to keep is mind is to use a privacy filter, it is important to maintain your privacy. Next, right click on that program, select More with the left mouse button, then select Run as Administrator with the left mouse button. If you are prompted to allow changes to your system, click Yes. Here is what it will look like:
2. View File Extensions
When using Windows Explorer, now known as File Explorer in Windows 10, by default you probably won’t see file extensions. Instead, you’ll see the prefix of files, but won’t see the endings of the file names. This will be the case when browsing for files to open or save as well. Sometimes you can rely on the icons associated with a file to know which program it’s associated with or the Type field in the list view, but sometimes there are conflicts. For example, an ANSYS Mechanical APDL macro file will have the extension .mac. You can probably guess that there is at least one other major company that can have software that uses that extension. By viewing the file extensions, even if the icons are wrong, we can more easily identify the files we need. Here is how it’s done:
Click Start, then File Explorer:
The default view using “Details” in File Explorer will look something like this (file names don’t include extensions):
To view the extensions, we click on the View menu in File Explorer, then Options, then Change Folder and Search Options.
The way I set this option for all folder on my computer is to then click on the View tab in the resulting small window, then uncheck the box for Hide extensions for known file types, then click Apply to Folders, then click OK.
Now the list view (using Details under the View menu) in File Explorer looks like this, with each file showing its extension in the list:
3. Define and Edit Environment Variables
Environment Variables are values that are used by certain programs to define settings. For example, an environment variable can be used to specify the license server for certain programs. It’s good to know how to define and edit these if needed. To do this, we bring up the control panel. In Windows 10, click on the Start button, then Settings:
A quick way to get there is to type “environment” in the search window in the resulting Settings window:
The search should find Edit the System Environment Variables. Click on that:
In the resulting System Properties window, click on the Environment Variables button in the Advanced tab:
A new window will open with a list of currently defined User variables (just for your login) and System variables (for anyone who is logged in), like this:
You can click on an environment variable to edit it using the Edit… button, or you can click on the New… button to create a new one. One ANSYS-related environment variable that occasionally needs to be set is ANSYSLMD_LICENSE_FILE. This is only needed if the default license server specifications aren’t working for some reason. You won’t need to set this under normal circumstances. Just in case, here is how to define it, using the New… button under System variables. We type in the Variable Name, in this case ANSYSLMD_LICENSE_FILE and then the Variable Value, which in this example is 1055@myserver.
When done defining and editing environment variables, we click on the OK button to complete the action and get out of that environment variable-related windows.
4. Check Usage of Your Computer Resources
As simulation experts, we are often pushing the limits of our computer resources. It’s good to know how to check those. First is disk space. An easy way to check disk space is to bring up File Explorer again. Click on This PC on the left side. This will give you a snapshot of the available space on each hard drive that is accessible on this computer:
Next, we may want to check CPU or memory utilization. Perhaps we want to make sure that our solution is running on multiple cores as we have requested.
To do this, hold down the Alt, Control, and Delete keys on the keyboard, all at the same time. Then click on Task Manager in the resulting window (it will look for a second like your computer is going to restart – it won’t actually do that).
In the resulting Task Manager window, click on More details:
In the resulting window, we can click on the Performance tab and view, for example, the current memory utilization, or we can click on Open Resource Monitor and get even more details, including utilization on each CPU:
5. Search for Large Files
It’s very common in the simulation world to end up filling up your disk drives. Therefore, it’s good to be able to find large files so we can delete them if they are no longer needed. For a simple way to do this, we’ll start with File Explorer again. This time, we’ll click in the search window at upper right, but won’t actually type in anything. We just want the search tools menu to appear:
Next, click on Search under Search Tools, followed by Size, then Gigantic (I will argue that 128 MB isn’t all that gigantic in the simulation world, but Microsoft hasn’t caught up with us yet):
Windows will now perform a search for files larger than 128 GB. If any of these are no longer needed, you can right click and delete them. Just make sure you don’t delete any files that are truly needed!
That completes our discussion on 5 computer skills every engineer should know. In conclusion, these basic skills should help you be more productive over time as you perform your simulation tasks. We hope you find this information useful, if it is is not enough, than visit this website for more infromation.
We are pleased to announce that PADT has been awarded a grant from America Makes to further our research into combining our three favorite things: Simulation, 3D Printing, and Product Development. We will work with our partners at ASU, Honeywell Aerospace, and LAI International to study lattice structures created in 3D Printing, how to model them in ANSYS simulation software, and then how to use that information to drive product design.
A copy of the press release is below. Or read the official press release or download a PDF .
Innovative Additive Manufacturing Research Project Led by PADT Approved as Part of America Makes Multi-Million Dollar Grants
Arizona State University, Honeywell Aerospace and LAI International join PADT in technical research and educational outreach in 3D Printing
TEMPE, Ariz., July 25, 2016 — In one of the most critically needed areas of research in Additive Manufacturing, Phoenix Analysis & Design Technologies (PADT), the Southwest’s largest provider of numerical simulation, product development and 3D Printing services and products, today announced its project proposal titled “A Non-Empirical Predictive Model for Additively Manufactured Lattice Structures,” has been accepted as part of a multi-million dollar grant from the National Additive Manufacturing Innovation Institute, America Makes. PADT’s proposal was one of only seven selected, and one of only two where the leading organization was a small business.
To complete the deliverables, Arizona State University (ASU), Honeywell Aerospace and LAI International are assisting PADT in technical research with contributions from Prof. Howard Kuhn, a Professor at the University of Pittsburgh and a leading educator in Additive Manufacturing, for workforce and educational outreach.
“While there are several efforts ongoing in developing design and optimization software for lattice structures in additive manufacturing, there has been little progress in developing a robust, validated material model that accurately describes how these structures behave,” said Dhruv Bhate, PhD, senior technologist, PADT and author and principal investigator of the proposal. “We are honored to be chosen to research this important issue and provide the tools to enable entrepreneurs, manufacturers and makers to integrate lattice structures in their designs.”
One of the most definitive benefits of additive manufacturing is the ability to reduce weight while maintaining mechanical performance. A way to achieve this is by adding lattice structures to parts before manufacturing. The advantages are crucial and can result in increased design flexibility, lower material costs and significant reductions in production time for industries such as aerospace and automotive.
Another aspect of PADT’s winning proposal is the development of a first-of-a-kind online, collaborative living textbook on Additive Manufacturing that seeks to provide comprehensive, up-to-date and structured information in a field where over 50 papers are published worldwide every day. In addition, the team will develop a training class that addresses manufacturing, testing, theory and simulation as well as how they are combined together to deliver robust predictions of lattice behavior.
“We have identified Additive Manufacturing as a key lever of innovation in our company and recognize lattice structures as an important design capability to reduce mass, improve performance and reduce costs,” said Suraj Rawal, Technical Fellow, Advanced Technology Center at Lockheed Martin Space Systems Company – a leader in implementing Additive Manufacturing. “We also recognize the significance of this work in lattice behavior modeling and prediction as an important contribution to help implement the design, manufacturing, and performance validation of structures in our innovative designs.”
The award of this grant is another example of the leadership role that Arizona is playing in advancing the practical application of Additive Manufacturing, better known as 3D Printing. PADT’s leadership role in the Arizona Technology Council’s Arizona Additive Manufacturing Committee, support of basic research in the area at ASU, and involvement with educating the next generation of users underscores PADT’s contribution to this effort and furthers the company’s commitment to “Make Innovation Work.”
About Phoenix Analysis and Design Technologies
Phoenix Analysis and Design Technologies, Inc. (PADT) is an engineering product and services company that focuses on helping customers who develop physical products by providing Numerical Simulation, Product Development, and Rapid Prototyping solutions. PADT’s worldwide reputation for technical excellence and experienced staff is based on its proven record of building long term win-win partnerships with vendors and customers. Since its establishment in 1994, companies have relied on PADT because “We Make Innovation Work.” With over 80 employees, PADT services customers from its headquarters at the Arizona State University Research Park in Tempe, Arizona, and from offices in Torrance, California, Littleton, Colorado, Albuquerque, New Mexico, and Murray, Utah, as well as through staff members located around the country. More information on PADT can be found at http://www.PADTINC.com.
If you have used or are using CFD tools like ANSYS Fluent or ANSYS CFX, then you already know how much of a pain extracting the fluid volume can be from a CAD model. Whether the extraction fails because of geometry issues, or if you’ve forgotten to create capping surfaces for all your openings it can be quite frustrating when you get the “non-manifold body” error.
We’ve done it the same way for a long time – create some super solid and do a Boolean subtract or try to close everything off and try to use a cavity function to fill in the model. Both can have headache inducing issues.
CLICK HERE for a PDF that shows how ANSYS SpaceClaim uses a different approach which can make the fluid volume extraction much easier for engineers.
PCB designers know that it is critical to design a board for temperature rise, thermal expansion and external structural loads. The difficulty has always been to capture a board’s structural makeup accurately without having an impractical effect on solve time.
CLICK HERE for a PDF that shows how ANSYS solves this challenge in a unique straightforward and effective manner. And as always feel free to reach out to us at email@example.com if you have any questions.
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 firstname.lastname@example.org and cite this post, or connect with me directly on LinkedIn.
“Why are there so many different software solutions in Additive Manufacturing and which ones do I really need?“
This was a question I was asked at lunch during the recently concluded RAPID 3D printing conference by a manager at an aerospace company. I gave her my thoughts as I was stuffing down my very average panini, but the question lingered on long after the conference was over – several weeks later, I decided to expand on my response in this blog post.
There are over 25 software solutions available (scheduling software for service technicians, etc.) and being used for different aspects of Additive Manufacturing (AM). To answer the question above, I found it best to classify these solutions into four main categories based on their purpose, and allow sub-categories to emerge as appropriate. This classification is shown in Figure 1 below – and each of the 7 sub-categories are discussed in more detail in this post.
1. Design Modeler
You need this if you intend to create or modify designs
Most designs are created in CAD software such as SOLIDWorks, CATIA and SpaceClaim (now ANSYS SpaceClaim). These have been in use long before the more recent rise in interest in AM and most companies have access to some CAD software internally already. Wikipedia has a comparison of different CAD software that is a good starting point to get a sense of the wide range of CAD solutions out there.
2. Build Preparation
You need this if you plan on using any AM technology yourself (as opposed to sending your designs outside for manufacturing)
Once you have a CAD file, you need to ensure you get the best print possible with the printer you have available. Most equipment suppliers will provide associated software with their machines that enable this. Stand-alone software packages do exist, such as the one developed by Materialise called Magics, which is a preferred solution for Stereolithography (SLA) and metal powder bed fusion in particular – some of the features of Magics are shown in the video below.
Scanning & File Transfer
3. Geometry Repair
You need this if you deal with low-quality geometries – either from scans or since you work with customers with poor CAD generation capabilities
Geomagic Design X is arguably the industry’s most comprehensive reverse engineering software which combines history-based CAD with 3D scan data processing so you can create feature-based, editable solid models compatible with your existing CAD software. If you are using ANSYS, their SpaceClaim has a powerful repair solution as well, as demonstrated in the video below.
Improving Performance Through Analysis
4. Topology Optimization
You need this if you stand to benefit from designing towards a specific objective like reducing mass, increasing stiffness etc. such as the control-arm shown in Figure 2
Of all the ways design freedom can be meaningfully exploited, topology optimization is arguably the most promising. The ability to now bring analysis up-front in the design cycle and design towards a certain objective (such as maximizing stiffness-to-weight) is compelling, particularly for high performance, material usage sensitive applications like aerospace. The most visible commercial solutions in the AM space come from Altair: with their Optistruct solution (for advanced users) and SolidThinking Inspire (which is a more user-friendly solution that uses Altair’s solver). ANSYS and Autodesk 360 Inventor also offer optimization solutions. A complete list, including freeware, can be availed of at this link.
5. Lattice Generation
You need this if you wish to take advantage of cellular/lattice structure properties for applications like such as lightweight structural panels, energy absorption devices, thermal insulation as well as medical applications like porous implants with optimum bone integration and stiffness and scaffolds for tissue engineering.
Broadly speaking, there are 3 different approaches that have been taken to lattice design software:
I will cover the differences between these approaches in detail in a future blog post. A general guideline is that the generative design approach taken by Autodesk’s Within is well suited to medical applications, while Lattice generation through topology optimization seems to be a sensible next step for those that are already performing topology optimization, as is the case with most aerospace companies pursuing AM technology. The infill/conformal approach is limiting in that it does not enable optimization of lattice structures in response to an objective function and typically involves a-priori definition of a lattice density and type which cannot then be modified locally. This is a fast evolving field – between new software and updates to existing ones, there is a new release on an almost quarterly, if not monthly basis – some recent examples are nTopology and the open source IntraLattice.
Below is a short video demo of Autodesk’s Within:
You need this if you do either topology optimization or lattice design, or need it for part performance simulation
Basic mechanical FE analysis solvers are integrated into most topology optimization and lattice generation software. For topology optimization, the digitally represented part at the end of the optimization typically has jarring surfaces that are smoothed and then need to be reanalyzed to ensure that the design changes have not shifted the part’s performance outside the required window. Beyond topology optimization & lattice design, analysis has a major role to play in simulating performance – this is also true for those seeking to compare performance between traditionally manufactured and 3D printed parts. The key challenge is the availability of valid constitutive and failure material models for AM, which needs to be sourced through independent testing, from the Senvol database or from publications.
7. Process Simulation
You need this if you would like to simulate the actual process to allow for improved part and process parameter selection, or to assess how changes in parameters influence part behavior
The real benefit for process simulation has been seen for metal AM. In this space, there are broadly speaking two approaches: simulating at the level of the part, or at the level of the powder.
Part Level Simulation: This involves either the use of stand-alone AM-specific solutions like 3DSIM and Pan Computing (acquired by Autodesk in March 2016), or the use of commercially available FE software such as ANSYS & ABAQUS. The focus of these efforts is on intelligent support design, accounting for residual stresses and part distortion, and simulating thermal gradients in the part during the process. ANSYS recently announced a new effort with the University of Pittsburgh in this regard.
Powder Level Simulation: R&D efforts in this space are led by Lawrence Livermore National Labs (LLNL) and the focus here is on fundamental understanding to explain observed defects and also to enable process optimization to accelerate new materials and process research
Part level simulation is of great interest for companies seeking to go down a production route with metal AM. In particular there is a need to predict part distortion and correct for it in the design – this distortion can be unacceptable in many geometries – one such example is shown in the Pan Computing (now Autodesk) video below.
A Note on Convergence
Some companies have ownership of more than one aspect of the 7 categories represented above, and are seeking to converge them either through enabling smooth handshakes or truly integrate them into one platform. In fact, Stratasys announced their GrabCAD solution at the RAPID conference, which aims to do some of this (minus the analysis aspects, and only limited to their printers at the moment – all of which are for polymers only). Companies like Autodesk, Dassault Systemes and ANSYS have many elements of the 7 software solutions listed above and while it is not clear what level of convergence they have in mind, all have recognized the potential for a solution that can address the AM design community’s needs. Autodesk for example, has in the past 2 years acquired Within (for lattice generation), netfabb (for build preparation) and Pan Computing (for simulation), to go with their existing design suite.
Conclusion: So what do I need again?
What you need depends primarily on what you are using AM technologies for. I recommend the following approach:
Identify which of the 4 main categories apply to you
Enumerate existing capabilities: This is a simple task of listing the software you have access to already that have capabilities described in the sub-categories
Assess gaps in software relative to meeting requirements
Develop an efficient road-map to get there: be aware that some software only make sense (or are available) for certain processes
In the end, one of the things AM enables is design freedom, and to quote the novelist Toni Morrison: “Freedom is not having no responsibilities; it is choosing the ones you want.” AT PADT, we work with design and analysis software as well as AM machines on a daily basis and would love to discuss choosing the appropriate software solutions for your needs in greater detail. Send us a note at email@example.com and cite this blog post, or contact me directly on LinkedIn. .
Joining Two of PADT’s Favorite Things: Simulation and 3D Printing
Recent advances in Additive Manufacturing (3D Printing) have removed barriers to manufacturing certain geometry because of constraints in traditional manufacturing methods. Although you can make almost any shape, how do you figure out what shape to make. Using ANSYS products you can apply topological optimization to come up with a free-form shape that best meets your needs, and that can be made with Additive Manufacturing.
A few months ago we presented some background information on how to drive the design of this type of part using ANSYS tools to a few of our customers. It was a well received so we cleaned it up a bit (no guarantee there all the typos are gone) and recorded the presentation. Here it is on YouTube
Let us know what you think and if you have any questions or comments, please contact us.