Getting to Know PADT: Part Scanning and Reverse Engineering

This is the first installment in our review of all the different products and services PADT offers our customers. As we add more, they will be available here.  As always, if you have any questions don’t hesitate to reach out to info@paditnc.com or give us a call at 1-800-293-PADT.

Product innovation doesn’t alway start with a blank sheet. Many times our customers need to begin with an accurate representation of their existing products, or a piece that theirs interfaces with, or even a competitive solutions.  That is why we offer scanning and reverse engineering services that take real world parts and convert them into an accurate and useful CAD model.

What is Part Scanning

Part scanning is a process where we use machines to measure geometry.  Before scanning someone would use rulers, calipers, and other measuring devices dating from the industrial revolution to get critical dimensions off of a part and painstakingly document what they find. That got better with Coordinate Measuring Machines (CMM) where you could accurately measure key locations on the geometry. The problem with this approach was that it only gave you data where you measured.  Fine for simple parts like a flange with bolt holes.  But not good when you have crazy free-form surfaces or many features. Another approach was to section the parts and project a shadow onto a piece of paper and trace it.  If you needed more measurements, cost went way up.

To solve this problem, people found a way to measure lots of points easily: scan the part with some sort of optical sensor and measure points on the part as you go.  Early scanning systems used lasers, measuring the beam that bounced back.  This worked well, especially for very large objects.  But was tricky on some surfaces and produced a lot of noise in the data. So researches figured out that they could project patterns of light and dark onto an object and measure how the edges of that pattern bent and warped.   This is called Structured Light Scanning, and Wikipedia has a good article giving more details on how it works. We use the “blue light” version of this process here at PADT for our optical scanning services.

The other process we use is Cross Sectional Scanning. As the name implies it scans the cross section of parts, and it does it by actually shaving off material one layer at a time and then taking a picture of the 2D cross section that is revealed.  Although you consume the part in the process, it is a very accurate and fairly affordable way to measure complex internal geometry.

What you get from both scanning approaches is what we call a point cloud.  What is a point cloud? A file with millions of points defined as an X, Y, and Z position in space that represent locations that sit on the surfaces of the object.  You can measure critical dimensions, compare different geometries, and use it as a basis to create a computer model.  The key thing to note is that PADT uses precise scanners and leading software, combined with the experience of our operators to produce an accurate and usable point cloud.

Creating Accurate Models from Scan Data – Reverse Engineering

For most projects, getting the point cloud is just the first step. In order for our customers to redesign, update, simulate, or interface with the part we scanned, they need an accurate computer model.  Instead of millions of points, the computer model contains a more concise mathematical representation of the surface defined by the points. The simplest thing we can do is simply fit triangles through those points.  This is refered to as a faceted model because it is made up of triangular facets.  This data is used for 3D Printing, rendering, and for design in some cases.  Most often we deliver an STL file for this type of model. If a more accurate representation is needed, our engineers can convert those facets into an actual Computer Aided Design (CAD) model.  It can be just a dumb solid, or we can even make key features parametric.  The geometry can be handed over in many different formats, including IGES, Paraolids, STEP, SolidWorks, SolidEdge, NX, or CREO.

How Part Scanning with PADT Different

To be blunt, the reason why we added scanning to our capabilities was that we had always outsourced this service for our customers.  We found plenty of people with scanners, but they just scanned a part, ran the software, and provided OK data for our customers.  The problem was they were not experts in the technology behind scanning, they lacked a theoretical understanding of math behind 3D computer geometry modeling, and they were not experts in product development.  It turned out that scanning the geometry was the easy part, what our customers needed was someone who knew how to scan it right and produce useful information.  Information they didn’t have to spend time cleaning and massaging. Our engineers combine all of these skills along with a firm understanding of quality requirements, GD&T, and most of the major CAD systems.  In addition, PADT is ITAR compliant and can deal with your confidential geometry and data requirements.  The fact that PADT is a recognized expert in Additive Manufacturing is often useful as well.  We could not find a service provider that had all of the things our customers required, so we decided to do it ourselves.

Leveraging PADT’s Part Scanning and Reverse Engineering Services

Getting parts scanned by PADT is actually fairly easy.  Step one is to contact PADT and talk to our engineers so they can produce a quote.  Ideally it is best for you to bring the part or parts in to our Tempe office. If that is not feasible we will need some basic pictures of your part and key dimensions like maximum length, width, and height. They will then talk with you to understand what you actually want to accomplish by scanning.  Armed with this information they will provide a quote for scanning and any geometry creation or other activities you need completed including cost, schedule, and a list of deliverables.

In  most cases, you will ship us or drop off the part or parts, and our team will go to work.  If needed, we can also come to where the parts are located and scan them there.  The deliverables vary from job to job, and are negotiated as part of the quoting process.  In general we will provide you with an STL or CAD file with the level of accuracy and detail that you ask for. If needed, we can also provide you with the point cloud  itself.  We can also complete inspection reports and provide comparisons between datasets.

Reach out to Give it a Try or Learn More

Our team is ready and waiting to answer your questions or provide you with a quote.  You can email us at info@padtinc.com or give us a call at 480.813.4884 or 1-800-293-PADT.

Still want to learn more? Here are some links to more information:

  • A more detailed blog post on scanning from early 2017, including a “Scanning 101” section with some great background on the technology
  • The 3D Scanning Wikipedia article.  This has lots of basic information as well as more links to greater details.
  • Information on the Geomagic Capture Scanner, an easy to use, compact, and very portable blue light scanner that we use for a lot of projects.
  • Details about the ZIESS Comet optical scanner, a professional and highly accurate blue light scanner that we use for our more demanding projects.
  • An overview of Cross Sectional scanning.
  • A brief summary of the Geomagic Software we use to create useful models from point clouds. It also has links to more in-depth information.
  • An article in Additive Manufacturing magazine about how PADT used our scanners to create a replacement part for a P-51 Mustang airplane.  It includes a great video as well.

 

Combining ANSYS Simulation with HPC

Engineering simulation has become much more prevalent in engineering organizations than it was even 5 years ago.  Commercial tools have gotten significantly easier to use whether you are looking at tools embedded within CAD programs or the standalone flagship analysis tools.  The driving force behind these changes are to ultimately let engineers and companies understand their design quicker with more fidelity than before.

Engineering simulation is one of those cliché items where everyone says “We want more!”  Engineers want to analyze bigger problems, more complex problems and even do large scale design of experiments with hundreds of design variations – and they want these results instantaneously.   They want to be able to quickly understand their designs and design trends and be able to make changes accordingly so then can get their products optimized and to the market quicker.

ANSYS, Inc. spends a significant amount of R&D in helping customers get their results quicker and a large component of that development is High Performance Computing, or HPC.  This technology allows engineers to solve their structural, fluid and/or electromagnetic analyses across multiple processors and even across multiple computing machines.  Engineers can leverage HPC on laptops, workstations, clusters and even full data centers.

PADT is fortunate to be working with Nimbix, a High Performance Computing Platform that easily allowed us to quickly iterate through different models with various cores specified.  It was seamless, easy to use, and FAST!

Let’s take a look at four problems: Rubber Seal FEA, Large Tractor Axle Model, Quadrocopter CFD model and a Large Exhaust CFD model.  These problems cover a nice spectrum of analysis size and complexity. The CAD files are included in the link below.

Click here to download geometry files that were used in the following benchmarks

TRACTOR AXLE FEA

This model has several parts all with contact defined and has 51 bolts that have pretension defined.  A very large but not overly complex FEA problem.  As you can see from the results, even by utilizing 8 cores you can triple your analysis throughput for a work day.  This leads to more designs being analyzed and validated which gives engineers the results they need quicker.

SUMMARY

  • 58 Parts
  • 51 x Bolts with Pretension
  • Gaskets
  • 928K Elements, 1.6M Nodes

Cores

Elapsed Time
[s]

Estimated Models Per 8 [hours]

2

14,525

2

4

9,710

3

8

5,233

6

16 4,009

7

 

RUBBER SEAL FEA

The rubber seal is actually a relatively small size problem, but quite complex.  Not only does it need full hyperelastic material properties defined with large strain effects included, it also includes a leakage test.  This will pressurize any exposed areas of the seal.  This will of course cause some deformation which will lead to more leaked surfaces and so on.  It basically because a pressure advancing solution.

From the results, again you can see the number of models that can be analyzed in the same time frame is signifcantly more.  This model was already under an hour, even with the large nonlinearity, and with HPC it was down to less than half an hour.

SUMMARY

  • 6 Parts
  • Mooney Rivlin Hyperelastic Material
  • Seal Leakage with Advancing Pressure Load
  • Frictional Contact
  • Large Deformation
  • 42K Elements, 58K Nodes

Cores

Elapsed Time
[s]
Estimated Models Per 8 [hours]

2

3,353

9

4

2,489

12

8 1,795

16

 


QUADROCOPTER DRONE CFD

The drone model is a half symmetry model that includes 2 rotating domains to account for the propellers.  This was ran as a steady state simulation using ANSYS Fluent.  Simply utilizing 8 cores will let you solve 3 designs versus 1.

SUMMARY

  • Multiple Rotating Domains
  • 2M Elements, 1.4M Nodes

Cores

Elapsed Time
[hours]
Speedup

2

2.1

1

4

1.2

1.8

6

0.8

2.6

8 0.7

3

 

EXHAUST CFD

The exhaust model is a huge model with 33 million elements with several complicated flow passages and turbulence.  This is a model that would take over a week to run using 1 core but with HPC on a decent workstation you can get that down to 1 day.  Leveraging more HPC hardware resources such as a cluster or using a cloud computing platform like Nimbix will see that drop to 3 hours.  Imagine getting results that used to take over 1 week that now will only take a few hours.  You’ll notice that this model scaled linearly up to 128 cores.  In many CFD simulations the more hardware resources and HPC technology you throw at it, the faster it will run.

SUMMARY

  • K-omega SST Turbulence
  • Multi-Domain
  • 33M Elements, 7M Nodes

Cores

Elapsed Time
[hours]
Speedup

16

26.8

1

32

13.0

2.1

64

6.8

3.9

96

4.3

6.2

128 3.3

8.2

As seen from the results leveraging HPC technology can be hugely advantageous.  Many simulation tools out there do not fully leverage solving on multiple computing machines or even multiple cores.  ANSYS does and the value is easily a given.  HPC makes large complex simulation more practical as a part of the design process timeline.  It allows for greater throughput of design investigations leading to better fidelity and more information to the engineer to develop an optimized part quicker.

If you’re interested in learning more about how ANSYS leverages HPC or if you’d like to know more about NIMIBX, the cloud computing platform that PADT leverages, please reach out to me at manoj@padtinc.com


Want to learn more about how ANSYS Simulation Software stacks up against CAD-Embedded Simulation tools?

Click the link below to register for our upcoming webinar covering both the why and the how of stepping up your simulation game by leaving CAD-Embedded Simulation behind!

This presentation will dispel common misconceptions, explain how to make the transition, and present topics that ANSYS can provide solutions for, such as:

  • Understanding fluid flow: accurate and fast CFD
  • Real parts that exist in assemblies
  • The importance of robust meshing
  • Advanced capabilities and faster solvers

Additive Manufacturing: 3D Printing a Metal Shift Knob for Faster Cooling

When Nathan Huber moved to Arizona from Colorado to join PADT he learned a lot, and one of the things he learned fast was that the inside of cars get very hot in the summer here.  In fact, the shift knob on his car was untouchable in July.  This coincided with his learning more about metal 3D Printing and an idea occurred, what about 3D Printing a metal shift knob designed to cool off faster, and that looked cool.  Oh, and use ANSYS to drive the design.

He blogged about it before (here and here), and Additive Manufacturing online picked up the story and added to it on their blog post “3D Printing a Metal Shift Knob for Faster Cooling”  Check it out, they did a nice job of explaining what we did and how Nathan used several of our tools like ANSYS Mechanical and our Concept Laser metal system to realize the design.

 

3D Printing Peer Group of New Mexico Tech Council Launching on June 22

We are very pleased to announce the launch meeting of the newest New Mexico Technology Council peer group: 3D Printing.  After the success of other peer groups, and a similar committee in the Arizona Technology Council, PADT is partnering with the NMTC to start a group focused on all things Additive Manufacturing, which is the more technical name for 3D Printing. Schools, businesses, and individuals who have any involvement or interest in this exciting and transformative technology will be able to network and organize to get greater value from 3D Printing. This includes understanding the technology, working together on research projects, and getting to know what services are available locally.  It will also serve as a platform to coordinate the use of 3D printing in STEM education.

    

For this launch event, PADT’s Rey Chu will share his thoughts on the latest and most interesting advancements in 3D Printing.

What: NMTC 3D Printing Peer Group Launch
Networking
Beer
Where: Rio Bravo Brewing Company, 1912 2nd St NW, Albuquerque, NM 87102
When: June 22, 2017
5:00 pm – 7:00 pm
Who: Anyone (21 years of age or older) involved in Academia, Industry, or Research that is involved or interested in Additive Manufacturing
Why: To build cooperation between the growing 3D Printing community in the state
How: Being social, creating connections, and joining the group to take action in the future

We will kick off the meeting with introductions around the room, then listen to Rey share his views on what is new and interesting in this industry, then talk about the peer group, answer questions, and start planning our next activities.  At around 6:45 or so we will commence with the networking.

Please contact PADT at info@padtinc.com if you have any questions before the event.   We hope to see you there.

Don’t forget to register, and please let anyone else you think might be interested know about the event.

 

Phoenix Business Journal: ​Remembering Kelley Johnson, aircraft design icon and project management superstar

One of my engineering idols is Clarence “Kelley” Johnson. He led the design of many of the coolest aircraft ever made, and he was a pioneer in managing large engineering projects.  In “​Remembering Kelley Johnson, aircraft design icon and project management superstar” I talk about why he was such an important figure in technology, and some rules he developed for effective project management. Even if you are not an airplane person, it is worth getting to know his work and his methods.

 

ANSYS Workbench Polyhedral Meshing

The ANSYS App Store contains all sorts of free and paid apps developed by ANSYS as well as trusted partners. These apps improve workflows and allow users to build in best practices. An app that has been of particular interest to me is Workbench Poly Meshing for Fluent

This app enables the power and capacity of Fluent Meshing, most notably the polyhedral meshing feature, with the ease of use of the ANSYS Workbench Meshing environment. In order to show the functionality of this app, I will demonstrate with the generation of a polyhedral mesh on a sample geometry from the Fluent Meshing tutorials.

To start out, I have imported a .igs file of an exhaust manifold into ANSYS SpaceClaim Direct Modeler, which has powerful repair and prepare tools that will come in handy. I notice that the geometry is comprised of 250 surfaces, which I need to fix in order to create a solid body. By navigating into the ‘Repair’ tab and selecting the ‘Stitch’ operation, SpaceClaim notes there are two stitchable edges in my geometry. I select the green check mark to perform this operation and am greeted with a solid geometry. I complete my tasks in SpaceClaim by extracting the fluid volume using the ‘Volume Extract’ tool in the ‘Prepare’ tab.

I setup my workflow in ANSYS workbench with my added ‘Fluent Meshing’ ACT module between the ‘Mesh’ module and ‘Fluent’ module. I can then proceed to create my desired surface mesh in ANSYS meshing and setup a few required inputs for Fluent Meshing.


Once this process has been completed, I can update my ‘Fluent Meshing’ cell and open the ‘Fluent’ setup cell to display my polyhedral mesh!

IMPORTANT NOTE: all named selections must be lowercase with no spaces, and the file path(s) cannot contain any spaces.


Want to learn more about how ANSYS Simulation Software stacks up against CAD-Embedded Simulation tools?

Click the link below to register for our upcoming webinar covering both the why and the how of stepping up your simulation game by leaving CAD-Embedded Simulation behind!

This presentation will dispel common misconceptions, explain how to make the transition, and present topics that ANSYS can provide solutions for, such as:

  • Understanding fluid flow: accurate and fast CFD
  • Real parts that exist in assemblies
  • The importance of robust meshing
  • Advanced capabilities and faster solvers

Phoenix Business Journal: Why medical startups should not focus on patients

It sounds counterintuitive, but it is one of those positions where you sometimes have take a different path to end up where you should. I  “Why medical startups should not focus on patients” in order to in the end, deliver better products and better outcome to their patients. I’ve observed too many good ideas fail because the creators are not paying attention to the people who will pay for and deploy the solution.

Advanced ANSYS Functionality

Just like any other marketplace, there are a lot of options in simulation software.  There are custom niche-codes for casting simulations to completely general purpose linear algebra solvers that allow you to write your own shape functions.  Just like with most things in life, you truly get what you pay for.

Image result for get what you pay for

 

For basic structural and thermal simulations pretty much any FE-package should suffice.  The difference there will be in how easy it is to pre/post process the work and the support you receive from the vendor.  How complicated is the geometry to mesh, how long does it take to solve, if you can utilize multiple cores how well does it scale, how easy is it to get reactions at interfaces/constraints…and so on.  I could make this an article about all the productivity enhancements available within ANSYS, but instead I’ll talk about some of the more advanced functionalities that differentiate ANSYS from other software out there.

  • Radiation

You can typically ignore radiation if there isn’t a big temperature gradient between surfaces (or ambient) and just model your system as conduction/convection cooled.  Once that delta is large enough to require radiation to be modeled there are several degrees of numerical difficulty that need to be handled by the solver.

First, radiating to ambient is fairly basic but the heat transfer is now a function of T^4.  The solver can also be sensitive to initial conditions since large DT results in a large heat transfer, which can then result in a large change in temperature from iteration to iteration.  It’s helpful to be able to run the model transiently or as a quasi-static to allow the solver to allow some flexibility.

Next, once you introduce surface to surface radiation you now have to calculate view factors prior to starting the thermal solution. If you have multiple enclosures (surfaces that can’t see each other, or enclosed regions) hopefully there are some processes to simplify the view factor calculations (not wasting time calculating a ‘0’ for elements that can’t radiate to each other).  The view factors can sometimes be sensitive to the mesh density, so being able to scale/modify those view factors can be extremely beneficial.

Lastly you run into the emissivity side of things.  Is the emissivity factor a function of temperature?  A function of wavelength?  Do you need to account for absorption in the radiation domain?

Luckily ANSYS does all of this.  ANSYS Mechanical allows you to easily define radiation to ambient or surface-to-surface.  If you’re using symmetry in your model the full radiating surface will be captured automatically.  You can define as many enclosures as possible, each with different emissivity factors (or emissivity vs Temperature).  There are more advanced features that can help with calculating view factors (simplify the radiating surface representation, use more ray traces, etc) and there is functionality to save the calculated view factors for later simulations.  ANSYS fluid products (CFX and Fluent) can also account for radiation and have the ability to capture frequency-based emissivity and participating media.

image

Automatic expansion of radiating surfaces across symmetry planes

image

Different enclosures to simplify view factor calculations

Long story short…you don’t have to know what the Stefan-Boltzman constant is if you want to include radiation in your model (bonus points if you do).  You don’t have to mess with a lot of settings to get your model to run.  Just insert radiation, select the surface, and run.  Additional options and technical support is there if necessary.

  • Multiple/Multi-physics

I’d expect that any structural/thermal/fluids/magnetics code should be able to solve the basic fundamental equations for the environment it simulates.  However, what happens when you need to combine physics, like a MEMs device.  Or maybe you want to take some guess-work/assumptions out of how one physics loads another, like what the actual pressure load is from a CFD simulation on a structural model.  Or maybe you want to capture the acoustic behavior of an electric motor, accounting for structural prestress/loads such as Joule heating and magnetic forces.

image

ANSYS allows you to couple multiple physics together, either using a single model or through data mapping between different meshes.  Many of the data mapping routines allow for bi-directional data passing so the results can converge.  So you can run an magnetic simulation on the holding force between a magnet and a plate, then capture the deflected shape due to an external load, and pass that deformed shape back to the magnetic simulation to capture the updated force (and repeat until converged).

image

If you have vendor-supplied data, or are using another tool to calculate some other results you can read in point cloud data and apply it to your model with minimal effort.

image

To make another long story short…you can remove assumptions and uncertainty by using ANSYS functionality.

  • Advanced Material Models

 

Any simulation tool should be able to handle simple linear material models.  But there are many different flavors of ‘nonlinear’ simulation.  Does the stiffness change due to deflection/motion (like a fishing rod)?  Are you working with ductile metals that experience plastic deformation?  Does the stiffness change due to parts coming into/out-of contact?  Are surfaces connected through some adhesive property that debonds under high loads?  Are you working with elastomers that utilize some polynomial form hyper-elasic formulation?  Are you working with shape memory alloys?  Are you trying to simulate porous media through some geomechanical model?  Are you trying to simulate a stochastic material variation failure in an impact/explosive simulation?

image

Large deflection stiffness calculations, plasticity, and contact status changes are easy in ANSYS.  Debonding has been available since ANSYS 11 (reminder, we’re at release 18.0 now).  ANSYS recently integrated some more advanced geomechanical models for dam/reservoir/etc simulations.  The explicit solver allows you to introduce stochastic variation in material strengths for impact/explosive simulations.

image

ANSYS also has all the major flavors of hyper-elastic material models.  You can choose from basic Neo-Hookean, Arruda-Boyce, Gent, all the way through multiple variations of Mooney-Rivlin, Yeoh, Ogden, and more.  In addition to having these material models available (and the curve fitting routines to properly extract the constants from test data) ANSYS also has the ability to dynamically remesh a model.  Most of the time when you’re analyzing the behavior of a hyperelastic part there is a lot of deformation, and what starts out as a well-shaped mesh can quickly turn into a bad mesh.  Using adaptive meshing, you can have the solve automatically pause the solution, remesh the deformed shape, map the previous stress state onto the new nodes/elements, and continue with the solution.  I should note that this nonlinear adaptive remesh is NOT just limited to hyperelastic simulations…it is just extremely helpful in these instances.

The ending of this story is pretty much the same as others.  If you have a complicated material response that you’re trying to capture you can model it in ANSYS.  If you already know how to characterize your material, just find the material model and enter the constants.  We’ve worked with several customers in getting their material tested and properly characterized.  So while most structural codes can do basic linear-elastic, and maybe some plastic…very few can capture all the material responses that ANSYS can.

  • MEMs/Piezo/Etc

I know I’ve already discussed multiple physics and advanced materials, but once you start making parts smaller you start to get coupling between physics that may not work well for vector-based coupling (passing load vectors/deformations from one mesh to another).  Luckily ANSYS has a range of multi-physics elements that can solve use either weak or strong coupling to solve a host of piezo or MEM-related problems (static, transient, modal, harmonic).  Some codes allow for this kind of coupling but either require you to write your own governing equations or pay for a bunch of modules to access.

If you have the ANSYS Enterprise-level license you can download a free extension that exposes all of these properties in the Mechanical GUI.  No scripting, no compiling, just straight-up menu clicks.

image

Using this extension you can define the full complex piezoelectric matrix, couple it with an anisotropic elasticity matrix, and use frequency dependent losses to capture the actual response of your structure.  Or if you want you can use simplified material definitions to get the best approximation possible (especially if you’re lacking a full material definition from your supplier).

 

Long story short…there are a lot of simulation products out there.  Pretty much any of them should be able to handle the basics (single part, structural/thermal, etc).  What differentiates the tools is in how easy it helps you implement more real-world conditions/physics into your analysis.  Software can be expensive, and it’s important that you don’t paint yourself into a corner by using a single point-solution or low-end tool.


Want to learn more about how ANSYS Simulation Software stacks up against CAD-Embedded Simulation tools?

Click the link below to register for our upcoming webinar covering both the why and the how of stepping up your simulation game by leaving CAD-Embedded Simulation behind!

This presentation will dispel common misconceptions, explain how to make the transition, and present topics that ANSYS can provide solutions for, such as:

  • Understanding fluid flow: accurate and fast CFD
  • Real parts that exist in assemblies
  • The importance of robust meshing
  • Advanced capabilities and faster solvers

Phoenix Business Journal: ​Automation is here and we need to pay attention

People talk about automation, mostly with respecte to manufacturing, like it is something that is comming.  But “Automation is here and we need to pay attention.” If you don’t understand how computer software, robotics, and sensors are changing every aspect of our lives, odds are you will miss how it will change your business.

When the going gets tough, the tough use ANSYS for CFD Meshing

If you do CFD simulations then you know the struggle that is involved in meshing. It is a fine balance of accuracy, speed, and ease of set up. If you have complex geometry, large assemblies, or any difficulty meshing then this blog article is for you.

Why should I spend time making a good mesh?

The mesh is arguably one of the most important parts of any simulation set up. A good mesh can solve significantly faster and provide more accurate results. Conversely, a poor mesh can make the simulation have inaccurate results and be slow to converge or not converge at all. If you have done any simulation then you know that hitting the solve button can feel like rolling the dice if you don’t have a robust meshing tool.

When is it going to matter?

A good mesh is going to matter on a Friday afternoon when you need to get the simulation started before you leave for the weekend because it takes two days to run and you need to deliver results on Monday but you are up against the clock because you have to get to your kid’s soccer game by 5pm and the mesh keeps crashing.

A poor mesh can do more than just reorganizing you’re social agenda. A poor mesh can drastically change results like pressure drop in an internal flow passage or drag over a body. If you go into that meeting on Monday and tell your boss that the new design is going to perform 10% better than the previous design – you need to be confident that the design is 10% better not 10% worse.

What should I do when I need to create a good mesh?

If you’re the poor soul reading this on a Friday afternoon because you are trying to frantically fix you’re mesh so you can get your simulation running before the weekend – I pity you. Continue reading for my proprietary step by step approach titled “How to get you’re CFD mesh back on track!” (Patent pending).

Step 1) Know your tools

ANSYS has been developing its meshing technology since the beginning of time (not really but almost) – it’s no surprise that its meshing algorithms are the best in the business. In ANSYS you have a large number of tools at your disposal, know how to use them.

The first tool in your toolbox is the ANSYS automatic meshing technology. It is able to predictively apply settings for your part to get the most accurate automatic mesh possible. It has gotten so good that the automatic mesh is a great place to start for any preliminary simulations. If you want to get into the details, ANSYS meshing has two main groups of mesh settings – Global Meshing Parameters and Local Meshing Parameters. Global mesh parameters are great for getting a good mesh on the entire model without going into detailed mesh settings for each part.

But when you do have to add detailed meshing settings on a part by part basis then local mesh settings won’t let you down.

Step 2) Know your physics

What is your primary result of interest? Drag? Pressure drop? Max velocity? Stagnation? If you can quantify what you are most interested in then you can work to refine the mesh in that region so as to capture the physics accurately. ANSYS allows you set local sizing parameters on bodies, faces, lines, and regions which allow you to get the most accurate mesh possible but without having to use a fine mesh on the entire part.

Step 3) Know your mesh quality statistics

Mesh quality statistics can be a good way to gauge the health of your mesh. They are not a foolproof method for creating a mesh that will be accurate but you will be able to get an idea of how well it will converge. In ANSYS meshing there is a number of mesh quality statistics at your fingertips. A quick and easy way to check your mesh is to look at the Minimum Orthogonal Quality statistic and make sure it is greater than 0.1 and Maximum Skewness is less than 0.95.

Step 4) Know your uncertainty

Every test, simulation, design, process etc… has uncertainty. The goal of engineering is to reduce that uncertainty. In simulation meshing is always a source of uncertainty but it can be minimized by creating high quality meshes that accurately model the actual physical process. To reduce the uncertainty in meshing we can perform what is called a mesh refinement study. Using the concept of limits we can say that in the limit of the mesh elements getting infinitely small than the results will asymptotically approach the exact solution. In the graph below it can be seen that as the number of elements in the model are increased from 500 – 1.5million the result of interest approached the dotted line which we can assume is close to the exact solution.

By completing a mesh refinement study as shown above you can be confident that the mesh you have created is accurately capturing the physics you are modeling because you can quantify the uncertainty.

If you currently just skip over the meshing part of your CFD analysis thinking that it’s good enough or if your current meshing tool doesn’t give you any more details than just a green check mark or a red X then it’s time dig into the details of meshing and start creating high quality meshes that you can count on.

For more info about advanced meshing techniques in ANSYS – see this PDF presentation that is a compilation of ANSYS training material on the meshing subject.

Advanced Techniques in ANSYS Meshing_Blog

If you still haven’t figured out how to get your mesh to solve and its 5pm on Friday see below*

*Common pitfalls and mistakes for CFD meshing:

  • Choose your turbulence model wisely and make sure your mesh meets the quality metrics for that model.
  • Make sure you don’t have boundary conditions near an area of flow recirculation. If you are getting reverse flows at the boundary then you need to move your boundary conditions further away from the feature that’s causing the flow to swirl in and out of the boundary.

Want to learn more about how ANSYS Simulation Software stacks up against CAD-Embedded Simulation tools?

Click the link below to register for our upcoming webinar covering both the why and the how of stepping up your simulation game by leaving CAD-Embedded Simulation behind!

This presentation will dispel common misconceptions, explain how to make the transition, and present topics that ANSYS can provide solutions for, such as:

  • Understanding fluid flow: accurate and fast CFD
  • Real parts that exist in assemblies
  • The importance of robust meshing
  • Advanced capabilities and faster solvers

 

Installing a Metal 3D Printer: Part 3A (Safety: Risks)

What are the safety risks in laser powder bed fusion metal 3D printing?

This is the 3rd post in a series of 5 on things we learned installing a metal 3D printer (laser powder bed fusion). Links to previous posts are below:

The most important discussions around installing and operating a metal 3D printer involve safety. The requirements can be difficult to pin down since they depend on several things: whether you are using reactive or non-reactive alloys (read a previous post on this subject here), the risk perception of your local building safety director and fire marshal, local regulations (and exceptions) and the volume of material you are dealing with. As with all things safety and more so because of how nascent metal 3D printing technology is, I list a few disclaimers at the bottom of this page.

There is so much to say about safety in this process that half-way through writing this post, it became clear it would not fit in one post. Therefore, I have split the content into two: in this post (3A) I talk about the risks: where they come from and why they matter. In the next post (3B), I will discuss how these risks can be mitigated.

1. Sources of Risk

Broadly speaking, I like to think of two sources of risk in this process since as an operator of these machines you have to think differently about how you interact with these sources.

1.1 Metal Powder

Metal 3D printing involves fusing together powder in a bed. Typical metal powders used for laser based 3D printing are spherical in shape and range from 10-70 microns in diameter, as shown in Figure 1. At this size, a metal can be prone to fire and explosion (under the right circumstances) and there is also the physiological concern of long-term inhalation of, and contact with, these powders. The powder also has a long life cycle and requires human interaction at many steps – from arriving in a container (as shown in Figure 2), through multiple recycling steps through final disposal. These risks come into play just when handling the powder (independent of its use in the process) – an additional risk comes from the melting process itself.

Fig 1. Typical powder particle size distribution is in the range of 10-70 microns for the laser powder bed fusion process.
Fig 2. Metal powders are delivered and stored in plastic containers such as the one shown above

1.2 The Laser Fusion Process

The powder in the bed described before is fused together into a solid using a laser that locally melts the powder one layer at a time. This is conducted in an inert atmosphere (Argon or Nitrogen) and is the second source of risk since these gases can displace Oxygen from a closed environment. Additionally, the process of laser melting of metals creates vaporized soot (see video below), some of which deposits on the process chamber and in the extraction module and filter. The smoke particles can be even finer than the powder itself, and need to be cleaned out with care on a regular basis.

2. Risks

There are 4 main risks arising from the laser powder bed fusion process: fire and explosion, powder inhalation and contact, inert gas asphyxiation and the environmental impact of the wastes generated.

2.1 Fire and Explosion

In May 2014, OSHA cited a 3D printing company for 10 violations deriving from the workplace safety standards surrounding the operation of a metal 3D printer (including not having the proper Class D fire extinguisher). The disregard of multiple safety measures during a routine build setup procedure resulted in a fire which caused life-threatening burns to the operator of the printer. While this incident was the result of gross negligence, it is nonetheless a cautionary tale that should drive us to understand the fundamental reasons why a metal 3D printer can cause fires and to appreciate the underlying reasons for why suppliers recommend the safety measures they do.

Fire and explosion require a combination of conditions as shown in the commonly cited image below used by OSHA and other agencies to communicate risks of powder handling.
As shown in Fig. 3, when handling powder in ambient atmospheres (with oxygen), all that is needed is a suitable ignition source to initiate a fire. Further, if this occurs in the presence of a dust cloud with many particles dispersed in a contained area (such as a small room or an air duct), this could lead to a more damaging explosion.

Fig 3. The oft cited fire triangle and explosion pentagon. Users of powder based metal 3D printing are often working with 2 of the 3 elements in the triangle and the key is to avoid the third.
  • Fire: When handling metal powder, the user needs to be aware that she/he already has 2 of the 3 requirements of a fire met and the main aim must be to ensure protection against any ignition source. There are several sources that could cause an ignition, the most likely one for a user of a metal 3D printer is static electricity. Additionally, it is possible that a fire can be initiated by hot surfaces, flames, hot gases and particles, mechanically generated sparks and strayelectrical currents.
  • Explosion: With regard to explosions, in addition to the 3 requirements above, dust clouds in contained areas can exacerbate any ignition to a much larger impact within milliseconds. Therefore, the prevention of the formation of metal dust clouds (as unlikely as that may seem), is of paramount importance.

In addition to the requirements above, there are levels associated with each requirement that need to be met together for an actual fire or explosion to occur. The risk of ignition increases with reducing particle diameter and given a certain particle size, the most significant factor governing risk is the nature of the metal. Reactive metals (Aluminum alloys, Titanium and its alloys, as well as smoke particles from both reactives and non-reactives) pose much higher risk than non-reactive metals (steels, Inconels, bronze, Cobalt Chrome alloys) – this is a subject I wrote about in more detail in a previous post.

2.2 Powder Inhalation & Contact

As discussed before, most metal 3D powder particles range in size from 10-70um. This is at the very edge of what is considered respirable and damaging to our lungs. While contact physically is to be avoided since it may initiate irritation and potential dermatitis, there is greater concern about the long-term inhalation exposure risks of these powders. Particles of the size range in this process can get deposited in the tracheo-bronchial region per Jenson [1] and Goldich [2]. Ultimately, these particles are discharged from the body or swallowed, but effects of long term exposure for the wide range of metals and alloys is not fully studied – which is why suppliers insist on respirators (more on that in the next post). It is worth pointing out though, from the work published by Jenson and Goldich, that it appears that while metal 3D printing powders are small enough to travel past the nasal cavity if inhaled, their sizes are large enough that respiratory damage in the lungs is highly unlikely – only particles under 2 microns are at risk of making it all the way to the alveoli and causing lung disease [2].

Fig 4. The human respiratory system. Particles in the 20-100 micron range, if inhaled, can make it to the trachea and bronchial regions [1, 2]  (Image Credit – public domain: National Institute of Health: National Heart, Lung and Blood Institute)

2.3 Inert Gas Asphyxiation

Inert gases are used in laser metal 3D printers to reduce the reactivity of the metal for processing purposes. Most metal 3D printers either use Nitrogen or Argon. Inert gas asphyxiation is the main risk due to oxygen being displaced by either of these gases that have leaked for some reason. Since both gases are not detectable by humans, victims do not realize that they are inhaling air depleted of oxygen and as a result this can have a serious impact. The human body is used to atmospheric percentages of oxygen (21%) and values below 19.5% can be harmful and are defined as oxygen-deficient per OSHA [3]. Thus, any user of nitrogen or argon gas (and this applies not just to any process using inert gases), especially in small spaces such as a closed room, needs to be aware of this risk and protect against it.

2.4 Environmental Impact

A key challenge with powder based processes lies in collecting and disposing the stray or “fugitive” powder from different locations such as the tool, PPE, containers and vacuum systems into temporary storage, during which the above risks of fire/explosion and inhalation remain. Additionally, the storage typically results in loose powder and solid waste as well as water with powder particles, both of which need to be disposed into the outside world and could pose an environmental hazard. I will discuss this further in a future post, when I attempt to look at some of the environmental aspects around this technology.

Fig 5. Metal powder settled at the bottom of the water column in the wet separator (vacuum cleaner). Where does it go next?

3. Disclaimers

  • This is intended to supplement the supplier training you must receive before using the equipment and not meant to replace it – in case of conflicting information, your supplier’s training and equipment requirements override any discussion here. PADT assumes no legal responsibilities for any decisions or actions taken by the readers of this document.
  • My personal experience derives specifically from the use of Laser-based metal 3D printing tools, specifically Concept Laser’s MLab Cusing R equipment. I expect majority of this information to be of use to users of other laser based powder bed fusion metal systems and to a lesser extent to Electron Beam systems, but have no personal experience to vouch for this.
  • Local, state and federal regulations vary, and are important – partner with your local fire marshal (or equivalent authority) as a starting point and take them along with you every step of the way. If in the US, familiarize yourself in particular with OSHA’s guidance on dust explosions [4] and NFPA 484 [5], the National Fire Protection Association’s standard for combustible metals (links below).

4. References

  1. J.M. Benson, “Safety considerations when handling metal powders,” Southern African Institute of Mining and Metallurgy, 2012
  2. R. G. Goldich, “Fundamentals of Particle Technology,” Chapter 15, Midland IT and Publishing, UK, 2002
  3. OSHA on Oxygen Deficiency
  4. OSHA’s Guidance on Dust Explosions
  5. National Fire Protection Association’s standard for combustible metals, NFPA 484
  6. D. Bhate, “Reactive and Non-Reactive Metal Alloys in Laser-based Powder Bed Fusion,” PADT Blog Post, 2016

Acknowledgements

Thank you to Perry Harlow-Leggett, the AM team at UL whose articles and webinars I have benefited from, and all the folks behind the scenes at OSHA and NFPA.

~

In part 3B, I will address mitigation strategies to address the risks described in this post. In the meantime, please read my prior posts below if you haven’t already, or send your inputs to me via message on LinkedIn. Thank you!

Stratasys – PolyJet Agilus 30 Webinar

Introducing New PolyJet Material: Agilus30

PADT is excited to introduce the newest polyjet material available from Stratasys, Agilus30! Agilus30 is a superior Rubber-like PolyJet photopolymer family ideal for advanced design verification and rapid prototyping.

Get more durable, tear-resistant prototypes that can stand up to repeated flexing and bending. With a Shore A value of 30 in clear or black, Agilus30 accurately simulates the look, feel and function of Rubber-like products. 3D print rubber surrounds, overmolds, soft-touch coatings, living hinges, jigs and fixtures, wearables, grips and seals with improved surface texture.

Agilus30 has applications in a number of areas, including:

  • Medical Models

  • Tooling needing rubber-like characteristics

  • Consumer Goods

  • Sporting Goods

  • General Prototyping

  • Overmolding & many more!

Want to know more about PolyJet’s toughest flexible material to date? 

Join PADT’s 3D Printing Application Engineer James Barker along with Stratasys Materials Business Manager Ken Burns for a presentation on the various benefits and attributes that Agilus30 has to offer, which machines are compatible with it, and how companies are making use of it’s unique capabilities.

Phoenix Business Journal: ​Technical training for employees is changing, is that a good thing?

Like so much else these days, the way that we deliver training to employees has changed over time to take advantage of new technologies. This is especially true for technical training on how to use hardware and software. The traditional classroom approach has been replaced with online and on-demand training. In “Technical training for employees is changing, is that a good thing?” I put on my curmudgeon hat and talk about why the traditional way has advantages that outway the negatives.

Phoenix Business Journal: ​5 things to think about when implementing a database product at your business

If you have ever implemented a Database appcliation at your business you know it can be a pain.  In “​5 things to think about when implementing a database product at your business” I go over some lessons that we have learned over time to make the whole process and outcome better.

3D Metal Printing: A Role in Military Fleet Readiness

The project to keep a 1944 P-51 Mustang flying was covered again, this time in 3D Metal Printing Magazine (Pg 23-33).   Concept Laser worked with PADT to reverse engineer and print the exhaust manifold from a P-51 to keep it flying.  Unlike the other article and video on the project, this reporter used this example as a great way to look at the readiness of military aircraft, and not just antique planes.

As PADT’s Rey Chu says ““This was a great exercise that’s suitable for numerous military applications and very relevant to the future use of 3D metal printing to maintain fleets in the field,” Chu says. “Maintaining spare-parts inventory has become a significant challenge, for example, to the Air Force. Additive manufacturing could be the solution.”