Phoenix Children's Hospital 3D printed heart model. (Image courtesy Phoenix Children's Hospital)

Workflow for Creating a 3D Printed Medical Model with Stratasys

For decades in the medical world, surgeons and their professional support teams have relied on X-rays, computed tomography (CT) scans and magnetic resonant imaging (MRI) data when performing their pre-surgical planning approach. These diagnostic tools have been literal lifesavers, yet the resolution and 2D perspective of these images can make it difficult to determine the full details of anatomical geometry. Subtle, critical abnormalities or hidden geometries can go unnoticed when viewing flat films and digital displays.

3D printed heart model produced by Phoenix Children’s Hospital. (Image courtesy Phoenix Children’s Hospital)

With the advent of 3D printing, many surgeons are now using 3D models for both surgical planning and patient communication. While cost is the primary hold-back, such models are seeing increased use. In addition, efforts are underway to quantify the benefits of reduced operating room time/expense and improved patient outcome; see Medical 3D Printing Registry (ACR/RSNA). Supporting this concept are the high-resolution, multi-material PolyJet 3D printers from Stratasys.

But how does the patient’s CT and MRI data become a unique 3D printed model you can hold in your hand? How do you segment out the areas of interest for a particular analysis or surgical model? This blog post describes the necessary steps in the workflow, who typically performs them, and the challenges being addressed to improve the process every step of the way.

Data Acquisition of Patient Anatomy

When we think of imaging throughout the decades, X-ray technology comes to mind. However, classic single 2D images on film cannot be used to drive 3D models because they are qualitative not quantitative. The main options that do work include the series of x-rays known as CT scans, MRI data, and to a lesser extent computed tomography angiography (CTA) and magnetic resonant angiography (MRA). Each approach has pros and cons and therefore must be matched to the proper anatomy and end use.

CT scans comprise a series of x-rays evenly spaced laterally across a particular body section, typically generating several hundred image files. These can be quickly acquired and offer high resolution, however, they do not do well displaying different types of soft tissue, and the process relies on extended exposure to a radiation source.

Sample multiple digital images generated as a CT scan is performed (Image courtesy nymphoenix/Shutterstock.com.)

Typical CT resolution is 500 microns in X and Y directions, and 1mm in Z. This is readily handled by Stratasys printers; for example, the print resolution of the J750 Digital Anatomy Printer is 42 microns in X, 84 microns in Y, and 14 to 27 microns layering in Z, which more than captures all possible scanned features.

Computed Tomography Angiography (CTA) involves the same equipment but uses a contrast agent. With this approach, brighter regions highlight areas with blood flow. This process is superior for showing blood vessels but does not differentiate tissue or bones well.

MRI data is based on a different technology where a strong magnetic field interacts with water in the body. This approach differentiates soft tissue and shows small blood vessels but is more expensive and not effective for capturing bone. Similarly, Magnetic Resonant Angiography (MRA) uses a contrast agent that can track small blood vessels which are important for identifying a stroke but cannot register tissue. MRI scans may also include distracting artifacts and offer poor regional contrast.

A final source of digital imaging data is Positron Emission Tomography (PET). Here, radioactive material is attached to a biologically active area such as cancer; the data obtained with sensors is useful but very local – it does not show surrounding tissue.

Segmentation: Conversion from DICOM to STL format

Whether generated by CT or MRI equipment, anatomic image data is stored in digital files in accordance with the Digital Imaging and Communications in Medicine (DICOM) standard. Two aspects of this standard are relevant to 3D printing medical models: DICOM files include patient-specific, HIPPA-protected information, and the data in the individual images must be merged and converted into a solid model, with the areas of interest defined and partitioned.

Various software packages and services are available that will convert DICOM data into an STL model file (standard format for 3D printer input) while stripping out the personal identifying information. (The latter must be done to comply with HIPPA regulations: never send a DICOM file directly to any service bureau.)

Segmentation involves partitioning a digital image into distinct sets of pixels, defining regions as organ, bone, blood vessel, tumor, etc., then grouping and combining those sub-sections into a 3D model saved as an STL file. Not only does this format offer more meaningful information than a stack of separate images, but it can then be exported for 3D printing.

Example of processed CT scans, combined into a multiple-view 3D visualization and saved as an STL file. (Image courtesy PADT Inc.)

The standard unit of measure for identifying and segmenting the different regions within the combined 3D series of CT scans is a Hounsfield unit. This is a dimensionless value, defined as tissue density/x-ray absorption; for reference, water = zero, a kidney =+40 and bone = +1000.

Human guidance is needed to set threshold Hounsfield levels and draw a perimeter to the area of interest. You can define groups with the same threshold level, cut out certain areas that are not needed (e.g., “mask” the lungs to focus on the spine), and use preset values that exist for common model types. Typically, a radiologist or trained biomedical engineer performs this task, since correctly identifying boundaries is a non-trivial judgement task.

A particularly challenging task is the workflow for printing blood vessels, as opposed to bones or organs. The output from CTA/MRA imaging is the blood pool, not the enclosing vessel. In this case, users need third-party software to create a shell of X thickness around the blood pool shape, then keep both model files (pool and vessel) to guide printing the vessel walls and their internal support structure (which, on the Stratasys J750 Digital Anatomy Printer, is soluble and dissolves out.)

So far, just a few medical segmentation software packages exist:

  • Materialise Mimics Innovation Suite is internationally known for its excellence in image analysis and allows you to write scripted routines for automating repeated aspects of the segmentation tasks. There are also tools for interpreting images with metal artifacts, designing support connections between parts, measuring specified features, and rendering a view of the resulting 3D model.
  • Synopsys Simpleware ScanIP is a 3D image segmentation, processing, and meshing platform that processes data from MRI, CT, and non-medical imaging systems. Simpleware ScanIP removes or reduces unwanted noise in the greyscale images, allows cropping to the area of interest, supports both automated and user-guided segmentation and measuring and includes API scripting. Modules are available for Cardio, Ortho, and Custom solutions.
  • Invesalius 3 is open-source software that can reconstruct CT and MRI data, producing 3D visualizations, image segmentation, and image measurements in both manual and semi-automated modes.
  • Embodi3D/Democratiz3D is an online service that lets you upload a series of CT scans, select a basic anatomy type (bone, detailed bone, dental, muscle, etc.), choose the free medium-to-low resolution or paid high resolution conversion service, and receive the link to an automatically generated STL file. (Users do not interact with the file to choose any masking, measuring, or cropping.) The website also offers downloadable 3D printable models and 3D printing services.

Note that these packages may or may not have some level of 510K FDA clearance for how the results of their processing can be used. Users would have to contact the vendors to learn the current status.

Setting up the STL file for printing

Most of the segmentation software packages give you options for selected resolution of the final model. As with all STL files, the greater the number of triangles, the finer the detail that is featured, but the model size may get too large for reasonable set-up in the printer’s software. You may also find that you still want to edit the model, either to do some hole repairs or smoothing, slice away a section to expose an interior view, or add mechanical struts/supports for delicate and/or heavy anatomy sections. Materialise Magics software will do all of this readily, otherwise, adding a package that can edit STL files or create/merge geometry onto an STL file will be useful.

Medical Modeling software workflow from CT scan to print, for typical Stratasys 3D printed model.

Whoever is setting the file up for printing needs to make a number of decisions based on experience. For Stratasys Connex3, J55, J8-series or J750 Digital Anatomy Printers, the process begins by bringing the file into GrabCAD Print and deciding on an optimized build orientation. Next, colors and materials are assigned, including transparent sections, percentages of transparent colors, and flexible/variable durometer materials, which can be for a single part or a multi-body model.

For the J750 Digital Anatomy Printer in particular, users can assign musculoskeletal, heart, vascular, and general anatomies to each model, then choose detailed, pre-assigned materials and properties to print models whose tactile response mimics actual biomechanical behavior, such as “osteoporotic bone.” (see Sidebar).

I tested out the free online Democratiz3D segmentation service offered by Embodi3D. Following their tutorial, I was able to convert my very own DICOM file folder of 267 CT images into files without patient ID information, generating a single STL output file. I chose the Bone/Detailed/Medium resolution option which ignored all the other visible anatomy then brought the resulting model into the free software Meshmixer to edit (crop) the STL. That let me zero in on a three-vertebrae section of my lower spine model and save it in the 3MF format.

Lastly, I opened the new 3MF file in GrabCAD Print, the versatile Stratasys printer set-up software that works with both FDM (filament) and PolyJet (UV-cured resin) printers. For the former case, I printed the model in ivory ASA on an F370 FDM printer, and for the latter, I was able to assign a creamy-grey color (Red248/Green248/Blue232) to give a bone-like appearance, printing the model on a J55 PolyJet office-environment printer.

GradCAD Print software set-up of 3MF vertebrae model, ready for printing in a user-defined bone color on a Stratasys J55 PolyJet full-color 3D printer. (Image courtesy PADT Inc.)
3D printed vertebrae parts created from CT scans: on left, ABS part from a Stratasys F370 FDM printer; on right, Vero rigid resin material from a Stratasys J55 PolyJet printer. (Image courtesy PADT Inc.)  

Experience helps in producing accurately segmented parts, but more features, such as AI-enabled selections, and more online tutorials are helping grow the field of skilled image-processing health professionals. Clarkson College (Omaha, NE) also recently announced the first Medical 3D Printing Specialist Certificate program.

Reach out to PADT to learn more about medical modeling and Stratasys 3D printers.

PADT Inc. is a globally recognized provider of Numerical Simulation, Product Development and 3D Printing products and services. For more information on Stratasys printers and materials, contact us at info@padtinc.com.

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Sidebar: J750 Digital Anatomy Printer

The Stratasys J750 Digital Anatomy Printer uses PolyJet resin 3D printing technology to create parts that mimic the look and biomechanical response of human tissue, organs and bones. Users select from a series of pre-programmed anatomies then the material composition is automatically generated along with accurate internal structures. Pliable heart regions allow practice with cutting, suturing and patching, while hollow vascular models support training with guide wires and catheters. General anatomy models can replicate encapsulated and non-encapsulated tumors, while bone structures can be created that are osteoporotic and/or include regions that support tapping, reaming and screw insertion.

Currently the Digital Anatomy Printer models present in the range of 80 to 110 Hounsfield Units. Higher value materials are under development which would help hospitals create phantoms for calibrating their CT systems.

Currently available Digital Anatomy Printer   Model/Section Assignments:

Structural Heart:

  • Clot
  • Frame
  • Myocardium
  • Reinforcement
  • Solid Tumor
  • Valve Annulus
  • Valve Chordae
  • Valve Leaflet
  • Valvular Calcification
  • Vessel Wall

General Anatomy:

  • Dense connective tissues
  • Hollow internal organs
  • Solid internal organs
  • Solid Tumor

Blood Vessels:

  • Clot
  • Fixtures
  • Frame
  • Gel Support
  • Inlets
  • Reinforcements
  • Solid Tumor
  • Valve Annulus
  • Valve Leaflet
  • Vascular Calcification
  • Vessel Wall

Musculoskeletal

  • Facet Joints
  • General Bone
  • Intervertebral Discs
  • Ligament
  • Long Bone
  • Nerves
  • Open End
  • Ribs
  • Skull
  • Vertebra

GrabCAD Print (the App): Making Work-from-Home Actually Work

I am so lucky in a zillion ways to be able to work from home while functioning in my position as a 3D Printing Application Engineer for PADT Inc., a Stratasys 3D printer reseller and engineering consulting/manufacturing company in Tempe Arizona.

Three things are making this possible:

1 – Awesome management and co-workers

2 – Great high-speed internet connection

3 – GrabCAD Print software, and more specifically, the GrabCAD Print phone app.            

Of all the apps on my phone, next to my gmail account, this is the app I check most often, because it is so handy!

First off, I can instantly see the status of the nine PADT printers we have on our Tempe network; I can also check other networks and accounts in other locations for which I have permission. That means I know the status of printers I’m running or want to run, and can tell how long someone else’s job is going to take – a very useful bit of information when it comes to telling a customer or our sales group what printer is open for running a part.

For example, this screen tells me:

–  a job is ready to start on our full-color PolyJet Objet500 Connex3,

–  one print just finished on our Fused Deposition Modeling (FDM) Fortus400,

–  my job is 43 percent complete on one of our FDM F370s, and

–  another of my jobs has just begun on the second F370 system.

I can even see that a print got cancelled on our older F250; in this case, I was expecting that, but it’s good information in case I wasn’t. But there is so much more…

Say I want to confirm the file name of what’s running on that first F370, and get some data about its status. I click on that printer’s name and the app shows me this screen:

Now I see that the print has just gotten to layer 2 of 123 slices total, it started at 1:58pm and it will finish at 6:12pm this evening. It also displays the file name of the part and shows that I’m the owner.

If I slide the image of the printer to the left, I then get the camera view, since an F370 has a build-chamber camera that updates about every ten seconds. Because this print had just started, you can’t really see much beside the build plate (brightly lit at the top), but I can come back to that as often as I like to monitor a particularly challenging geometry – say, perhaps a tall thin part where I added some extra support structure.

At this point I can access several more windows. If I click Job Material Usage, I see

This information is useful if I need a reminder of how much model and support material this print will consume.

The next line offers the bigger picture: clicking through, I see how much material remains in each canister, for both the model and support; it also shows what, if any, material is loaded in the second set of bays. Stratasys printers with double bays will do an automatic hot-swap as needed – a nice feature over the weekend or in the middle of the night.

Here’s another possible status screen: a paused build, where I had planned ahead, inserting a Pause Build instruction in the GrabCAD job set-up. In this case, I wanted to stop the part and remove it, to create a sample piece that exposes the hexagram infill I chose for lightweighting. Another reason to pause and resume an FDM print is to add hardware such as a flat washer to reinforce a deep hole.

The GrabCAD Print App also sends me email alerts (with a chime on the phone) when the status of a print job changes, such as the message below telling me the job has indeed paused as planned:

(I don’t get notifications for other people’s jobs, so I don’t get inundated with messages.)

This real-time information lets me keep track of all my print jobs from my 3D Printing Command Center deep in the heart of suburban Phoenix. I can do 98% of what I need to remotely.

Of course, I depend on the engineers in PADT’s Manufacturing group – essential workers who’ve been in the office non-stop throughout this crazy 2020 work-year. They change filament, load clean trays, run calibrations, remove parts, and put finished prints in our Support Cleaning Apparatus tanks (a PADT-developed system spun off to Oryx and OEM’d to Stratasys since 2009.) That step dissolves the soluble support. (For several of the engineering filaments I run, the support is break-away, and my team takes care of that, too.)

The GrabCAD Print App is available as a free download from the Apple app store. And all of this is in addition to how you can view and interact with GrabCAD Print itself from any computer, setting up a part to print as you sit in one city then uploading the print-ready file to a system across the state or across the country.

Got any questions about the app? We’d love to answer them.

PADT Inc. is a globally recognized provider of Numerical Simulation, Product Development and 3D Printing products and services. For more information on Stratasys printers and materials, contact us at info@padtinc.com.

3D Printing Infill Styles – the What, When and Why of Using Infill

Have you ever wondered about choosing a plain versus funky infill-style for filament 3D-printing? Amongst the ten standard types (no, the cat infill design is not one of them), some give you high strength, some greatly decrease material use or printing time, and others are purposely tailored with an end-use in mind.

Highly detailed Insight slicing software from Stratasys gives you the widest range of possibilities; the basic versions are also accessible from GrabCAD Print, the direct-CAD-import, cloud-connected slicing software that offers an easy approach for all levels of 3D print users.

A part that is mimicking or replacing a metal design would do best when built with Solid infill to give it weight and heft, while a visual-concept model printed as five different test-versions may work fine with a Sparse infill, saving time and material. Here at PADT we printed a number of sample cubes with open ends to demonstrate a variety of the choices in action. Check out these hints for evaluating each one, and see the chart at the end comparing build-time, weight and consumed material.

Infill choices for 3D printed parts, offered with Stratasys’ GrabCAD Print software. (Image courtesy PADT Inc.)

Basic Infill Patterns

Solid (also called Alternating Raster) This is the default pattern, where each layer has straight fill-lines touching each other, and the layer direction alternates by 90 degrees. This infill uses the most material but offers the highest density; use it when structural integrity and super-low porosity are most important.

Solid (Alternating Raster)

Sparse Raster lines for Sparse infill also run in one direction per layer, alternating by layer, but are widely spaced (the default spacing is 0.080 inches/2 mm). In Insight, or using the Advanced FDM settings in GrabCAD, you can change the width of both the lines and the spaces.

Sparse Double Dense As you can imagine, Sparse Double Dense achieves twice the density of regular Sparse: it deposits in two directions per layer, creating an open grid-pattern that stacks up throughout the part.

Sparse High Density Just to give you one more quick-click option, this pattern effectively sits between Sparse Double Dense and Solid. It lays rasters in a single direction per layer, but not as closely spaced as for Solid.

Hexagram The effect of this pattern looks similar to a honeycomb but it’s formed differently. Each layer gets three sets of raster lines crossing at different angles, forming perfectly aligned columns of hexagons and triangles. Hexagram is time-efficient to build, lightweight and strong in all directions.

Hexagram
Additional infill styles and the options for customizing them within a part, offered within Stratasys Insight 3D printing slicing and set-up software. (Image courtesy PADT Inc.)

Advanced Infill Patterns (via Custom Groups in Insight)

Hexagon By laying down rows of zig-zag lines that alternately bond to each other and bend away, Hexagon produces a classic honeycomb structure (every two rows creates one row of honeycomb). The pattern repeats layer by layer so all vertical channels line up perfectly. The amount of build material used is just about one-third that of Solid but strength is quite good.

Hexagon

Permeable Triangle A layer-by-layer shifting pattern of triangles and straight lines creates a strong infill that builds as quickly as Sparse, but is extremely permeable. It is used for printing sacrificial tooling material (i.e., Stratsys ST130) that will be wrapped with composite material and later dissolved away.

Permeable Triangle

Permeable Tubular This infill is formed by a 16-layer repeating pattern deposited first as eight varying wavy layers aligned to the X axis and then the same eight layers aligned to the Y axis. The resulting structure is a series of vertical cylinders enhanced with strong cross-bars, creating air-flow channels highly suited to tooling used on vacuum work-holding tables.

Permeable Tubular 0.2 Spacing
Permeable Tubular 0.5 Spacing

Gyroid (so cool we printed it twice) The Gyroid pattern belongs to a class of mathematically minimal surfaces, providing infill strength similar to that of a hexagon, but using less material. Since different raster spacings have quite an effect, we printed it first with the default spacing of 0.2 inches and then widened that to 0.5 inches. Print time and material use dropped dramatically.

Gyroid 0.2 Spacing
Gyroid 0.5 Spacing

Schwarz D (Diamond) This alternate style of minimal surface builds in sets of seven different layers along the X-axis, ranging from straight lines to near-sawtooth waves, then flipping to repeat the same seven layers along the Y-axis. The Schwarz D infill balances strength, density and porosity. As with the Gyroid, differences in raster spacing have a big influence on the material use and build-time.

Schwarz Diamond 0.2 Spacing
Schwarz Diamond 0.5 Spacing

Digging Deeper Into Infill Options

Infill Cell Type/0.2 spacing Build Time Weight Material Used
Alternating Raster (Solid) 1 h 57 min 123.77 g 6.29 cu in.
Sparse Double Dense 1 hr 37 min 44.09 g 4.52 cu in.
Hexagon (Honeycomb) 1 h 49 min 37.79 g 2.56 cu in.
Hexagram (3 crossed rasters) 1 h 11 min. 47.61 g 3.03 cu in.
Permeable Triangle 1 h 11 min. 47.67 g 3.04 cu in.
Permeable Tubular – small 2 h 5 min. 43.95 g 2.68 cu in.
Gyroid – small 1 h 48 min. 38.68 g 2.39 cu in.
Schwarz Diamond (D) – small 1 h 35 min. 47.8 g 3.04 cu in.
Infill Cell Type/0.5 spacing Build Time Weight Material Used
Permeable Tubular – Large 1 h 11 min. 21.84 g 1.33 cu in.
Gyroid – Large 57 min. 20.59 g 1.29 cu in.
Schwarz Diamond (D) – Large 58 min. 23.74 g 1.51 cu in.

Hopefully this information helps you perfect your design for optimal strength or minimal material-use or fastest printing. If you’re still not sure which way to go, contact our PADT Manufacturing group: get your questions answered, have some sample parts printed and discover what infill works best for the job at hand.

PADT Inc. is a globally recognized provider of Numerical Simulation, Product Development and 3D Printing products and services. For more information on Insight, GrabCAD and Stratasys products, contact us at info@padtinc.com.

Introducing TPU 92A – The latest FDM material from Stratasys

PADT is excited to announce the release of the latest FDM material from Stratasys: TPU 92A.
Thermoplastic Polyurethane (TPU) is a type of elastomer material, known for its flexibility, resilience, tear resistance, and high elongation. It’s a highly process-able material which makes it ideal for additive manufacturing.
TPU 92A is an elastomeric material that is ideal for prototyping highly functional, large, durable, complex elastomer parts. 

This material brings the benefits of an elastomer to the accurate and easy-to-use F123 3D Printer. Combined with soluble support, it lets you create simple to complex elastomer parts, and through printing on the F123 Series gives product developers more tools to expand their prototyping capabilities with reliable accuracy.
Curious to learn more about the unique properties that make TPU 92A such a great option for prototyping?Schedule a meeting to see the material for yourself.Click the link below to start a conversation with PADT’s resident material experts, in order to discuss the capabilities of this Thermoplastic Polyurethane material, and how your company can benefit from using it.

Don’t miss this unique opportunity, schedule a meeting today!

Getting to Know PADT: 3D Printing Services

This post is the sixth 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@padtinc.com or give us a call at 1-800-293-PADT.

If there is one service that most people connect PADT with it is our 3D Printing Services.  We have been making prototypes for companies using this ever-advancing technology since we started the company in 1994. As 3D Printing has become more popular and entered the mainstream even beyond engineering, what 3D Printing means to people has changed as well. Along with that, people’s understanding of exactly what it is we do in this area has drifted a little from what goes on. In this month’s installment of our “Getting to Know PADT” series, we will work to provide insight into what 3D Printing Services are and how they can benefit your company.

What is “3D Printing” and “3D Printing Services?”

To start, it should be called “Additive and Advanced Manufacturing and Prototyping Services, ” but people search for “3D Printing” so that is what we call it.  3D Printing is the common name for what is technically referred to as Additive Manufacturing, or AM.  Most physical parts are made (manufactured) by casting or shaping material into a shape you want, removing material from stock to get the shapes you want, and/or combining physical parts you get by the other two methods. Instead of these well-proven methods, AM creates a part by building up material one layer at a time.  That is why it is called additive – it adds layers of material to get a shape. Here is an older blog article showing the most common technologies used in AM.

The advantage of this approach is that you just need one machine to make a part, you can go straight from a computer model to that part, and you are not held back by the physical constraints of traditional processes. These features allow anyone to make a part and to make shapes we just could not create before.  At first, we only used it for prototypes before parts were made. Then we started to make tools to make final products, and now 3D Printing is employed to manufacturing end-use parts.

In the world of mechanical engineering, where 3D Printing is heavily used, we call companies that use additive manufacturing to make parts for others 3D Printing Service Bureaus or 3D Printing Service Providers. Therefore, the full process of doing manufacturing using the technology is called: 3D Printing Services.

The critical word in that last sentence is “full.”  Sending a computer model to a 3D Printer is just one of many steps involved in Additive Manufacturing.  When the service is employed correctly, it includes identifying the right type of additive manufacturing to use, preparing the geometry, setting parameters on the machine, printing the parts, removing supports, cleaning the parts, sanding, applying a surface finish treatment, and then inspection and shipping.  Anyone can send a part to a printer; the other steps are what make the difference between simply printing a part, and producing a great part.

What Services does PADT Offer?

Additive Manufacturing covers a wide range of technologies that create parts one layer at a time, using a variety of approaches. Some extrude, some harden, some use an inkjet print head, and still others melt material.  What they have in common is creating solid geometry one layer at a time. Each technology has its own unique set of advantages, and that is why PADT offers so many different 3D Printing technologies for our customers.  Each of these approaches has unique part preparations, machine parameters, and post-printing processes. Each with a unique set of advantages.  The key to success is knowing which technology is best for each part and then executing it correctly.

Currently, PADT’s 3D Printing Services Group makes parts for customers using the following technologies.  Each one listed has a brief description of its advantages.  See our website for more details.

Technology

Abbrv.

Advantages

Fused
Deposition Modeling

FDM

Strong parts

Easy operation

Reliability of systems

Broad material choice

Water soluble supports

Fast

Cost

Polyjet

PolyJet

Multiple materials in a single build

Broad material choices

Custom material choices

Multiple colors in single build

Water soluble supports

Accuracy

Stereolithography

SLA

Part quality

Material options

Speed

Speed

Material properties

Self supporting

Selective
Laser Sintering

SLS

Digital
Light Synthesis

DLS

Speed

Production capable

Surface Finish

Material Choices

Material properties

Orthotropic properties

Direct
Laser Melting (Metal)

DLM

Fully dense metal parts

Accuracy

Speed

Part strength

As a proud reseller for Stratasys systems, we feel strongly that the two primary technologies from Stratasys, FDM and Polyjet, are the best for customers who want to do Additive Manufacturing in-house or as a service provider. When customers need something different, they can come to PADT to take advantage of the unique capabilities found in each technology.

How is 3D Printing with PADT Better?

The difference is in what we know and how to execute the complete process.  As a provider of 3D Printing services for over 23 years, very few people in the industry even come close to the amount of experience that we bring to the table.  We also know product development and traditional manufacturing, so when a customer comes to us with a need, we understand what they are asking to do and why. That helps us make the right recommendation on process, material, and post-processing.

A few differentiators are:

  • We know our machines
  • We know our materials
  • We offer a wide range of plastic and metal materials
  • We understand post-processing
  • We understand support removal (we manufacture the leading support removal system)
  • We understand design and manufacturing
  • In-house machining, painting, and part finishing
  • In-house inspection and quality
  • Employees who are enthusiastic and dedicated to providing the right solution.

In addition to all of these things, PADT also offers On-Demand Manufacturing as a Carbon Production Partner. We combine Carbon’s DLS technology with our existing and proven manufacturing processes to provide low volume manufacturing solutions for plastic components.

We are also always looking at the latest technologies and adding what our customers need.  You can see this with the recent addition of systems from ConceptLaser, Carbon and Desktop Metal systems.

Next Steps and Where to Learn More

The very best way to learn more about PADT’s 3D Printing services is to have us print a part. The full experience and the final product will explain why, with so many choices, so many companies large and small count on us for their Additive Manufacturing. If you need to learn more, you can also contact us at 480.813.4884 or rp@padtinc.com.

Here are some links that you may find useful:

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Getting to Know PADT: Support Cleaning Apparatus (SCA) Manufacturing and Support

This is the third 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@padtinc.com or give us a call at 1-800-293-PADT.

PADT is in the business of helping people who make products.  So most people think of us as a provider of tools and services.  What they do not know is that PADT actually has a few of its own products.  The most successful of these is our line of Support Cleaning Apparatus systems, abbreviated as SCA.  These devices are used to remove soluble support material from parts 3D printed in Stratasys Fused Deposition Modeling Systems. They are robust machines manufactured and serviced by PADT, but sold through the Stratasys worldwide sales channel. As of July of 2017, over 10,800 units have been delivered to Stratasys.

Optimized Performance for Hands-Off Part Cleaning

The Stratasys 3D Printing systems that use Fused Deposition Modeling extrude plastic through a heated nozzle to build parts one layer at a time.  There are actually two nozzles. One puts down the building material and the other a support material that is dissolved in warm water that is slightly base.  The best way to remove that support material is to put it into a warm bath where the part is gently tumbled so that the water can works its way evenly into the part.  Stratasys tried several solutions for a companion washing system and eventually came to PADT and asked if we would try our hand at building a robust and efficient system.

The result was the SCA-1200.  Launched at the end of 2008 it met the design requirements for reliability, part cleaning time, and noise.  Over 7,000 of these systems were shipped and saw heavy usage. In fact, if you have a Stratasys FDM system there is a good chance you have an SCA-1200.  It contained a unique shower head design that was optimized with simulation, and a modular assembly that could be repaired easily in the field.

Based upon the success and lessons learned from the SCA-1200, we released the SCA-1200HT in 2014.  With the same basic form factor, this design replaced the off-the-shelf magnetically coupled pump with a simpler and more reliable custom design from PADT. The new unit also had a more pleasing visual design, several usability enhancements, and a greater temperature range. It has sold over 3,000 units and continues to be a popular system.  The latest release includes a no-temperature setting that allows it to be used to clean Stratasys Polyjet parts.

The success of both system lead to a request to look at building a larger machine that could clean more parts at one time as well as larger parts.  The SCA 3600 has three times the volume but shares many internal parts with the SCA-1200HT.  Both of the new systems are doing well in the field with even better reliability and faster part cleaning times. They are also simpler to debug and repair.

The SCA systems are sold as stand alone devices or are bundled with key Stratasys FDM machines.  You can learn more about them on our SCA page:  www.padtinc.com/sca or you can contact whoever you buy your Stratasys equipment from.

Here is a video for the SCA-1200HT that talks all about what it does:

Practicing what We Preach

One of the most rewarding aspects of designing and manufacturing the SCA family of products was that it forced us to practice what we preach. We talk to companies every day about using simulation, 3D Printing, design for manufacturing, proper product development processes, and many more things needed to get a product right.  With the SCA we were the customer. We had to Walk the Walk or stop talking the talk.

 

It has been a phenomenal experience that has made us even better at helping our customers produce their new products. We used CFD to optimize the gentle agitation design and shower head and worked closely with our vendors to minimize the cost of manufacturing.  The worst part was that when the schedule slipped, we couldn’t blame the customer (only slightly joking).  One of the best set of lessons came from doing the repair and refurbishment of systems that failed. Even though the failure rate was low, we learned a lot and were able to make improvements to future designs. Now when we sit across from a customer and talk about the design, test, and manufacture of their product, we can really say that we understand where they are coming from.

 

 

 

 

 

Learn About the New Stratasys 3D Printers and New Orleans

It was my first time visiting New Orleans. I have heard many stories of how good the food is and how everyone is really nice there so I was excited to visit this city for a business trip. Stratasys Launch 2017! There was some buzz going on about some new FDM printers that Stratasys has been working on and I was really excited to see them and hear what sets them apart from the competition. Rey Chu (Co-Owner of PADT), Mario Vargas (Manager of 3D Printer Sales), Norman Stucker (Account Executive in Colorado), and I (James Barker, Application Engineer) represented PADT at this year’s Launch.

The city did not disappoint! I ate the best gumbo I’ve ever tried. Below is a picture of it with some Alligator Bourbon Balls. The gumbo is Alligator Sausage and Seafood. Sooooo Good!!


My last night in New Orleans, Stratasys rented out Mardi Gras World. That is where they build all the floats for Mardi Gras. They had a few dancers and people dressed up festive. I was able to get a picture of Rey in a Mardi Gras costume.

After dinner at Mardi Gras World, I took Rey and Mario down Bourbon Street one last time and then we went to Café Du Monde for their world famous Beignets. Everyone told me that if I come home without trying the Beignets, then the trip was a waste. They were great! I recommend them as well. Below is picture of Mario and me at the restaurant.

As you can see we had a fun business trip. The best part of it was the unveiling of the new FDM printers! Mario and I sat on the closest table to the stage and shared the table with Scott Crump (President of Stratasys and inventor of FDM technology back in 1988). These new printers are replacing some of Stratasys entry level and mid-level printers. What impressed me most is that they all can print PLA, ABS, and ASA materials with the F370 being able to print PC-ABS. You also can build parts in four different layer heights (.005, .007, .010, and .013”), all while utilizing new software called GrabCad Print.

GrabCad Print is exciting because you can now monitor all of you Stratasys FDM printers from this software and setup queues. What made me and many others clap during the unveiling is that with GrabCad Print you no longer have to export STL files! You can import your native CAD assemblies and either print them as an assembly or explode the assembly and print the parts separately.

      

Everyone wants a 3D Printer that can print parts faster, more accurately and is dependable. You get that with the family of systems! Speed has increased big time, they are twice as fast as the Dimension line of FDM printers. Stratasys has published the accuracy of these new printers to be ±.008” up to a 4 inch tall part and then every inch past 4 inches, you add another .002”. These machines are very dependable. They are replacing the Uprint (Uprint SE Plus is still current), Dimension, and Fortus 250 machines that have been workhorses. Many of our customers still have a Dimension from 2002 when they were first launched. In addition to the 43 existing patents that Stratasys has rolled into this phenomenal product, they have an additional 15 new patents that speaks volumes as to the innovation in these 3D printers.

Stratasys Launch was a blast for me. Seeing these new printers, parts that were printed from them, and understanding why these are the best FDM printers on the market was well worth my time! I look forward to helping you with learning more about them. Please contact me at james.barker@padtinc.com for more information. If you would like to hear my recorded webinar that has even more information about the new F170, F270, and F370, here is the link.  Or you can download the brochure here.

Technology Trends in Fused Deposition Modeling

A few months ago, I did a post on the Technology Trends in Laser-based Metal Additive Manufacturing where I identified 5 key directions that technology was moving in. In this post, I want to do the same, but for a different technology that we also use on a regular basis at PADT: Fused Deposition Modeling (FDM).

1. New Materials with Improved Properties

Many companies have released and are continuously developing composite materials for FDM. Most involve carbon fibers and are discussed in this review. Arevo Labs and Mark Forged are two of many companies that offer composite materials for higher performance, the table below lists their current offerings (CF = Carbon Fiber, CNT = Carbon Nano Tubes). Virtual Foundry are also working on developing a metal rich filament (with about 89% metal, 11% binder polymer), which they claim can be used to make mostly-metal parts for non-functional purposes using existing FDM printers and a heat treatment to vaporize the binder. In short, while ABS and PLA dominate the market, there is a wide range of materials commercially available and this list is growing each year.

Company Composition
Arevo Labs CF, CNT in PAEK
CF in PEEK
Fiberglass in PARA
Mark Forged Micro-CF in Nylon
CF
Fiberglass
Fiberglass (High Strength High Temperature)
Kevlar

2. Improved Properties through Process Enhancements

Even with newer materials, a fundamental problem in FDM is the anisotropy of the parts and the fact that the build direction introduces weak interfaces. However, there are several efforts underway to improve the mechanical properties of FDM parts and this is an exciting space to follow with many approaches to this being taken. Some of these involve explicitly improving the interfacial strength: one of the ways this can be achieved is by pre-heating the base layer (as being investigated by Prof. Keng Hsu at the Arizona State University using lasers and presented at the RAPID 2016 conference). Another approach is being developed by a company called Essentium who combine microwave heating and CNT coated filaments as shown in the video below.

Taking a very different approach, Arevo labs has developed a 6-axis robotic FDM process that allows for conformal deposition of carbon fiber composites and uses an FEA solver to generate optimized toolpaths for improved properties.

3. Faster & Bigger

A lot of press has centered around FDM printers that make bigger parts and at higher deposition rates: one article discusses 4 of these companies that showcased their technologies at an Amsterdam trade show. Among the companies that showcased their technologies at RAPID was 3D Platform, that showed a $27,000 3D printer for FDM with a 1m x 1m x 0.5m printing platform. Some of the key questions for large form factor printers is if and how they deal with geometries needing supports and enabling higher temperature materials. Also, while FDM is well suited among the additive technologies for high throughput, large size prints, it does have competition in this space: Massivit is one company that in the video below shows the printing of a structure 5.6 feet tall in a mere 5 hours using what they call “Gel Dispensed Printing” that reduces the need for supports.

 4. Bioprinting Applications

Micro-extrusion through syringes or specialized nozzles is one of the key ways bioprinting systems operate – but this is technically not “fused” deposition in that it may not involve thermal modification of the material during deposition. However, FDM technology is being used for making scaffolds for bio-printing with synthetic, biodegradable or bio-compatible polymers such as PCL and PLGA. The idea is these scaffolds then form the structure for seeding cells (or in some cases the cells are bioprinted as well onto the scaffold). This technology is growing fast and something we are also investigating at PADT – watch this space for more updates.

5. Material Modeling Improvements

Modeling FDM is an important part of being able to use simulation/analysis to design better processes and parts for functional use. This may not get a lot of press compared to the items above, but is a particular interest of mine and I believe is a critical piece of the puzzle going to true part production with FDM. I have written a few blog posts on the challenges, approaches and a micromechanics view of FDM printed structures and materials. The idea behind all of these is to represent FDM structures mathematically with valid and accurate models so that their behavior can be predicted and designs truly optimized. This space is also growing fast, the most recent paper I have come across in this space is from the University of Wisconsin-Madison that was published May 12, 2016.

Conclusion

Judging by media hype, metal 3D printing and 3D bioprinting are currently dominating the media spotlight – and for good reasons. But FDM has many things going for it: low cost of entry and manufacturing, user-friendliness and high market penetration. And the technology growth has no sign of abating: the most recent, 2016 Wohlers report assesses that there are over 300 manufacturers of FDM printers, though rumor on the street has it that there are over a thousand manufacturers coming up – in China alone. And as the 5 trends above show, FDM has a lot more to offer the world beyond being just the most rapidly scaling technology – and there are people working worldwide on these opportunities. When a process is as simple and elegant as extruding material from a hot nozzle, usable innovations will naturally follow.

Fused Deposition Modeling (FDM) Properties: A Micromechanics Perspective

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.

FDM_01

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.

FDM-02

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  represents the cross-sectional area fraction of the contours.

FDM-3

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.

FDM-4

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.

fdm-5

Conclusion

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 info@padtinc.com and cite this post, or connect with me directly on LinkedIn.

Thanks for reading!

~

Two related posts:

Unexpected Joys at Rapid 2016

While much has been (justifiably) written about HP and XJet releasing new, potentially game-changing products at RAPID 2016, I wanted to write this post about some of the smaller, unexpected joys that I discovered. If I sound overly enthusiastic about the people and companies behind them, it is likely due to the fact that I wrote this on the flight back, staring out at the clouds and reflecting on what had been a wonderful trip: I own no locks, stocks or barrels in any of these companies.

1. Essentium Materials – Carbon Nanotubes and Microwaves to improve FDM mechanical properties
Over the past year, I have studied, written and made presentations about the challenges of developing models for describing Fused Deposition Modeling (FDM) given their complex and part-specific meso-structure. And while I worked on developing analytical and numerical techniques for extracting the best performance from parts in the presence of significant anisotropy, the team at Essentium has developed a process to coat FDM filaments with Carbon nanotubes and extrude them in the presence of microwave radiation. In the limited data they showed for test specimens constructed of unidirectional tool-paths, they demonstrated significant reduction in anisotropy and increase in strength for PLA. What I liked most about their work is how they are developing  this solution on a foundation of understanding the contributions of both the meso-structure and inter-filament strength to overall part performance. Essentium was awarded the “RAPID Innovations award”, first among the 27 exhibitors that competed and are, in my opinion, addressing an important problem that is holding back greater expansion of FDM as a process in the production space.
Website: http://essentiummaterials.com/

2. Hyrel 3D – Maker meets Researcher meets The-Kid-in-All-of-Us
I only heard of Hyrel 3D a few days prior to RAPID, but neglected to verify if they were exhibiting at RAPID and was pleasantly surprised to see them there. Consider the options this 3D printer has that you would be hard pressed to find in several 3D printers combined: variable extrusion head temperatures (room temp to 450 C), sterile head options for biological materials, a 6W laser (yes, a laser), spindle tools, quad head dispensing with individual flow control and UV crosslinking options. Read that again slowly. This is true multiple degree-of-freedom material manipulation. What makes their products even more compelling is the direct involvement of the team and the community they are building up over time, particularly in academia, across the world, and the passion with which they engage their technology and its users.
Website: http://www.hyrel3d.com/

3. Technic-Print: New Chemistry for Improved FDM Support Removal
If you manufacture FDM parts with soluble supports, keep reading. A chemist at Technic Inc. has developed a new solution that is claimed to be 400% faster than the current Sodium-Hydroxide solution we use to dissolve parts. Additionally, the solution is cited as being cleaner on the tank, leaving no residue, has a color indicator that changes the solution’s color from blue to clear. And finally, through an additional agent, the dissolved support material can be reclaimed as a clump and removed from the solution, leaving behind a solution that has a pH less than 9. Since PADT manufactures one of the most popular machines that are used to dissolve these supports that unbeknown to us, were used in the testing and development of the new solution, we had an enriching conversation with the lead chemist behind the solution. I was left wondering about the fundamental chemistry behind color changing, dissolution rates for supports and the reclaiming of support – and how these different features were optimized together to develop a usable end-solution.
Website: http://www.technic.com/techni-print-lp

 

4. Project Pan: Computationally Efficient Metal Powder Bed Fusion Simulation
I presented a literature review at AMUG (another Additive Manufacturing conference) last month, on the simulation of the laser-based powder bed fusion. At the time, I thought I had captured all the key players between the work being done at Lawrence Livermore National Labs by Wayne King’s group, the work of Brent Stucker at 3DSIM and the many academics using mostly commercially available software (mostly ANSYS) to simulate this problem. I learned at RAPID that I had neglected to include a company called “Project Pan” in my review. This team emerged from Prof. Pan Michaleris’s academic work. In 2012, he started a company that was acquired by Autodesk two months ago. In a series of 3 presentations at RAPID, Pan’s team demonstrated their simulation techniques (at a very high level) along with experimental validation work they had done with GE, Honeywell and others through America Makes and other efforts. What was most impressive about their work was both the speed of their computations and the fact that this team actually had complex part experimental validations to back up their simulation work. What most users of the powder bed fusion need is information on temperatures, stresses and distortion – and within time frames of a few hours ideally. It seems to me that Pan and his team took an approach that delivers exactly that information and little else using different numerical methods listed on their site (novel Hex8 elements, an element activation method and intelligent mesh refinement) that were likely developed by Pan over the years in his academic career and found the perfect application, first in welding simulation and then in the powder bed fusion process. With the recent Autodesk acquisition, it will be interesting to see how this rolls out commercially. Details of some of the numerical techniques used in the code can be found at their website, along with a list of related publications.

Website: http://pancomputing.com/

5. FDA Participation: Regulating through education and partnership
On a different note from the above, I was pleasantly surprised by the presence of the FDA, represented by Matthew Di Prima, PhD. He taught part of a workshop I attended on the first day, took the time to talk to everyone who had an interest and also gave a talk of his own in the conference sessions, describing the details of the recently released draft guidance from the FDA on 3D printing in medical applications. It was good to connect the regulatory agency to a person who clearly has the passion, knowledge, intelligence and commitment to make a difference in the Additive Manufacturing medical community. Yes, the barriers to entry in this space are high (ISO certifications, QSR systems, 510(k) & Pre-Market Approvals) but it seems clear that the FDA, at least as represented by Dr. Di Prima, are doing their best to be a transparent and willing partner.
Website: http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/3DPrintingofMedicalDevices/default.htm

What really makes a trip to a conference like RAPID worth it are the new ideas, connections and possibilities you come away with that you may not stumble upon during your day job – and on that account, RAPID 2016 did not disappoint. As a line in one of my favorite song’s goes:

“We’ll never know, unless we grow.
There’s too much world outside the door.”
– Fran Healy (Travis, “Turn”).

PADT and ASU Collaborate on 3D Printed Lattice Research

The ASU Capstone team (left to right): Drew Gibson, Jacob Gerbasi, John Reeher, Matthew Finfrock, Deep Patel and Joseph Van Soest.
ASU student team (left to right): Drew Gibson, Jacob Gerbasi, John Reeher, Matthew Finfrock, Deep Patel and Joseph Van Soest

Over the past two academic semesters (2015/16), I had the opportunity to work closely with six senior-year undergraduate engineering students from the Arizona State University (ASU), as their industry adviser on an eProject (similar to a Capstone or Senior Design project). The area we wanted to explore with the students was in 3D printed lattice structures, and more specifically, address the material modeling aspects of these structures. PADT provided access to our 3D printing equipment and materials, ASU to their mechanical testing and characterization facilities and we both used ANSYS for simulation, as well as a weekly meeting with a whiteboard to discuss our ideas.

While there are several efforts ongoing in developing design and optimization software for lattice structures, there has been little progress in developing a robust, validated material model that accurately describes how these structures behave – this is what our eProject set out to do. The complex internal meso- and microstructure of these structures makes them particularly sensitive to process variables such as build orientation, layer thickness, deposition or fusion width etc., none of which are accounted for in models for lattice structures available today. As a result, the use of published values for bulk materials are not accurately predictive of true lattice structure behavior.

In this work, we combined analytical, experimental and numerical techniques to extract and validate material parameters that describe mechanical response of lattice structures. We demonstrated our approach on regular honeycomb structures of ULTEM-9085 material, made with the Fused Deposition Modeling (FDM) process. Our results showed that we were able to predict low strain responses within 5-10% error, compared to 40-60% error with the use of bulk properties.

This work is to be presented in full at the upcoming RAPID conference on May 18, 2016 (details at this link) and has also been accepted for full length paper submission to the SFF Symposium. We are also submitting a research proposal that builds on this work and extends it into more complex geometries, metals and failure modeling. If you are interested in the findings of this work and/or would like to collaborate, please meet us at RAPID or send us an email (info@padtinc.com).

Our final poster and the Fortus 400mc that we printed all our honeycomb structures with
The final poster summarizing our work rests atop the Stratasys Fortus 400mc that we printed all our honeycomb structures on

Support Design and Removal for 3D Printed ULTEM-9085 (Case Study: Intake Manifold)

Editor’s note: Unfortunately this post and a few others were the victim of database munging that resulted in the images being lost. We are trying to recover them. We hope that you find the text useful even without the images. 

ULTEM-9085 is one of my favorite materials to 3D-print: one of the reasons is it is a high performance polymer that can and has been used for end part manufacturing (see my blog post about ULTEM in functional aerospace parts), but the other is because it is a demanding material to print, in ways that ABS, Polycarbonate and even Nylon are not. What makes it demanding is primarily that ULTEM supports are not soluble and need to be removed mechanically. An additional challenge comes from the fact that the support is best removed when the part is at a high temperature (175-195 C), which requires the use of gloves and reduces the user’s dexterity. For complex geometries with internal channels, this is particularly challenging and occasionally results in an inability to print a certain part in ULTEM-9085, which runs contrary to the design freedom this technology otherwise enables.

In this post, I accumulate what I have learned through working (and failing) on many an ULTEM-9085 job, as well as through discussions with other users, and share this here in terms of design and process guidelines. To demonstrate these guidelines, I use a recent geometry that we printed for the Arizona State University’s (ASU) SAE team for an engine intake manifold. These guidelines apply to the Stratasys Fortus platform (for Fused Deposition Modeling, or FDM) using the Insight software that accompanies these tools. The screen shots are from Insight 10.6, and a Fortus 400 was used to print the parts shown.

Summary of Guidelines:

  1. Orient the part to eliminate supports in regions where you cannot remove them
  2. Use the box support style
  3. Optimize parameter settings (support angle, contour width, layer thickness)
  4. Remove the supports as soon as the part comes out of the build chamber
  5. Other observations: the interface of separation

1. Part Orientation

The single most important factor in simplifying support removal is part orientation. Most users of the FDM process know that part orientation determines the amount of support material consumed and also impacts the time to build the part. When working with ULTEM-9085, the additional challenge is that it is possible to design in supports that cannot be removed and will require you to scrap the job. This is especially true of internal features. While the automatic orientation feature in Insight allows you to minimize supports, it does not account for the difficulty of removing them. Thus when you are dealing with internal features, you may need to manually orient your part such that the internal features are aligned as close to the vertical as possible, and above the support angle (to be covered later).

As shown in Figure 1, for the intake manifold, I oriented the internal pipe structure close to the vertical and had to iterate a few times and verify that I had no support in the hard-to-reach areas. While I did have supports internally, they were limited to areas that were easy to access.

Figure 1. Engine intake manifold, to be printed out of ULTEM-9085
Figure 1. Engine intake manifold, to be printed out of ULTEM-9085

Figure 2. Part orientation to avoid any internal supports
Figure 2. Part orientation to avoid any internal supports in inaccessible regions

2. Box Supports

In a recent software upgrade, Insight added the ability to create box supports. The support structures consist of adjacent boxes instead of a continuous raster, which has the effect of allowing for easier separation of the support, though does slow down the build time. In my experience this support strategy does help with removal – the one parameter to consider here is the “Perforations” setting, though the default values were used for this part. The perforation is a layer of model material that is inserted into the support to make for easier breaking off of the support material. All cleavage surfaces in Fig. 3 are at perforation edges and you can see the building like construction with each floor distinguished by a layer of model material. When you have supports in hard to access regions, consider increasing the interval height so as to ensure you get separation at the model-support interface on the part before it occurs within the support on a perforation layer.

Figure Box Supports
Figure 3. Box Supports after removal from an ULTEM-9085 part

3. Optimize Process Parameters

While orientation will have the most significant impact on the support you need, another variable to be aware of is the “Self-Support Angle” parameter. This angle is measured from the horizontal, and represents the minimum angle of the part wall that will be built without supports. As a result, to reduce support requirements, you want this number to be as low as possible so that a greater volume of the part can be self-supported. Stratasys recommends default values, but these scale as a function of the contour width, and layer thickness, as shown in Fig. 4. The values bottom out at 40 degrees for the 0.013″ layer thickness and 43 degrees for the 0.010″ layer thickness. Thus, all other things being equal, you will be able to reduce the support needed by choosing a 0.013″ layer thickness and a 0.026″ or larger contour width. Note that both of these will impact your ability to resolve thin walls and fine features, so ensure you scan through all the tool-paths to validate that the geometry is accurately filled in.

Figure 4. Graph showing how the default values of the self-support angle vary as a function of contour width for the two layer thickness options available for ULTEM. Lower the angle, less the support needed.

4. Remove Supports Immediately

Supports are best removed when the model-support interface is hot. The best time to do this is right after you remove the parts from the print chamber, which is held at 195 C for ULTEM-9085. Ensure you have safety glasses on, work with thermal gloves and have a plier handy to pull out the support. In theory the parts can be re-heated again (175 C is a reasonable value for the oven), but Stratasys suggests that each re-heat cycle actually strengthens the interface, making it harder to remove. As a result, the best time to remove the supports is immediately out of the printer. Figure 5 shows the results of support removal for the intake manifold parts, including the build sheet.

Figure 5. Support removal can be a messy affair as you beat the clock against the cooling parts. Ensure you have gloves, a plier and safety glasses on.
Figure 5. Support removal can be a messy affair as you beat the clock against the cooling parts. Ensure you have gloves, a plier and safety glasses on.

5. Other Observations: the Interface of Separation

It helps to visualize what we are trying to do when we remove supports. There are two interfaces in question here, as shown in Figure 6. One is the model-support interface, the other is the support-box structure interface. We need separation at the model-support interface since removing the thin piece of interface material can prove challenging if the box supports have broken off (as happened for the piece below). What this means is as you remove support, you need to not just pull the supports but also add some peeling force that creates the separation. Once you create separation at the correct interface, you can pull the supports and should have proper cleavage.

Figure 6. (top) Support-model interface surface, and (bottom) support structure interface - it is important to get separation at the former interface
Figure 6. (top) Support-model interface surface, and (bottom) support structure interface – it is important to get separation at the former interface

One final point to keep in mind is that in some cases, eliminating internal supports may be impossible, as shown for a different part in Figure 7 below. The point is to eliminate the support in places you cannot reach with your pliers and get enough peeling force applied to. In the case below, I chose to have supports at the wide opening since I had adequate access to them. With practice, you will get a better sense of what supports can and cannot be removed and use that intuition to better shape your design and process layout decisions before you print.

Figure 6. Support in internal features are alright as long as you have access to them
Figure 7. Support in internal features are alright as long as you have access to them

Figure 7. The final part!
Figure 8. The final part

The ULTEM intake manifold runner and plenum being put through its paces at the ASU Formula SAE test rig
Figure 9. The ULTEM intake manifold runner along with a plenum that we also printed, both being put through their paces at the ASU Formula SAE test rig (Photo Ack: Michael Conard)

Show your support for ASU’s Formula SAE team at their Facebook page and see a video about the endeavor here.

Constitutive Modeling of 3D Printed FDM Parts: Part 2 (Approaches)

In part 1 of this two-part post, I reviewed the challenges in the constitutive modeling of 3D printed parts using the Fused Deposition Modeling (FDM) process. In this second part, I discuss some of the approaches that may be used to enable analyses of FDM parts even in presence of these challenges. I present them below in increasing order of the detail captured by the model.

  • Conservative Value: The simplest method is to represent the material with an isotropic material model using the most conservative value of the 3 directions specified in the material datasheet, such as the one from Stratasys shown below for ULTEM-9085 showing the lower of the two modulii selected. The conservative value can be selected based on the desired risk assessment (e.g. lower modulus if maximum deflection is the key concern). This simplification brings with it a few problems:
    • The material property reported is only good for the specific build parameters, stacking and layer thickness used in the creation of the samples used to collect the data
    • This gives no insight into build orientation or processing conditions that can be improved and as such has limited value to an anlayst seeking to use simulation to improve part design and performance
    • Finally, in terms of failure prediction, the conservative value approach disregards inter-layer effects and defects described in the previous blog post and is not recommended to be used for this reason

ULTEM-9085 datasheet from Stratasys - selecting the conservative value is the easiest way to enable preliminary analysis
ULTEM-9085 datasheet from Stratasys – selecting the conservative value is the easiest way to enable preliminary analysis

  • Orthotropic Properties: A significant improvement from an isotropic assumption is to develop a constitutive model with orthotropic properties, which has properties defined in all three directions. Solid mechanicians will recognize the equation below as the compliance matrix representation of the Hooke’s Law for an orthortropic material, with the strain matrix on the left equal to the compliance matrix by the stress matrix on the right. The large compliance matrix in the middle is composed of three elastic modulii (E), Poisson’s ratios (v) and shear modulii (G) that need to be determined experimentally.

Hooke's Law for Orthotropic Materials (Compliance Form)
Hooke’s Law for Orthotropic Materials (Compliance Form)

Good agreement between numerical and experimental results can be achieved using orthotropic properties when the structures being modeled are simple rectangular structures with uniaxial loading states. In addition to require extensive testing to collect this data set (as shown in this 2007 Master’s thesis), this approach does have a few limitations. Like the isotropic assumption, it is only valid for the specific set of build parameters that were used to manufacture the test samples from which the data was initially obtained. Additionally, since the model has no explicit sense of layers and inter-layer effects, it is unlikely to perform well at stresses leading up to failure, especially for complex loading conditions.  This was shown in a 2010 paper that demonstrated these limitations  in the analysis of a bracket that itself was built in three different orientations. The authors concluded however that there was good agreement at low loads and deflections for all build directions, and that the margin of error as load increased varied across the three build orientations.

An FDM bracket modeled with Orthotropic properties compared to experimentally observed results
An FDM bracket modeled with Orthotropic properties compared to experimentally observed results

  • Laminar Composite Theory: The FDM process results in structures that are very similar to laminar composites, with a stack of plies consisting of individual fibers/filaments laid down next to each other. The only difference is the absence of a matrix binder – in the FDM process, the filaments fuse with neighboring filaments to form a meso-structure. As shown in this 2014 project report, a laminar approach allows one to model different ply raster angles that are not possible with the orthotropic approach. This is exciting because it could expand insight into optimizing raster angles for optimum performance of a part, and in theory reduce the experimental datasets needed to develop models. At this time however, there is very limited data validating predicted values against experiments. ANSYS and other software that have been designed for composite modeling (see image below from ANSYS Composite PrepPost) can be used as starting points to explore this space.

Schematic of a laminate build-up as analyzed in ANSYS Composite PrepPost
Schematic of a laminate build-up as analyzed in ANSYS Composite PrepPost

  • Hybrid Tool-path Composite Representation: One of the limitations of the above approach is that it does not model any of the details within the layer. As we saw in part 1 of this post, each layer is composed of tool-paths that leave behind voids and curvature errors that could be significant in simulation, particularly in failure modeling. Perhaps the most promising approach to modeling FDM parts is to explicitly link tool-path information in the build software to the analysis software. Coupling this with existing composite simulation is another potential idea that would help reduce computational expense. This is an idea I have captured below in the schematic that shows one possible way this could be done, using ANSYS Composite PrepPost as an example platform.

Potential approach to blending toolpath information with composite analysis software
Potential approach to blending toolpath information with composite analysis software

Discussion: At the present moment, the orthotropic approach is perhaps the most appropriate method for modeling parts since it is allows some level of build orientation optimization, as well as for meaningful design comparisons and comparison to bulk properties one may expect from alternative technologies such as injection molding. However, as the application of FDM in end-use parts increases, the demands on simulation are also likely to increase, one of which will involve representing these materials more accurately than continuum solids.

Constitutive Modeling of 3D Printed FDM Parts: Part 1 (Challenges)

As I showed in a prior blog post, Fused Deposition Modeling (FDM) is increasingly being used to make functional plastic parts in the aerospace industry. All functional parts have an expected performance that they must sustain during their lifetime. Ensuring this performance is attained is crucial for aerospace components, but important in all applications. Finite Element Analysis (FEA) is an important predictor of part performance in a wide range of indusrties, but this is not straightforward for the simulation of FDM parts due to difficulties in accurately representing the material behavior in a constitutive model. In part 1 of this article, I list some of the challenges in the development of constitutive models for FDM parts. In part 2, I will discuss possible approaches to addressing these challenges while developing constitutive models that offer some value to the analyst.

It helps to first take a look at the fundamental multi-scale structure of an FDM part. A 2002 paper by Li et. al. details the multi-scale structure of an FDM part as it is built up from individually deposited filaments all the way to a three-dimensional part as shown in the image below.

Multiscale structure of an FDM part
Multiscale structure of an FDM part

This multi-scale structure, and the deposition process inherent to FDM, make for 4 challenges that need to be accounted for in any constitutive modeling effort.

  • Anisotropy: The first challenge is clear from the above image – FDM parts have different structure depending on which direction you look at the part from. Their layered structure is more akin to composites than traditional plastics from injection molding. For ULTEM-9085, which is one of the high temperature polymers available from Stratasys, the datasheets clearly show a difference in properties depending on the orientation the part was built in, as seen in the table below with some select mechanical properties.

Stratasys ULTEM 9085 datasheet material properties showing anisotropy
Stratasys ULTEM 9085 datasheet material properties showing anisotropy

  • Toolpath Definition: In addition to the variation in material properties that arise from the layered approach in the FDM process, there is significant variation possible within a layer in terms of how toolpaths are defined: this is essentially the layout of how the filament is deposited. Specifically, there are at least 4 parameters in a layer as shown in the image below (filament width, raster to raster air gap, perimeter to raster air gap and the raster angle). I compiled data from two sources (Stratasys’ data sheet and a 2011 paper by Bagsik et al that show how for ULTEM 9085, the Ultimate Tensile Strength varies as a function of not just build orientation, but also as a function of the parameter settings – the yellow bars show the best condition the authors were able to achieve against the orange and gray bars that represent the default settings in the tool.  The blue bar represents the value reported for injection molded ULTEM 9085.

Ultimate Tensile Strength of FDM ULTEM 9085 for three different build orientations, compared to injection molded value (84 MPa) for two different data sources, and two different process parameter settings from the same source. On the right are shown the different orientations and process parameters varied.
Ultimate Tensile Strength of FDM ULTEM 9085 for three different build orientations, compared to injection molded value (84 MPa) for two different data sources, and two different process parameter settings from the same source. On the right are shown the different orientations and process parameters varied.

  • Layer Thickness: Most FDM tools offer a range of layer thicknesses, typical values ranging from 0.005″ to 0.013″. It is well known that thicker layers have greater strength than thinner ones. Thinner layers are generally used when finer feature detail or smoother surfaces are prioritized over out-of-plane strength of the part. In fact, Stratasys’s values above are specified for the default 0.010″ thickness layer only.
  • Defects: Like all manufacturing processes, improper material and machine performance and setup and other conditions may lead to process defects, but those are not ones that constitutive models typically account for. Additionally and somewhat unique to 3D printing technologies, interactions of build sheet and support structures can also influence properties, though there is little understanding of how significant these are. There are additional defects that arise from purely geometric limitations of the FDM process, and may influence properties of parts, particularly relating to crack initiation and propagation. These were classified by Huang in a 2014 Ph.D. thesis as surface and internal defects.
    • Surface defects include the staircase error shown below, but can also come from curve-approximation errors in the originating STL file.
    • Internal defects include voids just inside the perimeter (at the contour-raster intersection) as well as within rasters. Voids around the perimeter occur either due to normal raster curvature or are attributable to raster discontinuities.

FDM Defects: Staircase error (top), Internal defects (bottom)
FDM Defects: Staircase error (top), Internal defects (bottom)

Thus, any constitutive model for FDM that is to accurately predict a part’s response needs to account for its anisotropy, be informed by the specifics of the process parameters that were involved in creating the part and ensure that geometric non-idealities are comprehended or shown to be insignificant. In my next blog post, I will describe a few ways these challenges can be addressed, along with the pros and cons of each approach.

Click here to see part 2 of this post

3D Printed Plastics in Functional Aerospace Parts

Fused Deposition Modeling (FDM) is the most widely used 3D printing technology today, ranging from desktop printers to industrial scale manufacturing tools. While the use of FDM for prototyping and rapid tooling is well established, its use for manufacturing end-use parts in aerospace is a more recent phenomenon. This has been brought about primarily due to the availability of one material choice in particular: ULTEM. ULTEM is a thermoplastic that delivers compliance with FAA FAR 25.853 requirements. It features inherent flame retardant behavior and provides a high strength-to-weight ratio, outstanding elevated thermal resistance, high strength and stiffness and broad chemical resistance (official SABIC press release).

During an industry scan I conducted for a recent research proposal PADT submitted, I came across several examples of the aerospace industry using the FDM process to manufacture end-use parts. Each of these examples is interesting because they demonstrate the different criteria that make FDM preferable over traditional options, and I have classified them accordingly into: design opportunity, cost and lead-time reduction, and supply complexity.

Design Opportunity: In this category, I include parts that were primarily selected for 3D printing because of the unique design freedom that layer-wise additive manufacturing offers. This applies to all 3D printing technologies, the two examples below are for FDM in ducts.

ULA Environmental Control System (ECS) duct: As reported in a prior blog post, United Launch Alliance (ULA) leveraged FDM technology to manufacture an ECS duct and reduce the overall assembly from 140 parts to only 16, while reducing production costs by 57%. The ECS ducts distribute temperature and humidity controlled air onto sensitive avionics equipment during launch and need to withstand strong vibrations. The first Atlas V with these ducts is expected to launch in 2016.

ULA's Kyle Whitlow demonstrates the ECS duct that was printed using FDM
ULA’s Kyle Whitlow demonstrates the ECS duct that was printed using FDM

Orbis Flying Eye Hospital aircraft duct: The Flying Eye Hospital is an amazing concept from Orbis, who use a refurbished DC-10 plane to deliver eye care around the world. The plane actually houses all the surgical rooms to conduct operations and also has educational classrooms. The refurbishment posed a particular challenge when it came to air conditioning: a duct had to transfer air over a rigid barrier while maintaining the volume. Due to the required geometric complexity, the team selected FDM and ULTEM to manufacture this duct, and installed it and met with FAA approval. The story is described in more detail in this video.

FDM used to enable a complex duct connection on an Orbis DC-10 aircraft
FDM used to enable a complex duct connection on an Orbis DC-10 aircraft

Supply Complexity: 3D printing has a significant role to play in retro-fitting of components on legacy aircraft. The challenge with maintaining these aircrafts is that often the original manufacturer either no longer is in business or makes the parts.

Airbus Safety belt holder: Airbus shared an interesting case of a safety belt holder that had to be retrofitted for the A310 aircraft. The original supplier made these 30 years ago and since went out of business and rebuilding the molds would cost thousands of dollars and be time-consuming. Airbus decided to use FDM to print these safety belt holders as described in this video. They took a mere 2 hours to design the part from existing drawings, and had the actual part printed and ready for evaluation within a week!

Airbus used FDM to print safety belt holders for A310 aircraft when the original supplier went out of business
Airbus used FDM to print safety belt holders for A310 aircraft when the original supplier went out of business

Incidentally, the US Air Force has also recognized this as a critical opportunity to drive down costs and reduce the downtime spent by aircrafts awaiting parts, as indicated by a recent research grant they are funding to enable them to leverage 3D printing for the purpose of improving the availability of parts that are difficult and/or expensive to procure. As of 2014, The Department of Defense (DOD) reported that they have maintenance crews supporting a staggering 31,900 combat vehicles, 239 ships and 16,900 aircraft – and identified 3D printing as a key factor in improving parts availability for these crews.

Cost & Lead-time Reduction: In low-volume, high-value industries such as aerospace, 3D printing has a very strong proposition to make as a technology that will bring products to market faster and cheaper. What is often a surprise is the levels of reduction that can be obtained with 3D printing, as borne out by the three examples below.

Airbus A350 Electric wire covers: The Airbus A350 has several hundred plastic covers that are 3D printed with FDM. These covers are used for housing electric wires at junction boxes. Airbus claims it took 70% less time to make these parts, and the manufacturing costs plunged 80%. See this video for more information.

Airbus used FDM to manufacture wire covers for their A350 aircraft
Airbus used FDM to manufacture wire covers for their A350 aircraft

Kelly Manufacturing Toroid housing: Kelly Manufacturing selected FDM to manufacture toroid housings that are assembled into their M3500 instrument, which is a “turn and bank” indicator which provides the pilot information regarding the rate of aircraft turn. These housings were previously made of urethane castings and required manual sanding to remove artifacts from the casting process, and also had high costs and lead times associated with tooling. Using FDM, they were able to eliminate the need to do sanding and reduced the lead time 93% and also reduced per-piece costs by 5% while eliminating the large tooling costs. See the official case study from Stratasys here.

Kelly MFG housing FDM
Toroid housings manufactured for Kelly Manufacturing using FDM for significant cost savings and lead time reduction

These examples help demonstrate that 3D printing parts can be a cost savings solution and almost always results in significant lead time reduction – both of vital interest in the increasingly competitive aerospace industry. Further, design freedom offered by 3D printing allows manufacturing geometries that are otherwise impossible or cost prohibitive to make using other processes, and also have enormous benefit in overcoming roadblocks in the supply chain. At the same time, not every part on an aircraft is a suitable candidate for 3D printing. As we have just seen, selection criteria involve the readily quantifiable metrics of part cost and lead time, but also involve less tangible factors such as supply chain complexity, and the design benefits available to additive manufacturing. An additional factor not explicitly mentioned in any of the previous examples is the criticality of the part to the flight and the safety of the crew and passengers on board. All these factors need to be taken into consideration when determining the suitability of the part for 3D printing.