Understanding Honeycomb Structures in Additive Manufacturing – Three Papers from ASU and PADT

PADT is currently partnering with Arizona State University’s 3DXResearch group on exploring bio-inspired geometries for 3D Printing. As part of that effort, one of our engineers involved in the project, Alex Grishin, PhD, was a co-author on several papers that have been published during this project.

Below is a brief summary from Alex of each article, along with links.


An Examination of the Low Strain Rate Sensitivity of Additively Manufactured Polymer, Composite and Metallic Honeycomb Structures

PADT participated in the research with the above title recently published in the open-access online journal MDPI ( https://www.mdpi.com/1996-1944/12/20/3455/htm ). This work was funded by the America Makes Program under a project titled “A Non-Empirical Predictive Model for Additively Manufactured Lattice Structures” and is based on research sponsored by the Air Force Research Laboratory under agreement number FA8650-12-2-7230.

Current ASU professor and former PADT employee Dhruv Bhate was the Lead Investigator and wrote the original proposal. Dhruv’s research interests involve bio-inspired design (the study of structures found in nature to help inform human design efforts) and additive manufacturing. Dhruv is particularly interested in the bulk properties of various lattice arrangements. While investigating the highly nonlinear force-deflection response of various additively manufactured honeycomb specimens under compression, Dhruv discovered that polymer and composite honeycombs showed extreme sensitivity to strain rates –showing peak responses substantially higher than theory predicts at various (low) strain rates. This paper explores and quantifies this behavior.

The paper investigates hexagonal honeycomb structures manufactured with four different additive manufacturing processes: one polymer (fused deposition modeling, or material extrusion with ABS), one composite (nylon and continuous carbon fiber extrusion) and two metallic (laser powder bed fusion of Inconel 718 and electron beam melting of Ti6Al4V). The strain rate sensitivities of the effective elastic moduli, and the peak loads for all four processes were compared. Results show significant sensitivity to strain rate in the polymer and composite process for both these metrics, and mild sensitivity for the metallic honeycombs for the peak load.

PADT contributed to this research by providing ANSYS simulations of these structures assuming viscoplastic material properties derived from solid dog-bone test specimens. PADT’s simulations helped provide Dhruv with a proposed mechanism to explain why INSTRON compression tests of the honeycomb structures showed higher peak responses (corresponding to classical ultimate stress) for these specimens than the solid specimens.


Bioinspired Honeycomb Core Design: An Experimental Study of the Role of Corner Radius, Coping and Interface

PADT participated in the NASA-funded research with the above title recently published in the open-access online journal MDPI (https://www.mdpi.com/2313-7673/5/4/59/htm ). This work was guided by former PADT engineer and current ASU Associate Professor Dhruv Bhate.  Professor Bhate’s primary research interests are Bio-Inspired Design and Additive Manufacturing. It was only natural that he would secure a grant for this research from NASA’s  Periodic Table of Life ( PeTaL) project. To quote from the website, “the primary objective…is to expand the domain of inquiry for human processes that seek to model those that are, were or could be found in nature…”

This paper focuses on the morphology of bee honeycombs found in nature –the goal being to identify key characteristics of their structure, which might inform structural performance in man-made designs incorporating similar lattice structures. To this end, the paper identifies three such characteristics: The honeycomb cell corner radius, the cell wall “coping” (a localized thickening of the cell wall at the mouth of each cell seen in a lateral cross-section), and the cell array “interface” (a zigzag pattern seen at the interface of two opposing, or “stacked” arrays).

Most of this work involved material testing and measuring dozens of natural honeycombs (most coming from various museums of natural history found in the United States) at ASU’s state-of-the-art facilities. PADT  contributed substantially by verifying and guiding tests with simulation using the ANSYS suite of software.


A Comparison of Modeling Methods for Predicting the Elastic-Plastic Response of Additively Manufactured Honeycomb Structures

PADT participated in this research found in the reviewed article published in Proceedings of the 29th Annual International Solid Freeform Fabrication Symposium – An Additive Manufacturing Conference.

Figure 14. (left) 2D plane strain model with platens connected to honeycomb with frictional contacts and (right) close-up of an individual cell showing the mesh size as well as corner radius modeled after experimental measurements

The lead investigator was current ASU professor and former PADT employee Dhruv Bhate, whose research interests involve Bio-Inspired Design (the study of natural structures to help inform human design processes) and Additive Manufacturing. In this research, Dhruv investigates discrepancies between published (bulk) material properties for the Fused Deposition Modeling (FDM) of ABS honeycomb structures. The discrepancies arise as substantial differences between published material properties, such as Young’s Modulus and yield stress, and those determined experimentally from FDM dog-bone specimens of the same material (which he refers to as “member” properties).

Figure 4. (left) Homogenization enables the replacement of a cellular material with a solid of effective properties, (right) which can greatly reduce computational expense when simulating engineering structures

PADT’s role in this research was crucial for demonstrating that the differences in base material characterization are greatly exacerbated in nonlinear compression simulations of the ABS honeycomb structures. PADT used both the manufacturer’s published properties, and the dog-bone data to show substantial differences in peak stress under the two assumptions.

https://www.scopus.com/record/display.uri?eid=2-s2.0-85084948560&origin=inward&txGid=a19776da6deb7846e12bc8f7573181ab

3D Printed Parts Create a Tricked-Out Truck

PADT’s Austin Suder is a Solidworks CAD wizard, a NASA design-competition (Two for the Crew) winner and a teaching assistant for a course in additive manufacturing (AM)/3D printing. Not bad for someone who’s just started his sophomore year in mechanical engineering at Arizona State University.

PADT's Austin Suder 3D printed these custom LED reverse-light housings in carbon fiber PLA, then added heat-set inserts to strengthen the assembly and mounting structure. (Image courtesy Austin Suder)
PADT’s Austin Suder 3D printed these custom LED reverse-light housings in carbon fiber PLA, then added heat-set inserts to strengthen the assembly and mounting structure. (Image courtesy Austin Suder)

In last month’s PADT blog post about adding heat-set inserts to 3D printed parts we gave a shout-out to Austin for providing our test piece, the off-road LED light unit he had designed and printed for his 2005 Ford F-150. Now we’ve caught up with him between classes to see what other additions he’s made to his vehicle, all created with his personal 3D printers and providing great experience for his part-time work with Stratasys industrial printers in PADT’s manufacturing department.

Q: What has inspired or led you to print multiple parts for your truck?

I like cars, but I’m on a college budget so instead of complaining I found a way to fix the problem. I have five 3D printers at my house – why not put them to work! I understand the capabilities of AM so this has given me a chance to practice my CAD and manufacturing skills and push boundaries – to the point that people start to question my sanity. You can find more answers or receive more updates at glenoriegrowers.

Q: How did you end up making those rear-mount LED lights?

I wanted some reverse lights to match the ones on the front of my truck, so I designed housings in SolidWorks and printed them in carbon fiber PLA. Then I soldered in some high-power LED lights and wired them to my reverse lights. These parts made great use of threaded inserts! The carbon fiber PLA that I used was made by a company called Vartega that recycles carbon fiber material. (Note: PADT is an investor of this company.)

Q: In the PADT parking lot, people can’t help but notice your unusual tow-hitch. What’s the story with that?

I saw a similar looking hitch on another car that I liked and my first thought was, “I bet I could make that better.” It’s made from ABS painted chrome (not metal); I knew that I would never use it to tow anything, so this opened up my design freedom. This has been on my truck for about a year and the paint has since faded, but the printed parts are still holding strong.

An adjustable-height "topology optimized" trailer hitch Austin designed and printed in ABS. The chrome paint-job has many passersby doing a double-take, but it's just for fun, not function. (Image courtesy PADT)
An adjustable-height “topology optimized” trailer hitch Austin designed and printed in ABS. The chrome paint-job has many passersby doing a double-take, but it’s just for fun, not function. (Image courtesy PADT)

This part also gets questioned a lot! It’s both a blessing and a curse. In most cases it starts when I’m getting gas and the person behind me starts staring and then questions the thing that’s attached to the back of my truck. The conversation then progresses to me explaining what additive is, to a complete stranger in the middle of a gas station. This is the blessing part because I’m always down for a conversation about AM; the downside is I hate being late for work.

Q: What about those tow shackles on your front bumper?

Unique ABS printed tow shackles - another conversation-starter. (Image courtesy PADT)
Unique ABS printed tow shackles – another conversation-starter. (Image courtesy PADT)

Those parts were printed in ABS – they’re not meant for use, just for looks. I’ve seen towing shackles on Jeeps and other trucks but never liked the look of them, so again I designed my own in this pentagon-shape. I originally printed them in red but didn’t like the look when I installed them; the unusual shading comes because I spray-painted them black then rubbed off some of the paint while wet so the red highlights show through.

Q: Have you printed truck parts in any other materials?

Yes, I‘ve used a carbon-fiber (CF) nylon and flexible TPU (thermoplastic polyurethane) on filament printers and a nylon-like resin on a stereolithography system.

The CF nylon worked well when I realized my engine bay lacked the real estate needed for a catch can I’d bought. This was a problem for about five minutes – then I realized I have the power of additive and engineered a mount which raised the can and holds it at an angle. The mount makes great use of complex geometry because AM made it easy to manufacture a strong but custom-shaped part.     

Custom mount, 3D printed in carbon-fiber reinforced nylon, puts aftermarket catch-can in just the right location. (Image courtesy Austin Suder)
Custom mount, 3D printed in carbon-fiber reinforced nylon, puts aftermarket catch-can in just the right location. (Image courtesy Austin Suder)

After adding the catch can to my engine, I needed a way to keep the hoses from moving around when driving so I designed a double S-clip in TPU. The first design didn’t even come close to working – the hoses kept coming loose when driving – so I evaluated it and realized that the outer walls needed to be thicker. I made the change and printed it again, and this time it worked great. In fact, it worked so well that when I took my truck to the Ford dealership for some warranty work, they went missing. (It’s OK Ford, you can have them – I’ll just print another set.)    

Just-right 3D printed clips keep hoses anchored and out of the way. ((Image courtesy Austin Suder)
Just-right 3D printed clips keep hoses anchored and out of the way. ((Image courtesy Austin Suder)

Other parts I printed in TPU included clips for the brake-lines. I had seen that my original clip had snapped off, so when I had the truck up on jacks, I grabbed my calipers and started designing a new, improved version. Thirty minutes later I had them in place.

I also made replacement hood dampeners from TPU since they looked as though they’d been there for the life of the truck. I measured the old ones, used SolidWorks to recreate them (optimized for AM), printed a pair and installed them. They’ve been doing great in the Arizona heat without any deformation.      

New hood-dampeners printed in TPU have just the right amount of give. (Image courtesy Austin Suder)
New hood-dampeners printed in TPU have just the right amount of give. (Image courtesy Austin Suder)

My last little print was done on my SLA system in a material that behaves like nylon. (This was really just me showing off.) The plastic clips that hold the radiator cover had broken off, which led me to use threaded sheet-metal inserts to add machine threading to the fixture. I then purchased chrome bolts and made some 3D printed cup-washers with embossed text for added personalization and flair.  

Even the cup-washers got a 3D printed make-over on Austin's F150: printed in white resin on an SLA system, these parts got a coat of black paint and then some sanding, ending up with a two-color custom look. (Image courtesy PADT)
Even the cup-washers got a 3D printed make-over on Austin’s F150: printed in white resin on an SLA system, these parts got a coat of black paint and then some sanding, ending up with a two-color custom look. (Image courtesy PADT)

Q: What future automotive projects do you have in mind?

I’m working on a multi-section bumper and am using the project to standardize my production process – the design, material choice, sectioning and assembling. I got the idea because I saw someone with a tube frame car and thought it looked great, which led to me start thinking about how I could incorporate that onto my truck.

When I bought my F-150, it had had a dent in the rear bumper. I was never happy with this but didn’t have the money to get it fixed, so at this point the tube-frame look came full circle! I decided that I was going to 3D print a tube-frame bumper to replace the one with a dent. I started by removing the original bumper, taking measurements and locating possible mounting points for my design. Then I made some sketches and transferred them into SolidWorks.

The best part about this project is that I have additive on my side. Typical tube frame construction is limited by many things like bend allowance, assembly, and fabrication tooling. AM has allowed me to design components that could not be manufactured with traditional methods. The bumper will be constructed of PVC sections connected by 50 ABS printed parts, all glued together, smoothed with Bondo and filler primer then painted black. This is a large project!  It will take a lot of hand-finishing, but it will be perfect.

Q: If you were given the opportunity to work on any printer technology and/or material, what would you want to try working with?

Great question! If I had the opportunity to use AM for automotive components, I would redesign internal engine components and print them with direct metal laser sintering (DMLS), one of PADT’s other AM technologies. I would try printing part like piston rods, pistons, rocker arms, and cylinder valves. Additive is great for complex geometries with exotic materials.

Go Austin! Can’t wait to see what your truck looks like when you visit over semester break.

To learn more about fused deposition modeling (FDM/filament), stereolithography (SLA), selective laser sintering (SLS) and DMLS printers and materials, contact the PADT Manufacturing group; get your questions answered, have some sample parts printed, and share your success tips.

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.

Press Release: Grant to ASU, PADT, and Others for Advancement of 3D Printing Post-Processing Techniques

We are very pleased to announce that PADT is part of another successful Federal grant with ASU in the area of Additive Manufacturing.  This is the second funded research effort we have been part of in the past twelve months and also our second America Makes funded project.

It is another great example of PADT’s cooperation with ASU and other local businesses and also shows how Arizona is becoming a hub for innovation around this important and growing technology.

Please find the official press release on this new partnership below and here in PDF and HTML.

You can find links to our other recent research grants here:

If you have any questions about, additive manufacturing or this project, reach out to info@padtinc.com or call 480.813.4884.

Press Release:

$800,000 in Matching Funds Appointed to ASU, PADT and Other Partners by America Makes for the Advancement of 3D Printing Post-Processing Techniques

This Grant Marks PADT’s Second Federally Funded Project in the Past Year, and its Second America Makes Funded Project in the Past Two Years

TEMPE, Ariz., January 24, 2019 ─ PADT, a globally recognized provider of numerical simulation, product development, and 3D printing products and services, has announced it has joined ASU in a Directed Project Opportunity to advance post-processing techniques used in additive manufacturing (AM). The project is being funded by the Air Force Research Laboratory (AFRL) and the Materials and Manufacturing Directorate, Manufacturing and Industrial Base Technology Division and driven by the National Center for Defense Manufacturing and Machining (NCDMM).

ASU was one of two awardees that received a combined $1.6M with at least $800K in matching funds from the awarded project teams for total funding worth roughly $2.4M. ASU will lead the project, while PADT, Quintus Technologies, and Phoenix Heat Treating, Inc. have joined to support the project.

“Our ongoing partnership with ASU has allowed us to perform critical research into the advancement of 3D printing,” said Rey Chu, principal and co-founder, PADT. “We are honored to be involved with this project and look forward to applying our many years of technical expertise in 3D printing post-processing.”

The goal of this research is to yield essential gains in process control, certified processes, and the qualification of materials and parts to drive post-processing costs down and make 3D printing more accessible. PADT will be responsible for providing geometry scanning capabilities, as well as technical expertise.

PADT has deep experience in 3D printing post-processing techniques due to the development of its proprietary Support Cleaning Apparatus (SCA), the best-selling post-processing hardware on the market. Initially released in November 2008, more than 12,500 SCA systems have sold to-date. The SCA system was awarded a U.S. patent in October 2018.

This grant will be the second federally funded research project in 2018 which teams PADT and ASU to advance 3D printing innovation and adoption. The first project received a $127,000 NASA STTR grant and is aimed at accelerating biomimicry research, the study of 3D printing objects that resemble strong and light structures found in nature such as honeycombs.

For more information on PADT and its background in 3D printing post-processing, please visit www.padtinc.com.

About Phoenix Analysis and Design Technologies

Phoenix Analysis and Design Technologies, Inc. (PADT) is an engineering product and services company that focuses on helping customers who develop physical products by providing Numerical Simulation, Product Development, and 3D Printing solutions. PADT’s worldwide reputation for technical excellence and experienced staff is based on its proven record of building long-term win-win partnerships with vendors and customers. Since its establishment in 1994, companies have relied on PADT because “We Make Innovation Work.” With over 80 employees, PADT services customers from its headquarters at the Arizona State University Research Park in Tempe, Arizona, and from offices in Torrance, California, Littleton, Colorado, Albuquerque, New Mexico, Austin, Texas, and Murray, Utah, as well as through staff members located around the country. More information on PADT can be found at www.PADTINC.com.

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TechTHiNQ on behalf of PADT
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PADT, Inc.
Principal & Co-Owner
480.813.4884
eric.miller@padtinc.com

Phoenix Business Journal: ​Arizona solidifies position as a leader in space technology

Just-Published-PBJ-1The resent launch of OSIRIS-REx probe to visit the asteroid Bennu was a milestone for Arizona.  In “Arizona solidifies position as a leader in space technology” I review how ASU, UofA and Tempe’s Kinnetx played a key role in device design and development as well as mission and scientific control.

The PADT Hat Visits ASU’s Formula SAE Team

PADT was honored to be invited to come out and see the Formula SAE car that Arizona State University has been working on as part of their Press Day at the Bondurant School of High Performance Driving.  The PADT Hat came along and got a picture:

ASU-Formula-SAE

We helped out the team last year by printing them an intake manifold and by offering some assistance to the Aero design team.  It was a very nice design and in their first year of competition, they came in 24th out of 80 teams.DSC09593

Congratulations to all the students involved and we are looking forward to working with them in the coming season.