Join PADT at the 2012 Governor’s Celebration of Innovation

imageThe awards are all done and are sitting on Jen’s file cabinet.  It is time once again for the Arizona Technology Council’s Governor’s Celebration of Innovation (GCOI) Awards.  It does not seem like it could have already been a year since PADT won an award last year. But it has.  And we can not wait to celebrate what a great year it was.

Learn more about the event here.

We will be back  this year, in our booth before the ceremony, in the audience with everyone else waiting to see who wins, and afterwards at the dinner. Please stop on by and say hello.

Using 3D Printing to Make a Clock

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If you visit the lobby of PADT’s Tempe office you will notice something very cool on the wall – a large white and black pendulum clock clicking away on the wall.  Its gears are exposed and you can not only hear it tick-toking away, you can see the gears moving, and watch the timing mechanism rock back and forth.  It defiantly attracts the attention of our mechanically minded customers.

imageThe clock was built by our very own manufacturing engineer Justin Baxter based upon a design from a website called Brian Law’s Wooden Clocks (www.woodenclocks.co.uk).  Brian has a large array of very cool wooden clock designs that he has done for the hobbyist community.  Do take a look at his website to see the very cool designs he has developed. We have our eye on a few more to try out.

To make our clock, Justin took the Clock 1 design and modified it for use with the Stratasys FDM machines that we have in house.  Starting with the free 2D drawings on the website, he created 3D Solids of the assembly making only a few changes. He had to add a bit of thickness to the winding ratchet paul and added some brackets for rigidity because the ABS plastic is more flexible then wood.  It took about 20 hours to build up the CAD model in SolidWorks.

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He then set to work building the parts on our fleet of Stratasys 3D Printers and Manufacturing Centers.  To speed things up he spread the job up over three of our machines:  The FORTUS 400mc for the large white parts, the SST 1200es for the small black parts, and a few smaller parts here and there on the Elite.  Black and Ivory ABS was used for all of the parts that were made on the 3D Printers. He then spent about 15 hours post processing the parts.

The post processing was important because he found early on that friction between the ABS parts could be significant.  All of the sliding surfaces needed to be sanded and Acetone-Smoothed to get rid of any ridges that are a natural byproduct of the additive manufacturing process.  This proved to be the most difficult part of the entire process.

Meanwhile, he ordered and fabricated the few metal parts that he needed: the drive shaft (steel rod), the pendulum rod (aluminum tube), and the mass for the weight (stainless steel bar). I strong string was also found that could be used to suspend the weight.  Everything was then assembled and he spent some time tuning the mechanism to reduce as much friction as possible, and to get the timing worked out on the mechanism.  After all was said and done, the material costs were around $700, and the total machine running time was around 60 hours total.

The end result is shown here in this video:

 

When asked if he had any advice for someone who wanted to make his own clock, Justin replied “Do it, these plans make it quite simple to print one and with a lot more patience and skill you could even make one out of wood as the designer intended. I found making this clock to be a very enjoyable learning experience. “

We hope to have some time to try out some other designs, the PADT Colorado office is already making noise about wanting their own clock.  We will be sure to share the experience with everyone here on The RP Resource when we do.

Shopping for a Rapid Prototyping Service Provider

imageThere are a lot of companies out there providing Rapid Prototyping, Rapid Manufacturing and 3D Printing as a service to others.  As of this writing, Wholers Associates lists 98 around the world. That list does not include the smaller providers or companies who offer RP services as a side service.  It certainly does not include the hundreds of people with low cost 3D printers who will make parts for people. 

With so many choices, how do you pick the right one?

Well, the obvious answer is you just pick PADT to be your service provider.  That makes it easy and you can stop reading now.

Didn’t Work? Damn. Well it was worth a try.  So, taking off the PADT marketing hat and putting on the design engineer hat and engineering manager sweater, here is how I recommend that you make a logical decision:

Why are you Making a Prototype?

Before you do anything you need to ask yourself this question and get a good answer.  Sometimes, the real answer is because it is cool and you want to impress your boss or customer. That is OK. Just keep it in mind when you pick a vendor.  Somebody cheep and fast that delivers so-so quality may not be a good choice.

An important part of the question is also what will you use it for?  Most prototypes are made for visualization – a 3D image.  But many are also made to check fit, form, or function. How you plan to use your prototype should impact the technology you use, and the material choices you make for that technology.

Does it need to look like the production part? Does it need to perform as close to the production part as possible?  If the answer to either question is yes, then you need to really look at what post-processing (sanding, surface finish, texturing, painting) your prototype will need and which providers can supply it.

In fact, if your potential RP service provider does not ask what you want the prototype for, you probably are working with the wrong provider.

Establish what is Important to You

Every customer is different, and often every project is different.  A good place to start is to look at these typical priorities, grouped into three classes, and rank them for your company:

  • The Basics:Image
    • Cost
    • Speed
    • Quality
  • The Interaction:
    • Location
    • Responsiveness of Staff
    • Effort Required to Work With
  • The Capabilities:
    • Technologies Available
    • Material Offerings
    • Knowledge and Experience of Staff
    • Post Processing  Available
    • Down Stream Services Available

Too many customers that we see at PADT who have worked with other service providers, and who have had a bad experience, just look at the first two priorities – cost and speed.  The reality is that there are a lot of things that impact the overall effectiveness of your prototyping effort.  Once you know how you will use your prototype, you can better determine what is important to you.

So rank your priorities and evaluate your potential vendors on the important ones.

Assessing the Basics: Cost, Speed, Quality

Cost and speed seem very easy to obtain. You just send your part file to the potential vendors and get quotes with cost and delivery time. But, you have to look at what you get for the cost, and what the total cost and time are.  Do you need to post-process the part yourself?  Will the quality, surface finish, and material strength meet your needs?  A part made on a low cost 3D Printer may only be $50 versus $500 on an SLA machine.  But if it breaks during your test, how much will that cost?

If you have not worked with a provider before, quality can be tough to determine.  Ask for a reference.  If they are local, go see their shop and look at sample parts.  It might be good to have all of your potential vendors make a simple and inexpensive sample part for you so you can compare all of them before you go off and order $12,000 worth of prototypes.  After you get parts from a vendor, make a note of the quality. If you work for a larger company, maybe share that with purchasing so they know who delivers high quality, and who does not.  We all know that a purchasing person will simply go on the transaction cost if you do not give them other factors to work with.

The Price of Interaction

Manufacturing consulting meetingThis is by far the most difficult set of priorities to define and quantify.  This is the fuzzy stuff that deals with the time, money, and emotional capital that is invested by you during the process of getting your prototype quoted, purchased, made, and delivered.  I wish there was a formula, but you just need to make a gut decision on this one.

After you interacted with a vendor, ask yourself if you found the interaction enjoyable and productive?  Did you get the information you needed quickly and efficiently?  Did they call you back or respond to your email in a quick manner? Did you feel that you were working with them, or was it a bit of a battle? 

I consider this important because what we are talking about here is Rapid Prototyping. It is not “I’m way ahead of schedule, have plenty of budget, and can wait to get my part whenever –prototyping.”  You are doing RP because you need a part fast, you need it right the first time, and your whole product development schedule is probably being held up by it.

If your RP partner is hard to work with, when you get into those stressful I-need-it-tomorrow situations, you can not afford the emotional and financial cost of battling our coaxing your provider to help you out. You need to know you have someone on your team that will step up and come through for you in a pinch.  Never under estimate the importance of how hard or how easy it is to interact with your Rapid Prototyping service provider – keep it in mind and let it weigh heavily in your decision.  It will pay off when you get to crunch time.

What does your Vendor Bring to the Table? Capabilities

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Novices in the world of 3D Printing or Rapid Prototyping usually start of with the thought that they just “need a prototype.”  What they have yet to learn is that there are literally hundreds of different options – combinations of various technologies, materials, and post-processing steps.  Picking a service provider based upon capabilities is actually easy:

  1. They need to have most of the major technologies available (SLA, SLS, FDM, Polyjet).
    A provider that is focused on only one or two technologies will fit your needs into what they have. They only have a hammer, so whatever you ask for, you will get a nail.
  2. They must offer a wide range of materials for each technology they have in house.
    This is a big one.  Often customers can get a part that is the wrong stiffness or strength because they use a vendor that just does not offer the full range of materials.
  3. They can offer the post processing you need for your prototypes planned usage.
    A vendor that has to go outside for detailed sanding or painting is just not going to work. They need to be able to give you the part, looking like you want it to look, when they are finished and without running around and counting on other providers.  If they tell you that it is easy and you can do it yourself, walk away.
  4. The engineers on staff understand the strengths and weaknesses of each technology, material property, and post-processing option.
    All of the other capabilities are useless if you can not talk to someone who understand them. You need to be able to call or email someone at your vendor, tell them what you want to do with your prototype, and have them give you reasonable options on how to get there.  If they just have people processing your order through a piece of software, you will get burned in the end.

Cliché’s Exist for a Reason: Don’t be Afraid to Shop Around, Ask Questions, You Get What you Pay For

In conclusion, we should all remember what our grandmother probably told us a few times. I know mine did: Don’t be afraid to shop around. If I put my service provider hat back on I cringe at this. We would like all of our customers to stay with us forever and never stray.  But the truth is that it is a competitive market out there, and if you do not shop around, then you may not be getting the best product and we may not be as focused on making sure we keep you as a customer.  So in the end, we all benefit.

And another thing she said: “Eric, ask questions. It doesn’t hurt anyone to ask questions.”  So do that. The answer may not be as important as how a potential provider answers the question. Does it show they can listen, that they know their stuff, and that they care about you?

Lastly, and most importantly: You Get What you Pay For. There is not need to elaborate on that one.

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This is a short list, and there is a lot more to think about. Do not hesitate to contact us at PADT to ask more questions and to learn more about how to pick the right Rapid Prototyping service provider.

Another 2012 “Pumpkin” Launch… Well an Ice Ball Anyway

So, being engineers, we are not satisfied with the performance of actual pumpkins. We begin to ask ourselves “Hmmmm… is there a better material to use? What would happen if I tried to shoot _____”

So during this years Halloween launch festivities the team decided to try out an ice ball. 

Here is the result:

PADT Company Pictures Through the Years

As we get ready to launch the new website and the new blog, I find myself looking back on PADT’s 18 year history.  While looking for some lab pictures I found a directory buried about 6 levels down on my C:\ drive called “CompanyPictures”  And inside are all of the pictures that we have kept over the years. After looking at them I thought it might be fun to put them out there on the Blog.

Unfortunately we did not think to take a picture till 2000. So we were already 6 years old.  Since then we only missed 2004.  Take a look. Maybe you recognize someone you used to work with here, maybe you used to work here.  Let us know what you think in the comments.

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SBIR Awards at PADT

In 1999 PADT started looking for ways to leverage our various skills to further develop some intellectual property.  We had been doing projects for a variety of customers who were participating in the Small Business Innovative Research program through the federal government (SBIR), and we thought it might not be a bad idea to try going for a few SBIR’s of our own to help us get from that “startup” stage to the “established” phase.  It worked, over the following ten years PADT was successfully awarded 13 SBIR grants.

While we were in the thick of it we really did not keep track of things from a marketing perspective.  But as we prepare to launch the new Product Development portion of the PADT Blog, we thought it would be a good time to look back and summarize what we did and share it with our readers.

One thing that sets PADT apart in the world of SBIR’s is our high level of commercialization.  Although not all of the awards PADT received turned into commercial products, many did.  And bits and pieces from each project help PADT increase our experience and tool set.

Here is a list of the SBIR’s we have been awarded over the years:

Miniature Air Handling System for Portable Fuel Cell Power Supplies
US Army 1999 Phase I
VaneAlpha1This was our first SBIR and it was also our first project that involved pumping or blowing for fuel cells.  We learned a lot on this project and many of the follow on SBIR and commercial products we developed in this area are based on the technology developed here.
Ultra Low Weight Turbomolecular Pump
NASA 1999 Phase I
psys5JPL was interested in developing a very low weight vacuum pump (TMP) that they could use on their interplanetary explorers so they could run their experiments in a vacuum.  This project had a lot of issues to overcome, not the least of which was how to manufacture the thing.
Ultra Low Weight Turbomolecular Pump
NASA 2000 Phase II
TMP_050701_fOur proof of concept in Phase I was good enough to win PADT a Phase II contract for the ULWTMP design.  Now our ideas had to be put to work. We did solve a lot of the problems, especially the manufacturing issues. At the end of the project the only issue left undone was the rotordynamics problem that is encountered at the speeds of a TMP with a magnetic bearing.
Miniature Air Handling System for Portable Fuel Cell Power Supplies
US Army 2000 Phase II
vane-familly2PADT took what we learned in Phase I of this project and developed a family of vane compressors that met the unique needs of the US Army.  We developed an entire family of pumping solutions and tested them to develop a good understanding of their capabilities, strengths, and weaknesses.
Fuel Cell Based Portable Hybrid Power Supply
US Army 2000 Phase I
Hybrid-aThis phase I project involved the design of a portable hybrid power supply that combined batteries and a hydrogen fuel cell.  The end product was a conceptual design for a light way power solution for US soldiers.  PADT built a working demonstrator model that highlighted the control system, the custom fuel cell, and the pumping solution.
Fuel Cell Based Portable Hybrid Power Supply
US Army 2001 Phase II
hybridThis follow on project focused on the detailed design of a light weight portable power supply that used hydrogen to drive a fuel cell.  We produced a working demonstration product at the conclusion if of the effort. PADT was able to use all aspects of our company: simulation, design, test, prototyping, system integration, and manufacturing. The technology developed was used successfully to develop a complete hybrid system for a methanol fuel cell manufacturer who applied it to commercial applications.
Aerosol Collection Technology
US Army 2001 Phase I
impactor_bAfter the events of 9/11 the US Army had an interest in being able to detect air born biological weapons. Although they had good detectors, they needed a device that would use aerodynamics to collect air and separate out particles of a certain size. In Phase I of this project PADT used our CFD capability and rotating machinery design experience to develop a conceptual device for this application.
Aerosol Collection Technology
US Army 2003 Phase II
91010046For Phase II of this project PADT produced a working prototype and tested it with the help of Arizona State University. The testing showed that the technology was viable.  Fortunately, as time passed so did the potential threat and no market really opened up looking for such a device.
Low Cost Hot Anode Recycle Blower for SOFC Systems
DOE 2005 Phase I
invis_start_02_a32500_pic13PADT applied our fuel cell pumping knowledge to develop a pumping system that could work with the very high temperature Solid Oxide Fuel Cell systems that the government was looking at using for aircraft applications.
Miniature Disposable Drug Infusion Pump
DOD 2005 Phase I
clip_image002The department of defense is always focused on improving their ability to treat wounded soldiers in the field. One area that needed improvement in 2005 was the ability to deliver drugs in the battlefield with a portable lightweight design that had many special features which would allow a non-expert to administer the drugs. PADT investigated several different solutions and produced a conceptual design.
Low Cost Hot Anode Recycle Blower for SOFC Systems
DOE 2006 Phase II
clip_image002For the follow-up on this project PADT built a working system for pumping very high temperature fuel in a solid oxide fuel cell loop.  We also tested the system, at temperature, under a variety of operating conditions.
High Temperature Blower Development For SOFC Applications
DOE 2006 Phase I
clip_image002[5]PADT received an additional Phase I grant in this area to explore other options and to improve on the system developed as part of the low cost program.
Instruments and Devices To Preserve Molecular Profiles In Tumors
NIH 2009 Phase I
IMG_1448PADT first NIH project looked at developing a device that would freeze tissue biopsy samples during their extraction from a patient, or just after.  PADT developed a working prototype, the ReadyFreeze, that was very successful at allowing the user to freeze biopsy samples very shortly after extraction.

PADT’s very own Susanna Young Named as one of 2012’s Top Young Entrepreneurs by The Arizona Republic

imageMany PADT employees were looking through their newspaper (or browsing it online) and saw our very own Susanna Young made this years list of the Valley’s top Young Entrepreneurs.

Susanna worked as an intern at PADT while she was going to ASU and still works part time when she is not trying to make the world a better place by building G3Box into a viable company.  If you don’t know about their effort to make medical clinics from steel shipping containers, check out the website and learn more.

Here is a link to the article online:

http://www.azcentral.com/business/arizonaeconomy/articles/20121102young-entrepreneurs-arizona-2012.html 

Scroll to the end of the slideshow to read about Susanna. 

Congratulations. It is good to see good people, and an engineer, get recognized by the business press.

PADT Golf Team Makes Huge Improvement in Standing at 2012 SME Golf Tournament

Our local Society of Manufacturing Engineers (Phoenix Chapter 067) held their 22nd Annual Charity Golf Tournament and Fundraiser at the Arizona Grand Resort this weekend.  Fun was had by all and APDT was once again proud to be a sponsor. The weather was perfect and the event again raised money for the chapter’s scholarship fund.

We are extra proud to announce that PADT’s crack golf team made a big push, and some changes in their lineup this year, to power through and finish 7th out of 14.  That is a huge improvement from last years finish… which we shall not discuss. It looks like hiring Jonathon was a good investment for our prototyping sales efforts, and our golf game.

3D Printing, Rapid Prototyping, Additive Manufacturing? What is the Difference?

imageThe technology called 3D Printing is getting a lot of press lately. Articles like “3D Printing is the New Personal Computer” and “The New MakerBot Replicator Might Just Change Your World” are all over this place in the fall of 2012.  For those of us who have been printing 3D parts since the early 1990’s, this new frenzy can be a imagebit annoying. At every trade show that PADT goes to these days a large number of non-technical people come up and start telling us about 3D Printing and how it is going to “change everything.”  The next question is almost always “Is that a big 3D Printer?” as they point at a nice big FORTUS 400.  “Well, no, that is a digital manufacturing center, which is a rapid prototyping technology that uses similar technology to 3D Printing but it is much more precise, the material…” and by that point their eyes glaze over and they start playing with the model of the USS Enterprise we put out on the table to attract people.

By sorting through branding, media hype, and the confusing array of new low cost technologies, some clarity can be found and direction for those of us who use these technologies for product development. 

Additive Manufacturing

The first place to start is to recognize that we are talking about additive manufacturing technologies.  Taking a part definition and adding material through a variety of methods to make a physical part.  In almost every case, you build a part by adding thin layers of material one on top of another. The additive process differentiates this type of manufacturing from molding, forming, and machining – all of which remove or shape material.

The advantage of additive manufacturing is that you have very few constraints on the shape of your final part and there is no tooling, no programming, and very little manual interaction with the process.  This has huge advantages over the traditional manufacturing methods when it comes to speed.  Although you pay a price in strength, material selection, and surface finish, you can get parts quickly without a lot of effort.

Rapid Prototyping

Additive manufacturing took off in the late 80’s because it allowed engineers to make prototypes of their parts quickly and easily.  Rapidly.  And that is why for almost twenty years, most people who use additive manufacturing refer to it as rapid prototyping.  And to this day, most of the users of additive manufacturing use it for making prototypes as part of their product development process.  RP sounds better than AM, and better describes what you use the technology for rather than the technology. So that name took off and has stuck.

Other Names, Other Uses

As the technology got better, and especially as the materials got better, people started using additive manufacturing for other uses beyond making prototypes.  And, as is the way of companies that are trying to sell stuff, the manufacturers starting coining new names for the applications as users come up with them:

  • Rapid Patterns: making a part that will be used as a pattern in a downstream manufacturing process.  This is very common with jewelry in that the pattern is used in a lost-wax process for casting.  It is also used a lot with soft tooling, where the pattern is used to make a negative mold out of a soft rubber material.
  • Rapid Tooling: Making fixtures and molds using additive manufacturing. Tools can be used as patterns for forming, patterns for casting, or even for making molds for injection molding.
  • Direct Digital Manufacturing:  This is one of my favorite names and abbreviations – DDM.  The difference here is that the additive manufacturing process is used to make a final product, not just a prototype. 
  • Rapid Manufacturing: The same as Direct Digital Manufacturing, but without the alliteration.

3D Printing

According to Wikipedia the term 3D Printing was invented at MIT in 1995 when someone used an inkjet printing head to “print” a binder on to a bed of powder.  They used a printer to do their additive manufacturing, and used the term 3D Printing to describe it. By the way, they went on to form ZCorp, the second most popular additive manufacturing process in the world. 

Even though it started being used to refer to an inkjet printing based approach, the name spread over time. The term really caught on because it is so descriptive. Additive Manufacturing, and even Rapid Prototyping, do not make a lot of sense to non-engineers. 3D Printing makes sense immediately to pretty much anyone.

Those of us who are diehards really want 3D Printing to refer to lower cost, affordable devices that make lower end prototypes.  And if you look at how the name is applied by the manufacturers, that is generally how it was used.  Here is a screen shot of the Stratasys home page, and see how they split their systems into 3D Printers and 3D Production systems:

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But the name is working so well that we are seeing a shift towards refereeing to additive manufacturing as printing.  3DSystems is going full bore and as of this writing, refers to their whole line as “Printers” and differentiates them by calling them “personal, professional, and production.”

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What is Old is New Again

So it looks like the trend is towards 3D Printing becoming the new term for an old technology. And those of us who call them RP machines will have to stop doing that, or just accept that we will be met with blank stares when we do.  So next time someone comes up to tell me they just read an article in Good Housekeeping about how they will be able to make replacement parts for their dish washer in the garage with a 3D Printer, I will smile and say “That is great. In fact, we use almost all of the major 3D Printing technologies in house at PADT, and we resell the most popular 3D Printers from Stratasys, Inc.  That includes that big FORTUS 900.  It is a big and accurate 3D Printer”

PADT Medical Receives Support Award from AZBio, and Provides Awards to Others

On October 23rd, 2012 PADT was honored to receive an award at the AZBio Awards event in recognition for our support of Innovation in the Arizona Bio-Technology community.  It is a very cool little guy and is very happy on our awards shelf:

AZBio-15Years-Award-2012

In addition, we were very honored to be asked to manufacture many of the awards that were handed out.  The distinctive double-double-helix design was a big hit again this year, and it was a real honor to know that so many companies, educators, and individuals will have something PADT made in our Rapid Prototyping group on their shelf.

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Rapid Prototyping Technology Animations

Every once in a while we get asked to go out and do presentations on Rapid Prototyping. As part of that, we like to explain the four major technologies: SLA, SLS, FDM, and Polyjet. No matter how many hand gestures we use people just don’t seem to get it unless we show an animation.

So we thought it would be good to share those with the community so that they can either learn about the basics of the technology or use these to help educate others. They are crude, we are engineers and not artists.  But they get the point across. We hope to have time to update them and add text.

They are in the form of animated GIF’s, so you can put them on a website or throw them in a PowerPoint and you don’t need a viewer or special software to view them.  Click on the images to get the larger version.

Use as you see fit, just remember to mention where you found them: P – A – D – T.

FDM-Animation

PolyJet_Animation

SLA-Animation-3

SLS-Animation

PADT’s YouTube Videos for Rapid Prototyping

As we get this new blog, The RP Resource, off the ground, we thought we would start with some posting about some videos we have done in the past that people in the RP community might find useful.

We will start off with a simple slide show that shows some of the cool models we have built over  the years:

RP Part Examples Slideshow

 

Next up is one of our favorite side projects, a clock we made on our Stratasys FORTUS 400 prototyping system.  We took the design for a wooden pendulum clock and modified it to work with our FDM system.  Very cool:

PADT FDM Pendulum Clock

 

Sometimes the best way to make a prototype is not to print it, but to machine it.  In this video we show off our 3-Axis milling skills:

3-Axis Milling

Our most popular videos are HOW-To videos for working with the Dimension 3D Printers.  In the first video Mario shows how to load material in the Dimension, in the second one he shows how to do the same with a uPrint:

Loading a Stratasys Dimension Printer
Loading a Stratasys uPrint Printer

 

You can go to PADT’s YouTube page: www.youtube.com/padtinc to see more videos. And subscribe so you will know when we post a new video.

First Look: Pumpkin Launch 2012

For a couple of years now, PADT has had a tradition of shooting off pumpkin mortars on Halloween.  Originally we took dry ice, sealed it with some water in a 2 Liter bottle, put it in a tube with a pumpkin on top and “bang-whooosh” a pumpkin goes a flying.

Being engineers, we have to improve on the process… this year we used foam wadding, put cameras inside foam “pumpkins” and tried launching an ice pumpkin.  Here is the first attempt:

 

Pumpkin Launch

Look for more videos tomorrow.

Webinar Info: Getting Started with ANSYS Engineering Knowledge Manager (EKM)

imageLast Thursday (10/25/2012) Clinton Smith gave a well attended webinar sharing his experience getting the Engineering Knowledge Manager (EKM) up and running for him and how he used it on a project. As promised, the slides from that presentation and a link to the recording can be found here:

PDF of Presentation:

The Recording: https://padtincevents.webex.com/padtincevents/lsr.php?AT=pb&SP=EC&rID=5952687&rKey=eefe3ba0d2f0cbc6

Overcoming Convergence Difficulties in ANSYS Workbench Mechanical, Part II: Quick Usage of Mechanical APDL to Plot Distorted Elements

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In part I if this series, we saw how to use Newton-Raphson residual plots as an aid to vanquishing convergence difficulties in ANSYS Workbench Mechanical.  In part II, we will see how to quickly launch the ANSYS Mechanical APDL user interface to plot elements that have undergone too much distortion, thereby resulting in a convergence failure.  Several problems can cause convergence failures, but one that can be particularly frustrating is elements that have undergone too much distortion.

Currently there isn’t a way to isolate and view elements that have triggered a convergence failure due to too much distortion within the Workbench Mechanical user interface.  Fortunately we have access to the older ANSYS Mechanical APDL interface, which does allow us to select and visualize elements that have undergone too much distortion.  This can be useful in that it tells us exactly where in the model the elements are failing.  Hopefully we can use this information to take corrective action in Mechanical such as making local mesh modifications, adding more details to geometry, etc.

So, how do we do this?  Rather than try to give a lesson on how to use the Mechanical APDL interface, we’re just going to give the commands needed to be clicked with the mouse or typed in.  We’re following the K.I.S.S. principal, meaning Keep It Simple, Silly. 

The procedure to follow includes these steps:

1.  Identify the directory in which our results file resides.

2.  Launch ANSYS Mechanical APDL.

3.  Point to the results file identified in step 1.

4.  Modify the nodal coordinates so they are in the deflected state at the point of convergence failure.

5.  Plot those error-causing elements.

We will now go into more detail using a model that has convergence trouble.  This model solved successfully for the first 4 substeps, but on the 5th substep the solution failed to converge.  We get this error in the solver output (Solution Information):

*** ERROR *** CP = 2872.649 TIME= 16:29:51
One or more elements have become highly distorted. Excessive
distortion of elements is usually a symptom indicating the need for
corrective action elsewhere. Try incrementing the load more slowly
(increase the number of substeps or decrease the time step size). You
may need to improve your mesh to obtain elements with better aspect
ratios. Also consider the behavior of materials, contact pairs,
and/or constraint equations. If this message appears in the first
iteration of first substep, be sure to perform element shape checking.

Looking at the model, we see we have an indenter that is being pressed into a block of material.  The indenter is steel and the block is aluminum.  Both have nonlinear material properties defined.

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Total deformation for the last converged substep looks like this:

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The unconverged results show that we have some elements that have large nodal deflections:

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So, our error message tells us that one or more elements have become highly distorted.  Which elements are they?  The following procedure will show us how to view those for sure, using Mechanical APDL.

Here are each of the 6 steps mentioned above, in detail:

1. Identify the directory in which our results file resides:

We do this from the Workbench window, by clicking on View > Files.  Scroll down in the resulting list of files until you find file.rst, the ANSYS Result file.  The location will be listed in the resulting information, but the text is not selectable.  To make it easier, right click on the file.rst row and select Open Containing Folder. 

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From the top of the resulting Windows Explorer window, select the folder path and right click > copy. 

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2. Launch ANSYS Mechanical APDL:

Click Start > All Programs > ANSYS 14.0 > ANSYS Mechanical APDL Product Launcher.  In the resulting window, paste in the directory path in the Working Directory box:

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Click the Run button at the bottom of the window.  The Mechanical APDL user interface will start. 

3. Point to the results file identified in step 1:

Click on General Postproc on the left, then Data & File Opts.  In the resulting Data and File Options window, click on the […] button below Read single result file:

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You should see the result file, file.rst, available in the resulting window.  Click on that file, then click Open.  Click OK in the Data and File Options window.

We need to read in one set of results to load the model into the Mechanical APDL database.  Click General Postproc > Read Results > Last Set.

4. Modify the nodal coordinates so they are in the deflected state at the point of convergence failure:

Let’s plot the elements so we can see the model (this will show the elements with nodes in the original, undeflected positions).  We’ll just have you type in the command to make the element plot:  in the input line near the top of the window, type eplot, then return.

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The plot will show in the default “front” view, looking down the global Z axis.  Note that if weak springs are on in Workbench Mechanical, you will see these as line elements pointing away from the model in a few places.

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The nodal modification is performed in the preprocessor.  Click on the Preprocessor command on the left side of the window.  Type in this command in the input line to modify the nodal positions to those of the unconverged (last set) of results:

upgeom,,,,file,rst

Plot the elements again.  You should now see the deflected nodal positions.

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Using the view controls over on the right side, we can rotate and zoom in. A short cut is to use the right mouse button to box zoom and Ctrl + Right Mouse Button to rotate the model.  Now we can better see where the deformations are occurring.  We still have all elements selected and plotted, so the next step will be to filter the plot to show the error-causing elements.

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5.  Plot those error-causing elements:

Shape checking of elements consists of two levels, warning and error.  The solver will not continue if any elements exceed the error level.  Shape checking is discussed in detail in section 13.1 of the Theory Reference in the ANSYS Help.  We have the ability to plot both warning level elements and error level elements, using this procedure:

On the left side of the window, click on Meshing > Check Mesh > Individual Elm > Plot Warning/Error Messages. 

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With all boxed checked, this is the resulting plot in the front view.  “Good” elements are displayed in blue, “warning” elements in yellow, and “error” or failed elements are shown in red.image

When the elements are very highly distorted, their surfaces can’t always be displayed and it looks like there is a hole in the model.  This won’t always happen depending on how highly distorted the elements are, viewing direction, etc..

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If we uncheck the Good Elements (blue) box, then only the warning and error elements are displayed.

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When you are done viewing the elements, click on the Quit button near the top, and exit without saving to get out of Mechanical APDL.

So what does all this tell us?  For this model, the elements below the indenter body are experiencing too much deformation (red elements).  Some elements in the indenter body are at the warning level but not the error level (yellow elements).  The fix could be to apply the load more gradually (more substeps), refine the mesh at this location, or maybe a combination of both.  In this case we also changed the Workbench Mechanical shape checking from Standard to Aggressive Mechanical.

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ANSYS Penetration Model