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Archive for March, 2009

I’m really excited about a great new resource available to all those engineers, scientists, students, and enthusiasts out there that perhaps never got exposed to CNC machining while in their college years (like yours truly) and/or that wish to learn the basics on how to program and operate a Computer Numerical Control (CNC) milling machine.  It is a book  -actually  it’s a complete course with curriculum available for educators-  written by Charles Davis, General Manager at NEXGEN Manufacturing Systems, Inc., and is available at www. cncforengineers.com. 

On the website, you will also find information about upcoming training (4 day hands-on classes with limited enrollment offered at various locations around the country), on-site training, and educators can request information on curriculum, videos, lesson plans and PowerPoint presentations available to them, and/or how to sponsor training at their school. BTW, this book is already being used at the Massachusetts Institute of Technology (MIT). It was recently displayed at the ITEA (International Technology Education Association) Conference and received a very positive response from technical educators from around the U.S., and, although it is not exclusive of any particular kind of CAM/CAD software application,  SolidWorks 2009 files are available for completing the exercises (parasolid files also available), and is also being displayed by DS SolidWorks at all educational tradeshows.

While the book is no substitute for hands-on experience and won’t turn you into an expert machinist, it provides an excellent foundation, and is especially useful for those of us that desire to understand the CNC processes; what is doable, what goes beyond its limits, what would be too expensive to machine, what changes could be made to our design to improve its manufacturability and decrease cost, etc. Even if we never have to actually program and run a CNC machine ourselves, having some understanding of all this can greatly improve our designs.

I got my copy of this book a few days ago and I’m already reading. I plan to complement what I learn from it with a few classes at DeAnza or some other institution this fall (hopefully I’ll have reliable childcare by then). So far, it looks like an excellent book, but don’t take it from me, go and check it out yourself!

 

 

While at the partner’s pavilion during SolidWorks World 2009, I watched a very nice demo of a 3D modeling product known as SolidThinking. I must say, with my very limited knowledge of surface modeling in SolidWorks,  I was very impressed by how easy it was to create and modify all sorts of capricious shapes starting from very simple geometry and/or dragging around, pushing and pulling the already existing elements of the model. I remember thinking of it as virtual clay being shaped by an artisan. In a matter of minutes, a stylish armchair was created before my eyes, and even rendered in a nice dark brown leather texture, and positioned in the middle of a room where an invisible wall was made part of the surroundings, simply to catch the shadow of the chair as if it were really projecting on the image in the background, all to make the whole scene appear more realistic. A pair of sunglasses was also created with the greatest of ease, and modified into three different fashion styles, again making use of very simple geometry.  Amazing!

So, a bit after coming back home from  SolidWorks World, I went and downloaded a free 30 days trial version of SolidThinking from their website in order to give it a try.  I must say it is kind of easy to use, although not as easy as it looked during the demo, which is reasonable to expect from someone who has never before tried it and is used to work with SolidWorks, I guess, given that the whole interface (graphics area, tools, etc.) looks dramatically different from one application to the other, and, in general, there are also quite a few differences in how the 3D model is created.

A few quick examples of what is mentioned above:

In general, and although it also offers tools for solid modeling like prisms, spheres and such, the models you generate in SolidThinking  will be made up of  a group of NURBS surfaces. This is important to keep in mind. A model created this way may appear like a solid, but if you save it as an iges file and take it to SolidWorks, what you’ll see in your feature manager is a group of imported surfaces that make up the model.

 

As I said before, I really don’t have much knowledge on surfacing and didn’t have a lot of time to test it thoroughly, but I wonder if it’s precisely because it works with these kind of surfaces that it’s so flexible and makes it easy to shape the model practically any way you need or want to, simply by editing the surface and dragging control points, like you would for a spline.

Another big difference that takes some time to adjust to is the interface. By default, you are watching your model in four different views (Top, Front, Right and a perspective view); although you can change the layout at any time to include different views of the model.  Moving the model around is also done differently. Instead of simply dragging the model with your mouse, you have to drag while pressing a button in the graphics area. There’s one for panning and one for rotation.  I’m not sure I like it; maybe I just need to get used to it.

Also by default, you’ll be assisted by a series of grids that are there to help you place points and objects into the scene. You can define the grids, each with its own origin and spacing. It takes you by surprise at first, if you are not used to working with a grid, but it’s actually kind of useful. Having to define an origin at the beginning of many commands (like whenever generating a NURBS curve ), as well as finishing the command by pressing the spacebar also took a bit getting used to.

There is no feature manager, like in SolidWorks, but there’s something called the construction tree that keeps track of the history of your model and all the steps involved in its creation, all the curves, surfaces or parameters that have been either created or modified will be stored there and can be accessed  and modified at any time.

To tell you the truth, I find the way many of the tools in SolidThinking work both cool and confusing all at the same time.  Cool because in order to do something very similar to what we would call a sweep in SolidWorks, you don’t even need to have the profile, path and/or guide curves in touch with each other. No, you can draw one or a couple of NURB curves somewhere in one of your views, say the right view, and your profile, say a circle or ellipse, somewhere in the same right view, not even near the NURBS curves, and not even in another plane perpendicular to the curves, then use an operation called pipe or bi-rail to sweep the profile along the curves and create a cool shape.  That is so easy, it’s cool, but what’s confusing is how is it that by doing just that you end up with a shape like the one in this image, where the surface highlighted in red of this fountain pen was created by “sweeping” that green circle along a couple of curves that were drawn on the right view.  The two NURB curves on the right view should provide information about the shape of the surface as seen from the right, but what I don’t get is where does the shape as seen from the top comes from.

Rendering in SolidThinking reminds me a bit of PhotoView 360, if only because it gives nice results and is fast and easy. However, the renderer in SolidThinking allows the use of lighting and cameras, as well as a few tricks like that of the invisible wall to catch the shadows of an object or the use of panels of light to simulate the light coming from a window, for instance.

I wish I had had more time to explore the software, but all in all from what I’ve seen I think it’s a nice tool for conceptual design. I’m not so sure about how useful it may be for engineering applications, but it seems like a nice tool for the product designers to help bring their ideas out of their head and into life faster. Like I said before, it makes me think of virtual clay…

 

As some of you know, I’ve been using Twitter for a short while already. You can find me as avephoenix, if you wish to follow.  It is kind of useful at times, I suppose.  Hmmm, on second thought, don’t bother, because I may just cancel that Twitter account, anyway.

These are a couple of interesting articles that I found about the use of Twitter; just wanted to share them here and see what you think about them.

http://psychcentral.com/blog/archives/2009/02/23/the-psychology-of-twitter/

http://psychcentral.com/blog/archives/2008/09/08/does-twitter-draw-us-closer/

 Fear is one of the most powerful emotions a human being can ever experience.  It can trigger quick thoughts and actions that will help us fight back or flee from whatever situation we perceive as danger; it can be paralyzing, as well, robbing us of valuable experiences and opportunities that we may have otherwise enjoyed.  Take me for example: I used to be afraid of driving the freeway. The thought of it was so overwhelming that I avoided at all cost going anywhere that wasn’t  “local”, and even scheduled appointments with my doctor, who had his office in Mountain View,  ONLY whenever my husband was able to drive me there.  However, as careful as I always was to avoid the freeway, and given the fact that Murphy has made my home his residence, one day I ended up on I-880 just like that, and it was then that, in the midst of my panic attack, I realized that I was not afraid of the freeway, but of not knowing my way around the freeway. I was afraid of getting lost. Well, we found an easy solution for that by equipping my van with a GPS unit. My life has improved ever since! Now I get lost in style whenever the GPS takes me to the middle of a swamp and proudly declares, “You have arrived”… but at least the fear is gone.

But why did I have to tell you all this? Well, because I’m beginning to think that for many people it’s almost the same with FEA.  I’ve always been interested in simulation. I was excited to finally have access to simulation software through SolidWorks and be able to learn how to use it, but I soon became discouraged by comments I read and heard from people that didn’t consider FEA as a useful or even reliable part of design. Their idea was something like “I won’t trust results that I can’t calculate myself”, but the more I learn about how Finite Element Analysis works (not only SolidWorks Simulation), I honestly don’t see how they are going to be able to obtain results “by hand”  without the use of the finite element method or some other form of numerical method approach, or without making use of some extremely simplified mathematical model. Unfortunately, although it’s true that most practical problems  in engineering can be represented by mathematical models of the actual physical problem, and are generally governed by differential or integral equations that represent them, it is also true that due to complexities in geometry, boundary conditions, and others,  these equations can’t be solved at all without the use of numerical methods to obtain an approximate solution to the problem. The other option, of course, is to go through the loop of the build-test-build cycle as many times as necessary, but that can be expensive and time consuming, without mentioning that it doesn’t really provide the designer with much information about the behavior of the product until near the end of the process.

So, if FEA is only a way to provide a solution for the series of equations that describe the mathematical model and if those equations derive from applying exactly the same laws and theory that we would otherwise while solving the problem “by hand”, why is it that some people out there are so afraid of it?  I think it may be perhaps that, same as me and the freeway, people aren’t precisely afraid of the finite element method per se, but of “getting lost” in the Finite Element Analysis software. After all, your results are only going to be as good as your mathematical model and the input you provide, and you still need some common sense when it comes to interpreting the results of your analysis.  With this in mind, FEA software can be a great tool for design or just another way to get lost in style.

A quick example is in the following simple problem, taken from a popular engineering textbook. In the example, we have a stepped cylindrical shaft that is rigidly clamped on one end and that has a force of 1000 N applied to the opposite end.

 

I meshed the model using draft quality solid elements, and the default values for element size and tolerance.

 

Then generated a stress plot showing the normal stress in the X direction, the stress you would usually calculate using the simple formula 

 

where sigma is the normal stress, F is the force and A is the cross sectional area of the shaft at the location of interest. By using Probe to investigate the value of the stress at some node in the middle along the length of each step, I realized the results for this case are very similar to those obtained “by hand”.  

 

Notice how the value of the stress changes, however, as we approach the ends of each step and the transition between areas.

 

So then I wonder what would happen if I shortened the shaft. I created a second study using a short configuration of the model in which each step was only 0.01 m, instead of the previous 0.5 m. The diameters, fixtures and force all remained the same, and so did the quality of the mesh and even the element size and tolerance.  My results, however, didn’t match those obtained applying the same formula as before.

 

I even refined the mesh, used high quality elements and all, but the results still didn’t match.

 Then it occurred to me that the formulas we apply for the solution of this kind of problems were derived assuming, among many other things, that we were trying to figure out the stress in a section far away from the point of application of the load, because in general, the value of the stress at any point in the section is actually given by

And this value changes across the section and is very different from the average value given by the first equation. The variation is small in a section far away from the points of application of any loads, but very noticeable in the neighborhood of these points.  When the shaft gets shortened, the steps become so thin that there is no way to be far enough from the point of application of the load, so the assumption we made before doesn’t really work here.  What I wonder is what to think of the results obtained in this case by using SolidWorks Simulation.  Are these even meaningful results? Should refining the mesh even more work better in this case? Unfortunately, I will never know because I tried to refine my mesh even more and received a message saying I had insufficient memory and needed to increase the value of my elements.  I’m still very new to FEA and SolidWorks Simulation to know if there’s a different approach to this kind of problem, so if you have any ideas on this, please let me know.  I’m just excited to finally be learning about FEA.

 

Just received the news today that the proceedings from SolidWorks World 2009 are already out and available for all at www.solidworks.com/sww2009proceedings  

Notice that you will need to login to access the materials; simply use your username/email  and password that you use to sign up to the customer portal. If you don’t already have a login for the customer portal, you can create one by clicking on the login at the right top corner of the page, this will take you to the customer portal and there you can create your account.

Once you are logged in, you’ll be able to access the PowerPoint slides for all (or most) presentations,

as well as exclusive videos of the presentations, photos, podcasts, information about the exhibitors, and video of all general sessions.

This is really neat! If you attended SolidWorks World this year, then you’ll have instant access to video of ALL (or most) presentations. If you didn’t attend SolidWorks World, you’ll still have access to the videos, but you’ll be able to see only a few of them in the beginning and then more content will be added every week, over the next following months. At least, that’s I heard. These videos bring to you crystal clear what the presenter was showing on the screen, plus all the audio from the presentation.  It’s like being there!  The slides will be available for everyone, regardless of if they attended or not.

So, hurry up and take a look, download a few presentations, check out the pictures and/or upload any that you may have, and enjoy!