The Internet of Things, or IoT, is growing every day. This article starts with an encounter at the grocery store that leads to an explanation of what the IoT is and what your company should be doing to make sure you take advantage of this exciting change in how everything around us will work. Check out “My cat didn’t preheat the oven: Is your company ready for the Internet of Things?” in the PBJ TechFlash blog to learn more.
Have an idea for a product and feel like you need a prototype.Tishin Donkersley from the Arizona Tech Beat asked me over to their offices to do a short interview and share some pointers on the subject. Take a look at the result here.
While you are there, take a look around the sight. AZ Tech Beat is one of the best places to find out what is going on in the Arizona Tech Community as well as in tech in general. I especially like their gadget updates.
Metal 3D printing involves a combination of complex interacting phenomena at a range of length and time scales. In this blog post, I discuss three of these that lie at the core of the laser fusion of metals: phase changes, residual stresses and solidification structure (see Figure 1). I describe each phenomenon briefly and then why understanding it matters. In future posts I will dive deeper into each one of these areas and review what work is being done to advance our understanding of them.
Phase changes describe the transition from one phase to another, as shown in Figure 2. All phases are present in the process of laser fusion of metals. Metal in powder form (solid) is heated by means of a laser beam with spot sizes on the order of tens of microns. The powder then melts to form a melt pool (liquid) and then solidifies to form a portion of a layer of the final part (solid). During this process, there is visible gas and smoke, some of which ionizes to plasma.
The transition from powder to melt pool to solid part, as shown in Figure 3, is the essence of this process and understanding this is of vital importance. For example, if the laser fluence is too high, defects such as balling or discontinuous welds are possible and for low laser fluence, a full melt may not be obtained and thus lead to voids. Selecting the right laser, material and build parameters is thus essential to optimize the size and depth of the liquid melt pool, which in turn governs the density and structure of the final part. Finally, and this is more true of high power lasers, excessive gas and plasma generation can interfere with the incident laser fluence to reduce its effectiveness.
Residual stresses are stresses that exist in a structure after it reaches equilibrium with its environment. In the laser metal fusion process, residual stresses arise due to two related mechanisms [Mercelis & Kruth, 2006]:
- Thermal Gradient: A steep temperature gradient develops during laser heating, with higher temperatures on the surface driving expansion against the cooler underlying layers and thereby introducing thermal stresses that could lead to plastic deformation.
- Volume Shrinkage: Shrinkage in volume in the laser metal fusion process occurs due to several reasons: shrinkage from a powder to a liquid, shrinkage as the liquid itself cools, shrinkage during phase transition from liquid to solid and final shrinkage as the solid itself cools. These shrinkage events occur to a greater extent at the top layer, and reduce as one goes to lower layers.
After cooling, these two mechanisms together have the effect of creating compressive stresses on the top layers of the part, and tensile stresses on the bottom layers as shown in Figure 4. Since parts are held down by supports, these stresses could have the effect of peeling off supports from the build plate, or breaking off the supports from the part itself as shown in Figure 4. Thus, managing residual stresses is essential to ensuring a built part stays secured on the base plate and also for minimizing the amount of supports needed. A range of strategies are employed to mitigate residual stresses including laser rastering strategies, heated build plates and post-process thermal stress-relieving.
Solidification structure refers to the material structure of the resulting part that arises due to the solidification of the metal from a molten state, as is accomplished in the laser fusion of metals. It is well known that the structure of a metal alloy strongly influences its properties and further, that solidification process history has a strong influence on this structure, as does any post processing such as a thermal exposure. The wide range of materials and processing equipment in the laser metal fusion process makes it challenging to develop a cohesive theory on the nature of structure for these metals, but one approach is to study this on four length scales as shown in Figure 5. As an example, I have summarized the current understanding of each of these structures specifically for Ti-6Al-4V, which is one of the more popular alloys used in metal additive manufacturing. Of greatest interest are the macro-, meso- and microstructure, all of which influence mechanical properties of the final part. Understanding the nature of this structure, and correlating it to measured properties is a key step in certifying these materials and structures for end-use application.
Phase changes, residual stresses and solidification structure are three areas where an understanding of the fundamentals is crucial to solve problems and explore new opportunities that can accelerate the adoption of metal additive manufacturing. Over the past decade, most of this work has been, and continues to be, experimental in nature. However, in the last few years, progress has been made in deriving this understanding through simulation, but significant challenges remain, making this an exciting area of research in additive manufacturing to watch in the coming years.
- Mercelis, P., & Kruth, J. (2006). Residual stresses in selective laser sintering and selective laser melting. Rapid Prototyping Journal, 12(5), 254-265.
- Simonelli, M., Tse, Y.Y., Tuck, C., (2012) Further Understanding of Ti-6Al-4V selective laser melting using texture analysis, SFF Symposium
- King, W. E. and Anderson, A. T. and Ferencz, R. M. and Hodge, N. E. and Kamath, C. and Khairallah, S. A. and Rubenchik, A. M., (2015) Laser powder bed fusion additive manufacturing of metals; physics, computational, and materials challenges, Applied Physics Reviews, 2, 041304
Vibration induced by vortices in off shore oil rigs are a significant area of concern, and understanding them is a major area of research. In this paper, PADT’s Clinton Smith, PhD, and Tyler Smith are joined by Lubeena Rahumathulla from ANSYS, Inc. to describe how they used ANSYS FLUENT to model this situation. Get the paper here: proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=2465497
The design of semi-submersible platforms for offshore oil and gas operations requires an iterative process between early-stage design, numerical simulation, measurements, and full-scale design. Early stage designs are evaluated using numerical simulations, which are typically validated using measurements of a scaled model tested in a wave tank. Full-scale semi-submersibles present a unique challenge, because of the sheer size of the structure. Since VIV measurements of full scale structures are not possible, numerical simulation plays an important role for evaluating vortex-induced vibration (VIV) effects in the appropriate physical regime. The quantification of error in numerical simulation results is limited to verification-type studies, in which the error is reduced by converging the solution on the computational grid. The importance of grid convergence studies in this field cannot be understated, since it is the only way to judge solution accuracy in the absence of measurement data at the full scale. In this paper, a method for a grid convergence study of vortex-induced vibration (VIV) of a model scale semi-submersible platform is presented, in which solutions are obtained using the ANSYS Fluent CFD solver. Five levels of grid refinement are used, with the finest mesh acting as the reference solution for the coarser four levels. Qualitative results of vorticity, pressure and Q-criterion (vortex identification) are presented. Quantitative results such as the nominal amplitude (A/D) of the sway motion are used for judging the convergence of the solution as the grid is refined.
Direct Laser Melting systems have made fantastic improvements in the last five years or so, making 3D Printing of metal parts a reality. The accuracy and strength of the finished parts rivals cast parts in the same material, but with the advantages of Freeform Fabrication. In fact, everywhere we go, people have questions about Metal 3D Printing.
So we decided to hold a webinar to answer those questions all at once. Our manufacturing team, lead by Dhruv Bhate, PhD, will share with you what we have learned while working to develop our own metal 3D Printing capability and while consulting with many of our customers as they acquired their own systems.
If you would like to attend, or would like to receive a link to a recording of the event, please register here.
We look forward to sharing this exciting information with all of you.
There are so many aspects to numerical simulation worth talking about these days, and a lot of resources to get that information. Applications, theory, how-to, and where it fits into the business of making stuff. Here on The Focus we tend to concentrate on practical hot-to things, and the ANSYS Advantage magazine has focused on the application stories along with some how-to. What has been missing a a resource for how simulation impacts business, and how users of simulation are making other improvements in their business.
Enter “Dimensions.” This new e-publication is from the same team that does the ANSYS Blog and ANSYS Advantage, but it has a decided business slant – WAIT!!!. I know, your an engineer, the world “business” scares you. Don’t worry, this is value added info, not a bunch of fluff.
Take a look at the first issue here. I’ll be honest, I kind of opened up expecting to page through going “whatever,” “right, no one does that,” and “who cares.” But I found myself skimming all of the articles with interest, and reading a couple completely. There is some good stuff in here. LIke an interview with Airbus engineers on about the challenge they face in designing their products. Or who Whirlpool uses social networking to facilitate communication between their users around the world. There is some simulation stuff in there, like how Siemens Power leverages simulation to make better power generation products. And a lot more.
Take a look, it won’t hurt, I promise. If you want something more technical, forward the link to your boss at least.
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
- 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.
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.
- 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.
- 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.
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.
Colorado is a major contributor to the space industry, and they are quickly adopting 3D Printing to keep costs down and get to space faster. In this article, “Colorado Companies Bringing Space Costs Down to Earth” the DBJ explores how automation and 3D Printing can have a big impact on cost and schedule. Many of the companies sighted in the article are PADT customers, and PADT’s very own Norman Stucker was quoted extensively for the article.
The recent explosion of interest in 3D printing has been fascinating to engineers like myself that have been using what we call Additive Manufacturing as a standard tool for over two decades. It is easy to dismiss the interest of the general public and the media as hype and trendiness. But doing so would be a mistake. It is a big deal, but not for the reasons that most people think. “Why is 3D Printing Such a Big Deal” explains what the real power is behind 3D Printing.
This popular LinkedIn Post is a review of the things I learned at SalesConnect 2015 and how to use LinkedIn to sell more efficiently. “Successful Social Selling: What I learned at LinkedIn Sales Connect 2015” covers the overall theme of “Connect + Inspire + Transform, implementation lessons that people have learned, and the idea of the Social Selling Index, or SSI.
As our final contribution to the AZ Tech Council and PBJ’s TechFlash Column for year, we shared how “3-D Printing Hits Major Milestones in 2015.” The article give our picks for what was significant with Additive Manufacturing for the Materials, Medical, Manufacturing, Military, and Mainstream aspects of the business.
The 3-D industry had a typical year in 2015. Of course, when it comes to 3-D printing, “typical” means lots of change, growth and innovation. It’s always hard to tell which of the year’s innovations will have the biggest impact on the future, but that doesn’t take the fun out of forecasting.
PADT’s December contribution to the TechFlash column in the Phoenix Business Journal is a call to action for Arizona to step up their startup game. “Why Now is the Time for Arizona to Take the Next Step with Tech Startups” suggests the following actions:
- Work Together
- Make University IP Licensing Work
- Give Back by Taking More Risk
- Get Involved in Moving Startups Forward
- Stop Whining and Get to Work
After attending the Medica/Compamed 2015 shows in Dusseldorf, Germany, we summarized the experience in this article for the Phoenix Business Journal. As the title says, it covers “How the International Business Climate in the Medical Device Industry is Changing.” and what companies need to do to keep up with the changes.
In this, our first contribution to the AZ Tech Council and PBJ’s TechFlash column, we provide some basic advice on getting products to market faster: “5 Ways to Improve your Next Product.” The five suggestions are:
- Define requirements based on customer value
- Frontload the process with exploration and iterations
- Involve suppliers in the process
- Build in a culture of excellence and relentless pursuit of continuous improvement
- Use standardization when possible, without blocking flexibility
Suggestions and examples are given for each point.