Every manufactured part is not produced the same. There are slight deviations from the nominal design. Software can account for these deviations, even simulate the buildup of these deviations that lie within the tolerances inherent in the assembly process and in the piece parts themselves. A harder problem is simulating the accumulation of tolerances in assemblies composed of non-rigid parts, such as those made of sheet metal, rubber, and plastic. When dealing with individual parts, tolerance buildup is not an issue. But when it comes to assemblies—seat assemblies, dashboard assemblies—it is of vital concern.
A few years ago, Dimensional Control Systems Inc. (DCS; Troy, MI; www.3dcs.com) was awarded funding from the National Institute of Standards and Technology (NIST) to develop SOVA: stream of variation analysis. SOVA is a mathematical system for predicting the accumulated variations in assembled rigid and flexible parts influenced by material deformation. It models all the tolerances, simulates thousands of assembly builds, puts them all together, and shows for any group of parts in an assembly the gaps and variations between those parts, as well as the major contributors to a given measurement.
By removing the trial-and-error in estimating product quality and in identifying assembly problems from out-of-tolerance parts, the time for product development shrinks, especially in downstream assembly operations. It also lets engineers maximize part tolerances while controlling dimensional assembly requirements, according to John Sienkowski, new business development, for DCS. This leads to a reduction in tool rework, scrap, and warranty defects—all leading contributors to manufacturing costs.
SOVA is incorporated in 3DCS, the modeling and simulation system from DCS. 3DCS lets users model the effect of variation on an assembly, determine the robustness of the design, and test alternative tolerancing methods. (The tool can run standalone or integrated as another workbench within Catia V5 CAD.) Users statistically simulate producing “virtual assemblies.” They can then actually see the variations in the virtual assemblies. Tolerance analysis requires inputs such as geometry (from the solid model), moves (locating strategy and assembly order), tolerances (piece part and assembly), and the dimensional requirements to be analyzed. The flexibility of such non-rigid parts and assemblies are captured by FEA, which 3DCS incorporates into a Monte Carlo simulation of the assembly builds. After analysis, the outputs include standard deviation, percent out of specification, tolerance ranges, Cp, Cpk, and a histogram that displays the distribution for each measurement in the simulated build model (including whether it is in/out of spec), nominal distance of overlap, the range of variation, the specification limits of min/max variation, and the min/max variation from the simulated runs.
Engineers can click on individual measurements to see where those measure-ments appear in the solid model. Out-of-spec measurements, including clashes, show up in red. 3DCS can identify the key contributor for every measurement in a model, including the tolerance and assembly process responsible for variation. The program also gives engineers a statistical prediction as to whether the design will meet build requirements when it goes into production. By holding all tolerances in the model perfect, an engineer can move one tolerance at a time to its min/max, thereby seeing the effect of one tolerance on the whole assembly.
Alternatively, 3DCS Advanced Analyzer & Optimizer uses an equation to represent an entire assembly model. The module basically outputs a spreadsheet that lets users assess how one tolerance might affect other measurements in an assembly. Any change in a tolerance yields immediate feedback regarding the effect of that change. (The time-consuming alternative is to run and rerun the Monte Carlo simulation.) The module’s optimizer lets users apply a cost to each tolerance. An engineer can then determine the level of quality in an assembly produced on a fixed budget. Conversely, given a set of objectives, an engineer can use the optimizer to determine how much an assembly will cost. In the U.S., one seat for the base 3DCS module costs $19,000; a floating license is $24,700.
Ray of truth
Ray tracing is a 3D rendering technique that generates physically correct simulations of lighting, such as reflections and refractions. One problem: Ray tracing calculations are time-consuming. Clusters of workstations, grid computing, and multiprocessor workstations significantly reduce that compute time. So does specialized graphics processing hardware. So does optimized ray-tracing software. In all of these approaches, the goal is the same: Produce high-fidelity, highly accurate scenes in real time. From this, as with all digital design development tools, automotive engineers can better analyze product designs throughout product development with fewer prototypes. This capability becomes particularly enticing in hard-to-simulate scenes involving, say, new headlight designs or the potentially troublesome reflections from a windshield.
Mercury Computer Systems, Inc. (Chelmsford, MA; www.mc.com) has developed three chunks of software for real-time 3D ray tracing. OpenRTRT is a software development kit (SDK) so developers can incorporate real-time ray tracing in their existing 3D applications and shaders. The SDK includes an authoring/viewer tool, plus materials libraries for textures such as glass, car paint, leather, and so on. DirectViz is an extension to version 6 of Open Inventor, Mercury’s OpenGL-based 3D graphics software suite. DirectViz lets Open Inventor create 3D scenes using OpenRTRT rather than OpenGL. This lets users gain ray tracing benefits without changing application source code. Patchwork3D is the Big Kahuna for end users. This design visualization suite imports 3D CAD models from all the major CAD packages (as well as adjustable adaptive tessellations of NURBS surfaces), applies textures and lighting, and then projects interactive and realistic views for digital mockups. These mockups include flythroughs and walkthroughs, and realistic simulations of materials with texture diffusion (grain and fineness), reflectivity, transparency, and specular characteristics. Users can change the virtual lighting to analyze the virtual reflections. They can even stick labels and logos on surfaces. Patchwork3D runs on computers with the Microsoft Corp. Windows operating system and equipped with Nvidia FX (6800 and up, Quadro FX) graphic boards from Nvidia Corporation (Santa Clara, CA; www.nvidia.com). OpenRTRT and DirectViz single-developer licenses start at $7,200; cluster licenses start at $50,000. Patchwork3D licenses start at $27,000.
Free 3D sketch program
Free, powerful, and accurate CAD sketching/drafting/3D designing is here. SketchUp (www.sketchup.com), the result of an acquisition last year by Google (yes, that Google), is a 3D modeling program primarily for architect, engineering, and construction (AEC) industries, filmmakers, game developers, and the like. Actually, anybody wanting to make on their computer a quick 3D sketch of anything—and perform walkthroughs in those sketches—will find the program useful. And not to belabor the point, SketchUp is free.
SketchUp version 6 gives a peek at what “easy-to-use” 3D CAD really means. Here are some examples. Colors, lines, and text help users keep track of where they are in a design and what they are doing. Green dots show endpoints. Red dots show an edge. Cyan dots show the midpoint of an edge. Red, blue, and green lines indicate axis directions. Users can draw from two perspectives: 3D or the traditional 2D view used by draftsmen. Users can drag points and lines to the desired measurements, or just enter those measurements directly. SketchUp recognizes points or edges of interest when the cursor hovers over that particular item for a few seconds. Pressing and holding SHIFT locks that item in terms of directions and points. Moving objects and how they’re placed is based on where an object is “grabbed.” Users can create new, complex geometries by mashing multiple objects together; SketchUp will find the proper intersections between the geometries and delete the extra geometries to create new objects.
Users don’t have to create everything from scratch for their models. They can create 3D models by tracing photographs. They can also download models from Google’s 3D Warehouse, a searchable online database of objects. (Users can also upload objects to the Warehouse for safekeeping and for sharing.)
For those who want more features than are available in the free package, there is SketchUp Pro for $495. Users can export their work in a variety of major CAD and graphics formats (including 3DS, DXF, DWG, OBJ, and VRML). SketchUp Pro includes LayOut, which helps create 2D presentations from 3D creations. Users can add title blocks, callouts, photographs, and logos to those presentations, export to PDF, and give full-screen digital presentations. SketchUp runs on Microsoft Windows 2000 and XP (Vista is not yet fully supported) with Microsoft .NET 1.1. On Apple computers, SketchUp runs on Mac OS X v10.3.9 or higher (Mac OS X v10.5, also known as Leopard, isn’t supported yet, nor is Boot Camp or Parallels). Both computer systems require a video card that is 100% OpenGL compliant (and therein lies the gotcha with Windows Vista; compatible drivers are not yet available for all graphics cards).
Now for the “future-is-here” part. Sketchup can be used with Google Earth (earth.google.com), which lets users create objects (most likely buildings for starters) and incorporate them into virtual worlds based on satellite imagery, geographic information system (GIS) data, and data from public and private databases. Think “mash-ups.” Also think about anybody anywhere having a 3D modeling tool at their fingertips, and anybody anywhere merging telematics with CAD data to better understand the world they drive, play, and otherwise live in.