Foam Design Inc. of Lexington, Kentucky, builds a wide range of foam parts, including inserts for headliners used to protect against injuries in the event of a collision. Inspecting these components with a CMM was a tedious and error-prone process because of the difficulty involved in making contact with the part while not pressing down the soft material. A customer gave Steve Scrivner, quality manager for Foam Design, the idea of improving the speed and accuracy of the inspection process with a laser scanner. “The laser scanner has reduced the amount of time needed to lay out a first article from about an hour to under 20 minutes,” Scrivner said. “Just as important, the accuracy of the measurements has been substantially improved because this noncontact measurement method eliminates the danger of depressing the part surface.”
Federal Motor Vehicle Safety Standard 201 requires head- and shoulder-level trim in the cabin to protect unbelted passengers from major injuries during severe crashes and rollovers. The safety mandate requires energy-absorption capability to be an integral element of the material-selection process. The scenario is further complicated by the fact that various upper-trim components require different levels of energy absorption capability, which in turn affects part design, aesthetics and cost. All upper-vehicle interior components must be tested by impacting a 15-pound dummy shaped like a human head and traveling at 15 miles per hour. This velocity corresponds to the average velocity for the onset of severe injuries. Instruments in the dummy measure the amount of forces that are applied to the dummy and these forces must be held below maximum levels specified in the regulations.
Foam Design has 27 years of experience in foam processing and fabrication. Its customers include Honda, Raytheon Co., Panasonic, Gateway Computer, Hitachi, Boeing Co., Ford Motor Co., Mitsubishi, Porsche and General Dynamics, among others. One of the company’s major areas of business is building foam inserts for automotive headliners from STRANDFOAM polypropylene foam made by the Dow Chemical Co. STRANDFOAM is a strong, low-density, high-energy efficient polypropylene foam used in energy-absorbing automotive applications. Its unique honeycomb structure and strand orientation offers superior energy absorption with minimal displacement as well as excellent acoustical performance. Foam Design cuts planks of the material into shape with a programmable profile saw. To make thicker parts, the company laminates the planks. To produce contoured shapes, it heats the planks and puts them in a press mold.
Foam Design regularly produces new designs for automobile manufacturers that are introducing a new model or changing an existing vehicle. The manufacturer typically provides the geometry in the form of an i nternational graphics exchange specification neutral file. Foam Design’s engineers then develop a process for producing the part to the manufacturer’s specifications, including creating a program for the profile saw. During this process, they often produce prototype parts that require accurate measurement to evaluate the performance of the process. Once the engineers are satisfied, they set up the production operation and produce the first-article parts. These parts are carefully measured and compared to the manufacturer’s specifications.
The problem with using a CMM for these measurements is that the foam parts are so flexible that it’s difficult to contact the surface with a touch probe without creating an indentation that detracts from the accuracy of the measurements. In the past, Foam Design engineers tried a much less accurate optical comparator because of the difficulty of measuring a headliner without moving the material with the probe. Another problem in using a CMM to measure parts with 3-D contours is that, as the geometrical complexity grows, the number of points required for accurate measurements increases at an exponential rate. This greatly increases the amount of time needed to capture points one at a time on a CMM. "The bottom line," Scrivner says, "is that we had no proven measurement process established to fully evaluate parts until we discovered the laser scanner."
Scrivner saw the potential for overcoming these problems with laser scanning, a new technology designed to address today’s quality control and reverse-engineering challenges. Laser scanning systems work by projecting a line of laser light onto surfaces while cameras continuously triangulate the changing distance and profile of the laser line as it sweeps along, enabling the object to be accurately replicated. The laser probe computer translates the video image of the line into 3-D coordinates, providing real-time data renderings that give the operator immediate feedback on areas that might have been missed. Laser scanners are able to quickly measure large parts while generating far greater numbers of data points than probes without the need for templates or fixtures. Because there’s no contact tip on a laser scanner that must physically touch the object, the problems of depressing soft objects, measuring small details and capturing complex-free form surfaces are eliminated.
Instead of collecting points one by one, the laser scanner picks up tens of thousands of points every second. This means that reverse engineering of the most complicated parts can often be accomplished in an hour or two. Laser scanning can reverse engineer parts so complex that they would be practically impossible to measure one point at a time. Finally, the software provided with the scanner greatly simplifies the process of moving from point cloud to computer-aided design (CAD) model, making it possible to quickly generate a CAD model of the scanned part that faithfully duplicates the original part. Readily available software can be used to compare original design geometry to the actual physical part, generating an overall graduated color-error plot that shows where and by how much the surfaces deviate from the original design. This goes far beyond the dimensional checks that can be performed with touch probes on CMMs.
Scrivner evaluated a number of different laser scanners and selected the DM1620 from Laser Design Inc. This laser scanner features a line-range laser sensor that captures up to 14,400 points per second and features digital coordinate output, a class II rating for safe and easy-to-see operations and a long standoff design to prevent crashes. The scanner comes with a table with 16-in. × 20-in. × 14-in. travel, 0.00018 in. plus 0.000006 in. per in. linear accuracy, 0.000020-in. resolution and 0.00015 manual repeatability. The user can scan parts by simply moving the laser over the part. The laser line monitor provides constant field-of-view feedback to facilitate the scanning process. “I really appreciate the training and service that we got from the people at Laser Design,” Scrivner said. “They made every possible effort to help us get up and running and were extremely patient as we got acquainted with this new technology.”
Foam Design technicians now use laser scanning during the engineering process for inspecting prototypes and for measurement of first articles. In the past, they were only able to measure dimensional lines, but they can now capture the entire contour for the part. They import the resulting point cloud into the Geomagic QUALIFY Inspection software that’s provided with the laser scanner. The software automatically registers the as-built first article to the CAD model provided by the customers and highlights any differences. It provides a graphical comparison of the manufactured part vs. the CAD model, automatically performing first-article inspection, tool validation, wear analysis, object alignment, and 2-D and 3-D dimensional analysis. Reports can be generated automatically in many standard formats including Microsoft Word, PDF documents, Excel spreadsheets, customizable graphics formats or as VRML models embedded into HTML.
“First-article inspection with a laser scanning is substantially faster than with a CMM,” Scrivner says. “In the past, our technicians had to move the probe along a line to see where the part matches. Now, they can simply paint the part and perform the comparison on the computer. The time required to inspect first articles has been substantially reduced while at the same time improving the accuracy of the process. Our customers love being able to the view the as-built part on the computer screen overlayed against their design. We also see the potential to use laser scanning for inspection and reverse engineering of some of the other foam parts that we produce and we plan to begin investigating opportunities in these areas in the near future.”
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