The use of a laser scanner instead of a coordinate measuring machine reduced the time needed to reverse engineer an instrument panel section by 12 weeks while improving accuracy. The automobile original equipment manufacturer (OEM) wanted to make changes to the part geometry and material but the computer aided design (CAD) data originally used to define the part was no longer available. In addition, the part was too flexible to measure with a coordinate measuring machine (CMM) and the alternative of measuring the mold would have made it very difficult to account for the different shrinkage factor of the new materials. Instead, the mold builder, Hunt Machine of Talmadge, Ohio, sent the part to NVision, Inc.(Coppell, Texas; Detroit, MI) , which used a ModelMaker laser scanner to produce a surface model of the part that was accurate to a few thousandths. The mold builder then made the modifications requested by the OEM, produced several rapid prototypes for verification, and finally designed a new mold with the correct shrinkage factors for the new material. "The use of laser scanning made it possible to reverse engineer this part to a high level of accuracy while saving a huge amount of time," said Dave Hunt, President of Hunt Machine.

Hunt Machine and Manufacturing, a custom mold builder located in Northeast Ohio, has been producing injection and compression molds of an exceptional quality since 1952. The company's lengthy experience in creating molds for a variety of industries, coupled with timely deliveries and extensive design experience, has allowed it to enjoy a leadership position in the markets it serves. Hunt Machine's 40,000 square foot manufacturing facility has been expanded numerous times to house the latest in computer- integrated mold manufacturing equipment. Hunt Machine and Manufacturing molds have produced plastic, rubber and wood fiber products for internationally recognized leaders in the automotive, housewares, recreation, and construction industries. Whether prototype or production, single or multiple cavity, single or multiple molds, repair or new mold program, Hunt Machine has the equipment and facilities to meet any mold building need.

Lack Of Historical Data
Recent, a tier one automotive supplier asked Hunt to build a mold to produce an enhanced version of an existing interior trim component that sits on the top of the airbag module in an instrument panel. "The challenge came from the fact that we were given this task without any historical data that anyone felt comfortable with," Hunt said. The part has been in production for about five years. The company that built the original tooling had taken some CAD data and combined it with pattern makers' models to make the original mold. Both the models and the CAD data are no longer available. In addition, some subsequent changes were made to the part for which documentation is not available. The part was so soft and flexible that it would have been impossible to use a contact measurement method to determine its geometry. It would have been possible to measure the mold using a contact measurement method but this would have created the challenge of somehow backing out the shrinkage allowance for the original material and adding the shrinkage allowance for the new material. Another problem with using a CMM is that it measures points one at a time so it would have taken a long time to collect enough points to reproduce the contoured geometry of the instrument panel component. In addition, there were intricate cursive graphics on the part that would have been nearly impossible to reproduce using a CMM.

Hunt looked for an alternative method of digitizing the part. "We talked to many different people and tried several alternative technologies," he said. "I was particularly impressed by the technology of laser scanning which offers the advantage of not requiring contact with the part surface and generating a much denser point cloud than a CMM." Laser scanners work by projecting laser light onto surfaces, while cameras continuously triangulate the changing distance and profile of the laser as it sweeps along, enabling the object to be accurately replicated. "I was particularly impressed with the NVision people," Hunt continued. "They seemed to have the best technology and the deepest talent." NVision ModelMaker scanners work on the principle of laser stripe triangulation. The Modelmaker system captures surface shape in real time at over 23,000 points per second.

Reverse Engineering By Laser
"We reconstructed the instrument panel in our facility so we could mount the part exactly as it would be in a vehicle," said Bill Bonner, Director of Sales and Consulting for NVision. "We scanned all sides of the part with our ModelMaker W70 in only one day." The ModelMaker mounts to a portable CMM, allowing the technician to capture data rapidly and with a high degree of resolution. As the technician moves the sensor over the surface of the part, a dedicated PCI interface card translates the video image of the line into 3D coordinates. This creates a dense cloud of 3D data describing the surface of the part. The result was a point cloud consisting of over 1,000,000 points. They separately scanned the lettering using ModelMaker W35 scanner which has even tighter resolution with a 50 by 35 millimeter scan range. NVision used SDRC's Surfacer software to automatically generate surfaces through the point cloud. On the most critical front surface, they used the UV blend method which builds the surface from cross- sections in both the x and y direction.

Hunt Machine provided the resulting CAD file to a design firm that converted it to Pro/ENGINEER CAD format, performed modifications requested by the customer and provided an IGES surface model file to Hunt Machine. Hunt Machine engineers read the file into their Unigraphics CAD system, converted the surface model to a solid model and produced a prototype using a stereolithography system. The customer examined the prototype and request several additional modifications. The goal of these changes was to improve the fit of the part with the rest of the instrument panel. Hunt Machine made these modifications and provided a new prototype. The customer said they were happy and Hunt Machine engineers then began the process of designing the mold to produce the new design. "We took the solid model that was approved by the customer and applied shrinkage factors to it," Hunt said. "This was complicated by the fact that shrinkage for the new material was not constant across the different axes of the mold. We also changed the design of the lifters and slides in order to make the mold less expensive to build and run faster in production."

"Laser scanning provided substantial time savings while also improving accuracy on this job," Hunt concluded. "We prepared an estimated timeline for this project using traditional CMM methods and using laser scanning. It showed it would have taken 28 weeks to do the job using CMM compared to the 16 weeks that was actually required with laser scanning. The main reason for the improvement is that laser scanning generates a highly detailed point cloud in minimal time while with a CMM points must be laboriously collected one by one. The fact that the CMM measurements would have had to be taken on the mold while we were able to scan the actual part also saved considerable time. Another advantage was that we were able to produce a more accurate mold because the million-plus points generated in laser scanning made it possible to produce a solid model that accurately reflected the contours of the part."

For more information, contact NVision, Inc.:

417 Forest Ridge Drive, Suite 3, Coppell, Texas 75019. Phone: 972.745.8444. Fax: 972.745.0285 . Web site: www.nvision3d.com, Email: Email Contact

William Bonner, Director of Sales and Consulting, NVision, Inc., 28265 Beck Rd., Ste C22, Wixom, MI 48393. Direct: 248.444.2900, Fax:248.769.6079, Office: 248.468.2525, Email: Email Contact.

Visit NVision's Web site at www.nvision3d.com