NVision Service Reduces Airbag Cover Reverse Engineering Project By 12 Weeks
Track Seating, a stadium seating manufacturer, has improved its ability to re-use previous designs by using laser scanning to reverse engineer existing seats. The company frequently has the need to build new tooling for or make revisions to products that were designed before computer aided design (CAD) systems were available. In the past, it took weeks to capture geometrical data from the old products point-by-point with a coordinate measuring machine (CMM). More recently, the company began using a laser scanning service bureau to reverse engineer the seats. The bureaus’ scanner generates a point cloud consisting of millions of data points in minutes. This dramatically reduces the cost and time required while also generating a file that represents the contours of the seat to a much higher level of accuracy.
Track Seating, Inc. (Baltimore, MD) specializes in the design and manufacture of a full line of indoor and outdoor fixed seating. Many of these seats were designed in the 1970s when CAD systems were not available, so no computer-generated records of the designs were created. Even paper records are missing in some cases and where they exist, two-dimensional paper drawings cannot begin to define the complex three-dimensional contours used in the company’s seats. Most of these seats are blow molded and when the molds wear out, the seats need to be reverse engineered to build new molds. To redesign the seats was out of the question, so engineers came up with a mathematical definition of the existing seats for a starting point.
In the past, a CMM provided the most efficient method of re-engineering the seats. Both the CMM and the mechanical digitizer are contact devices, which means the technician must physically touch the object with a probe to record the x, y & z coordinate location of each point. This takes a lot of time, several weeks typically for a stadium seat, which raises costs issues since this process ties up a high burden rate machine. The other significant limitation posed by contact devices stems from the type of data they generate.
Since the effort of touching each coordinate location is time-consuming, the level of data collected can be less than what the designers need. Even if you scan every 5 millimeters, you can miss some detail of the surface. The graphical result of a scan with a contact device is a series of sections. Designers must generate surfaces from the sections. Although this works well enough with simple surfaces—since they can be extruded from the lines and curves—it is not effective for complex shapes such as a car seat since the area in between the sections is not a straight line. As a result, constructing CAD surfaces from scanned data is a very labor-intensive process.
When company reps first heard about laser scanning, they immediately recognized that it had the potential to substantially improve their reverse engineering process. To record the shape of a car body, the technician simply holds the laser sensor so that a line of laser light appears on the body. As the technician moves the sensor over the surface, a dedicated interface card translates the video image of the line into 3D coordinates. Real time rendering of the data gives immediate feedback. This is important because it lets the technician see areas that were missed and fill them in with another pass.
The system combines the coordinate data with the Cartesian and angular co-ordinates generated at each position of the mechanical arm. The result is a dense cloud of 3D data describing the surface of the object. When the scanning is finished, the point cloud data is converted into ASCII format and imported into CATIA. Tools within CATIA allow the designer to convert the imported data into surfaces.
Engineers at Track Seating were eager to try the new technology but recognized the company’s reverse engineering workload was too small to justify purchasing a laser scanner. They looked for a service bureau and found one operated by NVision Inc. (Wixom, MI). NVision demonstrated their knowledge and experience in laser scanning as well as a willingness to work with Track to ensure that the project met all the requirements. The company sent them a seat that needed to be reverse engineered in order to build a new blow mold tool. Track shipped the seat to NVision and after a single day’s work they emailed an IGES file with a surface model of the seat.
NVision used its Hand Held scanner, a portable laser scanner capable of capturing complex 3D geometry with a high degree of accuracy. The three sensors that make up the ModelMaker Z range capture over 23,000 points per second. The available stripe widths of 35mm, 70 mm and 140 mm ensure that there is a sensor for every application. Systems can be supplied with one, two or three sensors.
The side-mounted design makes the scanner unobtrusive and allows easy control and ergonomic handling. ModelMaker software allows data capture with the laser or hard probe without the need to remove the sensor. The scanner was recently evaluated in a series of tests by scanning a comparator gauge that provides a wide range of machined surfaces ranging from 500 microinches machined to 2 microinches lapped. The laser accurately scanned every surface on the comparator gauge except for the two smoothest, 4 microinches lapped and 2 microinches lapped.
The surface model produced by NVision was much more accurate than what Track was able to produce in the past with a CMM. Laser scanning generates the millions of points that are needed to accurately define complicated contours. It generates complete surfaces as opposed to the cross-sections produced on a CMM, eliminating the errors that are generated in patching together the cross-sections. Measurements are not affected by the operator to such a large extent because he is simply passing a beam of light over the object. The cost was substantially less than it would have cost to do the job on a CMM and dramatically more detailed.
Since the first project, Track Seating has sent NVision several existing seats when molds needed to be generated. The ability to accurately reverse-engineer has also helped save substantial amounts of engineering time in new seat design. Track recently needed to develop a new seat for a major professional football stadium. The availability of laser scanning made it possible to streamline the process by taking existing seat components and modifying them to the new design. The company sent the modified seat components to NVision, and they sent back a surface model which the company was able to use to cut production tooling. The ability to quickly and inexpensively reverse engineer existing products with laser scanning saved Track Seating substantial amounts of time and money.
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