AIA: Laser Trackers Enable Production Precision
Pico Europe (Solihull, UK) manufactures and installs automotive production lines worldwide for major manufacturers such as Ford (Dearborn, MI), Scania (Sodertalje, Sweden) and Volvo (Göteborg, Sweden).
As part of this process, Pico Europe first assembles all of the tools and stations that make up each line in the company's main manufacturing facility, where they are tested and certified. These tools are then taken apart and transported, piece-by-piece, to the customer's site, where the tools and line are reassembled, and submitted to another round of testing and certification.
Historically, Pico Europe assembled and certified its products using conventional stick micrometers, steel straight edges, optical levels, cubes and even piano wire. Not surprisingly, this approach could be time consuming and highly problematic.
For example, employing these methods, assemblers often had to move a previously installed component to position a straight edge or block. There were also occasions when a dispute would arise because the customer's panels didn't fit Pico Europe's tooling. This kind of situation could be extremely difficult to resolve, because there was no reliable method of measuring the tooling to verify its compliance to the customer's design.
To streamline and improve this process, Pico began using laser trackers from Leica Geosystems (Norcross, GA). These portable coordinate measuring machines (CMM) perform large-volume measurements using a laser interferometer, which tracks and measures the position of a target reflector to an accuracy of 10 microns per meter. Each system can measure up to 1,000 points a second and has a radial range of 35 meters.
Measurements can be made statically to a tooling hole, or they can be made dynamically for digitizing the surface of a door skin or press tool.
Typically, a tooling hole is measured using a precision-machined reflector holder that locates into the tooling hole. Once the reflector has been placed, the position of the hole is easily measured, because the dimensional relationship between the hole, reflector holder and reflector is known.
Operators use the laser trackers for a wide range of tasks, including checking each line's pre-machined tool bases for flatness. The trackers are also used to pinpoint the locations of dowels, fixing holes, and various tools and components.
After an assembly has been certified, tested and shipped to the customer's production site, each tool is positioned into its correct place, and engineers establish level datums at each end of the line. The laser trackers are then used to level and measure the alignment and spacing of the tools as they are installed.
The laser trackers are also used to perform repeatability and reproducibility studies on tooling. These types of measurements often require up to 30 relocation cycles. In preparation, operators will temporarily bond as many as eight reflectors to a panel, with the reflector positions spread evenly over the panel surface. They will then locate and clamp the panel into its position on the tooling, and measure the position of the various reflectors. The coordinates from this first measurement cycle become the reference coordinates for all other measurement cycles.
For the second and all subsequent cycles, operators employ auto-inspect software, which automatically directs the laser beam to the appropriate reference positions. Using this software, it is possible to perform a 30-cycle study in as little as 30 minutes.
For more on laser tracking on the production floor, call 920-906-7514 or visit www.leica-geosystems.com.