Mold to big to move? Portable CMM solves QC problem.

Measuring large automotive molds for quality certification can be a daunting task. Just try squeezing 30 tons worth of tooling onto a coordinate-measuring-machine (CMM) platform. Or consider the cost impact of tying up a milling machine for measurement duties. Proper Mold and Engineering Inc., a moldmaker in Warren, Mich., recently found a way around these difficulties when it adopted a six-axis, portable measurement arm from Faro Technologies Inc., Lake Mary, Fla.

With a 30-lb "FaroArm" in hand, Proper Mold's quality technicians have halved the time they spend measuring fascia molds and other large tools - both on their own shop floor and at customers' molding sites. And they've done so while maintaining the accuracy - often tighter than 0.25 mm - required for automotive tooling.

To get the reach and flexibility needed to get inside large molds, Proper Mold bought an 8-ft Silver Series arm with six axes of rotation: two axes at the base, two at the arm's elbow, and two at the wrist. The arm can fold back on itself at the middle joint, letting the operator reach into the mold's cavity and around and under the various components. Certified to ANSI B89 standards, the model used by Proper Mold has an accuracy of [+ or -]0.076 mm (single point, 2 sigma) throughout its working envelope, according to Dan Perreault, Faro's director of installation and applications.

Too big for CMMs

Proper Mold first turned to the portable arm because some of its molds were too big for its CMMs. "Each half of a fascia mold can weigh as much as 60,000 lb, which is too heavy and sometimes too large for our traditional CMMs," explains Keith Huck, managing associate for quality and training.

As an alternative to conventional CMMs, Proper Mold had previously used one of its large milling machines to inspect fascia molds and other large tools. "The procedure was time consuming, and it tied up a mill for a few days," says Huck.

Software streamlines job

Most of Proper Mold's work with the FaroArm involves CAD-to-part inspection - or comparing the actual mold to a customer's CAD file. More than just showing customers that a finished tool was "built to print," the inspections also reveal any flaws in the customer's tool design.

For example, the company recently used its portable arm to find out why a black rub strip in a rear fascia was not snapping into place properly. "It was a tight squeeze to get the strip in place," CMM operator Steve Carbary recalls.

He began the mold inspection by importing the customer's surface model of the part into AnthroCAM, Faro's 3-D AutoCAD-based software for inspection and reverse engineering.

Next, Carbary chose the surfaces he would need to measure, identified the necessary measurement points on the CAD model, and saved their nominal values, which he could then retrieve on the shop floor. By preplanning the inspection routine in this way, he cut the time spent measuring the mold from eight hours to four.

During the actual inspection, AnthroCAM showed the selected points directly on the CAD model and guided Carbary to each target point through the software's "home-in" function. Because each target point had a tolerance zone that he specified in advance, he needed only to move the probe to the zone to measure the point.

AnthroCAM compared the measured points to the CAD nominal surface and displayed the nominal and measured values along with the deviation from nominal and any out-of-tolerance value for each measured feature - all in real time.

In checking the relationship between the rub strip and fascia, Carbary found that the clearance was too small for the two pieces to mate properly. "Based on these findings," reports Huck, "we recommended welding the mold to add the necessary clearance and updating the electronic data to document the change. Once manufacturing made the repair, we rechecked the mold with the FaroArm to make sure that the alteration matched the new design."