Tooling Article

Whether called on to reverse-engineer a stamping die, digitize and inspect stamped-part surfaces, or capture the measurements of perishable die components to enable speedy machining of replacement parts, Atlas Tool Inc. has come to rely more and more on its white-light scanner. It’s used to inspect, measure and capture part and die dimensional data. Installed in 2006, the scanner, a Cognitens (Hexagon Metrology) Optigo, has proven to be ten-times more efficient than coordinate-measuring machines, according to Atlas quality manager John Watson.

Atlas quality manager John Watson, one of five at the firm trained to perform white-light scans, manipulates the three-camera Optigo RE head over the surface of a stamped automotive frame rail. Each snapshot covers an area 500 by 500 mm. He peers over his shoulder at the monitor behind him to track his progress as he moves over the surface to complete the scan, typically a 3- to 4-hr. process.

The firm, primarily a designer and manufacturer of medium- to large-sized dies to automotive OEMs and Tier One suppliers, took white-light scanning (WLS) to a new level in 2010 when it retrofitted its scanner with the Cognitens RE (reverse engineering) upgrade.

“The upgrade,” explains Watson, “captures two images with each snapshot and averages out the data to filter out much of the noise. We find that the images are extremely accurate and useful particularly when capturing measurement data at radiuses and complex curved surfaces. It triangulates everything and, rather than scanning and creating a lot of flat spots, it creates nice, continuous surfaces. And, also beneficial: it reduces the time to process cloud data by 30 percent or more.”

The RE model allows Atlas to operate the scanner in two modes—the more traditional dimensional-measurement mode, and the reverse-engineering mode. According to Hexagon Metrology literature, here are the overall benefits of the RE camera upgrade to its Optiva system:

• Offers adaptive point-cloud spacing for improved geometrical tracing in curved areas;

• Provides improved surface-data quality, creating smoother and cleaner 3D surfaces;

• Captures finer details and geometrical shapes on the target objects;

• Integrates measured feature dimensions into the generated 3D model.

Better Scans of Holes and Trim Edges

Along with its RE camera upgrade to its white-light scanner, Watson also notes software updates provided in recent years. “The most obvious benefit to the updated software,” he notes, “has been the system’s ability to process holes and trim edges when we’re scanning stamped parts to check dimensional accuracy. Triangulation during scanning can make it difficult to image features such as holes or trim edges, so oftentimes the WLS system operator would have to capture these features using several shots from different angles to gather enough data. Newer software versions have made this process much more efficient.”

Among the various screen displayed during the WLS process is this scan update (left) that shows the scan operator newly merged data (shown in orange). Screen updates show the operator the data that’s been computed, and what features need additional data, guiding him as he carefully positions the scanning head over the subject. Also shown (right) is a 3D color map of a stamped-bumper draw die, created with the WLS process. The map can be compared to original cad data for the part; green indicates dimensions within tolerance (±0.25 mm).

Scans create point clouds processed into an STL file format that then can be imported into CAD software, where designers can manipulate the data if needed. The firm designs in 3D solid models and has 12 seats of Catia and 16 seats of Unigraphics.

“Cloud data is very accurate, sometimes too accurate,” says Watson. “It picks up every little ripple and lump, too much detail for practical machining. So, our cad operators will manipulate the scan data and smooth it out to create die-machining programs.”

Machining Perishables from Scan Data

Atlas Tool works out of a 250,000-sq.-ft. building in Roseville, MI, and employs 170 people (130 on the shop floor) to turn out dies to 236 in. long that weigh as much as 140,000 lb. Asked to note any new trends in die build, Atlas vice president John Haas points to increased use of steel in new automotive dies, at the expense of iron.

“Subcomponents like posts and pads, which we used to machine from gray cast iron, now often are specified as steel,” Haas says, noting an uptick in the amount of dies being built to tackle advanced high-strength steel stampings. “Steel die components are more robust and easier to weld-repair.”

Many of the subcomponents Haas speaks of are among those typically white-light scanned, their measurement data archived.

Cloud data from the white-light scans can be too accurate for practical machining, so Atlas cad operators manipulate the data and smooth it out to create die-machining programs that are downloaded to the shop floor. Shown is a five-axis milling machine equipped with a carbide cutter to make fast work of a bumper die, of D2 tool steel.

“When our stamping customers know that particular die components will tend to wear or break, they’ll often ask us, as part of the quote, to include digitizing the part dimensional data. This allows us to quickly machine replacement parts when needed. Of course, the real benefit is that we don’t scan until the die has been proven out —after perhaps several trips back to the toolroom for fine-tuning. This way we capture the exact dimensions of the die and all of its subcomponents in the working, proven die. Compared to having to start from the original tool dimensions and rework and tryout all over again, we can shave days if not weeks off of a project’s lead time.”

WLS is “Game Changing”

The firm first learned of WLS technology in 2005 when it joined a research consortium to investigate springback analysis on advanced high-strength steels. Along with Ford, General Motors and others, Cognitens also participated in the project. “We got to know them and once we took a look at their WLS technology, we knew it was game-changing,” says Haas. “We immediately decided to invest, and now we’re close to purchasing a second system to further expand our scanning capacity.”

While Atlas doesn’t scan every die, the practice is becoming more and more popular. “A few years ago we scanned maybe 30 percent of the dies we either built ourselves or maintained for other stampers,” says Haas. Today we’re scanning more than half of the dies that come through here, and I can imagine that climbing to 80 percent or more in the next few years.”

General Motors started the recent trend toward more white-light scanning of dies, say Haas and Watson, then Chrysler and Ford followed suit. Nearly every day Watson or the four other Atlas technicians trained to operate the scanner will scan stamped panels and dies.

Scanning finished stamped parts allows Atlas to capture design modifications on current programs made to improve fitup on the assembly lines. “Typically for current automobile models, when we need to tweak a die to improve panel fitup,” Watson says, “once we get the panel to spec we’ll run a five-panel CMM study, then create a color map of the panel with the scanner. And we capture the new die surfaces as well.”

We watched Watson run a white-light scan a stamped frame rail. Prior to conducting the scan, he wiped the surface with a nonreflective coating to optimize light absorption by the scanner’s three synchronized 1.3-megapixel cameras. He then applied dozens of magnetic reflective dots to the entire workpiece surface. These serve as reference points so that the accompanying metrology software can stitch together the series of images created. Each scanned image covers a maximum area of 500 by 500 mm of the workpiece surface, comparable to some 400,000 CMM data points.

A New Application

Describing a whole new application for WLS technology, Watson describes how some customers have begun to ask him to scan the raw castings before beginning the machining process. Scan data tells them if there’s sufficient material to make the die or part.

“We find this practice becoming common when die parts have been weld-repaired,” says Watson. “The white-light scan will tell us if there’s enough weld metal there to machine the detail back to spec, or if there’s too much weld metal in an area. This situation would then prompt us to rough-machine that particular area prior to finish-machining.

“For example, in a die crash recently experienced by a customer, a wear plate fell off of the die and, when the press stroked, the plate went clear-through the pad,” Watson shares. “They weld-repaired the pad and brought it to us to machine. We scanned it first, to ensure they had deposited enough weld metal. Sure enough, we found that they needed to add another 10 mm of weld in some areas. A lot of time would have been wasted had we not done the scan and started machining immediately.” MF