Rugged Portable-Arm CMMs Perform on the Shop Floor

By: Louis A. Kren

Sunday, December 1, 2019

Portable CMM arms have their place in a metal stamper’s quality arsenal, enabling rapid shop-floor measurement capabilities for parts and tooling.
In metal stamping operations, inspection often can become a bottleneck, as parts and processes route to the quality lab to undergo time-consuming checks on large fixed-location coordinate measuring machines (CMMs). Balancing production and delivery demands sometimes supersedes quality inspection in the time-crunched stamping world.

But skimping on inspection, as we can imagine, has serious, and costly, consequences. Consider this true tale: A stamper supplying an automotive OEM faced a long wait for part-checking on its quality-lab CMM. Truckloads of a particular part run took to the road before a batch could be tested. More than one of those truckloads returned for more part rework, totaling $300,000, on top of raising the customer’s ire. All due to a CMM backlog.

For this and other good reasons, a portable CMM arm pays dividends. Such machines do not always replace their fixed counterparts, but definitely have their place in a metal stamper’s quality arsenal, even beyond part-quality functions. To explore the capabilities and benefits of portable-arm CMMs in stamping environments, MetalForming offers the expertise of Alex Green, 3D manufacturing Alabama/ Mississippi account manager at Faro, a provider of quality-assurance solutions.

Evolution of CMMs

Users of portable CMM arms can refine measurement data to report only tolerance-critical information deemed essential for quality and production personnel, or customers.
Introduced in the 1960s, fixed-location CMMs offered a way to capture complex geometries at high accuracy via a measurement bed, probe, computer and software to operate the probe. Limiting measurements: the range of the probe on the bed, and the probes ability to move only in three axes.

Growing from the need for more measuring and data-gathering flexibility, portable CMM arms entered the manufacturing arena, providing more portability and flexibility than a fixed CMM. These portable measurement arms determine and record the location of a probe in 3D space―calculating the exact position of the probe at each point through embedded encoders on each axis (or joint) in the arm, as explained by Faro officials―and report the results through software. The available software not only converts from various formats to enable compatibility with other CMM software employed by a manufacturer, but can even break down components into subsections for more effective inspection of individual features.

Typically offering working volumes of 4 to 12 ft. with radial reach from 2 to 6 ft., these arms primarily come in six- or seven-axis configurations depending on need. Fixed CMMs offer extreme precision, beyond that of portable CMM arms, but the two systems often are employed together to cover both rapid inspection and/or reverse engineering across a manufacturing location, and ultra-precise, extensive quality checks.

Speed Essential on the Shop Floor

Advantages of Portable-Arm CMMs

  • Measure full parts, including those with complex geometries
  • Measure on-demand, without needing to program a specific routine first
  • Operate in a variety of environments, unlike a traditional CMM that requires a temperature-controlled room
  • Transport the arm to where the part is made rather than bringing each part to a special room
  • Perform a full digital analysis and review the data at any time
  • Produce inspection reports for documentation and sharing
  • Use for die maintenance
  • Reverse engineer for part-design changes and replacement of worn or broken machine parts
  • Assure accurate positioning of fixtures
  • Gain hand-tool versatility
Production volume, a major benefit of metal stamping, enables efficient production that delivers parts in a short time frame as compared to other processes. The ability to provide quality measurements inline or close to the production process enhances that benefit, making portable CMM arms ideal in stamping operations, according to Green.

“A portable CMM arm can be taken to the line or nearby to scan a part every minute or two as a check to see if something is wrong,” he explains, noting that an automotive A-frame pillar can be scanned in about 1 minute, with perhaps another minute for data to run through the automated inspection program, yielding a 100-percent inspected part with statistical process control for every feature and every data point. “If so, the part can get a closer look at the fixed CMM. With the arm, instead of blocking and fixturing the part for a fixed-CMM scan, a user just sets it on a flat and stable surface for scanning in a fraction of the amount of time and pick up any surface deviations.”

With scanning via portable CMM arms yielding so much data, users can refine that data to report only tolerance-critical information or other data deemed essential for quality and production personnel, or customers.

Inspect Dies, Too

While many stampers expect to use a portable CMM arm for scanning parts to compare to CAD models, the equipment also enables die inspection without impacting run time.

“Users can transport the arm to the press area and the die, without using power cables (many arms feature batteries) or data cables, as scan information transmits wirelessly from the arm to the computer,” Green explains. “No wires to get in the way, with no lag in the scanning. The scan completes, and the die resumes its run.”

The CMM arm scans the die face, picking up data points no matter the material or any shiny, reflective coatings, Green reports. The scan converts from a point cloud to an STL surface file. The file then can be compared to a part file to assess the die.

“And, the saved scan can be compared to scans taken on a regular basis, perhaps every couple of months, by overlaying the scans to find differences,” explains Green. “This allows maintenance personnel to see wear patterns and hot spots. From there, personnel can identify areas perhaps 0.030 in. high or low and perform the necessary work to bring the die back to needed tolerances. Portable CMM arms make great tools for die preventive maintenance.”

Reverse Engineering Aids in Repair

Beyond inspecting parts and tooling, the reverse-engineering capabilities of portable CMM arms offer the means to adjust and repair fixtures, and produce replacement parts for machinery throughout the plant.

“Users can scan, digitize in 3D and create an STL model with one button click,” Green offers. “The model can be sent to a 3D printer to produce whatever piece is needed. This enables redesign or testing of current parts, fixtures or whatever. And, suppose that a gear on a lathe breaks. The gear can be reproduced via scanning, with the file sent to a CNC machine and produced in a quick time frame. This capability improves machine uptime throughout the plant.

“Also, fixtures must be calibrated once a year or at some set interval,” Green continues. “They can be scanned with the hard probe as an indicator to see problem areas. Suppose a tower on a fixture has been bumped and must be brought back to its needed position. Use the tip of the probe on that post, and learn that it must be adjusted a quarter of a degree. The applications are endless.

Are the Arms Rugged Enough?

Stamping operations can constitute rough environments. Can portable CMM arms handle such conditions?

“Any shop-floor use exposes the arms to environmental variables not experienced in a controlled quality-lab environment,” Green says. “Dust, humidity, temperature fluctuations and more are common on the shop floor, but the arms are built to handle that. For example, they contain temperature sensors in all axes that compensate for thermal expansion and contraction of internal components. For extreme changes, say where a bay door opens and brings in 30 F air, the Faro system in particular will alert the user that the portable CMM arm cannot compensate quickly enough for the temperature change and provide two options: continue measurements―okay for loose-tolerance parts or weldments―or wait for temperature normalization―for aerospace flight-safety components featuring tight tolerances, for example.”

And, Green says, “Faro’s newest Quantum arms are ISO-certified for contact and noncontact inspection, a rigorous analysis of how accurate a machine is in the real world. In addition, all of our arms are vibration- and drop-tested to military specifications.”

Built to function in adverse shop-floor environments, portable CMM arms provide rapid, accurate measurement and ideally complement fixed CMMs. Consider them not only for part inspection, but for tool preventive maintenance, reverse engineering and more. MF


See also: Faro Technologies Inc.

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