Are you using a giant coordinate measurement machine for inspection?
A Tech Briefs reader asked an industry expert if they should switch to laser radar…or just add a laser to their “CMM."
A CMM is one of a few choices for a manufacturer looking to make sure that components are being built to required tolerances and specifications.
On a production line, you mainly have two metrology options: offline or on-line.
Off-Line Metrology Tools
An offline CMM uses arms, trackers, and manual metrology meters to inspect parts, like underbody components and closures, for example.
Paul Lightowler, a product Manager at the Brighton, MI-based laser-radar manufacturer Nikon Metrology, believes the coordinate measuring machines are valuable, but also have drawbacks, due to their placement off-site.
"They provide a good gold standard," Paul Lightowler told attendees in a Tech Briefs webinar titled Reducing the Cost of Quality in Automotive BiW.
But you have to bring the part off the production line, to a CMM room. The areas can become overloaded with bad parts, creating a potential bottleneck.
"You either have to have a lot of CMMs, or you have to have very long shifts," Lightowler told the audience. "If there's a problem on the production line, then everything else has to stop and you have to move and try to get measurements into the CMM room to make decisions and get feedback on what's actually going on."
In-Line Metrology Tools
Another, in-line, metrology option removes the need for an extra room and integrates the the metrology into the production line, measuring parts as they are manufactured.
The high-resolution, fixed sensors have a fast, "go/no-go" way of measuring specifications.
The well-known sensor option, however, also has its disadvantages, says Lightowler. The in-line sensors are "relative" systems that only provide information in the context of its spot on the production line.
In other words, in-line metrology can tell you where a particular feature is, but it can't detect where a feature is relative to another feature.
"It cannot tell you where that feature is in a XYZ coordinate of the car body," said Lightowler. "It can only tell if it has moved from when you last made it."
An alternative option combines both in-line and off-line ideas: Laser radar.
Laser radar uses a long-range optical probe (a laser beam) to take measurements on the shopfloor. The tool's contactless measurements are performed on a variety of surfaces, including bare body panels and painted surfaces.
The radars can be installed on a standard 6-axis robot arm. The robot automatically positions the laser radar so it can then inspect areas otherwise hidden from the line of sight. The laser radar then automatically measures alignment points and features, such as holes, slots, pins, and studs.
Two laser radars, like the ones shown in the above image, can measure 700 features on a BIW vehicle in less than one hour, according to Nikon Metrology.
Some manufacturers, however, are mounting a laser scanner on their existing machines. Can that option work just fine?
An attendee had the following question for Lightowler:
"You mentioned that CMMs are slow to measure, but there is a general move toward laser scanning, which improves the speed of data collection with the same hardware. Doesn't that reduce the advantages of a laser radar solution?"
Read Lightowler's response below.
Paul Lightowler: To a certain extent, yes. To a certain extent, no.
A traditional CMM, if we think about it, is a touch probing system. Touch probing systems are relatively slow. You have to move the probe into the feature. You have to move it, take a point, move it again, take another point — it can take a very long time to measure each feature with the touch probing.
This is where the development of laser line scanners sort of helps. They've been around for many years, but they've not been as successful, if you like, in automotive as a lot of the companies wanted them to be. They've been taken up, and they can greatly improve the speed of those measurements.
From our own experience, typically what we see is that laser scanners can halve the time of those measurements, or double the speed, if you like. That is one way of increasing your measurement speed and decreasing measurement time.
But a laser radar can [perform] 6 times faster than a CMM, so we're still three times faster potentially than a CMM with a scanner on it.
If you don't want to invest into a new CMM, a scanner is a great way of upgrading your CMM. But if you need to replace your CMM, then you have to ask: "Do you want to replace it with another CMM, with the disadvantages, or do you want to look at something new, which could be a laser radar system, which gives you an even greater speed?"
Are you using CMMs? In-line sensors? Would you use laser radar? Send your questions and comments below.