The aerospace industry has some of the strictest quality requirements in all of manufacturing. Coordinate Measuring Machines (CMMs) are an essential tool for quality engineers working in aerospace because of their high accuracy and flexibility as measurement devices.
Selecting the right CMM for an aerospace application can mean the difference between your parts being delivered according to customer specifications and on time, or not. Although the search for a CMM can be a lengthy and difficult one, this article breaks the entire process down into three simple steps.
Step 1: Choose Your Model
There are four types of coordinate measuring machines: bridge, cantilever, gantry and horizontal arm.
Bridge CMMs are the workhorses of metrology: highly accurate but also flexible enough to accommodate a wide range of parts.
Gantry CMMs are for large parts: they offer similar advantages as bridge machines, but with a much greater measuring volume.
Cantilever CMMs go in the other direction: they’re more useful for small- and medium-sized parts, but they’re also typically designed to be loaded from three sides, which makes them suitable for shop floor environments with automated measurements.
Finally, horizontal arm CMMs go back to the machines’ roots: they offer the most flexibility in terms of loading, but also the least accuracy, which is why they’re most commonly used for coarser applications, such as body-in-white or sheet metal.
Depending on the manufacturer, you might find just one type or all four operating in the same plant, as Hexagon’s general manager for stational metrology devices and machine-tool measurement explains:
“I visited a customer last year who does plastics for aerospace applications, and they had two types of machines: cantilever on the shop floor and bridge CMMs in the measuring lab for higher accuracy,” says Jeorg Deller. “Another customer that makes blisks will check each one with a cantilever CMM on the shop floor and then take a percentage of them to the quality lab for more exact measurements on a bridge CMM.”
Although we’ve characterized the different models of CMM in terms of their accuracy and flexibility, it would be a mistake to think that these are opposed to one another. Accuracy is the primary advantage CMMs have over other metrology tools, and as such it should be the primary basis for your decision. If you need to measure with an accuracy of 1.5 microns, for example, then you’ll need a bridge CMM.
Step 2: Choose Your Accessories
Since high accuracy is a given for CMMs, the next step in selecting your machine is determining what your next highest priority is and what accessories you’ll need to achieve it. This can include hard configurations, software packages or—in the case of automation—both. In making this determination, it can be helpful to think about your needs today and in the long term.
“Do you have a government contract to produce the same aerospace part for the next 20 years?” asks Deller. “If so, then it’s easy to determine what you need and invest in exactly that. If that’s not clear yet because you might need more throughput or to add more features, then you should look for a machine that will be future-ready.”
A big part of being future-ready comes down to the CMM’s software and its interoperability with the rest of your manufacturing ecosystem. Traceability is crucial in aerospace, and for that reason you need your new CMM to play nicely with your CAD/CAM software, especially if you’re relying on digital twins as a cornerstone of your manufacturing process.
The other way to approach the question of what additional CMM hardware or software you need is to think in terms of retrofitting an existing machine, rather than buying a new one. Obviously, there are some cases where a retrofit won’t be enough—if you’re producing a new part that’s larger than your current machine’s measuring volume, for example. However, if your goal is just to improve accuracy, it may be worth considering an upgrade rather than purchasing a whole new machine.
“If you want to add sensors, for example, that’s where you’d come to the price/performance discussion,” says Deller. “Let’s say you have a 20-year-old machine with a touch trigger that was perfectly good for what it was, but today you need to have three high-end sensors and it was never prepared for that. In that case, you’d have to completely rebuild the machine—rewire it, put a new controller in, and so on. So, you’d have to look at the price/performance ratio to decided if it’s worth it.”
As a basic guideline, Deller suggests that if you’re within one hardware generation “more or less” and your machine is well maintained, then an upgrade might be your best option.
Step 3: Start Your Integration
When it comes to integrating a new coordinate measuring machine into your manufacturing process, there are several considerations that need to be taken into account. If the hardware configuration and software packages you’ve chosen are for automation, then you may need to connect your CMM to the rest of your production line—or at least have it set up to run overnight. In these cases, you’ll likely need a third-party integrator, although some companies, such as Hexagon, work with customers directly for product automation.
“It used to be a Wild West out there,” Deller notes, “with a lot of old-school automation using 24V input/output systems and the thousands of different BUS systems from Siemens, Beckhoff and so on. Today, we’re coming closer to a more harmonized approach with things like OPC UA: industrial standards that don’t care about what the device is connecting to at the other end.”
When downtime is as costly as it is in aerospace, the prospect of bringing in a third-party integrator to set up automated measurements may seem prohibitively expensive. However, the benefits of introducing automated measurements can be well worth the upfront cost. As an example, one Hexagon customer—Alloy Specialities—has been using a quality inspection system called Tempo that utilizes robotic loading with a CMM for one particular aerospace part. Thanks to this automation, the company can run that part 24/7 and thereby avoid a potential bottleneck from inspection.
Beyond the process integration for CMMs, aerospace manufacturers also need to consider the human side of the equation. Whether it’s a new machine or a significant upgrade to an existing one, the people who operate and program the machine will need training. Deller suggests approaching this issue from three levels:
“For the operators, they need to identify the part with something like a barcode scanner, load it, put the clamps down and press start. That’s a basic training you can do in one or two hours on-site.”
“For the programmers, we try to make the software as self-explanatory as possible, but we still need to train them on the program and the hardware, either online off-site or online on-site.”
“There’s also the broader training to understand metrology, which isn’t really dependent on the equipment you use, but it’s important to understand how you can measure the same part and get two results that are somehow both right.”
Selecting the Right CMM for Your Aerospace Application
There are other factors to take into account when shopping for a new coordinate measuring machine for aerospace applications. For example:
- What are your connectivity needs? Do you have multiple CMMs operating in different locations around the world that need to share data?
- What are your requirements for interoperability? Do you have PMI data embedded in your CAD files?
However, if you ensure that you’ve identified the right CMM model, hardware configuration software packages and determined your integration needs, you’ll be well on your way to purchasing the best coordinate measuring machine for your aerospace application.