Gear performance may sound like a simple concept at face value, but many variables can adversely affect a gear if not accounted for in the design stages. Many of those variables occur in the part’s surface shape and surface texture.
To interpret the details of a surface, it sometimes takes a company that can look beyond the numbers and take it to the next level. Enter Digital Metrology Solutions, who has been up to this challenge for more than 20 years.
“Everything about gear performance is related to surfaces, and the shape of these surfaces: roughness, waviness, form,” said Mark Malburg, president of Digital Metrology Solutions. “It’s all related to surface geometry. For example, in today’s context, gear noise is in front of everybody’s mind. Cars go electric, and we can hear everything now. That is all hiding in the gear’s surface texture.”
Predicting gear noise
Recently, Malburg worked with Caterpillar to develop software to support their patented approach for predicting gear noise. The software embodies adaptive mathematics for detecting the waves in a gear tooth, which are responsible for causing problems and noise.
Although Malburg’s experience with gears is extensive, he points out that the gear industry is actually moving slower than other industries when it comes to surface texture.
“In gears, we’ve generally seen people make surfaces smoother and smoother. In doing so, many have actually lost touch of some things like waviness,” he said. “Some of the highly polished gears I’m seeing, for example racing gears, are striving for shiny. They’re not realizing that they look nice, and they may be inside the profile tolerance, but there are waves that are being missed within the tolerance. Other industries have solved that or have addressed that and are already aware of that.”
In many ways, Malburg said Digital Metrology is building toolboxes to lead the evolution of the gear industry.
“Some of the work we are doing in gear profile analysis is based on work that we’ve done in roller bearings many years ago, but it’s leading edge in gear analysis,” he said. “As the gear industry is evolving, Digital Metrology is staying in front because of our work in other industries.”
Surface – not just a number
Malburg considers it Digital Metrology’s mission to help people understand that a surface isn’t just a number.
“That’s been really key as any industry evolves,” he said. “If you’re trying to improve a gear, or any other surface for that matter, it’s not just the roughness number that matters. It’s a shape we’re trying to deal with, and that shape has many aspects. Is it lumpy or fuzzy? Are there distinct peaks or bumps? These are aspects of a surface that are not easily captured in a single number. The understanding of surface shapes has been very, very key to any industry that has improved the performance of their surfaces. The cylinder bore of an engine has improved not because the roughness number has gotten better. In fact, the roughness number hasn’t really changed over time. But the shape or ‘picture’ of the surface is very different now. Similarly, two gears may have the same roughness numbers but very different shapes and performances. And that’s where we’re learning. We are developing better tools to simulate things. There are new mathematics that simulate contact stress better. We can even build these analyses right into a shop-floor roughness gauge. Our tools are evolving, along with gear evolution. And, it’s great to connect the two.”
Getting the raw data
When it comes to analyzing and solving problems, data is the raw material.
“When Digital Metrology is called in, the first thing we will need is raw data from the surfaces,” he said. “We look at profiles in digital form and 3D surfaces in digital form. With customer’s measured data and Digital Metrology’s software, we can start manipulating the surfaces and start finding surface features that relate to gear performance. A customer will approach me with, ‘These two parts are functioning differently. What’s different about them? Or perhaps Supplier A and Supplier B both meet specs, but only Supplier A’s parts are working. What’s the difference, because they both meet the print? Or we’ve got a new failure. We’ve tried to get more performance out of a gear, and it’s fretting, spalling, vibrating, or wearing.’ People approach us with parts that have a performance issue that can’t be measured or an improvement that they want to be able to measure. It’s always a measurement challenge.”
As an example, Malburg brought up an early project with gears that were historically noisy.
“There was a notorious pickup truck engine. It was so noisy that when you went to a drive-through window, you had to turn off the engine to speak into the speaker. It wasn’t combustion noise; it was gear noise,” he said. “That problem went on for years. Looking at the gear tooth profiles, everything met print. The K-charts were good. The roughness was good, the pitch, everything was good. However, hiding inside the surface, were bumps in the waviness profile. In fact, the number of bumps, combined with the teeth, directly correlated to the frequency of the noise. Furthermore, the height of the bumps was directly related to the amount of noise being experienced in the field.”
Simplifying the complex
Malburg says one of his company’s strengths is taking complex ideas and making them conceptually easier to understand and apply to real world problems.
“For example, simulating how a gasket will seal a surface,” he said. “You’ve made a surface, and we want to know if it’ll seal without putting a gasket on it. We can do that with surface measurements, in real time, right on the gauge. The same is true with the gear tooth; we can detect the critical bumps that are going to cause stress or noise. For Digital Metrology, as we are developing tools, the ‘win’ is where we can take something mathematically difficult or complex and turn it into a tool that you, and perhaps even your kids, can understand. Sometimes when we solve customer problems, it requires some crazy mathematical concepts and perhaps some computing power. The ‘win’ is when we can break that concept down to a description that anyone can understand and anyone can use as part of their job in creating and controlling their surfaces.”
Necessary roughness
Some texture is typically required to carry lubrication on interfaces, according to Malburg.
“I see so many so-called ‘high-performance’ gears being made smoother and smoother. It is as if people are trying to say, ‘Let’s make them smooth because smooth looks sexy.’ Unfortunately, many of these surfaces do not last long. There’s no lubrication,” he said. “The idea today of making them shinier is dangerous.”
“We’ve got to work on pictures and shapes, not just the value of Ra (roughness average). Using Ra alone is like coming home from a concert and saying it was the best show you’ve ever been to because it was 105 decibels. Decibels describe a concert much like the Ra describes a surface,” he said. “We need reliable measurements and great software to extract and display what really matters.”
That ideology circles back to Malburg’s working theme of surface measurement.
“My world is not easily a world of numbers; it’s a world of shapes,” he said. “I usually start my training with a 3D model of the Earth, and I say, ‘Can you describe this with a number?’ There is no single number that describes the shape of the world. That is the same as the shape of a gear tooth.”
“I see gears moving a little bit more toward where bearings are going today. In the bearing industry, we see a lot of emphasis on surface stresses, lubrication, and noise,” he said. “I think the same general concerns are at play in the gear field. We need to understand and control surface contacts, stresses, and lubrication. We need to manage the balance between too rough and too smooth. There needs to be a keen awareness and diligent control of waviness. Smoother isn’t necessarily better.”
21 years of Digital Metrology Solutions
Digital Metrology Solutions has been helping companies solve problems related to surface shape and texture for 21 years.
“If you’ve read or listened to any of Start with Why by Simon Sinek, I found that fascinating because it really hit home with me,” he said. “My ‘why’ is to help people have light bulbs turn on. I enjoy teaching. I enjoy helping people learn. The software tools we develop enhance that. The tag line at digitalmetrology.com is ‘Understanding Beyond Measure.’ It’s all about helping people understand. That’s what everything we do is really about — whether it’s consulting, custom software, off-the-shelf software, or training. It’s helping people understand what they have and how they can make it better.”
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