What makes an engineer is the ability to analyze a process that makes an excellent product—and find a cheaper way to do it. Staying competitive means always improving the process, and that was the challenge presented to Derek Anti. He is a manufacturing engineering technical specialist who improves CAM/CNC operations at Rolls-Royce Defense, Indianapolis.
“In early 2020 it was clear we needed to increase throughput through our machining centers,” he explained. “Since machining center costs are a significant expense to our business, and there are hundreds of centers throughout our company, improving throughput even by 10 percent would be significant.” A secondary problem was consumable tooling costs were too high. Rolls-Royce Defense needed a way to find more efficient processes that both reduced time and extended tool life.
If this sounds familiar, it should. Reducing machining time and improving tool life are age-old challenges for machining professionals. What is new is how Anti went about significantly improving the process, using finite element driven toolpath analysis simulation from Third Wave Systems embedded in the company’s Siemens NX design and manufacturing software.
“We did not understand enough in the machining process to correct it. We needed a better understanding when the tool met the metal,” Anti said. Using the tried-and-true method of cutting trials, consultations with tooling vendors and relying on experience and intuition was becoming expensive. Anti noted it sometimes takes between 60-80 engineer hours to fix machining problems, such as broken tools and chatter, not to mention wear and tear on the machining center itself. “It is no longer possible in today’s environment to rely on that from experienced machinists,” he said. The skill is quickly diminishing. “We needed a quicker, faster, more agile solution to solving these kinds of problems. Sometimes it takes years to prove out a machining process.”
One approach to a better understanding is analyzing the force of the tool on the workpiece, which rapidly changes over the toolpath, even when feeds and speeds are constant. Finding a way to understand those forces and optimize them meant improving cutting time and reducing tool breakage. “That is what CNC Force Optimization [techniques] do; they let you see what the tangential cutting force is as it is actually machining your part live.”
But how to do that? Enter Production Module from Third Wave Systems, Minneapolis, a machining toolpath analysis software that is driven by experimentally validated, FEA based material models, according to the developer. Third Wave Systems offers two packages, AdvantEdge and Production Module. AdvantEdge is the company’s flagship software, often used in designing cutting tools. Production Module, in contrast, is aimed at manufacturing engineers like Anti, who use tools designed by others. They neither have the time nor inclination to learn about the mathematics of finite element modeling, meshing, or numerical convergence.
What Production Module supplies is an updated machining strategy, via a G-Code program, that reduces (as much as possible) force spikes and valleys. “Force is a direct result of feed rate and toolpath,” explained Anti, along with tool geometry and workpiece material. Production Module does not alter the toolpath needed to produce a part but puts in additional constraints along the toolpath.
“What I mean by that is if you have a start point and end point for your program, and it is giving you some wacky forces in the middle, it will add additional (X, Y, Z) locations to tune the toolpath,” he explained. These are small changes, not affecting the geometry of the part, but enough to reduce sudden spikes in tangential force of the tool on the part or a sudden lack of it.
It also micro-manages the feed rate, adjusting it within the minute changes in the toolpath. This is somewhat novel, as it would be nearly impossible for a human to figure out and apply adjustments of such small changes in feed rate that would optimize the force.
Production Module adjusts many parameters, including those two. It does not affect spindle speed, so the spindle speed strategy that provides the best surface finish and avoids chatter and harmonics still has to be done by a human engineer. Anti also brought up another key point: the helix and rake angles of the cutting tool are imperative to make sure you get the right force outputs from the simulation. This is information not widely needed before now, so any user of Production Module needs to get that information from their tooling supplier. “Technical cutting tool data and the initial cutting toolpath are inputs to the simulation,” he said.
Rolls-Royce’s first test case of Production Module on a real-world problem was a controllable pitch propeller blade the company supplies to the U.S. Navy for the DDG-51 Arleigh Burke class destroyer. “Our best bang for the buck was to trial this on something that had a long run time. This was it. It had cycle times of 40-60 hours of machining per propeller on a five-axis PAMA horizontal milling machine,” Anti said. The initial goal was to reduce cycle time by 10 percent. What the project actually achieved was a 20-25 percent reduction in spindle time. “If you take something that takes 40 hours to run, and you take 25 percent and multiply that [across that product line demand], it adds up to $1 million [per year] of savings.”
Tracking consumable savings took a little more effort. Like many companies, Rolls-Royce tracks its tooling costs at the vending machine and tooling changes are prescribed in the process—say a plan that requires a change-out of a cutting insert every five parts. “In some legacy processes we are changing out inserts every two parts,” he said, or when the operator knows it has to be done. For this trial, Anti’s team ran a baseline operation without Production Module and tracked tool usage and wear.
A further concern highlights his working relationship with Third Wave Systems. With any simulation, proper inputs such as material properties are vital to an outcome that can be trusted. While Third Wave Systems has an extensive library of material properties, the concern was that Third Wave Systems had never dealt with any marine or naval products, according to Anti. The propeller blade is made of a nickel/aluminum/bronze alloy. For this trial, Third Wave Systems took a sample and measured the material properties of the propeller blade, a process they are willing to do both for their customers and to add to their library.
The test case showed that in addition to controlling forces on the part, Production Module also reduced the air gap—where the spindle is running in air before reaching the start of the process and cutting metal.
Anti projects that using toolpath analysis will eventually result in up to 40 percent spindle time savings. He also noted it is more useful in roughing operations, where tangential forces are greater, than in finishing operations.
While any user of a CAD system can use Production Module, Rolls-Royce has used the integrated Siemens NX experience for over 15 years, according to Anti. The company uses a standard process flow from CAD to post-processing and archives the program into Teamcenter. “A digital thread or digital twin concept using Siemens is well established,” he said. “The Production Module from Third Wave Systems shows up as a button in the Siemens User Interface. So, as a manufacturing engineer, I don’t have to use another software and then import geometry and export back out. I open NX and there is a little launch icon in their UI, and you have the Third Wave Systems Production Module right there.”
Vynce Paradise, director of NX CAM product development for Siemens Digital Industries Software, noted, “One of the great capabilities of the NX model-based system across CAD, CAM, CMM, and other functions that build a digital thread is the availability of the open tools that enable our partners to closely integrate their specialist solutions.” In particular, he pointed out that Third Wave Systems’ applications for material-based CAE analysis of machining processes complement NX CAM’s own advanced capabilities. “It’s good to see that our customers like Rolls-Royce Defense are realizing such high value,” he said.
For more information about Rolls-Royce, go to www.rolls-royce.com. For information on Third Wave Systems, visit www.thirdwavesys.com or call 952-832-5515. For information on Siemens Digital Industries Software, visit www.sw.siemens.com/en-US or call 800-498-5351.