5-axis strategy rapidly machines deep-pocketed parts

The right machining center, control, advanced 5-axis CAM software, and conical barrel-style end mills can optimize cutting efficiencies when making complex parts.

Manufacturers could slash 90% off finishing cycle times when machining deep-pocketed workpieces. This can be achieved by combining 5-axis tangent machining with conical barrel cutters. Additionally, tangential plane machining can produce excellent surface quality and longer tool life.

Aerospace Manufacturing and Design was given exclusive access to a recent seminar demonstrating this machining strategy for aerospace applications at Grob Systems in Bluffton, Ohio.

To showcase the new method, a Grob Systems G350, 5-axis horizontal machining center (HMC) used Open Mind Technologies’ hyperMILL computer-aided manufacturing (CAM) software – which enables the technique – and Emuge cutting tools adapted for the purpose.

Peter Brambs, Open Mind Technologies’ director of product innovation, explains the 5-axis machining strategy and use of conical barrel cutters. Since the barrel cutter features radii from 250mm to 1,500mm, it can be used for large step-overs. The tip on the barrel cutter can also machine corner radii, so machinists won’t need to switch cutters to finish adjacent areas such as rounded interior corners. The conical aspect of the barrel cutter allows the shank of the cutter to tilt away from deep pocket walls, thereby allowing shorter cutters. This makes it possible to use the tools on 5-axis machines with line increments from 3.0 mm to 8.0mm, instead of only 0.2mm to 0.4mm with a conventional ball-nose end mill, while achieving the same or better surface quality. Increased step-over also saves cutting time.

Five-axis machining makes it possible to cut challenging geometries, free-form surfaces, and deep cavities more efficiently, Brambs says. The CAM system generates tool paths automatically with automatic collision checking and avoidance.

The Grob G350 is compact, rigid, and offers many spindle and table configurations. The 5-axis model, with A/B table, enables single setup machining of five sides; complex, 5-axis simultaneous 3D surfaces; and multi-angled holes, forms, and profiles.

To work with the software, the machine includes acceleration-dependent, feed-forward control; a load-sensitive drive control; an optimized spindle design, drive unit, work space, and trunnion table.

The machine complements the CAM system by allowing linearized tool paths and the ability to reach programmed speeds faster with greater accuracy. While some large machines are fast only on straight lines, smaller machines can be more agile, optimizing the software’s performance.

Rapid machine movements also reduce the time spent not cutting, notes Stefan Moessmer, a Grob aerospace specialist.

The G350’s slim spindle and symmetrical milling head offers high cutting-volume rate, less interference, and retraction into a tunnel to reduce the chance of collisions. The horizontal spindle design optimizes chip disposal during pocket machining. The machining center’s chip conveyor is positioned directly below the trunnion table to speed chips away from the workpiece, toward the chip disposal at the machine’s rear.

The 31.69″ Z-axis stroke and three roller guide carriages for each guideway maximize stiffness. The tool axis (Z) damping performance is supported by having the motorized spindle guided along the Z- and X-axis, reducing vibration on tooling and the machining center.

The 15.7″ square table offers space for 5-axis machining, with part access enhanced by the A-axis tilting range of 225°.

Open Mind’s hyperMILL MAXX Machining performance package has modules for roughing, finishing, and drilling. It also enables the 5-axis tangent-plane machining strategy.

Roughing includes cycles for trochoidal tool path milling for high-performance cutting (HPC) of prismatic and curved component faces. Dynamic feed rate adjusts according to cutting conditions for maximum material removal, and algorithms remove a constant chip volume to reduce tool stresses and increase roughing speeds 20% to 70%.

The finishing module includes pre-finishing and finishing of planes and free-form surfaces with various barrel cutters. The surface finish depends on the step-over distance and barrel radius. The quality of a workpiece surface decreases as the line increment increases and improves as the tool diameter gets larger. Since the tool shank diameter can only be increased within the limits of the machine tool, barrel cutters only work with a section of the desired tool diameter – a circle segment. Larger step-over distances can be realized due to the bigger radius to achieve high-quality surface finish. The barrel cutter has single-point contact with the surface and has better cutting characteristics than swarf milling with the entire side profile of a cutter.

Managing director of Open Mind Technologies Alan Levine notes the hyperMILL MAXX Machining finishing process has been extended to other geometric shapes, such as ruled, curved surfaces.

Conical barrel cutters can machine geometry that is either too tall for efficient swarf milling or too tall for fast cutting with ball mills, such as aero-engine blisks.

In 5-axis helical drilling, holes can be machined with a forward lead angle. Tilting the angle to the side helps avoid collisions. For planes that do not need to be machined simultaneously or on large machine tools, the finishing module can also produce tool paths for 3+2 indexed machining. Only one tool is needed for different drill diameters, pre-drilling is not necessary, and the strategy supports hard-to-cut materials.

The programming process is easy by only selecting planar surfaces and having the system automatically detect boundaries, edges, and other features. Existing customers have implemented this new technique within an hour, Levine says.

Emuge Corp. circle-segment end mills, which Open Mind engineers describe as conical barrel cutters, enable more material removal with fewer passes in 5-axis machining, reducing cycle time up to 90% and providing smoother surface finishes.

Used for machining turbine blades, impellers, blisks, and in mold-making applications, the tools feature large radii in the cutting area of the mills, allowing a larger axial depth of cut during pre-finishing and finishing.

The solid-carbide end mills come in barrel-shaped, oval form, taper form, and lens shape geometries. Oval and taper form mills are for curved shapes such as blades or straight-walled pockets, engaging more of the cutting edge. Barrel shaped mills provide flank milling to the sides of spiral grooves, while lens shape mills excel in narrow channels.

Open Mind’s hyperMill CAM software computes the geometries of circle-segment end mills to achieve the tools’ design performance.

Traditional ball-nose end mills can prevent the tool from fully accessing features on workpieces. With a conical barrel cutter, the radius is ground along a cone angle relative to the cutter axis, offering better accessibility into deep pockets. Conical barrel cutters also reduce step-overs and the need to polish planar surfaces.

Path distances of 6mm and 8mm are possible, producing optimal surfaces and longer tool life. Conical barrel cutters can be applied to generalized surfaces found in landing gear, engine casings, and engine blisks.

Open Mind’s Levine points out that using standardized programming applications together with conical barrel cutters offers benefits including:

With growing pressures in aerospace to reduce production times and increase efficiency, advanced manufacturing methods can help reach those goals. The development of innovative tool paths enables cutters to perform better and faster, and using a machine optimized for the task can reduce machining times and increase tool life. These advantages offer manufacturers a better way to compete for aerospace business.

About the author: Eric Brothers is senior editor of AM&D and can be reached at 216.393.0228 or ebrothers@gie.net.

Leaders from top machine tool manufacturers discuss the future of the aerospace industry, the industrial economy, machine connectivity, and other trends at the EMO forum hosted by Kennametal.

During the EMO Hannover 2017 trade show – an event that drew more than 2,200 manufacturing technology exhibitors and 130,000 attendees – Kennametal and GIE Media, parent company of Aerospace Manufacturing & Design, gathered leaders of machine tool companies to discuss 2018’s outlook and Industry 4.0.

“We’re seeing tremendous strength in the aerospace sector, particularly with the tiered suppliers, and especially with the tiered suppliers working on engines.” — Fives Machining Systems Inc. President and CEO Steven Thiry, www.fivesgroup.com

“It’s generally a very optimistic market. Our main market outside of our domestic market in Japan is aerospace, and with a record backlog or aircraft yet to be delivered and engines to be built, we’re very optimistic. And we’re already looking forward to 2019 production because for 2018, we’re largely sold out for many of our large, application-specific machines.” — Mitsui Seiki USA CEO Robb Hudson, www.mitsuiseiki.com

“Boeing has notified its supply base at the last supplier conference that we have enough capacity to fulfill the current build rates. And Boeing now has announced that it will not go beyond the 50-to-55 planes per month build rate. There were plans to go to 60 or 70, which has trickled off.

I am not really optimistic beyond 2017 and 2018.” — Starrag Group Vice Chairman Frank Brinken, www.starrag.com

“We’re heavily focused on – and we still remain very excited and bullish – on aerospace because we feel there’s still a lot of uncertainty in the marketplace on the supply chain. It’s also very evident that around the world, defense is starting to ramp up. That’s leading to more and more specialty applications for unmanned aircraft, sophisticated surveillance equipment, improved and enhanced missile systems, and guidance technologies. — Mitsui Seiki USA CEO Robb Hudson

“Just 1% of aircraft components are made in China. If you go 15 or 20 years back, it was the same for automotive components. I have no doubt that in 5, 6, 7, 8 years, they will make 30% of aircraft components worldwide. Maybe not for Airbus or Boeing but for their own aerospace industry.” — WFL Millturn Technologies Board of Management Member Guenter Mayr, www.wfl.at/en

“Many of our machine tools that were put into the market 10 or 12 years ago, we are repurposing with newer technology to where their output is 15% to 20% more than when they were new. That’s a very different change in the industry where if you go back many years ago, when you rebuilt a piece of equipment, you brought it back to new. Today, we bring it back to beyond new because of new technologies. It’s causing many of our customers to rethink their CapEx approaches. — Fives Machining Systems Inc. President and CEO Steven Thiry

Changes to the global economy had been the cause of great concern in early 2017, but many of those worries have eased in recent months.

says the increase in global stability is improving confidence. “When you look at our customers deciding on buying an expensive piece of machinery, they need to have the confidence three and five years from now that they can fill that machine. What we’ve seen over the last six months is a renewed confidence that there’s going to be a business-friendly climate.”

Machine tool builders discussed the pros and cons of this rapidly growing market. A few highlights of the discussion include:

“Additive is here, but the question is which place in the manufacturing world will it take. It will find its place. How big it will be, nobody knows. Will it be as big as milling? No. will it be as big as EDM? Maybe.”

“Drilling, boring, milling, grinding. In 10-20 years, they’ll still be the dominant technologies. In the repair business, it makes sense to make something with additive technology, but this is a niche market.”

“A lot of the dialog is pitting additive against subtractive machining, and I think that’s wrong. The additive market is going to be a complete shift on how we design and bring products to market, how we can design new, complex parts that you couldn’t previously do. Subtractive will always win on a cost-per-piece basis. Additive is moving and progressing, but it’s going to do that by changing the entire product design-to-market process, not replacing subtractive machining.”

“It’s impossible for us to predict where additive is going to go. Because it’s changing so fast. Parts have to be redesigned before we can use this technology. That transformation takes a considerable amount of time to do. There’s absolutely room for both or for hybrids that bring both together.”

“This is an area that can only continue to expand. The more data you have, the more you can mine that data, the more you make good decisions.

In aerospace, there are a lot of constraints on how you can pull that data out and how you can access it. You can’t simply connect everything as readily as you can connect everything in your office environment.” — Fives Machining Systems Inc. President and CEO Steven Thiry

“I don’t think most companies are ready for the full IIoT solution at this stage. But they are ready to start. We have furnished thousands of adapters for machines.

Especially with aerospace manufacturing, difficult-to-cut material use is on the rise, and tool builders say that trend will only grow:

“The farther you go into (titanium and heat-resistant super alloys), the more critical it becomes to optimize not just your machine but the cutting tools and everything else involved. Working with metals like that is a lot like a racecar. A general car with a general engine goes down the road real nice, but if you want to turn in an Indy track at 200mph, it’s all got to be tuned. You can’t take an out-of-the-box piece of equipment, be it machine or cutting tool, and not optimize it if you want performance.”

“In the past, we dealt with simply programming the tool to remove the material in front of it. Now we really look at the depth of cut to make constant engagement, especially with titanium, to maximize tool life. You can go fast, you just can’t go long.”

“There is an innovation step on the tool side probably every five years. When you’re designing your machine tool to last 15 years, you have to anticipate what these guys will come up with.”

“You have to set the machines up in a particular way for nickel alloys versus titanium. A lot of customers think high-speed machining means high volumetric removal rates, and they’re not necessarily the same thing. It’s incumbent on us, together with our cutting-tool partners, to do a better job of educating the customers and manage expectations.”

This isn’t something that could be avoided. We need to embrace it and keep moving ahead.” — Mazak Corp. Chairman Brian Papke

“This data creates a lot of noise, and that noise can create a lot of distraction. If you don’t know what to focus on to prove your manufacturing processes, that noise gets in the way. So, you have to be very, very careful in what it is that you’re looking at, what you’re analyzing, and what corrective actions you’re going to put in place…

We’re facing fewer and fewer capable people at our customer sites that are able to actually act on the data they’re collecting and make sense of it.

It should fall more in the industrial control suppliers – Fanuc, Siemens – to help us standardize and come up with a standardized solution. Because if we rely upon our customers with the skills gap that we’re facing, we’re going to end up creating some severe bottlenecks in manufacturing. And instead of our customers enjoying increased spindle uptime and productivity, it’s going to drive it in the other direction.” — Mitsui Seiki USA CEO Robb Hudson

“Industry 4.0 is a great marketing vehicle. In all of our companies, we all employ a little Steve Jobs who thinks that he can create instead of a machine tool company a software house. But our main purpose is still producing parts and components and making chips. So, we as management have to be careful to divide what’s possible from what makes sense and what our customers are willing to pay us for. That’s the only thing that counts.” — Heller Group COO Manfred Maier, www.heller-us.com

“The collection of data is overwhelming. Many people are simply saying we’ll collect the data and try to figure out what to do with it. However, think about the importance for productivity to be able to find a mechanism to analyze and make good decisions. The speed and productivity of machine tools dramatically increased over the last 20 years, but I would suggest there’s a bit of a lull in performance.

Why is one machine more productive than another? Why is one operator doing more than another operator? This is where the data comes in. — Index Corp. President and CEO Tom Clark

Tolerances for many parts have shifted into the micron range, increasing machining difficulty when many manufacturers would like to increase output:

“We see machines getting more accurate, but we’re also seeing the software that goes with it getting more sophisticated.”

“There are a lot of external factors that play into process accuracy, not just machine accuracy. But you have to focus first on the machine tool. You have to make sure that you’re starting with a very good base platform, before you begin then to stack on your process, your workholding, your tooling, and then worrying about the environmental factors.”

“As accuracies get greater, your machine platform has to be better, the environment has to be better, and what you’re cutting or grinding has got to be consistent. It comes down to the entire process. You can’t have two out of the three and be successful.”

“You have to set up the machine, you have to work with the tool partner, and you demonstrate the process capability. So, it goes beyond just building an accurate machine. You are developing, together with the customers and the tool partner, a process solution for the customer.”

“The customer will expect that we also give them guidance or a clear solution on how to execute this way. Our origins are that we are machine tool builders. We aren’t software companies. All of this digitalization will be a combination between machine tools and software. No one will change from a machine tool builder into a clear software company.” — DMG MORI Executive Board Member Björn Biermann

“It’s not unlike where the PC industry was in the late ’80s and the early ’90s where you had multiple different platforms. Today, you buy a PC and they all hook together. They’ve standardized the systems. And we don’t have an industry standard. That makes it more difficult No. 1 when you’re hooking multiple machines together; and No. 2, even within given companies, one factory to another has a different system. So, we spend almost as much time looking into our customers’ systems as we spend putting systems into our machines.

Collecting the data on our equipment is not that challenging to us. It’s how do you get it hooked together and make it accessible in a common way.” — Fives Machining Systems Inc. President and CEO Steven Thiry

“Global, international companies are interested in data collection. Small companies are not interested at all. Some of them have a certain fear that they may have to pass their data to their customers.

We’re working with our biggest competitor, United Grinding, to design standards. That’s the way to develop an interface between the machine and the management information systems.” — Hardinge Grinding Vice President and Kellenberger Grinding Machines CEO Urs Baumgartner, www.hardingeus.com

“Data collection is nice, but making money out of the data is even nicer. And nobody has shown a solid business case on how we can make money out of it.

What about leased machines? Is the operator the one who owns the data? Or does it belong to the leasing company?

We see a lot of interest on the customer side. But then we say you have to pay for it, and they see it as a freebie.” — Starrag Group Vice Chairman Frank Brinken

The Pacific Northwest Aerospace Alliance (PNAA) hosts its 17th annual conference Feb. 12-15, 2018, in Greater Seattle at the Lynnwood Convention Center, 3711 196th St. SW, Lynnwood, Washington. Featuring aircraft program updates and networking opportunities with major original equipment manufacturers (OEMs) and tier suppliers, the event expects to draw more than 600 participants from 350 companies in 10 countries. Fiona McKay, PNAA’s business development director, offers the following details to potential attendees and sponsors.

FM: Our theme is Leading Through Change: Managing Transformation, focusing on technologies that enable companies to embrace innovation, optimize efficiencies, and reduce costs. Some of the technologies – automation, robotics, digital technologies, and data analytics – come under the Industry 4.0 umbrella, complementing developments in advanced materials and manufacturing. Our workshops will focus on technical and management challenges, supporting our main function of delivering market intelligence and industry insights.

FM: This is the first large aerospace conference of the year, letting attendees gather the knowledge and connections that ensure a successful 2018.

We bring executives together from across the U.S. and around the globe to share market intelligence and industry forecasts, review trends, and address global supply chain issues. The four-day event starts with factory tours and progresses to presentations and panels from leading industry players.

Attendees include C-suite and senior executives in business development, strategic planning, supply chain, and procurement. Because we’re in the heart of the aerospace cluster, we attract foreign delegations to come to network in Boeing’s backyard. B2B meetings for buyers and sellers in manufacturing offer an opportunity to establish business relationships, and our exhibit hall enables companies to showcase their products and services.

“Industry leaders make this conference a priority. They connect here, where innovation, new technologies, automation, robotics, data analytics, advanced materials, and manufacturing take flight. Companies looking to raise their level of visibility in the commercial aerospace marketplace should take advantage of attending, sponsoring, and exhibiting. They will not regret it.”

FM: We have planned a host of dynamic presenters and panels, including Dr. Kevin Michaels of AeroDynamic Advisory, who will address the transforming supply chain and changing dynamics among the OEMs. Returning attendee favorite, Richard Aboulafia of Teal Group will give the commercial aerospace forecast and share his insights. Additional speakers come from Boeing, Airbus, Dassault Systèmes, Triumph Group, Arconic, McKinsey, and Spirit AeroSystems, among others.

A special panel on industry disruptors will address global issues changing the relationship between OEMs and suppliers.

FM: It’s best to fly into Sea-Tac Airport and rent a car with a friend so you can drive in the car-pool lane, or use Uber or Lyft. We are arranging shuttle services from some of our hotel partners near Everett. Rates and details are on our website.

The only chair on an airplane without a seatbelt, lavatory structures have stringent safety requirements. Keeping passengers safe in these tiny private rooms requires extensive testing, something that has traditionally been a manual process. The Interior Systems Business of Rockwell Collins in Everett, Washington, primarily produces lavatories for commercial aircraft. Before the lavatory units can be installed in aircraft, they must be structurally tested to standards specified by the Federal Aviation Administration (FAA) in conjunction with Rockwell Collins’ customer.

“The FAA mandates a number of load cases that you have to meet,” says Jeff Whitaker, Rockwell Collins test engineering supervisor.

To test the integrity of the structures, Rockwell Collins’ test group executes a protocol that will push or pull on one or more lavatory surfaces simultaneously (see Figure 1, above). The tests ramp the force up to more than 10,000 lb max. loads, applied in different configurations by a series of hydraulic or pneumatic cylinders acting on the lavatory surfaces through mechanisms called whiffletrees, which distribute force from a single cylinder evenly across a surface through bars, poles, and linkages.

Historically, running the tests at Rockwell Collins was a very manual process, relying on the skill of a human operator who had to operate multiple hydraulic or pneumatic cylinders simultaneously.

“It could take 20 minutes to run a test, with the results recorded on a PC via LabVIEW software,” Whitaker says.

Besides being time-consuming, the human element reduced precise repeatability from one test to the next. Figure 2a (page 65) shows the forces applied by four cylinders in a typical test when run manually. The solid lines show the desired increase in force through time, while the jagged lines show the actual forces as measured by load cells on the cylinders.

The test group wanted to better control the hydraulics and settled on the idea of closed-loop control via an electronic motion controller. The advantage would be consistent and repeatable application of forces on the structure under test. In addition, selecting the right motion controller would make it much easier to operate multiple hydraulic cylinders in concert than it using the old manual system. Since the test team wanted to continue using LabVIEW, it was important to select a motion controller that easily interfaced to the PC running LabVIEW.

To fulfill these requirements, the Rockwell Collins test group selected the RMC150 8-axis motion controller from Delta Computer Systems Inc. of Battle Ground, Washington (see Figure 3, right). The motion controller gets a force feedback reading from a load cell attached to each cylinder. Precise hydraulic or pneumatic control of the force is accomplished by the Delta motion controller via proportional servo valves connecting directly to the RMC150.

During a structural test, the motion controller slowly increases the load being applied by each cylinder, holds it for 3 seconds at maximum load, and then reduces the load.

“So far, the largest number of cylinders that we’ve controlled in a single test is nine,” Whitaker says. “We can go up to 8 axes with a single RMC150, so we had to use two RMC150s for that test.”

To program and tune the motion, the Rockwell Collins team used RMCTools – development software from Delta Computer Systems. RMCTools includes Plot Manager, allowing the user to view key motion parameters in real time as the system operates (see Figure 2b, top right). This is helpful for motion tuning, as actual values obtained from the transducers can be plotted against target values generated by the motion program, to show an error that can be reduced by tuning.

“It’s easier to tell from a graphical reading that something’s wrong,” Whitaker says. “If there’s a problem, it shows up on the plot first.”

The RMCTools development package also includes graphical Tuning Wizard software which simplifies the task of setting the control loop gains for optimal operation.

“When we switch between hydraulic and pneumatic components, we use a different set of gains for the control loop parameters,” says Thor Stenfjord, Rockwell Collins test engineer. As Figure 2b shows, the force plots with Delta’s RMC150 in control allow actual forces being applied to precisely match the target forces (target and actual plot lines overlap).

“We previously depended on LabVIEW for handling data collection and control,” Whitaker says. “Now with the Delta motion controller managing the motion axes, LabVIEW is primarily used for data acquisition.”

RMCTools’ display capability is useful as an HMI during test operations, in addition to being a development environment. The Rockwell Collins test operator station includes two displays, one for the LabVIEW screen and one for motion plots the Delta software generates.

“Improved testing speed, efficiency, accuracy, and repeatability are the advantages of using closed-loop control of our test operation. With closed-loop control of the force loading system, the time required to run a typical test is reduced from 20 minutes to approximately three minutes,” Whitaker concludes.

About the author: Brad Smith, regional applications manager for Delta Computer Systems Inc., can be reached at smith@deltamotion.com or 360.254.8688.

Tom Raun, National Product Manager – Milling, Iscar Metals Inc., discusses milling challenges in aerospace.

TR: Mainly, I’m speaking of a way to modify or change the typical chip formation in a milling application. A few examples would be tools that approach the material with a shallow angle and small depth of cut (i.e., High Feed) or tools that segment (split) chips into small segments. A solid carbide end mill with a long flute length may have chip-splitting geometry to create smaller chip segments, making it easier to evacuate the chip while reducing power consumption. For tools using indexable inserts, advanced pressing and grinding techniques are used to create inserts with similar chip-splitting capability.

TR: Chip control is a must. The main aspects of chip control are chip thickness and chip evacuation. The ability to maintain the correct average chip thickness is critical for process stability and productivity. Depending on the type of cutting tool (90°, 45°, etc.), the width and/or depth of cut can affect chip thickness and the shape of the chip (length and width of chip). Another critical aspect of chip control is chip evacuation, since premature and catastrophic tool failure is almost certain if re-cutting of chips take place.

3) You mentioned High Feed tooling. What is a High Feed tool and how does it differ from the typical milling tool?

TR: High Feed tooling uses an extremely shallow depth of cut when compared to conventional milling techniques/tooling. The main idea is to achieve high material removal rates at, you guessed it, high feed rates. This is made possible by the extreme lead-angle design, which creates a much thinner chip, we must compensate for this by increasing the feed rate. High Feed tooling functions at feed rates 10x to 12x higher than typical milling tools running at conventional cutting parameters.

TR: Within the past year, Iscar has introduced a few new grades (IC882 & IC5820) for material groups of stainless steel and high-temperature alloys. The results have been 20% to 30% improvements, on average, over the old go-to grades typically applied in aerospace materials.

TR: In short, when there’s a lack of rigidity. The number one goal in any machining/milling process should be to create as rigid a scenario as possible. Of course, there are usually factors that force our hand and that reduce the rigidity of the milling process. A few examples of this would be deep cavities, tall and thin ribs, small corner radii/fillets, etc. This is when alternative cutting tools/geometries and proven programming techniques can be combined to keep productivity at a high level.

Post time: Apr-29-2019
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