Power Tools Help Small Bone MIS Continue to Grow - burrs tool

When it comes to the overall manufacturing process, optimized roughing can typically remove 90 to 95 per cent of the rough stock on a workpiece. This leaves only about 1 to 2 per cent of the tool diameter as finish stock for removal.

Overall cycle time is dependent on the part. If a part is near-net forged, for example, it will not require as much roughing as a solid block will. Another example is a mould cavity: It requires much more time to be spent in the finishing stage rather than the roughing stage because a smooth 3-D finish is required.

Optimized roughing uses a large DOC and light radial engagement to maximize metal removal rates. Photo courtesy of Seco Tools.

The best use of the optimized roughing technique is in situations that can use the full flute length of the tool, such as roughing long, straight walls. Photo courtesy of Seco Tools.

LONDON—On Wednesday, Jaguar Racing became the latest Formula E team to unveil its race car for the coming season. The sport has radical new technical rules for its third-generation race car, which is smaller, lighter, more powerful, and more efficient. This will be the British automaker's sixth season competing in the series, and its participation is for more than just marketing; Jaguar Land Rover's electrified road cars have benefited in tangible ways as a result, according to the team's technical manager, Phil Charles.

Easily access valuable industry resources now with full access to the digital edition of Canadian Fabricating & Welding.

2. Understand the power of CAM. It is impossible to program an optimized roughing strategy manually. You need to use a programming software package that will control the cutting strategy. But not just any programming software will work; it needs to be the right software for this application. A program designed only for high-speed side milling will not perform optimized roughing.

For the optimized roughing operation to be successful, a constant radial DOC must be maintained. This radial DOC also depends on the material being cut. For example, superalloys can have a radial DOC that is 5 to 7 per cent of the tool diameter, while tool steel under 50 HRC can use 7 to 10 per cent of the tool’s diameter as the radial DOC value.

"If you rewind back to 2017, that's the first time that [we used] our in-house inverter for the racing team," Charles told Ars. "We put a silicon carbide switching device, the Wolfspeed one actually... that gave us the ability to switch super fast. That was the push on our side—we want to switch faster and see if that can give us efficiency, which it did. So we've gotten over and over and over during these inverter development cycles, switching faster and faster and faster," he said.

Keep up to date with the latest news, events, and technology for all things metal from our pair of monthly magazines written specifically for Canadian manufacturers!

Optimized roughing is not for every part; it’s very component driven. If a part is a complex, 3-D component, optimized roughing is not going to be the most efficient way to get the highest metal removal rate during the roughing stage. When it can be employed, however, it can have a significant effect on cycle times.

“With any solid-carbide application in which you are trying to hold tight tolerances, the holders can make you or break you,” said Ball. “If you try to run these strategies and these processes in a collet that is not rigid or doesn’t contain the runout, you will struggle to achieve the metal removal rate and cycle time reduction this strategy can provide.”

"You've got so many big changes in the systems, that that's a big integration problem even if you had a long time. We've got quite short time; racing doesn't stop, the seasons keep coming, and you've got to send the car out. So it's a really compressed and tight schedule to deliver a really ambitious step-change across all the systems on the car," Charles told Ars.

An example of one of those lessons was the need to shield electronic components. "As you switch faster, the EMI that's given off from those switching devices gets more and more and more, and you start turning off your other systems on the racecar," Charles explained. "So we did lots of technical coatings in the first unit, very simple mechanical things to start with, where we tried to stop those components, the EMI getting outside of the inverter," he continued.

Today’s advanced optimized roughing is only effective if implemented properly. And while similar in nature to other strategies, optimized roughing entails specific best practices that shops must adhere to and common missteps they must avoid to achieve optimum results.

1. Use the right machine. Machines used for optimized roughing need two things: fast spindles and rigidity. The spindles must generate the necessary revolutions per minute for optimized roughing’s feed rates. The rigidity of the machine minimizes vibration and contributes to part quality.

Formula E's Gen3 race car has been an ambitious leap forward compared to the car that retired at the end of this season. The rear electric motor has gotten a significant power boost from 250 kW to 350 kW, and there's now a front generator unit that can't deploy energy but which can harvest an additional 250 kW under braking to make for a much more efficient race car. But development hasn't been entirely trouble-free for the teams, and the sport will begin in 2023 without its new fast-charging system, initially due to supply shortages.

An award-winning writer and graduate of the Sheridan College journalism program, he has published articles worldwide in a variety of industries, including manufacturing, pharmaceutical, medical, infrastructure, and entertainment.

Ball suggested milling chucks, shrink-fit holders, and high-precision collet chuck systems when using this milling strategy.

According to Ball, the best use of optimized roughing is in situations that use the full flute length of the tool. Roughing long, straight walls is a good example of this.

3. Don’t cut too deep. A cutting depth of 2xD that takes the full length of the cut in one pass is recommended. The shallow radial stepover enables the depth of the cut. A larger stepover would require a shallower depth of cut to achieve the same metal removal rates. However, a cut that is too deep, more than 3xD for example, creates cutting pressures greater than the tool can bear and causes deflection.

As the number of flutes increases, the stepover must decrease to maintain surface finish at faster feed rates. If the stepover is too large, feed rates must be lowered, and more heat is generated with the larger amount of metal removed in each pass. By decreasing the stepover, faster cutting speeds can be achieved. This requires more passes, but the metal removal rates are still higher than at slower speeds because of the increased feed rates.

“There might be some additional corner picking that you need to get closer to near net shape before you can move on to finishing, but this strategy takes the bulk of the material out,” said Ball.

“Today’s CAM software can be programmed to create an optimized roughing stage that uses a large DOC and light radial engagement to maximize metal removal rates. It’s a type of milling operation that is very well suited to pocketing and side profiling,” said Jay Ball, product manager for solid-carbide end mills – NAFTA at Seco Tools.

The amount of stepover that can be used depends on tool diameter and the number of flutes on the tool. For example, a 6-flute, 0.5-in. end mill cutting 4140 steel can use a 10 to 12 per cent stepover. With a 7-flute tool, the stepover is only 8 per cent. Moving to a 9-flute tool reduces the stepover to roughly 3 per cent.

4. Use the tooling manufacturer’s recommended cutting parameters. Do not rely on the default cutting speed and feed rate data from programming software suppliers. Cutting tool suppliers develop the recommended cutting parameters after research and through years of experience. Tool makers optimize cutting data for the tool’s design and specifications and for the material group you are working with.

"It's so crazy the technical freedom we have got. On the software side—completely free. On the motor and inverter—completely free, just a power limit. So we just could go completely bananas, and that's the result that you get now. I'm talking with my Jaguar Land Rover colleagues all the time because they're looking at us, going, "Wow, you did that. That's really cool. How did you deal with that? What was the problem?" And it sounds silly, but all those lessons that we learned, all the mistakes we've made, are shortcuts for these guys," he said.

"We also found very early on that the shuffle response in the car is really key," he said, referring to the way that torque from the motor winds and unwinds the driveshafts as well as loading the gears within the transmission. Although this is also an issue with internal combustion powertrains, it's exacerbated in an EV due to the near-instantaneous torque of an electric motor. "So we get that shuffle response happening all the time," he said.

“Instead of encasing the tool in 180 degrees of engagement, which creates a lot of heat and a lot of pressure, better metal removal rates are achieved with optimized roughing because machinists can take a 2xD DOC and use a 10 to 12 per cent stepover, depending on material. This means you generate less heat and have less radial engagement, which means you can accelerate feed rate and surface footage rate. This is what reduces cycle time,” he added.

Ars Technica has been separating the signal from the noise for over 25 years. With our unique combination of technical savvy and wide-ranging interest in the technological arts and sciences, Ars is the trusted source in a sea of information. After all, you don’t need to know everything, only what’s important.

At the time, few manufacturers looked at silicon carbide power electronics for road-going EVs. "Now everyone wants silicon carbide, and the reason they want it is the same reasons we do," Charles said. "So the tech that we pushed then has really caught up now—the race to road is really clear. If I kind of map our switching speed increase, we've done five evolutions with different topologies of the in-house inverter. Now the road cars are coming along and the benefit there is range, ultimately; it means smaller batteries."

"So we talked about the front powertrain kit... and once you start to optimize that, you then need to go back around the loop because it interacts obviously with your hydraulic brakes—sometimes you're blending between the two, but also, it's now mapping on the front axle and mapping on the rear axle. If you just did the rear axle without thinking about the front axle, it wouldn't work very well. So you learn a lot about that one. And then you say, 'Oh, that works in that way, I need to now go back and start to match or blend in the same way on the rear axle.' So maybe not the absolute optimum for the rear axle. But something that talks nicely with the front axle," he said.

Optimized roughing improves metal removal rates (Q), reduces the amount of time spent in the roughing phase, and increases tool life, all while reducing the load on the machine, according to Ball.

During the roughing phase, the vast majority of material is removed from the part, typically leaving only what is required for the finishing phase.

There are direct carryovers from the race car to road-going Jaguars and Land Rovers, too. "This inverter that we're working on now is absolutely road car-spec now," he pointed out. "So it's not like you need to say, 'Ah, that's a special one for the racecar, we'll make a road car version.' It literally is the same inverter module that can go into that car, the same cooling system."

Other lessons have involved drivability. "You've got such high capability to deliver torque so quickly, and the drivability that the drivers feel is very closely linked to how well you control now, so you can deliver [torque] instantly. It's not like you've got to turn the engine to deliver more quickly, we're delivering quickly already, but we got very accurate or very strong and quick capability to move the target," Charles said.

Joe Thompson has been covering the Canadian manufacturing sector for more than two decades. He is responsible for the day-to-day editorial direction of the magazine, providing a uniquely Canadian look at the world of metal manufacturing.

Walter has selected the D4120 and D3120 for use with the equally tough and wear-resistant Tiger·tec® Gold coated inserts. Users requiring high precision when drilling should select the D4120 while the D3120 is considered to be particularly economical and easy to use because it only requires one type of indexable insert.

Rigid workholding also is important to minimize vibration in the part or, in the worst-case scenario, movement of the workpiece.

Consequently, Jaguar Racing developed pretty substantial carbon-fiber driveshafts to carry torque to the rear wheels. "That's because we shifted the stiffness of the driveline to move that shuffle response away from the really tricky bit on the exit of corners where the drivers are at a certain partial throttle," Charles said. And that know-how has been passed along to the road car engineers at JLR as they develop EVs and plug-in hybrids.

“Niagara Cutter [a division of Seco] has a multiflute family of tools that is used for this type of cutting. They feature a 38-degree helix, large core diameters, and multiple flutes (6, 7, 9). The tools used for optimized roughing typically have some sort of corner protection (radius or chamfer) and are coated to provide both heat and abrasion resistance, typically an AlTiN coating,” said Bell.

“We have seen as little as a 30 per cent in cycle times and a high end of 80 per cent reduction,” said Ball. “In the upper range, the cycle time reduction also takes into account a reduction in rest roughing and semifinishing.”

A complaint that has been leveled at Formula E in the past is that the technical rules limit the amount of research and development that's possible due to a high number of spec components like the chassis and battery. Indeed, this was cited as a reason by Audi and BMW to withdraw from the sport. But Charles sees it differently.

One aspect of Formula E looks set to remain constant with the introduction of the new car—the high driver workload, which requires the driver to manage energy consumption on top of the car's balance throughout the race. "It's tricky to drive but... we are learning about her all the time," said Sam Bird, one of Jaguar Racing's pair of professional drivers. "I think that we've got the car in a window now where we're both quite comfortable in understanding what to expect from the car and its capabilities. I'm really looking forward to taking it to Valencia and then to Mexico because I do believe that with the package that we've got, we can go there, and we can compete."

The holder needs to provide less than 0.0004 in. of runout. A precise holder ensures the accuracy of the process, whereas a less secure holder will cause undesirable levels of vibration at optimized roughing’s high feed rates.

The number of flutes determines the stepover percentage because it determines the chip spacing. Tool diameter also plays a role. For example, a 0.5-in.-dia. tool with 9 flutes has less chip spacing than a 1-in.-dia. tool with 9 flutes.