The challenges of sawing new alloys

Once an oddball-type application, sawing difficult-to-cut workpiece materials has become significantly more common. Manufacturers continue to improve sawing machines, saw blades and coolant, but the machinability of many metals remains an issue. New alloys add to the challenge.

The most difficult-to-cut metals are nickel-base superalloys, according to Jay Gordon, North American sales manager for saws and hand tools at the saw division of The L.S. Starrett Co., Mount Airy, North Carolina. “People are running into them more often.”

For bandsaws, Dan Fernandes concurred that the materials with high nickel content, such as Inconel and stainless steel, pose challenges. He’s senior product marketing manager for the Lenox brand at Stanley Black & Decker Inc., New Britain, Connecticut. Nickel, cobalt, tungsten, titanium, manganese and chrome are the alloying elements that present the most difficulty for users, he noted.

Image courtesy of Dake

“Overall, nickel is probably the hardest element to work with when it is mixed in with other materials,” Fernandes stated. “These alloy combinations each have different levels of impact on the saw and can be difficult to work with based on their percentages.”

Similar to bandsaws, the most difficult materials encountered when circular sawing are stainless steel alloys, according to Fernandes. “These materials tend to generate a lot of heat rapidly, which wears out the circular saw tooth and inhibits overall blade life. With these materials, it is difficult for circular saws to duplicate a result, so users typically refrain from working with them under these conditions.”

Because these types of “exotic alloys” tend to workharden, Dennis Rice, saw line product manager for Dake Corp., emphasized that it’s critical that the cutting speed remains steady. To minimize workhardening, the speed should not increase or slow down during the cut. “You have to treat them with kid gloves the first couple cuts until you’re sure of what you have.” The Grand Haven, Michigan-based company builds cold saws, vertical and horizontal bandsaws and other machining equipment.

The sawing parameters not only have to remain consistent but must be correct. “With a carbon steel product, you can get away with the feeds and speeds being somewhat out of whack,” Gordon said. “But when you get into these difficult alloys, they have to be correct if you want to get any blade life and production out of it.”

Mystery Metal

While the compositions of standard alloys, such as Inconel 718 or Hastelloy C-276, are known, part manufacturers also must saw proprietary metals, Gordon noted. “Of course, when it is proprietary, you don’t know what’s in it.”

The Wave Tech process, which Lenox adds to some of its bandsawblades, enhances cutting ability for workhardening materials. Image courtesy of Lenox

To help, he recommended asking the material supplier what the proprietary metal cuts like. “It becomes a lot more dependent on the saw specialist to be able to read chips and determine what may be required.”

If the chips look black and blue because of excessive heat and are similar to chips produced on a turning machine, Gordon said something is wrong. Instead, chips should look like steel wool or the familiar curled shape, depending on the application.

“I would say there’s a lot of trial and error in some of these materials,” he said. “For proprietary materials, you just have to work your way through it and keep adjusting until you arrive at the best solution.”

Trial and error, while always an option, can damage blades. To limit blade damage, Fernandes suggested using a program, such as his company’s SawCalc, to determine the best way to saw a new proprietary metal based on another material that has similar physical properties.

In addition, consulting with a saw blade manufacturer can generate helpful insights. “Based on what materials need to be cut, what machine the user operates and the size of the blade, one of our technical representatives can calculate the proper feed and speed required to pull an effective chip and meet the customer’s goals and requirements,” Fernandes stated.

Nonetheless, some metals might be better left to other machining operations. Rice said casehardened Thomson rods, which typically have an outer shell hardness of 60 to 65 HRC, are one example. “The outside is shiny like chrome and only a few thousandths thick, but getting through that few thousandths will tear up the blade big-time. It’s hard enough that it’ll turn your blade into a butter knife in short order.”

Starrett offers Advanz MC5 and MC7 (pictured) carbide-tipped bandsaw blades, which utilize a multiple-chip grind with a high/low tooth sequence. Image courtesy of Starrett

It’s not only a metal’s composition that can cause fits when sawing. Workpieces with unusual shapes and features also present challenges because they can be difficult to clamp, Rice noted.

“So you have to get creative with your fixturing,” he said. “The tighter you can clamp it, the faster you can cut it. The last thing you want is to have the part roll out of the vise when you’re halfway through the cut.”

Lubricious Chill

Because an extensive amount of heat is generally generated when sawing difficult-to-machine metals, it’s important to apply an ample amount of coolant, according to Fernandes. He recommends a water-soluble oil because having an oil in the mix limits the heat.

Besides being able to cool the saw/workpiece interface, the metalworking fluid must provide lubricity for effective chip evacuation, Gordon said. “While an argument can be made for using straight cutting oil, with the advent of soluble oils, semisynthetic and full synthetic cutting fluids, this is typically the least attractive option. The key is a high-quality cutting fluid mixed appropriately for the application that both lubricates and cools.”

The SE 5X6 RCT benchtop horizontal bandsaw from Dake features a semiautomatic 2.5-hp motor, gravity down feed and reverse cutting technology. Image courtesy of Dake

Rice emphasized steering clear of oil and selecting a water-soluble coolant instead because it’s significantly cleaner and users should “flood it as much as you can.”

It’s essential not only to apply the right coolant but to do so at the proper concentration as well, as long as the concentration is within a suitable range. “You could always make the concentration a little heavier,” Rice said, “and instead of having to mix in more coolant when it evaporates, you just add a little water, and you still have the lubricity you need.”

However, if flood coolant isn’t an option, spraying a fine mist of vegetable oil on the blade gets the job done when the application is appropriate, he said.

In addition to asking customers whether they use coolant, Rice said one of the first things he asks about is the chip brush, which knocks chips out of the gullet so the blade functions as designed. “They say, ‘Yes, we use coolant, and what chip brush?'” Although most saws have one, the chip brush is removed when replacing a blade; many end users feel that it isn’t worth the time and effort to replace the brush, he noted. “They put the blade back on, and the brush walks away and is never to be seen again.”