New chip geometries, coatings rival performance of solid carbide drills
Since their introduction about 20 years ago, replaceable-tip drills have become increasingly accurate and cost-effective alternatives to solid carbide units.
New tip geometries, coatings and other modifications are enhancing their useful range, particularly when processing new alloys. And, as familiarity with these tools has grown, expert users are refining their methods of getting more than a single cycle of use out of their tips.
Add to that mix easier and faster changeouts for new tips, and the replaceable-head drill becomes an even more important factor in increasing throughput on high-volume production lines.
Better Design and Accuracy
The hole-making capability of the current generation of replaceable-tip drills “is almost equivalent to what you would get with a solid carbide drill,” said Dan Habben, tooling engineer for Sumitomo Electric Carbide. With accuracy in the range of ±0.0005″ (0.013 mm), also impressive is the finish produced by replaceable tips, being “pretty much equal” to what one would get with solid carbide.
The evolution of tip design has been vital to that performance. Sumitomo’s SMD series features tips with point geometries similar to those on standard carbide drills, Habben explained. “Our replaceable tip pretty much mimics and looks just like a solid carbide drill point. It has the same type of helix, the same type of gash for the web thinning. We’ve experimented with double margin vs. single margin, but we found the double margin really didn’t improve finish or tolerance enough to justify the extra cost.”
The “vast majority” of drilling applications are single-margin noted, Martin Hobbs, drilling and tapping product specialist for Sandvik Coromant, but the company will provide double margin if a customer requires such inserts. “We like to use the double margin drill when we’re going between crossholes, where there is potential instability. If you have a horizontal hole in a piece of material and you are going to drill vertically through that hole, that creates some instability around the drill tip. The double margin helps to stabilize that drill tip as it goes through that cavity.” But by and large, double-margin drills are not required for common jobs—for instance, producing a bolt-hole pattern around the flange of an oil valve.
The accuracy of today’s replaceable tips can reach IT8 on the 18-grade International Tolerance scale, according to Patrick Cline, national product manager for drilling at Iscar Metals. “The one solid piece of carbide can be ground to the tolerance of solid carbide, and only the tolerance of the pocket and the runout to the body will cause it to have slightly larger hole deviation as compared to a solid carbide drill,” Cline said. Iscar offers several replaceable tip lines:
- Sumocham, a replaceable head for precision high-production drilling or any premium drilling operation to reduce cycle time. The line has multiple head styles to allow optimum performance with a variety of materials.
- DR-Twist, an indexable insert drill for general drilling applications that do not require tight hole tolerances.
- TriDeep, an indexable insert-style gundrill for depths greater than 12×D. The available guide pad provides tight tolerances and good hole finish.
To improve the hole exit finish with cast irons, Mitsubishi Materials USA designed a new cast iron grade of tips with clipped corners that prevent breakout, or chipping, said drilling product specialist Nika Alex.
“We have the ability to go up to eight times the diameter [8×D] deep,” he notes. He would like to see these devices progress up to 15×D. “That is the challenge with a steel body,” he noted. “The longer you go, there is so much more torque, and sometimes the steel isn’t strong enough.”
Tip stability is achieved through a variety of methods of clamping inserts to the drill body, Alex explained.
“Everyone’s system is a little different,” he said. For instance, Mitsubishi’s original design features a serrated insert that must mesh with the inside of the drill body. A screw then tightens the serrated jaws to prevent lateral motion of the tip. The company’s newer small-diameter design does away with the serrations, instead complementing the jaw system with an internal screw on a small piece of carbide extending from the bottom of the insert. “There weren’t enough serrations to keep the smaller diameters in place,” Alex said. The advance further helped the company’s replaceable tips replicate the high tolerances of solid carbide drills.
Meanwhile, Seco Tools uses a cam-style clamping system on its new Crownloc Plus line “that only requires one wrench to change the tip,” said Manfred Lenz, product manager for holemaking. Designed for drilling steel and iron, these tips are “easily installed with one quarter turn of the wrench and runout less then 20 µm [and] can be changed at the machine with no resetting of length.” A precision claw and hook keeps the tip secure, he added. “The body features deep and wide flutes with polished surfaces for superior chip evacuation. Coolant is fed through the body and through the tips for efficient cooling of the cutting edge and long tool life.”
Walter USA’s drills also feature special geometries for cast iron, as well as coolant holes repositioned to ensure uniform application of coolant at the cutting zone, and other advances, said product manager Sarang Garud. The company’s new D4140 drills feature ground and polished flutes to facilitate chip evacuation, along with vacuum-hardened bodies, all helping “bring the performance of the drills closer to a solid carbide drill,” he said.
Walter employs corner chamfers on its inserts for cast irons; extra sharp edge geometry for nonferrous materials; and sharp geometry and strong edges for stainless steels and high-temperature super alloys. “For certain material groups such as cast irons [ISO K- pink color] and steels [ISO P- blue color], Walter offers ‘color-select’ technology, where the inserts have a cosmetic coat for easy recognition,” Garud added. Operators can pick the inserts based on color to match the material to be drilled.
Today’s improved cutting geometries are a far cry from the earliest iterations, Lenz explained, when “the tips were a flat blade with a drill point. These geometries were not very material-friendly. They produced a lot of heat in the cut and were not free cutting. Some were made of HSS and others were made of carbide. Coatings were usually just a layer of TiN, which didn’t address the heat and edge build-up. But now we have free-cutting geometries like a solid carbide drill. We can offer different cobalt contents in the substrate and thick coatings to deal with heat, cratering and built-up edges.”
The “typical” usage cycle for a replaceable-tip drill is anything but universal, based on application and materials, Hobbs said.
For some metals like aluminum, “we could drill tens of thousands of holes and go months and months without changing one of those tips,” he says, whereas with a stronger material like Inconel 718, “we might get, depending on the application, eight minutes of cut time.”
However, “if the user pays attention to the amount of wear they’re getting and pulls the tip soon enough that there is not excessive damage, they can be reground and recoated at least one time,” Sumitomo’s Habben advised. “We have a few customers who monitor usage so closely that they can get two regrinds out of them. But the tips aren’t very thick, so you don’t have a lot of material to remove to get a lot of regrind.”
Those customers tend to drill medium carbon steels—nothing as abrasive as cast iron or more exotic materials. And, softer steels don’t wear down the margin as much. “If the margin gets worn too much, you are not able to regrind the drill and hold the tolerances.”
According to Iscar’s Cline, replaceable drillheads can be resharpened two or three times “depending on the amount of material remaining on the head and the quality of the cutting surfaces of the worn drillhead.”
He advised users to “replace the head once it is worn, as continuing to run a dull head with a large amount of flank wear increases the forces on the pocket, which leads to premature plastic deformation and reduces the life of the body.” Choosing the correct head style for the material being processed is vital to maximizing performance, he adds: ICP for ISO P material, ICK for ISO K material and ICM for ISO M material. “The replaceable head and/or inserts are more forgiving in the event of any misalignment, as the steel body allows for a small amount of deflection without breaking like solid carbide does.”
Seco’s Lenz offered a handful of tips to properly use and maintain replaceable-head drills:
- Never be over 0.002″ (0.05 mm) of total indicated runout.
- Check coolant pressure, flow and concentration.
- Check cutting parameters to ensure the tipped drill does not “walk” off location.
At Mitsubishi, the launch about two years ago of its smaller-diameter drill tips with redesigned clamping system brought an unexpected bonus: The improved rigidity of the new system resulted in longer tool life compared to similar drill tip diameters from the original design, Alex said. But to extend the life of the company’s original system, he advises, users must lubricate the insert set screw after every index, as post-drilling debris can prevent full clamping of the jaws.
He said the typical replaceable-tip system of steel body and screwed-in drill inserts can last 20, 30 or more indexes—the number of times inserts can be changed before the body must be replaced—but that newer, more abrasive heat-resistant alloys pose a challenge to that longevity.
Handling New Materials
While high-value components in aerospace, health care and other industries become more complex and demanding, so too do the alloys from which they are made. But the exacting standards required to build parts that go into human bodies or carry them through the sky don’t necessarily apply in other areas—presenting some new approaches with replaceable-tip drills.
“I get calls almost on a daily basis from our sales force in the field saying, ‘I’ve got this material, what do you know about it?’ ” Sumitomo’s Habben said. “I spend a lot of time looking at the properties of these materials, what’s their ‘cake recipe,’ so to speak—how much carbon, how much chrome, how much nickel, how much titanium? Some of these materials do get very difficult to machine.”
Optimizing processes to take advantage of replaceable tips becomes a balance of combining years of drilling experience with keen awareness of materials developments. While 304 or 316 stainless steel were longtime standards, for instance, some foundries are now certifying material as 316/316L, the L standing for low carbon content, he said. “When they drop the carbon content, it becomes very sticky and gummy,” which can wreak havoc on chip control on finishes. In that case, an operator might have to run a replaceable-tip drill at about 20% slower RPM while increasing feed rate.
Habben is also encountering “a lot of different strains” of powdered metal being used in additive manufacturing, or 3D printing—new versions of carbon and stainless steel, especially in the automotive and diesel/heavy equipment arenas. To meet that challenge, Sumitomo is developing a new tip coating that could make its debut later this year. “That material can be so abrasive that you need a different coating to resist the abrasion.”
Multilayer high-hardness nanocoatings composed of alumina, titanium and chromium-alumina are a key feature of Sumitomo’s tip design that allows them to hold the high tolerances necessary for precision work. As temperatures at the cutting edge—which can approach 1200°F (649°C)—increase, the coating gets harder to resist wear.
In October, Sandvik Coromant also plans to release a series of new coatings for the geometries in its CoroDrill 870 series, Hobbs said, geared to handling these newer, abrasive, heat-shedding aerospace materials.
Drilling these superalloys might also require tougher, more wear-resistant steel bodies to achieve more indexes, said Mitsubishi’s Alex. At present, said Sandvik Coromant’s Hobbs, “I have seen some of our drill bodies go well over 200 drill tip replacements before that body wore out.”
The Cost Advantage
While solid carbide drills start getting more expensive—perhaps $300–$500—at about a 1/2″ (12.7 mm) diameter and larger, replaceable tips from about 7/16″ (11.1 mm) up to about 1 1/2″ (38.1 mm) cost more like $75–$100, said Sumitomo’s Habben.
The only caveat: the very rigid solid carbide drill will likely hold tighter tolerances with holes a 1/2″ (12.7-mm) diameter and up vis-à-vis the more flexible, steel-bodied replaceable-tip drill. Despite that, there are throughput advantages with replaceable tips.
“We can run extremely high feed rates with our drill,” he said, “equal to or in some cases even better than the solid carbide drill as far as the advance per revolution.” An average feed rate for a 1/2″ diameter replaceable tip drilling medium carbon steel might be 0.008–0.014″ (0.20–0.36 mm)/rev; that might increase to 0.010–0.020″ (0.25–0.51 mm) for a tip 1″ (25.4-mm) wide or wider.
Increased ease of use of today’s replaceable tip drills is keeping machines running longer and throughput higher, said Iscar’s Cline. Tip changeovers often take less than a minute.
“As more and more automation is incorporated into the manufacturing process, it becomes more important to maintain maximum machine up time,” he explained. “The current generations of replaceable head drills with their quick cutting head change and repeatability continue to help manufactures decrease not only the cycle time, but setup time as well. Automated production lines are of course a great fit for this technology, as well as any shop that needs to maintain a high level of throughput to keep up with production demands. Transfer lines and heat exchangers, cam lifter bodies and pressure fittings are just a few good examples.”
Another advantage is not having to maintain a large drill inventory, he added.
Adds Walter USA’s Garud, “these drills work well in laminate or stacked material applications” and are used in industries as varied as agriculture and energy (tube sheets, oil field components).
Down the road, users might see drill tips from Sandvik Coromant that will not require a guide hole up to 8×D, Hobbs said. However, 10×D and 12×D will still require a guide drill “due to the dynamics of the drill body being steel and wanting to flex.”