“For carbon steel, we recommend our carbon steel drill, or our Dream Drill general; for 304 stainless, we recommend the Inox version of our Dream Drill,” he said. “Each one of these drills has the proper geometry and coatings to best deal with those materials and those applications.”

The main advantage of MF4 is its positive cutting angle, which significantly reduces cutting forces to allow for higher cutting speeds and increased productivity. With the MF4 and the enhanced cutting data, the team was able to triple tool life and complete three parts.

For example, Main Manufacturing in Grand Blanc, Mich. – a family-owned business that produces hydraulic flanges and components – was experiencing short tool life and reduced productivity due to interrrupted cuts when machining high-pressure flanges from 304 stainless steel. “The severe interrupted cut was definitely affecting tool wear,” said Main Manufacturing’s plant supervisor Terry Bettinger. “We were only able to achieve about 1.5 parts per insert due to edge chippage.”

Sandvik Coromant’s Hobbs agreed the method used to hold drills is critical to the performance of the drill and to tool life. How securely a drill is held has a direct effect on hole quality, such as roundness and surface finish, and on tool life. Weaker toolholding methods allow for more runout at the tip of the drill.

“Heat shrink and hydraulic holders hold drills on center better than Weldon or collet chucks can,” he said. “This rigidity helps to prevent the drill from running out of round at the drill tip.”

Marlon Blandon, product manager for thread milling, Emuge Corp., West Boylston, Mass., said shops can leverage the life of their tools by picking correctly.

A solid-carbide drill, the Dream Drill, has a strong geometry for making a chip in steel. “It’s going to be completely different when you drill that same hole in stainless steel,” Pilger said. “So it has a geometry to give a better chip. It has a little hook design to help get that chip into the flute a little more precisely.”

Image

YG-1 has built drill selection based on the material to be processed into its 3-catalogs. “We say ‘hey, what are you drilling?’” Pilger said. “Are you drilling steel? You pick the steel drill. Are you drilling a stainless steel? You go with our Inox drill.”

“Using a double-margin flute geometry will help improve surface finish,” Blandon said. “The second trailing margin will help burnish the interior surface of the drilled hole during the drilling cycle.”

Higher feed rates are often used to break a chip by making the chip thicker and more prone to break. There are cases where it can be better to increase the surface footage and decrease the feed rate in order to break a chip, Hobbs said.

“Material-specific geometries play a huge role in reducing exit burr,” said Garud. “For example, Walter-Titex brand Xtreme-CI drills are designed for reducing exit burrs in cast irons.” The drills have an “edge-break” chamfer on the corners of the cutting edges that greatly reduces the burrs, he said.

Instead of cutting-edge chip breaker grinds, said Blandon, high-performance carbide drills such as the Emuge EF-Series incorporate various flute shapes that roll the material within the flute and cause it to fracture. When operated at the proper speed and feed rates (which influence the chip thickness), these drills eliminate long, stringy chip formations that lead to flute clogging and drill fracturing. The other benefit of a high-performance carbide drill design is that the elimination of long chips allows the drill to operate at a constant feed rate without peck cycles.

However, Henige and Miller weren’t done with their analysis. Another pass under the microscope revealed that the failure was now being caused by thermal cracking. “Large differences in temperature between the cutting edge and the insert can cause cracks perpendicular to the cutting edge,” explained Henige. “Interrupted cutting applications such as this one tend to generate high heat when in the cut, causing these temperature fluctuations.”

The flange starts out as a 2.25-in. by 1.5-in. rectangular plate, which is rough-faced down to a hub in the center of the part. The company was taking three passes at 0.100 in. each and a final pass at a depth of cut of 0.050 in. The job was running on a Doosan 240 CNC lathe at 300 sfm and a feedrate of 0.01 ipr.

YG-1’s Pilger pointed out there are several different ways to drill today, and probably where drill breakage is most common is with solid-carbide drills used for certain materials and for certain hole diameters. Shops use them for drilling holes that are fairly accurate, fast and repeatable, given that their diameter ranges fit the diameters offered.

Paramount, though, is using the right tool. “Drills break for many reasons, ranging from using improper cutting data to just using the wrong drill for the job at hand,” said Martin Hobbs, product specialist for drilling and milling, USA-West, for Sandvik Coromant, Fair Lawn, N.J. “New technologies will help; however, nothing extends tool life more than using the proper tooling setup and application.”

To control burrs, reduce the feed by 50 percent until the margins are engaged. Exit burrs are a little trickier but can also be improved by reducing the feed by 50 percent when the drill is 0.5 mm from the exit.

Manufacturers built their formulas into carbide drills, according to Steve Pilger, senior application engineer for threading and holemaking at YG-1 USA, Vernon Hills, Ill. “Let’s say we’re cutting a carbon steel; we have a carbon steel drill that has a fixed geometry, flute and chip removal system, coolant holes of a specific size, and a specific grade of carbide with a nano-thickness, multi-layer coating on it that works best for that specific material. So, it’s not like one drill does all.”

The method used for holding a drill becomes more critical the longer the drill becomes. Long drills that are 10, 15, 20, 30 and 40 times diameter should never be held in any type of holder that is not absolutely rigid, Hobbs added.

But if you want to step it up a little bit, eliminate runout, and hold the drill better, there are a couple of options. One is a shrink fit holder and the other is a collet chuck with hydraulic pressure. These two systems grip much more of the shank. In fact, university studies have shown that holding this way improves the runout by about 50 percent and improves tool life by 20-25 percent.

Picking the right toolholding system and inspecting it periodically to ensure it’s in good working order can extend tool life and help produce better holes.

“Your holder choice is really important when you get into high production environments like the auto industry,” said Pilger. “In most applications our customers typically hold our drills with collet holders with no issues. However, when drilling in high volume with high productivity, ridged holders with stronger gripping forces are needed.”

“We initially decided to run the TM4000 using the same parameters as a competitor’s tool,” said Seco’s Miller. “But, to everyone’s surprise, TM4000 performed no better than the competitive insert.”

For most solid drilling operations, a ballpark thrust (Z) force can be 3,000-4,000 N (674–900 lb/f), and a dull cutting edge can easily double that value. Consult the tool manufacturer for recommended speed parameters and stay within the range given, Tonne advised. For feed, always run more than the width of the edge prep and less than the maximum feed per revolution.

There is a time when you want to speed up. “In drilling, a very common way to improve your chip is to adjust one of the parameters on your machine,” Pilger said. “So, when you’re having chip issues and you want to get a better chip, you slightly increase the feed in steel [0.008-0.014 ipr or 0.2-0.36 mm/rev].”

Proper drill selection, the geometry built into the drills themselves, applying proper drilling parameters, and a few tips and tricks from the pros can address nagging drilling problems such as drill breakage, unbroken chips, tool runout, poor hole edges, and poor tool life.

“In a high production environment, we highly recommend a shrink fit system or a hydraulic chuck for our solid-carbide drills,” Pilger said.

Horn’s Tonne said in many cases end users use speed and feed parameters that are too low for the drilling system they are using.

Image

Sandvik Coromant’s Hobbs said inserted core drills such as his company’s CoroDrill 880 and CoroDrill 881 offer the ability to change the geometry and coating grades that help to break chips. By their nature, core drills produce a harmonic vibration that is helpful in breaking chips. These harmonic vibrations are at times not enough, and long or unbroken chips can still occur.

“Horn’s DDM and DDP system are an example of tailoring the drill point to the application,” said Tonne. “The DDM system works well in difficult alloys like titanium and nickel, but may not be the best choice for iron. Consult the drill supplier for the best recommendation.”

Pilger at YG-1 has noticed that when customers start using carbide drills, they often look at the speeds and feeds in the catalog, which seem really high, so they reduce the speed. As a result, the drill runs too slow and does not generate enough heat. Then the material adheres to the drill and flakes off, taking off the coating and carbide with it. Eventually, the drill loses size and breaks.

Garud said Walter’s DC170, with its unique combination of radial margins, coolant channels and solid-carbide mass directly behind the cutting edge, helps extend its life by effectively dissipating even extreme temperatures.

“We went from removing 3.6 to 12.483 cu-in./minute,” Bettinger said. “With our in-cut time reduced by one half, our part output increased from 17 pieces per hour to 54 pieces per hour. The improvements were beyond our expectations.”

“However, this was far from the result that we had anticipated,” Miller said. “We examined the inserts under our magnifying loupe, but couldn’t see any particular failure mode.” Then Miller and Henige decided to take a good hard look under the microscope, which provides 60 times the optical power of the loupe. This closer inspection revealed that there was an edge-chipping problem. The chip flow was eroding the back of the land on the MF4. By the wear pattern, they also noted that a larger nose radius would help increase edge strength. As a result of this analysis, they recommended that Main Manufacturing increase the feedrate to 0.016 ipr using a 0.0468-in. radius. Because they didn’t see any other heat-related problems, they left the cutting speed at 650 sfm.

The result was that Main Manufacturing saved 85 percent in cost as well as reducing machining time by 52 percent. “But even more exciting,” said Main Manufacturing general manager Bob Mackey, “is that we can take what we’ve learned from this experience and apply TM4000 to hundreds, maybe even thousands, of other similar jobs that we run.”

Drill makers also use geometry to make their products material specific, and to aid in chip evacuation, improving surface finish, extending tool life and preventing drill breakage.

Interrupted cuts can be tough on tools. The pounding tools take during interrupted cutting frequently leads to severe edge wear that cuts short tool life. However, by carefully analyzing the tooling wear pattern and making the appropriate grade and geometry changes, the ravages of interrupted cutting can be overcome.

Tonne advised using a high-performance collet system like Horn’s Fahrion Centro P, which can increase tool life by more than 50 percent due to the extremely tight tolerances of the taper and collet runout.

“Heat shrink and hydraulic toolholders, such as Sandvik Coromant’s CoroChuck 930, provide the most stable drill holding and when compared to methods such as ER collets, may even double tool life,” he said.

“The cutting speed must be high enough to avoid material build up or built-up edge [BUE],” he added. “When BUE occurs, the drill behaves like a dull tool and thus creates pressures too high for the drill point.”

Emuge’s Blandon urged regular maintenance. “Machining center spindles must be properly maintained to reduce or eliminate runout at the drill point,” he said. “If the spindle is dirty or worn, the drill will rotate unevenly. This can lead to uneven loading at the drill point, which can cause chipping on the cutting edges and drill failure. The best holder technology for drilling today is normally a hydraulic chuck or an Emuge FPC mechanical sleeve design,” Blandon stated.

The web geometry of a drill is also very important when it comes to chip evacuation, said Blandon. The web or core of the drill should be constant or parallel from the drill point to the rear of the flute. High-speed steel drills typically have an increasing web taper which reduces the flute space towards the shank. This restricts chip flow out of the flute.

Walter USA LLC, Waukesha, Wis., has different technologies to combat tool breakage, including newergrades of coatings, including its own TiSiAlCrN/AlTiN coating to resist wear, said Sarang Garud, marketing product manager. Walter offers full coating and point coating on its drills.

Edwin Tonne, training and technical specialist for Horn USA Inc., Franklin, Tenn., said selecting the drill geometry that matches the material and application is critical.

Image

“Some newer carbide HP drills that are designed for deeper hole applications now have reverse web taper where the web is actually smaller in the rear than it is at the point,” he said. “This provides the maximum amount of chip space within the flute.”

Proper drilling parameters, including speed and feed rates, can make a difference in drill breakage, chip evacuation, hole burrs, and surface finish.

“The further the drill tip is from the toolholder, the more damage to the drill tip and the greater the effect on hole quality is had by a drill that runs out of round,” Hobbs said.

Since the presence of coolant, which was water in this case, can increase the thermal cracking problem, the team decided to run the application dry to see what would happen. This change doubled tool life yet again to achieve 15 parts per corner, and now the failure mode was simply due to normal abrasive flank wear.

“Assuming that the cutting tool is manufactured to the highest quality standards, the tool life should be consistent from one tool to the next when it is used in the same material and application,” Blandon said. “If tool life is inconsistent, then the issue lies with either the consistency of the machined part material, the wear within the machine tool spindle, toolholder rigidity, the piece part fixturing or the coolant application.”

Blandon went on to suggest a checklist of possible reasons for problems if the right tool is already on the job. Surface coatings, geometry, and application parameters are on his list, but so are other influential factors.

“We knew that TM4000 was capable of high machining parameters,” said Henige. “So we upped the cutting speed to 650 sfm using the new MF4 chipbreaker, which is designed to provide consistent chip formation and breakage in stainless steel turning and other ISO materials.”

“Similar technology exists for aluminum drills as well,” Garud said. “Our DC170 drills have radial margins that help produce excellent finish on the holes. Adding extra ground margins (four instead of two) can also have significant improvement effect on the hole finish.”

“High-performance carbide drills are the best option for high production lot sizes or higher quality hole requirements,” he said. “They are more expensive but typically have flute and point construction designed to curl and snap chips into manageable sizes that can be efficiently evacuated away from the cutting edge.”

“Tool selection will greatly influence tool life,” he said. “High-speed steel drills are a low-cost solution but rarely the best option. High-speed cobalt drills will operate more effectively in elevated temperature applications, but tool life and performance cannot compete with carbide drills. While carbide drills will normally be the best option, many tool geometry and surface treatment options should be considered.”

At times, program interruptions in the feed motion can help break up chips or, in extreme cases, a pecking cycle may solve the problem, said Walter’s Garud.

Drill makers also use the geometry of the cutting edge to their advantage. A traditional chip breaker on a high-speed steel drill has a series of small notches ground on the cutting edge, which creates discontinuous chip formations, Blandon said. This, however, is not a practical design for a drill with a carbide substrate due to the brittleness of the material in comparison to high-speed steel.

With longer drills, said Hobbs, predrilling the hole is an unavoidable and necessary process to prevent breaking the longer drill. The process for longer drills also requires special attention to the longer drill entering the hole at slower speeds and feeds, as well as not turning the through-coolant on until the drill is in the hole and ready to drill. At this time, the proper cutting data and coolant can then be applied.

Sandvik Coromant’s Hobbs agreed that it’s very important to know what a drill’s proper cutting data range is for the material being drilled. “High feed rates may produce too thick of a chip or even overload the drill’s web, causing the drill to break,” he said. “Low feeds can cause long, stringy and undesirable chips.”

Main Manufacturing had been a long time user of tools from Seco Tools. Coincidentally, Seco had recently launched its new TM4000 Duratomic turning grades for stainless steel and was in search of a demanding interrupted-cut application. Seco’s sales and application specialists Joel Henige and Todd Miller asked if they could give the new grade a try. Seco Duratomic coatings rely on an alteration in the crystal structure at the atomic level, and have consistently provided both improved toughness and wear-resistance. In lab tests, the TM4000 construction had shown to improve resistance to crater wear and edge breakdown substantially.

Manufacturers have taken the guesswork out of many of the processes that shops used to have to figure out for themselves when selecting the right drill for cutting different materials—a carbon steel, for example, versus aluminum or stainless steel.

This runout results in one side of the drill cutting more than the other. When this occurs, not only does the drill cut and wear more on that side, but hole quality diminishes as a result of the drill wanting to walk off center and scar the side walls of the hole.

Where it is appropriate to decrease speeds and feeds is with cross-holes, Pilger said. When the drill is approaching the second solid portion, reduce the speed and feed by 50 percent and re-engage the hole. This gives the drill a moment to make a footprint and get engaged. Then crank the speed and feed back up.

The company’s DDP type tools are most suited for unalloyed steels, cast steel and alloyed steels with a tensile strength of up to 1,000 N/mm2. They, too, have internal cooling, although there is a variant suitable for flood coolant.

Blandon said manufacturers vary their drills’ flute construction and point geometry to match specific materials.

Horn’s DDM drill system is also intended for machining stainless and acid-resistant steels along with the titanium and nickel alloys Tonne mentioned. They’re designed with internal cooling and have new coatings that aid in longer tool life.

“We were pleased,” said Main Manufacturing’s machinist Craig Bendle. “Productivity doubled relative to our original setup, and tool life jumped to seven parts per corner, which was seven times better than we were getting.”

“Otherwise, you might hear a chatter, or break a drill, or you’ll see it’s walking,” he said. “What’s happening is you’re getting a mismatch because you’re hitting an uneven surface and you’re trying to minimize that mismatch.”