The Hole Story: A Deep Dive on Drilling

2023-03-16 17:49:16 By : Mr. Bruce Li

Drilling is one of the fastest and most precise production methods to remove material. Each of the three principal types of drills—solid carbide, exchangeable tip, and indexable—delivers quality performance when matched to the right application, a process that starts with uncovering the answers to critical questions about the scope of the project.

Questions that need answering include variations of the following: What is the hole used for? How many holes? What is the tolerance? What is the diameter? What is the material? What is the toolholding? What kind of machine, (new, modern, legacy)? What about finishing?

Here’s how some leading suppliers have shaped their drilling solutions. The goal is to maximize performance, while meeting material, production volume, and hole quality requirements.

Solid-carbide drills are still the workhorse for high-production applications with indexable and replaceable carbide-tip tools providing exceptional performance if properly matched to the application. “Traditional solid-carbide drills represented a major advancement from HSS (high-speed steel), delivering higher feeds and speeds and greater accuracy in diameters from one to 20 mm,” said Steve Pilger, product manager-holemaking, YG-1 Tool Co., Vernon Hills, Illinois.

“Most manufacturers have a variety of metric and inch drills in 3xD, 5xD, 8xD length off the shelf,” Pilger noted. “Carbide can run at higher speeds and handle heat much better than HSS, all major positives for increased production with lower tool costs. However, depending on the application, the brittleness of the carbide can work against you, causing tool breaks in poor unrigid setups for example.”

Of the three types of drills that YG-1 offers, one is solid carbide and two are insert drills. Solid-carbide drills called Dream Drills are available with and without coolant through and are material specific for alloys and carbon steel, stainless steel, and aluminum. Solid carbide is positioned at one end of the spectrum, exchangeable tip drills in the middle, and indexable drills at the other end, explained Jan Andersson, director product management-indexable inserts.

“Replaceable insert-tip drills feature a geometry similar to or the same as solid carbide without the cost and logistics of regrinding carbide,” Andersson said. “The larger the drill, the more advanced toward the indexable side; the smaller the drill, the more advanced closer to the solid-carbide drill with replaceable-tip drills in between. If we’re looking at hole quality, surface finish, and dimensional tolerances, the solid-carbide Dream Drill is going to be superior; indexable-insert drills are especially effective in what I call a hole punch when you need to drill a hole quickly, clear the hole, and the tolerance isn’t as critical,” Andersson added.

“A typical job shop application might involve a clearance hole for a bolt head where conventional tolerance doesn’t mean that much for clearance and an indexable might be the most economical solution. If you’re just punching a hole, an indexable makes a lot of sense. The reality is that if you are going to do secondary operations afterward, it doesn’t make sense to spend the money to buy a solid-carbide drill. At that point you are probably in between using an exchangeable tip or using an indexable,” Andersson explained. “The benefit of the indexable is that it is the most versatile, especially when you’re using the WCMX trigon-style drill. You can offset it so that can drill oversize, you can chamfer the hole after drilling.”

It all comes down to where the tool is going to be used, Pilger noted. Is it a dedicated application that is run every day? Or is it for a shop with many different types of jobs and materials?

To meet the variety in job shops, drilling offers the versatility of modular drills for various jobs and materials. “What’s nice about the modular drill is its flexibility,” Pilger continued. “Starting with a 10 mm diameter, our standard bodies will hold about six different diameters up to 10.4 mm on 3xD, 5xD, and 8xD lengths. And It’s very easy to change a tip geometry to cut steel, cast iron, and stainless.”

Iscar USA, Arlington, Texas, added a third flute to create its new line of LOGIQ3CHAM exchangeable-head flute drills. “It’s a game changer,” asserted Craig Ewing, product specialist. “It’s more of a production tool with significant gains in productivity with the versatility of the exchangeable head drill, using either the regular drilling head or the flat-bottom head.”

The line expands on the replaceable tip concept introduced by Iscar several years ago as SUMOCHAM. It features through-coolant holes, and is available in 1.5xD, 3xD, 5xD, and 8xD drilling depths with round and flat shanks. Each body accepts five head sizes in the smaller diameters and 10 head sizes on diameters of 15 mm and larger.

The third flute resulted in LOGIQ3CHAM generating 50 percent more chips that had to be evacuated through smaller gullets. Iscar redesigned the cutting edge to curl the chip differently to facilitate evacuation.

“Successful chip management of cast iron, alloy, and carbon steel makes applications in automotive, general purpose, heavy equipment, machine tools, off-road, and the heat exchanger industries good candidates for the LOGIQ3CHAM,” Ewing said. “The heat exchanger industry, for example, uses standard ISO P materials and drills holes by the thousands. When you are drilling thousands of holes in one part, like a heat exchanger, you can see the benefit of increasing feed rate by up to 50 percent,” Ewing said, adding that new geometries are being developed for materials such as stainless and high-temperature alloys.

“The main thing that helps our customers is the extra productivity from increased feed rate,” Ewing said. “If we’re cutting at five thou (thousand) per flute on a two-flute drill, we’ll be at 10 thou, but with a three-flute drill we’ll be at 15 thou per rev and that’s what increases feed rate and reduces cycle time. We typically see from 20 percent up to 50 percent reduction in cycle times with the LOGIQ3CHAM in production applications. In a job shop environment, depending on volumes, we might recommend staying with our regular exchangeable-head, two-flute SUMOCHAM drill,” he added.

“The biggest challenge for our customers is making holes, good holes, as fast as possible, whether for difficult-to-machine materials like Inconel 718 for aerospace or 4140 steel for general engineering,” said Martin Hobbs, drilling and tapping product specialist at Sandvik Coromant US, Mebane, N.C. “It all comes down to the GD&T (geometric dimensioning and tolerancing) demands of the hole application. If we’re looking for looser tolerances say for bolt holes, we use indexable insert drills extensively, giving us the opportunity to punch holes very quickly at a very low cost. If you are looking for very tight tolerances under 2,000, that’s where we have to use solid-carbide drills to do that tight work,” Hobbs said.

The most recent addition to Sandvik’s portfolio of solid-carbide drills and indexable and exchangeable-tip drills, the DS 20 insert drill is capable of 7xD drilling. Sandvik used new materials and technologies to develop a drill body and carbide to extend tool life while producing hole quality with more rigid material for deeper depths of cut.

“In recommending the right drilling solution for its customers, we focus on metal-removal rate, how many cubic centimeters of metal are removed to keep our customers as productive as possible,” Hobbs said. Success is measured by the “cost-per-good-hole per component,” he said, for the best holes at the lowest cost for a specific application.

“Anything under three-quarters of an inch and lower diameter, we can use solid carbide; exchangeable tip from 10 mm up,” Hobbs continued, noting the choice depends on dimensions and tolerances. “If I have a three-quarter-inch hole, I can use either an exchangeable-tip, an indexable, or a solid-carbide tool. It comes down to the customer’s requirement for hole tolerance and straightness, and diameter tolerance.”

Chief considerations include a hole’s:

“That’s where we bring in the indexable drills. They have higher tolerances, we’re talking north of 10 thou of an inch for hole diameters,” Hobbs explained. “Where we have bolt holes or hole lightening pattern to put into a flange to lighten the material, this is where insert drills do very well; anywhere we’ll be doing boring or reaming holes also in some threading the holes.

Exchangeable-tip drills are good choices above two thou in tolerance but under the 10 thou range. Anything under two thou it’s solid carbides, or we go into reaming if necessary for very tight hole tolerance.”

Job shop or high production? According to two product managers at Allied Machine & Engineering Corp., Dover, Ohio, the challenge to satisfy the requirements of both is the same: Provide drilling solutions that enable customers to meet their production requirements in a timely and cost-efficient manner.

“A lot of our customers, especially today, are looking for time-saving solutions to get products to their customers as quickly as possible,” said Bill Ruegsegger, product manager in charge of Allied’s high-penetration, higher-production style tools. “Our drills combine operations to create holes faster with better surface finishes, allowing our customers to move products through their operations faster,” he added.

“Our legacy products are tailored for the job shop market where these companies want high production to be able to run tools fast to process parts fast through their shop,” added John Weniger. “But shops don’t often have a lot of margin and a lot of wiggle room on price when it comes down to it.”

Weniger, who is responsible for Allied Machine’s legacy tools (including the high-precision T-A and T-A Pro lines), noted the challenge in finding the best of both worlds.

“Our newest T-A Pro is designed for a wider range of inserts per drill body compared to a lot of the high-penetration style tools,” Weniger said. “For different ISO grades, selections include carbide for the longer run jobs that the job shops have or a high-speed steel just for standard work, using a standard style insert for a few holes here and there. You kind of have both options to play with there and that makes sense.”

Agreeing with his colleague, Ruegsegger noted Allied Machine serves both high-production shops and job shops. “Having a solution to meet all of their needs is the challenge; whether it’s how do we get the product out faster or whether it’s how do we quote these jobs to their customers and be cost efficient. We’re trying to find the best cost per hole for them to be able to offer to their customers as well,” he said.

“Our GEN3SYS XT and GEN3SYS XT Pro high-penetration carbide drills are indexable so they’ll go on a high-speed steel body, which still allows for a cost reduction versus the prototypical solid-carbide drill,” Weniger added. “The Superion line of special solid-carbide drills and PCD tools are high-performance, high-penetration-style drills.”

Allied Machine’s latest products provide a cost-effective, replaceable-tip solution to drilling holes in a wide range of materials, according to Weniger.

The T-A Pro, for example, conforms with a lot of the existing T-A GEN2 style of inserts and has carbide and high-speed steel options for higher penetration rates.

“We want to be able to provide the complete solution for our customers whether it’s the automaker drilling thousands of holes a day or the mom-and-pop shop just trying to punch holes in oil field parts,” Ruegsegger said.

High-performance tools typically have a higher initial cost. But such tools may prove to be the less expensive option in the long run, asserted Jack Kerlin, applications engineer at Big Daishowa, Hoffman Estates, Illinois.

“Our target demographic is mostly high-production shops which, in itself, is a subjective term depending on who you’re talking to,” Kerlin said. “A lot of times shops don’t consider the total production run when deciding on tooling and equipment. But ultimately your best option is the one that is most cost efficient, regardless of initial cost. That’s our focus.”

However, he conceded, picking the more expensive option isn’t always the best choice. “If you’re a job shop, there’s nothing wrong with using less expensive tools for one-offs,” Kerlin pointed out. “Everything has its place. But once you start moving into high-production territory, in the long run using cheaper tooling will almost always cost you more money in the form of broken tools, poor surface finish, increased scrap, and machine downtime.”

As a result, he said, Big Daishowa is focused on high-quality toolholders and boring tools. The company’s Phoenix TC2 solid-carbide drills, which also are designed for high-production applications—in sizes up to 30xD and 10 mm diameters—and high-temperature alloys, feature coatings, coolant-through holes, and efficient chip evacuation to insulate against cutting heat, according to Kerlin.

“Work hardening is always a challenge in these materials, though a suitable coating and coolant-through to evacuate chips as quickly as possible help,” he continued. “For harder materials, a larger point angle, for example, 140° typically is used. The traditional point angle for drills is 118°, but this is largely a leftover from the days of manual machining. As materials have gotten tougher and drill point grinding has gotten more sophisticated, a larger point angle emerged as the standard because it’s more durable, more repeatable, and doesn’t walk as much.”

Big Daishowa’s new Nirox drill is a bridge between high-production and job-shop-type applications. Describing it as “remarkably tough,” Kerlin said the drill is designed for legacy machines that don’t have coolant-through and aren’t always stable. Nixrox uses coated carbide, flood coolant, and is available up to 9xD.

“Toolholders are also extremely important for high-production applications,” Kerlin noted. “We recommend a hydraulic chuck or a high-precision collet chuck for finishing. Experience has shown us that for every tenth of an inch increase in runout at the nose, there’s a reduction in tool life of 10 percent. Your typical production toolholder will have low runout, high repeatability, and be extremely well balanced for high speeds.”

Emuge-Franken USA, West Boylston, Mass., emphasizes the importance of consistency and precise location of drilled holes. To increase tool performance and improve the quality of threads generated by its taps or thread mills, the company designs and manufactures a full line of high-penetration drills, featuring carbide grades with PVD-applied coatings,high-end hones, and flute forms and point geometries adjusted to fit the application.

For holemaking in aluminum, Emuge developed the new PunchDrill, a high-productivity tool that reduces machining forces and optimizes chip breaking, producing cycle time savings of 50 percent or more when machining cast-aluminum alloys with at least seven percent silicon content and magnesium alloys. The PunchDrill doubles the feed rate compared with standard drills, without increasing axial force or spindle speed—and results in shorter machining times, fewer tool changes, and high metal-removal rates—in addition to higher productivity and reduced power consumption, according to the company.

The PunchDrill’s patent-pending geometry features an innovative chip breaker that produces short chips to control machining forces. Other features include newly developed surface treatments and a hard diamond-like coating to provide reliable chip removal and increased process reliability. The PunchDrill is available in drilling depth ranges up to about 8xD, the nominal diameter range from 0.129” to 0.472” (3.3-12 mm). Machining is done with a normal drilling cycle on CNC machines with cutting speeds and coolant pressures similar to conventional drilling.

Emuge-Franken also has developed a completely new drill, the MultiDRILL, which is a multipurpose, high-penetration rate drill that is suited for manufacturers that have limited quantity production runs or operate in a job shop environment with many materials, the company said. The MultiDRILL is made of a sub-micro grain carbide with an ultra-fine grain that is harder than conventional carbide grades used for drilling, while retaining the ability to withstand shock and chipping.