Drilling To The Limits
Innovative holemaking tools can improve cycle time, reduce cost per hole
By Jim Lorincz
Cutting tool manufacturers are employing various design and manufacturing strategies in their drilling products as they strive to meet the demands of their customers for improved productivity.
In applications as diverse as automotive, medical-device manufacturing, aerospace, and general engineering, manufacturers can choose from an array of highly engineered drills. They include high-penetration solid carbide drills, indexable-insert drills, replaceable-carbide-tip drills and, increasingly, multiple-function drills to drill small holes, deep holes, and holes that are drilled, chamfered, and counterbored to eliminate secondary operations.
Cutting tool manufacturers are drawing from advances in geometry, substrates, and coatings that enable them to introduce new product lines, expand existing products, and move custom-designed specials into their standard product offerings.
Working to their advantage are developments in CNC machine tools, particularly machining centers, Swiss-type turning centers, and even long-bed lathes that can optimize the performance of longer drills. Modern machines have the rigidity and ability to deliver coolant in volume or under high pressure so critical to the drilling process.
"The drive to reduce cycle times in metal-removal operations is in full swing and holemaking is no exception," says Robert Goulding, manager of product marketing, Seco-Carboloy Co. (Warren, MI). "At the same time, other industry needs such as hole tolerance are applying additional pressure."
Goulding cites the medical and aerospace industry segments, which require both very low runout and consistent tool life. Manufacturers face the challenge of machining advanced materials such as titanium, Inconel, and cobalt-chrome alloy. According to Goulding, solid carbide drills continue to be a good choice because of their inherent rigidity as well as four other engineered features that contribute to their effectiveness—carbide coating, geometry, land margin width, and back taper—typically to 25-mm diam.
"The most effective coatings are multilayered PVD with a smooth top layer to resist adhesion in combination with a tough carbide substrate with good chip resistance to permit higher feed rates," says Goulding. Other engineering design considerations are geometries, land margin width, and back taper. Goulding explains, "Geometries are engineered to each specific material, including difficult-to-machine materials. The land margin width is designed to provide both closer tolerance holes and the ability to increase penetration rates. The back taper affects the contact surface of the machined holes, and has to be exact for different materials to avoid rubbing, which can result in poor tool life."
Nachi America Inc. Cutting Tools Div. (Macomb, MI) has had success at Ford, GM, and Honda plants with its MQL drills. Nachi’s AG Power long drills, a noncoolant-through drill made of HSS-Co and coated with TiAlN, has doubled the number of oil holes drilled in crankshafts, matching the performance of a powder-metal drill, effectively saving 50% cost per piece.
Combining functions in one holemaking tool makes sense because machining time can be reduced and secondary operations eliminated. Manufacturing engineers at Ingersoll Cutting Tools (Rockford, IL), a manufacturer of precision rotary tool holders and other tooling with integral adaptions, recognized an opportunity to combine drilling, chamfering, and counterboring in one tool to achieve the tight tolerances required of its retention knobs. They combined these operations on their Qwik Twist replaceable point drills, reducing machining time by more than 7 min on this feature. The 0.875" (22.2-mm) diam hole is drilled, counterbored, and chamfered 3.87" (98.3-mm) deep in 4000-series alloy steel. The multifunction Qwik Twist drills are now offered as part of Ingersoll’s bore line of products, and a dedicated design and manufacturing staff is assigned to handle them.
For combining drilling and chamfering into one tool, Sumitomo Electric (Mount Prospect, IL) offers two systems, one for solid carbide drill bodies, and the other for SMD replaceable-carbide-tip drill bodies. The SumiChamfer system features a collar that fits securely around solid carbide drills mounted in collet chucks. There are three models available with chamfer head sizes capable of drilling and chamfering diam from 4 to 20 mm. The system uses industry-standard ER collets—larger sizes with more holding power as drill diam increases: ER20 (4–9 mm); ER25 (9–14 mm); and ER32 (14–20 mm). Two sumiChamfer-style standard inserts are used and one insert grade, the ACZ310, machines all materials. For replaceable-tip SMD drill bodies, Sumitomo has introduced its SMD sumiChamfer rings for metric or inch standard SMD drills for diam from 12 to 22.5 mm. The SMD rings use standard sumiChamfer-style inserts with or without chipbreakers, both in grades ACZ310.
Replaceable head drills with carbide tips offer the ability to cover a range of drill diam sizes with one HSS drill body, reducing inventory costs. Precision Twist Drill Co. (Crystal Lake, IL) is introducing its Hydra Drill in 3× and 5×-diam coolant-fed in both fractional and metric sizes, ranging from 35/64 to 57/64" (14–22.5 mm) for applications such as off-road equipment, automotive, and other similar end users of coolant-fed machining centers.
Designed for volume production, the Hydra Drill is an alternative in applications where a solid carbide drill can’t be used. The Hydra Drill comes with as many as five different head sizes for one HSS body size, enabling each drill to handle a diam range of about 1.5-mm. The Hydra Drill’s replaceable head can be changed without removing the drill body from the spindle. It can be used to machine a wide range of materials including cast iron, steel, stainless, nickel-based alloys, and titanium.
M.A. Ford Mfg. Co. Inc. (Davenport, IA) recognized the growing importance of special multifunction capabilities of carbide drills by establishing a Custom Tool Division to design drills that combine functions of step tools, such as drilling, counterboring, and chamfering. "We see a lot more applications, especially among automotive tier suppliers, for high-performance drills capable of drilling to 10× diam in the 1/4–1/2" [6.4–12.7 mm] range," explains Joe Kueter, products engineering manager. Drills range in flute length to 10" (254 mm) for drilling 15–20× diam in crankshafts.
To consolidate the number of different drills needed for a broad range of materials, M.A. Ford is introducing a new line of standard drills. The line will cover a broad range of materials from low-carbon steel to nickel-based alloys, Inconel, and titanium. Kueter says that drill considerations, such as changes to flute taper and web, back tapers, and choosing the coating to match the application, will improve the speed of drilling, productivity, and tool life.
BIG Kaiser Precision Tooling Inc. (Elk Grove Village, IL) has introduced two new Sphinx 6×-diam solid carbide drills, the Phoenix drill for small-diam holes from 1 to 4 mm, and the Quadro 15 Plus drill for diams from 4 to 20 mm. The Phoenix drill is designed to produce holes at higher speed and feed rates in steel, stainless, cast iron, and nonferrous materials. It features coolant-through down to 2.5 mm diam and Balzers Futura Nano Top TiAlN coating to improve wear resistance and chip evacuation.
The Quadro 15 Plus features a six-margin special point geometry, ultra-fine-grain carbide, and 15° helix angle, making it suitable for drilling long-chipping materials like steel as well as cast iron. The Quadro 15 Plus is said to produce a hole quality of H7, eliminating the need for subsequent finish operations.
Picco-MF multifunction indexable tools from Iscar Metals Inc. (Arlington, TX) combine drilling small precision holes with face turning, external turning, and internal turning/boring. The DR-MF line is designed for Swiss-type machines and machining miniature parts for the automotive, die and mold, aerospace, medical industry, and general engineering industries.
The DR-MF tool features two kinds of cutting edges for both drilling and turning. The high-helix cutting edge is designed to minimize cutting forces, and is said to provide optimal chip control at low feeds. The XCMT inserts are made from grade IC908, a submicron substrate with TiAlN multilayer coating. The DR-MF tools can be used as both right-hand and left-hand tools. Tool bodies are coated with a 60 Rc hardness coating for wear resistance and reduced surface friction to improve chip evacuation and prevent clogging.
For drilling deep holes, OSG Tap & Die Inc. (Glendale Heights, IL) has introduced its Exocarb-Max extra-long drills (FTO-GDXL) that are capable of nonstep drilling to 30× diam. By eliminating step drilling, cycle times are reduced as much as 15× compared with gundrilling. Exocarb-Max extra-long drills are coolant-through, feature TiAlN coating, and are available in sizes ranging from 2.5 to 20 mm.
Drilling small and deep is always an especially difficult proposition. Mitsubishi Materials USA Corp. (Irvin, CA) offers its MSE (Mini Star) solid-carbide drills in a diam range from 0.1 to 0.99 mm in 0.01-mm increments. The MSE is designed specifically for metal-cutting applications, such as medical and other precision applications using Swiss-style machines.
Mitsubishi Materials is adding a new deep-hole capability to its micro range of small-hole drills for 1–3-mm diam drilling applications. The MWS coolant-through drill features a longer flute and a wavy cutting edge to promote chip breakage and evacuation in holes to 10× diam for steels, stainless, alloy-based steels, and nickel-based alloys. The MWS-style wavy cutting edge is also the key to its new standard line of super-long carbide drills that enable deep-hole drilling to 30× diam and deeper by drills from 3–15-mm diam.
Kennametal Inc.’s (Latrobe, PA) HTS drilling system features big drills that can drill deep. HTS 8×-diam drills feature diams ranging from 1.5 to 10.6" (38–269 mm) that can drill 6–8' (1.8–2.4-m) deep. Custom drills to 15" (381-mm) diam are available.
"The tool is effectively one cutting edge as a series of inserts line up to fill in the gaps," explains Chet Parzick, Kennametal’ senior product manager-holemaking. Heads are adjustable within the diam range. "There is virtually no material that can’t be drilled, including steel, stainless, grey iron, ductile iron, titanium, and Inconel. The exceptions are extremely hard materials," he says.
Applications have included drilling holes in steel paper mill rolls with a 12" (305-mm) diam drill to 6–8' (1.8–2.4 m) and drilling K-Monel cast material with two 4" (101.6-mm) diam drills to 2' (0.61 m), indexing the workpiece 180°, and repeating the drilling to create two 4' (1.22-m) holes. Parzick advises that machines must be reasonably rigid and deliver coolant in volume to remove the large quantity of chips created
Sandvik Coromant Co. (Fair Lawn, NJ) has introduced the CoroDrill 805, a hybrid indexable drill based on the CoroDrill 800 body with external chip evacuation and internal coolant. The CoroDrill 805 is designed for deep-hole drilling with conventional machines such as machining centers, lathes, and turn-mill machines rather than moving the workpiece to a dedicated deep-hole drilling machine. The 805 has a diam range from 0.984 to 2.559" (25–65 mm) and can drill to 13× diam, producing a surface finish of Ra 32.
Walter Inc. (Waukesha, WI) has extended the Xtra-tec B 401x series of drills, which now features 60 new drill diam and two grades and geometries for steel, cast iron, and stainless. Available in lengths of 3×, 5×, and 7× diam, the drill is said to perform at twice the feed of conventional indexable insert drills, and produce holes to close tolerance and with good finish.
The B401x series features a through-hardened body with a nickelized protective coating to reduce both chip friction and corrosion. The drill is available in 12–31-mm diam range, and designed with positive insert geometry and spiral flutes like those typically found on an HSS drill.
Round holes with square drills
It might be easy to assume that drilling a round hole requires a round tool.
Yet there is a type of drilling application in which round holes are drilled in extremely difficult applications with a square drill. The main application for this type of drill is removing broken HSS taps. The Omegadrill from T3 Enterprises Inc. (Kinnelon, NJ) has a square-flute design to provide the stiffness and strength required for extreme drilling applications. The square external flutes increase the cross-sectional stiffness of the drill, which is used to drill down through the web of the broken tap. The tiny fragments of the tap flutes left behind are easily removed with a scriber or pick. The Omegadrill is manufactured from carbide, and features a negative point geometry to enable drilling in super-hard materials to RC 70. Other applications include drilling out broken twist drills, broken dowel pins, and broken screw extractors. It can be used for materials such as Stellite, chilled cast iron, hardened steel, and even granite.
This article was first published in the April 2006 edition of Manufacturing Engineering magazine.