Boosting productivity is all well and good, but Sandvik Coromant Co. finds that high-volume part manufacturers are generally more concerned about enhancing and achieving a predictable tool life, noted John Dotday, drilling product and industry specialist for the toolmaker. That’s especially the case when drilling steel workpieces, which can have slight variations between material batches that cause tool breakage, he added.
Sandvik Coromant developed the solid-carbide CoroDrill 860-PM to enable secure and productive steel drilling, including hardened and softer steels. Soft, gummy, low-alloy steels, such as 1018 and 1020, create the biggest drilling challenge because of built-up edge and chip control problems, according to Dotday. While it is difficult to break chips in those materials, the CoroDrill 860-PM creates small chips with tiny tails, he said.
Courtesy of Sandvik Coromant
The CoroDrill 860-PM is for steel holemaking applications. In cross-hole applications where hole diameters differ, end users should always drill the largest diameter first to minimize burr formation and prevent the drill from walking to one side.
In addition to optimizing the drill’s geometry for steel applications, Dotday explained that the drill’s edge-rounding treatment and reinforced drill corner prevent corner chipping, giving strength and security to the drilling process. The treatment is performed by applying abrasive brushes on a grinding machine.
He added that the new edge-prep reinforced corner and tough 4234 carbide substrate prevent premature tool wear, enabling machinists to hold tight tolerances and impart fine surface finishes. “We want a controlled wear pattern,” Dotday said.
The drill not only provides a predictable tool life but a longer one. Compared to other drills, the Sandvik Coromant CoroDrill 860-PM lasts 20 to 40 percent longer, according to Dotday.
The drill’s through-coolant capability also enhances chip control, and Dotday recommends a coolant pressure of at least 220 psi. For end users without through-coolant capability on their machines, he noted that a limited assortment of external-coolant tools are available, but they should apply them only for making holes up to 3 diameters deep and reduce the cutting speed and feed 25 percent. For the through-coolant variety, the toolmaker recommends a feed of about 0.010 ipr and a speed of 400 to 800 sfm for soft steels and 200 to 330 sfm for harder steel grades.
Once the drill produces manageable chips, post treatment brushing of the tool’s multilayer TiAlN coating enhances lubricity and chip evacuation, Dotday noted, adding that the coating appears as if it were polished.
Standard drills are from 3mm to 20mm, are available to drill holes up to 8 diameters deep and, depending on the diameter, have a tip point from 139° to 144°. The tip angle is one reason starter holes are not recommended even when drilling convex and concave surfaces, Dotday explained. “Unless you have the proper center drill with that geometry, a starter hole will create problems and break down the drill faster,” he said.
When a drill needs reconditioning, the toolmaker requires that it perform reconditioning to provide the same life as a new tool because of the special grinding and edge prep required, according to Dotday. He added that reconditioning reduces tool length about 1mm while slightly increasing the diameter when recoated. A drill can be reconditioned three times, but beyond that the additional coating layers will experience flaking issues. Because reconditioning reduces tool length, Dotday pointed out that a user needs to specify a drill that’s still long enough for an application after several reconditionings, not just when brand new.
The CoroDrill 860-PM will be available in March.
For more information, contact Sandvik Coromant Co., Fair Lawn, N.J., at (800) SANDVIK or visit www.sandvik.coromant.com/us.
Related Glossary Terms
- abrasive
abrasive
Substance used for grinding, honing, lapping, superfinishing and polishing. Examples include garnet, emery, corundum, silicon carbide, cubic boron nitride and diamond in various grit sizes.
- brushing
brushing
Generic term for a curve whose shape is controlled by a combination of its control points and knots (parameter values). The placement of the control points is controlled by an application-specific combination of order, tangency constraints and curvature requirements. See NURBS, nonuniform rational B-splines.
- built-up edge ( BUE)
built-up edge ( BUE)
1. Permanently damaging a metal by heating to cause either incipient melting or intergranular oxidation. 2. In grinding, getting the workpiece hot enough to cause discoloration or to change the microstructure by tempering or hardening.
- burr
burr
Stringy portions of material formed on workpiece edges during machining. Often sharp. Can be removed with hand files, abrasive wheels or belts, wire wheels, abrasive-fiber brushes, waterjet equipment or other methods.
- center drill
center drill
Drill used to make mounting holes for workpiece to be held between centers. Also used to predrill holes for subsequent drilling operations. See centers.
- coolant
coolant
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
- cutting speed
cutting speed
Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).
- feed
feed
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
- grinding
grinding
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
- grinding machine
grinding machine
Powers a grinding wheel or other abrasive tool for the purpose of removing metal and finishing workpieces to close tolerances. Provides smooth, square, parallel and accurate workpiece surfaces. When ultrasmooth surfaces and finishes on the order of microns are required, lapping and honing machines (precision grinders that run abrasives with extremely fine, uniform grits) are used. In its “finishing” role, the grinder is perhaps the most widely used machine tool. Various styles are available: bench and pedestal grinders for sharpening lathe bits and drills; surface grinders for producing square, parallel, smooth and accurate parts; cylindrical and centerless grinders; center-hole grinders; form grinders; facemill and endmill grinders; gear-cutting grinders; jig grinders; abrasive belt (backstand, swing-frame, belt-roll) grinders; tool and cutter grinders for sharpening and resharpening cutting tools; carbide grinders; hand-held die grinders; and abrasive cutoff saws.
- lubricity
lubricity
Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.
- titanium aluminum nitride ( TiAlN)
titanium aluminum nitride ( TiAlN)
Often used as a tool coating. AlTiN indicates the aluminum content is greater than the titanium. See coated tools.
Author
Alan holds a bachelor’s degree in journalism from Southern Illinois University Carbondale. Including his 20 years at CTE, Alan has more than 30 years of trade journalism experience.
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