Holemaking goes high-tech.
We recently asked a few leading tool manufacturers for their opinions about what's going on in the field and what they're doing to keep pace with the rapidly changing market.
Steven Burns, manager of product engineering for Vermont Tap & Die, Lyndonville, VT, says the reason for the dramatic changes is simple: "Most often, tapping is the last operation performed on a part. Without a properly drilled hole you can't get a good thread. People can't scrap parts anymore, particularly one that's got $3000 or $4000 invested in it, just because it's got a couple of bad threads."
Frank Knox at SKF Tools Corp, Asheville, NC, agrees. "Drills and taps were not seen as high-performance products. They were simply purchased, replaced when they broke, and that was that."
That's all changed, driven by the demands of the marketplace. Tony Yakamavich, drilling tools product manager for Sandvik Coromant, Fair Lawn, NJ, says his customers want high production, higher rpm, and cutting speeds of 300 sfpm or higher. They want tight tolerances, high-quality holes in one pass, and surface finishes of 40 rms or better. They want to eliminate pre-drilling and finishing. They want longer tool life. "What they all want," he says, "is better quality at lower cost."
Peter Matysiak, president of Emuge Corp, Northborough, MA, agrees. "The quality issue is so important that we're now selling through engineering instead of through purchasing. Manufacturing engineers are getting directly involved in the purchasing process. They're willing to pay four times more for a tap because they know they'll get twenty times the tool life. That also means they'll be getting high-quality threads over a much longer period," he says.
To address quality and tool life concerns, Sandvik recently introduced Coromant Delta-C solid, fine-grain carbide drills. Designed to produce high-quality holes in lengths up to 5 times diameter, the drills feature spiral coolant holes. Mr Yakamavich says they work best in stable machines with high rpm capacity.
"Stable machine" is the operative phrase here. The entire setup--machine, spindle, and toolholder--must be completely rigid to achieve high quality.
The same applies to carbide taps. "A carbide tap is unforgiving," says Mr Matysiak. "To introduce an advanced carbide tap into your system, you have to solve all other machining problems. There can be no misalignment. Everything must be rigid."
Carbide taps offer potential life hundreds of times longer than HSS, if process and material variability can be reduced enough to take full advantage of carbide's wear resistance, Mr Matysiak says. So far, very few manufacturers are to this point.
Tool materials and coatings
Almost all tool suppliers in the drilling and tapping field are experimenting with new tool geometries and materials, as well as with new types of coatings. Vermont's Mr Burns says that while Tin coatings have proved very successful, the company is looking at a number of other coatings, the details of which he couldn't discuss. Sandvik is experimenting with diamond coatings, while Emuge is working with the Norton Co, Worcester, MA, on diamond-film-coated ceramic taps.
Kennametal Inc, Latrobe, PA, has introduced KC935, an aluminum oxide-coated insert grade, designed to provide longer tool life at higher operating speeds. OSG Tap & Die Inc, Glendale Heights, IL, is about to introduce its HY-Pro EX-DC-HT line for tapping cast aluminum. Made of 3% vanadium HSS, the taps are coated by an ion nitriding process to increase surface hardness and wear resistance without losing the toughness of the cutting edge.
Another tap development is Emuge's Rekord Druck Roll Form tap that produces internal threads by displacing material instead of cutting chips. It's made from cobalt-enriched HSS and is suited for such ductile materials as stainless steel, aluminum, brass, and copper. It eliminates chip-related problems and minimizes tool breakage and wear.
At SKF the emphasis is more on tool geometry. The company recently introduced its ADX line of TiN-coated HSS drills, as well as CDX carbide drills. Both use a specialized point geometry that makes them compatible with the performance requirements of CNC machines. Flute geometry was also changed to provide more space for chip removal. Convex cutting lips protect the outer corners of the drill, allowing it to handle faster feeds and speeds, and therefore higher penetration rates.
In one recent application, ADX was used to drill 125 holes in steel end plates used to mount heat conversion tubes. By switching from carbide drills to ADX, the customer was rewarded with longer tool life, as well as a 30% reduction in overall cost since the ADX drills can be reground in-house without special fixturing.
Also focusing on tool geometry is Precision Twist Drill Co, Crystal Lake, IL. Available in HSS or cobalt steel versions, the company's QC twist drills feature a self-centering positive-rake point and computer-modeled flute form that result in higher speeds and feeds and improved chip evacuation.
Through-the-tool cooling has been around a long time, and has proved useful in removing chips from the hole, particularly blind holes. But the kind of coolant used is coming under new scrutiny. Industry wants to replace oil-base coolants with synthetic coolants because of environmental considerations, but, according to Sandvik's Mr Yakamavich, the new coolants tend to reduce tool life. As a result, Sandvik and several other companies are looking at ceramics and cermets as basic tool materials because of their high-temperature capabilities.
Dan Sullivan, president of Danco Inc, a tool distributor in Waterbury, CT, takes a different view. Machining centers, he says, are now using pure vegetable lubricants to good effect. Vegetable lubricants not only prolong tool life, but allow faster feedrates. They also eliminate the need for solvent-cleaning of parts.
Many drills and taps that used to be considered special are now standard, but specials still play a big role in the business. In any machining situation, says Vermont's Mr Burns, you start with the application. You want the best standard tool available, one that minimizes costs and cuts delivery leadtime. But often the part configuration or, for example, an oversize pitch diameter, means that you have to go to a special.
That's not as bad as it sounds. Mr Burns points out that in high-volume applications, customers will get better performance at lower cost per hole if they "optimize the tool." He says the trend among US tool manufacturers is to convert their former specials to off-the-shelf products, giving customers almost immediate delivery on drills and taps matched to their workpiece material, machine capabilities, and other variables.
A good example of a true special is the drill recently produced by Ingersoll Cutting Tools, Rockford, IL. A company in California came to them looking for a tool to drill a 6" hole through 11.5" of annealed 4140 steel (23/24 Rc) in one pass. The result was the longest drill ever made by Ingersoll, one with a narrow shank and six through-the-tool inside coolant stations.
The previous process required several tools and two to three hours to complete. The customer started with a 2" HSS drill and worked its way out with a succession of boring bars. The tools heated up quickly and needed constant resharpening. Chip evacuation was a problem. The new 6" drill runs at 355 rpm, 550 sfpm, and cuts the 11.5" hole in 8 min.
Zagar Inc, Cleveland, OH, contributes to increased productivity with its new Thruster line of automatic drilling/tapping machines. To be shown at this year's IMTS in September, they are available for single-spindle operation or for coupling with Zagar's multiple-spindle drilling heads. The units are designed to extend the production capabilities of most CNC milling, turning, and grinding machines.
Used for through-hole drilling, the machines let operators drill and tap a hole in a single pass. In blind hole drilling, after the drill has been withdrawn, the tap automatically indexes into position, minimizing machine downtime for changeover. Four machine sizes will be available, offering from 0.5 to 7.5 hp and from 250 to 2000 lb of drilling thrust at shop air pressure.
James Crockett, Kennametal's product manager for indexable drills, says the standard tool in holemaking today is the helical flute twist drill. But, he adds, advances in holemaking technology plus machine tools with greater control, rigidity, and capabilities for expanded feeds and speeds have made indexable carbide inserts important in drilling.
These inserts can operate at speeds up to five or six times faster than conventional HSS spiral flute drills, making for quick penetration of the material. They're generally used for holes with diameters of 5/8" to 3" and depths of 1" to 9". Smaller diameters call for special tools with high horsepower requirements and special coolant delivery/chip evacuation designs.
Among its many lines, Kennametal offers positive geometry insert KUB drills licensed from Komet of America Inc, Schaumburg, IL. The positive trigon inserts feature a new chipbreaker geometry that increases fracture resistance and improves chip control. The drills are said to have increased tool life and feedrates, provide better hole finish, require less horsepower, and allow drilling into uneven surfaces without prefacing the workpiece.
Mr Crockett points out that drilling with nested positive inserts places different requirements on the carbide substrates; therefore, different grades are generally used to handle the difference in thrust and surface speeds. Typically, the inside insert is set 0.012" to 0.20" off-center to eliminate the zero velocity point. The edge trepans a small cone at the core while cutting. The outboard insert travels faster and determines the hole size.
Higher surface speeds are not the only benefit from indexable insert drills, says Mr Crockett. "The accuracy of the positive trigon drill often allows the user to go directly to the finished hole size, eliminating finishing operations. Also, lost production time to remove, replace, and resharpen a conventional drill makes the indexable drill attractive when you want to increase the productivity of your holemaking manufacturing operations."
In keeping with industry trends, Kennametal lets users customize their drilling operations by employing Tin, TiN-TiCN, and aluminum oxide coatings in a variety of combinations. In its KC990 grade, for example, the coating is a TiCN backing layer 6 microns thick, an active zone of three alternating aluminum oxide layers separated by Tin layers, and a top layer of TiCN flashed with Tin. Re cobalt substrate with 7% cubic carbides provides the required toughness and hardness.
What you need to know about tap chucks
Kennametal's Jerry Hanna says he sees a lot of confusion among customers regarding tap chuck selection. He points out that there are five basic types:
Type Use Tension/compression General purpose Self-releasing Controlled depth Self-reversing High production Torque control adaptor Tap breakage prevention Solid tap chuck Synchronous tapping
Tension/compression chucks use spring-operated axial float to compensate for differences in machine feed and tap lead. Every tap has fixed feedrate equal to its lead. For example, a #10-32 tap has 32 threads per linear inch. It will advance one inch in 32 revolutions, meaning a lead of 0.03125 ipr. The machine tool feedrate must exactly match that lead to successively cut accurate threads. Until synchronous feed controls came along, most machine tools couldn't execute these precise feedrates. With tension/compression chucks, they can.
Self-releasing chucks can be used as tension/compression chucks for through holes, or for controlling thread depth when tapping blind holes. The inner slide of the chuck drives the tap into the hole until the slide reaches the end of its tension stroke. It is then released into a neutral position, and the tap stops cutting. The tap is then reversed and driven out of the hole. This provides an accurate way to control thread depth and prevents the tap from bottoming.
Self-reversing tap chucks provide the fastest method available for tapping holes and are best suited for high-production tapping on machining centers. They automatically reverse the rotation of the tap without reversing the machine spindle, greatly reducing wear and tear on the machine tool. They're easily installed on most machining centers.
Torque control adaptors are designed to prevent excessive torque (the twisting force applied to a tap as it cuts threads) from breaking the tap. They use a clutch mechanism that can be adjusted to match the tapping torque requirements of a specific machining operation. The mechanism will spin freely to prevent the tap from breaking.
The sole function of the solid tap chuck is to hold the tap with no movement while it is threading a hole. The demand for these chucks is increasing with the use of synchronized feed controlled tapping cycles on CNC machine tools. The control can exactly match the machine feedrate to the lead of the tap, producing the desired thread every time.
For more information from companies mentioned in this article, circle the appropriate numbers below:
Vermont Tap & Die 238 SKF Tools Corp 239 Sandvik Coromant 240 Emuge Corp 241 Kennametal Inc 242 OSG Tap & Die Inc 244 Precision Twist Drill Co 245 Ingersoll Cutting Tools 246 Zagar Inc 247 Komet of America Inc 248
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|Title Annotation:||includes related article on tap chucks; drilling and tapping operations|
|Publication:||Tooling & Production|
|Date:||Jul 1, 1992|
|Previous Article:||Tooling is in sync with production.|
|Next Article:||A profile on optical comparators.|