New Tech Offers Improved Drilling Productivity for Steel, Cast Iron
Article From: May 2021 Manufacturing Engineering, Jim Lorincz, Contributing Editor, SME Media
Advances in geometries, coatings, coolant, combination tools mean better holes faster
It’s fair to say that holemaking accounts for the largest share of machining both in small shops and large production facilities today. And the bulk of that holemaking is drilling in steel and cast iron up to 1″ (25 mm) in diameter. What is driving drilling and tapping performance are advances in substrate, coatings, three-flute designs, and combination tools. Just as important are advances in coolant delivery, using different size holes and shapes to facilitate chip evacuation.
You might be able to use some of the recent developments described here by several leading toolmakers.
Drew Strauchen, executive vice president, GWS Tool Group, Tavares, Fla., noted that part of the evolving trend in holemaking (and metalworking in general) is the customization of holemaking solutions to more perfectly fit the customer’s exact application while minimizing operations. “Being able to pick the best substrate, geometry, coating, and tool lengths for the shop’s specific application is paramount to more manufacturers looking to compete in a global market. Along with customization is combining two or more tools to further reduce operations and cycle times—the very definition of optimization,” he said.
In addition to implementing new advancements in technologies, GWS Tool Group is designing combination tools that permit customers to perform multiple drilling operations with one tool, instead of two, three or sometimes even four tools. “Being able to tailor a tool for a specific application is critical for reducing operations and cycle times,” said Strauchen. He supplied an example of a combination tool developed for an electric car manufacturer.
“The tool was designed for a highly abrasive, high-silicon aluminum component. The tool’s geometry combined a counterbore, chamfer and drill in a one-step tool that eliminated costly cycle time,” Strauchen said. “Previously, the process required three operations, three tool changes and inventory management of three different part numbers. The three-flute, high-shear design features coolant passages behind each cutting edge to maximize feed as well as super-polished flutes to further improve chip evacuation. Feed rates in this application exceeded 300 ipm.”
The substrate was ultra-fine grain carbide with reduced cobalt content to reduce the possibility of built-up edge. The tool coating was a material-specific ALU coating that extends tool life while maintaining sharpness.
Three-Flute Steel Drilling
Steel applications are also benefiting from three-flute drills for a number of reasons, according to Strauchen. Formerly used effectively just for aluminum applications, three-flute drills are becoming increasingly popular for materials like cast iron and steel. “New flute forms married with coolant-through technology have expanded the capability for ferrous materials. Adding the latest in ultra-smooth PVD coatings and integrating reverse web tapers has further enhanced our capacity to produce drills that optimize productivity while ensuring stable chip evacuation,” he said.
The number one challenge of drilling with three flutes in steel is getting the chips to evacuate through a flute volume that naturally gets smaller with the addition of the third flute. “Aluminum chips are softer and more malleable so they can be ejected out of the hole even if the chips are longer,” Strauchen said. “Steel chips, on the other hand, are far less forgiving if not broken and controlled adequately. With the addition of a third flute it’s critical to produce small chips (6’s and 9’s) to ensure stable, consistent results.”
Combination tools are versatile, as this selection from GWS suggests. “Each tool has its own story and problem it solved,” said Strauchen. “One drill creates three steps within the part with mirror finishes. Another is a four-step high precision reamer with 45˚ coolant ports in each flute. This design maintains tolerance within 2 μm and finish under 8 RMS.”
He also described a large brazed-carbide reamer with staggered coolant ports in each flute. This brazed-carbide reamer features an independent rotating plunger designed to detect blind or undersized holes. It detects these holes by compressing when meeting an obstruction and blocking coolant, which stops the machine prior to the tool breaking.
Designed for Specific Materials
YG-1 USA, Vernon Hills, Illinois, is a full-line supplier not only of holemaking tools but also of carbides, round tools and inserts as well as high-speed steel, powdered metals and cobalt. It produces some 60 million round tools a year, according to Steve Pilger, national product manager, holemaking. “We service our customers with the latest CNCs as well as legacy Bridgeports. The holemaking challenge for shops is to make a higher quality product and make it in the shortest time possible to the highest tolerances with tools that have superior life and application capabilities,” said Pilger.
YG-1’s premier product is the Dream Drill solid-carbide drill, according to Pilger. “Dream Drills maximize tool life and chip evacuation when running cast irons and steels,” he said. “For example, for steel applications to perform at the most efficient feeds and speeds, a split-point style drill might be recommended, while for a stainless steel you might use a more positive four-facet style.” Dream Drills are available from 1-20 mm diameters in 3xD, 5xD and 8xD lengths. YG-1 also offers them in 10xD, 15xD, 20xD, 25xD and 30xD extra-long drills, all from stock. “Some customers are changing how they run some steels like 4140 alloy steel. They want to process high quality parts at high production rates,” said Pilger. “They need higher speed cutting, taking the average 350 to 450 sfm to produce the highest quality parts and achieving the longest tool life.” For these high-production, high-volume environments, YG-1 offers the Dream Drill Pro line for alloy steels and cast-iron auto parts.
For drilling steel and cast iron where flexibility is valued and the highest speeds and feeds aren’t required, YG-1 offers the I-Dream Drill General line, which offers versatility in drilling steels, carbon, alloy, and cast irons.
The newest addition to YG-1’s drill lineup is the I-ONE modular interchangeable head drill, available in 3xD, 5xD and 8xD lengths. The steel body offers flexibility and can hold five or six different size inserts cutting from the same flexible steel body. I-One offers the advantages of a carbide drill with flexibility of a steel body.
For coating, YG-1 has developed a post-coat treatment for its proprietary H coating that aids chip evacuation in deep-hole drilling. “The treatment smooths out the peaks and valleys that result in coating. We found that we can pick up about 20 percent more tool life by applying polish to inserts, insert tips and normal sized drills,” Pilger said. “For deep-hole drilling, high-pressure coolant delivery on machining centers has enabled shops that 15 years ago were forced to gundrill parts at 1-2 ipm on dedicated gundrill machines. Now they can process the same deep holes on CNC machining centers at 20 to 30 ipm.”
Exchangeable Head Drilling Lines
Advanced technologies used in Iscar USA’s two-flute SUMOCHAM exchangeable head drilling line form the basis for the design of its three-flute LOGIQ3CHAM exchangeable head drill line. “When you think of a hole, it seems to be very simple—just a radius projected into a third dimension. But it’s a common feature that is used for producing products in job shops and high production environments, like automotive. [It is also common in] high-precision applications like die mold, medical and off-road industries,” said Craig Ewing, national product specialist-drilling for Iscar USA, Arlington, Texas.
SUMOCHAM, which is available in diameters ranging from 4 to 32.9 mm (0.157 to 1.295″) in 0.1 mm (0.004″) increments, offers a variety of edge preps for various carbon and alloy steels, as well as high-temperature steel alloys and stainless. SUMOCHAM features a clamping system that enables improved productivity output rates, while enabling more insert indexes. The shank itself is designed with twisted nozzles and has a durable and stably constructed body. The indexable heads are available in ten different standard geometries designed for drilling steel, exotic materials, cast iron or aluminum, according to the company.
The unique pocket design of the SUMOCHAM drill takes advantage of the cutting forces that are mechanically exerted upon the tool. These forces are converted into gripping forces used for tightening the insert towards the back of the pocket—the more cutting forces applied, the better gripping forces obtained.
SUMOCHAM exchangeable head drills offer a variety of styles for the common alloy steel applications, said Ewing. “They are available in 1.5D, 3xD, 5xD, 8xD and 12xD depths for typical machining center applications with CAT 40 and 50 shanks, HSK, CAPTO, live tools in lathes and for use in multifunction machines like the Mazak Integrex,” he said.
LOGIQ3CHAM is a three-flute exchangeable head drill line available in diameters from 12 to 25.9 mm (0.472-1.020″) diameters. Drill bodies come in 1.5xD, 3xD, 5xD and some of the sizes in 8xD. The extra flute enables higher feed rates to be obtained, which increases productivity. “We’re seeing the third flute as being more beneficial in high-production applications as well as increasing tool life,” said Ewing.
LOGIQ3CHAM is designed for carbon and steel materials ISO P and ISO K cast irons and nodular irons. It can increase productivity by up to 50 percent when compared with common two-flute drills with exchangeable heads, according to Iscar. Concave cutting edges enable smooth penetration into the work material, as well as excellent centering and stable drilling. Features include a durable drill body made from a hard, high-strength steel grade for better wear resistance. Polished flute surfaces ensure smooth, easy chip evacuation,, and dovetail clamping prevents the drilling head from being extracted from the drill pocket during retraction, according to the company.
Steel Alloy, Iron Threading Challenges
Threading a hole is one of the last critical production steps and having the right tap is critical for avoiding part rework or even scrapped parts, according to Mark Hatch, product director, Emuge Corp., West Boylston, Mass. “When working with materials such as steel alloys and iron, there are a broad range of complexities to address for proper tap selection,” he said. “When tapping alloyed steels, [there are] variations in chip shape, size and length due to variables in chemical properties and heat-treatment. The type and percentage of each chemical element, in conjunction with heat treatment, combine to produce different mechanical properties which affect machinability. When choosing a tap for the application at hand, factoring in the tap substrate, coating and geometry is key. “
When selecting a substrate, several machining factors are critical, such as torque, thermal stability and wear factors. A powdered metal HSSE-PM substrate, for example, offers added wear resistance for better quality tool edges.
Over the past five years, Hatch points to improvements in tap tool life and process consistency due to improved tool coatings. “Emuge has developed optimized coatings that are designed for excellent thermal stability, wear resistance and a low friction coefficient. Because coating adhesion on taps can be challenging due to the tools’ peaks and valleys, Emuge has engineered coatings that are precisely distributed across surfaces and will stay put,” Hatch said.
Tool geometry is a key factor for the efficient threading of steel alloys. Choosing a straight flute or a spiral flute such as low helix angle (slow spiral flute) or high helix angle (fast spiral flute) will depend on the machinability of the material—how hard it is and its heat treatment. The choice directly affects the chip produced and the tap chosen for the job. If the material is annealed, a long chip will be produced and a high spiral tap may be a good option. However, as the steel hardens, this type of tap may break.
Manufacturers have good options in both roll forming (chipless production of internal threads) and cutting taps. For example, Emuge offers Innoform–Steel-M, a line of HSSE-PM taps for forming threads with improved surface quality, while increasing static and dynamic thread strength, in medium strength steels up to 44 HRC.
Innoform-Steel-M Taps feature polygon geometry for low torque and longer tool life. A special powdered metal substrate and a TiN-66 coating with increased hardness reduce friction and extend tool life. Innoform-Steel-M Taps are recommended for forming cold-extension steels, cementation steels, castings, heat-treatable nitriding and cold work steels, as well as high-alloyed and hot work steels.
When long chips are the challenge, taps are available with cutting face geometry and spiral flute form, which combine to affect chip flow, chip curl and chip length. Emuge chip-breaking technology (Emuge CBTz) produces short, broken, controllable chip formations that eliminate flute clogging and potential failure of the machine tap due to chipped cutting teeth or breakage, according to the company.
The CBTz tap is surface treated with TiN to reduce friction between the tap and workpiece, which results in improved thread finishes and increased tool life in carbon and alloy steels, cast and forged steels, tool and die steels and 300 stainless steel up to 35 HRC.
For short chipping hardened steel and cast iron, Emuge A-H Taps are a new generation of Premium HSS-E and HSSE-PM taps that are especially efficient for tapping abrasive materials and materials with high hardness levels, such as cast iron, common in the heavy equipment and agricultural vehicle markets. Emuge A-H Taps are available with or without coolant through holes and with TiCN coating, or NT nitride surface treatment, for improved tool life.
Important Tap Holder Considerations
Successful tapping applications depend on several important factors. These can include axial compensation on CNC machines, internal coolant supply, and special advantages related to self-reversing tapping attachments, according to Mark Johnson, president of Tapmatic Corp., Post Falls, Idaho. “Rigid or synchronized tapping on CNC machines has become an industry standard,” he said. “Even though the synchronization of the machine’s feed advance to the spindle rotation is accurate, there will always be a small discrepancy between the actual pitch of a specific tap and the machine’s synchronized movement.”
Using a completely solid holder means that even a very small discrepancy will cause high axial forces on the flanks of the threads. “This has a negative effect on tap life and thread quality,” said Johnson. “Using a tap holder with a small amount of axial compensation allows the tap to better follow its pitch and this reduces the axial forces for a dramatic improvement in tap life and thread quality.”
Tapmatic’s SynchroFlex tap holders include a machined flexure that provides a small amount of axial compensation. “The SynchroFlex flexures have a high spring rate, which is important for avoiding axial miscutting,” he said. “If the spring force is too soft, like in the case of traditional tension-compression tap holders with a large amount of axial compensation, axial miscutting can occur. This is especially true when using free-cutting, high-speed taps often recommended for synchronized or rigid tapping cycles. SynchroFlex is designed to provide just the right amount of compensation for synchronized tapping.”
Lubrication is important for tapping in general and especially for roll form tapping. “Using a tap holder with internal coolant capability allows the use of taps with either an axial coolant hole for blind holes, or radial coolant holes for through hole applications,” said Johnson. “This gets the coolant where it is needed for the cutting or forming of the threads. It also greatly helps with clearing chips out of the hole when using cutting taps.”
Tapmatic’s SynchroFlex tap holders all include a balanced, high-pressure internal coolant system. Pressure up to 80 bar or 1,200 psi can be used and because the system is balanced, the coolant pressure does not influence the tap holders axial compensation.
Self-reversing tapping attachments offer special advantages compared to synchronized tapping. “With synchronized tapping, because the machine spindle needs to stop and reverse within a very limited number of revolutions, it is not possible for the machine to maintain the programmed spindle speed. Using a self-reversing tapping attachment allows the machine spindle to turn continuously in one direction at the actual program speed. The result is a shorter cycle time,” said Johnson.
For example, in one test using rigid tapping to tap ten M8 holes at 2,500 rpm, cycle time was 18 seconds. Repeating the same test at 4,000 rpm saved just one second. Using a self-reversing tapping attachment at 2,500 rpm to tap the same ten M8 holes took just 11 seconds. “In addition to improving cycle time, using a self-reversing tapping attachment also allows the tap to run at the recommended speed, and this provides longer tap life as well,” said Johnson.