Drilling holes with high precision on difficult-to-machine materials can be highly challenging. To successfully machine difficult-to-machine materials, including large titanium alloy or composite parts from the aviation industry, to very small size Inconel alloy medical devices, various difficulties need to be overcome, including cutting heat, high abrasive (e.g. composites), high hardness (e.g. quenched steels), and high viscous (e.g. austenitic stainless steels). To address these issues, a comprehensive approach is required, optimizing the drill geometry, edge preparation, substrate grade, tooling cutting edges and coolant delivery, among other aspects.

Forming chips that are easy to handle

AMEC’s director of research and development, Joseph Nuzzi, pointed out that “the end user always wants higher chip removal rates, longer tool life, and better hole shape quality. At our annual technical training seminars for users and dealers, we always tell them that in any efficient drilling operation, the first thing that must happen is that small enough chips must be formed that they can be easily removed from the hole. The drill bit must have a reasonable cutting edge geometry, and once the proper chips are formed, the cutting fluid medium must provide sufficient dynamic energy to remove the chips from the hole by flow. To achieve smooth chip removal, a cooling fluid system consisting of internal cooling tools and high-pressure cooling fluid is essential, since the proper cooling fluid system can remove more heat from the tool.”

The geometry, cutting edge strength, material grade and coating of the AMEC's GEN3SYS XT replaceable nozzle type efficient drill are specifically developed for drilling stainless steel, high temperature alloys and nickel based alloys (such as Hastelloy, Monel and Waspaloy alloys).Austenitic stainless steel (usually 304, 316, 350, 321 series) used in the food machinery and pressure vessel industries is difficult to machine. These materials have a large strain rate (the ratio of chip thickness to feed per tooth) and in drilling stainless steel, the large strain rate is converted into a very thick chip. In this case, the drill must have the correct geometry and the cutting edge must be prepared with the appropriate coating to ensure that the drill is not easily broken and can withstand cutting temperatures.

Nuzzi pointed out that “GEN3SYS XT bits (‘SS’ flute pattern) form ideal chips when drilling austenitic stainless steel. It is important to remember that efficient drilling is not possible without good chip formation. To ensure smooth chip removal, it is necessary to form tight conical chips, or tight ‘6’ and ‘C’ chips. The deeper the hole to be drilled, the more difficult chip removal becomes.”

Nuzzi said, "Composites, metal matrix composites, phenolic materials and carbon fiber composites all have very low tensile strength and are extremely abrasive, so drilling these materials is like sanding the drill bit with sandpaper, the back face of the cutter is very easy to wear. We have developed a range of TA drill bits for drilling composites, as well as a range of GEN3SYS drill bits with diamond film coating or PCD coating, and we have developed a vacuum suction drill bit for the TA drill bit product line that can remove the dust generated when drilling composites."

Predictable tool wear

Sandvik Coromant's drilling products and John Dotday pointed out that when machining hardened materials or composites, end users want tooling wear to be predicatable. "Disaster machining materials cause some special machining problems, but as long as we select the right tooling and cutting parameters, we can overcome these difficulties. If we tell the user that a certain type of drill can drill 100 holes in one day, they will expect that drill to consistently drill 100 holes per day. The trend today is to drill in the hard condition of the material, as opposed to drilling in the soft condition of the material in the past, and then hardening the workpiece and performing reaming operations. Maybe secondary drilling is required if necessary. Now, users want to directly drill the hard workpiece, thus eliminating the subsequent process." Sandvik Coromant has launched a new CoroDrill 860 PM 4234 solid carbide drill, which is coated with TiAlN, with a diameter range of 3-20mm, suitable for machining automotive parts made of stainless steel sheets and wear-resistant sheets with materials from 1018 steel to tool steel.

Composite materials is a special processing field. Sandvik Coromant has launched CVD coated drills CoroDrill 854 and 856 for composite material cutting. The 854 drill is for drilling composite materials with a high carbon fiber content (over 50 per cent); the 856 drill is for materials with a high resin content (over 50 per cent). For the hand-held electric drill, often used in the aviation industry, the company has launched an uncoated 452 series drill, which prevents material tear and delamination when drilling composite parts.

Kennametal offers a complete line of drilling solutions for a variety of specific applications, including solid carbide drills, replaceable insert drills, and modular drills, as well as precision reamers and tapping tools. The company’s new solid carbide drill portfolio includes solutions for machining high-temperature alloys and precious metal materials. “The Beyond solid carbide drill family, launched by Kennametal, features new Beyond material grade, which maintains its excellent performance whether it is a new tool made by a tooling manufacturer or a tool that has been regrinded by a factory,” said Frank Martin, global product manager at Kennametal. “The Beyond drill features a propriety surface treatment technology that reduces drilling pressure and torque, and improves chip flow and drilling performance. As a result, Beyond technology is able to improve both tool life and machining consistency simultaneously.”

The Knauf offering for a specific application of a drill bit combination also includes the Y-TECH drill bit developed for drilling difficult-to-machine materials. The unique cutting geometry of this bit can reduce the freedom of the drilling motion, overcome the tendency of the drill bit to wander, and improve the straightness, roundness, cylindricality, and parallelism of the hole. Martin explained, "All drills— whether they are high-speed steel drills, hard alloy drills, or indexable drill bits—when they enter the workpiece, the workpiece material forces the drill to wander, thus making its cutting path triangular and constantlying, resulting in a poor hole shape. This is also the fundamental reason why subsequent hogging operations are required. The Y-TECH drill bit features an asymmetric cutting edge and land design to counteract the irregularing of the drill bit, making its motion more predictable and significantly improving the quality of the hole.

The SumoCham replaceable-tipped drill from Iscar (Iscar.com) that features a “M”-style cutting edge is well-suited for drilling titanium alloys, Inconel alloys, Waspaloy alloys, Hastelloy alloys and stainless steel. “The SumoCham drill uses two small holes that run the length of each flute to deliver coolant,” said Ben Davis, product manager for Iscar’s drilling portfolio. “This dual-hole design routes more coolant to the bottom of the hole and flushes chips out of the hole, compared to a single inner cooling hole that routes coolant through the center of the drill body. Positioning the cooling holes inside the flute also increases flute depth to enhance chip evacuation.” The company’s DR Twist family of drills also uses the same coolant-delivery method.

Davis pointed out that "when machining workpiece materials, it is usually necessary to rely on the chips to take away a portion of the cutting heat, but the heat absorption and heat dissipation capabilities of high-temperature alloys are poor, so it is necessary to reduce the heat at the cutting edge by using appropriate tool geometry, coatings, and coolants. Therefore, I suggest that when drilling high-temperature alloy materials, the cutting speed should be lower than that for drilling materials such as alloy steels. Reducing the drilling speed can reduce the cutting heat and prevent the workpiece from work hardening."

Improve drilling quality

The MHS WSTAR family of twist drill bits, provided by Mitsubishi Materials America Corporation, is designed for drilling tool steel and other hard materials. It features a 6-8% thickened shank than traditional twist drill bits. In addition, the double-lip design ensures straight holes, preventing the drill bit from wandering and breaking. Nika Alex of the company explains, “To increase the strength of the drill bit, the spiral angle of the MHS drill bit is slightly smaller than that of our conventional drill bit, while the main and secondary relief angles on the flute are larger. All these changes in parameters are to ensure that the drill bit does not break easily when the cutting force increases.” The company’s MCS family of twist drill bits for drilling CFRP materials is available in eight sizes. The drill bit uses a newly developed PVD diamond-coated grade, with the flute surface extending down from the top of the flute tip and a larger flute surface to improve the chip removal performance of the drill bit.

The Phoenix drill from BIG Kaiser Precision Tooling Company features a distinctive drill point geometry that reduces cutting forces acting on the drill when machining hard steels and stainless steels, extending tool life. A more recent addition to this product line is the Power-Phoenix deep hole drill, capable of drilling depths up to 30 times the hole diameter. This drill can effectively process even at low coolant pressures. To facilitate chip evacuation, the flute of the drill is precisely ground and coated. The processing materials include small stainless steel and titanium alloy devices used in the medical industry for implantation in the human body, as well as parts made of stainless steel, titanium alloys, and high-nickel alloys used in the aerospace industry.

Diamond coated drill bits for processing composite materials

Mark Blosser, of the Komet Company in the United States, pointed out that the advent of nano-grained diamond coated cutting tools represented a major technological breakthrough, with tooling that has very high hardness, an extremely sharp cutting edge, and is well-suited to drilling or milling composites, aluminum and aluminum alloys, and graphite materials. Blosser explained that “high-purity ultra-fine grain diamond coating can be applied to a wide range of tool sizes, including large tools and tools with complex surface shapes. The result is a significant improvement in the adhesion, stability and mechanical properties of the coating, as well as control of the surface roughness of the coated surface. The application of nano-grained coated tools has already benefited end users in the aerospace, mold making and energy industries. Examples include: doubling feed rates when cutting carbon fiber composites; and increasing tool life by a factor of 8 when drilling carbon fiber/aluminum/titanium composites.”

Secotools has launched new drill bits for drilling CFRP composites. "We have two different drill geometries," said Thomas Sandrud, product manager for drilling at the company. "The C1 bit is optimized for drilling carbon fiber and titanium/carbon fiber laminates, or aluminum/carbon fiber laminates with a carbon fiber layer at the exit." To prevent carbon fiber materials from tearing and delaminating at the exit of the hole, this diamond-coated bit features a double flute and two different drill bit nose angles. The C2 bit is used for drilling laminates with a carbon fiber layer at the entrance and a titanium or aluminum layer at the exit, and by controlling the chips, it prevents the metal chips from scuffing the carbon fiber surface. Both the C1 and C2 bits are coated with CVD Dura coating.

Sumitomo Electric Hard Metal offers three families of drills for drilling difficult-to-machine materials: the MDW GS family, SMD replaceable-tipped drills, and diamond-coated drills for processing CFRP materials. The MDW GS drill family comes in two different types: non>:内冷GS drills and HGS inner-cooled drills with two flute edges. Coatings used on the drills include TiSi and TiAlCrN composite superlattice PVD coatings. High hardness chromium-containing coatings contribute to achieving long-length drilling (The length and diameter ratio are 12D、20D、25D and 30D) of high-temperature alloys such as Inconel alloys and titanium alloys. The company recommends that with these new coated drills, higher feed rates than ever before can be used with these new coated drills.

Patrick Nehls of Walter USA stated, “Our Walter Titex X-treme drill bits are suitable for small and large quantities of drilling operations on a variety of stainless steels, carbon steels, cast irons, non-ferrous metals, titanium alloys and hard materials. It is important to minimize the cost per part when considering the number of holes to be drilled in order to maximize the return on investment. The improved performance of the X-treme drill bit extends tool life. We have been testing the bit since its introduction at the end of 2009 and have been helping end users replace their Alpha 4 bits with the X-treme bit for more efficient drilling operations. Although we may sell fewer bits to these users due to the increased tool life, the superior drilling performance of the X-treme bit will provide us with more opportunities and bring in new business.”