High-speed holemaking: Drilling Performance

Although high-speed machining and holemaking initially were employed largely by defense and aerospace manufacturers working with nonferrous materials, increasing demand for higher production and the use of new alloys and harder metals have resulted in vastly improved high-speed holemaking tools.

The Need for Speed

The definition of high-speed holemaking varies widely depending on the material, the tool, the application and other considerations.

For general purposes, Steve Pilger, North American product manager for holemaking at YG-1 Tool (USA) Co. in Vernon Hills, Illinois, defines high-speed holemaking as “having a minimum of 5,000 rpm spindle speed based on popular diameters of carbide drills.”

Martin Hobbs, drilling product specialist at Sandvik Coromant Co. in Mebane, North Carolina, measures high-speed holemaking in terms of cubic inches or millimeters of material removed per minute.

“In terms of spindle speed,” said Bill Ruegsegger III, product manager at Allied Machine & Engineering Corp. in Dover, Ohio, “I would place the threshold at 20,000 rpm. Another way to express it would be three to 10 times faster than conventional drilling.”

Among the primary considerations for successful holemaking are the characteristics of the machine and the fixturing.

“Stability is paramount,” Hobbs said. “Both the fixture and the machine, as well as the toolholding method, have to be capable of resisting the feed forces.”

Ruegsegger agrees.

“High speeds require higher horsepower and the ability to generate torque at higher rpm,” he said. “Reserve power is also necessary in that a machine operating at 100% will wear out more quickly.”

Pilger said requirements go far beyond speed.

The material-specific GEN3SYS XT Pro insert combines a substrate coating and geometry designed to achieve optimal results in different ISO material classes. Image courtesy of Allied Machine & Engineering

“Machine capability, coolant considerations, including pressure and volume, and the need for precision-ground spindles all come into play” he said. “It’s also essential to know the machine spindle runout.”

Rigid fixturing is likewise necessary to prevent vibration and chatter. This is true even in five-axis applications.

“Early five-axis machines can have ‘give’ in the tables,” Ruegsegger said, “but this has been largely remedied. Still, the fixturing must be adequate to the application.”

Pilger said the material affects both the tooling and programming of a machine.

“In aluminum applications,” he said, “it’s possible to drill at speeds of up to 650 sfm. When it comes to materials like Inconel, titanium or special alloys, the speed has to be substantially reduced — sometimes to 70 to 100 sfm. Drilling some types of high-temperature alloys too fast will literally result in enough heat to workharden the part. On the other hand, running carbide drills too slow in many types of steels can result in a built-up edge and destroy the coating.”

Hobbs said successful drilling of heat-resistant alloys calls for the correct speed and higher feed forces.

“In the automotive industry,” he said, “ISO P (steels), ISO K (cast and ductile irons) and ISO N (aluminum) are used extensively. These materials can range from short-chipping to long-chipping materials with a variety of compositions that require a vast range of cutting edges and coatings. This makes indexable drilling solutions very popular.”

Other Challenges

New alloys and increasingly complex part requirements, especially involving deep-hole drilling, have resulted in demand for new tooling materials and techniques.

“Carbide substrates have been vastly improved, and coated carbide with post-coat treatment is the tooling of choice for deep-hole drilling in the 1 mm (0.04″) to 20 mm (0.79″) range,” Pilger said. “Beyond these diameters, we typically go to other tool designs, including modular replaceable tip, indexable insert drills and spade drills. For larger-diameter holes, a steel-bodied holder with a carbide tip is effective because the steel body is not brittle and inclined to break.”

Ruegsegger said in the past, deep-hole drilling always was done with solid carbide.

“Today,” he said, “inserts are increasingly favored because, thanks to improved coatings and geometries, they perform extremely well in hard or abrasive materials.”

Hobbs cites advances in multipurpose tooling.

“Tools that can perform more than a single function,” he said, “such as creating the pilot hole while then drilling to spec, chamfering and counterboring, not only save tool-change times but deliver greater accuracy because multiple operations can be performed in the same cycle.”

Successful holemaking depends highly on matching the drill to the correct toolholder. For routine operations, a collet holder is sufficient, but deep-hole drilling demands both increased strength and vibration dampening.

“We’ve seen a good deal of progress in conventional holders,” Hobbs said. “For instance, our ISO 9766 holder reduces the runout that you would find in a traditional Weldon holder. When it comes to deep-hole drilling, the choice would fall between shrink fit and a hydraulic chuck. The hydraulic chuck is the better choice over the long term because it is more economical and safer since it does not require high temperatures to connect the tools to the holders.”

Pilger recommends a hydraulic chuck with a sleeve for solid-carbide drills over eight times diameter.

“The hydraulic reduces runout to within 2.5 microns,” he said, “and the hydraulic fluid also acts as a vibration dampener. We’ve also found that tool life improves up to 25%.”

Few areas affecting tooling have advanced as fast as coatings.