Slam dunk

When discussing holemaking, the range of requirements and options can be daunting. In most advanced metalworking applications, precision is a top priority, particularly if threading is involved.

There are many factors deriving from application requirements that specifically affect how best to proceed. Three stand out: the materials, the size of the hole, and the quality required. This article examines the benefits of such techniques, including alternatives for composite materials.

Dual carbide for high performance

For high performance drilling, a good choice is ATI Stellram’s dual carbide approach. The company says this marquee solid carbide technology can cut holemaking costs dramatically.

“This is a patented technology,” says Steve Ortiz, director of marketing at ATI Stellram in Nashville, TN. “It has two carbide substrates—combining an outer and an inner substrate manufactured in one extrusion process—with the design optimized to address the characteristics of drilling.”

Specifically, one grade of carbide is tailored to the higher speed of the tool’s outer diameter for wear resistance, with a second being tough enough to handle the lower speeds at the tool centre to resist point breakage. In the past there was a trade off, performance for durability, because the carbide grade chosen for the tool had to compensate.

“By combining this technology with ATI Stellram’s unique precision grinding, geometrical design, edge prep and the new generation of TiAlN Nano coating,” says Ortiz, “we can significantly improve productivity and tool life.”

The company’s trials have also found that the dual carbide, trademarked as HardCore Technology, can reduce tooling cost by delivering up to four times the life and two times faster production speeds than other high performance drills in the market.

And though the main product areas are either indexable inserts or solid carbide, there is also the option of using high feed milling cutters for larger holes.

“For a bigger hole a customer could use our 7792 high feed cutter for helical interpolation,” says Ortiz. “The hole range would depend on the size of the insert; it could be one to 12 in.”

Some customers may not want to change tools, and would rather just go with a bigger drill. Depth can also be an issue with a cutter. But given the advantage of high feeds and helical interpolation, a tool like the 7792 high feed cutter is definitely worth considering for bigger holes.

A thrilling proposition

Thrilling combines thread milling with short-hole drilling, and it does this in one process using a single spindle and a single cutting tool. Any CNC with helical interpolation can thread at high speeds in a blind hole.

“A thriller can drill, chamfer, and thread in a single operation,” says Mark Hatch, manager of threadmilling at Emuge Corp. in Sudbury, MA.

“These are primarily used in the automotive sector where there is high part volume, and where they are very concerned about cycle time per hole. If you consider millions of screw heads over the course of a production year, to save a few seconds off a hole is quite significant.”

Thrillers eliminate tool changes, but are most often seen in high production scenarios in cast aluminum and iron, and not so much in lower volume industries such as aerospace, medical, or oil and gas.

“We have a deep level of technology available for different industries. It really depends on the parts and the materials,” says Hatch. “When you get to aerospace, for example, it is all about having predictable processes, as opposed to automotive which is very much about speed.”

Hatch says that Emuge’s fastest growing group is thread milling, with many customers switching away from traditional tapping to take advantage of 3D helical interpolation.

“As older machinery gets replaced with newer machines, and as North American manufacturers are diversifying in response to the recent downturn, more complex jobs have better profit margins, so you are seeing shops looking at threadmilling because the simpler stuff is going overseas.”

A special case: carbon reinforced plastics

High tolerance holemaking in composites benefits from a material-specific approach. In response, Sandvik Coromant has recently come out with its new CoroDrill 452 drills for high tolerance holemaking in composite materials. This a range of drills is used for rivet and bolt holes in carbon reinforced plastics and metallic stack materials.

“About 50 per cent of composite drilling is done by hand,” says Randy McEachern, a product manager at Sandvik Cormorant in Mississauga, ON. “In aerospace, for example, components are hand drilled at the assembly stage and require high accuracy, tolerance, and excellent surface finish.”

Carbide-based drills are suitable for unstable operations, but with hand-tools thrust may be uneven, with variations in clearance. As well, carbide is strong but wears quickly in abrasive materials, and PCD (polycrystalline diamond) is wear resistant, but brittle. The CoroDrill 452 is specifically for CFRPs (carbon fibre reinforced polymer) and stacked materials. It uses vein technology to integrate the PCD-edge in the carbide drill body.

“With vein technology, PCD powder is packed into a slot at the tip,” says Hatch. “That way, the diamond is veined right into the carbide—not like a solid piece of PCD that is brazed on.”

Vein technology, which is not just for composites, is more costly, but also delivers significantly increased tool life and can reduce overall cost. With regard to carbon fibre, each material has its own demands, which increases the risk for delamination or splintering, with the CoroDrill 452 designed to ensure that stringent hole tolerances are met with decent finish and quality.

“We also have a couple of CNC drills, the 854 and 856, that are specifically designed for composite drilling,” says McEachern. “And we just launched our CoroDrill 881, which offers more security in tougher, smaller diameter ranges and non-rotating applications.”

At the end of the day, selection is made according to the character of the CFRP, with different cutting geometries and selection of PCD grades. The right drills will make holes in CFRPs that vary from fibre-rich to resin-rich, as well as being a general alternative for stacked materials. CM

Tim Wilson is a regulator contributor and freelance writer based in Peterborough, ON.

www.atistellram.com

www.emuge.com

www.sandvik.coromant.com/ca

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