Horrendous Holes

Horrendous Holes_Walter_alloy

Nickel and cobalt-based superalloys may not be Kryptonite, but drilling holes in Hastelloy X, Inconel 625, Waspaloy and Haynes 25 is about as tough as it gets in the world of metal removal. With machinability ratings in the low teens, these nightmare materials test the patience of even the most cool-headed machinist.

Unfortunately, modern aircraft won’t fly without superalloys, and nuclear power plants wouldn’t run. Their high strength, fatigue and corrosion resistance, and excellent mechanical properties make these materials the perfect choice for gas turbine blades, rocket motor components, oil and gas applications, and a host of other demanding environments. It also makes them a real bugger to cut.

Drilling in particular can be a super-challenge—chip evacuation and heat buildup are a concern in any holemaking operation, and doubly so in superalloys. Fortunately, four holemaking experts are here to share their insights on drilling these toughest of all materials, the superalloys.

Allied Machine & Engineering Corp., Dover, OH, manufactures replaceable-tip drilling systems and custom holemaking solutions. Product manager Robert Brown says there are several key factors to successful drilling of superalloys. “These materials have poor heat transfer properties, and can be quite abrasive. Because of that, we generally recommend indexable products running at greatly reduced speeds and feeds.”

But not too low, warns Brown, as work hardening is also a concern—managing feed rates is a balancing act between drill breakage and premature failure. “You can expect lots of flank wear, with rounding of the drill corners. Tool life is normally about 25 per cent of a comparable alloy steel job.”

If you’re a newbie to super-drilling, Brown says you should double your expectations for tool usage. That’s why drills with replaceable tips are a good idea—swapping out a $30 insert is far more cost-effective than replacing a $300 drill body when a superalloy gets the upper hand during holemaking.

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