When it comes to precision machining, aerospace parts routinely require advanced process, equipment, and cutting technologies. But close behind aerospace, and possibly on a par, in technology needs are components for oil and gas drilling machinery on land and under the sea. Emuge Corp., a specialist in cutting tools, thread mills, taps, end mills, holders, and attachments, commercialized this month a line of solid carbide thread mills with innovative design features for making petrochemical drilling parts.
The line includes 20 standard tools in inch and metric shanks and a range of forms and sizes that thread holes of up to 6 in dia. They feature innovative left-hand spiral flutes, higher-than-average flute counts and core diameters, and multilayer TiALN-T46 (titanium aluminum nitride) coatings.
The thread mills are engineered for low radial cutting pressure, deep thread access, and low-vibration machining. They have four cutting edges, which are combined with the increased flute count (five to six compared with three to four on most thread mills) to ramp up productivity, extend tool life, and reduce cycle times. They come in NPT and API LP specifications (an insert program includes acme and stub-acme threads) and have precision-ground rake and relief angles for high chip-per-tooth loads.
While left-hand flute designs are not new, Mark Hatch, product director for taps and thread mills at Emuge, in West Boylston, Mass., says these may be the first ones offered by a supplier as standard catalog items.
“Many people view aerospace as the pinnacle of complexity when it comes to machining technology,” Hatch remarks. “But the oil and gas industry is technologically advanced too. The complexity and cost of parts and the materials in use are comparable to aerospace requirements, or just a little behind.”
OEMs and subcontractors routinely machine oil and gas parts from Inconel alloys, 4140 and 4340 chrome-moly steels, and stainless steel. Common parts such as blowout preventer (BOP) valves can be 6 ft high and 6 ft wide and weigh 25,000 lb. These parts are expensive, so machining mistakes are costly, Hatch notes.
Also of concern is timely supply of these parts. The oil and gas industry usually operates on just-in-time delivery schedules and can experience equipment breakdowns that call for rapid replacement parts. “If a well has to be shut down because a BOP valve is late, the cost of lost production is huge,” Hatch says. “Oil and gas companies need suppliers that run secure processes to assure on-time delivery of parts.”
All of these factors influenced the design of Emuge’s thread mills. The left-hand flute, for example, feeds the tool into the workpiece counter-clockwise compared with a right-hand spiral or a straight-cut mill. The generated axial force drives the tool holder into the spindle taper, which increases cutting stability under high feed rates and minimizes harmonics, which can cause cracks, splitting, and other thread defects.
These enhanced thread-milling capabilities reduce cycle times — in some cases by 50 percent or more, Hatch says. One undisclosed company that machines BOP valves with 18 screw inserts achieved cycle times of only 7 min per part compared with 90 min using previous tools.
The thread mills are manufactured using the most advanced grinding technology that Emuge has and consequently carry a cost premium of 30 to 35 percent. Hatch says, however, that they have at least twice the lifespan of the company’s most common thread mills.