Tapping out the benefits for aerospace manufacturers

Developed to offer consistent and repeatable results, optimised geometry on the new taps for titanium includes a small positive rake angle for challenging materials and an innovative, wear resistant ACN (Aluminium Chromium Nitride) coating that helps prevent weld formations.

To avoid chip jamming in challenging material, the taps also have a high flank clearance for reduced friction. For truly stable tapping, the tools for nickel-based alloys feature a reduced helix of 10°.

The thread mills are produced with MJ thread forms with a 27° helix, the optimum angle for threading exotic materials. MJ thread forms are prevalent in the aerospace industry as they help reduce stress in the thread root of components.

“When tapping nickel alloys, the most important factor is creating the correct hole size for thread size required,” explained Steve Shotbolt, Global Product Manager, Threading at Sandvik Coromant.

“Decreasing thread engagement reduces the torque necessary to drive the tap and helps eliminate any potential for tap breakage. Conventional thread engagement values of 75% have been found to be unnecessary with high strength materials; usually engagements of 50-60% are sufficient for most requirements.”

The tapping of titanium alloys such as Ti6Al4V is more challenging than most alloyed materials. For example, titanium is not a good conductor of heat, which means temperatures tend to elevate on the faces and edges of cutting tools instead of dissipating through the part and machine structure. This retained heat can result in chipped edges and reduced tap life.

In addition, titanium’s fairly low modulus of elasticity and high tensile strength gives it ‘springiness’, producing the effect of ‘closing in’ on the tap, a factor that can cause thread galling and tearing. It also increases torque on the tap and shortens its life.

The new taps from Sandvik Coromant are designed to counter these issues, helping to boost the manufacture of many aerospace engine components, including casings, shafts and discs, in fact any engine part made from ISO S materials that features bosses and/or flanges. The tools will also prove suitable for other sectors where titanium and nickel-based alloys are commonplace, such the oil and gas, pump and valve, and medical industries.

Introduced is the CoroTap 200 SM for tapping through holes in titanium, as well as the CoroTap 300 SM (blind holes, titanium) and CoroTap 300 SD (blind holes, nickel-based alloys). For thread milling, Sandvik Coromant is releasing the R217 for MJ thread forms.

In a customer performance test, the CoroTap 300 SM was able to more than double the number of tapped holes produced on an Inconel 718 workpiece, from 8 (using a competitor tap) to 17. Using a DMG DMU 60 CNC machining centre with eight percent external coolant, the cutting data was identical for both tools: 251rpm spindle speed; 6m/min (19.685 ft/min) cutting speed; and 0.907mm/min (28 TPI) feed rate.