High performance thread forming breakthrough

Citation

(2009), "High performance thread forming breakthrough", Aircraft Engineering and Aerospace Technology, Vol. 81 No. 4. https://doi.org/10.1108/aeat.2009.12781dab.003

High performance thread forming breakthrough

Article Type: Aerospace technology From: Aircraft Engineering and Aerospace Technology: An International Journal, Volume 81, Issue 4

A major breakthrough for the internal threading of blind and through holes that enables higher processing speeds, gives extended tool life and stronger and higher quality thread forms has been achieved by LMT Fette with the development of its HPF forming taps. The new threading system comprises an interchangeable solid carbide insert with through the holder coolant feed direct to the cutting zone. In addition to higher productivity gains, the replacement cost of the carbide threaded insert should also be less than a one-piece solid carbide tap.

Now available from tooling specialist LMT Fette of Coventry, the HPF design incorporates a special toolholder, that is able to accept a solid carbide insert with a choice of metric, UNC, UNF and BSP forms that is secured by a central locking screw.

Thread depths can be produced to a ratio up to three times the diameter and because the form is rolled, thus creating a compacted grain flow rather than cutting across the grain of the material. The resulting thread is stronger and has a hardened, burnished surface to high orders of precision and consistency.

As a result this new tool provides excellent levels of security in the machining process. Tool life is also extended by the use of a coated solid carbide insert enabling flank wear to be reduced, chipping of the flute is eliminated and breakage unlikely, even when the tool is driven by a high-torque spindle in difficult materials.

Applications in materials with an elongation co-efficient of more than eight per cent and tensile strength up to 1,000 N/mm² are ideal and Fette TiCN Plus PVD multi-layer coated thread inserts are available in M8 × 1.25 p-M18 × 2.5 p, 5/16-3/4 UNC and UNF and between G 1/8 and G 1/2 in. BSP thread forms.

The toolholder body has high-torsional stiffness with a series of unevenly spaced drive dogs to ensure the mating carbide threading insert is positively located in the correct position. Side coolant ducts in the body, set at an inclination of 5° to the axis of the tool, automatically align with the lubrication feed grooves on the periphery of the threaded insert.

A tough, wear resistant fine-grain carbide is used for the insert that is secured via a central locking screw and the number of forming edges is optimised according to the pitch of the thread. Also, the crest of each thread has a specially developed form to ensure a strong adhesion of the coating.

Recent applications include engine connecting rods in C70 steel when a M16 × 1.5 blind hole was threaded 40 mm deep. The spindle speed was able to be doubled to 20 m/min, tool life increased by 60 per cent to 3,100 threads and over a batch of 500,000 components, a total saving of £137,000 was achieved. A union nut produced out of nickel chrome steel and tapped M18 × 1.5 by 10 mm deep into a blind hole enabled tool life to be improved by a factor of 13 times. Meanwhile, a saving of 2.6 s/part was achieved on M10 × 1.5 threaded bush with a 12 mm deep blind hole thread that ensured the lead time for a batch of 4,000 parts was reduced by 29 h.

A range of heavy duty, solid carbide drills are also available from LMT Fette to suit the thread sizes as well as Bilz SCN Synchro slim chucks that provide up to 4 mm of length adjustment and options of internal coolant supply. Bilz is an LMT company.

Details available from: LMT Fette Limited; Tel.: +44 (0) 24 7636 9770; Fax: +44 (0) 24 7636 9771; web site: www.LMT-tools.com