A Shell Mill in Action
A major production machining shop in Michigan soon had a major productivity gain after meeting with Advent Tool & Manufacturing during a recent trade show. The workiece, a ductile iron carrier housing, had two large diameter threaded holes of 5 and 7” diameters with 2,0mm pitches. The existing tooling was developed as a special by a major tool builder and required a blanket order and a long lead time for a cutter of 4 flutes and 4.5” diameter. The inserts were specials also and were TiN coated carbide. Run dry because the tool was never designed to evenly distribute coolant on the cutting edge of the inserts, the customer had been running this tool for 1-1/2 years prior to Advent Tool’s visit.
Utilizing their own 4.5” Diameter precision ground shell mill, Advent Tool sent two bodies along with TiCN Coated Inserts of the 2,0mm (ISO) form that were 1.5” long. This tool was capable of holding 14 flutes, but the original load was set for 7. Built for coolant through, the coolant was turned on for the first time as it was felt that coolant could be applied evenly to the inserts, unlike in the previous design. Initial tests were spectacular. Using a relatively new CAT50 class machining center with a relatively good setup, the original program involved running the tool at a .002” chipload per tooth – as that was the feedrate for the previous tool. As the previous tool was only a four (4) fluter, the Advent Tool at seven (7) flutes was nearly double the feed rate with the same speed. After inspection showed the thread form was to spec the fun began. Chiploads were increased to .004” per tooth and Surface Feet Per Minute was increased as well, from 350 to 550SFPM in light of the coolant application.
As tool life with the TiCN coated inserts was very good with 1200 holes per load, the tool has remained in the spindle with 7 flutes. It has been felt by both parties that loading all the flutes with inserts would be a difficult exercise due to the tool length – at over 8” from gage line. As such, productivity gains have been made in coatings; the customer is now using AlTiN inserts and running at 625SFPM. Tool life has remained consistent at 1200 holes before wear necessitates modifying the inserts. Modifying, you ask? As the thread form is only .425” long, the worn portion of the insert is ground off and the tool is reset in the Z axis to insert the cutting tool further into the workpiece! This is done twice before the insert is discarded.
The end user, the one who receives the carriers, has never been happier with the fit and finish of the threaded form. At first they had asked how their vendor was “grinding that thread form” inside the bore! With a good, balanced and well made tool and with the right programming, this is what is possible!
