The change has been made to what was a secondary operation using conventional twist drills following pre-turning when producing 3.2 mm diameter by 145 mm deep holes in M2 tool steel for through-coolant feed holes.
As part of method improvement, not only did Mollart’s application engineer recommend the change to single-cycle operation for the production sequence using a Botek Type 113 solid carbide gundrill, but also introduced Mollart’s own Spraymist system. As a result more efficient chip removal was achieved from the drilled hole and both the drill’s guide/support pads and the cutting edge zone of the tool were lubricated.
The Integrex process involved the initial drilling of a pilot hole 8 mm deep to provide a ‘bush’ support for starting the gundrill. The gundrill was then fed into the pilot hole while counter-rotating at 50 rpm until the drill point was within 2 mm of the bottom of the pilot hole ready for the Spraymist to be switched-on. The spindle speed was then increased to 4,500 rpm and a constant feed rate of 35 m/min applied up to the final hole depth. The spindle was then stopped, the Spraymist closed down and the gundrill retracted.
Botek Type 113 gundrills are available between 0.7 and 12 mm diameter and can be used for depth-to-diameter ratios up to 80:1. Each tool has a special nose grind and a highly polished flute with kidney-shaped coolant channel to ensure maximum evacuation of chips from the cutting zone.
The Mollart-developed Spraymist system is highly efficient for deep holes, using compressed airline pressures up to 10 bar, which absorbs precisely timed pulsed jets of vegetable-based cutting oil from an integrated reservoir. The system can be retrofitted to existing machine tools, and to illustrate the increased efficiency, when a gundrill is removed from the component, it will be immediately cool to the touch.
The oil is used to lubricate the tip of the tool and its guide/support pads, which prevents seizure occurring, especially in extra depth holes. Meanwhile the air effectively cools the cutting edge, as well as the component, and helps to force the swarf chips to evacuate the cutting zone through the vee grove in the tool.
