Page 234 - Demo

232 ISCAR DEEP HOLE DRILLINGMethod of BTA System STSThe BTA system is based on external coolant supply and internal chip evacuation through the hole in the drill (Figure 6.6.1.1). The BTA tool is directed into the workpiece during penetration by guide bushing, while a motor turns either the tool or the workpiece or both tool and workpiece. To minimize runout, the drill is supported by support bushing along the drill length. The diameter of the drill pipe (stem) is smaller than the diameter of the drill head, which provides an annular gap between the walls of the machined hole and the outer diameter of the drill pipe. This space is also known as %u201coil room%u201d and in conjunction with a coolant induction unit or a pressure head. In addition, it makes it possible to direct filtered high volume coolant to the drill head cutting edge. Coolant is injected into the pressure head under high pressure. This feature of the coolant supply requires the use of a special hermetic seal between the workpiece and the pressure head. The sealing between the pressure head and the workpiece is ensured by a sealing ring. This pressure head seals against the entry side of the workpiece to be drilled. Also, this directs the coolant to the detachable drill head; in other words, this coolant supply scheme allows the coolant to be delivered directly to the cutting edges, and large volumes of fluid (compared to the ELB drilling system) quickly remove the chips from the cutting area and send them through the hole in the stem to the chip receiver.These factors determine the need to use specialized deep hole drilling machines. But despite the mandatory use of special equipment, tooling and technological methods, the technology of drilling deep holes with an external coolant supply solves the most complex problems of machining parts with deep holes, which are inaccessible for solution by any other technologies, and is recognized as the most advanced deep hole drilling technology.Figure 6.6.1.1workpiece drill head chip boxmaterialdrill tube sealing guide bush oil pressure headsupport bushing