Mollart Engineering aims for straighter deep holes with Acubore steerable technology development

The ability to steer a drill head has been widely adopted in the oil and gas exploration industries to target specific areas underground. However, this has not been so far achieved in the production engineering environment to monitor and correct the drill path on very deep holes. This technology would provide, for instance, a distinct process advantage when drilling parts from solid having very thin wall sections or multiple series of close pitch centre holes, offering total automated control over hole straightness and breakout positioning. The Mollart Acubore process is being developed at the company's Chessington headquarters for hole sizes between 5 and 65 mm, using non-destructive, laser ultrasonic technology (LUT) and a series of programmable three point roller steadies, which support slight rotation of the component being processed to correct the path of the drill. The whole process is based upon specially developed software algorithms integrated within a Fanuc 31i control. Using the computed data captured from multi-point LUT system to monitor the progress and position of the drill point's progress relative to the outside profile of the component, minute positional changes can be accommodated. LUT technology is already proven in the checking of turbine blades for instance, but it is believed the first time it has been used as part of a live, integrated in-process production drilling operation. High penetration rates, precise hole sizing, surface finish and hole geometry (roundness and straightness) have always been an important benefit of the gundrilling process, with much of its capability based on effective tool design, a balance of speeds, feeds and coolant pressure. However, future applications from industry sectors such as nuclear and oil and gas are calling for even greater guarantees of precision that will allow very thin wall sections to be maintained, without creating deformation or break-out on the outside surfaces of a shaft, for instance, and to precisely target the other end of the deep hole. The Acubore machine will drill holes between 5 mm and 17 mm diameter using the gundrilling process, while for larger holes, up to 65 mm diameter, BTA drill heads are incorporated. Straightness values are to be maintained within an initial target of 1 mm per 2,000 mm of hole depth. Following an initial start hole in the component, the Acubore process slightly retracts the drill head, enabling the laser to approach and collect its first data point from the drilling centre line. The laser then collects two further data points, one above and one below by rotating the part in the machine's B-axis. Here, the latest generation high speed ultrasonic laser, able to operate on curved internal and external surfaces to determine voids, depths and thicknesses in its path, remotely generates a non-contact high frequency ultrasound pulse that propagates into the component and returns to the surface where a receiver captures it and where any displacement of the bore is then automatically calculated. The level of monitoring can be programmed according to the demands of the application as the hole drilling cycle progresses, with the control software algorithms calculating any deviation based on the start position datum. Any adjustment is carried out automatically by re-orientating the component and using the three-point steadies positioned along the bed of the machine to help maintain the straightness of the hole. The 7-axis (C, U, W, X1, X2, X3 and Z) Acubore machine has a Z-axis stroke of 3,500 mm and will accept parts up to 300 mm diameter weighing up to 1.5 tonnes. The machine has a 30 kW drive giving up to 5,000 rpm and develops up to 666 Nm of torque, with feed rates being programmable up to 5,000 mm/min.