GB826943A - Apparatus for use in machining parts to a predetermined surface contour - Google Patents

Abstract

826,943. Grinding turbine blades and the like. NAPIER & SON Ltd., D. Nov. 16, 1956 [Dec. 1, 1955], No. 34477 /55. Class 60. Apparatus for machining a workpiece, such as a turbine blade 30, Fig. 4, to a pre-determined contour comprises a cutting member having an effective surface which is substantially in the form of a surface of revolution, means for bringing the cutting member into engagement with the workpiece, means for moving the workpiece relative to the cutting member in a predetermined manner including a work-supporting platform 28, a pair of supporting members 25 connected to two spaced points on the platform, and means for automatically moving the supporting members independently and in a predetermined manner in two directions at rightangles to each other and at right angles to the axis of revolution of the cutting surface. The turbine blade 30 is machined by abrasive belts 80, 81, Fig. 1, passing over guides 82, 83 of part-cylindrical shape, and is clamped to the platforms 28 which is pivotted on pins 27 to members 25, mounted on trunnions 24 in two brackets 23. Each bracket 23 is carried by a pair of vertical rods 17, 18 axially-movable in a housing 11(12) slidable on horizontal guides 13, 14, 15, 16. One of the pins 27 is located in a sliding block 34 to accommodate relative movement between the two pins during transverse and axial movements of the bracket. The horizontal movements of the housings 11, 12 and therefore the turbine blade are effected by two cams 44, 45 on a main cam shaft 40 acting through followers 42 on the housings which are spring-urged against the cams. Vertical movement of the rods 17, 18 and turbine blade is effected by cams 50, 51 cooperating with cam followers 52, levers 54 and members 60 in engagement with plates 21 which connect each pair of rods 17, 18. The abrasive bands 80, 81 pass over the guides 82, 83, rollers 90, 91 and driven pulleys 92, each band being tensioned by a spring-pressed roller 93 on an arm 94 and a stop 96 limiting the inward movement of the roller 93 to allow the bolt to be loose when the guide is withdrawn from its operative position. The guides are disposed on a carriage 110, which is reciprocable on guides 111, 112 by a pneumatic piston-and-cylinder device 113, Fig. 6, and linkage 114, 115, and carries adjustable abutments 118, 119 cooperating with movable stops 116, 117 controlled in a step-by-step manner by tapered rods 120, 121 to govern the depth of cut. A pneumatichydraulic system controls the movement of the rods 120, 121, compressed air being supplied to piston-and-cylinder devices 130, 131 to cause levers 134, 135 to urge the rods 120, 121 rearwards and thereby the stops 116, 117 to move further apart to allow progressively deeper cuts to be taken by the abrasive bands. In operation, with the cam shaft started, a solenoid-operated valve connects the air supply to the devices 130, 131 and to one end of the cylinder 113 to bring one of the guides, say 83, into operation upon one side of the blade 30. The device 130 by means of lever 134, applies pressure to a hydraulic cylinder 142 and a hydraulic escapement 144, imparts a small movement to the cylinder 130, rod 120 and stop 116. After a half turn of the cam shaft 40, a micro-switch 191, Fig. 2, is actuated which causes the solenoid-operated valve to connect the air supply to the opposite end of the cylinder 113 to bring the other guide 82 into operative position to machine the other side of the workpiece and to a pneumatic ram which operates the hydraulic escapement to allow the cylinder 141 to impart a small movement to the piston in the cylinder 131, rod 121 and stop 117. On completion of one turn of the cam shaft, micro-switch 192 reverses the process which is continued until the levers 134, 135 contact switches 193, 194 to stop the camshaft when the machining operation is completed. Air is also fed for cooling purposes to pipes 84, 85, Fig. 6, in the guides 82, 83 and a nozzle 183 above the blade. Specification 825,205 [Group XXII] is referred to in the Provisional Specification.