Patent GB-775856-A (GB)
Title: A new or improved process and apparatus for machining or grinding or polishing or finishing work-pieces
Inventor: SHARMAN JOHN CHARLES
IPC: B24B17/02
Filed: 1952-04-18
Abstract: 775,856. Grinding . GARRINGTONS, Ltd. July 20,1953 [April 18, 1952], No. 9817/52. Class 60 [Also in Group. XXII] Apparatus for surfacing an elongated work blank, such as a gas turbine blade, which is of irregular cross-section and provided with a groove, recess or shoulder disposed at an angle to its longitudinal axis comprises means for subjecting a matrix of form corresponding with the desired form of the finished work piece and a work blank to synchronized rotation or oscillation about spaced parallel axes, means for engaging a tracer with the matrix surface and for utilizing the relative movement between the tracer and the matrix ta control the relative position of a surfacing tool in operative engagement with the work blank so as to shape the surface of the same to a configuration identical with that of the matrix, means for advancing the work blank and tool relatively longitudinally of the blank so that the tool describes a helical path thereon, the means operative when the tool is at the inclined groove, recess or shoulder for changing the angle of the helix so that it corresponds with the inclination of such formations. As applied to the grinding of a blade 15, Fig. 1, which projects from the inclined face 21 of a shoulder platform 18, a tool in the form of an abrasive band 38, Figs. 4 and 5, and the tracer constituted by a roller 44 are supported in a hollow head 39 carried at the ends of parallel liriks 45, 46 so as to be disposed above the work blank 15 and matrix 30 which are mounted on a longitudinallymovable slide 25. Chucks 27, 28, Fig. 7, on the slide receive the root ends of the matrix and work blank, respectively, the opposite ends of which are supported in tailstocks 31. The drive of the chucks from an electric motor 37, Fig. 4, is through infinitely-variable gearing 36, chain drive 34, shaft 33 on the fixed frame and gearing 32 so arranged as to effect the drive while permitting movement of the slide 25. The gearing 36 is controlled by a pneumatic or hydraulic ram so as to maintain a constant linear relative velocity between the band 38 and surface of the blank which it engages, this effect being produced by a cam 77b, Fig. 7, which is shaped peripherally to correspond with the cross-section of the blade, rotates with the chuck 27, and actuates the control valve of the ram. The band 38, which is driven by a motor 42, passes over idler pulleys 40 and( at the point of engagement with the blank, a barrel-shaped roller 43. The tracer roller 44, which is also barrelshaped, is rotatable on an axis parallel with that of the roller 43 and carried by a vertically-adjustable slide 50. The inclination of the head 39 to the vertical is continuously varied during each revolution of the blank so that the band makes substantially point engagement with the blank and its operative surface is maintained tangential to the blade surface. For this purpose, the pivot 52, Fig. 4, of the upper pair of links 45 is formed as an eccentric rotatable by a pneumatic or hydraulic ram 56 as controlled by a valve 56a, Fig. 7, actuated by a cam 56b which rotates with the chuck 28 and is shaped peripherally to correspond with the variation around the cross-section of the blade of the inclination of the blade surface measured longitudinally of the blade and relatively to its axis. The control valve 56a is carried by an arm 56c pivotable about the axis of the chuck and engaging at its outer end a sine bar 56d which is mounted on the fixed frame for adjustment out of the horizontal whereby the action of the cam may be advanced or retarded 'in accordance with the degree of twist of the blank. The roller 43 is given one to-and-fro oscillation about a vertical axis during each rotation of the blank so as to provide a smooth surface finish and ensure that, when the band is dealing with that part of the blank adjacent the inclined face 21 of the platform 18, it lies parallel to such face when operating on both sides of the blank. For this purpose, the roller 43 is supported on a vertical spindle 58, Fig. 8, having a lateral arm 60 engaging an inclined cam slot in a plate 61 on a carrier 62 which is movable vertically by pneumatic or' hydraulic ram 64; the control valve of the ram is actuated by a cam rotating with the chucks 27, 28. The slide 25 is advanced slowly to feed the blank and matrix past the band. and tracer during the finishing of the main portion of the blank (so that the tool and tracer describe helical paths on the blank and matrix) by an electric motor 68, Fig. 4, which drives a crank disc 67 carrying an adjustable crank-pin 69 connected to the slide by a rod 70 incorporating a doubleacting pneumatic or hydraulic ram 71; during this operation, the ram is ineffective and one of a pair of adjustable stops 73 on the rod 72 of the ram contacts an abutment 74 on the ram. When the band 38 reaches a position adjacent the inclinedplatform face, the slide is reciprocated to and fro for the distance a, Fig. 1, once for each revolution of the blank by the sole action of the ram (to provide the desired change in the angle of the aforesaid helical path); the control valve of the ram which acts through a servo-valve is controlled by a cam 71b, Fig. 7, rotating with the chuck 27. The ram is rendered operative for this purpose when a dog 88 moving with the slide acts through a stop 86 to slide coupled bars 82, 84 whereby an abutment 81 opens both a switch 79 to stop the motor 68 and a valve 78 to permit the supply of pressure fluid to the control valve of the ram. To achieve this effect, the slide bar 82, which is coupled by cranks or eccentrics 83 to the bar 84, had previously been set by a hand knob 90 to its extreme right-hand position so that the abutment 81 is correctly placed to operate as described above under the action of the dog 88. At the end of the operation, the hand knob 90 is turned to slide the bar 82 leftwards so as to actuate the valve 78 and switch 79 to stop the ram 71 and start the motor 68 in reverse for the return of the slide 25. When the slide reaches its extreme withdrawn position, the dog 88 acts through a stop 87 to slide the bars 82, 84 whereby an abutment 93 opens a switch 95 to stop all the motors; the actuating member of the switch also actuates the control valve 49a of a ram 49, Fig. 4, which by its connection to the lower pair of parallel links 46 lifts the head 39 clear of the blank and tracer. After the insertion of a new blank, the turning of the knob 90 slides the bar 82 to cause the abutment 93 to actuate the switch 95 to re-start the motors and lower the tool head The above arrangement may be modified by providing a separate abrasive band for operating upon each of a number of parallel blanks or one band passing around a series of pulleys for action upon all the blanks, and, if desired, the abrasive band may be replaced by a grinding wheel or milling cutter. Specifications 777,857, 777,858, and 777,859 are referred to. The Provisional Specification describes also the actuation of a trip arm on the slide 25 at the appropriate time in the machine cycle to bring a follower into engagement with the cam 71b which thereafter controls the ram 71 to reciprocate the slide in the neighbourhood of the shoulder platform.