Contour belt grinding device

Abstract

A propeller grinding device and method employs two endless grinding belts which are transported past a grinding station to finish the front and back surfaces. A propeller blank is inserted between the belts and the belts are distorted by platens, each of which includes a plurality of independent platen vanes. Two cams selectively bear upon two camming surfaces of the vanes and move the vanes into desired positions corresponding to the surface contours to be formed on the front and back surfaces of the propeller blades. The cams are rotated as the blade is moved. They also may be moved along the camming surfaces. Additionally, the cams and platens may be moved parallel to the direction of cam rotation with respect to the belts. SUBACKGROUND OF THE INVENTIONThe present invention relates to grinding devices and, more particularly, to a grinder having an endless grinding belt capable of grinding contours, such as the airfoil shape of a propeller.Belt grinders have been used in the past for finishing a flat surface. U.S. Pat. No. 2,706,873, issued Apr. 26, 1955 to Gifford, shows a sanding device having an endless sanding belt, which belt is continuously rotated and urged into contact with the workpiece by a plurality of rollers. U.S. Pat. No. 3,129,535, issued Apr. 21, 1964, shows a similar grinding arrangement in which two grinding belts grind opposite sides of the workpiece simultaneously. This eliminates the need for backing arrangements opposite the belts to offset the grinding forces applied by the belt mechanisms.U.S. Pat. No. 3,670,458, issued June 20, 1972, to Faure, shows a multiple-position grinding arrangement in which a plurality of workpieces are ground simultaneously. Cam mechanisms are used to present the workpieces in predetermined attitudes to the grinder and to alter the orientation of the grinding belts.As shown in U.S. Pat. No. 2,723,505 issued Nov. 15, 1955 to Krafft, the flexibility of a grinding belt may be utilized advantageously to grind predetermined contours as well as flat surfaces of a workpiece. In the Krafft devices, a repetitive pattern is ground by using an appropriately contoured metal roller as the backup roller for a flexible abrasive belt. The contoured metal roller of the Krafft device is rotated at the same speed as the abrasive belt.It has been recognized that a need exists for a machine capable of grinding relatively complex contours. One approach, shown in U.S. Pat. No. 3,049,839 issued Aug. 21, 1962 to Smith, and U.S. Pat. No. 3,859,757 issued Jan. 14, 1975 to Heesemann, is to provide a flexible plate as the platen for the abrasive belt at the grinding station. This flexible plate can be distorted in shape to the appropriate contour. Both the Smith and Heesemann machines use a plurality of air-actuated cylinders for distorting the flexible platens. The dimensions of such cylinders, however, necessitate the use of relatively few cylinders across the width of the abrasive belt, thereby limiting the complexity of the contour which may be ground.U.S. Pat. No. 3,685,219 issued Aug. 22, 1972 to Palmenberg, discloses another approach to altering the contour of a driven abrasive belt. In the Palmenberg patent, a patent is provided having a plurality of air holes. Pressurized air is forced through these holes and generates an air cushion against which the abrasive belt is urged. The Palmenberg device is said to be particularly useful in grinding the airfoil shapes of a turbine vane.U.S. Pat. No. 2,426,764 issued Sept. 2, 1947 to Czarnecki, shows a machine useful in finishing propeller blades. An abrasive belt is moved past a cam which defines the desired airfoil shape at the grinding station. The cam is rotated in synchronism with the movement of the propeller blade past the grinding station such that the contour being ground is changed continuously. The cam acts directly upon the back of the abrasive belt, with an intermediate rubber cusioning belt provided in between.None of the belt grinders disclosed above provide an arrangement for grinding a range of airfoil shapes without substitution of machine parts. While Czarnecki does permit a continuous abrasive belt grinding operation for a propeller blade, the contour roller acts directly upon the abrasive belt so that only a single propeller blade size can be machined with a given roller. Additionally, the roller tends to wear, even when an intermediate belt is positioned between the back of the abrasive belt and the roller.SUMMARY OF THE INVENTIONA contour grinding device has a grinding belt which is movable past a grinding station and a platen adjacent the belt for distorting the belt into a desired contour. The platen includes a plurality of independently movable platen vanes which define a first camming surface. A cam means including a first cam bears upon the first camming surface for moving the vanes into desired positions. Means are provided for moving the cam means with respect to the vanes such that the relative positions of the vanes may be altered. A wear-preventing belt, interposed between the platen vanes and the grinding belt, is moved periodically and minimizes the wear of the vanes by the grinding belt.A second camming surface may be provided on the vanes, with a second cam in contact therewith. Means are provided for moving the second cam into contact with the second camming surface as the first cam is moved out of contact with the first camming surface, to provide an unbroken transition in contour on the workpiece. Both the first and second cams may be rotated as well as moved along their respective camming surfaces. The cams and the platen may also be moved with respect to the grinding belt in a direction which is parallel to the axis of cam rotation.A dual belt grinding machine having first and second endless grinding belts may be provided in which the contour shapes of the belts are controlled by corresponding first and second belt platen means. Each platen means includes a plurality of vane members and dual cams which bear upon each of the vane members and which urge the belts into the desired contours.Accordingly, objects of the present invention are to provide a contour grinding device and method in which an endless grinding belt grinds the desired shape for a workpiece, in which the contour to be ground is determined by a cam acting upon a plurality of vanes, which vanes in turn form a platen acting upon the belt; in which the cams may be rotated as the workpiece is moved and translated with respect to the vanes such that a plurality of contour surfaces may be specified; and in which dual endless grinding belts simultaneously act upon opposite sides of the workpiece.It is also a particular object of the invention to provide a method and apparatus for the finishing of the contour of aluminum propeller blades from forged propeller blanks, to apply by, profile grinding, the inboard and outboard airfoil sections of the blade simultaneously along the front and back surfaces of the blade to provide for the smooth transition between the inboard and outboard sections, and to control accurately and automatically the amount of material removed from the blank so as to form a finished or substantially finished blank.A further object of this invention is the provision of a controllable grinding apparatus provided with a pair of grinding belts together with a multiple element platen for controlling the contour of the belts at a grinding station for the purpose of forming in a blank or a workpiece contours simultaneously on upper and lower surfaces thereof, such as the forming of the airfoil shape on an aluminum propeller blade, as outlined above.It is also an object of this invention to provide a method of removing metal from a blank, such as a propeller blade blank, involving the steps of moving belt grinding surfaces in opposed relation at opposite sides of a grinding station, moving a propeller blade blank between the grinding surfaces in contact therewith at the grinding station in a spanwise direction and simultaneously altering the contour of the belt surfaces at the grinding stations with the movement of the blank, so that the surfaces of the blank at the grinding station are finished. The method may provide the further steps of moving the blank in rotation during grinding or otherwise tilting or moving the blank to accommodate for the twist of the blade, the tilt of the blade, and/or the sweep of the blade.These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.

Description

Claims

1. A contour grinding device comprising a grinding belt movable past a grinding station, platen means positioned adjacent said belt at said grinding station for distorting said belt into a desired contour, said platen means including a plurality of independently movable platen vanes having thereon first and second camming surfaces, a first cam having a first contour thereon for bearing upon said first camming surface for moving said vanes into desired positions, a second cam having a contour thereon different from that of said first cam for bearing upon said second camming surface, and means for moving said first and second cams selectively into contact with said respective first and second camming surfaces.

2. The contour grinding device of claim 1 further including means for moving said first and second cams in translation along said first and second camming surfaces, respectively, and means for rotating said first and second cams.

3. The contour grinding device of claim 2 further comprising workpiece chuck means for holding a workpiece and moving the workpiece past said grinding station such that a continuous surface is ground at said grinding station, and means for orienting said workpiece and said chuck means as said workpiece is moved past said grinding station.

4. A dual belt, contour grinding machine, comprising a first endless grinding belt having an inner backing surface and an outer grinding surface, means mounting said first belt for continuous movement of said grinding surface past a grinding station, a second endless grinding belt having an inner backing surface and an outer grinding surface, means mounting said second belt for continuous movement past the grinding station in the same direction as said first belt, means for holding and positioning a workpiece such that portions of said workpiece are placed between said first and second belts at the grinding station, first and second belt platen means, positioned adjacent said backing surfaces of said first and second grinding belts, respectively, for urging said belts against the workpiece in the desired contours, each of said belt platen means including a plurality of individual pivotally mounted vane members, each of said vane members bearing upon the backing surface of an associated said grinding belt at the grinding station and each of said vane members being independently movable about its pivot point with respect to the other vane members, separate cam means for each of said platen means, each of said cam means bearing upon the associated said vane members and urging said vane members into contact with the belt such that said belt is distorted into a desired contour, and means for moving each of said cam means along its associated said vane members with respect to the pivot points of said vane members to alter the position of the belt at said grinding station.

5. A grinding machine for applying an airfoil surface to a forged aluminum aircraft propeller blank, comprising:

a pair of endless grinding belts,

means for mounting said grinding belts for movement in opposed relation thereby defining a grinding station therebetween,

chuck means for supporting said blank for relatively spanwise movement between said belts at said station,

platen means for deforming at least one of said belts concurrently with said spanwise movement to apply a desired airfoil contour to said blank, said platen means having a plurality of individual vanes positioned in side-by-side relation, means mounting said vanes for pivotal movement, said vanes bearing on said one belt for deforming said one belt at said station,

a cam having at least a portion of the desired finished blade contour thereon positioned to engage said vanes thereby to impart to said one belt the contour of said cam,

means for moving said cam in translation generally radially of the pivot point of said vanes to permit the grinding of a family of propeller blades haing generally the same airfoil contour, and

means at said chuck means for rotating said blank concurrently with said spanwise movement in accordance with the twist of the propeller blank.

6. The machine of claim 5 further comprising means for rotating said cam concurrently with said spanwise movement of said blank to affect a change in belt contour in accordance with said spanwise movement.

7. The machine of claim 5 further comprising a second cam selectively engageable with said vanes, and means on said second cam forming a continuation of the airfoil contour of said propeller blade.

8. A dual belt, contour grinding machine, comprising a first endless grinding belt having an inner backing surface and an outer grinding surface mounted for continuous movement of said grinding surface past a grinding station, a second endless grinding belt having an inner backing surface and an outer grinding surface mounted for continuous movement past the grinding station in the same direction as said first belt, means for holding and positioning a workpiece such that portions of said workpiece are placed between said first and second belts at the grinding station, and first and second belt platen means positioned adjacent said backing surfaces of said first and second grinding belts, respectively, for urging said belts against the workpiece in the desired contours, each of said belt platen means including a stack of vanes arranged in side-by-side relation, each of said vanes bearing upon the backing surface of an associated grinding belt at the grinding station, and each of said vanes being independently movable with respect to the other vanes, a cam bearing upon said vanes and urging said vanes into contact with the belt such that said belt is distorted into the desired contour, means for rotating said cam with respect to said vanes to alter the contour of the belt, and means for moving said cam in translation with respect to said vanes.

9. A grinding machine for forming the airfoil surface on a forged aluminum propeller blade blank comprising:

chuck means for supporting a propeller blade blank,

an endless grinding belt movable past a grinding station in a direction generally parallel with the span of the finished blade,

means for moving said blank relative to said belt in a generally spanwise direction,

platen means at said grinding station for transversely deforming said belt in accordance with a desired airfoil contour including first cam means having the outboard portion of the blade airfoil contour formed thereon and selectively effective to impart said contour to the corresponding portion of said blank, and

second cam means having the inboard portion of the finished blade contour formed thereon and selectively effective to impart such inboard contour to the inboard section of the blank.

10. The grinding machine of claim 9 in which said platen means includes a plurality of transversely oriented fingers engageable with said belt at said station and having a first surface in a plane extending through the pivot point of said fingers engageable with said first cam means and having a second surface also lying in a plane intersecting the pivot point thereof and engageable with said second cam means.

11. The grinding machine of claim 10 in which said first cam means is movable along said first surface toward and away from said pivot point to vary the relative position of said fingers at said gring station.

12. The grinding machine of claim 11 in which each of said cam means is movable along its respective said surface toward and away from said pivot point to vary the relative position of said fingers at said grinding station.