GB2025284A - Machine and Method for Removing Material from a Workpiece - Google Patents

Abstract

A centreless grinder has a regulating wheel 22 and a grinding wheel 20 which undergo relative pivotting about an axis 32 near to an outlet end 25 of the machine to accomplish in feed grind operations on a plurality of parts fed stepwise through stations S1, ... Sn between the wheels from an infeed end 24. Thus a coarse feed occurs adjacent the inlet end and a fine feed adjacent the outlet end. The grinding and regulating wheels may have frustoconical surfaces so that a frustoconical surface 26 produced on a workpiece at one station is engaged along its entire length by the grinding and regulating wheels when it is moved to the next adjacent station, the final workpiece surface being ground cylindrical at the station at the outlet end. <IMAGE>

Description

SPECIFICATION Machine and Method for Removing Material from a Workpiece A first aspect of the present invention relates to a machine having a working element for removing material from surfaces of workpieces which are advanced intermittently along a path through the machine. A centreless grinding machine is an example of a machine to which the invention can be applied. The invention also relates to a method of removing material from a succession of workpieces.

One prior art method of centreless grinding cylindrical parts of rotation is to stack them and simultaneously grind a plurality of workpieces carried between the wheels of a centreless grinder. The workpieces are stacked end-to-end and "infeed", or plunge ground, by the grinding wheel. By progressive profiling of the regulating wheel, the cylindrical parts will have progressively stepped diameters, from a rough, stack-entering workpiece; to a smaller diameter, finished stackexiting workpiece. After each grinding operation, the workpieces and regulating wheel are retracted from the grinding wheel and the workpiece stack is advanced to the next subsequent grinding station.However, one difficulty is inherent in this method of progressively producing the stacked workpieces, in that since the regulating wheel is linearly fed towards the grinding wheel, the same amount of grinding stock is removed from each workpiece in the same time interval.

When grinding, it is generally preferably to rough grind a relatively large amount of stock from a workpiece per unit time, shaping to a predetermined diameter, then later finish grinding the workpiece by removing a relatively small amount of stock per unit time from the predetermined intermediate diameter to the finished size, since wheel pressures and resulting deflections of the workpiece will be lessened during the finish grinding operation and the workpiece will tend to have a truer size and shape and better surface finish.

According to a first aspect of the invention, there is provided a machine defining a path along which workpieces are advanced intermittently from an inlet end of the path through a series of work stations to an outlet end of the path, the machine including a working element engageable with workpieces occupying said working stations to remove material from surfaces of the workpieces and a control element engageable with workpieces occupying the working stations to restrain displacement of the workpieces away from the working element by forces exerted on the workpieces by the working element, wherein the working element and the control means are arranged for relative pivotal movement about a pivot axis which is nearer to the outlet end of the path than it is to the inlet end of the path.

Relative pivoting of the working element and control element towards each other during grinding causes at each work station a feed stroke, the length of which is proportional to the distance of the feed station from the pivot axis.

Thus a coarse feed movement occurs adjacent to the inlet end of the path and a fine feed movement occurs adjacent to the outlet end of the feed path.

In the preferred arrangement, the working element is adapted to form on the workpieces at at least some of the work stations respective frusto-conical faces and there are provided on the working element for engagement with workpieces at the work stations respective working faces which are so inclined that the beginning of a feed stroke the inclination of one working face to a corresponding face on the control element is equal to the inclination of an adjacent working face to a corresponding face of the control element at the end of a feed stroke.

With this arrangement, a frusto-conical face produced on a workpiece at one work station is engaged along its entire length by both the working element and the control element when these are brought into engagement with the workpiece at the next work station.

According to a second aspect of the invention, there is provided a method of removing material from a succession of workpieces to form on each workpiece a surface of revolution wherein the workpieces are advanced intermittently along a path from an inlet end of ths path through a series of work stations to an outlet end of the path, whilst the workpieces occupy respective work stations they are engaged concurrently by a working element and a control element, the working element removes material from each workpiece, the control element restrains movement of the workpieces away from the working element and wherein, whilst engaged with the workpieces, the working element and the control element undergo relative pivoting towards each other about a pivot axis which is nearer to the outlet end of said path than to the inlet end of the path.

Examples of machines in accordance with the first aspect of the invention and which can be used in performance of the method according to the second aspect of the invention will now be described with reference to the accompanying drawings wherein:~ Figure 1 is a plan view of a prior art centreless grinder performing a constant stock removal rate infeed grind operation on a plurality of workpieces.

Figure 2 is a plan view of a centreless grinder performing variable stock removal rate infeed grind operations on a plurality of workpieces.

Figure 3 is an elevational view of the centreless grinder taken in the direction of arrow 3 of Figure 2.

Figure 4 is an enlarged plan view of the grinding zone of the centreless grinder of Figure 2, and Figure 5 is a plan view of the grinding zone of a centreless grinder, illustrating a modification of the machine shown in Figures 2 to 4.

Figure 1 depicts one prior art grinding machine 10 capable of grinding a plurality of workpieces 11 which are carried on a work support 12 between a grinding wheel 13 and a regulating wheel 14. The surfaces to be ground on the workpieces 11 depicted are cylindrical, and it is desired to grind them in an "infeed" grinding mode, i.e. the workpieces 11 remain axially stationary while being ground. The workpieces 11 are successively reduced in diameter from an entering, "rough", workpiece size to an exiting, "finish" workpiece size, and the regulating wheel 14 is therefore generally stepped along its length to maintain contact with the range of workpieces 11.Feed movement is accomplished by rectilinearly moving the regulating wheel 14 radially with respect to the grinding wheel 13 along a feed screw 15, and, therefore consequently removing stock at a constant rate from each workpiece 11, simultaneously. After a grind operation, the regulating wheel 14 is retracted and the workpiece stack is axially advanced by a feeding mechanism (not shown) to index the workpieces 11 to their next successive work stations W1,W2.. defined in a phantom along the face 1 6 of the grinding wheel 13, and a new rough workpiece 11 enters at the inlet end 17 between the wheels 13, 14.

The plan view depicted in Figure 2 illustrates a centreless grinding machine 18 having a base 19, and a working element in the form of a grinding wheel 20 rotatably carried in a grinding wheelhead 21 which in turn is affixed to the base 19. A control element in the form of a regulating wheel 22 is rotatablyjournaled in a regulating wheelhead 23 and is movable relative to the grinding wheel 20, defining a path with an inlet end 24 and an outlet end 25 between the wheels 20, 22. A plurality of workpieces 26 are carried on a work support 27 between the wheels 20, 22 in conventional manner, and the exemplary workpieces 26 depicted are cylindrical rods stacked for infeed grinding. The workpieces 26 occupy a pluralityof work stations S" S2. ..Sn along the face 28 of the grinding wheel 20 and the grinding wheel 20 is shaped to conform to the desired workpiece profile at the work stations S1, S2. . .Sn. The work support 27 is carried on a slide 29 which is radially movable in a rectilinear fashion with respect to the grinding wheel 20 by means of an infeed unit 30 affixed to the base 19.

A feed screw 31 is threadably engaged in the slide 29 to provide adjustment, and a piston 31 a is operable in a cylinder 31 b to retract the screw 31 and slide 29 to provide clearance between the workpieces 26 and the grinding wheel 20 when advancing the workpieces 26 to their subsequent work stations S" S2. . .Sn. The regulating wheel 22 is step-profiled along its length to conform to successively reduced workpiece sizes from the inlet end 24 to the outlet end 25 of the wheels 20, 22. In the preferred embodiment, the grinding wheel 20 is shaped such that the workpieces 26 will be concentric, thus tending to minimize relative slip between the workpieces 26. It may be appreciated that the wheel 20 may be shaped in similar fashion to the prior art wheel 13.

The regulating wheelhead 23 is pivotabre on the slide 29 about a pivot axis 32 established by a pivot pin 33 relatively fixed in the slide 29 and having a slip fit in a co-operating bore 34 in the regulating wheelhead 23. The pivot axis 32 is located proximate to the outlet end 25 of the path defined between the wheels 20, 22 i.e. at the rear 35 of the regulating wheelhead 23, while a fluidoperated cylinder 36 is clevis-mounted to the slide 29 proximate to the front 37 of the regulating wheel head 23 by a bracket 38. The cylinder 36 is connected by fluid lines 39a, b, to a suitable fluid power source (not shown), and the external rod end 40 of the relatively movable piston 41 is clevis-mounted to the regulating wheelhead 23 by a bracket 42 affixed to the front 37.Thus, as the piston 41 is powered in the cylinder 36, the regulating wheelhead 23 will pivot through a feed stroke from the phanton position shown to the solid position, and the reverse. Feed movement, therefore, is arcuate about the pivot axis 32. Total movement is compounded of straight movement for clearance and arcuate movement for grinding. When the grind operation has been completed, the regulating wheel 22 is retracted and the workpieces 26 are advanced to their next subsequent stations, while a rough workpiece 26 enters the system by means of a workpiece axial indexing mechanism (not shown) and the next grind operation is ready to commence.

To compensate for grinding wheel wear, the slide 29 and regulating wheel 23 are compensatingly advanced by the feed screw 31.

The regulating wheelhead upper portion 23a if moved relative to the lower portion 23b to compensate for regulating wheel wear.

Figure 3 depicts the slide 29 on the base 19 where it may be linearly fed by the feed screw 31 or piston 31 a, and the slide 29 carries the pivotable wheelhead 23 and the work support 27.

Figure 4 is an enlarged view showing the grinding zone of Figure 2 during a feed operation.

Here it may be seen that the workpieces 26 vary in diameter from the inlet end 24 to the outlet end 25 of the path between the wheels 20,22 and the grinding wheel 20 is shaped to conform to the desired workpiece profile at the plurality of work stations S" S2. . .Sn, defined along its face 28. The regulating wheel 22 is step-profiled to maintain contact with the progressive work sizes, and, as the regulating wheel 22 is fed arcuately in the direction of the arrow, it will be seen that the amount of stock removal F1, F2.. .Fn will be directly proportional to the radial distances from the pivot axis 32 to the workpieces 26, R1, R2..

.run. All stock removal takes place during the same time interval, and in this fashion, therefore, a coarse-grind rate is achieved at the inlet end 24 and a fine-feed grind rate is obtained at the outlet end of the wheels 20, 22 and proportional feed rates on all the workpieces 26 therebetween.

It can be seen, however, that such a pivotable feed arrangement may cause grinding action to initiate at the leading edge 26a of the stationadvanced workpiece 26, which may operate to the detriment of the operation by increasing wheel breakdown and contributing to any workpiece instabilities.

Figure 5 illustrates a modification for producing a cylindrical workpiece with the pivotable regulating wheelhead arrangement of Figures 2, 3 and 4.

Using the terminology associated with Figure 4, the respective wheel faces at each work station, S" S2. . .Sn are angled to produce a finished workpiece 26 having the shape of a truncated right cone of included cone angle 8,, 02.. On, wherein the finished cone angle of a given work station is the beginning, or "rough", cone angle of the next successive work station; that is, the beginning cone angle is the angle formed by the grinding wheel face and the retracted regulating wheel face.

An endstop 41 is depicted as a way to maintain axial positioning of the workpieces 26; and may be movable by a suitable mechanism (not shown) to reposition the workpieces 26.

The work support blade (not shown) is likewise configured to keep the workpieces coaxial.

The progressive angle development of the respective work stations thereby causes the grind to start substantially along the entire length of the workpiece 26, thereby tending to increase grind efficiency and equalize wheel wear. The included angle on of the last workpiece 26 is, of course, by design, O to produce the desired cylinder at the outlet end 25 of the wheels 20,22. It can be readily appreciated, however, that workpieces having angled surfaces, or combinations of angled, flat, and varied profiles may be produced utilizing the teachings of this invention.

It is preferable to provide identical angles on the wheel faces, to maintain the parts in a coaxial manner, and to facilitate common wheel dressing elements. Although there may be slip between the parts due to their different diameters, in a maintained coaxial condition, the slip is symmetrical around the axis, and the effect is purely angular. There are no radial influences introduced to affect roundness.

Claims (8)

Claims

1. A machine defining a path along which workpieces are advanced intermittently from an inlet end of the path through a series of work stations to an outlet end of the path, the machine including a working element engageably with workpieces occupying said working station to remove material from surfaces of the workpieces and a control element engageable with workpieces occupying the working stations to restrain displacement of the workpieces away from the working element by forces exerted on the workpieces by the working element, wherein the working element and the control means are arranged for relative pivotal movement about a pivot axis which is nearer to the outlet end of the path than it is to the inlet end of the path.

2. A machine according to claim 1 adapted to support workpieces at the work stations for rotation about a rotary axis coinciding with a longitudinal centreline of said path wherein the working element is adapted to form on the workpieces at at least some of the work stations respective frusto-conical faces.

3. A machine according to claim 2 further comprising means for causing relative pivoting of the working element and the control element towards each other through a feed stroke whilst material is being removed from workpieces at the work stations and wherein there are provided on the working element for engagement with workpieces at the work stations respective working faces which are so inclined to the rotary axis that at the beginning of a feed stroke the inclination of one working face to a corresponding face on the control element is equal to the inclination of an adjacent working face to a corresponding face of the control member at the end of a feed stroke.

4. A method or removing material from a succession of workpieces to form on each workpiece a surface of revolution wherein the workpieces are advanced intermittently along a path from an inlet end of a path through a series of work stations to an outlet end of the path, whilst the workpieces occupy respective work stations they are engaged concurrently by a working element and a control element, the working element removes material from each workpiece, the control element restrains movement of the workpiece away from the working element and wherein, whilst engaged with the workpieces, the working element and the control element undergo relative pivoting towards each other about a pivot axis which is nearer to the outlet end of said path than to the inlet end of the path.

5. A method according to claim 4 wherein at some of the work stations there are formed on each workpiece respective frusto-conical surfaces with included angles decreasing from a work station adjacent to the inlet end of the path towards a work station near to the outlet end of the path.

6. A centreless grinder substantially as herein described with reference to and as shown in Figures 2, 3 and 4 of the accompanying drawings.

7. A centreless grinder according to claim 6 modified substantially as herein described with reference to and as shown in Figure 5 of the accompanying drawings.

8. A method of grinding a plurality of workpieces substantially as herein described with reference to Figures 2, 3 and 4 of the accompanying drawings or with reference to Figure 5 of the accompanying drawings.