GB2203366A

GB2203366A - Dressing grinding wheels

Info

Publication number: GB2203366A
Application number: GB08708247A
Authority: GB
Inventors: Peter Huw Davies
Original assignee: Unicorn Industries Ltd
Current assignee: Unicorn Industries Ltd
Priority date: 1987-04-07
Filing date: 1987-04-07
Publication date: 1988-10-19
Also published as: GB8708247D0

Abstract

Apparatus for dressing a grinding wheel comprises means for rotating the grinding wheel 10 about its central axis 11, a plurality of dressing tools 12, 13, 14, 15, and means for effecting relative movement between the grinding wheel and each dressing tool to bring the tool into dressing engagement with the periphery of the grinding wheel. Each dressing tool is so shaped and orientated as to form only a portion of the required cross-sectional profile of the grinding wheel so that the effect of the dressing tools in combination is to form the entire required profile. Computer controlled means are provided for adjusting each dressing tool in a manner to vary the shape of that portion of the profile which it forms, whereby the shape of the entire profile may be varied by suitable adjustment of the individual dressing tools. <IMAGE>

Description

"Apparatus for dressing grinding wheels" The invention relates to the dressing of grinding wheels, by which is meant the shaping of the outer peripheral surface of a grinding wheel to ensure that the wheel is perfectly circular and to provide its peripheral surface with an accurate cross-sectional profile of the required configuration.

In addition to forming the initial profile on a grinding wheel, it is necessary to re-dress the wheel, usually many times, during its working life to remove worn abrasive material and metal particles from the peripheral surface of the wheel as well as to restore the required exact cross-sectional profile to the peripheral surface.

Profiled grinding wheels are used for the accurate shaping of many different types of rotary machine parts, such as engine cam shafts. Grinding wheels are normally manufactured from grains or particles of abrasive material held together and moulded into disc form by a bonding agent. Typical abrasive materials are aluminium oxide and silicon carbide. Various bonding agents are used such as synthetic resins, metals or vitrified materials.

The shaping of the profile of the outer peripheral surface of a grinding wheel is normally effected by a dressing, or trueing, tool having a surface cross-sectional profile which is the inverse of the required profile of the grinding wheel. The tool may be a rotatable dressing wheel which is brought into peripheral engagement with the grinding wheel, or it may be a stationary profiled block across which the grinding wheel is traversed in a direction at right angles to its axis of rotation.

The surface of the dressing tool must obviously be formed from material which can cut or abrade, without undue wear itself, the hard surface of the grinding wheel.

Typically, therefore, dressing tools consist of natural or synthetic diamond particles, or other cutting elements, embedded in a hard material such as nickel, tungsten carbide or other hard matrix.

Dressing tools are comparatively expensive to manufacture due to the nature of the materials involved and the necessity for extremely accurate shaping of the forming surface. While this is perfectly acceptable where the tool will be required to perform a very large number of dressing operations during its life, the cost may be unacceptable in cases where only a few grinding wheels of a particular profile require to be manufactured and subsequently dressed. Also, while a particular profile is under developement, it may be desirable to make changes in the profile and this may necessitate expensive scrapping or alteration of the dressing tool.

In order to form or dress grinding wheels which are only required in small quantities, or even as a "oneoff" item, use is sometimes made of a dressing apparatus where a comparatively fine movable tool is traversed in an axial direction across the periphery of the rotating grinding wheel, the position and orientation, of the tool being varied during such traverse to form the desired profile. The variation of the position and orientation of the tool may be effected by the tool being mounted on a pantograph which follows a master template corresponding to the desired profile, or the tool may be under computer control, following instructions input into the computer to define the desired profile.

Such a forming process is time consuming, particularly where parts of the required profile are deep, in view of the large number of passes necessary to remove the required amount of material from the surface of the grinding wheel. Also, since the tool must be small enough to form the smallest details of the profile, it is subject to comparatively rapid wear as a result of which the accuracy of the final profile may suffer.

The present invention therefore sets out to provide an improved apparatus for dressing a grinding wheel which does not require the manufacture of a dressing tool accurately preformed according to the complete profile required, and which allows rapid and accurate formation of a predetermined profile on the grinding wheel, while at the same time permitting the shape of the profile to be readily adjusted if required.

According to the invention there is provided apparatus for dressing a grinding wheel to form thereon a peripheral surface of a required cross-sectional profile, the apparatus comprising means for rotating the grinding wheel about its central axis, a plurality of dressing tools, means for effecting relative movement between the grinding wheel and each dressing tool to bring the tool into dressing engagement with the periphery of the grinding wheel, each dressing tool being so shaped and orientated as to form a portion of said required crosssectional profile of the grinding wheel so that the effect of the dressing tools in combination is to form the entire required profile, and means for adjusting each dressing tool in a manner to vary the shape of that portion of the profile which it forms, whereby the shape of the entire profile may be varied by suitable adjustment of the individual dressing tools.

The means for adjusting each dressing tool may include means for permitting replacement of the tool, or a part thereof, by a tool or part thereof of different configuration.

The means for adjusting each dressing tool may also include an adjustable mounting for the tool whereby translational movement of the tool may be effected relatively to the grinding wheel. For example, said permitted translational movement may be in a direction parallel to the axis of rotation of the grinding wheel, at right angles to said axis, or in a combination of such directions.

The means for adjusting each dressing wheel may also include an adjustable mounting for the tool whereby the angular orientation of the tool with respect to the grinding wheel may be varied.

At least one of said tools may comprise a plurality of relatively movable forming elements, and in this case the adjustment means may include means for varying the relative positions and/or orientations of said elements.

The adjustment of said dressing tools may be effected manually or under the action of a control mechanism, for example under computer control. In the latter case, means are preferably provided to sense the cross-sectional peripheral shape of the grinding wheel, or of the workpiece on which the grinding wheel is acting in the case of continuous dressing, and to send feedback signals to the computer corresponding to the parameters of such shape, such signals being used to control operation and/or adjustment of the dressing tools.

The relative positions and orientations of the dressing tools will normally be pre-adjusted before dressing of the grinding wheel begins, but the invention does not exclude arrangements where such adjustment may be effected during dressing.

The dressing tools may be spaced apart around the periphery of the grinding wheel, being brought into dressing engagement with the grinding wheel by movement towards the peripheral surface thereof. In this case the dressing tools may be brought into dressing engagement with the peripheral surface of the grinding wheel simultaneously or in succession, or only preselected ones of the dressing tools may be engaged with the grinding wheel, according to the profile required.

Alternatively the dressing tools may be linearly spaced apart in a direction perpendicular to the axis of rotation of the grinding wheel, and the rotating grinding wheel may be brought into engagement with the tools in succession by translatory movement of the grinding wheel along the dressing tools.

In a further alternative arrangement, the dressing tools may be mounted at spaced intervals on a movable carrier, such as a rotating capstan, whereby they may be brought successively into engagement with the periphery of the grinding wheel by rotational indexing of said carrier, the axis of rotation of the grinding wheel remaining fixed, or being adjustable towards and away from the carrier.

The apparatus may be combined with grinding apparatus on which a grinding wheel is mounted to act on a workpiece, whereby the grinding wheel being used in the grinding apparatus may be dressed without removing it from said apparatus. The arrangement may be such that the grinding wheel may be dressed while grinding, for example continuously dressed, or the grinding wheel may be displaceable between a grinding position and a dressing position.

In any of the above arrangements the dressing tools may be of any appropriate type, including stationary dressing blocks or rotary dressing wheels, and may incorporate, for example, natural diamonds, synthetic diamonds or other hard materials conventionally used in dressing tools.

The following is a more detailed description of embodiments of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a schematic representation of one form of grinding wheel dressing apparatus in accordance with the invention, Figure 2 is a schematic view of an alternative form of apparatus, Figure 3 is a schematic view of a further form of apparatus, and Figure 4 is a diagrammatic view in a direction perpendicular to the axis of rotation of a grinding wheel, showing the manner in which the dressing tools may form a required profile.

Referring to Figure 1, the grinding wheel to be dressed is indicated diagrammatically at 10 and is rotatable about an axis 11. A plurality of dressing tools are spaced apart around part of the periphery of the grinding wheel. In the example shown four dressing tools are provided and are indicated at 12, 13, 14 and 15 respectively. The dressing tools may be of any of the forms of construction normally used for this purpose. For example, they may be in the form of rotating dressing wheels which are rotatable about axes parallel to the axis of rotation 11 of the grinding wheel, although in this case the orientation of the axes of the dressing wheels may be adjustable for the purpose to be described.

Alternatively, one or more of the dressing tools may be in the form of a fixed abrasive profiled block.

In each case the dressing tool is so mounted that it may be indexed towards or away from the axis of rotation 11 of the grinding wheel 10, as indicated by the arrows 16, so that each tool may be urged into dressing engagement with the outer periphery of the wheel 10.

In addition each tool is adjustably mounted for translational movement and angular adjustment relatively to the axis of rotation of the grinding wheel.

In a conventional dressing arrangement there is normally only be provided a single dressing tool and this is preformed with the inverse of the entire required profile of the periphery of the grinding wheel. In accordance with the present invention, however, each of the dressing tools 12, 13, 14 and 15 is shaped to provide only part of the profile shape. The number of dressing tools, and their shape, may be varied according to the required profile, but one typical arrangement is shown, by way of example, in Figure 4.

In this case, the periphery of the grinding wheel 10 is required to comprise two outer conical portions 17 and 18 disposed at different angles to the axis of rotation 11 and leading into a central cylindrical portion 19 formed with a central V-sectioned groove 20.

In order to form this profile the dressing tools 12, 13 and 14 are in the form of plain cylindrical rollers whereas the dressing tool 15 is in the form of a disc-like wheel having an angularly tapered periphery.

As previously mentioned, all of the dressing wheels are so mounted that, in addition to being indexable into and out of engagement with the periphery of the grinding wheel 10, their indexed position and the orientation of their axes of rotation may be adjusted relatively to the axis of rotation 11 of the grinding wheel. Thus, the axis of rotation and indexed position of the wheel 12 are preset according to the required angle and width of the surface 17, and the orientations and positions of the other dressing wheels are preset according to the required orientations and dimensions of the surfaces which they are to form.

Consequently, the combined effect of the four dressing wheels on the grinding wheel 10 is to form the required profile, of which each dressing wheel forms only a portion.

The angular orientations and indexed positions of the dressing wheels may be preset manually or they may be preset automatically by signals from a computer indicated diagrammatically at 21. Information regarding the required profile of the grinding wheel is fed into the computer 21 which is programmed to convert this information into the necessary orientations and positions of the four dressing wheels. The indexing of the individual dressing wheels into dressing engagement with the grinding wheel may also be under control of the computer and it will be appreciated that the dressing wheels may be indexed into engagement with the grinding wheel individually in succession, or simultaneously, or in different combinations.

A sensor 22 may be mounted adjacent the periphery of the grinding wheel 10 to detect at any instant the shape of the periphery of the grinding wheel and to feed this information to the computer 21 so that the instructions to the dressing wheels from the computer may be modified to achieve the desired shape.

Alternatively, the sensor might be disposed to feed back to the computer information as to the profile of the workpiece on which the grinding wheel is acting, in the case where the wheel is being dressed while grinding.

In the example shown each of the four dressing wheels contributes to the shape of a different portion of the required profile. This profile may be varied considerably by adjusting the positions and orientations of the different dressing wheels. However, to give an even greater range of possibilities for the profile shape there may be provided a greater number of different and differently adjustable dressing tools spaced around the periphery of the grinding wheel. The shapes of the different tools are chosen such that a great variety of different profiles can be achieved by different permutations and combinations of dressing tools in different positions and orientations.

Thus, by use of a limited number of dressing tools of standard shapes a grinding wheel may be dressed rapidly to any peripheral cross-section which can be formed by the dressing tools acting in combination. A single grinding wheel, or only a few grinding wheels, may thus be dressed economically and accurately without the expense of manufacturing an accurately tailored dressing tool to form the whole profile or without the timeconsuming method, susceptible to inaccuracy, using a single dressing tool moving under pantograph or computer control.

Instead of the dressing tools being disposed around the periphery of the grinding wheel, they may be linearly spaced apart as indicated diagrammatically at 23, 24, 25 and 26 in Figure 2. In this case the grinding wheel 27 is traversed in a direction perpendicular to its axis of rotation 28 as indicated by the arrows 29 and is also mounted for displacement towards and away from the dressing tools as indicated by the arrows 30.

As in the previously described arrangement, the effect of the dressing tools on the periphery of the grinding wheel may be adjusted by adjusting the angular orientations of the tools and by adjusting their positions relatively to the axis 28 of the grinding wheel. Again, the control of the dressing tools may be under computer control or they may be preset manually.

Figure 3 shows a still further arrangement in which the dressing tools 31, 32, 33 and 34 are mounted on a turret or capstan 35 which may be rotationally indexed to bring the dressing tools successively into dressing engagement with the periphery of. the grinding wheel 36.

As in the previously described arrangements, the dressing tools are adjustably mounted for angular and translational movement with respect to the grinding wheel so as to alter the effect that each tool has on the peripheral surface of the wheel.

In any of the arrangements described there may be associated with the apparatus a much greater number of dressing tools than the number which may be used at any one time. The tools are then detachable from the apparatus so that each tool can, if required, be replaced by any other tool from the large number available. This further increases the range of possible shapes of profile which may be formed.

Furthermore, an individual tool may itself be adjustable in configuration. For example, in the case of a tool in the form of a rotatable dressing wheel, the wheel may be made up of a number of discs of different diameters, axial lengths and peripheral cross-sections clamped together on a common shaft. By selecting different shapes and sizes of discs from a common pool, dressing wheels of different configurations may be built up for use in the apparatus according to the invention.

Other methods of adjusting the configuration of an individual dressing tool may also be employed. For example, where the dressing tool is in the form of a shaped stationary block different parts of the block may be adjustably mounted with respect to each other to allow the configuration of the block to be varied.

The apparatus according to the invention may be used by itself or may form part of grinding apparatus, so that a grinding wheel may be re-dressed without the necessity of removing it from the grinding apparatus in which it is employed. In the arrangement of Figure 1, where the dressing tools may operate simultaneously on the grinding wheel, the grinding wheel can be continuously dressed while grinding. In the other arrangements where not all the dressing tools act on the grinding wheel at the same time, the grinding wheel requires to be displaced from the workpiece area where it is grinding a workpiece to a dressing area where it is re-dressed by the apparatus according to the invention.

Claims

1. Apparatus for dressing a grinding wheel to form thereon a peripheral surface of a required cross-sectional profile, the apparatus comprising means for rotating the grinding wheel about its central axis, a plurality of dressing tools, means for effecting relative movement between the grinding wheel and each dressing tool to bring the tool into dressing engagement with the periphery of the grinding wheel, each dressing tool being so shaped and orientated as to form a portion of said required crosssectional profile of the grinding wheel so that the effect of the dressing tools in combination is to form the entire required profile, and means for adjusting each dressing tool in a manner to vary the shape of that portion of the profile which it forms, whereby the shape of the entire profile may be varied by suitable adjustment of the individual dressing tools.

2. Apparatus according to Claim 1, wherein the means for adjusting each dressing tool include means for permitting replacement of the tool, or a part thereof, by a tool or part thereof of different configuration.

3. Apparatus according to Claim 1 or Claim 2, wherein the means for adjusting each dressing tool also include an adjustable mounting for the tool whereby translational movement of the tool may be effected relatively to the grinding wheel.

4. Apparatus according to Claim 3, wherein said permitted translational movement is in a direction parallel to the axis of rotation of the grinding wheel, at right angles to said axis, or in a combination of such directions.

5. Apparatus according to any of Claims 1 to 4, wherein the means for adjusting each dressing wheel also include an adjustable mounting for the tool whereby the angular orientation of the tool with respect to the grinding wheel may be varied.

6. Apparatus according to any of Claims 1 to 5, wherein at least one of said tools comprises a plurality of relatively movable forming elements, and the adjustment means include means for varying the relative positions and/or orientations of said elements.

7. Apparatus according to any of Claims 1 to 6 wherein the adjustment of said dressing tools is effected manually.

8. Apparatus according to any of Claims 1 to 6, wherein the adjustment of said dressing tools is effected under computer control.

9. Apparatus according to Claim 8, wherein means are provided to sense the cross-sectional peripheral shape of the grinding wheel, or of the workpiece on which the grinding wheel is acting, and to send feedback signals to the computer corresponding to the parameters of such shape, such signals being used to control operation and/or adjustment of the dressing tools.

10. Apparatus according to any of Claims 1 to 9, wherein the dressing tools are spaced apart around the periphery of the grinding wheel, being brought into dressing engagement with the grinding wheel by movement towards the peripheral surface thereof.

11. Apparatus according to any of Claims 1 to 9, wherein the dressing tools are linearly spaced apart in a direction perpendicular to the axis of rotation of the grinding wheel, and the rotating grinding wheel may be brought into engagement with the tools in succession by translatory movement of the grinding wheel along the dressing tools.

12. Apparatus according to any of Claims 1 to 9, wherein the dressing tools are mounted at spaced intervals on a movable carrier, whereby they may be brought successively into engagement with the periphery of the grinding wheel by rotational indexing of said carrier, the axis of rotation of the grinding wheel remaining fixed, or being adjustable towards and away from the carrier.

13. The combination with apparatus according to any of the preceding claims of grinding apparatus on which a grinding wheel is mounted to act on a workpiece, whereby the grinding wheel being used in the grinding apparatus may be dressed without removing it from said apparatus.

14. The combination according to Claim 13, wherein the grinding wheel is displaceable between a grinding position and a dressing position.

15. Apparatus for dressing a grinding wheel substantially as hereinbefore described with reference to the accompanying drawings.