EP1721704A1

EP1721704A1 - Dressing tool, method for dressing grinding wheels and machine for carrying out the method

Info

Publication number: EP1721704A1
Application number: EP06113861A
Authority: EP
Inventors: Maurizio Frari
Original assignee: Meccanodora SpA
Current assignee: FMT FUTURE MANUFACTURING TECHNOLOGY S.R.L.
Priority date: 2005-05-13
Filing date: 2006-05-12
Publication date: 2006-11-15
Also published as: ITTO20050329A1

Abstract

The dressing tool (UR') comprises a side surface (LU) on which a helix (2) is made, on which a deposit of dressing abrasive material suitable for dressing a grinding wheel (M) is provided.

Thanks to the helix arrangement (2) the grinding wheel (M) can be dressed by rotating the tool (UR') around its axis (AR) with no need of translating it along the axis (AR) itself.

The invention further relates to a method for dressing grinding wheels (M) and a machine or device arranged for carrying such method out.

Description

Field of the invention

The present invention relates to a tool, a method and a device for dressing grinding wheels.

Background art

The grinding wheels wherein cubic boron nitride (CBN) or other materials having comparable or greater hardness are used as abrasive, due to the hardness of such materials are dressed at present ("ravvivare" or "diamantare" in italian language) with a single tip dressing tool or with a rotary diamond disc (reference UR in Figure 1).
In order to dress the whole side surface LM of a cylindrical grinding wheel M it is therefore necessary to make the dressing tool suitably translate: with reference to Figure 1, in order to dress the whole side surface LM of a cylindrical grinding wheel M, the dressing disc UR is caused to translate along its rotation axis AR. The dressing machine must be provided with suitable devices for implementing such translational movement.
An object of the present invention is enabling a simplified construction, in comparison with known dressing machines, of dressing machines for grinding wheels, in particular but not necessarily grinding wheels wherein cubic boron nitride or abrasives are used, having comparable or greater hardness.

Summary of the invention

This object is achieved, in a first aspect of the present invention, with a dressing tool having the features according to claim 1.
In a second aspect of the present invention, this object is achieved with a dressing method having the features according to claim 8.
In a third aspect of the present invention, this object is achieved with a dressing machine having the features according to claim 13.
Using a drum dressing tool provided with a suitable dressing abrasive material -such as natural or synthetic, monocrystalline or polycrystalline (in English PCD) diamond arranged on the side surface of the tool itself so as to provide at least a helix portion that winds round the predetermined rotation axis of the tool, allows the whole side surface of a grinding wheel to be dressed with no need of translating the dressing tool along the rotation axis of the tool itself or of the grinding wheel, or of translating the grinding wheel relative to the tool. This allows providing simpler dressing devices - for example as regards as the mechanical, electrical or control construction.
Further advantages achievable with the present invention will appear more clear, to the person skilled in the field, from the following detailed description of some particular preferred but non-limiting embodiments, shown in the following schematic figures.

List of Figures

Figure 1 shows an instant of the dressing of a grinding wheel with a disk-shaped dressing tool of known type;
Figure 2 shows an instant of the dressing of a grinding wheel with a drum dressing tool according to a first preferred embodiment of the present invention;
Figure 3 shows a detail of the cross-section of the helix projection of the dressing tool of Figure 2;
Figure 4 shows the side view of a dressing tool according to a second preferred embodiment of the present invention;
Figure 5 shows a detail of the cross-section of the helix projection of the dressing tool of Figure 4;
Figure 6 shows a detail of the cross-section with a flat contact side of a helix projection of a dressing tool;
Figures 7 and 8 show the side views of a dressing tool according to a third and fourth preferred embodiment of the present invention, respectively:
Figure 9 shows, in side view, an instant of the dressing of a grinding wheel of a preferred embodiment of a method according to the present invention.

Detailed description

Figures 1,2 refer to a first embodiment of a dressing tool according to the present invention; such tool UR' is substantially shaped like a drum defining a cylindrical side surface LU, and is suitable for rotating around the symmetry axis AR of the cylinder - in the present description also referred to as "predetermined rotation axis AR" of the dressing tool. According to the present invention, on the cylindrical side surface LU a radially protruding projection 1 is provided - having, in the present embodiment, the shape of a continuous ribbing that forms an helix portion 2 which winds round the rotation axis AR; moreover dressing abrasive material (in the Figures depicted with thicker darker lines or zones), suitable for dressing a grinding wheel M, is provided on the top part of the radially protruding projection 1.
During the dressing, the grinding wheel M rotates around one of its rotation axes AM.
In the present preferred embodiment, the abrasive material of the grinding wheel M is based on cubic boron nitride (CBN), the dressing abrasive material is a material suitable for dressing the grinding wheel M, such as an industrial polycrystalline grain diamond, and the helix 2 formed by the projection 1 extends at least over a suitable portion - indicatively at least from 80% up to 100% - of the whole height HM (Figure 2) of the side surface LM of the grinding wheel M, or - preferably - beyond the whole height HM of the side surface LM of the grinding wheel M (that is, like in the situation of Figure 2: the height HU by which the helix 2 extends over the side surface LU of the dressing tool UR' is greater then the height HM of the side surface LM of the grinding wheel M).
This way, the whole side surface LM of the grinding wheel M can be dressed by simply rotating the dressing tool UR' around the axis AR with no need of translating the tool UR' along the axis AR or along the rotation axis AM of the grinding wheel, or further with no need of translating the grinding wheel relative to the dressing tool.
This allows providing simpler dressing devices -for example, having a simpler mechanical, electrical or control construction.
In the preferred embodiment of Figure 2 the projection 1 forms a helix 2 that in its turn forms a single turn substantially extending over the whole side surface LU of the dressing tool UR', that is the helix 2 has a pitch substantially not smaller than the height HM of the side surface LM of the grinding wheel to be dressed. This way, during the dressing there is only one single contact zone between the dressing abrasive material provided on the helix 2 and grinding wheel M.
An advantage provided by such a single turn dressing tool is that it is particularly suitable for dressing grinding wheels M having a side surface LM with a shape substantially not complementary shape -be it concave or convex- to the side surface LU of the tool itself: as an example, Figure 9 shows the case of a grinding wheel M' having a slightly hourglass-shaped side surface LM', dressed with a tool UR^V having a substantially cylindrical side surface LU^V.
In order to dress the grinding wheel M' , the rotation of the tool UR^V around its rotation axis AR^V can be coordinated with a displacement -at least a translation one- in a direction perpendicular, or however transverse, to the axis AR^V itself -see arrow F of Figure 9-, so that the contact zone between the crest of the helix 2 and the grinding wheel M' matches the shape of the side surface LM' of the latter.
Accordingly, the dressing device or dressing machine that carries this way of dressing out will be provided with suitable means for coordinating or synchronising the rotation of the dressing tool AR^V with its translation in a direction normal to its rotation axis AR, as well as with suitable driving devices for allowing the dressing tool UR^V to translate in a direction normal to its rotation axis AR.
Alternatively the rotation of the tool UR^V can be coordinated with a displacement of its rotation axis in a direction parallel - or however not longitudinal to- the rotation axis AM of the grinding wheel to be dressed.
However, in other not shown embodiments the dressing tool helix can form also several turns, and have a smaller pitch even than the height HM of the side surface LM of the grinding wheel to be dressed, so as to have two or more simultaneous contact zones, during the dressing, between the helix 2 and the grinding wheel M.
Figure 3 schematically shows a detail of the cross-section of the radially protruding projection 1, according to a cross-section meridian plan containing the rotation axis AR of the tool UR': the top part of the projection 1 defines a contact side 10, having such shape that its cross-sections are substantially not flat - in the example of Figure 3, the cross-sections of the contact side 10 are convex; Figure 6 shows an example of a contact side 10 having flat cross-section. This way the dressing tool UR' is prevented from "polishing" the side surface LM of the grinding wheel M.
With grinding wheels wherein the CBN is used as abrasive material, the phenomenon of the polishing is more marked that in other kinds of grinding wheels and therefore, in order to avoid or however to reduce such phenomenon, is prefearable that the cross-sections of the contact side 10 -in particular the projecting parts thereof- have radiuses of curvature not greater than 0,4 millimeter.
Still more preferably the cross-sections of the contact side 10 - in particular the projecting parts thereof- have radiuses of curvature not greater than 0,2-0,3 millimeter. In the preferred embodiment of Figures 4-5 the choosen radius of curvature R is about 0,15 millimeter.
The present invention further relates to a method for dressing a grinding wheel M with a tool UR' as previously described.
Such dressing method, according to an aspect of the present invention, comprises the following steps:

bringing at least a portion of the dressing abrasive material of a tool UR' as described above in contact with a grinding wheel M to be dressed;
turning the tool UR' at least around its predetermined rotation axis AR so as to displace the contact zone, between the dressing abrasive material and the grinding wheel M to be dressed, along a predetermined rotation axis AM of the grinding wheel.

According to a preferred embodiment of such method, during the dressing of grinding wheel M the dressing tool UR' is not translated along its rotation axis AR or, more generally, is not translated with a substantially non-null displacement component longitudinally to its rotation axis AR.
According to another preferred embodiment of such method, during the dressing of the grinding wheel M the dressing tool UR' is not translated in a direction parallel to the rotation axis AM of the grinding wheel or, more generally, is not translated with a substantially non-null displacement component longitudinally to the rotation axis AM of the grinding wheel M.
According to a further preferred embodiment of such method, during the dressing of a grinding wheel M the positions of the rotation axis AR of tool UR', and of the rotation axis AM of the grinding wheel M to be dressed, are kept in positions fixed one relative to another, and neither the grinding wheel nor the dressing tool UR' can slide with substantially not null displacement components longitudinally to the respective axes AM, AR.
Concerning the relative displacements between the rotation axes AM of the grinding wheel and AR of the tool, the dressing can be carried out either without displacing the axes AM and/or AR in directions normal to themselves, or by displacing at least one of the two axes in a direction normal to itself - in this second case the dressing is called "plunge dressing".
A third aspect of the present invention relates to a dressing device or to a dressing machine suitable for carrying out the dressing methods previously described, wherein the wording "dressing device" is referred to a device substantially comprised in a machining station for a different working -such as a grinding machine, while the wording "dressing machine" indicates roughly and substantially a stand-alone machine or working station substantially.
According to a preferred embodiment, such dressing device or dressing machine lacks means suitable for translating the dressing tool with a substantially non-null displacement component longitudinally to its own predetermined rotation axis AR relative to the grinding wheel, during the dressing: as an example the drum of the tool UR' can be fixed on a shaft or on another suitable support -not shown- so as to block its sliding along or relative its rotation axis AR, during the dressing operation only or permanently. In combination or alternatively to that, a dressing device or dressing machine according to the present invention can lack means for translating the dressing tool with a substantially non-null displacement component longitudinally to the predetermined rotation axis AM of the grinding wheel during the dressing: as an example the drum of the tool UR' can be fixed on a shaft or on another suitable support - not shown- so as to block its sliding along or relative to the rotation axis AM of the grinding wheel M, during the dressing operation only or permanently.
The preferred embodiments previously described are susceptible of various modifications and variations without departing from the scope of the present invention. As an example, the dressing tool UR' can comprise a drum in its turn provided with a side surface LU having not only cylindrical shape, but more generally having axial or radial symmetry relative to a predetermined rotation axis AR. That side surface LU can have longitudinal cross-sections, according to meridian section-planes, having also a convex profile (such as in Figure 7, which shows a substantially barrel-shaped drum dressing tool UR^III), a concave profile (such as in Figure 8, which shows a substantially hourglass-shaped drum dressing tool UR^IV) or a concave-convex profile. In another preferred embodiment, not shown, the dressing tool can comprise a substantially frustum-conical drum. Furthermore the grinding wheel M to be dressed can have not only a substantially cylindrical shape, but also define more generally a side surface LM having axial or radial symmetry relative to a predetermined rotation axis AM of the grinding wheel M itself.
The dressing abrasive material can be a deposit - or an insert- of not only monocrystalline-but also polycrystalline industrial diamond, and can be arranged on the side surface LU of the tool so as to form one or several helix portions that winds round/that wind round a predetermined rotation axis AR, respectively. That helix can have a constant or variable pitch, and to be single- or multi-threaded, and/or can be provided not only with a continuous ribbing 1 that winds round axis AR but also a sequence of several radially protruding projections - for example ribbings or bosses- separated one from another.
In the present description, the wordings relating to the translations of the dressing tool relative to a grinding wheel to be dressed are to be understood as relating to a movement of the grinding wheel and the tool relative one to another, and comprising the case of a tool that translates relative to a grinding wheel, wherein that grinding wheel does not translate relative to the frame of the dressing station, as well as the case of a tool fixed relative to a grinding wheel that translates relative to the frame of the dressing station.

Claims

Tool (UR') for dressing grinding wheels (M), comprising a drum which in its turn comprises:
- a side surface (LU) having substantially axial or radial symmetry relative to a predetermined rotation axis (AR);

- a dressing abrasive material suitable for dressing the grinding wheel (M) and arranged on the side surface (LU) so as to form at least a portion of a helix (2) winding round the predetermined rotation axis (AR).
Tool according to claim 1, characterised in that the at least a helix portion (2) comprises at least a radially protruding projection (1) on which the dressing abrasive material is arranged, wherein the top part of the cross-sections of the at least a radially protruding projection (1) is provided with a contact side (10) suitable for contacting the grinding wheel (M), wherein the contact side (10) is substantially not flat.
Tool according to claim 2, characterised in that the contact side (10) is provided with at least a radially protruding portion having a radius of curvature not greater 0,4 millimeter.
Tool according to claim 3, characterised in that the contact side (10) is provided with at least a radially protruding portion having a radius of curvature (R) not greater than 0,2 millimeter.
Tool according to one or more claims from 1 to 4, characterised in that the dressing abrasive material is suitable for dressing grinding wheels (M) the abrasive material of which comprises cubic boron nitride.
Tool according to claim 5, characterised in that the dressing abrasive material comprises monocrystalline or polychrystalline diamond.
Tool according to one or more claims from 1 to 6, characterised in that the at least a helix portion (2) provides a substantially single turn extending on the whole side surface (LU) of the drum.
Method for dressing a grinding wheel (M) which provides a side surface (LM) having substantially an axial or radial symmetry relative to a predetermined rotation axis (AM) of the grinding wheel itself, comprising the following steps:
- bringing at least a portion of the dressing abrasive material of a tool (UR') according to one or more claims from 1 to 7 in contact with the grinding wheel (M);

- making the dressing tool (UR') to turn at least around its predetermined rotation axis (AR) so as to make the at least a contact zone between the dressing abrasive material and the grinding wheel (M) to move along the predetermined rotation axis (AM) of the grinding wheel (M).
Method according to claim 8, wherein the at least a helix portion (2) has a pitch substantially not smaller than about 80% of the height (HM) of the side surface (LM) of the grinding wheel (M) to be dressed.
Method according to claim 8 or 9, wherein said dressing tool (UR'), at least during the dressing of the grinding wheel (M), is substantially not displaced, relative to the grinding wheel (M), with a substantially not null displacement component longitudinally to its predetermined rotation axis (AR).
Method according to one or more claims from 8 to 10, wherein said dressing tool (UR'), at least during the dressing of the grinding wheel (M), is substantially not displaced with a substantially not null displacement component longitudinally to the predetermined rotation axis (AM) of the grinding wheel.
Method according at least to claim 9, wherein the grinding wheel (M) and the dressing tool (UR^V) are provided with respective side surfaxes (LM', LU^V) having shapes substantially not complementary one with another, said method being characterised by comprising the step of displacing the dressing tool (UR^V) in a direction substantially normal to its rotation axis (AR^V), and/or in a direction substantially normal to the rotation axis (AM) of the grinding wheel (M') during the dressing of the grinding wheel (M) itself, so to keep the helix (2) of dressing tool (UR^V) in contact with the side surface of the grinding wheel (M) during the dressing.
Dressing machine suitable for carrying out the method according to one or more claims from 8 to 12.
Dressing machine according to claim 13, characterised by lacking one or more of the following means:
- means suitable for making the dressing tool (UR') to translate, relative to the grinding wheel (M) and during the dressing, with a substantially not null displacement component longitudinally to its predetermined rotation axis (AR);

- means suitable for making the dressing tool (UR') to translate with a substantially not null displacement component longitudinally to the predetermined rotation axis (AM) of the grinding wheel (M) during the dressing.