EP1722922B1

EP1722922B1 - Centerless grinder

Info

Publication number: EP1722922B1
Application number: EP04712663A
Authority: EP
Inventors: Salvatore Vaccaro; Carlo Cerinotti; Mauro Baggiolini
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-02-19
Filing date: 2004-02-19
Publication date: 2007-08-15
Anticipated expiration: 2024-02-19
Also published as: DE602004008351T2; ES2293228T3; WO2005080046A1; DE602004008351D1; CN1929951A; CN1929951B; EP1722922A1; ATE369937T1

Abstract

A centerless grinder has a stress structure including a machine bench, a template blade (5) mount for supporting the work-piece (W) and a regulating wheel (C) both mounted on a first carriage longitudinally movable by a first linear axis control device on said bench and means for advancing said regulating wheel (C) toward said template blade mount for bearingly engaging and spinning the supported work-piece (W), a grinding wheel (G) supported on said stress structure for removing stock from the surface of the supported work-piece spun by said regulating wheel (C) on said template blade (5), a first truing tool for periodically machining the cutting surface of said grinding wheel (G), mounted on said first carriage, sideway of one end of the regulating wheel, a second truing tool for periodically machining the surface engaging the work-piece of said regulating wheel (C), at the end of a pivoting arm, mounted sideway of the end to the grinding wheel (G) at the opposite side of said end of the regulating wheel (C), and means for swiveling the axis of said regulating wheel about the axis of said grinding wheel when grinding according to a through feed mode.

Description

FIELD OF THE INVENTION

The present invention relates to centerless grinders, as per the preamble of claim 1. An example of such a grinder is disclosed by EP 1080839 A . More particularly, the present invention pertains to centerless grinders of enhanced rigidity and requiring a reduced number of distinct linear axis control devices and related screw driven carriages and functional parts for periodically re-truing the profile of the outer surfaces of the grinding wheel and of the regulating wheel.

BACKGROUND OF THE INVENTION

A centerless grinder is a machine tool that can be used to grind cylindrical work-pieces such as wires, rods, pins, shafts and the like. The work-piece may require a constant cross-sectional diameter or alternatively sections of different diameters with step-like changes of diameter and even slightly tapered sections.
Centerless grinders include three main components. A work or grinding wheel, a regulating wheel and a work-piece supporting blade. The work wheel or more commonly called the grinding wheel is the machine component that performs the actual removal of stock from the work-piece. The grinding wheel thus determines the surface finish and overall configuration of the work-piece. The surface texture of the work wheel may vary depending upon the particular grinding operation to be performed. In case of work-pieces to be ground on portions of different diameters, the work wheel may be composed of grinding wheels of different diameters and of different surface texture.
The regulating wheel, often made of an elastomer loaded with abrasive particles, is the machine component that directs and holds the work-piece against the grinding wheel and is also responsible for spinning the work-piece during the grinding process.
The work-piece support or template blade is the machine component that supports the work-piece in the gap between the two counter rotating wheels, normally above or sometimes below the centerline of the two wheels. The regulating wheel spins the work-piece supported on the rest blade in one direction, while the grinding wheel, rotating in opposite direction, removes the amount of stock necessary to obtain the desired diameter or taper of the work-piece. The template blade may have horizontal, stepped or angled support surfaces onto which the work-piece rests. In many cases, it has a profile specular to the profile of the peripheral surface of the regulating wheel.
Generally, depending on the geometry of pieces to be rectified, three modes of operation of the centerless grinder are implemented. A first so-called "in-feed mode" is employed when pieces having an end or intermediate flange-like abutment (or stepped diameters) are to be ground, either cylindrically or conically on their shaft portions.
The "cantilever mode" is used to machine end portions of relatively long work-pieces adequately supported also by an auxiliary side rest.
The "through feed mode" is used exclusively for working cylindrical work-pieces without any stepwise diameter change and is useful for machining pieces of a length greater than the width of the grinding wheel at enhanced productivity, being typically associated to the use of automatic feed and discharge conveyors of the work-pieces.
These main modes and variations thereof are well known to the skilled operators, each requiring specific regulations, relative positioning and swiveling of the regulating wheel axis in respect to the axis of the grinding wheel and even special geometrical configurations of the work-piece supporting blade.
Whichever the profiles of the peripheral surface of the grinding wheel and of the regulating wheel are, in order to impart a desired peripheral surface profile to the work-piece, the operative surfaces of both wheels must be periodically re-trued because of their unavoidable progressive wear and loss of ideal straightness of the profile of their operative surface or surfaces.
The periodically re-truing machining (generally more frequently needed for the grinding wheel and relatively less frequently needed for the regulating wheel) are performed by stopping the feeding of work-pieces to the machine for the time required to perform a wheel surface re-truing cycle, during which precisely positioned truing tools are driven across the width of the wheels to machine the peripheral surface of the grinding wheel and/or of the regulating wheel to refresh the exactness of the work profiles of the peripheral surfaces of the two wheels.
The document EP 1 080 834 A (D1) discloses a centerless grinder that requires two distinct truing runs, one for truing the grinding wheel and the other for truing the regulating wheel and the intrinsically heavy grinding wheel assembly is displaceble along two axis, according to a most common architecture.
Generally, the truing tool of the grinding wheel and the truing tool of the regulating wheel both require dedicated two-axis control actuators for precisely producing the desired profile on the working portions of the peripheral surfaces of the respective wheel to be re-trued.
The re-truing of the peripheral surface of the regulating wheel, often having its axis swiveled by a certain angle in respect to the axis of the grinding wheel, in order to promote a desired transversal progression of the work-piece or for maintaining the spinning work-piece having a stepped diameter in stable abutment against the side of the grinding wheel, raises the problem of re-truing the peripheral surface of the regulating wheel according to a hyperboloid shape to ensure a substantially straight line of contact with the spun work-piece. These computational problems may be greatly alleviated by machining the slanted regulating wheel with a tool the trajectory of which is made to coincide as much as possible with the line of contact of a peripheral surface of the wheel with the work-piece during the grinding process, that is by machining the peripheral surface of the regulating wheel with a truing tool positioned in front of the regulating wheel rather than at the rear or at the top thereof as is customary in the art.
In any case, it is evident the cumulative cost of numerous independent linear axis control devices to be deployed in the machine.
A basic requisite of the stress structure of a centerless grinder is rigidity, in consideration of the relatively large mass of the grinding wheel assembly often subject to thrusts and impacts that may cause vibrations. Indeed, the precision of laboriously found optimal trim regulations may be jeopardized by vibrations caused by accidental shocks of extraordinary intensity even in case of generously sized stress structures supporting the heavy and fast spinning grinding wheel. Besides upsetting the laboriously found trim, vibrations may damage or even break irreparably the truing tools, generally of expensive synthetic diamond. The need of mounting the heavy and fast spinning grinding wheel on multiple linearly moving carriages (for moving along two orthogonal axis under accurate control), reduces overall rigidity and render the assembly more susceptible of vibrations.
On another account, the grinding fluid that is normally fed to the grinding wheel at relatively large flow rates must be continuously and effectively drained to prevent flooding the work zone because of occasional cloggings.

OBJECTS AND SUMMARY OF THE INVENTION

To the fulfillment of these important and even contrasting requisites, the present invention offers an outstandingly effective and simple technical solution, by means of the grinder of claim 1.
It has been found that while allowing implementation of a surface truing machining of the work surfaces of the two cooperating wheels in substantial coincidence with the respective lines of contact with the work-piece, the grinding wheel may be mounted on a single carriage driven by a relative linear axis control device sideways along only a transversal axis for carrying out a surface truing phase of the peripheral surfaces of the grinding wheel and/or of the regulating wheel.
By employing only a single transversally moving carriage, instead of the usual pair of orthogonal moving carriages, improves the rigidity characteristics of the grinding wheel assembly as a whole which becomes less susceptible of vibrations.
Preferably, the grinding wheel assembly, including the single carriage for moving the grinding wheel through a lateral swing, orthogonal to the longitudinal axis of the bench of the machine, during a truing phase, is supported on a plane of the stress structure of the machine inclined with respect to the plane of the machine bench (commonly horizontal), on which the regulating wheel and the work-piece template blade are supported, by an angle that may be comprised between few degrees and 90°.
In case of particularly heavy grinding wheel assembly, the angle of inclination is preferably limited to 45° as maximum.
Such an optional and in many situations preferred arrangement further improves the tolerance of accidental thrusts and impacts on the grinding wheel assembly besides significantly improving the conditions for an easier and quicker drainage of the cooling fluid that is fed to the grinding wheel.
The truing tools for machining the peripheral surfaces of the two wheels are respectively installed one (for truing the surface of the regulating wheel) on the grinding wheel assembly and the other (for truing the surface of the grinding wheel) on the longitudinally driven carriage that supports the regulating wheel assembly, sideway of one end and of the opposite end of the grinding wheel and of the regulating wheel, respectively.
The truing tool for the regulating wheel, mounted on the grinding wheel assembly is on a pivotally held arm to be placed in a stand-by or retracted position during the grinding process and to be moved to a forward extending position for machining the peripheral surface of the regulating wheel during a re-truing cycle.
The relative position of the regulating wheel and of the template blade mount for supporting the work-piece carried on said longitudinally moving carriage may be adjusted by either a manually operated pilot wheel or alternatively by employing a secondary carriage carrying the regulating wheel, longitudinally shiftable on the (primary) carriage moving on the bench, by a third linear axis control device.
The regulating wheel is held in a swivel mount to permit swiveling of its axis by a certain angle (usually comprised between 1° and 9°) when operating according to a "through feed" mode.
Optionally, the bench of the machine onto which the regulating wheel assembly may be rotated in the horizontal plane of the bench through a certain angle, to grind conical workpieces.
Either the movement of the primary longitudinally moving carriage carrying the template blade mount, the truing tool for the grinding wheel and the swivel mounted regulating wheel assembly, and/or of the secondary carriage for longitudinally shifting the regulating wheel, or the movements of both primary and secondary longitudinally moving carriages and the transversal travel of the grinding wheel assembly and of the truing tool for the regulating wheel may be coordinately controlled to produce the desired refreshed profile of the peripheral surface of the grinding wheel and/or of the regulating wheel when the respective truing tool carried on the grinding wheel assembly is placed in an operative position to machine the peripheral surface of the regulating wheel.
In practice, the total number of linear axis control devices required for truing the operating surfaces of the grinding wheel and of the regulating wheel may be just two or, according to an alternative embodiment, three, thus affording a sensible cost saving; compared with the more numerous linear axis control devices employed in known machines of comparable capabilities and performances.
In any case, the most critical (because of its relatively large weight and spinning speed) grinding wheel assembly employs a single transversally moving carriage, thus affording an enhanced rigidity and substantial absence of vibrations.
The fact that the machining of the grinding wheel surface and of the regulating wheel surface take place at their respective front sides, in other words, along a trajectory of the tip of the truing tool practically coincident with the line of contact of the wheel with the work-piece, greatly simplify a most accurate interpolation of the mutually orthogonal movements of the assemblies of the two wheels carrying the respective truing tools and effectively produces a rectilinear profile, even when the axis of the regulating wheel is swiveled off parallelism with the axis of the grinding wheel.
The invention is more precisely defined in the annexed claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a general view of a centerless grinder according to a first embodiment of this invention.
Figure 2 is a general view of a centerless grinder according to an alternative embodiment.
Figure 3 is a perspective view of the centerless grinder of Figure 2, depicting a grinding phase.
Figure 4 is a perspective view of the centerless grinder of Figure 2, depicting the machining of the peripheral surface of the grinding wheel.
Figure 5 is a perspective view of the centerless grinder of Figure 2, depicting the machining of the peripheral surface of the regulating wheel.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Figure 1 is a basic representation of a centerless grinder according to a preferred sample embodiment of this invention.
The machine has a basement 1 onto which is securely fastened a horizontal bench element 2 and a separate support structure 3 for the grinding wheel G.
The horizontal bench element 2 may be rotated in the horizontal place around the pin 4 to handle conical workpieces, as commonly provided for these machines.
The template blade 5, supporting the work-piece W, is held in a template blade mount 6, which is fastened to a first carriage 7, onto which is also mounted an upright stand piece 18, at the top of which is fastened a truing diamond tool 17 for machining the surface of the grinding wheel G. The carriage 7, carrying the swivel mounted regulating wheel C, the swivel pin of which is indicated with 8, is longitudinally shifted on the horizontal bench element 2 by a first linear axis control device, schematically indicated by the actuating motor M1 and the screw 9.
The regulating wheel C, in the embodiment shown is mounted on a secondary carriage 10, longitudinally shiftable on the primary carriage 7 by acting on a hand-operated pilot wheel 11 turning the screw 12 for adjusting the distance of the regulating wheel C from the workpiece supported on the template blade 5.
The grinding wheel G is mounted on a single carriage 13 moving transversally of the longitudinal axis of the machine.
The transversal movement of the grinding wheel assembly is actuated by a second linear axis control device, schematically indicated by the actuating motor M2 and the screw 14.
A truing tool 15 for periodically machining the peripheral surfaces of the regulating wheel C is carried at the end of a pivoting arm 16, mounted sideway of the grinding wheel. The pivotally held arm 16 may be rotated from its rest position to an active position to carry out a truing phase of the peripheral surface of the regulating wheel C.
In Figure 2 an alternative embodiment of the machine of this invention is shown. Practically according to this alternative embodiment a third linear axis control device indicated by the actuating motor M3 substitutes the hand operated pilot wheel 11 of the embodiment of Figure 1.
Figure 3 is a perspective view of the machine of Figure 2, depicted during a grinding process of the workpiece W.
In this perspective view it may be observed with more ease the position of the truing diamond tool 17 for machining the surface of the grinding wheel G mounted at the top of the upright stand piece 18, fastened on the primary carriage 7 together with the template blade mount 6.
According to an essential feature of the machine of this invention, both truing tools 15 and 17, are disposed in a way to machine the respective wheel at the "front" side thereof. More specifically, during the execution of a truing phase, the spatial trajectories of the cutting tips of the truing tools 15 and 17, relative to the work surfaces of the wheel machined by the tool, are parallel to and substantially coincide with the lines of contact of the respectively machined wheel with the work-piece W, during the grinding process.
This condition of carrying out a truing machining of the work surfaces of the grinding wheel and of the regulating wheel practically eliminates the need of accurately calculating a best fitting hyperboloid curve as it would be necessary in many circumstances to do for ensuring a straight line of contact of the machined wheel with a cylindrical work-piece surface, accounting for the eventual angle of swivel of the axis of the regulating wheel in respect to the axis of the grinding wheel as it is normally necessary for promoting a certain velocity of progression of the work-pieces W transversally during grinding, according to a so-called "through feed" mode.
According to the machine of the embodiment shown in Figure 1, the truing of a certain work profile of the grinding wheel G and of the regulating wheel C is accomplished by coordinately controlled movements of two carriages, namely the longitudinal axis of movement of the first carriage 7, carrying the regulating wheel C and the truing tool 17, and the transversal axis of movement of the second carriage 13, carrying the grinding wheel G and the truing tool 15.
The relative position of the regulating wheel C in respect to the template blade mount 6, in function of the dimensions of the work-piece W is adjusted either manually by turning the pilot wheel 11 in the embodiment of Figure 1, or automatically by the third linear axis control device M3, in the alternative embodiment of Figure 2.
Of course, the use of a third linear axis control device will enhance the possibilities of implementing a fully automatically control of the work process, including the search and maintenance of optimal trim conditions of conducting the grinding process.
In any case, the total number of linear axis control device for a machine made according to the present invention remains smaller than the number usually employed in machine of comparable capabilities and performances.
In the embodiment shown, the plane of the stress structure supporting the grinding wheel assembly is not horizontal but is in inclined by an angle α. Although this condition is not strictly essential to accomplish the objectives of this invention in terms of a minimization of the number of linear axis control devices, it further promotes the rigidity of the grinding wheel assembly to make it less subject to vibrations. The angle of inclination α that is preferably equal to or less than 45° in case of relatively large and heavy grinding wheel assemblies, but may even reach 90°.
In any case, a slanting of the plane of support of the grinding wheel in respect to the plane of the bench 2 improves the conditions for a quicker and less problematic discharge of the grinding fluid.
Figure 3 is a perspective view of the machine of Figure 2 depicting a grinding phase. In this perspective it is easier to locate with more precision the functional elements described above with reference to Figures 1 and 2.
As schematically shown the regulating wheel assembly mounted on the secondary carriage 10 can be swiveled in the vertical plane as schematically depicted by the arrows symbol traced around the swivel pin 8, of Figures 1 and 2, in order to slant the axis of the regulating wheel C in respect to the axis of the grinding wheel G by a certain angle to promote the advancement of work-pieces transversally along the work surfaces of the two wheels, when operating the machine in a "through feed" mode. This is generally done for grinding long cylindrical work-pieces (larger than the width of the wheels). The swivel angle of the axis of the regulating wheel may be of about 1° or up to about 9°. Even when swiveling the axis of the regulating wheel C, the position of the truing tool 17 remains unchanged because the tool 17 is mounted on the primary carriage 7, together with the template blade mount 6.
Figure 4 is a perspective view of the machine illustrating the execution of a truing phase of the peripheral surface of the spinning grinding wheel G.
To carry out such a periodic truing phase of the grinding wheel G, the feeding of workpieces to the machine is momentarily interrupted, the linear axis control device M1 of the longitudinally moving primary carriage 7 and the linear axis control device M2 of the transversally moving carriage 13 of the grinding wheel assembly are co-ordinately driven to produce the desired machining of the peripheral surface of the grinding wheel G during its transversal swing by the diamond tool 17 carried by the longitudinally moving powering carriage 7. When the truing machining has been completed the carriage 7 carrying the tool 17 is retracted and the grinding wheel assembly is returned to its normal working position by the respective linear axis control device M2.
Thereafter, the grinding parameters are reset and the grinding processing of workpieces may resume.
Figure 5 is a perspective view of the machine illustrating the execution of a truing phase of the spinning regulating wheel C by the relative truing tool 15 carried at the tip of the pivoting arm 16.
This operation may be performed simultaneously to a truing operation of the grinding wheel or separately, by modifying the relative positions of the regulating wheel and of the diamond tool 17 by shifting on the secondary carriage 10.
For carrying out such a retruing phase of the regulating wheel C, the feeding of workpieces is momentarily interrupted in the event that the bench 2 was set in a slanted position (rotated in the horizontal plane) because of a conicity of the workpieces fed to the machine the bench 2 is returned momentarily to a perfect alignment with the longitudinal axis of the machine.
The pivoting arm 16 is rotated to place the truing tool 15 in an operative position and the linear axis control device M1 of the primary longitudinal carriage 7 and the linear axis control device M2 of the transversally moving carriage 13 are coordinately activated to drive the grinding wheel assembly transversally to machine the peripheral surface of the spinning regulating wheel C along a line parallel to and practically coinciding with the line of contact of the regulating wheel C with the workpiece during a grinding phase.
Once the truing machining has been completed, the carriage 7 is retracted and the grinding wheel assembly returns to its normal working position, the pivoting arm 16 is raised to its rest (inoperative) position, and the grinding of workpieces may be resumed (after returning the bench 2 to the desired slanted orientation if this is the case). By contrast, the slanting the axis of rotation of the regulating wheel C, if set for the particular processing being performed, is maintained also during the truing phase of the regulating wheel C, for the above-discussed reasons.
The ability of carrying out the truing machining of the grinding wheel and of the regulating wheel surfaces along spatial trajectories of the tools practically coinciding with the line of contact of the respective wheels with the spinning work-piece, ensure an almost perfectly straight line machining of the wheel surfaces irrespectively of the angle of swivel of the axis of the regulating wheel C in respect to the axis of the grinding wheel G that may be set for conducting a certain grinding process, without burdening with complex calculations a central processing unit governing a correct interpolation of the mutually orthogonal movements of the carriages or of independent tool holder assemblies driven by respective linear axis control actuators.

Claims

A centerless grinder comprising a stress structure (2,3) including a machine bench (2), a template blade (5) mount (6) for supporting the work-piece (W) and a regulating wheel (C) both mounted on a first carriage (7) longitudinally movable by a first linear axis control device (M1) on said bench and means for advancing said regulating wheel (c) toward said template blade mount (6) for bearingly engaging and spinning the supported work-piece (W), a grinding wheel (G) supported on said stress structure (3) for removing stock from the surface of the supported work-piece spun by said regulating wheel (C) on said template blade (5), a first truing tool (17), for periodically machining the cutting surface of said grinding wheel, mounted on said first carriage (7), sideway of one end of the regulating wheel (C), a second truing tool (15) for periodically machining the surface of said regulating wheel that engages the work-piece at the end of a pivoting arm (16), mounted sideway of the end of the grinding wheel (G), at the opposite side of said end of the regulating wheel (C), and means (8) for swiveling the axis of said regulating wheel (C) about the axis of said grinding wheel (G) when grinding according to a through feed mode, characterized in that
said grinding wheel (G) is mounted on a single carriage (13) movable by a second linear axis control device (M2) on a plane of said stress structure (3) in a direction orthogonal to the longitudinal axis of said bench (2);

said single carriage (13) being moved transversally by said second linear axis control device (M2) to have the surface of the grinding wheel (G) machined by said first truing tool (17) and/or the surface of the regulating wheel (C) machined by said second truing tool (15) when purposely positioned by said pivoting arm (16).
The centerless grinder according to claim 1, wherein the longitudinal movement of said first carriage (7) and the transversal movement of said second carriage (13) are coordinately controlled during a truing phase to produce the desired profile of the peripheral surface of the wheel (G, C) being machined by the respective truing tool (17,15).
The centerless grinder according to claim 1, wherein said plane of the stress structure (3) supporting said grinding wheel (G) mounted on said transversally movable second carriage (13) is inclined with respect to the plane of said bench (2).
The centerless grinder according to claim 3, wherein the angle of inclination is equal or less than 45°.
The centerless grinder according to claim 3, wherein the angle of inclination is equal or less than 90°.
The centerless grinder according to claim 1, wherein said means for adjusting the relative position of said regulating wheel (c) from said template blade mount (6) and from said first truing tool (17) are in the form of a secondary carriage (10) carrying said swivel (8) mounted regulating wheel (c), longitudinally shiftable on said first carriage (2) by a hand operated pilot wheel (11) turning a screw (12).
The centerless grinder according to claim 1, wherein said means for adjusting the relative position of said regulating wheel (c) from said template blade mount (6) and from said first truing tool (17) are in the form of a secondary carriage (10) carrying said swivel (8) mounted regulating wheel (c), longitudinally shiftable on said first carriage (7) by a third linear axis control device (M3).
The centerless grinder according to claim 1, wherein the trajectories of the cutting tips of said truing tools (17,15) are parallel to and substantially coincident with the lines of contact of a peripheral surface of the respective wheel with the spinning work-piece, when swinging transversally said single carriage (13) even if said swiveling means (8) hold the axis of said wheels (G, C) off a perfect parallelism.