The application relates generally to grinding wheels and, more particularly, to cooling in such grinding wheels.
When a grinding wheel grinds or machines a workpiece, heat is generated at the grinding zone. Coolant delivery to the machining zone ensures the extraction of heat, but also provides lubricity and allows for chip evacuation. Failure to deliver the required amount of coolant at the correct location may result in wheel failure and part damage, and may also cause equipment damage in case of fire when using oil based coolants. Superabrasive machining processes are particularly sensitive to coolant delivery, and coolant should be delivered as close as possible to the machining zone.
In one aspect, there is provided a grinding wheel for grinding a workpiece through rotation at a predetermined rotational speed, the wheel comprising: a grinding wheel body having a hub defining a wheel inlet; and an impeller structure disposed within the wheel body around the hub, the impeller structure having a plurality of circumferentially spaced apart blades, the blades cooperating to define a plurality of grooves each extending between a groove inlet end in fluid communication with the wheel inlet and a groove outlet end adjacent an outer circumference of the impeller structure, wherein each groove is defined between first and second walls of adjacent one of the blades with the first wall being located in front of the second wall with respect to a direction of rotation of the wheel, and wherein an angle between the second wall adjacent the groove outlet and a tangent to the outer circumference adjacent the groove outlet is defined as
where Q is a desired flow rate of the coolant through the wheel, N is the predetermined rotational speed of the grinding wheel in min−1, R2 is the radius of the outer circumference, A2 is a combined surface area of the groove outlets, and α2 is a desired angle of exit of the coolant from the groove outlets with respect to the tangent to the outer circumference adjacent the groove outlet, a value for α2 being selected to be at most 15 degrees.
In another aspect, there is provided a grinding wheel for grinding a workpiece through rotation at a predetermined tangential speed, the wheel comprising: a grinding wheel body having a hub defining a wheel inlet; and an impeller structure disposed within the wheel body around the hub, the impeller structure having a plurality of circumferentially spaced apart blades, the blades cooperating to define a plurality of grooves each extending between a groove inlet end in fluid communication with the wheel inlet and a groove outlet end adjacent an outer circumference of the impeller structure, wherein each groove is defined between first and second walls of adjacent one of the blades with the first wall being located in front of the second wall with respect to a direction of rotation of the wheel, and wherein an angle between the second wall adjacent the groove outlet and a tangent to the outer circumference adjacent the groove outlet is defined as
where Q is a desired flow rate of the coolant through the wheel, A2 is a combined surface area of the groove outlets, U2 is the tangential speed of the grinding wheel, and n is at least 0.9 and less than 1.
In a further aspect, there is provided a method for distributing a coolant to a grinding site of a grinding wheel, the method comprising: rotating the grinding wheel; injecting the coolant in an inlet of the grinding wheel, the inlet being disposed proximate to an axis of rotation of the grinding wheel; moving the coolant fluid from the inlet along a plurality of internal grooves of the grinding wheel outwardly towards a plurality of outlets; and expelling the coolant outwardly from the plurality of outlets at an angle of at most 15 degrees with respect to a tangent to a circumference of the grinding wheel at the outlet.
Reference is now made to the accompanying figures in which:
A grinding wheel will be described herein. Such a grinding assembly may be used, for example, in machining of components of a gas turbine engine, including, but not limited to, turbine discs, integrally bladed rotors.
Conventional methods of coolant delivery usually rely on using external nozzles to bring coolant into the machining zone in a spraying technique. Such a technique may be limited to having a clear line of sight from nozzle orifice to the machining zone. In case of grinding of internal part features, the line of sight is often blocked and it may require a complicated nozzle design to reach the machining zone; the nozzle may also provide interference in the tool path to avoid collision with the part. Accordingly, a grinding wheel providing internal coolant delivery is described herein.
Referring to
Referring to
Turning now to
In a particular embodiment, the body 102 and impeller structure 108 are made of metal including, but not limited to, one of steel, aluminium and titanium, and integrally formed (i.e. it is a monolithic piece). It is contemplated that the body 102 and impeller structure 108 could be made of an appropriate material other than metal, including, but not limited to, one of carbon fiber and glass reinforced nylon. In a particular embodiment, the body 102 and impeller structure 108 are made by additive manufacturing. Examples of additives manufacturing include selective laser sintering, fused deposition molding or direct metal laser sintering.
It is also contemplated that the front and rear walls 104, 106 and impeller structure 108 could be separately manufactured and interconnected through any appropriate method. Other suitable methods of manufacturing the grinding wheel 100 include, but are not limited to, casting methods such as sand casting, die casting, investment casting or metal injection molding.
In the embodiment shown in
Referring back to
The outer surface of the hub 111 curves outwardly such as to merge with the front wall 104, while remaining inwardly spaced apart from the curved inner annular section of the rear wall 106. This curvature forms a funnel 103 which guides the coolant entering the inlet 112 and redirects the coolant from an axial flow 120 to a flow W2 relative to the wheel 100 (
In a particular embodiment and as can be seen in
Referring more specifically to
The blades 122 extend outwardly beyond the front and rear walls 104, 106. Portions 123 of the blades 122 extending beyond the front and rear walls 104, 106 are coated by an abrasive layer 125. The portions 123 are the elements of the grinding wheel 100 which effectively grinds the workpiece 70, 70′. In a particular embodiment, the coating layer 125 is superabrasive and is made of cBN. It is contemplated that the coating layer 125 could be abrasive yet not super abrasive and could be made of a superabrasive material other than cBN. For example, the coating layer 125 could be made of diamond vitrified material or resin bonded abrasive such as for example aluminium oxide or silicon carbide. In a particular embodiment, the coating is applied using single layer electroplating. It is contemplated that other coating techniques could be used to coat the portions 123 with the abrasive layers 125. For example, brazing could be used. It is contemplated that the abrasive layer 125 could be connected to the portion 123 of the grinding wheel 100 subject to machining by methods other than coating. For example, the abrasive layers 125 could be assembled or bonded to the portions 123.
The circumferentially spaced blades 122 define a plurality of grooves 124 therebetween, each extending from and communicating with the annular passage 128. Each of the grooves 124 is defined by a first blade wall 132 belonging to a first blade 122, and a second blade wall 134 belonging to a second blade 122 adjacent to the first blade 122. Accordingly, the groove 124 is bounded by the first and second blade walls 132, 134, with the first blade wall 132 being disposed in front of the second blade wall 134 with respect to the direction of rotation, i.e. the first blade wall 132 is the first one to pass a fixed point when the wheel 100 is rotating, and the second blade wall 134 “pushes” the coolant in the circumferential direction as the wheel 100 rotates. The first and second blade walls 132, 134 allow the coolant to be directed to the grinding site.
Referring to
Although the groove inlets 130 are shown as communicating with the wheel inlet 112 through the annular passage 128, it is understood that other types of communications may be provided, including, but not limited to, each groove inlet 130 separately communicating with the wheel inlet 112. In the embodiment shown, the grooves 124 have a curved shape with the outlet 136 of each groove 124 being circumferentially offset from the inlet 130 of the groove in a direction opposite the direction of rotation of the wheel 100.
In a particular embodiment, velocity triangles can be used to estimate coolant flow at the groove inlets 130 and outlets 136. Coolant absolute velocity C can be calculated as the sum of a relative velocity W of the coolant with respect to the wheel 100 and a tangential velocity U of the wheel 100 or impeller structure 108. Still referring to
A1=2πR1b1
with R1 being the radial position of the groove inlet 130, and b1 the axial dimension of the blade 122 at the inlet 130 (see
and the tangential velocity U1 of the impeller structure 108 at the groove inlet 130 is expressed by
where N is the rotational speed of the grinding wheel 100 in min−1.
Assuming no coolant rotation at the groove inlet 130, an angle α1 between the tangential velocity U1 of the impeller 108 and the absolute coolant velocity C1 is 90°, and a relative flow angle β1 between the relative coolant velocity W1 and the absolute coolant velocity C1 at the groove inlet 130 can be calculated from
Focusing now on the groove outlet 136, point P2 is defined at an intersection of the second blade wall 134 (the “pushing wall”) and the groove outlet 136. At the groove outlet 136, an absolute coolant velocity C2 as well as a relative coolant velocity W2 (relative to the rotating wheel 100) may be determined. The absolute coolant velocity C2 may be split into a tangential absolute coolant velocity component C2U, representing the component of the absolute coolant velocity extending along a tangential direction of the wheel 100 and accordingly parallel to the tangential velocity U2 of the wheel, and a transverse absolute coolant velocity component C2m which extends perpendicularly to C2U. The transverse absolute coolant velocity component C2m, can be calculated from
where A2 is the combined area of the groove outlets 136, which can be calculated as
A2=2πR2b2f
where R2 is the radial position of the groove outlet 136, b2 the axial dimension of the blade 122 at the groove outlet 136 (see
It can be seen from
In a particular embodiment, the angle β2 is selected such as to have a value for the angle of exit of the coolant flow α2 between 0 and 15 degrees; in a particular embodiment, having the absolute coolant velocity C2 as close as possible to the tangential direction may help the coolant to go through the air barrier created as the grinding wheel 100 rotates. The angle β2 may thus be expressed as a function of the angle of exit of the coolant flow α2.
By definition, the tangential absolute coolant velocity component C2U at the outlet 136 may be expressed as
and the tangential velocity U2 of the wheel 100 at the outlet 136 may be expressed as
where R2 is the radial position of the groove outlet 136 and N is the rotational speed of the grinding wheel 100 in min−1.
The tangential absolute coolant velocity component C2U may also be expressed as a function of the tangential velocity U2 of the wheel 100 at the outlet 136 as
By combining equations B and D above:
Then, by combining equation E with equations A and C above:
Accordingly, by using the maximum value for the desired angle of exit of the coolant flow α2 in equation F above, the value of the angle β2 between the second wall 134 of the groove at the outlet 136 and the tangential direction may be found. In a particular embodiment, a value of at most 15 degrees for the desired angle of exit of the coolant flow α2 is used. In another particular embodiment, a value of at most 10 degrees for the desired angle of exit of the coolant flow α2 is used. In another particular embodiment, a value of at most 5 degrees for the desired angle of exit of the coolant flow α2 is used.
Alternately or in addition, the value of the angle β2 between the second wall 134 of the groove at the outlet 136 and the tangential direction may be determined based on a desired value for the tangential absolute coolant velocity component C2U, as a portion of the value to the tangential speed U2 of the grinding wheel 100, i.e. to have
C2UnU2 [equation G]
where in a particular embodiment n is as close as possible to 1.
In a particular embodiment, the wheel 100 is configured to obtain a value of the tangential absolute coolant velocity component C2U being at least 90% of the tangential speed U2 of the grinding wheel 100, i.e. with n being at least 0.9. In a particular embodiment, n is less than 1. Accordingly, in a particular embodiment, 0.9≦n<1. From equation D above, we can define the value of the angle β2 between the second wall 134 of the groove at the outlet 136 and the tangential direction as
By combining equations A and G into equation H, we find
Accordingly, by using a desired value of n in equation I above, the value of the angle β2 between the second wall 134 of the groove at the outlet 136 and the tangential direction may be found. As mentioned above, in a particular embodiment, a value of n of at least 0.9 is used. In a particular embodiment, a value of 0.9≦n<1 is used.
In a particular embodiment, the angle β2 is found using equation F above, and then the tangential absolute coolant velocity component C2U is calculated to verify that it is at least a given proportion of the tangential speed U2 of the grinding wheel 100, for example at least 90%. In another particular embodiment, the angle β2 is found using equation I above, and then the angle of exit of the coolant flow α2 is calculated to verify that is it smaller than or equal to a maximum predetermined value, for example 15 degrees.
In a particular embodiment, the angle between the first wall 132 of the groove at the outlet 136 and the tangential direction is also defined by β2.
Turning back to
φ=ωT
The time T is function of the average velocity Wavg of the coolant relative to the grinding wheel 100, and of a distance L (not shown) traveled inside the impeller structure 108:
In a particular embodiment, Wavg is calculated as the average between the relative coolant velocity W2 at the outlet 136 and the relative coolant velocity W1 at the inlet 130, and the distance L is measured as the length of a center line of one of the grooves 124. Accordingly, in a particular embodiment, the angular shift φ is calculated, and the circumferential position of the nozzle 80 is then selected to be at the angle φ with respect to the circumferential location where contact between the wheel 100 and the workpiece 70, 70′ occurs, such that coolant may be delivered where it is required. Accordingly, in a particular embodiment, the partial nozzle 80 may help minimize coolant waste.
In use, the grinding wheel 100 is rotated about its rotational axis 90. The motor rotates the shaft 60 which in turns rotates the grinding wheel 100. The coolant is then injected into the inlet 112 of the grinding wheel 100 by the coolant nozzle 80. In a particular embodiment, the airflow created through the grooves 124 by the rotation of the wheel 100 produces a “sucking” force which helps to drive the coolant to the inlet 112 of the grinding wheel.
As the coolant reaches the funnel 103, it is directed to the annular passage 128 toward the groove inlets 130. The second blade wall 134 pushes circumferentially on the coolant travelling radially, and directs the coolant toward the groove outlets 136. As it rotates, the impeller structure 108 transfers energy to the coolant. Because the impeller structured 108 is enclosed by the front and rear walls 104, 106 of the body 102, the impeller blades 122 transfer mechanical energy from the spindle to the coolant, which is converted to internal energy by increasing coolant static pressure and to kinetic energy by increasing coolant velocity. Having the combined groove outlet area A2 smaller than the combined groove inlet area A1 may contribute to the coolant being accelerated from the groove inlets 130 to the groove outlets 136.
The coolant is then expelled from the plurality of groove outlets 136 at the angle of exit α2 (i.e. angle between the absolute coolant velocity at the outlet C2 and the tangential direction of the grinding wheel 100 at the outlet 136), which in a particular embodiment is at most 15 degrees. In a particular embodiment, the coolant is alternately or also expelled from the plurality of groove outlets 136 such that the tangential absolute coolant velocity component C2U at the outlet 136 is at least a 90% of the tangential speed U2 of the grinding wheel 100.
Although the method is described for the grinding wheel 100 and the coolant nozzle 80, it is should be understood that the method could be used on any alternate embodiment of the grinding wheel and the coolant nozzle.
In a particular embodiment, the internal centrifuge assisted coolant delivery through the impeller structure 108 may allow to grind or machine a workpiece having various shapes and dimensions including those which have no line of sight while delivering coolant at the grinding zone. In addition, in a particular embodiment, the grinding wheel 100 may allow coolant delivery for various sizes, shapes or extensions of a machine spindle and a delivery of the coolant in a near proximity of the grinding or machining zone. In a particular embodiment, the impeller structure 108 allows to deliver coolant close to a tangent to the grinding wheel 100 and as close as possible to the machining zone, and allows to have a coolant speed close to the grinding wheel circumferential surface speed to overcome the air barrier that usually forms around the grinding wheel.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
This application is a divisional of U.S. application Ser. No. 14/159,121 filed Jan. 20, 2014, the entire contents of which are incorporated by reference herein.
Number | Name | Date | Kind |
---|---|---|---|
1928314 | Koss | Sep 1933 | A |
2087012 | Zimmerman | Jul 1937 | A |
2307312 | Whiting | Jan 1943 | A |
2470350 | Harrington | May 1949 | A |
2527762 | Pratt | Oct 1950 | A |
2599952 | Strayer | Jun 1952 | A |
2697878 | Oberley | Dec 1954 | A |
2746220 | Thomas | May 1956 | A |
3110993 | Grage | Nov 1963 | A |
3161995 | Lindblad | Dec 1964 | A |
3187475 | Sopcak | Jun 1965 | A |
3483858 | Jansen | Dec 1969 | A |
3574975 | Liss | Apr 1971 | A |
3579928 | Held | May 1971 | A |
3872630 | Ali | Mar 1975 | A |
4158935 | Robert | Jun 1979 | A |
4193228 | Bowler | Mar 1980 | A |
4216630 | Smart et al. | Aug 1980 | A |
4791760 | Noll | Dec 1988 | A |
5111624 | Shoenhair et al. | May 1992 | A |
5259148 | Wiand | Nov 1993 | A |
5423717 | Boaz | Jun 1995 | A |
5544986 | Kudo et al. | Aug 1996 | A |
5993121 | Fiesta | Nov 1999 | A |
6299522 | Lee | Oct 2001 | B1 |
6312325 | Van Osenbruggen | Nov 2001 | B1 |
6471573 | Reitmeyer | Oct 2002 | B1 |
D466912 | Lee | Dec 2002 | S |
6551181 | Lee | Apr 2003 | B2 |
6739960 | Sauer | May 2004 | B2 |
7377839 | Schrottner | May 2008 | B2 |
7582004 | Schwartz et al. | Sep 2009 | B2 |
8246425 | Schudel | Aug 2012 | B2 |
8562396 | Piliguian | Oct 2013 | B1 |
20030143926 | Piliguian | Jul 2003 | A1 |
20070128996 | Ficai | Jun 2007 | A1 |
20120190279 | Ficai | Jul 2012 | A1 |
20130052922 | Ahn | Feb 2013 | A1 |
Number | Date | Country |
---|---|---|
2437933 | Nov 2007 | GB |
Number | Date | Country | |
---|---|---|---|
20160158913 A1 | Jun 2016 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 14159121 | Jan 2014 | US |
Child | 15045406 | US |