[0001] The invention relates to a method and apparatus for grinding.
[0002] The present invention seeks to provide an improved method and apparatus for grinding.
Grinding apparatus is described in
US6123606.
[0003] According to a first aspect of the invention there is provided apparatus for high
speed grinding comprises a grinding wheel on an axle having a circumferential grinding
surface, a machine for mounting and rotating the grinding wheel about the axle, a
coolant supply system including a slot nozzle arranged to direct coolant fluid secantly
to the grinding surface, the slot nozzle having an elongate axis and a short axis
wherein the elongate axis is parallel to a chord through the grinding wheel and tilted
relative to the axis of the grinding wheel.
[0004] By tilting the exit of the slot nozzle an improved flow distribution to the grinding
surface is achieved.
[0005] Preferably the elongate axis is tilted between 5 and 20 degrees to the axis of the
grinding wheel.
[0006] The slot nozzle may have a length along the elongate axis that is longer than the
width of the circumferential grinding surface.
[0007] The extended length provides a flow of coolant over the edges of the grinding surface
to further improve cooling of the grinding wheel. Preferably the length of the elongate
axis is more than 5% longer than the width of the circumferential grinding surface.
[0008] The machine for mounting and rotating the grinding wheel may be capable of rotating
the wheel at peripheral speeds between 10 metres per second and about 80 metres per
second.
[0009] The coolant supply system may deliver a jet of liquid from the nozzle at a pressure
of between 40 and 70 Bar (4000kPa - 7000kPa).
[0010] Preferably the apparatus further comprises an alignment tool having a first edge
for alignment with a side of the grinding wheel, a second edge for alignment with
the grinding surface and a third edge for alignment with an edge of the nozzle.
[0011] The tool may be provided by a sheet of material.
[0012] The invention will now be described by way of example only and with reference to
the accompanying drawings in which,
Figure 1 is a schematic diagram illustrating an embodiment of the invention;
Figure 2 depicts a nozzle for use in the system of Figure 1;
Figure 3 is a schematic depicting the nozzle of Figure 2 presented to a grinding wheel;
Figure 4 is a diagram of a nozzle, alignment tool and grinding wheel;
Figure 5 is a diagram of a nozzle, further alignment tool and grinding wheel;
Figure 6 depicts a supply pipe for supplying coolant fluid to the nozzle.
[0013] For the purposes of illustrating the principles of a grinding process incorporating
the invention, Fig. 1 shows a grinding set-up which comprises a grinding wheel 2 rotating
in the direction of arrow 4 while a workpiece 6 is fed past the wheel 2 in the relative
direction of arrow 8. In the illustrated example this produces an operation known
in the art as "down" grinding in a contact region generally indicated at 9. The invention
is found to work just as well with "up" grinding. Essentially the process of the invention
is a developed form of the process known as creep-feed grinding, although this may
be regarded as something of a misnomer since the enhancement results is very much
faster removal of workpiece material.
[0014] The grinding wheel 2 is mounted on a rotary spindle 10 carried by a tool head or
chuck 12 which is part of a standard multi-axis machine. The workpiece 6 is held by
means of a mounting fixture 14 on a surface mounting table 16. Since, in this embodiment,
a "one-pass" grinding process is shown the width of the grinding wheel can be determined
by the corresponding width of the ground surface required. We have found no significant
variation of results using grinding wheels in a width range of 10 mm to 45 mm providing
the surface speed is maintained constant. On the other hand we have found no indication
of a width limit and the invention may be expected to be useful regardless of the
width of the grinding wheel, other considerations aside.
[0015] The range of values of surface speed for the type of grinding wheel employed is from
about 10 metres per second up to about 80 metres per second. Wheels of various diameters
gave consistent results providing surface speed was matched with all other parameters.
The maximum diameter of grinding wheel used to date is around 220mm, but this upper
limit was imposed by physical clearance in the operative region of the machine, rather
than by the inherent stability of the wheel construction. Obviously grinding wheels
by the nature of their composition and construction possess limitations in terms of
maximum rotational speed, depth of cut achievable to name but two, but in this example
these did not curtail the operational parameters of the process. Thus, where the machine
permits in respect of size, and speed higher figures may be expected to be achieved
e.g. up to 400mm or more.
[0016] A jet 18 of liquid coolant, comprising a water soluble oil, is directed through nozzle
means 20 at an aiming point 19 on the periphery of wheel 2. The nozzle 20 is the outlet
of a closed-loop coolant delivery, collection and filtration system. Spent coolant
ejected from the wheel is collected in a sump 22, in the lower part of the machine,
and drawn-off through an efficient filtration system 24 to remove debris down to a
particle size, typically of at least, about 10 micron.
[0017] Integral with the filtration system 24 is a very high pressure pump system 26 which
delivers coolant under pressure through outlet 28 to the delivery nozzle 20. In the
illustrated embodiment the coolant supply is delivered via the outlet 28 at a pressure
of up to 100 bar (10000kPa), typically between 40 bar and 70 bar (4000 to 7000 kPa),
at a flow rate of up to about 130 litres per minute.
[0018] The nozzle 20 is positioned close to the periphery of wheel 2 to deliver the very
high pressure jet 18 of coolant at the wheel at a point approximately 45 degrees in
advance of the cutting region on workpiece 6. The nozzle is a slot nozzle 20 constructed
and arranged to direct a jet 18 of coolant fluid to the periphery of the wheel with
the impact point across the full width of the wheel. In the embodiment the nozzle
20 has a jet orifice which is approximately rectangular having a length approximately
equal to the width of the wheel 2, but preferably slightly longer, and which is 0.5
mm to 1 mm in depth. This orifice, therefore, directs a jet 18 of coolant in the shape
of a sheet or fan at the periphery of the wheel.
[0019] Also, in Figure 1, a pair of radii 30,32 are shown (in chain-line) centred on the
wheel spindle 10. A first radius 30 is drawn through the impingement region of the
jet 18 on the periphery of the wheel 2, while the second radius 32 is drawn through
the contact point between the wheel 2 and the workpiece 6. The included angle between
these two radii 30,32 defines the circumferential position of the impact point of
jet 18. It will be apparent from the illustration of the present embodiment, which
used a wheel diameter of approximately 80 mm at the smaller end of the range, that
this included angle is approximately 45 degrees and the jet 18 is in advance of the
grinding wheel contact point. Other included angles may be appropriate.
[0020] A more detailed view of the nozzle is shown in Figure 2. As may be observed the nozzle
body has an inlet portion 40, a tapering portion 42 and a flow forming portion 44
before the nozzle outlet 46 which offers a consistent laminar flow from the nozzle
and helps to reduce the amount of air in the coolant flow and can reduce, where the
substrate suffers, tarnishing and oxidation at the grinding point. Figure 2 depicts
a perspective view (Fig. 2a) a top view (Fig. 2b) and a side view (Fig. 2c). In an
alternative arrangement the inlet portion has a nut or other connecting feature for
connecting the nozzle to pipework which supplies the cooling fluid to the nozzle.
[0021] The nozzle may be formed from stainless steel pipe manufactured on customised jaws
and aperture former to produce the elongate nozzle shape.
[0022] Figure 3 depicts the preferred alignment of the nozzle 20 to the grinding wheel 2.
The nozzle 20 directs the coolant fluid as a jet 18 secantly to the wheel such that
it impacts the grinding surface from an angle that is leant relative to the true radius
of the wheel. In the most extreme case the jet is directed tangentially to the wheel
but normally angle of the nozzle is between 5 and 20 degrees from the tangent. The
tem secantly includes the arrangement where the fluid is directed tangentially.
[0023] As shown in Figure 3b the nozzle is presented to grinding wheel to supply coolant
to the grinding face which is the circumferential face. It has been found that the
orientation of the nozzle relative to the circumferential face is important; not just
the secant angle onto the circumferential face but also the angle e of the elongate
axis of the nozzle to the axis of the grinding wheel. By arranging the elongate axis
of the nozzle at an angle e between 5° and 15°, and preferably at around 10° to the
axis of the grinding wheel an improved cooling distribution is achieved.
[0024] Where a particularly wide grinding face is used it may be necessary to use more than
one elongate coolant nozzle which may be at different angles relative to each other
and to the axis of the grinding wheel. The nozzles may overlap to provide extra coolant
to particular regions of the grind face. One or more of the nozzles may be parallel
to the axis of the grinding wheel.
[0025] The tip (exit orifice) of the nozzle 20a,20b in use is preferably positioned very
close to the peripheral, circumferential surface of the grinding wheel 2. To aid simple
alignment of the nozzle a tool may be used as show in Figure 4. The tool 102 has a
first datum face 104 to align with a side of the grinding wheel, a second datum face
106 to align with the grinding face of the grinding wheel, a third datum face 107
to locate the axial position of the end of the nozzle relative to the grinding face
to ensure overlap and a fourth datum face 108 to align the angle of the elongate nozzle
to the axis of the grinding wheel. The tool may be formed from readily available sheet
metal offering a simple and elegant solution to what could be a complex and costly
set up process.
[0026] A further alignment tool an example of which is shown in Figure 5 may be used which
locates the nozzle in its correct secantial or tangential position relative to the
edge of the grinding wheel. The tool has an elongate member 110 which is long enough
to span the distance between the nozzle 20 and the edge of the grinding wheel 2 and
a notched portion 112 which engages with the nozzle. To align the nozzle the notched
portion is placed into engagement with the nozzle and the elongate member then the
axis of the wheel or the entry to pipework supplying fluid to the nozzle moved till
the elongate member is at the desired secantal or tangential angle to the grinding
wheel.
[0027] Figure 6 shows top view (Fig. 6a) and a side view (Fig. 6b) for an option of pipework
which may be used to supply the cooling fluid to the nozzle. The pipework is made
of three separate sections which are joined together, preferably by welding, to avoid
significant bending of a full length pipe and fluctuations in bore size at the bending
points and weakness in the material. The bends are all kept below 90 degrees so that
fluctuations in flow are minimised.
1. Apparatus for high speed grinding comprises a grinding wheel (2) on an axle having
a circumferential grinding surface,
a machine for mounting and rotating the grinding wheel about the axle (10),
a coolant supply system (26,28) including a slot nozzle (46) arranged to direct coolant
fluid secantly to the grinding surface,
the slot nozzle having an exit with an elongate axis and a short axis wherein elongate
axis is parallel to a chord through the grinding wheel and tilted relative to the
axis of the grinding wheel.
2. Apparatus according to claim 1, wherein the elongate axis is tilted between 5 and
20 degrees to the axis of the grinding wheel.
3. Apparatus according to claim 1 or claim 2, wherein the slot nozzle has a length along
the elongate axis that is longer than the width of the circumferential grinding surface.
4. Apparatus according to claim 3, wherein the length of the elongate axis is more than
5% longer than the width of the circumferential grinding surface.
5. Apparatus according to any preceding claim, wherein the machine for mounting and rotating
the grinding wheel rotates the wheel at peripheral speeds between 10metres per second
and about 80 metres per second.
6. Apparatus according to any preceding claim, wherein the coolant supply system delivers
a jet of liquid from the nozzle at a pressure of between 40 and 70 Bar (4000 and 7000
kPa).
7. Apparatus according to any preceding claim further comprising an alignment tool having
a first edge for alignment with a side of the grinding wheel, a second edge for alignment
with the grinding surface and a third edge for alignment with an edge of the nozzle.
8. Apparatus according to claim 7, wherein the tool is provided by a sheet of material.