Information
-
Patent Grant
-
6619642
-
Patent Number
6,619,642
-
Date Filed
Monday, August 13, 200122 years ago
-
Date Issued
Tuesday, September 16, 200320 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Nguyen; George
- Shanley; Daniel
Agents
-
CPC
-
US Classifications
Field of Search
US
- 269 138
- 269 135
- 269 136
- 269 46
- 269 47
- 074 54
- 261 900
- 261 309
- 261 216
- 261 217
- 261 99
- 261 100
-
International Classifications
-
Abstract
A clamp for clamping a workpiece such as a forging of an aerofoil component comprises a support body 24 to which a clamping member 26 is hinged. The clamping member 26 has a workpiece clamping element 54 having pads 58 for engagement with the workpiece. The workpiece clamping element 54 is pivotable relatively to the clamping member 26 by means of a ball and socket connection including a ball element 40. This enables the workpiece clamping element 54 to self-align with the profile of the workpiece, for example with a surface of the blade 6 of the aerofoil component.In an alterative embodiment, the workpiece clamping element 54 is formed integrally with the clamping member 26, but is connected thereto by a necked region of the clamping member 26 which permits flexure of the workpiece clamping element 54 relatively to the clamping member 26.
Description
FIELD OF THE INVENTION
This invention relates to a clamp for clamping a workpiece, and is particularly, although not exclusively, concerned with a clamp for clamping an aerofoiled component for machining purposes.
BACKGROUND OF THE INVENTION AND PRIOR ART
The secure clamping of aerofoiled components presents difficulties because the aerofoil sections do not have flat, parallel surfaces. Also, aerofoil components formed by forging have dimensional and shape differences from one another which means that a clamping structure shaped to fit perfectly with one component will not fit perfectly with another. Such imperfect fits can result in inadequate clamping and/or marking of the aerofoil surface.
A forged aerofoil component, for example a compressor rotor blade of a gas turbine engine, must undergo various operations after forging in order to remove forging flash and forging locating pips, to form blade edge and root profiles and to tip the blade to the required length. To perform these operations, the component must be held securely while exposing those parts on which the operations are to be performed. Hand polishing, followed by a vibro-polishing operation, is commonly used to form the desired circular profiles of blade chordal edges, but this often results in the chordal edges having flats or facets which, while within engineering tolerances, do not provide optimum aerodynamic performance, resulting in a loss of efficiency of the compressor module. It is thus desirable for the aerofoil finishing operations to be performed by machine, which requires secure fixing of the component while the machining and polishing operations are performed.
An object of the present invention is to provide a clamp which is able to support a workpiece having variable profiles and dimensions.
A further object of the present invention is to provide a clamp with a workpiece clamping element which is pivotable to adapt to the surface profile of a clamped workpiece.
A yet further object of the present invention is to provide a clamp which provides firm support to parts of a component during the performance of machining and polishing operations.
SUMMARY OF THE INVENTION
According to the present invention there is provided a clamp for clamping a workpiece, the clamp comprising:
a support body;
a workpiece supporting element mounted on the support body:
a clamping member mounted on the support body for displacement towards and away from the support body;
a workpiece clamping element mounted on the clamping member;
securing means adapted to retain the clamping member in a clamping position in which, in use, the workpiece clamping element applies a clamping force to a workpiece clamped between the workpiece clamping element and the workpiece supporting element; and
connecting means which connects the workpiece clamping element to the clamping member for pivoting displacement relatively to the clamping member about axes lying in a plane extending transversely of the line of action of the clamping force, and for linear movement relatively to the clamping member in a direction substantially transverse to the line of action of the clamping force, whereby the workpiece clamping element is self-aligning with the surface of a clamped workpiece.
Because the workpiece clamping element is self-aligning, it is able to adapt to variations in surface profile and dimensions of the clamped workpiece, for example a forged aerofoil component.
The pivoting displacement of the workpiece clamping element may be limited, for example by contact between the workpiece clamping element and the clamping member.
In one embodiment in accordance with the present invention, the pivoting displacement is achieved by means of a ball and socket connection. The ball and socket connection may comprise a part-spherical ball element mounted on the clamping member, which engages a socket formed in the workpiece clamping element. Separate means, for example a transverse pin, may be provided to retain the workpiece clamping element on the clamping member.
Resilient means may be provided for biasing the workpiece clamping element into engagement with a face of the workpiece, the biasing force extending transversely of the line of action of the clamping force.
In an alternative embodiment, the pivoting displacement of the workpiece clamping element may be provided by connecting the workpiece clamping element to the clamping member by means of a resilient connecting element. This connecting element may comprise a necked region between the clamping member and the workpiece clamping element, the clamping member, the necked region and the workpiece clamping element then being integral with each other. The connecting element may be situated generally centrally of the workpiece clamping element.
Around the connecting element, the workpiece clamping element may be separated from the clamping member by machined slots, closure of the slots upon deflection of the workpiece clamping element limiting the extent of displacement of the workpiece clamping element relatively to the clamping member.
The clamp may include at least one locating element, spaced from the workpiece supporting element and the workpiece clamping element, for engagement with a surface profile of the workpiece to locate the workpiece within the clamp. The locating element may comprise a recess for receiving a protrusion or pip on the workpiece.
The support body may be mounted on a fixture for removable fitting to a machine tool or other workpiece processing equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:
FIG. 1
shows a forged workpiece in the form of an aerofoil component;
FIG. 2
is a partly sectioned side view of a clamp holding the component of
FIG. 1
;
FIG. 3
is an enlarged sectional view of part of the clamp indicated by an arrow III in
FIG. 2
;
FIG. 4
is a view taken in the direction of the arrow IV in
FIG. 3
;
FIG. 5
is a sectioned side view of another clamp holding the aerofoil component of
FIG. 1
, following processing in the clamp of
FIG. 2
;
FIG. 6
is a view taken generally on line VI—VI in
FIG. 5
;
FIG. 7
is a top view of the clamp shown in
FIG. 5
, with the clamping member omitted; and
FIG. 8
is a partially sectioned view corresponding to FIG.
5
.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The workpiece
2
shown in
FIG. 1
comprises an aerofoil component
4
having a blade
6
and a root
8
. The component
4
is surrounded by a region of forging flash
10
. The forging flash
10
has a tip end
14
, a tip location pip
16
and a root location pip
18
.
The workpiece
2
must undergo several operations in order to finish the aerofoil component
4
. Thus, the forging flash
10
must be removed, along with the location pips
16
an
18
, the root
8
must be machined to a desired configuration, and the blade
6
must have its chordal edges
20
and tip
24
machined to the required dimensions and profiles.
To perform these operations, the aerofoil component must be clamped firmly so that it is prevented from moving under the machining forces. This clamping is achieved by means of the clamps shown in
FIGS. 2
to
4
, and
FIGS. 5
to
8
. The clamp shown in
FIGS. 2
to
4
is employed to hold the workpiece during finishing of the blade chordal edges
20
, while the clamp shown in
FIGS. 5
to
8
is employed during machining of the root
8
.
Referring first to the clamp shown in
FIGS. 2
to
4
, this comprises a support body
124
to which a clamping member
126
is hinged for movement about a hinge axis
128
. The support body
124
is secured to an EROWA base fixing
130
having a spigot
132
for releasable fitment to, for example, a machine tool for performing operations on the workpiece
2
.
The support body
124
has a workpiece supporting element
134
which is formed integrally with the support body
124
. The clamping member
126
has a workpiece clamping element
138
which is formed integrally with the clamping member
126
. The connection between the clamping member
126
and the workpiece clamping element
138
is shown more clearly in FIG.
5
. The clamping member
126
at its end region adjacent the workpiece clamping element
138
has a generally rectangular cross-section. Slots
140
having a relatively narrow outer region
142
(having a width, for example, of 0.25 mm) and a wider inner region
144
(having a width, for example, of 0.5 mm) extend inwardly from all four sides of the clamping member
126
, leaving a central connecting element or pillar
146
connecting the clamping member
126
to the workpiece clamping element
138
. This pillar may, for example, have a cross-sectional area which is not greater than 20 mm
2
, for example it may have a square cross-section with a side of 4 mm.
The slots
140
may be formed by electrical discharge wire cutting.
The slots
140
permit resilient pivoting of the workpiece clamping element
138
about the pillar
146
. The pivoting movement is limited by closure of the narrow regions
142
of the slots
140
, so that the maximum pivoting angle of the workpiece clamping element
138
is not greater than 2°, for example it may be 1.5°.
The workpiece clamping element
138
and the workpiece supporting element
134
each have two pads
158
and
160
respectively, for engagement with the blade
6
of an aerofoil component
2
. Each pad
158
extends the full length of the respective workpiece supporting element
134
and workpiece clamping element
138
, and engages the component
2
close to the respective chordal edge of the blade
6
.
A stud
162
is secured to the support body
124
and extends through an opening
164
in the clamping member
126
. A nut
166
engages the top end of the stud
162
and can be tightened to exert the required clamping force between the workpiece supporting element
134
and the workpiece clamping element
138
.
The support body has two locating elements
168
and
170
, which are spring-loaded upwardly, as seen in
FIG. 4
, by means of springs
172
and
174
. The locating elements
168
and
170
have V-shaped recesses
176
and
178
at their upper ends, which, in use, receive the locating pips
18
and
16
of the aerofoil component (FIG.
1
).
A spring-loaded domed platform location pin
180
is provided in the workpiece supporting element
134
for abutment with the annulus surface of the root
8
from which the blade
6
extends. Although not shown, a separate clamping device may be provided for retaining the tip pip
16
in the locating recess
178
.
For use, as shown in
FIG. 4
, the aerofoil component
2
is positioned on the workpiece supporting element
134
and located by engagement of the locating pips
16
and
18
in the recesses
176
and
178
. The position of the workpiece
4
in the lengthwise direction of the blade
6
is established by the location pin
180
. The clamping member
126
is then lowered to bring the workpiece clamping element
138
into engagement with the upper side of the blade
6
, and the nut
166
is tightened to clamp the blade
6
between the workpiece supporting element
134
and the workpiece clamping element
138
. Variations in the profile and dimensions of the blade
6
are accommodated by flexure of the pillar
146
, allowing the workpiece clamping element
138
to align itself with the profile of the upper surface of the blade
6
. When the workpiece
2
is clamped, machining, profiling and polishing of the blade chordal edges can be performed. While in the clamp of
FIGS. 2
to
4
, the blade
6
may be tipped to length, and the locating pip
16
removed. However, it is alternatively possible for this operation to be performed separately.
The workpiece
2
is then transferred to the clamp shown in
FIGS. 5
to
8
, which comprises a support body
24
to which a clamping member
26
is hinged for movement about a hinge axis
28
. The support body
24
and the clamping member
26
are formed from aluminium. The support body
24
is secured to an EROWA base fixing
30
having a spigot
32
for releasable fitment to, for example, a machine tool for performing operations on the workpiece
2
.
The support body
24
has a steel workpiece supporting element
34
secured to it by means of machine screws
36
. The clamping member
26
has a steel workpiece clamping element
38
which is located relatively to the clamping member
26
by means of a ball and socket connection comprising a part-spherical ball element
40
cooperating with a hardened hemi-spherical recess
42
(
FIG. 6
) formed in the workpiece clamping element
38
. The ball element
40
is secured to the clamping member
26
by a machine screw
44
, in such a way that there is limited freedom of movement of the ball element
40
in the general direction towards and away from the root
8
of the clamped aerofoil component
2
.
It will be appreciated that the ball element
40
does not retain the workpiece clamping element
38
on the clamping member
26
. This function is performed by a pin
46
which is secured within the clamping member
26
by a grub screw
48
. The pin
46
extends with a clearance through a bore
50
formed in the clamping element
38
.
The clearance between the pin
46
and the bore
50
, and the freedom of movement of the ball element
40
, permit limited pivotal displacement of the workpiece clamping element
38
relatively to the clamping member
26
about the axes defined by the ball element
40
, as well as limited linear displacement.
A spring
52
acts between the clamping member
26
and the workpiece clamping element
38
to bias the workpiece clamping element
38
in a direction which is generally transverse of the line of action of the clamping force exerted by the workpiece clamping element
38
in the direction of the workpiece supporting element
34
. Thus, with reference to
FIG. 2
, the workpiece clamping element
38
is biased towards the annular surface of the root
8
of the aerofoil component
4
shown clamped between the workpiece supporting element
34
and the workpiece clamping element
38
. This brings a hardened support pad
54
, provided on the workpiece clamping element
38
, into contact with the annulus surface of the root
8
from which the blade
6
extends. A similar hardened pad
56
is provided on the workpiece supporting element
34
.
The ball element
40
has a flat guide surface
70
which engages a complementary surface
72
formed on the clamping member
26
. The surface
72
, as shown in
FIG. 2
, is slightly angularly offset (for example by 3°) from the plane extending perpendicular to the line of action of the clamping force exerted by the clamping member
26
. The result of this is that the clamping force applies a wedging action on the workpiece clamping element
38
so assisting the spring
52
in biasing the workpiece clamping element
38
into contact, via the pad
54
, with the annulus surface of the root
8
of the workpiece
2
.
The workpiece clamping element
38
and the workpiece supporting element
34
each have four hardened blade-engaging pads, with two adjacent each chordal edge of the blade
6
, as shown in FIG.
6
. These pads are plated with cubic boron nitride (CBN) that serves to prevent slip between the pads
158
and
160
and the blade
6
.
A pair of jaws
182
,
184
are secured to the workpiece supporting element
34
. The jaw
182
is a fixed jaw and is rigidly fixed to the workpiece supporting element
34
by screws
186
. The jaw
184
is a movable jaw and is retained on the workpiece supporting element
34
by screws
188
. There is a clearance between these screws
188
and the holes in the movable jaw
184
in which they are received, which permits limited movement of the movable jaw
184
towards and away from the fixed jaw
182
. The movable jaw
184
is biased towards the fixed jaw
182
by means of a leaf spring
190
which is fixed at one end to the workpiece supporting element
34
and bears resiliently at its other end on a side face of the movable jaw
184
.
A retaining bar
192
is resiliently mounted on the support body
24
. The bar
192
extends from a journal
194
which is pivotably mounted on the support body
24
by bearings
196
. An operating lever
198
depends from the journal
194
and is acted upon by a spring
200
.
To install the workpiece
2
in the clamp shown in
FIGS. 5
to
8
, the bar
192
is raised and the blade
6
is laid under it on to the pads
60
on the workpiece supporting element
34
. To assist this, the jaw
184
is displaced away from the jaw
182
, and, when released, is moved by the leaf spring
190
to engage the adjacent chordal edge
20
of the blade
6
to push the blade
6
into contact, at the opposite chordal edge, with the fixed jaw
182
. The bar
192
is released, and is biased by the spring
200
, acting through the lever
198
, to contact the upper edge of the blade
6
so as to provide a preliminary holding force on the workpiece
2
. The workpiece clamping element
38
is then lowered to bring the pads
58
into contact with the upper surface of the blade, these pads straddling the bar
192
.
A stud
62
is secured to the support body
24
and extends through an opening
64
in the clamping member
26
. A nut
66
engages the top end of the stud
62
and can be tightened to exert the required clamping force between the workpiece supporting element
34
and the workpiece clamping element
38
.
As shown in
FIGS. 5 and 6
, the forged workpiece of
FIG. 1
is held by the clamp with the root
8
exposed for machining. Thus the pads
58
on the workpiece clamping element
38
and the pads
60
on the workpiece supporting element
34
engage opposite faces of the blade
6
and grip the blade
6
firmly under the action of the nut
66
on the stud
62
. During clamping, the ball and socket connection provided by the ball element
40
and the hemi-spherical socket
42
permit the pads
58
on the workpiece supporting element
38
to align themselves with the contacted surface of the blade
6
so that an adequate clamping pressure can be applied to the blade
6
without marking it. The CBN plating on the pads
58
and
60
avoids slippage of the blade
6
so that the workpiece
2
will remain held securely during machining operations on the root
8
. Additional support is provided by the pads
54
and
56
. When installing the workpiece in the clamp, the annulus surface of the root
8
is abutted against the pad
56
on the fixed workpiece supporting element
34
, the workpiece clamping element
38
then being biased by the spring
52
and the wedging action of the surfaces
70
and
72
to bring the pad
54
into abutment with the annulus surface.
The workpiece supporting element
34
has a recess
68
to accommodate the tip locating pip
16
if it has not been removed in a previous operation.
It will be appreciated that various modifications can be made to the clamps shown in
FIGS. 2
to
8
to suit particular applications. For example, although four pads are shown on each of the workpiece clamping elements
38
,
138
and the workpiece supporting elements
34
,
134
, satisfactory results may be achieved with, for example, three pads on each element.
Also, a single support body
24
,
124
could be provided with separate workpiece supporting elements
34
,
134
and corresponding separate clamping members
26
,
126
so that a workpiece can be re-positioned on the same fixture to present appropriate parts of the workpiece for machining at different stages of operation.
Claims
- 1. A clamp for clamping a workpiece, the clamp comprising:a support body; a workpiece supporting element mounted on the support body: a clamping member mounted on the support body for displacement towards and away from the support body; a workpiece clamping element mounted on the clamping member; securing means adapted to retain the clamping member in a clamping position in which, in use, the workpiece clamping element applies a clamping force to a workpiece clamped between the workpiece clamping element and the workpiece supporting element; connecting means which connects the workpiece clamping element to the clamping member for pivoting displacement relatively to the clamping member about axes lying in a plane extending transversely of the line of action of the clamping force, and for linear movement relatively to the clamping member in a direction substantially transverse to the line of action of the clamping force, whereby the workpiece clamping element is self-aligning with the surface of a clamped workpiece, the connecting means having a ball and socket connection which includes a part-spherical ball element mounted on the clamping member and a socket formed in the workpiece clamping element, the part-spherical ball element engaging the socket; and a retaining pin which engages the workpiece clamping member and which extends with clearance through a bore in the workpiece clamping element for retaining the workpiece clamping element on the workpiece clamping member.
- 2. A clamp as claimed in claim 1, in which the pivoting displacement of the workpiece clamping element is limited by contact between the workpiece clamping element and the clamping member.
- 3. A clamp as claimed in claim 1, in which the clamping member is hinged to the support body.
- 4. A clamp as claimed in claim 1, in which resilient means is provided for biasing the workpiece clamping element relatively to the clamping member in the direction of linear movement.
- 5. A clamp as claimed in claim 4, in which the workpiece clamping element has an abutment face for engagement with a surface of a workpiece under the action of the resilient means.
- 6. A clamp as claimed in claim 5, in which the workpiece supporting element has an abutment face for engagement with a surface of a workpiece, the abutment face of the workpiece supporting element being fixed with respect to the workpiece supporting member.
- 7. A clamp as claimed in claim 1, in which the support body is on a fixture which is adapted for releasable fitting to a machine tool.
- 8. A clamp as claimed in claim 1, which is adapted to receive a workpiece in the form of an aerofoil component.
- 9. A clamp for clamping a workpiece, the clamp comprising:a support body; a workpiece supporting element mounted on the support body: a clamping member mounted on the support body for displacement towards and away from the support body; a workpiece clamping element mounted on the clamping member; securing means adapted to retain the clamping member in a clamping position in which, in use, the workpiece clamping element applies a clamping force to a workpiece clamped between the workpiece clamping element and the workpiece supporting element; and connecting means which connects the workpiece clamping element to the clamping member for pivoting displacement relatively to the clamping member about axes lying in a plane extending transversely of the line of action of the clamping force, the connecting means comprising a necked region formed integrally with and extending between the clamping member and the workpiece clamping element, the workpiece clamping element projecting on all sides beyond the necked region, whereby the workpiece clamping element is self-aligning with the surface of a clamped workpiece.
- 10. A clamp as claimed in claim 9, in which the pivoting displacement of the workpiece clamping element is limited by contact between the workpiece clamping element and the clamping member.
- 11. A clamp as claimed in claim 9, in which the clamping member is hinged to the support body.
- 12. A clamp as claimed in claim 9, in which the necked region is defined by slots extending inwardly from the outer surface of the clamping member.
- 13. A clamp as claimed in claim 9, in which each slot has a width which is not greater than 0.5 mm.
- 14. A clamp as claimed in claim 9, in which the cross-sectional area of the necked region is not greater than 20 mm2.
- 15. A clamp as claimed in claim 9, in which the maximum pivoting angle of the workpiece clamping element relatively to the workpiece clamping member is not greater than 2°.
- 16. A clamp as claimed in claim 9, in which the support body comprises a locating element which is spaced from the workpiece supporting element, which locating element is adapted to engage a region of the workpiece to locate the workpiece on the support body.
- 17. A clamp as claimed in claim 16, in which the locating element comprises a recess adapted to receive a protrusion on the workpiece.
- 18. A clamp as claimed in claim 9, in which the support body is mounted on a fixture which is adapted for releasable fitting to a machine tool.
- 19. A clamp as claimed in claim 9, which is adapted to receive a workpiece in the form of an aerofoil component.
- 20. A method of performing operations on a workpiece, which method comprises:securing the workpiece in a clamp comprising: a support body; a workpiece supporting element mounted on the support body: a clamping member mounted on the support body for displacement towards and away from the support body; a workpiece clamping element mounted on the clamping member; securing means adapted to retain the clamping member in a clamping position in which the workpiece clamping element applies a clamping force to the workpiece clamped between the workpiece clamping element and the workpiece supporting element; and connecting means which connects the workpiece clamping element to the clamping member for pivoting displacement relatively to the clamping member about axes lying in a plane extending transversely of the line of action of the clamping force, and for linear movement relatively to the clamping member in a direction substantially transverse to the line of action of the clamping force, whereby the workpiece clamping element is self-aligning with the surface of a clamped workpiece, the connecting means having a ball and socket connection which includes a part-spherical ball element mounted on the clamping member and a socket formed in the workpiece clamping element, the part-spherical ball element engaging the socket: and a retaining pin which engages the workpiece clamping member and which extends with clearance through a bore in the workpiece clamping element for retaining the workpiece clamping element on the workpiece clamping member; and performing the operation on the clamped workpiece.
- 21. A method of performing operations on a workpiece, which method comprises:securing the workpiece in a clamp comprising: a support body; a workpiece supporting element mounted on the support body: a clamping member mounted on the support body for displacement towards and away from the support body; a workpiece clamping element mounted on the clamping member; securing means adapted to retain the clamping member in a clamping position in which the workpiece clamping element applies a clamping force to the workpiece clamped between the workpiece clamping element and the workpiece supporting element; and connecting means which connects the workpiece clamping element to the clamping member for pivoting displacement relatively to the clamping member about axes lying in a plane extending transversely of the line of action of the clamping force, the connecting means comprising a necked region formed integrally with and extending between the clamping member and the workpiece clamping element, the workpiece clamping element projecting on all sides beyond the necked region, whereby the workpiece clamping element aligns with the surface of the clamped workpiece; and performing the operations on the clamped workpiece.
Priority Claims (1)
Number |
Date |
Country |
Kind |
0020220 |
Aug 2000 |
GB |
|
US Referenced Citations (6)
Foreign Referenced Citations (2)
Number |
Date |
Country |
0 739 683 |
Oct 1996 |
EP |
1 289 541 |
Mar 1970 |
GB |