A METHOD OF NON-DESTRUCTIVE INSPECTION AND A DEVICE FOR
IMPLEMENTING THE METHOD
The present invention relates to a method of non
destructive inspection of a mechanical part , such as a
5 turbine blade, by causing high energy electromagnetic
radiation to be transmitted through the part, and the
invention also relates to a device for implementing the
method,
Among the various known techniques for non-
10 destructive inspection , there is the technique of
directing high energy electromagnetic radiation , such as
X-rays, towards a part for inspection and in recovering
the radiation that emerges therefrom by means of a
detector in order to form an image representative of the
15 interaction between the electromagnetic radiation and the
internal structure of the part far inspection, thus
making it possible to reveal the presence on absence of
defects in the part.
Nevertheless , in that technique, the radiation
20 emitted by the source impacts against all of the part for
inspection and is diffused by the surroundings of the
part and by the internal structure of said part, thereby
leading to diffuse zones and to a loss of contrast in the
resulting images that prevents the presence of defects
25 being detected.
That drawback is particularly significant when
inspecting hollow blades such as the blades of a turbine
stage of a turbine engine . Such blades present an
internal three-dimensional structure that is complex and
30 they also have a thermally protective coating that leads
to a large amount of the radiation being\,diffused inside
the blades.
In order to reduce those difficulties, proposals
have been made to place filter means such as a plate of
35 beryllium between the source of electromagnetic radiation
and the part for inspection so as to eliminate the low
2
energy components of the incident radiation, which
components form a large part of the diffuse radiation,'
It is also known to place an absorbent mask around
the part for inspection so as to limit or eliminate
5 radiation diffused by the surroundings of the part.
Nevertheless, neither of those two solutions is
found to be satisfactory since with the first solution
not only are the filter means insufficient for
eliminating all of the radiation diffused by the internal
10 structure of the part, but they also lead to a loss of
contrast and of detection sensitivity by eliminating a
fraction of the incident radiation, while in the second
solution, the mask is ineffective against radiation
diffused by the internal structure of the part.
15 A particular object of the invention is to provide a
solution to those problems that is simple, effective, and
inexpensive.
To this end, the invention provides a method of nondestructive
inspection of a mechanical part, such as a
20 turbine blade in particular, the method consisting in
directing high energy electromagnetic radiation emitted
by a suitable source onto the part for inspection, in
picking up the radiation that has passed through the
part, and in forming an image of the part from the
25 radiation that is picked up, the method being
characterized in that it consists in interposing a mask
between the source and the mechanical part, the mask
being of material that is suitable for absorbing the
electromagnetic radiation and that has an opening, and in
30 aligning the opening with the source and a given zone for
inspection of the part, the shape and 'the dimensions of
the opening being determined so that only said zone for
inspection of the part is exposed to the electromagnetic
radiation.
35 According to the invention, the mask is arranged
between the electromagnetic radiation source and the part
for inspection and it allows the incident radiation to
3
pass only towards a certain zone for inspection of the
part, thereby enabling optimum detection sensitivity to°
be obtained, since this zone receives all of the energy
components of the emitted radiation,
5 The shape and the dimensions of the opening in the
mask are determined relative to the shape and the
dimensions of the zone for inspection of the part,
thereby avoiding other portions of the part being exposed
to the incident radiation and preventing diffuse
10 radiation being formed inside the part by those other
portions.
The mask may be positioned at any distance from the
source and from the part, it merely being necessary for
the shape and the dimensions of the opening to be adapted
15 appropriately for limiting exposure to the given zone for
inspection, as mentioned above.
According to another characteristic of the
invention, the shape of the opening in the mask
corresponds to the projection of the outlines of the
20 given zone for inspection onto a plane perpendicular to
the axis of the beam emitted by the source, and the
dimensions of the shape of the opening are then
determined by applying a scaling ratio that is a function
of the axial position of the mask relative to the
25 mechanical pant and the source.
Advantageously, the edges of the opening are in
alignment with the peripheral rays of the beam emitted by
the source so as to avoid the incident radiation being
diffused by the edges of the opening,
30 According to another characteristic of the
invention, the absorbent mask is made 'ii the form of a
lead plate of a thickness that depends on the nature of
the electromagnetic radiation.
The electromagnetic source may be an X-ray source,
35 in which case the thickness of the lead plate is about
H millimeters (mm), or else it may be a gamma ray source
in which case the lead plate presents a thickness greater
4
than 8 mm, because of the strong power of gamma rays to
penetrate through the material.
The invention also provides a device for
implementing the method as described above, the device
5 comprising means for supporting and positioning the
absorbent mask, means for supporting and positioning the
mechanical part, and means for aligning the opening in
the mask and the zone for inspection of the mechanical
part with the radiation source.
10 In a first embodiment of the device of the
invention, the support and positioning means comprise a
hinged robot arm suitable for taking hold of a mechanical
part in order Lo place a given zone of said mechanical
part in an inspection position.
15 Advantageously, the support and positioning means
comprise a table movably mounted relative to the
stationary source and having a plurality of housings for
absorbent masks so as to bring each mask in succession
into alignment with the source and a given zone for
20 inspection of the part.
In this embodiment, the robot arm takes hold of a
part and orients it in a predetermined position for
observing a given zone of the mechanical part, and then
the table is moved to put a mask corresponding to the
25 given zone for observation into alignment with th source
and said given zone, Thereafter, electromagnetic
radiation is emitted and an image is acquired. The
above mentioned operations are repeated in order to
perform non destructive inspection of a plurality of
30 zones of the part using different masks of shapes and
dimensions that are adapted to observing.those zones.
In a second embodiment of the invention, the support
and positioning means comprise a structure having first
and second stages superposed along the axis of the
35 electromagnetic beam, the second stage being arranged
between the first stage and the source and including at
least one location for receiving an absorbent mask in
5
alignment on the axis of the beam with at least one
location for a parts support of the first stage,
According to another characteristic of the
invention, the structure is movable in translation along
5 an axis perpendicular_ to the axis of the beam, and each
of the first and second stages includes a plurality of
the above mentioned locations in alignment along said
perpendicular translation axis.
Advantageously, each support mounted in a location
10 of the first stage includes projections for positioning
at least one mechanical part for inspecting a given zone
of the mechanical parts
In this second embodiment, the operator places at
least one part on the support, with the projections of
15 the support enabling a given zone for inspection of the
part to be put in a predetermined orientation, the
support then being mounted in a location of the first
stage, The mask having an opening adapted to exposing
the given zone is mounted in the location of the second
20 stage that is in alignment with the axis of the beam.
The part is then exposed to radiation and an image of the
given zone is obtained.
The structure is then moved along its translation
axis so as to bring a location of the first stage and a
25 location of the second stage onto the axis of the, beam of
electromagnetic radiation and the above operations are
repeated with a different support and a different mask
suitable for observing another given zone of the
mechanical part,
30 The invention can be better understood and other
details, advantages, and characteristibm of the invention
appear on reading the following description made by way
of non-limiting example and with reference to the
accompanying drawings, in which:
35 o Figure 1 is a diagrammatic view of a prior art
device for non--destructive inspection by emitting
electromagnetic radiation;
6
Figure 2 is a diagrammatic view of the none
destructive method of the invention for inspection by
emitting electromagnetic radiation;
Figure 3 shows a turbine blade of a turbine engine
5 and the given zone corresponds to the leading edge which
is the only zone exposed to the electromagnetic
radiation;
Figure 4 also shows a turbine blade, the given
zone that is exposed to the electromagnetic radiation
10 corresponding to the root of the blade;
Figure 5 is a diagrammatic view of a device for
implementing the method of the invention;
Figure 6 is a perspective view of a mask
supporting turntable used with the Figure 5 device;
15 Figures 7 and 8 show another device for
implementing the method of the invention;
Figure 9 shows a parts support for use with the
device of Figures 7 and 8;
Figure 10 is a diagrammatic perspective view of a
20 mask used with the device of Figures 7 and 8; and
Figure 11 is a diagrammatic view of the edges of
an opening in an absorbent mask used in the method of the
invention.
Reference is made initially to Figure 1, which shows
25 a device 10 for inspecting a mechanical part 12 by
transmitting electromagnetic radiation 14 through the
part 12° The device 10 has a source 16 of high energy
electromagnetic radiation, Le, radiation capable of
passing through the mechanical part 12° The mechanical
30 part 12 is placed facing the source 16 in the beam that
it emits, A detector 18 is in alignment, with the source
16 and the part 12, and it is arranged on the opposite
side of the part 12 remote from the source 16 so as to
receive the radiation transmitted through the mechanical
35 part 12° A gray'scale image is thus obtained and it
represents the attenuation of the radiation on passing
through the mechanical part 12° With such an image, it.
7
is possible in principle to detect the presence or the
absence of defects in the part 12 relative to a reference
image.
Nevertheless, that device 10 is not satisfactory
5 since the incident radiation is not limited to the zone
20 for inspection, and some of the incident radiation 22
emitted by the source 16 interacts with other zones 24 of
the part 12, thereby generating radiation 26 that is
diffused inside the part 12, which radiation is in
10 addition to the radiation diffused by the zone for
inspection, thereby leading to fuzzy zones being formed
in the images that are obtained and reducing sensitivity
for detecting defects.
In addition to the diffusion of the incident
15 radiation by the internal structure of the part 12, it is
also possible for the surroundings of the part to diffuse
radiation, thereby leading to further degradation of the
resulting images.
This is particularly true with turbine blades 12
20 having a three dimensional internal shape that is
complex, as mentioned above, Z\s a result, the inspection
of critical zones, such as the leading edges of blades or
the roots of blades, for example, cannot be performed in
satisfactory manner.
25 The invention provides a solution to this prblem by
interposing a mask 28 that absorbs the electromagnetic
radiation between the part 12 for inspection and the
radiation source, the mask having an opening 30 for
passing a fraction of the incident radiation without
30 absorption towards a given zone 20 for inspection of the
mechanical part 12. The shape and the dimensions of the
opening are determined relative to the given zone for
inspection in such a manner that only said zone for
inspection is exposed to the electromagnetic radiation
35 when the opening is in alignment with the source of
radiation and the zone for inspection (Figure 2)e
8
With such a method, no radiation is diffused by the
other zones of the part or by the surroundings of the
part, thereby enabling contrast to be increased in the
images of the zones that are exposed to the radiation and
5 thus improving the sensitivity with which defects are
detected.
In practical manner, the shape of the opening in the
mask corresponds to the projection of the outlines of the
given zone for inspection onto a plane perpendicular to
10 the axis of the beam emitted by the source, and the
dimensions of the shape of the opening are then
determined by applying a scaling ratio that is a function
of the axial position of the mask 28 relative to the
mechanical part 12 and to the source 160
15 Figure 3 shows a turbine blade 31 of a turbine
engine, the blade comprising ari airfoil 33 connected to a.
root 350 The airfoil 33 has a leading edge 32 and a
trailing edge 34. By using the method of the invention,
it is possible for exposure to the electromagnetic
20 radiation to occur on only an upstream portion of the
blade including the leading edge (portion 36 outlined in
shaded lines in Figure 3), or indeed on only a portion of
the blade root (portion 38 outlined in shaded lines in
Figure 4), with this being done by using a mask having an
25 opening of the same shape as the given zone 36 o38 for
inspection, except that the dimensions of the opening 30
in the mask 28 are reduced by a scale factor as a
function of the position of the mask 28 between the
source 16 and the mechanical part 12,
30 In the description below, two devices for
implementing the method of the invention are described.
Each of these devices includes means for supporting and
positioning the absorbent mask, means for supporting and
positioning the mechanical part, and means for aligning
35 the opening in the mask and the zone for inspection of
the mechanical part with the radiation source.
9
In a first embodiment shown in Figures 5 and 6, the
device 40 has a stationary source 42 emitting
electromagnetic radiation towards a mechanical part 44
carried by a hinged robot arm 46 suitable for taking hold
5 of a mechanical part, eeg, stored in a magazine 48
situated nearby (Figure 5), The robot arm 46 has six
degrees of freedom so as to enable any zone of the
mechanical part 44 to be placed facing the radiation
source 420
10 A circular turntable 50 is mounted between the
radiation source 42 and the mechanical part 44 and has a
plurality of recessed housings 52 arranged in a circle at
its outer periphery (Figure 6)o Each housing 52 is for
receiving a flat absorbent mask 54 having a single
15 opening 56.
Each housing 52 includes keying means for use when
installing the absorbent mask 54. These keying means
comprise two rods 58 and 60 formed on an internal rim 62
of a housing 52 and extending towards the source 42, one
20 of the rods (58) being of square section and the other
rod (60) being of tapering shape. The two keying rods 58
and 60 are received in corresponding orifices 62 and 64
of the mask 50 so as to guarantee that the mask 50 is
correctly installed in its housing 52 and thus that the
25 opening 56 of each mask 50 is positioned in a known
predetermined position designed to pass the
electromagnetic radiation towards a given zone for
inspection of a part.
The turntable 50 is mounted to turn about an axis 66
30 relative to the stationary source 42 so that turning the
turntable 50 brings the opening in each of the masks 54
in succession into alignment with the source 42 and a
given zone for inspection of a mechanical tart.
An image intensifier 68 is mounted on a support 70
35 and serves to convert the high energy electromagnetic
radiation transmitted through the part 44 into light
radiation that is picked up by a camera 720
10
The device 40 is used as follows in order to
implement the method of the invention. Firstly, the
robot arm 46 is controlled so as to take hold of a
mechanical part 44 in the magazine 48 and bring a given
5 zone for inspection, e.g. the blade root, into a
determined orientation facing the source. The turntable
50 is turned about; its axis 66 so as to bring the opening
of a mask 54 corresponding to the blade root into
alignment with the source 42 and the blade root. The
10 source 42 is then caused to emit high energy
electromagnetic radiation, a fraction of which is
absorbed by the mask 54 while the remainder passes
through the opening in the mask„54 and impacts the blade
root. The transmitted radiation is then converted by the
15 image intensifier 68 and is then picked up by the camera
72.
In order to inspect the leading edge portion of the
blade, it suffices to change the orientation of the part
44 so that this zone faces the source 42. The turntable
20 50 is turned so that the mask 54 corresponding to
observing the leading edge portion is in alignment with
the source 42 and the part 44, and a new acquisition is
performed.
In this device, the opening of a mask 54 is aligned
25 with a given zone for inspection of a mechanical part
essentially by means of the hinged robot arm 46 making
use of its six degrees of freedom, with the turntable 50
serving to position the mask in register with the source
42.
30 Figures 7 to 10 show a second device 68 for
implementing the method of the invention.
This second device 68 has a high energy
electromagnetic radiation source 70 arranged above a
structure 72 having uprights 74 supporting a first stage
35 76 and a second stage 78 that are superposed along the
axis of the beam. The second stage 78 is arranged
between the first stage 76 and the radiation source 70.
11
Each stage has three locations 80, 82, and 84, or 86, 88,
and 90. The locations in the first and second stages are
positioned in such a manner that a location of the first
stage is in alignment on the axis 92 of the beam with a
5 location of the second stage. The locations in each
stage are also in alignment along an axis 94
perpendicular to the beam axis 92, the axis 94 defining
an axis along which the structure 72 can be moved.
Each of the locations 86, 88, and 90 of the second
10 stage 78 is for receiving an absorbent mask 96 in the
form of a plate having at least one opening 98
(Figure 9), Each absorbent mask 96 is engaged axially in
a location 86, 88, or 90 of the second stage '78 on an
axis 100 that is perpendicular both to the axis 92 of the
15 electromagnetic beam and the axis 94 in which the
structure 72 is moved in translation.
The parts 102 for inspection are mounted in supports
104 having projections 106 for positioning a given zone
of each part 102 in a position in which said given zone
20 is in alignment with an opening 98 of a mask 96 and with
the source '70 (Figures 7 and 9)0
Each support 104 for a part is engaged by being
moved in translation along the axis 100 into a location
80, 82, or 84 of the first stage 76.
25 Abutment. [leans (not shown) are provided at t he rear
ends of the locations 80, 82, 84, 86, 88, and 90 in the
first and second stages 76 and 78, and they serve to
provide indexing along the axis 100 for each mask 96
relative to the associated support 104 for a part, and
30 thus perform indexing along the axis 100 of the openings
98 in each of the masks 96 relative to'the given zones
for inspection of the parts 102 mounted in the associated
supports 104.
The parts supports 104 and the masks 96 are
35 dimensions in such a manner as to be received in their
respective locations without slack along the travel axis
94 of the structure so as to provide indexing along this
12
axis 94 of the openings 98 in the masks 96 of the second
stage 78 relative to the given zones for inspection of
the parts 102 mounted in the supports 104 of the first
stage 76.
5 When used in combination with the projections 106 of
the supports 104, these indexing means serve to ensure
accurate alignment of the openings 98 in the masks 96 of
the second stage 78 with the given zones for inspection
of the parts on the first stage 76.
10 Although not shown in the figures of this second
device, keying means may also be provided to prevent the
masks 96 and the parts supports 104 being wrongly mounted
in their respective-0locations.
In a particular embodiment, a first mask 108 has
15 four openings 110 adapted to observing leading edge
portions of four turbine blades, and a first parts
support has projections adapted to positioning the
leading edge portions of four different blades. Thus,
when the mask 108 is engaged in a location 86 of the
20 second stage 78 and the support is engaged in the
associated location 80 of the first stage 76, each of the
openings 110 in the mask 108 is in alignment with a
leading edge portion of a different blade. Thereafter, a
high energy electromagnetic beam is emitted and generates
25 radiation thaf. is transmitted simultaneously through the
four leading edge portions of the four blades, the
transmitted radiation being picked up by a receiver 112
(Figures 7 and 8)a
This second device 68 thus presents the advantage
30 relative to the first device of enabling given zones to
be inspected simultaneously in a plurality of parts,
thereby reducing the time needed for inspecting those
parts.
Thereafter, in order to inspect other zones of these
35 blades simultaneously, it suffices to position the blades
in a second support having projections provided for this
purpose and then to engage the second support carrying
13
the repositioned blades in the location 82 of the first
stage 76, with the associated location 88 of the second
stage 78 then including a mask having four openings
appropriate for exposing only those other zones to the
5 electromagnetic radiation. The structure 72 is then
moved in translation along the axis 94 to bring the
source 70 of electromagnetic radiation into alignment
with the openings in the second mask and with those other
zones of the blades on the second support (Figure 8),
10 It is not difficult for an operator to move the
blades manually into a second support, and that avoids
any need for the operator to handle the absorbent masks
which are very heavy, these masks remaining in position
in their respective locations.
15 By way of example, the parts supports used in the
second device may be molded out of resin.
The absorbent masks 54, 96, or 110 may be made of
lead and they are about 8 mm thick when the
electromagnetic radiation is X-rays. Other radiation
20 sources may be used, and in particular a gamma ray
source. Under such circumstances, the masks 54, 96, or
110 are thicker, being about 15 mm thick, given the high
penetration power of this type of radiation.
The lead masks are advantageously covered in a fine
25 layer of aluminum so as to avoid the operators w1{) handle
the masks being contaminated with lead. Nevertheless,
the edges of the openings are not provided with aluminum
in order to avoid diffuse radiation being formed by the
edges of the openings.
30 In order to avoid any radiation being diffused by
the edges 114 of a mask opening, it is`desirable for the
edges 114 of the opening 116 to be in alignment with the
peripheral rays 118 of the beam emitted by the source
120, as shown diagrammatically in Figure 11,
35 The invention may be used in combination with an
absorbent mask of the prior art mounted around the
mechanical part.
14

CLAIMS
1. A method of non---destructive inspection of a mechanical
part, such as a turbine blade in particular, the method
consisting in directing high energy electromagnetic
5 radiation emitted by a suitable source (16) onto the part
(12) for inspection, in picking up the radiation that has
passed through the part (12), and in forming an image of
the part from the radiation that is picked up, the method
being characterized in that it consists in interposing a
10 mask (28) between the source (16) and the mechanical part
(12), the mask (28) being of material that is suitable
for absorbing the electromagnetic radiation and that has
an opening (30), and in aligning the opening (30) with
the source (16) and a given zone (20) for inspection of
15 the part (12), the shape and the dimensions of the
opening (30) being determined so that only the given zone
(20) for inspection of the part (12) is exposed to the
electromagnetic radiation.
20 2. A method according to claim 1, characterized in that
the shape of the opening (30) in the mask (28)
corresponds to the projection of the outlines of the
given zone for inspection onto a plane perpendicular to
the axis of the beam emitted by the source (16), and the
25 dimensions of the shape of the opening (30) are [lien
determined by applying a scaling ratio that is a function
of the axial position of the mask (28) relative to the
mechanical part (12) and the source (16),
30 3. A method according to claim 1 or claim 2,
characterized in that the edges (114) of, the opening
(116) are in alignment with the peripheral rays (118) of
the beam emitted by the source (120)0
35 4. A method according to any one of claims 1 to 3,
characterized in that the absorbent mask (54, 96, 110) is
15
made in the form of a plate of a thickness that depends
on the nature of the electromagnetic radiation.
5. A method according to any one of claims 1 to 4,
5 characterized in that the source of electromagnetic
radiation (16, 42, 70, 120) is an X--ray source or a gamma
ray source.
6. A method according to any one of claims 1 to 5,
10 characterized in that another mask suitable for absorbing
the electromagnetic radiation is arranged around the
mechanical part (12)0
7. A device for implementing the method according to any
15 one of claims 1 to 6, the device being characterized in
that it comprises means for supporting and positioning
the absorbent mask, means for supporting and positioning
the mechanical part, and means for aligning the opening
in the mask and the zone for inspection of the mechanical
20 part with the radiation source.
8. A device according to claim 7, characterized in that
the support and positioning means comprise a hinged robot
arm (46) suitable for taking hold of a mechanical part
25 (44) in order to place a given zone of the mechanical
part in an inspection position.
9. A device according to claim 7 or claim 8,
characterized in that the support and positioning means
30 comprise a table (50) movably mounted relative to the
stationary source (42) and having a plurality of housings
(52) for absorbent masks (54) so as to bring each mask
(54) in succession into alignment with the source (42)
and a given zone for inspection of the part (44)0
35
10, A device according to claim 7, characterized in that
the support and positioning means comprise a structure
16
(72) having first and second stages (76, 78) superposed
along the axis (92) of the electromagnetic beam, the
second stage (78) being arranged between the first stage
(76) and the source (70) and including at least one
5 location (80, 82, 84) for receiving an absorbent mask
(96) in alignment on the axis (92) of the beam with at
least one location (86, 88, 90) for a parts support (104)
of the first stage (76)0
10 11. A device according to claim M, characterized in that
the structure (74) is movable in translation along an
axis (94) perpendicular to the axis (92) of the beam, and
in that each of the first and second stages (76, '18)
includes a plurality of the above--mentioned locations
15 (80, 82, 84, 86, 88, 90) in alignment along said
perpendicular translation axis (94)0
12. A device according to claim 10 or claim 11,
characterized in that each support (104) mounted in a
20 location of the first stage includes projections (106)
for positioning at least one mechanical part (102) for
inspecting a given zone of the mechanical part (102).