FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An expanding mandrel for aligning a lamination stack formed there around
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
INVENTORS
Keluskar Chandrasekhar and Patil Sharad, both of Crompton Greaves Ltd, M 6 Division, Kanjur Marg (East), Mumbai - 400042, Maharashtra, India, both Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to an expanding mandrel for aligning a lamination stack formed there around and more particularly to an expanding mandrel for aligning a stator lamination stack formed there around.
BACKGROUND OF THE INVENTION
In the forming of a stator, loose individual stator laminations are stacked around a mandrel to form a stator lamination stack. The stator laminations in the stator lamination stack are thereafter aligned with respect to each other by means of a stator key. The aligned stator lamination stack is thereafter riveted. The stator key is held within a groove on an outer surface of the mandrel such that it extends, normally 1 mm, beyond the outer surface of the mandrel. It is ensured during advancing each individual stator lamination around the mandrel that the notches at the inner circumference of the stator laminations are facing with the stator key, A minimum clearance is required to be maintained between the stator key and notches at all times. If such clearance is not maintained, removing the riveted lamination stack out of the mandrel becomes difficult. However, maintaining the clearance, although required, poses a problem that the stator laminations in the stack are never perfectly aligned which affects the quality of the stator. Therefore, there is a need of a mandrel which can be expanded selectively to remove the clearance for a perfect alignment of the stator lamination stack.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, there is provided an expanding mandrel for aligning a lamination stack formed there around, the expanding mandrel comprising a mandrel housing which being a hollow cylindrical body mounted on a base, a plurality of spaced apart key housings held within a longitudinal groove on an outer surface of the mandrel housing, an alignment key held within each key housing in a longitudinal slit on an outer surface of the

key housing, a plurality of spaced apart push pads held on an inner surface of each key housing along the length of the slits on the corresponding outer surface of each key housing such that the push pads extending into the hollow portion of the mandrel housing through corresponding slots provided on an inner surface of the mandrel housing, a spring extending circumferentially within a wall of the mandrel housing through the key housings and the respective alignment keys therein, a cam assembly comprising a cylindrical cam housing held rotatably on the base within the hollow portion of the mandrel housing and a plurality of spaced apart cams held on an outer surface of the cam housing such that an outer surface of each cam facing the inner surface of the mandrel housing and maintaining a clearance therewith, the number of cams being equal to the number of push pads in a key housing, the outer surface of each cam comprising a plurality of spaced apart protrusions, the number of protrusions on each cam being equal to the number of push pads facing the outer surface of each cam, wherein the placement of the cams around the cam housing being such that in an unexpanded position of the mandrel said protrusions being disposed adjacent to the corresponding push pad and upon rotation of the cam housing said protrusions being brought in front of the push pads for creating a push switch effect on the push pads wherein upon said pushing of the push pads the spring-held alignment keys within the key housings being pushed by the corresponding push pads beyond the outer surface of the mandrel housing thereby expanding the mandrel and upon retracting the cam housing back to its original position, the alignment keys being retracted back to its original position in the absence of push-switch effect and loss of spring tension.
According to a preferred embodiment, the cams are held on the outer surface of the cam housing by means of circlips and aligned with respect to each other on the outer surface of the cam housing by means of a plurality of cam keys held within respective slots provided on the outer and inner surfaces of the cam housing and cams respectively. The base is a double layered structure with a hole at the center of an upper surface thereof and the mandrel housing being mounted on the upper layer of the base such that the hole opens coaxially into

the hollow portion of the mandrel housing. The cam assembly is adapted to be rotatable by means of a rack and pinion means actuated pneumatically. A bottom end portion of the cam housing is adapted to be a pinion of a rack and pinion means for rotating the cam housing within the hollow portion of the mandrel housing. The bottom end portion is held on a lower layer of the base such that the cylindrical portion of the cam housing extends within the hollow portion of the mandrel housing through the hole on the upper layer of the base. The rack of the rack and pinion means engages with the pinion through a window provided at one side of the base between the two layers of the base.
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 is a schematic view of an expanding mandrel for aligning a stator lamination stack formed there around according to a preferred embodiment.
Fig 2 is a schematic view of the expanding mandrel of Fig Iwith the stator lamination stack formed there around.
Fig 3 is an exploded view of an expanding mandrel of Fig 1.
Fig 4 is a schematic view of a mandrel housing of the expanding mandrel of Fig 1.
Fig 5 is a schematic view of a key housing of the expanding mandrel of Fig 1.
Fig 6 is a schematic view of a cam assembly of the expanding mandrel of Fig 1.
As shown in Figs 1 to 3, an expanding mandrel 1 for aligning a stator lamination stack 2 formed there around comprises a double layered 4 & 5 base having a circular hole 6 at the center of its upper layer 5. A mandrel housing 7 which is a hollow cylindrical body is mounted coaxially to the hole 6 on the upper layer 5 of the base. Thus the hole 6 communicates with the hollow portion of the mandrel housing 7. The outer diameter of the

mandrel housing 7 is provided less than the inner diameter of the stator lamination stack 2 formed there around for maintaining a clearance there between. As shown in Fig 4, an outer surface of the mandrel housing 7 comprises four equally spaced apart longitudinal grooves 3. Three equally spaced apart rectangular slots 9 are provided on the inner surface of the mandrel housing 7 along the length of each groove 3 on the outer surface of the mandrel housing 7. A key housing 8, as shown Fig 5, is held slidingly within each groove 3. An outer surface of each key housing comprises a longitudinal slit 10 for accommodating an alignment key 11 therein. The shape and size of the alignment keys 11 is such that when the stator lamination stack 2 is formed around the mandrel housing 7, the alignments keys 11 can be received within the notches 12 provided on an inner circumference of each stator lamina for perfectly aligning the notches 12 with respect to each other. Three equally spaced apart push pads 13 are held along the length of the slit 10 on a corresponding inner surface of the key housing 8. The push pads 3 are held such that a portion thereof projects into the hollow portion of the mandrel housing 7 through the corresponding slots 9 provided on the inner surface of the mandrel housing. A spring 14 is provided extending through apertures in the wall of the mandrel housing 7 and through the key housings 8 and respective alignment keys 11 therein.
Further, a cam assembly 15, as shown in Fig 6, comprises a cylindrical cam housing 16 and three equally spaced apart cams 17 held on an outer surface of the cam housing 16 along the length thereof. The cam assembly is held within the hollow portion of the mandrel housing 7 such that an outer surface of the each cam 16 faces the inner surface of the mandrel housing 7 and maintains a clearance therewith. The cam assembly is adapted to be rotated within the mandrel housing by a rack and pinion means 18. A bottom end portion of the cam housing 16 is adapted to be a pinion 19 and supported on the lower layer of the base 4. The cylindrical portion of the cam housing 16 extends upwardly from its bottom end within the hollow portion of the mandrel housing 7 through the circular hole 6 on the upper layer 5 of the base. The rack 20 of the rack and pinion means 18 engages with the pinion 19 (bottom end

of the cam housing) through a window provided on a side of the base between the two base layers 4 & 5. The rack 20 may be actuated manually, pneumatically or through other possible means to rotate the pinion 19. The three equally spaced apart cams 17 are held on the outer surface of the cam housing 16 by means of circlips. The cams 17 are held aligned with respect to each other on the outer surface of the cam housing 16 by means of a couple of equally spaced apart cam keys held within corresponding slits provided on the outer and inner surfaces of the cams 17 and cam housing 16 respectively. An outer surface of each cam 17 comprises four equally spaced apart protrusions 23 preferably corresponding to the size of a push pad 13. The protrusion is preferably 1 mm. It is to be ensured that for each push pad 13 there is provided a protrusion 23 on the cam 17. Accordingly, the number of cams 17 and protrusions 23 thereupon and the placement of cams 17 around the cam housing 16 is determined. Following rule can be followed in determining the number of cams 17 and number of protrusions 23 thereupon. The total number of cams 17 corresponds to the total number of push pads 13 provided on a key housing 8 and the total number of protrusions 23 on each cam 17 corresponds to the total number of push pads 13 facing an outer surface of each 17 in the hollow portion of the mandrel housing 7.
The placement of cams 17 and hence the protrusions 23 is such that in the unexpanded position of the mandrel 1, the protrusions 23 are disposed adjacent to the respective push pads 13. As shown in Fig 2, upon rotating the cam assembly 15 by actuating the rack and pinion means 18, each protrusion 23 is brought in front of the corresponding push pads 13 for creating a push switch effect on the push pads 13. Upon pushing of the push pads 13, the spring held alignment keys 11 are pushed by the push pads 13 against the spring 14 beyond the outer surfaces of the key housing 8 and mandrel housing 7 thereby expanding the mandrel 1. Upon reversing the direction of rotation of the cam housing 16, the alignment keys 11 are forced to retreat back due to loss of spring tension in the absence of any push from the push pads 13.

Individual stator laminations are stacked one upon the other around the unexpanded mandrel housing 7. During the advancement of each stator lamination around the mandrel housing 7, it is ensured that the notches 12 on the inner circumference of each stator lamination face the corresponding alignment key 11. As shown in fig 2, the mandrel is now expanded by rotating the cam housing 16 by actuating the rack and pinion means 18. This in turn rotates the cams 17 held onto it. Thus, the protrusions 23 positioned adjacently to the corresponding push pad 13 comes in contact with the push pads 13 and pushes them thereby creating a push switch effect. The direction of rotation of the cam housing is such that for expanding the mandrel, the protrusions 23 travel towards the corresponding push pads 13. Each push pad 13 upon being pushed, pushes the respective spring 14 held alignment keys 11 within the respective key housings 8 beyond the outer surface of the key housing 8 and mandrel housing 7 thus expanding the mandrel 1. The alignment keys 11 now breaches the clearance between the stator lamination stack 2 and itself and is received into the respective notches 12 on the stator lamination stack 2 facing it. Thus any imperfections in the placement of the stator laminations in the stator lamination stack 2 is removed thereby perfectly aligning the stator laminations within the stator lamination stack. Once a perfect alignment is achieved, the stator lamination stack is riveted. After riveting, the direction of the rotation of the cam housing 16 is reversed. This withdraws the push to the push pads 13 thereby leading to a loss spring tension thereby retracting back the alignment keys 11 in the respective housings.Thus the expanded mandrel is reset to its original position.The perfectly aligned stator lamination stack 12 is thereafter removed.
It will be apparent to a person skilled in the art the above mentioned mandrel is not limited for aligning only a stator lamination stack and can be used for any other kinds of laminations. Also, the number of key housings, push pads, cams etc are not limited to mentioned above and may vary depending upon the application.
According to the invention, the expanding mandrel facilitates riveting of a stator lamination stack when all the stator laminations therein are perfectly aligned with respect to

each other thereby improving the quality of the stator formed out of the stator lamination stack.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We claim:
1. An expanding mandrel for aligning a lamination stack formed there around, the expanding mandrel comprising a mandrel housing which being a hollow cylindrical body mounted on a base, a plurality of spaced apart key housings held within a longitudinal groove on an outer surface of the mandrel housing, an alignment key held within each key housing in a longitudinal slit on an outer surface of the key housing, a plurality of spaced apart push pads held on an inner surface of each key housing along the length of the slits on the corresponding outer surface of each key housing such that the push pads extending into the hollow portion of the mandrel housing through corresponding slots provided on an inner surface of the mandrel housing, a spring extending circumferentially within a wall of the mandrel housing through the key housings and the respective alignment keys therein, a cam assembly comprising a cylindrical cam housing held rotatably on the base within the hollow portion of the mandrel housing and a plurality of spaced apart cams held on an outer surface of the cam housing such that an outer surface of each cam facing the inner surface of the mandrel housing and maintaining a clearance therewith, the number of cams being equal to the number of push pads in a key housing, the outer surface of each cam comprising a plurality of spaced apart protrusions, the number of protrusions on each cam being equal to the number of push pads facing the outer surface of each cam, wherein the placement of the cam on the cam housing being such that in an unexpanded position of the mandrel said protrusions being disposed adjacent to the corresponding push pad and upon rotation of the cam housing said protrusions being brought in front of the push pads for creating a push switch effect on the push pads wherein upon said pushing of the push pads the spring-held alignment keys within the key housings being pushed by the corresponding push pads beyond the outer surface of the mandrel housing thereby expanding the mandrel and upon retracting the cam housing back to its original position, the alignment keys

being retracted back to its original position in the absence of push-switch effect and loss of spring tension.
2. The expanding mandrel as claimed in claim 1, wherein the cams are held on the outer surface of the cam housing by means of circlips.
3. The expanding mandrel as claimed in claim 1, wherein the cams are held aligned with respect to each other on the outer surface of the cam housing by means of a plurality of cam keys held within respective slots provided on the outer and inner surfaces of the cam housing and cams respectively.
4. The expanding mandrel as claimed in claim 1, wherein the base is a double layered structure with a hole at the center of an upper surface thereof and the mandrel housing being mounted on the upper layer of the base such that said hole opening coaxially into the hollow portion of the mandrel housing.
5. The expanding mandrel as claimed in claim 1 and 4, wherein a bottom end portion of the cam housing being adapted to be a pinion of a rack and pinion means for rotating the cam housing within the hollow portion of the mandrel housing, said bottom end portion being held on a lower layer of the base such that the cylindrical portion of the cam housing extending coaxially through said hole within the hollow portion of the mandrel housing, the rack of the rack and pinion means engages with said pinion through a window provided at one side of the base between the two layers of the base.
6. The expanding mandrel as claimed in claim 5, wherein the rack is actuated by pneumatic means connected therewith for rotating the cam housing.