METHOD FOR PRODUCING A CURVED METAL SHEET STRIP, AND SAID CURVED METAL SHEET STRIP

Abstract: The method is for producing a curved metal sheet strip for manufacturing a stator or rotor motor frame. The method comprises the steps of (a) cutting an elongated, substantially linear strip (8) from a metal sheet (a), the strip having two longitudinal sides and extending in a plane, the strip having an elongated band section (13) provided with a series of regularly spaced apart teeth (14) along one of the longitudinal sides; and (b) incurvating each portion of the band section joining two adjacent teeth in a direction perpendicular to the plane in such a manner that each portion has an increasing radius from one of the longitudinal sides to the other longitudinal side, thereby providing the curved metal sheet strip. According to the present invention, there is also provided a curved metal sheet strip.

Description: METHOD FOR PRODUCING A CURVED METAL SHEET STRIP, AND SAID CURVED METAL SHEET STRIP BACKGROUND OF THE INVENTION: In electric motors, a rotor turns concentric relative to a fixed stator. In general the stator is external to the rotor. In the case of a motor wheel or a ceiling suspended " fan, the rotor is external to the stator. The stator or rotor is provided with peripheral teeth around which windings are wound. The stator or rotor frame is made of circular shaped metallic sheets stacked together. To produce a frame, circular shapes are usually cut out from metal sheets. With this production method, each time a circular shape is cut out from a metal sheet, the remaining metal material of the metal sheet is wasted. This is not a problem when cheap material is used, but when the sheet is made of an expensive metal material, the waste of material is a major drawback because of the cost of the wasted material. To overcome the above described drawback, a method for producing a curved metal sheet strip with minimal waste of the metal sheet material is proposed. According to the present invention, there is provided a method for producing a curved metal sheet strip for manufacturing a stator or rotor motor frame, comprising the steps of : a) cutting an elongated strip from a metal sheet, the strip having two longitudinal sides and extending in a plane, the strip having an elongated band section provided with a series of regularly spaced apart teeth along one of the longitudinal sides; and b) incurvating each portion of the band section joining two adjacent teeth in a direction perpendicular to the plane in such a manner that each portion has an increasing radius from one of the longitudinal sides to the other longitudinal side, thereby providing the curved metal sheet strip. According to the present invention, there is also provided a curved metal sheet strip suitable for manufacturing a stator or rotor frame, the strip having two longitudinal sides and extending in a plane, the strip having an elongated band section provided with a series of regularly spaced apart teeth along one of the longitudinal sides, each portion of the band section joining two adjacent teeth being incurvated in a direction perpendicular to the plane in such manner that each portion has an increasing radius from one of the longitudinal sides to the other longitudinal side, thereby providing the curved metal sheet strip. BRIEF DESCRIPTION OF THE DRAWINGS: Figure 1 is a view from above of a metal sheet from which a circular shape has been cut out according to prior art, showing the proportion of wasted metal material in crossed hatched pattern. Figure 2 is a view from above of a single strip cut out from a metal sheet according to an embodiment of the present invention. Figure 3 is a view from above of a two strips cut out from a metal sheet according to another embodiment of the present invention. Figure 4 is a view from above of several strips cut out from a metal sheet according to an embodiment of the present invention. Figure 5 is a view from above of a two strips cut out from a metal sheet according to further embodiment of the present invention. Figure 6 is a partial perspective view from above of a segment of a cut out strip after it has been processed according to the present invention. Figure 7 is a view across section 7-7 of figure 6. Figure 8 is a perspective view of a curved metal sheet strip having a circular shape according to the present invention. Figure 9 and 10 are perspective views of curved metal sheet strips having a cylindrical helix shape according to the present invention. DESCRIPTION OF THE DRAWINGS: Figure 1 illustrates the metal sheet (6) after a circular shape (7) has been cut out. The cross hatched pattern indicates the remaining parts of the metal sheet that is wasted in the process. The wasted material can constitute a very large percentage of the metal material from the original sheet. The present invention relates to a method for producing a curved metal sheet strip for manufacturing a stator or rotor frame that avoids undue waste of metal material . Referring now to figure 2, the first step of the method is shown. It consists in cutting an elongated, substantially linear strip (8) from a metal sheet (9) . The strip (8) has two longitudinal sides and extends in a plane. The strip has an elongated band section (13) provided with a series of regularly spaced apart teeth (14) along one of the longitudinal sides. A single elongated strip (8) is cut from the metal sheet (9) . Several other geometrical patterns can be considered to cut the metal strips from metal sheets, examples of which are presented on figures 3, 4, and 5. Referring again to figure 2, the material between the teeth (14) is cut away and wasted. This technique creates a certain amount of wasted material but still considerably less than in the prior art technique. The main advantage of this embodiment is that it allows any desired geometry for the teeth pattern. Referring now to figure 3, in an alternative embodiment two metal strips (8) having their toothless longitudinal sides disposed side by side are cut out of a single sheet (9) . This method has the same advantages and drawbacks of the one shown in figure 2, but has in addition the advantage of being time-saving and less costly. Each of the teeth (14) has an enlarging free end. Each portion of the band section joining two adjacent teeth has an edge (10) that is concave. A further embodiment can be seen on figure 4. In this embodiment, the teeth pattern is cut out of a rectangular metal sheet (9) in such a manner as to obtain several metal strips (8) out of a single sheet (9) without any waste of material . This method is harder to implement but minimises to the extreme the amount of wasted material. The strips (8) are grouped by pair. Each pair of strips have their longitudinal sides with teeth (14) disposed side by side so that the metal portions that are cut out to form the teeth (14) of one strip of the pair are used to form the teeth (14) of the other strip of the pair. This embodiment however imposes for the teeth (14) and the sections between the teeth to be of the same size. A way to avoid this restriction is shown in figure 5, where a small quantity of material is cut away from the sides of the teeth (14) to reduce their width so that the teeth (14) are narrower than the portion of the band section joining two adjacent teeth. Referring now to figures 6 and 7, there is shown the result of the second step of the method which consists in incurvating each portion of the band section (13) joining two adjacent teeth (14) in a direction perpendicular to the plane in such a manner that each portion has an increasing radius from one of the longitudinal sides to the other longitudinal side, thereby providing the curved metal sheet strip. A variation can be imagined where the incurvating is done to produce a curved strip with teeth (14) projecting inward. Referring more specifically to figure 6, There is shown a curved metal sheet strip (8) suitable for manufacturing a stator or rotor frame. Of course in this figure 6, only a segment of the strip (8) is shown. Several segments can be added to form a cylindrical helix shape where each layer of the cylindrical helix shape are stacked and held together to form a stator or rotor frame. The strip (8) extends in a plane. The strip (8) has an elongated band section (13) provided with a series of regularly spaced apart teeth (14) along one of its longitudinal sides. Each portion of the band section joining two adjacent teeth is incurvated in a direction perpendicular to the plane in such manner that each portion has an increasing radius from the first longitudinal side to the second longitudinal side, thereby providing the curved metal sheet strip (8) as shown in this figure 6 and in figures 8 to 10. Referring now to figure 8, the length of the strip (8) and the incurvating pattern may be chosen so the strip forms a circular shaped metal sheet strip. The length of the strips (8) and the incurvating pattern can also be adjusted to result into a few large arc sections to be assembled together to form the desired circular shape, or into a cylindrical helix shape of more than one turn stacked up one above the other. Such cylindrical helix shapes are illustrated on figures 9 and 10.

Claims: CLAIMS : 1. Method for producing a curved metal sheet strip for manufacturing a stator or rotor motor frame, comprising the steps of : a) cutting an elongated strip from a metal sheet, the strip having two longitudinal sides and extending in a plane, the strip having an elongated band section provided with a series of regularly spaced apart teeth along one of the longitudinal sides; and b) incurvating each portion of the band section joining two adjacent teeth in a direction perpendicular to the plane in such a manner that each portion has an increasing radius from one of the longitudinal sides to the other longitudinal side, thereby providing the curved metal sheet strip. 2. Method according to claim 1, wherein each of the teeth has an enlarging free end, and each portion of the band section joining two adjacent teeth has an edge that is concave . 3. Method according to claim 1, wherein a single elongated strip is cut from the metal sheet . 4. Method according to claim 1, wherein: in step (a) , two elongated strips that have their longitudinal sides that are without teeth, disposed side by side are cut from the metal sheet; and step (b) is executed for each of the elongated strips of step (a) . 5. Method according to claim 1, wherein: in step (a) , several elongated strips are cut from the metal sheet, the strips are grouped by pair, each pair of strips have their longitudinal sides with the teeth, disposed side by side so that the metal portions that are cut out to form the teeth of one strip of the pair are used to form the " teeth of the other strip of the pair; and step (b) is executed for each of the elongated strips of step (a) . 6. Method according to claim 5, further comprising a step of cutting away metal material from the teeth to reduce their width so that the teeth are narrower than the portion of the band section joining two adjacent teeth. 7. Method according to claim 1, wherein the curved metal sheet strip has predetermined length and curved shape to form a circle. 8. Method according to claim 1, wherein the curved metal sheet strip has predetermined length and curved shape to form a cylindrical helix. 9. A curved metal sheet strip suitable for manufacturing a stator or rotor frame, the strip having two longitudinal sides and extending in a plane, the strip having an elongated band section provided with a series of regularly spaced apart teeth along one of the longitudinal sides, each portion of the band section joining two adjacent teeth being incurvated in a direction perpendicular to the plane in such manner that each portion has an increasing radius from one of first longitudinal sides to the other longitudinal side, thereby providing the curved metal sheet strip. 10. Curved metal sheet strip according to claim 9, wherein each of the teeth has an enlarging free end, and each portion of the band section joining two adjacent teeth has an edge that is concave. 11. Curved metal sheet strip according to claim 9, wherein the teeth are narrower than the portion of the band section joining two adjacent teeth. 12. Curved metal sheet strip according to claim 9, having predetermined length and curved shape to form a circle. 13. Curved metal sheet strip according to claim 9, having predetermined length and curved shape to form a cylindrical helix.

Inventors: FORCIONE ALAIN, HARBEC GERMAIN, IBISHIAN MISSAK, FORCIONE, ALAIN, HARBEC, GERMAIN, IBISHIAN, MISSAK
Applicants: FORCIONE ALAIN, HARBEC GERMAIN, HYDRO QUEBEC, IBISHIAN MISSAK, FORCIONE, ALAIN, HARBEC, GERMAIN, HYDRO-QUEBEC, IBISHIAN, MISSAK
Application year: 1999
Main classification: B21D53
IPC codes: B21D53, H02K1, H02K15