WO2022264116A1

WO2022264116A1 - Die for producing a stator

Info

Publication number: WO2022264116A1
Application number: PCT/IB2022/055711
Authority: WO
Inventors: Stephen FARDON
Original assignee: Aeristech Ltd
Priority date: 2021-06-18
Filing date: 2022-06-20
Publication date: 2022-12-22
Also published as: GB202108811D0

Abstract

A die (100) for producing a stator of a motor is described. In embodiments the die comprises a punch (110) for punching laminations (180) from a strip of material (170); a block (120) for receiving the punch, wherein the block is shaped to a cross-sectional profile of the stator and wherein the block is configured to retain the laminations after punching; a hydraulic system for supporting the laminations and for damping the punching force exerted by the punch; and wherein the hydraulic system is configured to dampen the punching force such that the laminations retract lower than the top of the block such that the block can receive a subsequent lamination from the strip of material.

Description

DIE FOR PRODUCING A STATOR

Field

The present invention relates to a die for producing a stator and methods of use thereof.

Background

Conventional electric machines (in the context of this disclosure, motors, generators and motor-generators) typically feature a rotor arranged within a bore defined by a hollow cylindrical core of a stator. The stator is a non revolving component comprising a series of radial apertures and a central bore. The apertures are filled with metallic windings, with the bore configured to receive a rotor.

A stator for use in high performance contexts, where the rotor of the electric machine is subject to high RPM, is typically formed of a plurality of laminations. The number of laminations could be up to and in excess of 1000 laminations for a single stator. Laminations used to form stators in high performance contexts are metallic and have a thickness in the order of 0.1 mm. This low thickness is desirable because of the reduction of eddy currents generated during use in an electric machine. The laminations are therefore thin and comprise sharp edges, having been stamped from a strip of material. The handling and assembling the laminations into a stator with an assembly jig is therefore time-consuming and potentially hazardous.

The laminations need to stacked and bonded such that the various parameters associated with the stator are produced with very close tolerances. Example parameters include roundness, alignment of laminations, concentricity of the bore and outside diameter, degree of parallel alignment between the end faces of the stator (i.e. the end faces must be ‘square’).

Conventionally, lamination stamping tools are made in the form of progressions. All of the operations are done in increments that progress from one stage to another through the tool. The movement of laminations from one stage to another compromises the degree of concentricity between the bore and outside diameter, which usually means a further operation of precision cylindrical grinding may be required after bonding to correct alignments. This is time consuming and costly.

An alternative to progressing the laminations is to mechanically interlock the laminations in the press. However, this compromises the efficiency of the motor because direct contact is created between the laminations. This interferes with the magnetic fields created by the permanent magnets of the rotor and is therefore undesirable.

The present invention aims to at least partially ameliorate some of the above- mentioned problems.

Summary

According to a first aspect of the present invention, there is provided a die for producing a stator of a motor. The die comprises: a punch for punching laminations from a strip of material; a block for receiving the punch, wherein the block is shaped to a cross-sectional profile of the stator and wherein the block is configured to retain the laminations after punching; and a hydraulic system for supporting the laminations and for damping the punching force exerted by the punch. The hydraulic system is configured to dampen the punching force such that the laminations retract lower than the top of the block such that the block can receive a subsequent lamination from the strip of material. Advantageously, providing a block for retaining the laminations after being punched out of the strip of material eliminates the need to handle a plurality of laminations separately, and also removes the need for a separate assembly jig.

An additional advantage of the use of the block is that the laminations are kept aligned to close tolerances. In an exemplary stator, up to and potentially in excess of 1000 laminations are bonded together. This means that any small differences in alignment are exaggerated significantly across the length of the stator.

Using a hydraulic system to retract lower than the surface of the block advantageously allows the process of punching laminates using the die of the present invention to be repeatable without needing to remove the laminates. The combined height of the retained laminations and the hydraulic system remains consistent between iterations, and so the punch need only lower a set amount for each iteration. Further advantageously, a hydraulic system to support the laminations can help to ensure that the face of each of the laminations remain at least substantially parallel to one another. Use of a mechanical system to retract the laminations could in time lead to misalignment of the end faces of the laminations. This would then be amplified across the length of the stator, given the large number of laminations

Advantageously, the die of the present invention allows the laminations to be punched, stacked and bonded in a single step. The hydraulic system may comprise an anvil configured to support the laminates within the block; and a hydraulic piston coupled to the anvil to provide the damping force to the punching force exerted by the punch. The hydraulic system may further comprise a guide bearing for guiding the piston to reduce lateral movement of the piston during operation. Advantageously, use of a guide bearing to reduce lateral movement of the supporting piston reduces any potential misalignment of the laminations during production of the stator.

The hydraulic piston may comprise a piston rod coupled to the anvil and a hydraulic cylinder at least partially filled with fluid configured to receive the piston rod. The base of the piston rod may be configured to form a watertight seal with the interior of the hydraulic cylinder. The height of the anvil may determined by the volume of fluid present in the hydraulic cylinder.

The fluid may be a substantially incompressible fluid. Examples of such a fluid include water, oil and other liquids.

The watertight seal between the piston rod and the interior of the hydraulic cylinder advantageously prevents hydraulic fluid from flowing over the piston rod, instead ensuring that the base of the piston rod sits on the surface of the fluid. Advantageously, this aids in maintaining a level surface of the anvil during the stamping process, which reduces the risk of the faces of the laminations not being at least substantially parallel.

The height of the anvil being determined by the volume of liquid advantageously allows for a user to adjust a starting height of the anvil by varying said volume of liquid. This is desirable to allow the die to be used with different operating parameters, such as the thickness of the strip of material from which the laminations are punched. The hydraulic cylinder may comprise at least one restriction orifice configured to allow fluid to leave the cylinder on the application of the punching force to the anvil; and a non-return valve fluidly connected to the restriction orifice to prevent the fluid re-entering the cylinder once the force is released.

A restriction orifice comprises a small aperture in the cylinder configured to restrict the flow of the fluid out of the hydraulic cylinder. On application of the punching force by the punch, the anvil will lower, forcing fluid through the aperture. The restriction of flow provides the damping force to the punch motion. Once the pressure from the punch has stopped, the non-return valve ensures that fluid does not re-enter the cylinder and no further fluid flows through the restriction orifice. This maintains the height of the anvil at the level to which it was displaced by the punch during the punching process. The size of the aperture may be variable dependent on the magnitude of the damping force desired.

The hydraulic cylinder may comprise a refill orifice configured to receive fluid.

The hydraulic system may comprise a pump and a one-way valve fluidly connected to the refill orifice, configured to refill the cylinder with fluid and prevent fluid leaving the cylinder through the refill orifice.

Refilling the hydraulic cylinder will cause the height of the block to raise. This advantageously allows for a user to reuse the die, or to vary the initial height of the block.

The strip of material may comprise a pressure-activated adhesive. Advantageously, this prompts a punched lamination to at least partially secure to any laminations retained in the block when pressured by the punching force of the punch. This forms a stack of bonded laminations to form the stator. Advantageously, the punching and securing is performed in one motion of the punch. This reduces the number of machining steps to produce the stator, improving both cost and time efficiency. Additionally or alternatively, the strip of material may comprise an anaerobic adhesive. When a punched lamination is retained in the block and pressurized by the punch, any air trapped between the punched lamination and the one or more retained laminations will be removed. This activates the adhesive, at least partially securing the punched lamination to the one or more retained laminations within the block.

The surface of the anvil may comprise at least one protrusion, configured to retain a punched lamination in place and prevent rotation of the lamination within the block.

The one or more protrusions may be positioned such that they interact with a radial aperture of a punched lamination. The one or more protrusions may comprise two diametrically opposed protrusions, each configured to fit within a radial aperture of a punched lamination. In an example, the protrusions may be configured to fit within a fixed number of laminations, before the at least partial bonding between the punched laminations and stack of laminations retained within the block Is sufficient to prevent rotation of the punched laminations.

According to a second aspect of the invention, there is provided a method for producing laminate stacks for a stator using the die of any of the embodiments of the first aspect. The method comprises the steps of:

(a) feeding a strip of material across the surface of the block;

(b) punching the strip of material into a lamination and into the block with the punch;

(c) retracting the punch;

(d) advancing the strip of material across the surface of the block; and repeating steps (b) to (d) to form a stator comprising a plurality of stacked laminations. As discussed with reference to the first aspect, the method is repeatable without needing to remove individual laminations. Advantageously, this reduces the complexity and potential hazards association with handling a plurality of thin, sharp discs.

The method may further comprise the step of:

(ai) at least partially coating the strip of material with a pressure- activated adhesive prior to feeding the strip of material across the surface of the block.

The force exerted by the press when punching laminations may be sufficient to activate the adhesive, at least partially securing the punched lamination to the laminations constrained within the block. As discussed with reference to the first aspect, this advantageously reduces the number of steps required to produce the stator.

The method may further comprise the steps of:

(e) removing the stator from the die; and

(f) resetting the position of the hydraulic system; wherein steps (e) and (f) are performed after the desired number of laminations have been pressed to form the stator.

Resetting the position of the hydraulic system may comprise raising the anvil of the hydraulic system to a starting height for receiving the first lamination.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

Brief description of Drawings

Embodiments will be described, by way of example only, with reference to the drawings, in which figure 1 illustrates a die according to an embodiment of the present invention; figure 2 illustrates a section of the die according to an embodiment of the present invention; figure 3 illustrates a method of producing a laminate stacks for a stator according to an embodiment of the present invention..

It should be noted that the Figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these Figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar feature in modified and different embodiments.

Detailed description of embodiments

Figure 1 illustrates schematic (not to scale) of a a die 100 for producing a stator of a motor according to an embodiment of the present invention. The die 100 comprises a punch 110 for punching laminations 180 from a strip of material 170. The laminations 180 are retained in a block 120, and supported by a hydraulic system 130, 140. The hydraulic system comprises an anvil 132 for supporting the laminations 180 and a hydraulic piston 130, 140 coupled to the anvil. The hydraulic piston 130, 140 is configured to allow the height of the anvil 132 to vary relative to the top surface of the block 120, and to provide a damping force to resist the punching force exerted on the strip of material 170 and the anvil 132. On application of the punching force to the anvil 132, the anvil 132 is lowered relative to the top surface of the block 120.

The hydraulic piston 130, 140 comprises a piston rod 134 coupled to the anvil 132 and comprising a base 136, and a hydraulic cylinder 140. The hydraulic cylinder is at least partially filled with a fluid 150. The base 136 of the piston rod 134 forms a watertight seal with the interior wall 142 of the hydraulic cylinder 140. This may be achieved, for example, with the use of an O-ring 138 or similar seal around the base 136 of the piston rod 134. The base 136 of the piston rod 134 sits on the surface of the fluid 150, and as such the height of the piston rod 134 (and so the anvil 132) is defined by the volume of fluid 150 within the hydraulic cylinder 140.

The hydraulic cylinder 140 comprises a restriction orifice 144 fluidly connected to a non-return valve 145, which is in turn fluidly connected to a storage tank 160. On application of the punching force by the punch 110, the piston 130 is forced downwards. This pushes fluid 150 out of the hydraulic cylinder 140 through the restriction orifice 144. It is from the pressure generated by the resistance to the flow of the fluid 150 through the restriction orifice 144 that the damping force originates. The size of the restriction orifice 144 may be variable, dependent on the damping force desired. A restriction orifice 144 with a larger aperture will offer less resistance to flow, and a damping force of lower magnitude. A restriction orifice 144 with a smaller aperture will provide a damping force of greater magnitude.

Once the punch 110 is retracted, the non-return valve 145 prevents fluid re entering the hydraulic cylinder 150 through the restriction orifice 144. This maintains the volume of fluid 150 within the hydraulic cylinder 140 at the point that the force is lifted, and therefore the height of the anvil 132 relative to the top surface of the block 120 (i.e. the anvil 132 does not continue to travel after the punch 110 is retracted)..

The hydraulic cylinder 140 also comprises a refill orifice 146, which is fluidly connected to a pump and one-way valve 147, which is in turn fluidly connected to the storage tank 160. The arrangement prevents fluid 150 from flowing out of the refill orifice 146, and only entering through the refill orifice 146 when pumped (i.e. only when desired). Introducing fluid 150 from the storage tank into the hydraulic cylinder 140 increases the volume of the fluid 150 within the hydraulic cylinder 140, allowing a user to raise the height of the anvil 132 relative to the top surface of the block 120. This enables the position of the anvil 132 to be reset once the desired number of laminations 180 have been punched from the strip of material 170 and stacked within the block 120.

Storage tank 160 comprises a vent 165 to allow the movement of air in/out of the storage tank 160 when fluid 150 enters or leaves. This prevents a vacuum being formed during the punching process, which would restrict motion of the piston 130 (and so the height of the anvil 132 would become stuck).

The die 100 also comprises a guide bearing 190. The guide bearing 190 surrounds the piston rod 134, to reduce lateral movement or tilting of the piston rod 134 during the vertical motion of the piston 130. This helps to maintain the lamination stack 180 in a constant position, reducing the risk of misalignment of the laminates 180.

Figure 2 illustrates a schematic (not to scale) of a section of a die 200 according to an embodiment of the invention. Die 200 is substantially the same as die 100, but features are omitted for clarity.

Figure 2 illustrates how a lamination can be machined from a raw strip of material 270 using a progression tool including die 200. Pre-laminate 271a has had the radial protrusions of the stator punched out. Pre-laminate 271b is further along the machining progress, with the bore being punched out.. Laminate 271c in in the process of being punched out . Unlike in previous steps, where the desired product was the pre-laminates 271a, 271b still present in the strip of material (with the scrap materials from the pre-laminates 271a, 271b being removed) the laminate 271c is punched out of the strip of material 270 and is retained by the block (not pictured) as part of laminate stack 280.

The strip of material 270 may have been at least partially coated with a pressure-activated adhesive prior to the laminate 271c being punched out of the strip of material 270.. The punching force from the punch (not pictured) and resistance provided the hydraulic system (not pictured) would be sufficient to activate the adhesive, at least partially bonding the laminate 271c to the lamination stack 280 being retained by the block. An example of a pressure- activated adhesive that could be used to coat the strip of material is Glu- Lock®.

The remaining scrap material 271d after the laminate 271c has been punched out of the strip of material 270 may then exit the progression tool and be cut up by a scrap chopper stage.

The lamination stack 280 is supported by the anvil 232, which is coupled to the hydraulic piston rod 234. These features are substantially the same as described with reference to Figure 1.

Figure 3 illustrates a method 300 of producing laminate stacks for a stator using the die of any of the embodiments of the present invention, comprising the following steps.

Step 302: Providing a strip of material from which the laminations are punched.

Step 303 (optional): At least partially coating the strip of material with a pressure-activated adhesive.

As discussed with reference to Figure 2, the force exerted by the punch (and resistance provided by the damping force) is sufficient to activate the adhesive on the strip of material. This at least partially secures the punched lamination to any laminations retained in the block, forming a bonded laminate stack.

Step 304: Feeding the strip of material across the surface of the block.

Step 306: Punching the strip of material into a lamination and into the block with the punch. The punch applies a force on the strip of material to punch a lamination into the block. The block retains the laminations after punching. The hydraulic system is configured to support the laminations, and to lower the height of a single lamination during the punching step, whilst resisting the motion with a damping force.

Step 308: Retracting the punch. Retracting the punch lifts the force being exerted on the punched lamination and hydraulic system. This brings the hydraulic support system to rest, as discussed with reference to Figure 1.

Step 310: Determining if a sufficient number of laminations have been punched to produce the laminate stack for the stator.

If the desired number of laminations have been produced to form the laminate stack (path 310Y), then subsequent steps 312 and 314 are performed. If further laminations are required to be added to the laminate stack (path 31 ON), then steps 302 through 310 can be repeated until the desired number of laminations have been produced. In an example stator, this could be in the order of 1000 laminations per laminate stack. Step 312: Remove the laminate stack from the die.

Step 314: Reset the position of the hydraulic system to a starting height.

Resetting the position of the hydraulic system after removal of the laminate stack enables the process to be repeatable, and for a series of substantially identical laminate stacks to be produced without adjusting other parameters (e.g. punch height, punching force, material thickness). From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art and which may be used instead of, or in addition to, features already described herein.

Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

For the sake of completeness it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, and reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A die for producing a stator of a motor, said die comprising: a punch for punching laminations from a strip of material; a block for receiving the punch, wherein the block is shaped to a cross- sectional profile of the stator and wherein the block is configured to retain the laminations after punching; a hydraulic system for supporting the laminations and for damping the punching force exerted by the punch; wherein the hydraulic system is configured to dampen the punching force such that the laminations retract lower than the top of the block such that the block can receive a subsequent lamination from the strip of material.

2. The die of claim 1 , wherein the hydraulic system comprises: an anvil configured to support the laminations within the block; and a hydraulic piston coupled to the anvil to provide the damping force to the punching force exerted by the punch.

3. The die of claim 2, wherein the anvil comprises at least one protrusion configured to retain a punched lamination in place and to prevent rotation of the lamination within the block

4. The die of claim 2 or claim 3, wherein the hydraulic system further comprises: a guide bearing for guiding the piston to reduce lateral movement of the piston during operation.

5. The die of any of claims 2 to 4, wherein the hydraulic piston comprises: a piston rod coupled to the anvil; and a hydraulic cylinder at least partially filled with fluid configured to receive the piston rod, wherein: the base of the piston rod is configured to form a watertight seal with the interior of the hydraulic cylinder; the height of the anvil is determined by the volume of fluid present in the hydraulic cylinder; and the fluid is a substantially incompressible fluid.

6. The die of claim 5, wherein the hydraulic cylinder comprises: at least one restriction orifice configured to allow fluid to leave the cylinder on the application of the punching force to the anvil; a non-return valve fluidly connected to the restriction orifice to prevent the fluid re-entering the cylinder once the force is released.

7. The die of any of claims 5 to 7, wherein the hydraulic cylinder comprises a refill orifice configured to receive fluid; and wherein the hydraulic system further comprises: a pump and a one-way valve fluidly connected to the refill orifice, configured to refill the cylinder with fluid and prevent fluid leaving the cylinder through the refill orifice.

8. The die of any preceding claim, wherein the strip of material comprises a pressure-activated adhesive.

9 A method for producing laminate stacks for a stator using the die of any of claims 1 to 8, the method comprising the steps of:

(a) feeding a strip of material across the surface of the block;

(b) punching the strip of material into laminations and into the block with the punch;

(c) retracting the punch;

(d) advancing the strip of material across the surface of the block; and repeating steps (b) to (d) to form a stator comprising a plurality of stacked laminations.

10. The method of claim 9, further comprising the step of:

(ai) at least partially coating the strip of material with a pressure- activated adhesive prior to feeding the strip of material across the surface of the die; and wherein the force exerted by the punch when punching laminations is sufficient to activate the adhesive, securing the punched lamination to the laminations constrained within the block.

11. The method of claim 9 or 10, further comprising the steps of:

(e) removing the stator from the die; and

12. The method of claim 11, wherein the hydraulic system comprises an anvil configured to support the laminations within the block; and wherein resetting the position of the hydraulic system comprises raising the anvil to a starting height for receiving the first lamination.