The structure of axial flux and distributed winding

1. The stator

In the figure below, it was conducted stator structure in AutoCAD in order to make known geometrical characteristics. Ferromagnetic core shows notches with parallel walls, for which teeth will be trapezoidal shape.

Schematic representation of the stator

        Winding notches arranged in distributed mode is a step of winding, meaning that for the first coil bundle of carrying will be placed in the notch 1, and return the cluster will be placed in the notch 4.

The structure of the stator of the axial flux machine

Winding arrangement in notches

2.      The rotor

          The program was conducted previous and rotor structure, specifying the angle at which the magnets were placed together with the geometrical characteristics falling.            Since I could not get hold of magnets whose form we ensure a better distribution of the field lines and coverage increased rotor surface (magnets type trapezoidal-spherical), I limited the type magnetic disc.

Schematic representation of the rotor

        The image below illustrates the final shape of the rotor, we can see how the alternate location and surface polarity magnets.           As far as we can notice, the rotor shaft flange in the middle shows that ensure a snug fit on the shaft and shaft stability when performing tests.

The structure of the final rotor with permanent magnets

        The rotors were made of OL52 (steel). This type of steel has a maximum permissible magnetic induction = 2.2 [T]. An induction exceeding this value would cause the magnetic circuit to quickly reach saturation, thus affecting the performance of the machine.            The configuration for closing field lines made in this project is of the N-S type They leave the polarity N, pass through the stator of ferromagnetic material and reach the polarity S on the opposite rotor. Given the pattern in which the field lines are to be closed through the stator, i.e. through the static teeth, the flat was made with channels at an angle of 60 degrees to rotate one of the two rotors and bring the magnets with surfaces of the same polarity, face to face. This facilitates work with other configurations such as the N-N type, where the field lines close through the static yoke.


Round structure with permanent magnets, with clamping flange and modification in an angle of 60 surface

2. Execution of the stator structure

This step involves trimming, processing at a long time, deburring (cutting surface imperfections) and making the burring. The stationary core is made from the strip of non-oriented ferromagnetic crystal material, rolled in a circular form with the following characteristics:

        • D ext=220 [mm]
        • D int=100 [mm]
        • g st=40 [mm]

The notches were made at the milling cutter to capture the desired shape, which was made at a height of 15 [mm], a width of 10 [mm] and an angle between 20 interp heads.

Since the strip of ferromagnetic material, used to make the stator core, could have become detached during trimming, two steel rings were required, modeled according to the desired characteristics (outer diameter, inner diameter, respectively).
Once the trimming stage has been completed, the rings have been removed, the loose material in the package has been removed and two welding points have been made to prevent other defects from appearing during the construction.
As the trimming process often shows slight imperfections, we have intervened with slight adjustments to the ferromagnetic core. The created Cour were subjected to a deburring process, using a metal pellet to round off their ends. The deburring process is carried out thoroughly, as very sharp edges can destroy both the isolation of the infant and the burring itself, following the arrangement in the crestaries. Destruction of the insulation may cause the electrical circuit to be closed through the stator, affecting the integrity of the machine and operator concerned.
A next step is to lay out the insulation in the creates, made of electroinsulating (pre-span) cardboard. The electroinsulating board consists of pulp and chemical agents based on sulphate. It is used in low voltage applications because it has good electrical, mechanical and dielectric properties such as oil transformers, capacitors, resistors, switches and other applications in the electro-technical field. Electroinsulating cardboard has been used for both the outside of the ferromagnetic core and the inside, as seen in the following figure.

4. Performing windings

Within the N-S configuration, the selected infation is a distributed one, which facilitates the closing of the field lines through the teeth of the stator, from the polarity N to the polarity S. Trimming shall be arranged on both sides of the stationary structure. The coils were made using plastic templates and a fully wrapped machine. The templates are located on a cross-adjustable stand which is driven by a continuous motor powered by a 12V power source. We mounted the templates at an appreciable distance, which gives us the possibility of shaping the final product and a better distribution in the creams. The fully-wrapped machine is equipped with roll-out rolls of the wire, which cause a uniform distribution.

          The wire used is of copper and has a diameter of 0.8mm, together with double layer insulation of terephthalic email. The ends of the coils have been attached with adhesive paper tape so that we can work more easily and make the modeling we need in the designs.

          A more difficult process in the stator construction was the placing of coils in the designs, due to the working space between the coils and their rigidity. The active parts of the infants are also isolated by pre-span and pressed creams for uniformity of construction surfaces.

The coils are attached with plastic clips to the inactive parts to ease the positioning in the crestings and ensure an increased filling factor. At the same time, we chose to use a modeling epoxy agent to fill the space left free in the designs and to fix the wires without affecting the performance of the machine.

Once all the coils are placed in the designs, the ends of the conductors will be stripped and prepared to make the connections for each phase. 6 coils are inserted on each side of the stator on each phase. Before this step, test the insulation of the infasations using a special measuring apparatus, which will check the continuity of the circuit of each coil. If there are areas where the insulation layer has been removed or pierced by any contact between the conductor and the ferromagnetic core table, the apparatus shall show resistance 0. The test can also be seen in Figure 30 where one of the terminals is connected at one end of the coil and the other touches the stationary structure.

         Following the insulation tests, we have established that the infant has not been damaged with the mounting in the brains and we can move on to the insertion operation. Coil winding-up is performed on the basis of a diagram shown, for one of the stationary ferromagnetic core parts.

Figure 31

         The infant heads are stripped and washed with de-scour paste to be able to bond as best as possible the fludor conductors and eliminate excess material. The parts between which the adhesive has been made are inserted into non-insulating tubes of textile material with glass fiber, and then they are tightened as closely as possible to the inactive side so that they do not occupy the space required to center the stator in the case . The infant heads will be noted for a better differentiation between phases. It is also recommended to maintain an additional driver supply as connections will be made to the power terminals mounted on the housing.


Construction of machine with axial flux- ring winding to yoke

1.      The stator

          In the graphic drawing program AutoCAD, we have drawn according to the data from the design calculations, the graphic shape of the stator. The shape of the grooves is parallel walls and the shape of the teeth, V-shaped. The stator with 18 grooves on one side, which means there are 36 designs in total and the angle between two notches is 20º. Notch dimensions:

  • Height of the cut – h1=10[mm]
  • Notch width – b1=10[mm]

Graphic representation of the stator in 2D

Graphic representation of the stator in 3D

          The static magnetic circuit has 36 notches in total 18 on the top and 18 on the bottom, parallel positioned and shown in Figure 21. The winding for this stator construction is a ring type winding also called toroidal winding. The stator is made of cold-rolled, silicious sheet with oriented graunts.

Graphic representation of the stator in 3D

2.      The rotor

Also in the autocad graphic drawing program, we drew the rotor shape along with permanent magnets, with alternating polarity. Rotor with an external diameter of 220 [mm] and a disc thickness of 10 [mm]. 6 permanent magnets are positioned on the rotating disc, made of rare earths, namely NdFeB (Neodium), with alternating polpolarities, at an angle of 60°, one from the other. The permanent magnets used are the magnetization grade N42 with a residual induction of 1.29 [T] to 1.32 [T] and a maximum working temperature of approximately 80 °C.

Graphic representation of the stator in 2D

          A clamping flange with dimensions shown in the graphic drawing in Figure 23 is attached to the rotating disc. Permanent magnets having a diameter of 60 [mm] and a thickness of 5 [mm]. Permanent magnets used in the practical application are magnetized axially. The inside diameter of the rotational disc retaining flange shall be 20 [mm] diameter, which also represents the hub diameter. The rotating disc is made of steel.

Graphic representation of the stator in 3D

3. Toroidal winding

The winding for the axial flux generator and permanent magnets chosen for study is a toroidal winding called and wound into the ring. This envelope is centered around the magnetic core, thus concentrating magnetic field lines through the stationary ferromagnetic core. The toroidal winding consists of 18 coils, resulting in every phase 6 coils. A coil consists of 68 turns, where the length of a turn is approximately 20 [cm]. Envelope step y1=3.

Toroidal winding (ring)

4. The manufacturing technology of the electric machine with axial flux and permanent magnets

In this chapter I will present the technological stream of making electrical machines with axial flux and permanent magnets. Once the graphical representation of each component is completed, it shall be made physically. A first step in the construction of electrically powered machines with axial flux is the construction of the stator.

Making the notches

The static magnetic circuit is made up of silica sheet, with oriented graunts, with a thickness of 0,5 [mm] in roll form. The bundle of sheet constituting the stator magnetic circuit is 40 [mm] high, the outer diameter being 220 [mm] and the inner diameter being 100 [mm]. A machine – trimming tool has been used to make the cut in the packet. Milling is the process of cutting-off generation of surfaces, which is carried out with special cutting tools of the shape of a rotating body having several cutting edges called the milling cutter, on machine-tools for milling. The groove achieved through the trimming process is 10 [mm] wide and 10 [mm] high and 20 [mm] magnetic core height.

Make the notches through the trimming process

          At the end of the scoring process, the stator is cleaned by metal chips (chips) from cutting through the groove trimming process. After this cleaning step, a metal pellet is used to remove the burrs due to the trimming process.

Carry out the insulation of the stator and the winding This step is to isolate the cut from an electrical point of view, using a known pre-cut electroinsulating cardboard. The electro-insulating board is made of cellulose fibers, a process similar to paper production without the use of binders or resins. The outer and inner parts of the stator core are electrically insulated, as well as the scoring with the electroinsulating cardboard. This insulation is shown in Figure 30. For toroidal winding purposes, a wooden material template shall be used, and may be called and sucveically, so that the coil is around the ferromagnetic core. The winding around the ferromagnetic core is made with A Copper wire (Cu) with a diameter of 0,8 [mm] with double insulation of terephthalic email. Each coil terminal is inserted a glass fiber tube for temperature protection, but also serves as electrical isolation between the other terminals.

Complete the winding process

Conclusions: Switching from the Radial to axial flux generator seems an attractive solution due to constructive simplicity. The coil in the ring on the stator has two active parts compared to the coil distributed at which the length of the front parts is approximately 3 times longer. To achieve the same power value as the radial flux generator, it is necessary to stack several modules with axial flux. This can be seen when laboratory tests are to be carried out on the two models.