There are three methods for making flat copper wires for new energy vehicles: continuous extrusion, wire drawing, and precision rolling. The processing of flat copper wire requires a large aspect ratio and high precision in size. The current mainstream process routes are wire drawing and precision rolling.

Continuous extrusion: low production efficiency and limited application

The working principle of continuous extrusion technology: The mold cavity is located on the side of the extrusion wheel, and the billet enters the extrusion cavity under the drive of the rotating extrusion wheel. Under the action of the friction force of the wheel groove, the temperature of the billet increases and the pressure increases. After reaching a certain value, it is extruded from the mold hole to form a product.

The workflow of continuous extrusion of copper flat wire: An oxygen free copper rod produced by the up drawing method is discharged from the billet discharge plate under clean surface conditions, and after straightening, it is directly fed into the continuous extrusion machine. When the billet enters the groove of the extrusion wheel, it is pulled into the extrusion cavity formed by the extrusion wheel and the mold cavity under the frictional force of the groove wall. Due to the blocking block preventing the copper rod from continuing to move forward, under the high pressure and high temperature generated by the frictional force, the metal is extruded through the mold mouth to form a copper flat linear material. After being extruded into copper flat wire products through an extruder, the temperature is high at this time, so there is an anti oxidation device and cooling system at the outlet of the extruder product. Finally, the cable is wound into a coil by a cable winding machine through devices such as meter counting, oiling, and swing arm.

The advantages of continuous extrusion technology:

Using continuous extrusion to produce copper flat wire, the temperature of the copper billet before the extrusion die can reach over 600 ℃, the pressure can reach over 1000MPa, and it is subjected to triaxial compressive stress. Under such high temperature and high pressure conditions, the original internal defects of copper billets, such as pores, can be eliminated during continuous extrusion.

Due to the fact that continuous extrusion of copper flat wire only requires one process to directly extrude the copper coil into a finished copper flat wire product, the surface of the copper flat wire will not produce surface defects such as burrs, and the copper flat wire has good surface quality.

Due to the use of a single billet, various specifications of copper flat wire products can be produced simply by changing the mold, and annealing is not required. Therefore, the production cycle is very short, achieving "delivery on the same day" without the need for inventory and preparation of various specifications of billets, greatly shortening the production cycle, reducing capital occupation, improving material utilization and yield, especially suitable for the production of multiple varieties and small batches of copper flat wires.

The material and structure of the mold can ensure that the product has high dimensional accuracy, not only meeting the requirements of national standards, but also ensuring that the same batch of products have the same size.

The entire production line adopts advanced computer control systems, which can automatically monitor and operate the production process, achieving automated production and reducing the labor intensity of operators.

The continuous extrusion process is not widely used in the field of new energy vehicle flat wires due to its low production efficiency.

Wire drawing forming: mainstream process route, production accuracy depends on the mold

The principle of wire drawing process: Wire drawing process is a metal pressure processing process that, under the action of external forces, forces the metal to pass through the mold, causing plastic deformation of the metal. The cross-sectional area is compressed, the length is increased, and the required cross-sectional shape and size are obtained through the processing method.

Drawing process flow:

Thread threading: Release the wire from the winding reel and pass it through the wire rack, various drawing molds, annealing equipment, and wire winding iron shaft in sequence. When threading wire drawing molds, use matching equipment to polish the wires, reducing the wire diameter and making it easier to pass through the holes of various stages of the drawing machine.

Wire drawing: refers to the process of plastic deformation of wire blanks through multi-stage die holes under a certain pressure, resulting in a smaller cross-section and an increase in length. It is gradually pulled by the tower wheel shaft of the wire drawing machine. During the wire drawing process, the drawing liquid plays a role in lubrication, cooling, and cleaning.

After wire drawing, continuous annealing is required to heat the wire that becomes hard due to lattice changes during the cold drawing process to a certain temperature, eliminate internal stress and defects, improve elongation, and restore it to its physical and mechanical properties before wire drawing, which is conducive to the subsequent process.

Wire collection and inspection: The wires of each diameter specification are fixed to length and rewind on the wire collection iron plate, which is used as enameled specification wires or drawing process wires. The appearance and size of each axis specification wire are fully inspected, and the elongation of the process wire is also checked.

The advantages of wire drawing process:

Drawing can produce products with precise dimensions, smooth surfaces, and complex cross-sectional shapes.

The production length of pull products can be very long, the diameter can be very small, and the cross-section is completely consistent throughout the entire length.

Drawing can improve the mechanical properties of products.

Precision rolling forming: expensive equipment, no dependence on molds, high production accuracy

The working principle of a finishing mill is that the motor provides kinetic energy, and the hydraulic transmission system changes the torque and power. The workpiece is repeatedly rolled through the movement of the rollers and stroke, ultimately achieving the required size and shape. Rolling mills are widely used in industries such as steel and non-ferrous metals.

Advantages of precision rolling machines: Advanced precision rolling processes have the advantages of enhancing traditional wire drawing and extrusion processes, overcoming the shortcomings of both traditional processes. The bare wire produced by the finishing mill can fully achieve:

The bare wire is rolled by rollers, and the appearance quality can reach a mirror finish;

The metallographic structure of the conductor is uniform, the conductivity is better than the national standard, and the mechanical properties are good;

The bare wire size is automatically adjusted according to the set deviation, and the size is precisely controlled within ± 0.01mm. It has memory and locking functions, and there is no impact of product size on resistance balance between batches. It does not rely on molds and has a wide range of applications;

The production process runs smoothly, with low noise, low vibration, high production efficiency, low equipment energy consumption, and high degree of automation; The quality of the products produced using this equipment can fully meet the quality requirements of high-end electromagnetic wires.

Comparison of three processes: wire drawing is the mainstream but relies on molds, precision rolling equipment is expensive but has better performance

The "continuous extrusion method" and "wire drawing method" rely on mold forming, and the size uniformity of the mold has a great impact on the resistance of the flat wire winding, thereby affecting the performance of the flat wire. The mold must be replaced regularly due to wear and tear. The continuous extrusion method and the wire drawing method share a common feature: the shape is guaranteed through molds. The difference between the continuous extrusion method and the wire drawing method is that the working temperature of the mold is between 450 and 550 ℃, and it cannot be produced using polycrystalline molds (artificial diamond molds). Due to the inability to use polycrystalline materials as extrusion molds, the production weight of each extrusion mold will not exceed 58 tons (the service life of wire drawing polycrystalline molds is generally between 80-100 tons).

Article source: RIO electric drive

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