Motor winding welding is a critical production process in motor manufacturing. This includes welding the main winding to itself, welding the main winding to the lead wires, and welding the copper bar rotor bars to the end rings. All these steps directly affect the motor's operational reliability and quality. Different types and sizes of motors involve unique welding processes and cannot be simply treated the same. Today, Ms. Can will discuss common winding welding methods with you.
Welding methods can be divided into two main categories: fusion welding and brazing. Fusion welding directly melts two workpieces together, requiring the metal at the joint to be heated to a molten state to complete the weld. Brazing uses a filler metal with a melting point lower than that of the base metal. The workpieces and filler metal are heated to a temperature higher than the filler metal's melting point but lower than the base metal's melting temperature. The liquid filler metal wets the base metal, fills the joint gap, and diffuses with the base metal to achieve a weld connection. Welding of motor windings mostly uses brazing. Although fusion welding also occurs, in most cases, hard brazing is used as an auxiliary method to compensate for defects in fusion welding.
Common welding methods for motor windings
Silver-copper soldering (gas welding)
This welding method is suitable for applications with high operating current, high temperature, and high reliability requirements, and is also the welding method used by most motor manufacturers. The welding equipment is an acetylene-oxygen welding torch. During welding, to prevent burns to the motor wire insulation near the wire end, a water-soaked asbestos rope should be wrapped around the wire end. At the same time, it is necessary to prevent solder and flux from flowing into the coil gaps, which could burn the insulation and cause a short circuit.
Soldering
Soldering is convenient and produces strong welds, making it the most widely used method, but it operates at relatively low temperatures. Common soldering methods include iron soldering and pouring solder. Pouring solder can be used when soldering a large number of wire ends. Due to the low melting point of solder, it is only used in small motors and motor windings with low temperature rise.
Arc welding
When the winding conductors are thin, arc welding can be used for welding. Arc welding is characterized by not requiring flux and being quick and convenient. However, when multiple circuits are connected in parallel or there are many wire ends, it is easy to miss welds or produce weak welds if the operator is not skilled.
Copper-aluminum welding and oxygen welding
During welding, the connecting part of the copper wire or copper lead wire is first tinned. Then, cleaned aluminum wire is twisted onto the copper wire, with the aluminum wire slightly higher than the copper wire. A layer of aluminum soldering powder is then applied, and the aluminum wire is melted using a neutral flame from an oxy-acetylene torch, fusing the aluminum to the top of the copper wire to form a spherical solder joint. This method is used in the welding process between the main wire and the lead wire in many motor factories.
Argon arc welding
Argon arc welding (ATW) is a welding technique based on the principle of ordinary electric arc welding. It utilizes argon gas to protect the metal welding material, and a high current melts the welding material into a liquid state on the substrate, forming a molten pool. This allows the welded metal and the welding material to achieve a metallurgical bond. Because argon gas is continuously supplied during the high-temperature molten welding process, the welding material cannot come into contact with oxygen in the air, thus preventing oxidation. This welding method is particularly effective for improving the welding quality of multi-turn windings.
High-frequency induction brazing
Induction brazing involves placing the metal workpiece to be welded (usually copper) inside an induction coil, passing a high-frequency alternating current through it, generating an induced electromagnetic field. This field couples to the workpiece surface, creating an induced electromotive force and forming eddy currents on the metal surface. The eddy currents generate heat, and solder powder is typically applied to the welding area. Welding is completed when the workpiece reaches the melting temperature of the brazing filler metal. Induction brazing is currently the cleanest and most environmentally friendly heating welding method in the world. This type of welding is widely used in copper bar rotors because it operates on several weld points simultaneously, resulting in good consistency of process parameters and effectively reducing weld deformation. It is a superior process in terms of efficiency, reliability, and aesthetics. However, due to the relatively high cost of the equipment and the particularly expensive induction coils, not every manufacturer adopts this welding technology.
Medium frequency induction brazing
Medium frequency induction brazing equipment assembles cleaned workpieces together in an overlapping manner, placing brazing filler metal near or between the joint gaps.
Medium-frequency induction brazing equipment can replace outdated heating methods such as oxy-acetylene heating, coal-fired furnace heating, and box-type electric furnace heating for brazing and quenching heat treatment. It can greatly improve product quality, effectively save energy, and improve working conditions. When the workpiece and brazing filler metal are heated to slightly above the melting point of the filler metal, the filler metal melts (while the workpiece does not melt) and is drawn into and fills the gap between the solid workpiece through capillary action. The liquid filler metal and the workpiece metal diffuse and dissolve into each other, and after condensation, a brazed joint is formed.
Features of medium-frequency induction brazing equipment: 1. Because the principle of medium-frequency induction heating is electromagnetic induction , the heat is generated by the workpiece itself. This heating method has a fast heating rate , minimal oxidation , high heating efficiency , good process repeatability , and only very slight discoloration on the metal surface . A light polishing is sufficient to restore the surface to a mirror-like shine , thus effectively obtaining consistent material properties. 2. Uniform heating and high temperature control precision : Uniform heating ensures a small temperature difference between the heating core and the surface . The temperature control system allows for precise temperature control , ensuring product repeatability.
Medium frequency induction brazing is widely used in the welding of bare copper bar rotor conductors. This welding method has strict requirements on the cutting and forming of the conductors and the shape of the related parallel head sleeves; otherwise, the welding effect will be greatly reduced.
Based on the above information, each motor manufacturer should conduct a comprehensive evaluation considering the characteristics of their own equipment and products. However, reliable welding quality is a key technology in manufacturing.
