An amorphous alloy transformer used in a full-bridge inverter welding machine transfers high-frequency power, changes voltage, and provides electrical isolation between the input and output circuits. Its design and manufacturing process depend on the input voltage, output current, switching frequency, and rated duty cycle of the welding machine. Unlike conventional power transformers, this type of transformer requires careful consideration of high-frequency core losses, winding skin effect, and insulation design.
The manufacturing process generally includes electrical specification review, amorphous core selection, winding design, insulation treatment, core assembly, and performance testing.
Confirm the electrical and magnetic design parameters
Before manufacturing the transformer, establish the main electrical specifications and circuit topology of the welding machine. These include the rated input voltage, number of input phases, welding current range, output voltage, rated power, duty cycle, and inverter switching frequency.
In a typical three-phase 380 V full-bridge inverter welding machine, the incoming AC supply is rectified and filtered to produce a DC bus voltage. The IGBT full-bridge circuit then converts this DC voltage into high-frequency pulses that supply the transformer primary winding. The DC bus voltage depends on the rectifier, filtering, and voltage regulation circuits. The 380 V AC input should not be treated as the operating voltage applied directly to the transformer primary.
The transformer turns must therefore be calculated from the actual DC bus voltage, switching frequency, maximum duty cycle, effective core cross-sectional area, and permitted flux swing. The conventional 4.44 sine-wave equation used for line-frequency transformers cannot be directly applied to a full-bridge PWM inverter.
The insulation requirements, cooling method, and allowable temperature rise must also be established before selecting the core and designing the windings.
Select and prepare the amorphous alloy core
Select a suitable amorphous alloy
Iron-based amorphous alloy cores, such as Metglas 2605SA1 and 1K101, can be considered for this application. Core selection should be based on saturation flux density, core loss at the intended operating frequency, magnetic stability, and core dimensions.
Metglas 2605SA1 has a typical saturation induction of 1.56 T. Supplier data for 1K101 also list a reference saturation induction of 1.56 T, together with core loss data measured under specified high-frequency conditions.
Saturation induction is not the same as the design operating flux density. For a high-frequency inverter transformer, core losses must be evaluated using the actual switching waveform and operating frequency. The saturation value alone is not sufficient to determine the working flux density.
Determine the core structure and dimensions
Determine the effective core cross-sectional area, winding window area, and magnetic path dimensions according to the transformer power rating, switching frequency, and winding arrangement. The effective core area is used in flux density calculations, while the window area must accommodate the primary winding, secondary winding, and insulation structure.
A welding current rating such as 500 A is not sufficient on its own to determine the required core dimensions. The welding voltage, duty cycle, inverter waveform, and cooling conditions must also be considered.
Prepare the amorphous core
Amorphous alloy ribbon is thin and requires careful handling. Avoid impact, bending, and localized pressure during transportation and assembly. When cutting or machining is required, use equipment designed for amorphous materials. Improper cutting or grinding can fracture the ribbon and affect its magnetic properties.
Keep the core surfaces and mating joints clean. Before assembly, check for burrs, dust, and other contaminants that could interfere with proper contact.
Some amorphous cores require controlled magnetic field annealing to obtain the specified magnetic properties. The annealing temperature, duration, and field conditions must follow the material and core manufacturer's instructions. Processing parameters from one alloy grade should not be transferred directly to another.
Design and wind the transformer coils
Determine the primary and secondary winding specifications
The primary winding turns are determined by the DC bus voltage and the high-frequency pulse waveform generated by the inverter. The secondary winding must be designed according to the required welding output voltage, current, rectifier circuit, and output inductor.
The welding machine's rated input voltage and output voltage do not directly represent the actual voltage across the transformer windings. Rectifier voltage drops, duty cycle adjustment, and operating load must also be included in the design.
Some transformers also contain auxiliary control windings for control or auxiliary power circuits. Their turns, positions, and insulation requirements depend on the circuit design.
Select the winding conductors
The conductor sizes for the primary and secondary windings depend on their effective currents, conductor cross-sectional areas, allowable current density, and cooling conditions.
High-frequency transformers must also account for skin effect and proximity effect. For high-current secondary windings, multiple insulated copper strands, Litz wire, or appropriately sized copper foil can be used to meet current-carrying and AC loss requirements.
When using enamelled wire such as QZY-2/180, check the specific product's insulation class, thermal performance, and mechanical properties to confirm that it is suitable for the winding arrangement.
Control the winding process and insulation arrangement
CNC winding equipment can be used to control conductor placement and winding tension. Adjust the tension according to the conductor diameter and winding structure. The wire should remain evenly arranged without damaged enamel, crossed turns, or coil deformation.
An insulation barrier must be provided between the primary and secondary windings to meet the required electrical isolation. Common materials include polyimide film, DMD composite insulation, and other electrical insulation materials approved for the application.
Insulation thickness, overlap, winding spacing, and end insulation must be determined according to the rated voltage, insulation class, and applicable electrical safety requirements. A fixed thickness of 0.2 mm polyimide film or 1 mm DMD insulation paper should not be applied to every transformer design.
Insulation treatment and varnish impregnation
After winding, the coils may require drying and insulation treatment according to the insulation system. For coils that use varnish impregnation, pre-drying is generally carried out first to reduce moisture inside the winding. Impregnation and curing then follow the material manufacturer's process requirements.
Depending on the equipment and product requirements, atmospheric-pressure impregnation or vacuum impregnation can be used. Vacuum impregnation helps the insulating varnish penetrate gaps between the windings and improves the bonding between insulation materials and conductors.
During impregnation, control the process according to the varnish viscosity, solid content, and winding structure. The curing temperature and duration must follow the material supplier's technical documentation to achieve the specified cured condition.
The 1032 melamine alkyd impregnating varnish mentioned in some process descriptions should not be treated as a universal material for amorphous alloy welding transformers. Its compatibility with the conductor insulation and other insulation materials must be confirmed before use, and the product's technical data sheet should be checked.
Assemble the core and electrical connections
After insulation treatment, assemble the windings and amorphous core according to the designed structure. For split or cut core assemblies, align the mating surfaces correctly to avoid unintended gaps at the core joints.
The core clamping structure must provide sufficient mechanical support without applying excessive pressure that could damage the ribbon or deform the core.
Where dust protection or sealing is required, select a suitable sealing material according to the mechanical design. Do not allow sealant to enter the effective mating surfaces of the core, as this may change the magnetic gap.
Connect the primary and secondary windings according to the electrical schematic. Terminals, copper busbars, and cable lugs must be selected for the corresponding current requirements. Ensure adequate contact area and secure mechanical fastening. Tightening torque should follow the terminal and equipment manufacturer's specifications.
Performance testing and safety verification
After assembly, test the transformer and its associated welding power circuit to confirm that the electrical and insulation performance meets the design requirements.
Basic electrical checks
Measure the DC resistance of the primary and secondary windings. Check the turns ratio, winding polarity, and connection arrangement. Inductance and leakage inductance measurements can provide additional information about the core and winding construction.
No-load and loss testing
Measure the transformer's no-load current and related losses under the specified DC bus voltage, switching frequency, and test waveform. For a high-frequency amorphous core, particular attention should be paid to core loss and temperature rise at the actual operating frequency. Conventional line-frequency transformer loss limits should not be applied directly.
Load and temperature rise testing
Install the transformer in the corresponding full-bridge inverter welding machine and test it under the specified welding load and duty cycle. Check the secondary output voltage, current, and winding temperature rise.
During testing, monitor the temperature of the winding insulation, core clamping structure, and electrical connections. Confirm that the transformer meets the required thermal stability under the designed operating conditions.
Insulation and safety testing
Carry out insulation resistance, dielectric withstand, and relevant protection function tests according to the applicable electrical safety standards and product specifications. The complete welding machine also requires checks of protective earthing, rated no-load voltage, thermal performance, and relevant safety protection functions.
High-voltage withstand tests and short-circuit protection verification must be performed by qualified personnel under an approved test procedure. Fixed values such as 2,000 V for one minute or a primary current limit of 1.2 times the rated current should not be treated as universal acceptance criteria for all welding transformers.
After testing, mark the product with the required rated voltage, output parameters, insulation class, and other identification information. Keep the corresponding inspection records.
Custom machining for welding and industrial equipment components
Welding equipment and its associated production machinery may require mounting brackets, mechanical connectors, structural components, and other non-standard machined parts. We provide custom precision machining based on customer drawings and technical specifications, supporting both individual components and small production batches.
Hansheng Automation also provides drawing-based machining services for components used in other industries. These include tobacco packaging machinery parts, filling equipment components, precision structural parts for remote-control racing cars, and yacht equipment components. We manufacture each part according to its specified dimensions, tolerances, and machining requirements.
