The following steps are generally involved in making transformer cores from silicon steel sheet coils:

Uncoiling and shearing
Equipment debugging: first of all, the uncoiler and shear equipment debugging. According to the specifications of the silicon steel coil and the size of the transformer core design required, adjust the tension control device of the uncoiler to ensure that the steel coil in the unfolding process to maintain the appropriate tension, to prevent the coil loose or wrinkles. At the same time, calibrate the cutter position and cutting length setting of the shearing equipment to ensure the precision of the cut size.
Uncoiling operation: Install the silicon steel sheet coil on the uncoiler, start the uncoiler and slowly unroll the coil. During the process of uncoiling, the operator should closely observe the unfolding of the steel coil, and stop the machine immediately for checking if there is any abnormality.
Shearing: The unfolded silicon steel sheet is sent to the shearing equipment through the conveying device, and is sheared according to the pre-set dimensions. For large transformer cores, it may be necessary to cut the silicon steel sheet into long strips; for small transformer cores, it may be directly cut into specific shaped sheets.

Punching sheet processing
Mold preparation: According to the shape and size requirements of the transformer core, select or make a suitable stamping mold. The stamping die should have high precision, high hardness and good wear resistance to ensure the quality of the punched sheet and the service life of the die.
Stamping operation: The sheared silicon steel sheet is fed into the mold of the stamping press, and pressure is applied by the press to stamp the silicon steel sheet into the required shape, such as the common E-type, I-type, C-type and other stamping sheets. In the stamping process, the stamping speed, pressure and stroke should be controlled to ensure the dimensional accuracy and shape accuracy of the stamped sheet.
Punching quality inspection: carry out quality inspection on the silicon steel punches after stamping, mainly checking whether the size of the punches meets the design requirements, whether the edges of the punches are smooth and free of burrs, and whether there are defects such as deformation and cracks in the punches.

Stacking assembly
Preparation of stacked assembly platform: clean up the stacked assembly platform to ensure that the surface of the platform is flat, clean and free of debris and oil. Draw positioning lines and markings on the platform according to the assembly requirements of the iron core, so as to accurately place the punched pieces.
Stacking operation: Stack the punches according to certain rules and order. Generally adopt the staggered stacking method, that is, the seams of two adjacent layers of punches are staggered each other, in order to reduce the magnetic resistance of the core and eddy current loss. In the process of stacking, pay attention to keep the punching piece neat and close to avoid excessive gap or skewed punching piece.
Fastening and shaping: After stacking is completed, the core needs to be fastened. The core can be fastened together by steel banding, bolt fastening or welding. After fastening, the core is shaped, through adjustment and correction, to make the overall size and shape of the core meet the design requirements, to ensure the flatness and verticality of the core.

Insulation treatment
Insulation material preparation: according to the voltage level and performance requirements of the transformer, choose suitable insulation materials, such as insulating paper, insulating paint and so on. Insulating materials should have good electrical insulation properties, heat resistance and mechanical properties.
Insulation processing methods
Insulating paper wrapping: for some small transformer core or insulation requirements are not particularly high occasions, you can use insulating paper wrapping. The insulating paper is cut into suitable size, wrapped in the surface of the iron core and winding installation parts, play the role of insulation isolation.
Insulating paint impregnation: for large transformer core or higher requirements for insulation performance occasions, usually using insulating paint impregnation method. The core is put into the insulating varnish groove, so that the insulating varnish fully penetrates into the gaps and holes of the core, and then drying treatment, so that the insulating varnish on the surface of the core to form a layer of uniform, dense insulating coating.

Iron core test
Appearance inspection: Check whether the appearance of the iron core meets the requirements, including whether the surface of the iron core is smooth, burr-free and damage-free, whether the insulating coating is even and without peeling off, and whether the size and shape of the iron core are consistent with the design drawings.
Dimension Measurement: Use gauges to measure the key dimensions of the iron core, such as the thickness, width, height, window size, etc., to ensure that the dimensional deviation is within the allowable range.
Magnetic performance test: use professional magnetic performance test equipment to test the magnetic induction strength, permeability, iron loss and other magnetic performance parameters of the iron core. Compare the test results with the design requirements to determine whether the magnetic performance of the iron core meets the working requirements of the transformer.
Insulation performance test: use insulation resistance tester, voltage resistance test equipment, etc. to test the insulation performance of the iron core. Measure the insulation resistance of the iron core to check whether it meets the requirements of the specified insulation resistance value. At the same time, the iron core for voltage withstand test, apply a certain voltage, observe the iron core whether there is discharge, breakdown and other insulation failure phenomena.