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Electro sheet stamping

Stator packages made from electro sheet metal for electric motors

The technology of shear-action cutting or stamping is versatile and has a very broad range of potential uses. Stamping electro sheet is one application of this manufacturing process, but at the same time the various processes involved in production and the requirements of tools should not be underestimated.

Shear-action cutting or stamping can be found in both artisanal workshops and industrial operations. In series production, complex tools make it possible to produce very precise products. Here, stamping technology becomes even more interesting when combined with other manufacturing processes such as drawing, shaping, bending and coining. Different combinations permit the coverage of a huge variety of products, ranging from household items to complex components for the automotive industry, and even production of electro sheets for large-scale electricity generators. For financial reasons, in mass production there is a preference for complex follow-die, composite follow-die, or complete cutting tools that permit the use of a combination of the above-mentioned manufacturing processes.

Manufacturing processes of electro sheet metal packages
Rotor and stator sheet packages and other electro sheet packages are manufactured primarily with follow-die cutting and packaging tools on fast-running punch presses designed especially for the purpose. These packages consist of thin, individual sheets (down to a minimum of 0.3 mm) layered on top of one another. This helps to avoid eddy current losses that can have a considerable effect on the efficiency-value of the electric motor.

Rotor and stator packages made of electro sheet
Rotor and stator packages made of electro sheet

The bonding techniques by which the loose sheets are joined to the package include not only welding or gluing, but also clinching or punch-packaging, a mechanical process that is being applied ever more frequently to join individual sheets within the punching operation.

In practice, clinching is often referred to as punch-packaging. The follow-die cutting tools used for clinching are likewise referred to as punch-packaging tools.

Punch-packaging combines the processes for punching, forming and mechanical joining in one manufacturing process. Individual sheets are punched out of a strip, their joining elements (“knobs”) formed and, in a final stage, cut, arranged and joined. The electro sheet metal packages emerge from the cutting tool finished or half-finished. The tool sequences for “coining” and “blanking” form the crucial dimensions in relation to this. During the “coining” stage, the knobs are shaped by a coining punch (the moving part of the tool) and a coining die (the non-moving part of the tool). During the “blanking” stage, the sheet is punched by the main punch and die and, in the same stroke, joined with the next sheet by the joining punch (also referred to as the joiner).

Punch-packaging demands the utmost accuracy
The dimensional repeatability of the punched parts demanded by the customer places high demands on the process of punch-packaging. If there is minimal eccentricity of just a few hundredths of a millimeter between the internal and external files of an electric motor, vibrations will occur while the motor is running as a result of the imbalance of the armature. Depending on the type of motor, the air gap between the rotor and the stator will be just a few tenths of a millimeter and must be kept within a very narrow band of tolerance. Alongside the form and position tolerance of the individual sheets, close attention must be paid to other details of the dimension and form of the layered sheets for the further processing of the packages. Hence, for example, transformer packages require adherence to flatness tolerance of hundredths of a millimeter in automated systems to continue to function reliably. Depending on the dimensional repeatability required, various types of packaging can be used based on the form and type of the knobs, for example round packaging, rectangular packaging and ring packaging.

Requirements of the stamping tools
The high demands on the production of the punch-packaging tool start to emerge as early as the development of the product. The construction specifications lying within a narrow area of tolerance require high-precision production processes and can only be implemented with the most accurate of production machines and skilled specialists. For the punching operation itself, the high-volume production of sheet packages represents a difficult, high-precision task that demands optimum cooperation by the process components of the process system.

In a subsequent blog entry, you’ll find out more about:
Requirements for the set-up of the cutting tool for the stamping of electro sheet

3 thoughts on “Electro sheet stamping

  1. Excellent explanations RE why machining must be absolutely precise! Thanks for posting; will be very helpful for clients and students.

  2. That’s crazy that just a few hundredths of a millimeter can make the difference in whether the motor will run properly! I had no idea that steel sheets went through such a detail-oriented, intense measuring process. If I were in a business that required steel sheet services, I would want to work with experts that really understand how crucial those details are.

  3. thanks for the blogs very useful

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