Abstract
The cores of electrical motors and transformers are made by blanking, piercing and stacking of thin metallic sheets having various features cut from the original blank. The material experiences local plastic deformation near the cut edge due to the blanking operation. The quality and efficiency of the produced products are directly affected by the mechanical and magnetic properties of the blanks at the cut edge. The effects of the blanking process on deformation evolution in thin sheets of high Si electrical steels was investigated. In-situ blanking experiments together with the digital image correlation (DIC) technique were used to quantify local deformation evolution during thin sheet blanking operations. Magnetic hysteresis losses were measured using a purpose-built single sheet tester and linked to the measured deformation maps. The residual stresses were qualitatively assessed by means of nano-hardness measurements while the local microstructural properties and dislocation generations were determined using EBSD analysis of the blanked parts. The results indicated that for the tested materials with 0.1t blanking clearance, electrical steel sheets with 0.2 mm thickness experiences larger deformation prior to fracture during blanking compared with samples having 0.35 mm thickness. This has a direct relationship with the measured hysteresis losses. However, the dislocation maps indicated that dislocations of GNDs are more pronounced for thicker samples that aligns with the effect of dislocations on magnetic power losses rather than hysteresis losses measured in this research.
Highlights
Electrical steels (ES) or silicon steels are primarily used in the production of laminations used in the energy and power sector as a component of electric motors and transformer
It is already known that at higher cutting speeds smaller roll-over zone and burr are formed that results in a lower required mechanical work to plastically deforming the materials during these stages, reducing the total force required for the process [8]
Given the higher thickness of 0.35 mm sheets, the material is more affected by this local temperature rise, lowering the mechanical strength, the reduction of blanking forces is more pronounced for samples with 0.35 mm thickness
Summary
Electrical steels (ES) or silicon steels are primarily used in the production of laminations used in the energy and power sector as a component of electric motors and transformer. The Si content in these materials could reach as high as 6.5% with most of commercial alloys having silicon content of < 3.2% [1]. This high Si% improves properties such as electrical resistivity and magnetic permeability, formability of these alloys are adversely affected making them brittle and very difficult to cut and handle at low strip thickness [2]. The material experienced large plastic deformation at the vicinity of the cut edge during blanking that negatively affects magnetic properties of the produced laminations [8]. Due to the high rate of productivity in blanking it is not being fully replaced by alternative techniques making it critically important to understand blanking induced defects on the new generations of ES with reduced thickness that is required for better functional performance
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