Study On The Processing Characteristics Of Iron-Based Amorphous/Nanocrystalline Alloy Strips With Stacked Shear

Iron-based amorphous/nanocrystalline alloy strips are now widely used in the field of preparing transformer cores as new green energy-saving materials,due to its magnetic properties such as high permeability and low loss,which can effectively improve the utilization of electric energy.Before laminating the transformer cores,the amorphous and nanocrystalline alloy coils need to be edged and slit by a circular knife process to obtain strips with the required width and good edge quality.As the use of amorphous/nanocrystalline alloy strips continues to increase,higher demands are placed on the productivity and shear quality of precision shear processing.In this thesis,the shearing productivity can be increased 2?3 times by using the amorphous/nanocrystalline alloy strip stacked shear processing method,but the shear fracture mechanism of amorphous/nanocrystalline alloy strip under the stacked shear method needs to be studied.What's more,the influence of the stacked shear process parameters and lubrication conditions on the shear quality of amorphous/nanocrystalline alloy strip to investigate the influence mechanism.Firstly,nanoindentation,large load scratching and stacked bending experiments were carried out on Fe-based amorphous and nanocrystalline alloy strips to investigate their hardness,elastic modulus,scratch morphology,shear band morphology and bending fracture morphology.It was found that circular shear bands appeared near the nanoindentation of amorphous alloy strips,while no obvious shear band marks appeared around the indentation of nanocrystalline alloy strips.The amorphous alloy strips showed a dense shear zone at the end of the indentation,while the nanocrystalline strips did not show this phenomenon.Amorphous alloy strips are more likely to crack at the bending arc due to their brittleness,while nanocrystalline alloy strips are less deformed by the tensile side and have a smoother bending arc.Secondly,a strip shearing stress model was established based on the shearing process of amorphous/nanocrystalline alloy strips and the stress-strain state of each layer of amorphous alloy strips during the shearing process was analyzed with finite element simulation.Compared with the single-layer shearing process,the shearing force between the stacked strips can be transferred to the rest of the strips due to the force transferability,which can generate vertical and circular shearing force from the rolling shears and rubber pads.The amorphous/nanocrystalline alloy strips are mainly subjected to type II/III composite crack extension during shear fracture,and the amorphous alloy strips form parallel shear zones on the surface,while the nanocrystalline alloy strips tend to form secondary shear zones.Finite element simulation reveals that the trend of stress state changes in the shear direction for each layer of the amorphous alloy strip is more consistent,while the trend of strain state changes in the single layer amorphous alloy strip differs significantly from that of the rest of the amorphous alloy strip.Furthermore,the effect of the number of stacked layers on the shear quality of amorphous/nanocrystalline alloy strips,including the effect on burr height,section integrity and magnetic domain structure,was investigated,and it was found that the stacked layers slightly increased the burr height and slightly decreased the section integrity of the strip crosssection,but still met the overall shear requirements of amorphous/nanocrystalline alloy strips.The impact of the shear parameters which such as shear speed and shear overlap on the shear quality of amorphous/nanocrystalline alloy strips was further investigated through systematic experiments.It was found that as the shear speed increased,the burr height of each layer of amorphous alloy strips increased while the section integrity decreased and the width of the shear zone increased.Moreover,the burr height of each layer of nanocrystalline alloy strips showed a decreasing trend,while the section integrity and the width of the shear zone increased.As the radial overlap increased,the burr height of each layer of amorphous alloy strip tends to decrease and then increase,and the section integrity tends to decrease,but the width of the shear zone increases.Furthermore,the burr height of each layer of nanocrystalline alloy strip tends to increase and then decrease,and the section integrity tends to decrease and increase,but the width of the shear zone increases.Finally,the effect of lubrication conditions(type of lubrication and lubricant viscosity)on the shear quality of amorphous and nanocrystalline alloy strips was further explored by conducting shear processing experiments on amorphous/nanocrystalline alloy strips under different lubrication conditions,combined with the lubrication model of the strip-to-tool contact interface.It is found that both amorphous and nanocrystalline alloy strips can achieve good shear section and cross-sectional morphology under liquid lubrication.It is further found that the burr height of both amorphous and nanocrystalline alloy strips increases and the section integrity decreases with the increase of lubricant viscosity.From the section burr height and section integrity of amorphous/nanocrystalline alloy strip stacked shear process,single-layer shear is the best,double-layer shear second,and triplelayer shear worse.Therefore,comprehensive shear edge quality and processing efficiency of double-layer shear processing has better results.