What is Earing of Aluminum Circle Plates

The earing rate proves to be an important factor in estimating the quality of an aluminum circle plate. After an aluminum circle plate goes through the cup punching test, sometimes uneven edges appear by the cup mouth. These edges looks like human ears, and thus the phenomena is also known earing. Analysis of earing rate of circle plates helps aluminum circle manufacturers to evaluate anisotropy of the plates.

The production characteristics of aluminium circle for cookware products, usually thin, lead to varied performances of the circle in different directions in the plane. These differences are mainly represented by variations in the strength index σs and σb, plastic index δ and φ, hardening index of formability index n and plastic strain ratio R. This phenomenon of different properties is called planar (in-plane) anisotropy, which is generally measured by the planar anisotropy index △r.

R0, r90 and r45 in the formula are measured respectively by taking tensile specimens (aluminum circle plates) parallel to, perpendicular to and 45 degrees from the rolling direction. The appearance of earing is related to △r value. △r=0 indicates that the r values in different directions are basically the same, and there is no ear-making after cupping test. △r > 0 indicates that the R values of materials in the direction of 0 and 90 degrees are higher than those in the direction of 45 degrees, and that the cup-shaped parts would produce ear-making in the direction of 0 and 90 degrees. △r < 0 indicates that the r value in the direction of 45 degrees is higher, so ear-making will occur in the direction of 45 degrees of cup-shaped parts, as shown in the figure.

A standard ear-making test usually has cup-shaped parts made when the percentage shrinkage of drawing is 40%. Then the ear-making height in different directions is measured to determine the maximum height Hmax, the minimum height Hmin and the average height h, and the ear-making rate (%) of an aluminum circle plate is obtained by putting all the values in the formula of (hmax-hmin) / h * 100.