Hardness testing of metal stampings is an important means of evaluating material properties and processing conditions. Various methods are commonly used, and the appropriate method must be selected based on the characteristics of the part and the purpose of the test. The Brinell hardness test uses a cemented carbide ball indenter, applies a test force and holds it for a certain time, measures the indentation diameter to calculate the hardness value, and is suitable for materials with non-uniform microstructures, such as cast iron. Larger indentations provide more stable results, but can damage the surface and are not suitable for thin-walled parts or finished products. The Rockwell hardness test determines hardness by measuring the indentation depth. It is simple and fast to operate, produces small indentations, and offers various scales such as HRA, HRB, and HRC, each suitable for materials with different hardness ranges. HRB or HRC scales are commonly used for metal stampings, but it is important to note that the sample thickness should be greater than 10 times the indentation depth. The Vickers hardness test uses a diamond pyramidal indenter, measures the diagonal length of the indentation to calculate the hardness, and offers high accuracy and a wide test force range, from a few grams to tens of kilograms. It can measure both microhardness and macrohardness, and is particularly suitable for thin sheet metal stampings and carburized or coated layers, accurately reflecting hardness changes in the microscopic regions of the material. Leeb hardness testing is a dynamic rebound method. Its small size makes it portable and suitable for on-site testing of large stamped parts, but its accuracy is affected by operational factors. Knoop hardness testing is used for extremely thin layers or brittle materials.
When testing metal stamped parts, the following should be noted: the surface should be flat and clean, free of oxide scale and oil; appropriate test force and holding time should be selected; for thin sheet metal parts, ensure proper support to prevent errors; the depth of the hardened layer should be measured point by point from the surface inwards. Correctly applying these methods can yield accurate hardness data, providing a basis for process control and product acceptance.