Aim: Erichsen Cupping Test

Objectives:

1. To describe formability of material.

2. To perform test for the determination of formability.

Equipment and material needed:

1. Erichsen Cupping Test apparatus,

2. Specimens of various materials.

Introduction:

Erichsen cupping test is used to find out the formability of the material. Formability is defined as the ability of sheet material to be formed into a specific shape or configuration. The testing machine works on the principle that a cup is formed in a sheet by means of pressing a spherical punch against the clamped specimen until there is a visible crack developed on the sheet. After the crack develops, the force application is stopped, and the depth of the cup is measured and gives the test results.

                                                                                                 Erichsen cupping test machine

Procedure:-

This Test is commonly used in Europe. The principle of the Erichsen test is illustrated in Figure.

1. Adjust the punch actuating wheel at zero reading.

2. Hold the sheet between two ring-shaped clamping dies. Fit the sheet with rotating the wheel.

3. Rotate the punch actuating wheel so that a hemispherical punch of 20 mm is forced against one side of the sheet until fracture occurs or there is sudden drop in the load.

4. Observe the crack in the mirror, as it appears stop rotating wheel.

5. Note down the reading on micrometer scale. This is the height of the dome. This is reported in mm as a measure of formability.

The Cup height is very sensitive to the thickness of sheet and increases approximately by 0.24 mm with every 0.1 mm increase in sheet thickness. The results are not consistent because of metal pull-in from the clamped dies and inconsistent lubrication, if lubricant is applied on the sheet metal to be tested.

The visual examination of dome gives information regarding grain size, anisotropy of sheet etc. A rough appearance of dome indicates a large grain size. Radial cracks indicate equal strength of the sheet in all the directions (i.e. sheet is isotropic) and circumferential cracks indicates anisotropic nature of the sheet. If the cracks are in one direction, it indicates variation in ductility in different directions. Erichsen standard curve show typical values of expected depth of cup for various thicknesses of metals. However, this does not indicate suitability of the material for a specific application or operation.

Conclusion:  As dome height of MS is more than that of Al, hence MS has more formability than Al. Moreover Al has radial cracks, it indicates that Al is isotropic and MS has circumferential cracks so it is anisotropic.