How should the bumping operation start when forming aluminum over a mold?

Starting the bumping operation by using light tapping around the edges is considered the best practice when forming aluminum over a mold. This technique allows for a gradual distribution of forces into the material, which is crucial for minimizing the risk of crimping or wrinkling. Light tapping around the edges helps to allow the material to conform more easily to the mold’s contours without deforming unexpectedly.

By focusing the initial force at the edges instead of the center, the aluminum can begin to take shape evenly, setting a foundation for the rest of the forming process. This method also helps in managing the overall stress within the material, which is particularly important with aluminum, as it has unique properties that can lead to uneven forming if not approached correctly.

Other methods, such as hard, quick taps in the center, can lead to localized stress that might not distribute evenly, potentially causing defects. Pressing down hard from the start could crush or mar the material before it has a chance to form properly. Rolling the material is not applicable in this context, as it pertains more to a different process of material manipulation rather than bumping and shaping over a mold.