In the body maintenance work, when flattening large uneven sheet metal parts, rough flattening should be carried out first, so that the parts can be roughly restored to their original state. In order to obtain more accurate curvature and surface smoothness, the fitting flattening (commonly known as polishing) process should be adopted to flatten the small concave and convex remaining on the surface of the component more finely, or to deform the concave with less damage without damaging the paint surface. Leveling operation is called fine leveling. Fine leveling technology after rough leveling? Choose the right pad and drop the right hammer? First of all, when operating, select a shim with a suitable cross section and stick it to the back of the small bump. Use a light hammer with a large flat wall (40mm in diameter) (wooden hammer with iron embedded in the end face, commonly known as straight hammer) to gently tap around the uplift or small depression of the metal surface, so that the surface of the sheet metal part becomes smoother and flatter. The characteristics of "lighting" leveling are as follows: 1. The drop point of the sheet metal hammer must coincide with the pad surface of the pad iron to realize one-to-one correspondence from point to point; Second, always cling to the back of the straightening surface, that is, the shim accurately corresponds to the hammering position, and it is necessary to prevent the shim from "knocking empty" because it is not in place and damaging the surface of the component that tends to be flat. Before starting the operation, carefully observe and analyze the leveling area, correctly select the leveling point, and determine the hammering strength and corresponding process. Generally speaking, the operation should start from the part with large damage. If the damage degree is similar, it should start from the part where the operator is far away or inconvenient to operate. Pay attention to the correct cooperation between hands and eyes when operating, and ensure that the center of the hammer end face falls on the hitting point. The action of the pad should be synchronized with the action of the hammer, and the number of blows should be less, and the hammer should be as effective as possible every time. The shape of the working face of the shim, leveling knife (commonly known as thin steel plate and crowbar) and hammer should be consistent with the curvature of the body parts as far as possible, otherwise the leveling purpose will not be achieved. Never knock before without analysis and thinking, which may bring a lot of trouble to future homework.