176 Section 2 Nonstructural Repairs Copyright Goodheart-Willcox Co., Inc. Introduction This chapter explains how to straighten damaged sheet metal. It begins by discussing the skills needed to perform basic straightening operations. It then describes the basic nonstructural repair operations: analyzing damage, planning the repair, accessing the damage, roughing out, and finishing. These operations are then combined in a section on repairing specific types of nonstructural damage. Fundamentals of Damage Repair In this section, an empty soda can will be used to demonstrate the damage repair process. The side of the can is a high-crown surface. Lateral force on a high- crown surface will cause arrowheads. Press on the side of the can with your thumb to make arrowheads. Look closely at the damage. The arrowheads point away from each other. The metal between the arrowheads is flat, and the flattening extends out to both ends of the can. This flattened area is displaced metal, which is undam- aged but held out of position by the arrowhead buckles. To correct the damage, pinch the arrowheads as shown in Figure 9-1. The buckles at the arrowheads will be released, and the can will pop back to its normal shape. Next, damage the can severely by pressing one side in so far that it touches the opposite side. Notice how the ends of the can move toward each other as the crown collapses. To straighten this damage, first pull the ends away from each other. This will begin to restore the length, and the flattened metal will begin to rise. Pinch the buckles out as you pull on the ends of the can. The metal may tear from metal fatigue, but the approximate shape will be restored by pulling on the ends and pinching the buckles. Of course, vehicle panels are not made of thin aluminum and generally do not have a high crown like the soda can, but you can learn about vehicle repair from this type of demonstration. Buckles hold damage in place. If the buckles are released, the displaced metal will return to its proper position. Also, if a change in length is present, length must be restored as the buckles are released. You would not be able to straighten the severely damaged can if you did not restore the length as you released the buckles. Keep these simple can demonstrations in mind as you read the rest of this chapter. Chapter 4, Fundamentals of Collision Damage, explained that there are only two ways a panel can be damaged, longitudinally and laterally. Longitudinal force causes folds or simple hinge buckles in an immo- bile flat panel. Overall panel length is reduced. In an immobile panel with body lines, a longitudinal force causes collapsed hinge buckles, again reducing overall length. Lateral force on a flat panel first moves the ends of the panel closer together. It then stretches the metal, increasing the surface area. On a high-crown panel, lateral force causes arrow- heads. In an arrowhead, the crown is flattened and the surface area is reduced. All buckles are the result of grain rearrangement. The grains in the metal are too small to be seen, but their arrangement determines the shape of the metal. A force greater than the yield point will rearrange the grain set, causing buckles and changing the shape of the panel. A stretch, or an increase in surface area, means that the grains have been thinned, flattened, and elongated. An upset, or a reduction in surface area, means that the grains have been shortened, thickened, and bunched together. A stretched area is repaired by shrinking the surface area. An upset area is repaired by stretching the surface area. Nonstructural Panel Repair Steps The following section outlines the individual steps in the nonstructural panel repair process. A combi- nation of these operations is used to complete most nonstructural panel repairs. The entire repair sequence involves reading the estimate, analyzing the damage, planning the repair, accessing the damage, roughing out, and finishing. Reading the Estimate The first step in any repair is to read the estimate or repair order. Study each line of the estimate. Find out which parts will be repaired and which parts must be replaced. Goodheart-Willcox Publisher Figure 9-1. Pinching the arrowheads on this soda can will release the buckles.