206 Section 2 Nonstructural Repairs Copyright Goodheart-Willcox Co., Inc. Summary • Displaced metal is undamaged but held out of position by the arrowhead buckles. • 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 means that the grains have been thinned, flattened, and elongated. • An upset means that the grains have been shortened, thickened, and bunched together. • Only after you carefully examine and analyze the damage will you be able to decide if the damaged part should be repaired or replaced. • Easily replaced, low-cost panels, such as fenders and door skins, are often replaced if they have more than minor damage. • To repair panel damage caused by longitudinal force, the panel’s length must be restored. • To repair damage caused by lateral force, not only must the length be restored but the surface area may also have to be changed. • Before you can begin the repair of a damaged panel, various components must be removed from the vehicle to allow access to the damage. • Roughing out restores the damaged panel to its approximate contour, and finishing completes the repair by restoring the exact contour of the panel. • When metal is upset, its surface area is reduced and its thickness is increased. Stretching restores the metal to its correct dimensions. • A false stretch is a bulge that pops in when pressed and out when released. • Shrinking reduces the surface area of stretched metal. • Uncontrolled use of heat on a low-crown panel will cause warp damage. • Kinking involves the use of a shrinking hammer (serrated-faced hammer) or a sharp pick hammer to reduce the surface area by gathering the metal together. • Chasing the dent occurs because the low-crown metal is floppy and is easily pushed in. • Picking raises small lows and lowers small highs. • Filing is used to identify high areas and low areas. • In a one-sided repair, only the outside of the panel is worked. This type of repair is performed when the damaged panel is boxed or if accessing the back side of the panel is difficult. • In a two-sided repair, both sides of the panel are worked. Access to the back side of the panel is required in a two-sided repair. • Metal finishing is the continuation of the pick and file process started during roughing. If metal finishing is done correctly, no filler will be used in the repair. • Filling involves the use of filler to restore panel contour once roughing out is completed. • Steel particles left over on grinder disks, sandpaper, and files will contaminate bare aluminum. • Do not heat an aluminum panel to more than 400° F. • When performing shrinking, leveling, or raising operations on an aluminum panel, the hammer blows must be softer than those used on steel. Activities 1. Write up a damage analysis on the nonstructural damage of a vehicle chosen by your instructor. 2. On a vehicle chosen by your instructor, straighten a damaged panel close to its original contour. Keep a record of the tools and methods you used, and any difficulties you encountered. Review Questions Answer the following questions using the information provided in this chapter. 1. The damage repair sequence involves analyzing the damage, planning the repair, accessing the damage, _____, and finishing. 2. A bend of reflected light on a panel indicates a(n) _____ in the panel’s surface. 3. A straightedge can be used to locate dents in panels that are _____ in only one direction. 4. A damaged panel is replaced if the cost of repair is at least _____ % of the cost of replacement. 5. Wheel opening moldings may be fastened with clips that fit into square holes or tapered _____ that fit into round plastic inserts in the quarter panel. 6. Explain the lift reaction.