Procedures
STANDARD PROCEDURE - PLASTIC BODY PANEL REPAIRFig. 1:
Resin Transfer Molded (RTM) body panels are reinforced with a continuous fiberglass mesh. Epoxy resin is injected into a gel-coated and fiberglass lined mold to form a body panel. Sheet molded compound SMC) body panels are constructed with fiberglass strands usually 1 inch or shorter, epoxy resin formed into sheet stock and pressed in mold flowing material to form a sheet molded compound (SMC) body panel. RTM and SMC body panels can be repaired with epoxy adhesive after market products. Refer to instructions provided by the manufacturer of products being used to repair RTM or SMC. Daimler Chrysler Corporation recommends that a trained automotive body technician perform body panel repair procedures (Fig. 1).
SAFETY PRECAUTION AND WARNINGS
WARNING: EYE PROTECTION SHOULD BE USED WHEN SERVICING RTM AND SMC COMPONENTS. PERSONAL INJURE CAN RESULT. USE AN OSHA APPROVED BREATHING DEVICE WHEN MIXING EPOXY, GRINDING RTM AND SMC, AND SPRAYING PAINT OR SOLVENTS IN A CONFINED AREA. PERSONAL INJURY CAN RESULT. AVOID PROLONGED SKIN CONTACT WITH EPOXY RESIN, PETROLEUM, OR ALCOHOL BASED SOLVENTS. PERSONAL INJURY CAN RESULT.DO NOT VENTURE UNDER A HOISTED VEHICLE THAT IS NOT PROPERLY SUPPORTED ON SAFETY STANDS. PERSONAL INJURY CAN RESULT.
- When holes must be drilled or cut in body panels, verify locations of internal body components and electrical wiring. Damage to vehicle can result.
- Do not use abrasive chemicals or compounds on undamaged painted surfaces around repair areas. Damage to finish can result.
Fig. 2:
If it is required to section a large panel for an SMC or RTM repair, it will be necessary to reinforce the panel with epoxy structural adhesive (rigid repair adhesive) (Fig. 2). To bond two plastic panels together, a reinforcement must overlap both panels. The panels must be "V'd" at a 20 degree angle. The area to be reinforced should be washed, then sanded. Be sure to wipe off any excess soap and water when finished. Lightly sand or abrade the plastic with an abrasive pad or sandpaper. Blow off any dust with compressed air or wipe with a clean dry rag.
When bonding SMC or RTM panels, use a two-part epoxy adhesive. Properly mix parts A and B, and apply it to the panels being repaired. Be sure that enough adhesive has been applied to allow squeeze out and to fill the full bond line. Once the pieces have been brought together, do not move them until the adhesive is cured. The assembly can be held together with clamps, rivets, etc. A faster cure can be obtained by heating with a heat lamp or heat gun.
After the parts have been bonded and have had time to cure, rough sand the seam and apply the final adhesive filler to the area being repaired.
Smooth the filler with a spatula, wooden tongue depressor, or squeegee. For fine texturing, a small amount of water can be applied to the filler surface while smoothing. The cured filler can be sanded as necessary and, as a final step, cleanup can be done withy soapy water. Wipe the surface clean with a dry cloth allowing time for the panel to dry before moving on with the repair.
PANEL REINFORCEMENT
Fig. 3:
Fig. 4:
Structural repair procedures for rigid panels such as Sheet Molded compound (SMC) or Resin Transfer Molded (RTM) with large cracks and holes will require a reinforcement backing. Reinforcements can be made with several applications of glass cloth saturated with epoxy structural adhesive, semirigid or flexible repair materials should be used for semirigid or flexible part repairs (Fig. 3) and (Fig. 4). Open meshed fiberglass dry wall tape can be used to form a reinforcement. The dry wall tape allows the resin to penetrate through and make a good bond between the panel and the epoxy adhesive. Structurally, the more dry wall tape used, the stronger the repair.
Another kind of repair that can be done to repair large cracks and holes is to use a scrap piece of similar plastic and bond with structural adhesive. The reinforcement should cover the entire break and should have a generous amount of overlap on either side of the cracked or broken area.
Fig. 5:
When repairing plastic, the damaged area is first "V'd" out, or beveled. Large bonding areas are desirable when repairing plastic because small repairs are less likely to hold permanently. Beveling the area around a crack at a 20 degree angle will increase the bonding surface for a repair (Fig. 5). It is recommended that sharp edges be avoided because the joint may show through after the panel is refinished.
Fig. 6:
- Panel repair for both flexible and rigid panels are basically the same. The primary difference between flexible panel repair and rigid panel repair is in the adhesive materials used (Fig. 6).
- The technician should first decide what needs to be done when working on any type of body panel. One should determine if it is possible to return the damage part to its original strength and appearance without exceeding the value of the replacement part.
- When plastic repairs are required, it is recommended that the part be left on the vehicle when every possible. That will save time, and the panel will remain stationary during the repair. Misalignment can cause stress in the repair areas and can result in future failure.
VISUAL INSPECTION
Sheet Molded Compound (SMC) and Resin Transfer Molded (RTM), because they are composites, react differently to impact that sheet metal does. Composite materials can mask the severity of an accident. Adhesive bond lines, interior structure of the doors, and steel structure need to be inspected carefully to get a true damage assessment. Close inspection may require partial removal of interior trim or inner panels.
Fig. 7:
Fig. 8:
Identify the type of repair:
Puncture or Crack - Damage that has penetrated completely through the panel. Damage is confined to one general area; a panel section is not required. However, a backer panel, open fiberglass tape, or matted material must be bonded from behind (Fig. 7).
PANEL SURFACE PREPARATION
If a body panel has been punctured, cracked, or crushed, the damaged area must be removed from the panel to achieve a successful repair. All spider web cracks leading away from a damaged area must be stopped or removed. To stop a running crack in a SMC or RTM panel, drill a 6 mm (0.250 in.) hole at the end of the crack farthest away from the damage. If spider web cracks can not be stopped, the panel would require replacement. The surfaces around the damaged area should be stripped of paint and freed from was and oil. Scuff surfaces around repair area with 360 grit wet/dry sand paper, or equivalent, to assure adhesion of epoxy repair materials.
PATCHING PANELS
An RTM or SMC panel that has extensive puncture type damage can be repaired by cutting out the damaged material (Fig. 8). Use a suitable reciprocating saw or cut off wheel to remove the section of the SMC or RTM panel that is damaged. The piece cut out can be used as a template to shape the new patch. It is not necessary to have access to the back of the panel to install a patch. Bevel edges of cutout at 20 degrees to expose a larger bonding area on the outer side. This will allow for an increased reinforcement areas.
PANEL PATCH FABRICATIONS
A patch can be fabricated from any rigid fiberglass panel that has comparable contour with the repair area. discard SMC or RTM panels. Lift gates and fenders can be used to supply patch material. If existing material is not available or compatible, a patch can be constructed with epoxy and reinforcement mesh (dry wall tape). Perform the following operation if required:
Fig. 9:
1. Cover waxed paper or plastic with adhesive backed nylon mesh (dry wall tape) larger than the patch required (Fig. 9).
2. Tape waxed paper or plastic sheet with mesh to a surface that has a compatible contour to the repair area.
3. Apply a liberal coat of epoxy adhesive over the reinforcement mesh (Fig. 9). If necessary apply a second or third coat of epoxy and mesh after firs coat has cured. The thickness of the patch should be the same as the repair area.
4. After patch has cured, peel waxed paper or plastic from the back of the patch.
5. If desired, a thin film coat of poesy can be applied to the back of the patch to cover mesh for added strength.
PANEL PATCH INSTALLATION
1. Make a paper or cardboard pattern the size and shape of the cutout hole in the panel.
2. Trim 3 mm (0.125 in.) from edges of pattern so patch will have a gap between connecting surfaces.
3. Using the pattern as a guide, cut the patch to size.
4. Cut scrap pieces of patch material into 50 mm (2 in.) squares to use as patch supports to sustain the patch in the cutout.
5. Drill 4 mm (0.160 in.) holes 13 mm (0.5 in.) in from edge of cutout hole (Fig. 8).
6. Drill 3 mm (0.125 in.) holes in the support squares 13 mm (0.5 in.) from the edge in the center of one side.
7. Scuff the backside of the body panel around the cutout hole with a scuff pad or sandpaper.
8. Mix enough epoxy to cover one side of all support squares.
9. Apply epoxy to the support squares on the half with the hole pre-drilled in it.
Fig. 10:
10. Using number 8 sheet metal screws, secure support squares to back side of body panel with epoxy sandwiched between the panel and squares (Fig. 10).
Fig. 11:
11. Position patch in cutout against support squares and adjust patch until the gap is equal along all sides (Fig. 11).
12. Drill 3 mm (0.125 in.) holes in the support squares through the pre-drilled holes in the patch.
Fig. 12:
13. Apply a coat of epoxy to the exposed ends of the support squares (Fig. 12).
Fig. 13:
14. Install screws to hold the patch to support squares (Fig. 13). Tighten screws until patch surface is flush with panel surface.
15. Allow epoxy to cure, and remove all screws.
Fig. 14:
16. Using a 125 mm (5 in.) 24 grit disc grinder, grind a 50 mm (2 in.) to 75 mm (3 in.) wide and 2 mm (0.080 in.) deep path across the gaps around the patch (Fig. 14). With compressed air, blow dust from around patch.
Fig. 15:
17. Apply adhesive backed nylon mesh (dry wall tape) over gaps around patch (Fig. 15).
18. Mix enough epoxy to cover the entire patch area.
Fig. 16:
19. Apply epoxy over the mesh around patch, and smooth epoxy with a wide spreader to reduce finish grinding. Use two to three layers of mesh and epoxy to create a stronger repair (Fig. 16).
PATCHED PANEL SURFACING
After patch panel is installed, the patch area can be finished using the same methods as finishing other types of body panels. If mesh material is exposed in the patched area, grind surface down, and apply a coat of high quality rigid plastic body filler. Prime, block sand, and paint as required.
STANDARD PROCEDURE - HEAT STAKING
1. Remove trim panel.
2. Bend or move the trim panel components at the heat staked joints. Observe the heat staked locations and/or component seams for looseness.
3. Heat stake the components.
a. If the heat staked or component seam location is loose, hold the two components tightly together and using a soldering gun with a flat tip, melt the material securing the components together. Do not over heat the affected area, damage to the exterior of the trim panel may occur.
b. If the heat staked material is broken or missing, use a hot glue gun to apply new material to the area to be repaired. The panels that are being heat staked must be held together while the applying the glue. Once the new material is in place, it may be necessary to use a soldering gun to melt the newly applied material. Do not over heat the affected area, damage to the exterior of the trim panel may occur.
4. Allow the repaired area to cool and verify the repair.
5. Install trim panel.