To meet the demands of lightweight vehicle bodies, plastic parts are widely used in non-structural components such as body panels due to their light weight and corrosion resistance. This not only effectively reduces vehicle weight and fuel consumption but also lowers manufacturing costs. Furthermore, plastic materials themselves have excellent sound insulation, noise reduction, and vibration damping effects, effectively improving passenger comfort during driving.
1. Classification of Plastics
Plastics are generally classified into two main categories based on their thermal properties: thermosetting plastics and thermoplastic plastics. Thermosetting plastics can only be molded once; once cured, they do not soften upon heating. These plastics are not easily deformed under pressure and have good heat resistance, but their mechanical properties are relatively poor. Common thermosetting plastics include epoxy resins, phenolic resins, and amino resins. Thermoplastic plastics soften when heated and harden upon cooling, allowing for repeated heating and molding. These plastics are easy to process and have good mechanical properties, but their heat resistance is relatively poor, and they are prone to deformation. Common thermoplastic plastics include polyethylene (PE), polyvinyl chloride (PVC), and polypropylene (PP). Currently, domestically produced automotive front and rear bumpers are generally injection molded using toughened (modified) polypropylene (PP) as the raw material.
2. Plastic Bumpers
Automotive bumpers, primarily made of plastic, provide shock absorption and cushioning in low-speed collisions, protecting the vehicle's structural components from damage. Their deformation and energy absorption also significantly reduce injury to third parties. Furthermore, in vehicle design, bumpers also serve a decorative purpose, forming an important part of the exterior styling.
3. Repair of Cracked Front Bumpers
As a protruding part of the vehicle body, the bumper is frequently damaged in traffic accidents. Cracks are a common form of damage to bumpers. If not repaired promptly, these cracks not only affect the vehicle's overall appearance but may also continue to widen during vehicle use, seriously impacting driving safety.
Currently, auto repair shops typically prefer to replace damaged plastic bumpers. This approach mainly involves disassembling the original part and installing the new one, making the operation relatively simple, the repair difficult, and requiring minimal skill from the repair personnel. However, directly replacing minor bumper damage with new parts leads to significant resource waste, and the old plastic parts may end up in unlicensed recycling centers, which is both uneconomical and environmentally unfriendly. To promote green auto repair and build a resource-saving society, it is recommended that minor plastic parts, especially bumpers which are prone to damage, be repaired using damage repair methods. Therefore, fast and efficient bumper crack repair has significant economic and environmental value.
Before developing a bumper repair plan, the condition of the damaged part should be assessed. If the damage is severe and beyond repair, or if the repair cost is close to the cost of replacing the part, replacement is an option. If the damage is minor, the crack in the plastic part is small or there is only one crack, and the cost of replacing the part is too high, repair is more economical. The specific solution chosen depends on the extent of the bumper damage and the customer's preferences, determined by the repair personnel.
For cracked front bumpers of high-end cars, plastic welding repair technology can be used. By fusing stainless steel reinforcing mesh into the fracture, the repaired bumper can achieve higher strength at the fracture point while maintaining its vibration damping performance. The repair steps for cracked car bumpers are as follows:
(1) Inspect the location and extent of the crack.
(2) Drill a stop hole at the end of the crack to prevent further expansion.
(3) Use a single-action grinder with 80-grit sandpaper to sand the paint surface at the crack, removing the surface paint coating.
(4) After feathering the edges, create a slope on both sides of the crack to allow space for fusing the stainless steel reinforcing mesh into the plastic part.
(5) Cut the stainless steel reinforcing mesh to a size that covers the crack, folding the edges.