Headlamp assemblies

The transportation market has used polyurethane adhesives for such diverse applications as bonding FRP and sheet molding composite (SMC) panels in truck and car applications, polycarbonate headlamp assemblies, door panels, and weatherstrip flocking. 

Instant-Fix Bonding of Headlamp Assemblies by Reactive Warm Melts... 

Headlamp assemblies (Figs. 95 and 96) made from different plastics can be bonded with a unique system consisting of plasma pre-treatment followed by application of a patented, warm melt adhesive using special adhesive pumping/delivery equipment. This section describes the advantages of this unique system over one or two-component conventional adhesives and butyl rubber containing hot melt sealants. 

Headlamp assemblies basically consist of two parts a transparent cover shield and body. The cover shield is generally made of polycarbonate (PC), which is scratch-protected by a hard coat e.g. by a UV-cured coating system. The body is generally polypropylene (PP) which is modified with fillers like talc. Headlamp... 

Figure 95 Automotive headlamp assembly, new BMW Limousine 5 series, produced at Hella KG Hueck Co.

Sealants or adhesives are traditionally used for producing headlamp assemblies. The most common techniques for bonding the two parts comprising the headlamp assembly are summarised below ... 

In-line production of headlamp assemblies is a very fast process. The principal targets for the bonding system are ... 

From the adhesives and sealants listed above, reactive warm melts (RWM) provide the best match to the manufacturers requirements for bonding headlamp assemblies. The unique headlamp bonding system consists of a plasma pretreatment of polypropylene and the use of reactive warm melt technology (Fig. 97). 

New system for bonding headlamp assemblies (Fig. 97). The new system for bonding headlamp assemblies is simple to install in manufacturing facilities and includes ... 

Complex reflectors within new vehicle headlamp assemblies typically must withstand temperatures of up to 400°F. Appropriate thermoplastic materials must be selected not only for the lamp backcan and lens, but also for the electronic/electrical connectors. Variations on filled polyester, poly(imides), bulk molding compound (a sheet molding compound [SMC] analogue), and nylon/poly(phenylene oxide) alloys are typically utilized in these applications. Poly(carbonate) (PC) or impact-modified PC is typically used in the lens applications where high heat is required. Acrylic plastics can and are most typically utilized in lens apphcations that do not require high heat, such as rear stop mount designs. 

The large volume applieations for moisture-euring polyurethanes are diseussed briefly in the applieations seetion below. These adhesive offer superior low temperature, high temperature, and speeifie adhesion performanee in comparison to conventional hot melts. These attributes have allowed them to excel in various product assembly applications, including structures such as windows, doors, furniture, and automotive headlamps and trim. Newer applications include bookbinding, fabric laminating, and assembly of athletic shoes. 

Automotive headlamp manufacturers usually heat-fuse glass to join lenses to reflectors and to seal assembly holes. Heat-curing epoxy adhesives provide some energy savings over the fusion process but still require long heating times and substantial capital investment. 

As with many mechanical systems, this process improved with each new machine that was built, and it is a good example of the benefit of close cooperation between the adhesive manufacturer, the equipment supplier, and the applicator. Another good example of automation is the application of paste epoxies to bond the lens to the reflector of halogen auto headlamps. The degree of automation is not quite as complete since most of these machines still use human operators to load and unload lenses on the adhesive application system. The primary objective in this case is to apply a very uniform bead of adhesive around the perimeter of the lens. In this process, a two-dimensional curve-following robot carries multiple extrusion nozzles around several lenses placed on a turntable. Lenses are then manually placed on the lamp reflector. The assembly is then carried on a chain conveyor into the curing oven. 

Plastic headlamp lenses have only recently become legal in Europe, and their use is now incorporated in ECE R20. However, plastic headlamp lenses have been legal in Japan for many years, and in the USA since 1979. The appropriate standard there is FMVSS 108, whose heat distortion and scratch requirements are met only by polycarbonate, with a silicone hard coating. A plastic lens only weighs half as much as glass the main incentives however are the lower assembly costs represented by plastics and the much greater design freedom, especially for flat low aspect ratio lenses, suitable for low-front aerodynamic bodies. 

BMC shapeability and low cost often make it the preferred plastics for headlamp and fog lamp reflectors. BMC reflectors provide a good fit with other components in the lighting assembly, good metallizing, and heat resistance to withstand headlamp bulb temperatures of392°F (200°C). 

Ninety percent of headlamp reflectors in North America are made from metallized BMC, and 10 percent from Ultem PEI for higher-priced cars such as the Ford Lincoln Town Car and BMW Series 3. BMC has dimensional stabihty, strength properties, and temperature resistance for this application, and it provides a good assembly fit. Temperature resistance is higher than 392°F (200°C). Improvements are made for BMC fog lamps and headlamps with base coatings and metaUization. ... 

Unsaturated polyester and vinyl ester SMC molded into radiator support assemblies are integrated with radiator front grill reinforcements and headlamp mountings. 

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