What Materials are Used for a Automobile Bumpers
Modern bumpers are made with a combination of materials. The first element is an impact absorbing spring device, usually gas-filled cartridges which mount the front bumper to the chassis. This allows the bumper system to absorb minor impacts without any damage.
The next part is the steel or aluminum support structure, which is a lateral beam.
On top of that is a honeycomb or egg-crate shaped plastic piece made of HDPE which defines the bumper's ultimate external shape and supports the shape of the bumper cover. On the rear, these can be attached to the car's other bodywork or components. In a more serious accident, this part of the bumper structure is usually the part that is damaged, but not visible.
Finally a urethane or other flexible polyethylene plastic bumper cover is applied to the outside to give the car a finished appearance. These are either charcoal or flat black, or they can painted to match the car finish. They are designed to be impact resistant and can take a hit with little or no damage.
Actually, bumpers in cars are meant for absorbing shock or impact at low velocity like accidentally hitting while reversing the car.
Now coming to the selection of material for making bumper, the material should have the capability to absorb the impact (i.e.) either nullify the effect or reduce the effect of the strike.
Lets consider metals as bumpers, metals transfer the load applied at one end to the other with negligible loss, so metals are not optimum material for bumpers. Lets consider plastics as bumpers, they have tendency to absorb load and reduce the effect of the impact also rubbers have the tendency to absorb and almost nullify the effect.
Looking into design and processing aspect, bumpers are big in size so they are processed by techniques like injection molding, blow molding and roto-molding. Considering the above processing techniques plastics are suitable material of choice.
Considering the above said processing methods, most commonly ABS, PC/ABS is injection molded and blow molded ABS are used in cars like Hyundai, Ford. When processed by roto-molding pulverized HDPE is processed easily and is used in making bumpers.
The cars from a few decades back used steel and aluminum and used springs or hydraulic units to provide both protection and cushioning allowing the bumper to absorb impact and remain relatively undamaged. In terms of styling and practicality, many manufacturers used rubber to absorb the impact and protect the chrome metal bumper. I much preferred this to the modern plastic covered styrofoam and aluminum. The new ones scuff, crack and chip from something as slight as a car hitting it while parking.
Here are the top 13 high performance plastics used in automotive hardware. While all 13 may easily be used in a single vehicle, just three types of plastic make up approximately 66% of the total high performance plastics used in a car: polypropylene (32%), polyurethane (17%) and PVC (16%).
1) Polypropylene (PP)
Polypropylene is a thermoplastic polymer used in a wide variety of applications. A saturated addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.
Application: automotive bumpers, chemical tanks, cable insulation, gas cans, carpet fibers.
2) Polyurethane (PUR)
Solid Polyurethane is an elastomeric material of exceptional physical properties including toughness, flexibility, and resistance to abrasion and temperature. Polyurethane has a broad hardness range, from eraser soft to bowling ball hard. Other polyurethane characteristics include extremely high flex-life, high load-bearing capacity and outstanding resistance to weather, ozone, radiation, oil, gasoline and most solvents.
Application: flexible foam seating, foam insulation panels, elastomeric wheels and tires, automotive suspension bushings, cushions, electrical potting compounds, hard plastic parts.
3) Poly-Vinyl-Chloride (PVC)
PVC has good flexibility, is flame retardant, and has good thermal stability, a high gloss, and low (to no) lead content. Polyvinyl chloride molding compounds can be extruded, injection molded, compression molded, calendered, and blow molded to form a huge variety of products, either rigid or flexible depending on the amount and type of plasticizers used.
Application: automobile instruments panels, sheathing of electrical cables, pipes, doors.
4) ABS
Acrylonitrile Butadiene Styrene is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance.
Application: automotive body parts, dashboards, wheel covers.
5) Polyamide (PA, Nylon 6/6, Nylon 6)
Nylon 6/6 is a general-purpose nylon that can be both molded and extruded. Nylon 6/6 has good mechanical properties and wear resistance. It is frequently used when a low cost, high mechanical strength, rigid and stable material is required. Nylon is highly water absorbent and will swell in watery environments.
Application: gears, bushes, cams, bearings, weather proof coatings.
6) Polystyrene (PS)
Naturally clear, polystyrene exhibits excellent chemical and electrical resistance. Special high gloss and high impact grades are widely available. This easy to manufacture plastic has poor resistance to UV light.
Application: equipment housings, buttons, car fittings, display bases.
7) Polyethylene (PE)
Polyethylene has high impact resistant, low density, and exhibits good toughness. It can be used in a wide variety of thermoplastics processing methods and is particularly useful where moisture resistance and low cost are required.
Application: car bodies (glass reinforced), electrical insulation.
8) POM (polyoxymethylene)
POM has excellent stiffness, rigidity, and yield strength. These properties are stable in low temperatures. POM also is highly chemical and fuel resistant.
Application: interior and exterior trims, fuel systems, small gears.
9) Polycarbonate (PC)
high performance plasticsAmorphous polycarbonate polymer offers a unique combination of stiffness, hardness and toughness. It exhibits excellent weathering, creep, impact, optical, electrical and thermal properties. Because of its extraordinary impact strength, it is the material for car bumpers, helmets of all kinds and bullet-proof glass substitutes.
Application: bumpers, headlamp lenses.
10) Acrylic (PMMA)
A transparent thermoplastic, PMMA is often used as a lightweight or shatter-resistant alternative to glass. It’s cheaper than PC but is also more prone to scratching and shattering.
Application: windows, displays, screens.
11) PBT (polybutylene terephthalate)
The thermoplastic PBT is used as an insulator in the electrical and electronics industries. It is highly chemical and heat resistant. Flame-retardant grades are available.
Application: door handles, bumpers, carburetor components.
12) Polyethylene Teraphthalate (PET)
PET is mostly used to create synthetic fibers and plastic bottles. You may recognize it on clothing labels under the name “polyester.”
Application: wiper arm and gear housings, headlamp retainer, engine cover, connector housings.
13) ASA (acrylonitrile styrene acrylate)
Similar to ABS, ASA has great toughness and rigidity, good chemical resistance and thermal stability, outstanding resistance to weather, aging and yellowing, and high gloss. Be careful not to burn this material. It will cause a toxic smoke.
Application: housings, profiles, interior parts and outdoor applications.
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