Materials Used in Body Panels - Essay Example

Materials Used in Body Panels Aluminum Over the of time, automobile manufacturers have used various materials in the manufacturing of body panels. Steel, aluminum, plastic, fiberglass, and composites have all been used. The reasons for the different materials vary from durability to cost. Of course, even these reasons vary from manufacturer to manufacturer, with some preferring the use of one material over the other. The use of aluminum for car and truck body panels is on the increase. What this means for the vehicle owner is the possibility of a longer wait for parts and uneven quality for those awaiting crash repairs because the number of trained technicians is not keeping up with the rising demands for the lightweight material. According to Tom McGee, CEO of Inter-industry Conference on Auto Collision Repair, the growth of aluminum will be a challenge. Because aluminum is a lighter material than steel, it is used by automakers to reduce the weight of the vehicle, and in turn improving fuel economy and performance. It is also used to add additional features without adding a great amount of weight to the vehicle. Within the industry, there is some disagreement over the safety of aluminum. Although the Audi A8 is considered one of the safest cars in a crash because of the design of its aluminum skeleton, Mercedes-Benz has a preference for high-strength in areas such as roof pillars and other critical areas. Even though the rest of the bodies of these luxury vehicles are made of aluminum, it is generally felt that strength rather than weight is of greater importance in these areas. All aluminum bodies are customarily found on high-priced cars, whereas aluminum hoods, fenders, and tailgates are more provincial to trucks because of their need in meeting targeted fuel economy. Aluminum also lightens the hoods of trucks and lift gates of sport utility vehicles, which makes them easier to handle. It is predicted that within the next five years, the extensive use of aluminum body panels will find their way into the economy vehicles as well. A major disadvantage of using aluminum at this point is the lack of enough technicians to handle the workload. More training is the solution to the problem, and though it does not require that much more time or expense to repair aluminum body panels, there still need to be qualified technicians to do it because it is different than repairing steel or plastic body panels. However, the difference is so great that many shops fail to tackle any serious aluminum repairs. In fact, there are only eleven shops in the USA and Canada who have certified technicians to repair damage to the Audi A8L and the A8 predecessor although there are an additional fourteen who are qualified to fix damage of a lesser degree. Repairing cars made of aluminum is a much longer process and more complex. Unlike repairing a vehicle made of steel, there is no coming back and cleaning it up if the work is not done correctly the first time. Bob Porazzo, an aluminum repair instructor at I-Car and a teacher at one of Boston's vocational schools says this increases the cost of aluminum to 15-20% over the cost of steel because of the cost of the products and the extra care that must be taken. Body shops need to have separate areas and tools that are exclusive to the repair of aluminum-bodied vehicles. The initial investment for the tools alone is approximately $10,000. If a separate area is not used, the potential of contamination from steel or dust from steel repairs exists, opening the doors for the corrosion of the aluminum. Composites Glass-mat-thermoplastics (GMT) has been around for a number of years though only thus far in the interiors of the vehicles. These materials consist of short-glass-fiber mat in different thermoplastic bas resins. So far, they have not gained popularity as exterior automotive components because of concerns with cosmetic, structural, and production. As a result, this has limited their appeal for widespread use. This line of thinking may soon change. GE Advanced Materials has been working on various ways to increase the use of these materials in automotive body panels as well as other large-part vehicles such as recreational vehicles. Recently in the United Kingdom, GE and BII Composites created a hood for a sports car from Azdel Superlite. This material is polypropylene-based with a glass content range of 42-55%. This composite hood went into production in 2004 with stringent Class A finish requirements by the old standard of polypropylene-friendly primer in addition to a coat of paint. Azel also produces the hoods with a thermoplastic composite that has about the same stiffness as steel without the weight. Since these GMT materials can be formed on lower pressure than steel, it also means a reduction in cost. "Low-pressure forming reduces the size and cost of processing equipment." And slashes tooling costs, explains Luca Saggese, a project engineer in GE's Large Part Group (Ogando Paragraph 2). GE's plans for the future include developing ways to use compression molded GMT along with a thermoformed skin that will be made from the company's SLX film. By doing this, the automotive body panels or other large parts would be able to offer a Class A finish without the use of paint. The target goal of this technology is not just vertical panels but horizontal panels as well. Of course, there is much work to be completed on materials and process development before this type of composite technology is ready for utilization. Before this type of materials system can be put into operation, a couple of problems must be resolved. The first problem involves the adhesion between the film and GMT layer. While paint tends to fail in a flaky and brittle manner, films tend to delaminate (Ogando Paragraph 6). Presently, it is not clear to what degree of strength the bond needs to be between film and other materials. New materials will probably help with adhesion, and although GMT has usually been based on polypropylene, grades based on polycarbons, PBT and combinations of both of these materials are in various stages of development. Not only do these other resins boost the structural properties beyond those of polypropylene based GMT, they also provide a diffusion bond with the SLX resin that is used in the film. Another aspect to note in the use of the new material and process is that it has the capability of becoming a close match to a Class A paint finish. On the down side, it can easily develop defects as it goes through the process. The key to avoiding this is to maintain the surface throughout the entire process. One part of the trick to this is the use of sophisticated thermoforming, but unfortunately, not all thermoforming houses have the kind of machines that are capable of making cosmetic skins that are adhere to automotive standards. Steel Armed with the knowledge that smaller is lighter, design engineers responded in the beginning by downsizing vehicles. As the weight-saving strategies began to reach their limitations, they turned they turned their attention to the development of more low density materials such as plastic and aluminum for use in steel cars. This substitution of materials was first used on interior parts such as instrument panels, now made almost exclusively of plastic. Engine blocks fabricated from aluminum instead of heavy cast iron are on the increase, especially in higher performance cars. This technology results in an increase in nonferrous materials usage of 100% since 1975. During that period, iron and steel decline from being about three quarters of a car's total weight to about two-thirds. Part of the decreasing use of iron and steel can be explained by the use of wider use of higher-strength steels that are able to perform the very same functions while using less metal. These iron alloys have yield strengths in excess of 40,000 pounds per square inch and now account for about one-fifth of the entire ferrous content of new cars. As a result, their use is steadily on the increase. Because of these weight reduction efforts over the past 30 years, the average passenger car now weighs 1,000 pounds less, and the average gas mileage has increased from 14 to 28 miles per gallon. The job is nowhere near be completed, though, and it is expected that federal requirements regarding fuel economy will become more stringent as will the competition for fuel economy. Metallurgical engineers are working diligently to either develop or refine higher performance steel as well as ensuring that the physical attributes of certain steel grades remain consistent in each batch produced. Manufacturing engineers, on the other hand, are looking for economical and effective processing methods while auto-structure engineers are looking into developing new high-efficiency structural concepts. Sheet steel is still the material that is preferred despite all attempts to find efficient alternatives for car bodies today and in the near future. The man reason for this preference is that it is the most cost-effective material available to perform the job. Sheet steel costs about thirty-three cents per pound where aluminum cost about $1.50 per pound. The formability of steel, especially in sheet form, as well as its strength, durability, and crashworthiness have been shown many times. With all the facts in front of us, it's difficult to see how the situation will change any time in the near future. It is believed that unless some significant change in the regulatory industry or something exceptionally innovative is introduced, steel cars are going to be around for a long time to come. Dual-phase steels feature yield strengths from 75,000 to 150,000 pounds per square inch. Alloying iron with magnesium and silicon with a special processing to follow typically produces these dual-phase steels. The bad part is that there is a lot of alloy in these particular grades, which makes them more costly and harder to weld and zinc-coat in order to reduce corrosion. Thus far, dual-phase steels have been used on a limited basis in commercial applications. Steel grades with even higher strength levels (up to 215,000 pounds per square inch) are available, but because of their limited formability, their commercial use is slow. Their hardness and brittleness requires special processing methods to be used. When designing these steel components, it is for the purpose of either strength or stiffness. The purpose of designing for strength is in order to handle crash loads. Higher strength steels are used in more crash-sensitive areas such as impact beams, bumper bars, rockers, and B-pillar reinforcements. Recently the focus has placed more focus on stiffness for an improved ride, vibration, and harshness quality. A trend toward making efficient structural parts with tube-hydro forming processing is another area being investigated for the cost-savings effort. This process involves manufacturing complex shapes in tubular components, which leads to a consolidation of parts, eliminates the need for weld flanges, and reduces weight. Several new vehicles incorporate these type of parts, with the most notable of these being the HSS sub frame of the new Chevrolet Corvette. Other uses of this process include the instrument panel beam in new Chrysler minivans and the radiator encloses on the Dodge Dakota. Engineers feel it is also useful for fabricating engine cradles, lower and upper longitudinal body rails, steering-column energy=absorption bellows, D-pillars for station wagons, and much more. Industry leaders believe that hydro-formed tubing will be included in every vehicle within the next five to ten years. Tailor-welded blanks is another emerging technology in United States car manufacturing that has potential to reduce cost and improve performance on a high scale level. Tailor-welded blanks are patchworks of sheet metal with different gauges of thickness, strengths, or coatings. Processing enables engineers to tailor the blank so that the best attributes of each material are located exactly where they are needed. This also allows car manufacturers to put thickness and strength where it is needed, thus optimizing the amount of steel that is used. This process has been used in Europe for many years. With steel being the primary structural material for today's cars, the steel industry is working hard to assure its continued use. There is currently a steel-industry effort to develop a low-mass steel car with a unibody type steel structure but stiffer and cheaper than traditional body structures that weight 25% more. In conclusion, it comes down to cost vs. efficiency. Each component has both advantages and disadvantages, but in terms of durability, many still prefer steel for the more crash-prone areas. On the other hand, looking at the price of fuel today, and the fact that a heavier vehicle is going to have a lower fuel economy, how does one incorporate both of these into one automobile Overcoming the question about weight vs. durability is a question that needs to be answered in today's market of rising gasoline prices as well as a high percentage of accidents. The future will be the key element in showing us the most efficient and safe material to use for body panels. BIBLIOGRAPHY http://www.usatoday.com/money/autos/2003-07-01-aluminum_x.htm, "Not All Cars Are Made of Steel," James R. Healey, July 1, 2003 http://www.designnews.com/article/CA382694.html, "Composite Body Panels, Hold the Paint," Joseph Ogando, February 26, 2004 http://www.memagazine.org/backissues/february97/features/steelcar/steelcar.html, "Steel Cars Face a Weighty Decision," Steven Ashley Read More