Project on Weight Reduction

INTRODUCTION

In recent years it has become important for automobiles to satisfy many conflicting demands, as the demand for the automobiles increased, the engineers then stepped up their efforts to cut costs and look for processing methods that require fewer operations, less time and less materials. Due to this competition among automakers, engineers started making automobiles, which would increase power and performance, lower fuel consumption; lower polluted emission, decreased vibration and noise.So the need arose for the reduction in weight of the entire automobiles structure. Newer materials and alloys were used to reduce the weight. Also material substitution started taking place thus the concept of rationalizing the entire auto structure began with the addition of never materials to reduce weight came many more advantages.

Here in this seminar, I have tried to present how effectively the weight of an automobile can be reduced with increase in its efficiency, performance, etc.

NEED FOR WEIGHT REDUCTION

More weight implied more fuel consumption. This reduces the efficiency of the engine. Fuel economy is a thing of primary concern. Fuel (petrol/diesel) being a non-renewable source of energy, it is fast getting depleted or exhausted. Nevertheless its demand is increasing, ultimately its prices are touching the sky. Hence weight reduction becomes necessary to increase fuel efficiency and better the engine performance and reducing the costs also.bulkier the automobile, the less elegant it is in its 

Movement drive. Weight reduction enhances its performance i.e. mobility. The vehicle has a greater pick-up smooth drive, more speed less vibrations and less noise.In order to improve the fuel consumption of a vehicle, it is of general idea to improve consumption of a vehicle, it is of general idea to improve combustion efficiency to minimize aerodynamic drag and rolling resistance. Here reducing vehicle weight is much effective in minimizing the rolling resistance. Also it is becoming necessary to control exhaust gases fuel to increased public concern in these years.Thus considering all these advantages weight reduction is the in-thing in the automakers mind.

TYPES OF WEIGHT REDUCTION METHODS

From the automobile manufactures perspective, there are four basic approaches to weight reduction.

1.Material substitution.

2.Load reduction at the source.

3.Load averaging.

4.Load control.

With regard to materials substitution the objective involves replacing an existing material or component with one that its lighter overall but still capable of delivering the desired performance. Thus weight reduction can the achieved by using high strength lightweight alloys materials having high heat resistance and materials that provide highly effective sound insulation.

Load reduction can be achieved by reducing not only load but vibratory forces and heat emission as well. According to these principles, sound reduction at the source can reduce the amount or sound insulating material required or as another example the use of heat insulating glass could enable a reduction in the size of air conditioning units.

Weight reduction by load averaging results from optimizing structures and shapes and reducing excess materials. Load control or the high precision evaluation of load fluctuation enables weight reduction by using materials and structures at their performance limits.

WEIGHT REDUCTION METHOD

Various weight reduction technologies have been developed. Based upon the basic approaches to weight reduction outlined above. As depicted in the following fig., these technologies can be broadly categorized as design, materials and processes, each of which has close inseparable linkages with the others. The idea of reducing weight by rationalizing the arrangements of important parts in the car began the letter half of 1970 and is now widely improved. An example of this is the conversion of wheels from rear wheel drive to front wheel drive. At present approximately 70% of Japanese passenger cars use front wheel drive. The front wheel drive enable an approximately  4% weight reduction in the vehicle as well as space improvements. The concept of rationalizing the overall auto structure can be extended to individual parts as well by applying such techniques as integration, reduction, downsizing thinning and hollow structure design. For an example, the change of the Nissan Primera’s fuel tank steel to plastic enabled a weight reduction of approximately 30 % It is also possible to apply rationalization to fabrication.  

An example is a leaf spring for the front suspension of some models of the Nissan Vanette. Prior to 1985 the spring was made of multiple steel leaves. With the development of an industrial filament winding method, however if became possible to use a single piece glass fibre reinforced plastic which was then capable of accommodating tailored designs. The new leaf spring contributed to an approximately 70% weight reducing as well as improved ride for the vehicle. Another example of material substitution is the plastic outer body panel employed by the Nissan Be - 1. In addition to enabling a surface profile that is possible only with plastics an approximately 25 % reduction in weight was achieved. By substituting aluminum in the outer body panel and other part of three Nissan modes weight reduction of as much as 45 % were achieved which is far greater than reduction achieved with plastics.

THE STATUS OF WEIGHT REDUCTION

Prior to the turn of the century, the first automobiles were made primarily of wood and canvas. Soon however the changes were made to steel sheet and high-tension steel sheet has long since been applied. With the recent push towards weight reduction however steel has consequently become the subject of intense scrutiny. Even though steel sheet are now being used in variable thickness it no longer has exclusivity in a number of application, for example panels made of aluminum alloys and plastics are being used although the quantity is very small. In general the major advances in steel related weight reduction technologies might have already been made. Indeed it is possible to conclude that with regard to weight reduction most of the rationalization opportunities have been exploited as such the major area of innovation is materials substitution.

ROLE OF ALUMINIUM IN WEIGHT REDUCTION

Automotive applications of aluminum sheet are on the rise and are expected to accelerate throughout the decade. The metal’s low-density revocability fabricability gives it an edge over steel, plastics or copper depending on application. Demand fro aluminum automotive body sheet is projected to 

increases to 45000 tones annually by 1997 up from its current level of 10000 tones. Aluminum’s position with   respect to steel has been enhanced in recent years by the development of stronger alloys and also aluminum unlike plastics can be handles and formed using the existing plant infrastructure originally installed to process steel sheet. The aluminum heat exchanger market is larger and better established than body sheet aluminum continues to displace copper in radiators evaporators condensers and better heater cored and its share of these applications now exceeds 60 %.

Also wrought cast and forged aluminum sheets are used for wheels, which now account for 38 % of the market. Thus it has been said that aluminum is the material with the highest potential to impact automobile weight.

ROLE OF PLASTICS IN AUTOMOBILE

Plastics are now days extensively used as a major lot in the purpose of weight reduction. Plastics are contributing a lot in the purpose of weight reduction. New types of plastics are being developed which have excellent propertied useful in automobile industry. Fields in the use of plastics such as plastic gears piston rings casings of different parts, thermoplastics olefins, manifolds are now being shaped by plastics. There are also less costly and satisfy all the requirement such as temperature condition, smoother surfaces oil and grease resistance and can also be moulded to any shape.

Plastics are also used for the under hood application such as air filter housings radiator and tanks and cooling tanks. Some examples of plastics used in under-hood applications are Glass-Reinforced Nylon 6/6 and Hifax Series Thermoplastics.

THE CHANGING UNDERHOOD ENVIRONMENT

Higher corporate average fuel economy (CARE) requirement favor the substitution of lightweight component for traditional metal parts. Tougher emission standard foster the development of cleaner burning fuels, which can attack metals and other materials used to handle conventional gasoline. The corrosive potential of other automotive fluids-coolant, grease motor oil and brake fluid also must be considered in materials selection decisions.

Another important factor is a materials heat resistance. Underhood temperatures continue to rise at designers pack more hardware into as engine compartment that is shrinking due to styling trend such as sharply made hoods. In addition earlier weight reduction programme contributes to increased levels of noise vibration and harshness. Quarter running vehicles will rely at least in part on UTH components made of materials that demand engine noise and vibration.

SMC: -

Growth in the use glass fibre reinforced sheet moulding 

compound (SMC) and bulk moulding compound (BMC) materials based on vinyl ester resins is expected.

A glass fibre constant of 20 to 30 wt. Imparts adequate strength 

for a component such as valve corner.

SMC is a proven material for exterior body parts and is now 

being considered for value corners, oil pans and similar UTH component. Detroit Diesel and Cummins Engine are replacing car aluminum covers with SMC covers. Reported advantages of the switch include reduced valve train and other engine noise, elimination of machining via parts consolidation and improved seal integrity due to better dimensional stability weight and cost saving of 30 % and lower stricture borne noise levels are predicted by substitution SMC vinyl ester for aluminum in the oil pan for the engine German automakers also hope for a boost in engine performance i.e. oil should heat up faster because of the plastic’s lower thermal conductivity.

ROLE OF CERAMICS IN WEIGHT REDUCTION

Ceramic materials offer new and unique solution to engine design issues. They offer advantages of lower density, excellent wear resistance increased stiffness low thermal expansion and more high temperature capability over the traditionally used metals. The use of ceramic requires consideration of reliability defining specification for good wear resistance and controlling and reducing cost through optimization of the materials for the application.

LIGHT WEIGHT BENEFITS OF CERAMIC

Ceramic of high strength silicon nitride composition offer densities one half to one third that of the austenitic stainless and nickel alloys which are only suitable for moderate temperature application. This combination of low density with good high strength make ceramic ideal materials for light weight valves and valve train component, piston pins and piston crowns. The weight ceramic valve offers a good example of the benefits of weight reduction and the need for a systems approach. The valve weight for an example spark ignited engine can be reduced as shown in table.

Analysis indicates that the resultant weight decrease would allow the valve spiting opening load to be reduced from 500 N to 260 N while maintaining suitable valve gear  dynamics. For the system analyzed the opening spring load reduction would produce a resultant improvement in vehicle fuel economy of 0.8%. Not considered are the additional potential benefits of higher 

engine operating speed, more rapid valve opening and closing with their resultant higher power. Engine allowable speed could be increased because of the lighter weight if no change in the spring occurred. Camshaft stresses at the original engine speed will be reduced  approximate 20 % if the 260 N spring open load is viable. Also as the ceramic materials have low co-efficient of thermal 

expansion they can be used in engine construction.

USE OF METALS AND METAL ALLOYS IN WEIGHT REDUCTION

Automakers continue to effectively use metals to reduce the weight and improve the performance of auto engine. Although plastic are finding more applications in automobiles engines automakers rely on the use of metal products for several engine component such as engine blocks piston connecting rod and valve trains. This extensive use of metals provides opportunities for weight reduction and automakers who are seeking cost effective applications of light metals, metal-matrix composites and microalloyed steels in mass-produced engines.

IMPROVING POWER TO WEIGHT RATIOS

Proven methods to reduce weight in mass-produced autos include the use of aluminium and magnesium alloys as replacement for steel and cast iron. Magnesium castings are attractive candidates for engine applications because they are lightweight and have good strength and stiffness at both room and elevated temperatures. However they are not yet widely used by U. S. automakers in mass-produced engines. The average magnesium content of a U.S. built vehicle is about 1 Kg., with only a fraction of that being used in the engine.

Current engine applications include valve covers, cylinder head covers, intake manifolds, rocker arm covers, air intake adapters, induction systems and accessory drive brackets. In addition to magnesium’s low density, these applications may take advantage of the material’s high damping capacity and the thin wall capability of the magnesium die-casting process.

Aluminium alloys, on the other hand are widely used in high production engines because of their low density, corrosion resistance and good forming & casting characteristics.

A large weight reduction can be achieved by replacing cast iron 

engine blocks with either aluminium blocks having cast iron liners or liner less hypereutectic silicon-aluminium engine blocks.

Further weight reduction of engine blocks is possible by using reinforced aluminium metal matrix composite (MMC) liners. For Example, Honda Engg. Company Ltd., Japan has developed an aluminium block that incorporates cylinder liners made of alumina/ graphite short fibre reinforced aluminium. The block provides higher performance, is smaller and weighs less than either cast iron blocks or aluminium blocks with iron liners. The liner starts as a thin walled (2 mm., 0.08 in.) fibre perform, which undergoes a die casting process that allows aluminium to penetrate the fibre without causing damage to the perform.

The MMC liners are machinable, although the hardness of the 

alumina fibre requires the use of tooling having sufficient wear resistance, such as polycrystalline diamond cutting tool.

Other successful applications of aluminium MMC in automobile 

include drive shafts and pistons. In drive shafts, weight reduction is the primary benefit. A one-piece composite shaft, such as the graphite fibre, reinforced aluminium MMC also eliminates the need for a centre bearing.

ALTERNATE MATERIALS FOR WEIGHT REDUCTION

Material substitution is an effective approach for automotive 

engineers trying to reduce part weight. Consolidate parts, enhance efficiency and cut costs. Conventional materials have been replaced with aluminium matrix composites, thermoplastic composites, recycled resin, titanium and ductile iron.

ALUMINIUM COMPOSITES REPLACES CAST IRON

Engineers at Toyota replaced the cast iron hib of a crankshaft damper pulley with an aluminium matrix composite to reduce weight and engine vibrations. The pulley drives the alternator and power steering pump and acts to reduce torsional and bending vibrations of the crankshaft significantly.

One of the hub’s essential function is to maintain tension at the boss through which the hub is bolted to the crankshaft. Conventional aluminium alloys  deform plastically at the boss when the temperature rises because of thermal expansion difference between bolt and boss. They also deform because of creep after the bolt is tightened. However, when aluminium is reinforced with short aluminium fibres, it resists deformation and expands less when heated. To fabricate a composite hub and crankshaft pulley, fibre preforms were made by vacuum forming, then infiltrated with molten AL – S – MG alloy. Here weight was reduced by about 40% and crankshaft pulley weight was reduced by about 20%. These reductions allow the engine to rotate faster, enhancing engine performance.

ALUMINIUM COMPOSITE LINES CYLINDERS

Engine cylinder blocks cast entirely of iron were common until 

aluminium die cast blocks were introduced in the late 1970’s. However, the cylinders were typically linked with cast iron because aluminium has poor abrasion resistance and warps at cylinder temperatures. Although the aluminium block significantly reduces engine weight, the high-density iron liners hindered further improvements. To overcome aluminium lacks of wear and heat resistance in this application, Honda engineers developed an aluminium blocks with an integrally cost aluminium matrix  composite liner. The MMC layer consist of 12% alumina fibre and 95graphite fibre in an aluminium matrix and ranges from 1.5 to 2.5 mm. Thick depending on location.

Test shows composite wear depth is only one third that of the monolithic aluminium silicon alloy and is approximately equal to that of cast iron. Both scratch and seizure limits of the cylinder liners vs. the piston rings move upward as alumina fibre volume rises and they are pushed even higher when graphite fibre are added to alumina. However, total fibre volume has been set at 21% to facilitate finishing of the inner cylinder surface.

In addition to wear improvements, cooling efficiency is also improved. The temperature measured between the cylinder bores of a four cylinder engine operating under maximum load is approximate 10% lower than of cast iron liners. As a result of improved abrasion resistance and cooling 

performance, the block can be made smaller and engine can run faster. Overall weight is reduced by 50% compared with a cast iron block and by 20% compared with aluminium block having cast iron liners.

REPLACEMENT FOR BUMPER FASCIA

Conventional elastometer modified polypropelene (EMPP) has been a successful bumper fascia material because of its low co-efficient of thermal expansion (CIE), high impact resistance or toughness and paintability. However, attempts to cut the weight of large EMPP fascia by reducing material thickness have been accompanied by an unacceptable decrease in touchness. To overcome this problem, engineers at Toyota took a non-traditional approach to design EMPP materials and came up with “Super Olefin Polymer”. This new material has the thermal expansion characteristics, low  temp., impact resistance and portability of EMPP plus increased stiffness, which is required, for thin section parts, a higher melt flow rate or fluidity, which ensures high productivity in molding and high surface quality (rivaling that of sheet) in thin section and enhanced hardness, which makes fascia more resistant to scratching. Other reported advantages over conventional EMPP include a 11% total cost reduction and the ability to withstand 120 C paint baking cycles without deforming. In addition, the weight of a typical fascia is reduced by about 15% when super olefin polymer is substituted for conventional EMPP.

Recycling of the new material is said to be easy because all resin components are thermoplastic. And repeated recycling has no negative effect on low temperature impact resistance, stiffness, paintability or other properties and performance characteristics.

ALUMINIUM COMPOSITE BRAKE ROTORS 

Brake rotors made of aluminium matrix composites combine the low density of aluminium and wear resistance of ceramics. They weigh only about half as much as cast iron system, conduct heat three times more efficiently, and also reduce noise and vibration. The matrix alloy closely approximates the Al-Si casting alloy 359.0. the addition of 20% SiC particles greatly enhances wear resistance, increases thermal conductivity, raised room temperature strength & stiffness and improves high temperature strength in addition to its properties of weight reduction.

TITANIUM CONNECTING RODS BOOST POWER

An automobile engine’s connecting rods convert the reciprocating motion generated by combustion of the air/fuel mixture into high-speed rotary motion. Connecting rods must withstand high stresses and the surfaces that mate with pistons and crankshaft must resist wear at high surface pressures. For these reasons, connecting rods require usually high levels of strength, stiffness and wear resistance.

Connecting rods for production engines are generally made of medium carbon steel. Potential weight saving material for these parts include higher strength carbon steel and lower density materials such as titanium. Titanium alloys are particularly good candidate because they provide higher specific tensile and fatigue strengths than competing materials. Unfortunately, the alloys compare very unfavorably with other metals in terms of wear resistance (abrasion, seizing and scuffing, formability and machinability).

ADVANTAGES OF USING TITANIUM AS CONNECTING RODS 

Test data confirms that the new connecting rods offer better fatigue characteristics and an ample margin of strength when compared with parts made of medium carbon micro alloyed steel. The titanium parts weigh approximately 30% less than steel; connecting rods which translates into a weight saving of 1.2 kg. Lighter connecting rods reduce engine inertial force, which helps increase the seizure limit by thickening the oil film between crankshaft and connecting rod. The result, an increase provides a significant increase in output power. Use of the titanium parts also lowers engine vibrations and noise levels.

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ENGINE WEIGHT REDUCTION

It was found that by application of lightweight materials, the engine performance of weight-reduced engine could be improved. That is improvements in response and friction loss. In particular, weight reduction of the major moving components such as connecting rods not only contributes to reduce friction loss but leads to a weight reduction for other components.

Applying weight reduction measures to an engine is not so effective in improving fuel consumption of a vehicle because engine weight accounts for no more than 10-15% of the vehicle one. However, since reduced engine weight induces to decreased external loads to chassis components, such as engine mounting systems and base carrier components including suspension, and engine should be so designed as to reduce these weights as a whole. Therefore, reducing engine weights brings about a reduction in overall vehicle weight, which results in fuel consumption for the vehicle. As means for reducing weight, there are several methods available including substituting lightweight materials for conventional materials, that is to decrease specific gravities, rationalization of structure(decrease number of the parts through integration) and dominizing (decrease the volume of each part).

The engine weight could be reduced by 37 kg. From a base one of 162 kg. (excluding engine oil and coolant). This corresponds to 23% weight reduction. As shown in fig. 13, the components weight ratio of the materials are 53% steel for the weight reduced engine (86% in the base engine), 33%(13%), aluminium alloys 7% (1%) plastics and elastomers , 6% (0%) other light weight materials such as titanium alloys and magnesium alloy, and 1% (0%) ceramics.

CONCLUSION

With the help of this seminar, I hope, I have been able to show how much important it is to reduce the weights in an automobile. As newer technologies are coming up, newer metals or alloys are being invented which are light in weight. Also the reduction in weight also reduces the cost to some extent in most of the cases. Also aluminium, plastics, ceramics, MMC’s are being used in automobiles in large quantities than ever before. Now a day more and more cars can be seen on the road. I would like to end my seminar saying that this aspect of automobiles is very important for the future years.