EMERGING WORK MATERIALS
Posted : August 27, 2004 at 4:15 pm [IST]
Traditional materials and processes are undergoing major changes. The challenge today is the competition. The new materials are coming up to provide manufacturing ease. Automobile manufacturers are searching for materials that will make vehicle lighter and thus make it more fuel- efficient. A 10% mass reduction yields a 6-8% increase in fuel economy.
Nodular iron casting (e.g. crankshaft, connecting rods, camshafts, knuckles, etc.) and powder compacting/ sintering (e.g. oil pump gears, crankshaft/ camshaft sprockets) are replacing steel forging. Nodular cast irons offer higher strength and toughness because of spherical inclusions of carbon in metal matrix. Gray cast irons are still widely used for engine blocks, brake disks, brake drums, and housings. The controlled foundry processes now produce these parts more accurately with very thin walls with significant reduction in overall weight and machining allowance.
Modified cast irons with high carbon content or inclusions of niobium carbides are being tried for parts such as brake disks to face the competition from alternate work-piece materials. Compacted cast irons with graphite shaped like coral provide higher toughness and are in use for parts such as cylinder blocks of diesel engines or other truck components. Compacted cast irons are also 30% lighter than gray irons.
Aluminum: A significant trend in automotive industry is the increasing use of aluminum alloys. Aluminum provides about 50% weight reduction over cast iron. Aluminum engine blocks, in one case, weigh 21.3kg, where a similar cast iron block would weigh 39.5kg.. The earlier disadvantages of aluminum castings such as higher scrap rates due to micro cracks and porosity have been overcome with new innovations in casting methods. Lost-foam process is one such process. Metal compression forming is another innovation, developed by Thompson Aluminum Casting (Cleveland, USA) to deal with porosity in aluminum castings. Metal compression forming process eliminates micro-cracking and cavitation problems, which earlier required forging. Aluminum also enables significantly extended tool life. As reported from Saturn study, tools on the machining line for aluminum parts last five to ten times longer than tools used for machining gray cast iron.
Aluminum Metal Matrix composites (MMC) are another new materials being developed for automotive application because of weight advantage. MMC also offer high yield strength, good ultimate strength, and excellent high temperature properties.
Magnesium will be the next to capture a larger number of applications in automotive manufacturing. Magnesium alloys offer a potential for significant weight reduction. For example, magnesium 380mm wheel rims weigh just 2.7 kg against 5.4kg rims in use. A new process called thixo-molding will eliminate much of the machining required now for components produced by die-casting.
Requirements of the aerospace industry have also made significant contribution in developing the next generation of work-piece materials. While weight reduction was always the issue, other factors such as corrosion resistance, high fatigue strength and temperature resistance also required attention. Heat resistant materials such as Inconel and other Ti-alloys are used for parts like rotors and disks. These material are difficult to machine. Manufacturing trends are to machine some parts from solid blocks instead of joining components. Example is the machining of the disk and blades of a turbine as an integral unit. Some airframe components are also being machined out of solid Ti-alloy blocks
Another very significant innovation is that of functional gradient materials that are composed of metals and other materials. The functional gradient approach also allows variations in concentration of alloys from point to point along the part to achieve specific properties, such as wear resistance or higher compression strengths required at different locations.
Industry will be increasingly switching over to exotic, composite, engineered, honeycomb, and sandwich materials to reduce weight, cost and manufacturing requirements. New materials under development will offer improved performance characteristics, such as greater wear, temperature, or corrosion resistance in specific applications.
- Indra
Category: Manufacturing |
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