Kadla Ni Jod Cast

[Jordan Tucker]

Statementvintage silver kadla anklet that can also be worn as a kada. Crafted by skilful artisans with a heavy silver round cast, the ends are hand beaten for the tapered effect. Beautiful piece from Gujarat, that bring back memories and stories of that time.

The global automotive industry is facing challenges in several key areas, including energy, emissions, safety, and affordability. Lightweighting is one of the key strategies used to address these challenges. Maximizing the weight reduction (i.e., minimizing vehicle weight) requires a systems-engineering design optimization and iteration process that combines material properties and manufacturing processes to meet product requirements at the lowest mass and/or cost. Advanced high-strength steels, aluminum and magnesium alloys, and carbon-fiber-reinforced polymers have emerged as important materials for automotive lightweighting. This article presents examples of how coupling materials science with innovative manufacturing processes can provide lightweight solutions in automotive engineering.

The machines that move people and goods on land, sea, and air have undergone major changes over the past 50 years, and the key enabler for the improvements has been the development of new materials and their associated manufacturing processes. Covering the broad nature of the materials and subsystems in the various transportation modes is well beyond the scope of this article. Therefore, we concentrate on automobiles, which, on an annual basis, consume the majority of the materials measured in both weight and cost used during the manufacturing of transportation machines.

The dramatic growth in vehicles operated around the world has presented societal sustainability challenges, including safety, congestion, tailpipe emissions, and petroleum consumption. 5 Fuel economy has emerged as a particular concern. The focus on fuel economy first surfaced when the Organization of Petroleum Exporting Countries oil crises of 1973 and 1979 drove oil and gasoline prices sharply higher. The continued volatility of oil prices, coupled with concerns surrounding CO2 emissions from the burning of fossil fuels, has made fuel economy one of the greatest challenges facing the transportation sector.

The substantial improvement in power density is even more impressive when one considers that smog-forming emissions (hydrocarbons and nitrogen oxides) have been reduced by more than 99% at the same time. 5 Although the progress in improving the internal-combustion engine has been impressive, the largest energy loss in an operating vehicle is from the combustion process in the engine (see Figure 1). The benchmark performance in thermal efficiency is above 30% for gasoline engines and 40% for diesels, with approaches defined to achieve an additional 5%. 6 Improvements in efficiency beyond that level can be achieved through the introduction of partially electrified hybrids and fully electric vehicles. The materials community is being challenged to deliver improvements in all of the main components of vehicle electrification, including batteries, fuel cells, motors, and power electronics.

Typical vehicle-level energy utilization in a compact sedan with a four-cylinder engine and automatic transmission based on the US Federal Test Procedure (composite city/highway drive cycle). The circled areas show that the energy loss is highest in the engine and also that reducing vehicle mass could provide potential benefits. Figure courtesy of General Motors.

To optimize the use of advanced materials, it is not sufficient to reduce the weight of a particular component; rather, a complete systems-engineering approach is required. Therefore, it is not surprising that the greatest weight reductions have been obtained in clean-sheet designs. Table I lists the weight reductions that can be obtained by substituting advanced lightweight materials for the baseline low-carbon steel that dominated vehicle material usage for over a century. Also reported are the percentage increases in cost associated with the material substitutions. In the following sections, we review examples of how materials scientists and engineers work collaboratively to first develop new alloys and then invent new manufacturing processes to achieve these weight reductions at the cost required to maintain the affordability of the automobile.

Current commercially applied advanced high-strength steels evolved from significant early work on DP steels in the late 1970s and early 1980s at General Motors (GM). Figure 3, a classic figure from the work of Rashid and Rao, 17 shows the effects on the mechanical properties of a conventional HSLA steel of intercritical annealing (where the metal is heated to between its lower and upper critical temperatures to allow partial transformation of the matrix into austenite) followed by quenching. The data shown are for a plain-carbon steel, an HSLA steel (SAE 980X), and the same HSLA steel after intercritical annealing and quenching to produce a DP steel (referred to as GM 980X). In contrast to the HSLA steel, the DP steel exhibits continuous yielding and a significant increase in elongation with essentially the same ultimate tensile strength.

In addition to DP steels, AHSS grades that are currently being applied or are under increased investigation by steel suppliers, include CP and TRIP steels. These three steel grades are referred to as first-generation AHSS. The austenitic stainless steels, TWIP steels, lightweight steels with induced plasticity, and shear-band-strengthened steels are referred to as second-generation AHSS. An overview of representative tensile properties, compared to those exhibited by conventional steel grades, is shown in Figure 4 22,23 The first-generation AHSS concepts were developed in fairly dilute compositions and are primarily ferritic-based multiphase microstructures. DP steels are currently the most applied AHSS grades in the automotive industry. Interest in DP steels results from improved strength and formability, good weldability, relative ease of processing, and availability. 24

Enhanced-strength/enhanced-elongation combinations are clearly obtained for TRIP steel grades, where strain-induced transformation of retained austenite into martensite results in increased strain hardening. The second-generation advanced high-strength steels clearly exhibit superior mechanical properties, but these austenitic grades are highly alloyed, resulting in a significant cost increase. In addition, industrial processing of these alloys, specifically the TWIP steels with high manganese contents, has proven to be extremely challenging, and the TWIP grades have also been shown to be prone to delayed cracking. 25

Recent research indicates that the embrittlement susceptibility can be reduced by aluminum alloying, although the exact mechanism involved is still under investigation. 25 From Figure 4, it is clear that a property gap exists between the currently available AHSS grades of the first and second generations and defines a property band for future third-generation AHSS. Current research is hence focused on filling this property window using modified or novel processing routes where special attention should naturally also be given to industrial feasibility and cost effectiveness. 14,15,26

In addition to the increasing penetration of AHSS, the use of light metals (aluminum and magnesium) in the automobile industry has increased significantly over the past 20 years and is poised for further growth given the increasing emphasis on vehicle fuel economy.

Originating from the early work of Kaufman and Bernstein, 27 the CALPHAD (calculation of phase diagrams) approach, 28,29 based on computational thermodynamics, has matured over the past few decades to calculate phase diagrams and predict phase equilibrium for complex multicomponent systems. Many commercial software packages, such as Thermo-Calc, 30 FactSage, 31 and Pandat, 32 have become important tools in the development of new materials and products.

The solidification paths of the AE42 and AE44 alloys calculated using the Scheil model, 38 based on the assumption of complete mixing in the liquid but no diffusion in the solid, are superimposed on the phase diagram shown in Figure 5. Based on the simulation results, the solidification sequence for both alloys is as follows:

Utilizing the new materials developed by materials researchers in vehicles requires the parallel development of new manufacturing processes that are robust in terms of quality and capable of global production at scales on the order of millions of units per year. As in the aerospace sector, the structural components are critical for safety, but automobiles also need to be designed to be reliable without inspection for over a decade. This section provides some examples of how lightweight materials, when combined with innovative manufacturing processes, can provide lightweight solutions in automotive chassis and body structures.

Lightweight and efficient chassis structures are very important for several key performance attributes, including ride, handling, and noise and vibration control. Over the past 50 years, new aluminum and magnesium alloys and their manufacturing technologies have enabled reduced mass and improved performance and productivity of automotive chassis structures such as the front engine as an example. 5

With the introduction of lightweight materials, there are always new or improved manufacturing processes to enable applications of these materials. GM introduced the first all-wrought-aluminum cradle in the 1999 Chevy Impala. It consisted of 15 extruded sections and two stampings and weighed 18 kg; in comparison, a typical steel-sheet construction has about 48 parts and weighs 28 kg. Advanced robotic aluminum welding technology, namely, pulsed-gas metal arc welding, was used to join the complex extrusions, and this occurred along a welding line of 40 robotic welders in four welding stations. 40

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