Processing of materials—monolithic to composites |
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Authors: | Anil K Gupta |
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Affiliation: | (1) Metals and Alloys Group, National Physical Laboratory, 110012 New Delhi, India |
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Abstract: | A multimillion rupee 500-ton hydraulic extrusion/forging facility established at NPL, New Delhi, has been used to undertake
extensive studies in forming, the process of plastically deforming, which is the most important way of shaping materials.
Wrought materials are used extensively for making useful products employing extrusion and forging, the two important secondary
processing techniques used to convert materials into useful shapes and sizes and also to improve the mechanical and metallurgical
properties. The success of these processes depends on the proper control and eventual optimization of different process variables.
Different ferrous and non-ferrous materials including 316 and 321 stainless steels (using glass lubrication), aluminium brass,
admiralty brass and 70/30 and 90/10 cupro nickels have been extruded at a lab-scale production level to determine the influence
of different extrusion variables such as temperature, strain rate, extrusion ratio, different die design and several different
compositions of lubricants on pressure requirement and surface quality of the products.
In the case of ferrous extrusions, the choice of billet-container lubricant has a marked effect on the shape of pressure-distance
curves by influencing the effective coefficient of friction and heat transfer coefficient. Temperature, extrusion ratio and
strain rate mainly influence the level of pressure-distance curves. Significance of specially designed dish shaped dies, avoiding
the dead metal zone and the importance of extrusion limit diagrams for different materials on the available press capacity
has also been highlighted.
Deformation behaviour of the hi-tech materials; discontinuously reinforced metal matrix composites (MMCs) and aluminium-lithium
alloys using hot extrusion and closed die forging, have been carried out. Parameters have been optimized to extrude rods and
thin walled circular MMC tubes of aluminium alloy (2124/6061)-SiCp MMCs having varying volume fractions of SiCp. This developmental
work has been carried out using powder metallurgy, liquid metallurgy and spray atomization and deposition routes, in joint
collaboration with several R & D organizations.
Hot extrusion being an important production technique, results of these experiments can be directly transferred to industries.
Similar deformation studies either by closed die or by isothermal forging have been made to develop components.
The pilot plant level facility is available for any industry for carrying out developmental R & D work. NPL welcomes such
collaboration. |
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Keywords: | Composites forming extrusion metal matrix composites aluminium-lithium alloy |
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