Processing of materials—monolithic to composites

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.