In this thesis, experiments and simulations have been carried out on the multi-hole extrusion process. The effects of different process parameters on extrusion load and quality of the extruded products are studied. The parameters considered are extrusion ratio, lubrication, die land length, die pockets and vibration. A series of experiments have been carried out with different types of dies to observe extrusion load and product quality. For product quality, bending, hardness, tensile strength and surface finish of the extruded products are studied. It is observed that the die land length and lubrication influence the extrusion load, bending of the extruded products and mechanical properties as well as surface finish of the extruded products. A good qualitative agreement of experimental results with the finite element simulations using DEFORM 3D® is observed. A constrained multi-hole extrusion process is proposed, set up is developed and its performance is compared with the free multi- hole extrusion process. The constrained multi-hole extrusion process is found to produce straight and equal length extrudates. The developed process is suitable for small-length components. The major drawback of constrained extrusion process is that it consumes more power than the free extrusion process. However, when a multi-hole constrained extrusion process is compared with a single-hole free extrusion process, this fact gets undermined.
Multi-hole microextrusion process has been proposed and set up has been developed. Wax and lead alloy were extruded and products with average diameter of 350 µm have been produced. Billet length and ram speed influence the extrusion load. The die pockets are also found to be effective parameter in multi-hole
microextrusion. The hardness and tensile strength of the extruded lead products are also studied.
The conclusions of the thesis can be summarized as follows:
• In multi-hole extrusion process, ram force depends on different parameters such as the number of holes, die land length and lubrication. Ram force decreases with increase in number of holes.
The smaller die land length and lubrication reduce the ram force in multi-hole extrusion. Ram force increases with the increase in ram speed. The decrease in billet length also reduces the ram force as the friction at the billet-container interface decreases.
• Imposed vibration helps in reducing friction during extrusion process. Much difference in ram force was not observed in extrusion with lubricated dies as compared to unlubricated dies with imposed vibrations. Hence, the imposed vibrations can substitute lubrication and thus help in green manufacturing.
• The extrusion loads obtained from finite element simulations are found to be in good agreement with the extrusion loads obtained from the experiments. Simulations indicated about 15% reduction in ram force for dies having no die land length as compared to the dies with 10 mm die land length.
• From experiments and finite element simulations, it was observed that dies with larger die land length produce less curved products.
Peripheral holes produce less curved products than the centre hole.
Less curved products were obtained from the unlubricated dies than the lubricated ones.
• Extruded products obtained from the dies having larger die land lengths have better strength compared to the products obtained from the dies of smaller die land lengths. Higher extrusion ratio and die land length help to improve the mechanical properties of the extruded products. The ironing effect at the die land region helps in improving the mechanical properties of the extruded products.
Effect of extrusion ratio is less significant on hardness of the extruded products obtained from smaller die land length (3 mm) as compared to the products from larger die land length (10 mm).
• For both lead and aluminum extrusion, extrusion ratio, die land length and lubrication are found to be significant factors for surface finish of the extruded products. Low extrusion ratio and lubrication help in reducing the surface roughness of the extruded products.
• Die pockets in multi-hole extrusion help in balancing material flow and thus more uniform extruded product lengths are obtained. For a particular die design, the optimum die pocket depth exists for obtaining the least extrusion load. Simulations indicate that the effective strains are the maximum at the entry of the die land region and decrease with increase in pocket depth. The radii of curvature of the extruded products were found to decrease with increase in pocket depths.
• The constrained multi-hole extrusion proposed in this work produces equal lengths of the extruded products. The extruded products of constrained multi-hole extrusion have better mechanical properties than those obtained from the free extrusion. The increase in mechanical properties is due to more work hardening of the extruded products. The average ultimate tensile strength of the extruded products from constrained extrusion was about 14% greater than that of the products from free extrusion for 5-hole dies. In case of 9-hole dies, the average ultimate tensile strength of the extruded products from constrained extrusion was about 22% greater than that of the products from free extrusion. The constrained multi-hole extrusion consumes more power than the free extrusion. Still the improvement in geometric accuracy and mechanical property of the extruded products makes a strong case for the use of this process.
• In this thesis, the multi-hole microextrusion set up is developed. The average hole diameter of 350 µm are produced on 5-hole die. During
experiments with microextrusion set up, the difficulties encountered were considered in modifying the set up. It was observed that just scaling down of the set up is not enough for carrying out extrusion at micro level successfully. Wax and lead alloy were extruded. The increase in extrusion load was found with increase in ram speed. The reduced die land length produces low extrusion load.
• Significant differences in extruded product lengths of lead were observed. The friction factor at billet-container interface and at die land region was found to be most influencing factor. The extruded products length from centre hole is higher than that of peripheral holes. This is in contrast with macro extrusion.
• In multi-hole microextrusion, higher hardness value is observed with the peripheral products as compared to the products from centre hole in contrast to macro extrusion. The die land length also affects the hardness distribution in extruded products along radial and axial directions. Higher tensile strength is also observed with the products coming out from the peripheral holes as compared to the centre hole products.
• Removal of extruded products from the die land region was found to be a difficult task. Heating of the die was carried out to remove the lead metal from the die land region. This method is time consuming and the die quality deteriorates due to repeated heating. There is a need to develop a better method.