Role of localized heating on the workability of powder metallurgical Al–4% Ti components in cold compression

In the present work, localised heating has been adopted at the damage site of the cold upset materials and the role of this mechanism on the workability has been analysed. Cylindrical specimens containing 96% aluminium and 4% titanium were prepared through powder metallurgy technique with an aspect ratio (height to diameter) of 1 by suitable pressures. A series of cold upsetting test was conducted and the material properties for various preforms initial relative densities (80%, 85% and 90%) were determined under the stable strain rate. The flow of metals was analysed using a finite element tool and it was observed that the metal flow starts from near the centre zone to the equatorial zone and the damage happens in the outer position because of more amount of accumulated stresses and the pores. These stresses and pores decrease the workability of the final component. Hence, the present research is intended to reduce the stresses and minimize the pores by applying a localized heating (100 °C–250 °C) at the equatorial sites of the components and thereby increasing the workability of the material. Also, heating selectively at the equatorial site of the workpiece improves the workability due to change in grain size and it was noticed that the grain size of the developed porous preforms was high for the higher heating conditions due to the growth of the grains. Therefore, the localized heating adopted in this work is a superior method to enhance the workability of the powder samples and this novel technique could be useful in improving the workability of the structural components that have extensive applications in the automobile and aerospace industries.

A novel method to improve the critical damage parameter of powder metallurgical components during the cold upsetting

In the metal forming process, the understanding of metal flows and the fracture strains are most significant to the failure/damage of the components. Usually, in metalworking, damage occurs because of nucleation, growth and coalescence of the void into a small fracture. These small fractures increased in the circumferential path due to the existence of stresses and the pores which leads to failure at the equatorial position during the upsetting of porous samples. Hence, the fracture of the workpieces strongly depends on the stresses and the pores. Such form of stresses and pores if relieved will give a better damage limit of the material. Therefore, in this research, a novel scheme of localised heating is adopted at the equatorial position of the compressed samples to enhance the critical damage parameter. The powder metallurgy route was used to prepare the required compacts with different relative densities (80%–90%) and 1 aspect ratio by applying suitable powder forming pressures. The upsetting test was performed on the obtained porous samples for various weight percentages of titanium (2%–6%) in the aluminium at the stable strain rate (0.1 s−1) and the damage location was noticed for various components. After the identification of damage position, various temperatures (100 °C–250 °C) of localised heating were attempted on the failure site of the specimens after some incremental stages of upsetting tests. The experimental results were analysed using various damage criteria and it was found that the initiation of failure is delayed and increased the critical damage value by selectively heating the samples because of relieving the stresses, reduction in porosity and changes in microstructure.

IMPROVING THE MECHANICAL PROPERTIES OF Al-Cu-Mg-Mn ALLOY TUBES THROUGH PLASTIC DEFORMATION

The effect of plastic deformation upon the grain structure and mechanical properties of Al-Cu-Mg-Mn alloy tubes under upsetting was investigated. It was found that plastic deformation techniques such as cold upsetting can overcome the disadvantages of the cutting process, such as the anisotropy of the original material, no grain structure, and not high mechanical properties, while also improving the mechanical properties of the product in local plastic deformation zones by changing the grain and fiber structure of the material. This article presents the results of our research and evaluates the increase of material durability in the tubes’ deformation zones compared with the initial state. In this study Al-Cu-Mg-Mn alloy material had been cutting with turn machine and plastic deformation by upsetting. Microstructures and hardness variations of cut surfaces that are obtained with different processes have been investigated.

Understanding the process of making fuse contacts by upsetting of aluminium bars

This paper describes the results of a study that looked at an innovative wastefree process of cold upsetting to make power fuse contacts from the commercial aluminium grade AD1. The process involves upsetting and extrusion of a workpiece cut from steel bar stock in the same die in one process step. It is proposed to use this process instead of making each separate fuse contact part, i.e. when the fuse base and the knife are notched out of a steel bar and are then stamped together. The new process is less labour intensive due to less pieces of die tooling used, less equipment required, less personnel involved and due to a significantly higher metal utilization factor – 1 instead of 0.7. Solid models have been developed for the solid part of fuse contact and for the die tooling so that this process could be performed in a die. A procedure has been developed for making fuse contacts by cutting a steel bar in the die with a flat end punch followed by upsetting and extrusion of the workpiece. The dimensions of the primary blank and the forces acting at different process steps have been determined. The upper-bound method was applied to conduct a theoretical study of kinematic parameters and forces involved in the process. Physical and mathematical modelling helped establish how a steel bar changes its shape under upsetting and extrusion. Having analyzed the block models of the extrusion process with kinematically possible velocity fields, the authors identified what conditions lead to defect formation and offered some measures to prevent such defects. Force-geometry relationships have been defined. Experimental die tooling has been made and a prototype die – designed to implement this process in practice. A pilot batch of fuse contacts has been produced.

Application of software for determination of mechanical properties of metal materials under multi-transition deformation

The application of software for determining of the mechanical properties of metallic materials under conditions of multi-junction deformation is considered. The composition of the software and the tasks to be performed: the determination of the stress-strain state using software systems, the quantitative calculation of the structure parameters and the assessment of the mechanical properties of the material using the developed computer programs are clarified. Technological solutions for determining of the strain hardening of low-carbon steels during cold upsetting and the recrystallization process assessment of austenitic steel during free forging are presented.

Evaluation of the Mechanical Properties of Carbon Nanotube (CNT) Reinforced Aluminum (6061) Composites Using Closed Die Forging

In this study, the closed die forging of aluminium based compoistes reinfoced with CNTs (1vol% and 3vol%) were investigated. Initially, the composites were fabricated using high energy ball milling followed by compaction and sintering. The microstructural results showed that finer grain size and homogeneous dispersion of CNTs were obtained. Composites with up to 97% densification were produced when fine open porosities were removed by closed die forging. The results imply that the hardness and compressive strength of composites with 3vol.% of CNTs has improved without any deterioration. In addition, workability behaviors of composites were investigated by cold upsetting test. For that pore reopening test was performed to confirm the closure of micro-pores after the closed die forged, and to further analyze the densification of the composites. Typical cases, as the pores were not re-opened even after increasing the strain, additional forming is possible up to large deformations.

Determining Conditions for Thermoplastic Processing Guaranteeing Receipt of High-Quality Wire Rod for Cold Upsetting Using Numerical and Physical Modelling Methods

This paper presents the results of research with regard to determining the conditions of the thermoplastic processing of steel wire rod for cold upsetting, which ensures that a finished product with an even and fine-grained microstructure, without a clear banding and with increased cold deformability is obtained. The material used for the studies was 20MnB4 low carbon steel, and the studies were carried out on wire rod with a final diameter of 5.5 mm. Numerical modelling of the analysed process was carried out using commercial FORGE 2011® and QTSteel® programs, based on the finite element method. The GLEEBLE 3800® metallurgical process simulator was used for the physical modelling studies. The obtained theoretical and experimental results were then verified in industrial conditions. Based on the obtained results, it was found that the optimum strip temperature before deformation in the RSM finishing block of the rolling mill is about 850 °C. The best cooling variant after the deformation process was the one in which the cooling rate was 10 °C/s. Such parameters of thermoplastic processing ensure that a final product with a favourable complex of mechanical and technological properties as well as a fine-grained, even microstructure, lacking clear banding, is obtained.

Resource-saving preparation of the 38KHGNM steel surface for heading of automobile components

To produce high-quality fasteners for motor group components of automobiles it is necessary to follow the increased requirements to calibrated rolled stock in terms of surface defects. Therefore, the goal of this paper is to study the reasons, types and depth of the surface defects on the calibrated rolled stock from steel 38KHGNM Ø 12.0 mm on the basis of the metallographic analysis. Before cold upsetting, the hot-rolled products are subjected to metal flow and removal of unacceptable surface defects by means of expensive turning operation during which the screw cuts and cracks might appear. It has been defined, that the hot-rolled stock from steel, grade 38KHGNM, diameter 12.0 мм has nonuniform mechanical properties, grooves, laps and partial decarburization on the surface. The heat treatment of the rolled stock with a decarburized layer on the surface contributes to its further decarburization. Poor alignment of calibrated stock during its turning at the turning machine does not enable to completely remove the decarburized layer with minimum skinning of rolled stock. It has been shown that the use of rolled stock from steel 38KHGNM with surface defects and unreasonably high decarburized layer on the surface increases its rejection by 8% and raises the consumption of rolled stock for manufacturing of important fasteners for the motor group of automobiles.