Dead Metal Zone Research Articles

Design and analysis of streamlined extrusion die for round to hexagon using area mapping technique, upper bound technique and finite element method

Extrusion is one of the most important metal forming process commonly used for the manufacturing of the hexagonal rods. Extrusion of metal through a conventional shear faced die experiences few practical limitations such as dead metal zone, more redundant work etc. Most of the research works have proved that the streamlined die used for extrusion is more efficient than the conventional shear faced die. Design of streamlined die using arbitrarily shaped curves and conventional curves have been done by many researchers. In this study, a new approach of transforming the peripheral point on the surface of round to corresponding point on the extruded hexagon has been obtained by an analytical method. Further the prediction of force required to extrude, the development of stresses and strain have been solved with a combined approach of upper bound theorem and finite element technique by considering the profile as cosine curve. Later the experimental study has been conducted for validating these approaches to register the benefit of cosine profile.

Non-symmetric Hollow Extrusion of High Strength 7075 Aluminum Alloy

A hollow extrusion process by varying pocket geometry in welding chamber and bearing length to obtain a uniform material flow is studied. Finite element analysis and Taguchi method are used to obtain a better porthole type extrusion die design. The research results show that the billet has the best uniform material flow and minimum dead metal zone in Double arc type, and the ramp load shows that R of 40mm is smaller than 45mm. In addition, unequal bearing length makes metal flow more uniform. Finally, extrusion die with port-hole die structure has been manufactured and a successful extruding process has been conducted which proves the better design using the double arc pocket and unequal bearing length.

Grain size and workpiece dimension effects on material flow in an open-die micro-forging/extrusion process

The interactive effect of grain size and specimen dimensions on the material flow and microstructural evolution was studied in a progressive open-die microforming process. Particular interest was paid on the effect of the number of grains over the initial specimen thickness, on the evolution of the dead metal zone (DMZ) in the final micro-component's microstructure. Such a DMZ is deemed unfavorable for mechanical properties of the pin. Interestingly, experimental results revealed that the DMZ can be removed at the pin surface by increasing the initial grain size. This behavior was attributed to the role of the strain gradient on the deformation. In the aspects of the forming load and dimensional measurements of the final parts, there were no significant size-effects observed in this process. This is because the neutral plane, which demarcates the two directions of material flow in the open-die forging/extrusion process, determines the amount of material flow towards the die orifice, regardless of the initial grain size.

Experimental and Finite-Element Method Study of Zn-22Al Alloy Pipe Hot Extrusion Using a Porthole Die

To reduce the pollution caused by lead alloys, environmentally friendly alloys are selected to fabricate metal tubes for delay detonators. Zn-22Al alloy was selected in this study as the tube metal because of its high environmental friendliness and low cost. The first step in metal tube production is to prepare a pipe. In this study, the Zn-22Al alloy was hot extruded using a porthole die. A finite-element method (FEM) was used to optimize the porthole-die extrusion of the Zn-22Al alloy pipes. The flow stress data for the alloy in the temperature range of 200-350 °C and strain rate range of 0.1-10 s−1 were measured. The FEM results showed that two stages existed for any random position of the interface during porthole die extrusion, viz., the bonded interface-forming period, and the post-bonded period. The dead-metal zones existed at the corners between the container and die face and between the bottom and sidewall of the welding chamber. The effects of the extrusion temperature and the chamber height of the die on the welding quality index were studied. Pipes with an outer diameter of 18 mm and an inner diameter of 10 mm were fabricated successfully by the hot-extrusion method at 200 °C using a porthole die with a chamber height of 15 mm.

Metallographic Analysis of the Dead Metal Zone In Metal Cutting With a Rounded-Edge Tool

Abstract The experimental results show that a small dead region is seen in front of the rake face during cutting with a rounded-edge cutting tool. Although this fact was accepted, metallographic analysis of the dead metal zone had never been conducted. A quick stop device was used to obtain chip root samples that are representative of the deformation taking place during dynamic (actual) cutting conditions. A metallographic analysis was performed on selected specimens to identify the microstructure and formation. The photomicrographs were analyzed and an effort made to explain the dead metal zone microstructure.

Room temperature equal-channel angular pressing of a magnesium alloy

Equal-channel angular pressing (ECAP) of magnesium alloy Mg–3Al–1Zn (wt.%) has been carried out at room temperature by applying a back-pressure three times larger than the yield stress in a 90° die. In a single pass, the initial grain size of ∼10μm originating from twin-roll casting was reduced down to ∼3μm. {101¯2} tensile twins were observed by orientation imaging up to ∼40% volume fraction in grains that remained relatively high after ECAP. Regions with small grain size did not show twinning. The small lattice curvatures indicated that dynamic recovery/recrystallization took place during testing. The 90° ECAP deformation field was approximated by two-stage simple shear due to a large dead metal zone appearing at the outer corner of the die. Using this strain path, the viscoplastic self-consistent (VPSC) model was employed to model the texture evolution in the version where a parameter (α) tunes the interaction equation between a grain and the homogeneous equivalent medium. The textures were reproduced in good accord with experiments only if the α parameter corresponded to the Tangent VPSC model. Twinning was simulated in a quantitative way by introducing the volume transfer scheme in the VPSC model without employing a criterion for selection of the six possible twin variants.

Design of a computer aided quick-stop device for study of dead metal zone formation

The use of quick-stop device allows observing a sequence of frozen images focused on the chip formation area when machining in orthogonal turning tests. This work records the development of a quick-stop device employing a servo motor. The present invention relates generally to a quick stop device, for combination with a cutting machine that is able to abruptly interrupt the cutting process between a cutting tool and the surface being cut. A dead metal zone is clearly seen when using rounded-edge cutting tools. In this study, variation of the dead metal zone is examined with the computer aided quick-stop device (CAQSD). It is clear from the experimental photomicrographs that as the cutting edge radius increases, dead metal zone increases.

Using contrast material techniques to determine metal flow in screw extrusion of aluminium

Screw extrusion is a new continuous solid state processing method for aluminium. In this process, small pieces of aluminium are continuously inserted into a container wherein a rotating screw pushes the material forward. The material is heated, consolidated and extruded through a die in front of the end of the screw in one single continuous process. Understanding the material flow and the pressure generating mechanism is vital for optimizing screw, container and die designs, thereby increasing capacity, material quality and process stability. Full scale experiments using a prototype extruder were chosen as the means of investigation. In this paper, it is reported on the development of a novel contrast material technique to visualize material flow in the screw channels and the extrusion chamber. Extrusion of Ø 10mm aluminium profiles was performed using both single and double flight screws. The experimental technique provided a means for evaluating the frictional conditions between the aluminium and the surface of the extruder. Different feeding schemes were used to identify regions of high material flow rate together with dead metal zones in the screw channels and in the extrusion chamber. It is demonstrated how newly fed material interacts with and displaces material already present and how the screw pushes material into the extrusion chamber. The instantaneous extrusion velocity was measured and significant variations were detected for all feed rates. An explanatory model of the extrusion pressure generating mechanism in the extrusion chamber and the screw channel is presented linking the material flow and the consolidation process to the extrusion velocity variations.

Slip-line metal cutting model with negative rake angle

A small dead region is seen in front of the rake face of the tool during cutting with negative rake. The lack of knowledge about the stagnant region in the cutting with negative rake requires researching new models. In this work, cutting mechanism of the metal cutting with negative rake angle tools and the stagnation zone formation were studied. A model was generated from the experimental work by usage of the Dewhurst and Collins' matrix technique for solving the slip-line problem numerically. This model was applied at negative rake angles from 0o to -70o. All slip line angles in the slip line model that consist of three regions were resolved with the help of the experimental data. Variation of the dead metal zone and slip line regions with negative rake angle was determined. Effects of the negative rake angle on the cutting and thrust forces were investigated according to the cutting speed.

The dead metal zone in high-pressure torsion

Plastic deformation behavior during high-pressure torsion (HPT) was analyzed by the finite element method in order to investigate heterogeneous deformation in HPT-processed disks. The effective strain and strain rate developed increase from the center to the edge of the HPT-processed disk; however, they decrease to zero at the surface corner of the disk due to the vertical wall constraint under high pressure, resulting in a stagnant region termed the “dead metal zone”.

A Slip-Line Approach to the Micro-Cutting Process with a Rounded-Edge Tool

The effect of tool edge roundness attracts growing attention due to increasing applications of precision, micro-and nanomachining technologies. A new slip-line model and its associated hodograph are proposed for cutting with a rounded-edge tool in this paper. New model considers stagnant metal region called as dead metal zone formed in front of the rake face of tool during cutting process. Dewhurst and Collinss [ matrix technique for numerically solving the slip-line problem is employed in the mathematical formulation of the new model. The unknown slip-line angles were solved depending on the force data obtained from experiments and variation of the sub-regions with cutting edge radius was determined.

A Slip-Line Approach to the Micro-Cutting Process with a Rounded-Edge Tool

The effect of tool edge roundness attracts growing attention due to increasing applications of precision, micro-and nanomachining technologies. A new slip-line model and its associated hodograph are proposed for cutting with a rounded-edge tool in this paper. New model considers stagnant metal region called as dead metal zone formed in front of the rake face of tool during cutting process. Dewhurst and Collinss [ matrix technique for numerically solving the slip-line problem is employed in the mathematical formulation of the new model. The unknown slip-line angles were solved depending on the force data obtained from experiments and variation of the sub-regions with cutting edge radius was determined.

Effect of Strain Rate on Metal Flow Pattern in T-Section Extrusion Process

Extrusion is a deformation process used in metal sections fabrication. Metal flow pattern during extrusion process is of great importance. How circular initial section of billet changes to final section provides more details of extrusion process, and plays an important role in optimizing the extrusion energy. Extrusion in flat-faced die, without intermediate section, needs much more energy than is required for die having intermediate section. The aim of this study was to investigate the effect of strain rate on metal flow pattern in T-section extrusion process. Four different ram speeds were applied to realize how the shape and position of intermediate section would be affected. Flat-faced die with “T” final section was designed and manufactured. Straight layout of metal was of top concern in die design. Commercial purity aluminum, Al 99.5, was extruded in flat-faced die in hot condition. Graphite was used as lubricant in deformation process. After partial extrusion of billets, the residual part of billets pounced out of container and then mounted for metallographic tests. This part of billets consisted of dead-metal zone and deformation zone. Then, step-by-step decreasing of specimen height followed by macro-etching of metal surface paved the way for determining the metal flow pattern. An egg-shaped intermediate section appeared between initial round section and final “T” section. The size and position of the intermediate section changed by varying the strain rate of extrusion process; It was also revealed that as the strain rate of extrusion process is increased, the dead-metal zones become narrower and the dead-metal zone semi angle increases.

Experimental and Numerical Investigations on Metal Flow during Direct Extrusion of EN AW-6082

In extrusion processes metal flow has an important influence on the microstructure and the mechanical properties of the extrudates. Thus, a deep knowledge about the metal flow during the forming process is required as basis for further computations of the microstructure evolution. In this study experimental and numerical investigations on the influence of friction on the metal flow in extrusion processes were carried out using visioplastic methods and finite element method (FEA). The objective was to determine the influence of ram speed, ram displacement and billet temperature on the material flow during extrusion of the aluminum alloy AlMgSi1 (EN AW-6082). For this purpose the forming stroke was varied at constant temperature so that a butt length of 100 mm and 150 mm could be produced. Further the influence of different ram speeds at 4.22 mm/s, 6.33 mm/s and 8.44 mm/s was investigated. In order to identify the metal flow and in special the shear zone as well as the dead metal zone, the billets of 250 mm length and a diameter of 140 mm were prepared with round aluminum indicator pins with a diameter of 4 mm which were placed in the plane of symmetry of the billet. For the experimental investigations a compact direct extrusion press with a nominal force of 10 MN (SMS Eumuco) was used. The numerical simulations were carried out using the commercial FEA system simufact.forming 8.1. After extrusion the billets were cut in the plane containing the indicator pins and the surface was polished and etched. The visioplastically determined flow lines and calculated strains were compared with computed flow lines in order to verify the results and to parameterize the simulation. Tresca’s friction model was used in the simulations to describe the frictional conditions between the billet and the tool components. The results of the experimentally and numerically determined strains of the billet at the container wall show a good similarity. With respect to the rigid modeling of the tool components and the fact that Tresca’s friction model considers relative speeds only indirectly the computed ram force curves show also quite good agreement with measured curves. However, the simulation results demonstrates that in further numerical studies advanced plastic flow criteria and flow rules should be used that take into account the anisotropy and inhomogeneity due to the changing grain size and microstructure of the workpiece material.

Design and Experimental Verification during Extrusion of Square Sections from Round Billets through Curved Dies

Extrusion is one of the widely used metal forming processes. The extrusion process is carried out conventionally using a shear faced die, but shear faced dies have many practical problems such as a dead metal zone, more redundant work. In the present investigation, the evolution of uniform microstructure in extruded product with improved mechanical properties for quality products to get dimensional accuracy. A mathematically contoured non-linear converging die has been designed for extrusion of square section from round billet. CAD models of die profile have also been developed. The experiments have been conducted to verify the proposed theoretical model. The extrusion test rigs have been fabricated to carry out extrusion through mathematically contoured dies.

FVM Simulation of the Effect of Preventing Ring Structure on Continuous Extrusion Process

Continuous extrusion is an advanced process for manufacturing copper bus-bar while preventing ring is an important factor affecting forming. Due to the severe plastic deformation, FE simulation of continuous extrusion extending deforming is inaccurate and inefficient because of frequent remesh. Based on finite volume method (FVM) which can avoid re-mesh effectively, this paper simulates continuous extrusion forming, and analyzes the effect of different preventing ring structure on metal flowing velocity. The results show that: preventing ring with the curve transitional surface is beneficial to metal uniform flowing than that with the plane transitional surface; As radius of preventing ring increases, the metal flow rate of the sides is faster than the middle part; As opening width of preventing ring increases, the dead metal zones become smaller in the middle area.

Study of Temperature Evolution and Metal Flow of 6005A Aluminum Alloy during Indirect Extrusion

A numerical model has been build up to study temperature evolution and metal flow for the indirect extrusion of 6005A aluminium alloy. Model validation was carried out by comparison between experiments and simulations. Results show a good agreement with each other. The influence of the extrusion parameters on the profile temperature and metal flow were studied according to the real industrialized process. It was found that the profile temperature increases with the ram speed as well as the peak load of the total press force. However, a too slow extrusion process would cause increasing of the total force at the end of the extrusion because of heat dissipation to the environment. In addition the dead metal zone at the top of the billet was shrunk during the extrusion process. The ram speed would have little influence on the distribution and shape changing of dead metal zone. Once the extrusion went into steady stage, the strain rate of metal flow would keep a stable situation relatively.

Shape Complexity, Metal Flow, and Dead Metal Zone in Cold Extrusion

Nonhomogeneous metal flow through an extrusion die can directly affect product quality, productivity, and die life. The complexity of a die profile is an indicator of how difficult it is to extrude the profile. Some investigations about the effect of die complexity on extrusion pressure, product quality, and die life can be found in the published literature. However, the effect of profile complexity on metal flow through the extrusion die has not been explored much. Such a study can directly contribute toward die design improvement and reduction of extrusion defects related to metal flow. This article investigates the effect of shape complexity on the dead metal zone (DMZ) and metal flow through cold extrusion experiments and finite element simulations on some solid profiles. Experiments were performed using flat-face dies of different complexities and different billet materials. 2D and 3D finite element simulations were carried out. One significant conclusion is that currently existing definitions of extrusion shape complexity cannot satisfactorily explain the variations in DMZ size under different conditions. Factors such as die profile symmetry and extrusion ratio may play significant roles in the formation of DMZ and distortion of metal flow through the die.

Electromagnetic radiation during plastic deformation under unrestricted quasi-static compression in metals and alloys

Abstract Intermittent electromagnetic radiation (EMR) emissions from metals and alloys during deformation under unrestricted quasi-static compression are reported in this paper. The end surface conditions of the compressing platens, whether lubricated or unlubricated, influence the EMR emission characteristics. The EMR emissions under compression show shape anisotropy. The first EMR emission invariably occurs near the yield. The EMR emission characteristics are also influenced by the crystal structure. During axial compression, dead metal zones formed on the top and bottom portions of the specimens possibly generate a climbing motion of edge dislocations in the radially outward mid-regions. During the climbing motion, these edge dislocations form accelerated electric line dipoles and emit electromagnetic radiation. These EMR emissions can be used to evaluate the degree of damage in metallic components under compression.

Temperature Changes with Die Profile in Axisymmetric Forward Extrusion Process

Temperature effect due to varying die opening shapes in the direct extrusion of lead have been numerically simulated and presented. Using upper bound method of analysis the internal heat generation due to plastic deformation and frictional heat at various stages of the extrusion process for different die opening geometry are simulated. A C++ program simulates the deformation and frictional power at die land region which is converted to temperature change using finite difference program. At the extrusion die land region, temperature rises with increasing complexity of die openings geometry with I-shaped section, giving the highest temperature rise, followed by T-shaped section, rectangular, circular shaped die openings with square section die opening, giving the least temperature rise for any given extrusion parameter. The die land zone shows increasing temperature rise with increasing friction coefficient, while increasing friction coefficient has no overall effect on the dead metal zone temperature rise. The proper choice of die land is, therefore, imperative if excessive generation of heat at the emergent section is to be avoided to maintain good quality and metallurgical structure of the product.