Extrusion Industry Research Articles

A risk-estimation methodological framework using quantitative assessment techniques and real accidents’ data: Application in an aluminum extrusion industry

The risk estimation presumably is the most crucial part of the entire procedure of assessing hazards/unsafe situations in the work, and especially in the industries’ and constructions’ worksites, where the working conditions are unstable. We can consider the risk as a quantity, which can be estimated and expressed by a mathematical relation, under the help of real accidents’ data. The aim of this work is quadruplicate: (a) the development, elaboration and explanation of two new quantitative risk-assessment techniques, (b) the improvement of specific points of other scientific works, as far as concerns quantitative risk estimation, (c) the application of these techniques on an industrial productive procedure (as a case study) and (d) the comparison of their outcome risk-estimation results. Particularly, we develop and analyze the theoretical background of the two techniques, which we call as “proportional technique” and “decision matrix technique”, and apply them on an aluminum extrusion industry's worksite, which is situated in Greece, by using real data of potential sources of hazards, recorded by safety managers, during the 5.5-year time period of 1999–2004. Comparing the results of the two quantitative risk-assessment techniques, we infer that they are compatible. Therefore, the most important hazard source in the aluminum industry is the “squeezing and hits by dropping objects (transported by derricks)”, and imposes that immediate suppressive measures must be taken place to abolish the danger source.

New methods for the fast simulations of the extrusion process of hot metals

Being able to find alternatives to the costly and time-consuming trial and error current practice in die design based on know-how acquired by practitioners throughout years is of primary importance in the aluminum extrusion industry. In this paper, two programs aimed at helping extruders in estimating the performance and feasibility of processes and simulating in details the flow of material in the press, are presented. Although they have been used so far for aluminum alloys, they could also be applied to other extrusion applications like that of other metals and polymers for instance. Together with a process simulator, which enables one to obtain a fast estimate of the extrusion process performances and computer-aided production of aluminum extrudates, a three-dimensional software dedicated to the design of dies with complicated shapes is also described.

An analytical solution for the spread extrusion of shaped sections

Spread extrusion could be used for manufacturing of wide profiles in the extrusion industry. In this paper a new method of design and analysis has been presented for such a problem. Special dies were designed for profiled sections such as square, rectangular, elliptical and cross shapes. These dies force the material to flow sideways and spread so as to extrude sections with wider dimensions than the initial billet or the maximum container diameter. The geometry of the deforming zone in the die was formulated and based upon that, a kinematically admissible velocity field was derived. Using this velocity, we estimated the field upper bound on extrusion power. Profile sections with different aspect ratios were investigated and the influence of other process parameters such as friction and reduction of area on the extrusion pressure were studied. Optimum die lengths for each die were calculated so as to minimize the extrusion pressure. Finite element analysis for the numerical simulation of the process was also carried out. The finite element results were also used as an aid to the design process of the extrusion dies. Dies were manufactured for different sections such as square, rectangle, and ellipse and cross shapes. Experiments were carried out to obtain data to verify the theory. Comparison of the results showed good agreement between the theoretical, numerical and experimental data. It was concluded the present method could be used to design dies for the spread extrusion of different shaped dies.

FEM simulation of aluminium extrusion through two-hole multi-step pocket dies

Multi-hole pocket dies are a type of extrusion tooling setup commonly used across the aluminium extrusion industry for efficient production of solid aluminium profiles. Such dies are designed on the basis of experience and corrected after a number of trial extrusion runs before becoming usable. Computer simulation based on the finite element method (FEM) is in principle capable of predicting metal flow through the dies designed, but it is yet a huge technological challenge to simulate the extrusion process to produce profiles of industrial significance. The present research was attempted to investigate the effect of steps in the die pocket on metal flow to produce two chevron profiles with unequal thicknesses through two-hole dies, by means of 3D FEM simulation of extrusion in the transient state. The results showed that the pocket step could be effectively used to balance metal flow. Extrusion experiments validated the predictions of metal flow, extrudate temperature and the pressure required for extrusion through the pocket dies with three different designs. 3D FEM was demonstrated to be a powerful tool in optimising die design and decreasing the number of trial extrusion runs.

A new three-dimensional solution for the extrusions of sections with larger dimensions than the initial billet

A new analysis for the three-dimensional solution for the extrusion of sections with larger dimensions than the initial billet or container is presented in this paper. A generalized kinematically admissible velocity field was formulated using the upper bound theorem. The problem tackled in this paper is a practical one encountered in the extrusion industry where for the production of sections whose dimensions are larger than the container or billet diameter there exist some difficulties and sometime it is impossible to produce such products. The solution to this problem was suggested in a new design for the extrusion die which was done using the upper bound analysis. In this design unlike flat-faced dies the material has to flow over two kinds of surfaces namely converging and diverging surfaces, the combination of which causes the material flow in a smooth manner and with the correct speed so that the required final shape would be achieved. For such geometries kinematically admissible velocity fields were obtained. Using this new formulation, extrusion of shapes such as square and rectangle were analyzed. Influence of the process parameters such as friction, extrusion ratio and aspect ratio on the extrusion load was investigated and the optimum die length was obtained. Finite element analysis for the same problem was also carried out and the comparison of the results showed good agreement. The finite element simulation was especially used to assist the theoretical analysis with regards to the material flow and filling of the die cavity. Based on the analytical results, extrusion dies for the rectangular sections were designed and manufactured and experiments were carried out. The results of the tests showed that the dies performed very well and complete filling of the die cavity and a successful extruded profile was observed.

Optimal Die Design for Three-Dimensional Porthole Extrusion Using the Taguchi Method

Empirical knowledge and the trial-and-error method are still common design approaches used in the extrusion industry. However, the service life of three-dimensional extrusion dies is generally unstable and extremely short, especially for high-strength aluminium extrusions, which clearly increases production cost and lowers efficiency. This paper proposes a method for establishing optimal die design for three-dimensional extrusions using the Taguchi method and the finite element method (FEM). Taguchi's orthogonal array is applied to plan the simulation of FEM. After Taguchi's response analysis, the influence of each factor on the die stress was understood and an optimum design was obtained.

Recent advances in barrier screw design

Barrier screws have been ubiquitous in the moulding and extrusion industry for almost half a century. However, conventional barrier screws have some drawbacks that limit their applicability. One of the most serious drawbacks of barrier screws is that they are more susceptible to solid bed plugging; severe plugging results in process instabilities (surging). Chris Rauwendaal describes how the optimum design of barrier screws can largely eliminate the chance of plugging while improving the melting and mixing performance.

New screw design for cooling extruders

Heat transfer is a critical issue in most polymer extrusion operations. In plasticating extrusion, the objective is to add the right amount of heat to melt the polymer and to achieve the desired melt temperature. In some extrusion operations, however, the objective is to remove heat from the polymer. This is the case in tandem foam extrusion lines where the secondary extruder is used to cool down the mixture of polymer melt and blowing agent. Cooling extruders reduce the polymer melt temperature by a substantial amount, about 100 °C, to achieve a melt consistency that is conducive for foaming. Little information has been published about the design of cooling screws in the open literature. The present study discusses basic issues related to the design of cooling screws and presents a new screw geometry to achieve improved cooling. As the foam extrusion industry faces pressure to move from HCFC (hydrogenated chlorofluorocarbon) blowing agents to nitrogen and carbon dioxide (CO2), the cooling capacity becomes more critical. CO2 is less of a viscosity depressant than most HCFC blowing agents. As a result, with CO2 more viscous heating occurs in the cooling extruder and more effective cooling is required to achieve the same reduction in melt temperature.

Finite element modelling simulation of transverse welding phenomenon in aluminium extrusion process

Transverse welds occur in the billet-to-billet extrusion process, which is often used in modern aluminium extrusion plants for the purpose of continuous production. The transverse weld introduces a discontinuity at the weld interface in the extruded product and in many structural applications. This is not acceptable because it can severely reduce the strength and is detrimental to the quality of the extruded product. For this reason the length of transverse weld material needs to be cut out of the extrusion. But this then decreases the overall yield of the product and so the transverse weld length should, therefore, be kept as minimum as possible. The experimental studies carried out in the past mainly concentrated on the quality and strength of the extruded products containing a weld interface. The behaviour of metal flow and the factors affecting the transverse weld length have not been systematically studied. Currently, the transverse welding pattern and length of the extrudate containing a transverse weld are determined purely by experience and simple empirical models. In this study, the formation and metal flow behaviour of transverse welds in the aluminium extrusion process were investigated using the finite element modelling (FEM) simulation technique. It was shown that inhomogeneous metal flow occurred and a transverse welding pattern was revealed. The design parameters influencing the transverse weld length were also investigated and discussed. This study concentrated on improving the understanding of the behaviour and the formation mechanisms of transverse welds with the aim of providing general guidance for the aluminium extrusion industry in minimising the transverse weld length of the extrudate.

Simulation and control of microstructure evolution during hot extrusion of hard aluminium alloys

Controlling the microstructure distribution in the final product is challenging and demanding work for the aluminium extrusion industry. This can only be achieved when the microstructure evolution during deformation is fundamentally understood. In this paper, some physical models which are based on dislocation density, subgrain size, and misorientation have been integrated into a commercial finite element modelling program simulating extrusion. The volume fraction recrystallised after press quench and the recrystallised grain size after solution treatment are studied. The influences of die configuration, container temperature and die temperature on the recrystallisation behaviour are detailed. Following this successful prediction, a uniform distribution of microstructure along the length of the extrudate has been obtained by adjusting the ram speed according to the calculated subgrain size at die exit. The calculated histories of temperature and subgrain size during deformation are presented. The problems of this new process are illustrated. Further work on simulation and control of microstructure is finally discussed.

3D FEM simulation of the whole cycle of aluminium extrusion throughout the transient state and the steady state using the updated Lagrangian approach

Aluminium extrusion involves the generation of free surface, thermal effects, large deformations and complex geometries. The established finite element method (FEM)-based 3D simulation tools using the updated Lagrangian approach, or the Eulerian approach or the arbitrary Lagrangian Eulerian approach all have limitations in describing the process that develops from the transient state to the steady state before reaching the end when the steady state is disturbed. As a result, the simulation of aluminium extrusion performed so far has been restricted to simple geometries, small length-to-diameter ( L/ D) ratios, the beginning stage or steady-state conditions. This paper reports on an unprecedented attempt to simulate an entire cycle of aluminium extrusion from a billet with an L/ D ratio of 4 to a solid cross-shaped profile, using the DEFORM 3D software based on the updated Lagrangian approach. Simulation successfully predicts a complete extrusion pressure/ram displacement diagram that begins with a pressure breakthrough and ends with another pressure rise due to the inhibition of metal flow by the rigid dummy block. The developments of velocity, effective strain and temperature inside the deforming billet indicate that the process is non-steady, even in the steady state, as a result of continuous heat generation and sticking condition at the billet–container interface. The non-steady characteristics are reflected in the expanding deformation zone and shrinking dead metal zone. Simulation also reveals the patterns of the maximum temperature variations in the workpiece and in the tooling, due to heat generation and exchange. Even at a relatively low ram speed of 2 mm/s, the maximum temperature of the workpiece, after an initial steep rise, increases gradually till the end of the process, which may well lead to the occurrence of hot shortness. On the basis of these results, a change of the conventional mode of aluminium extrusion is recommended, which at present operates almost all at a constant ram speed and often begins with a uniform billet temperature across the aluminium extrusion industry in the world.

New directions for extrusion: compounding with single screw extruders

Over the past several decades relatively few major new developments have occurred in the plastic extrusion industry, in particular in single screw extrusion. In fact, many people consider plastics extrusion a mature technology where radically new developments are no longer possible. However, nothing is further from the truth, argues Chris Rauwendaal of Rauwendaal Extrusion Engineering, because several technologies are now being developed that will allow major advances in extrusion technology in the near future. He explains these developments to Plastics Additives & Compounding.

FEM simulations of the extrusion of complex thin-walled aluminium sections

The finite element method can be used for the simulation of the extrusion process. However, the application of this kind of simulations in the extrusion industry is limited because of the complexity involved. In this paper, a method is presented for the simulation of the extrusion of complex profiles, which can be used in an industrial environment. To this end, the bearing area is modelled with an equivalent bearing model. In this way, it is possible to describe the resistance in the bearing without using a large number of elements. To avoid the time-consuming and complex work necessary for the development of the FEM model for a particular die, a specialised pre-processor is developed. This pre-processor provides a direct link between the die design in the CAD system Pro/Engineer and the simulations in the FEM code DiekA. The method is demonstrated for a particular die and the results are compared to results obtained in practise.

A Mathematical Model to Predict the Strength of Aluminum Alloys Subjected to Precipitation Hardening

A number of alloys, notably most of the aluminum alloys, can be heat treated by aging. This aging due to time-dependent precipitation hardening increases the strength and hardness as well as modifying other mechanical properties. Precipitation hardening has been a popular strengthening mechanism for many decades; therefore, extensive information is available in literature about the precipitation-hardening response of various series of aluminum alloys. The age-har dening response of these alloys is usually represented in graphical form as plotted between property changes and aging time for different temperatures. In designing a suitable precipitation-hardening strategy, one can refer to these graphs. However, for automatic control of aging furnaces, as well as for decision making regarding optimal selection of aging conditions (time/temperature combination), it is desirable to express these relationships in a formal mathematical structure. A mathematical model is developed in this article for widely used heat treatable aluminum alloys used in the extrusion industry. This model is a condensed representation of all σ=f(T, t) curves in different series of aluminum alloys, and the parameters of this model characterize the various compositions of the alloys in the series.

The effect of thermal history on the distribution of residual stresses in PMMA rods

AbstractA nondestructive technique based on the photoelastic properties of transparent polymers has been used to monitor the distribution of residual stress components in circular rods of poly(methyl methacrylate) (PMMA). The influence of various thermal histories on these stresses as well as on the molecular birefringence has been determined. The technique has been further simplified to obtain the values of maximum tensile and compressive residual stresses with the help of just two photoelastic measurements. The stresses so obtained are within 10% of the values obtained using detailed experimental measurements and their analysis. The simplified procedure is, therefore, suitable for “on‐line” determination of residual stresses in extrusion industry.

ON‐LINE MEASUREMENT of DYNAMIC RHEOLOGICAL PROPERTIES DURING FOOD EXTRUSION

ABSTRACTDynamic rheological properties of extruded rice dough were measured continuously using a Rheometrics On‐line Rheometer, an instrument designed for rubber and plastics applications. Storage and loss moduli were successfully measured over a moisture content range of 24 to 50% wet basis; however, the instrument is difficult to use in food research due to numerous problems: high pressure required to move material through the unit, internal dead spots causing build up of material, cleaning problems due to difficult disassembly. As a result of the development project discussed here, these problems are being addressed by Rheometrics (Piscataway, NJ) with the goal of producing an on‐line rheometer acceptable to the food extrusion industry.

Third International Aluminum Extrusion Technology Seminar

The Third International Aluminum Extrusion Technology Seminar, co-sponsored by the Aluminum Association and the Aluminum Extruders Council, was held April 24–26, 1984, in Atlanta, Georgia It addressed the contributions made by improved processes and equipment, die design, automation, and billet and extrusion technology which have increased productivity in the aluminum extrusion industry. Contributors from 10 nations presented over 100 papers. The conference reviewed a series of papers addressing the importance of understanding the physical metallurgy of aluminum extrusion alloys in economical production.

NEW POLYMERS FOR COLD EXTRUSION

TEFLON fluorocarbon resin has been used for many years as a low friction material (its anti‐stick properties for foods in pots and pans are well known), but these properties have not been available to the metal extrusion industry because of application and adhesion problems. ‘Teflon’ is basically a long chain of tetrafluoroethylene groups —about 10 to 30 thousand. This polymeric chain melts at 621°F and has a very high melt viscosity which allows negligible flow at this temperature. It is essentially insoluble in all common solvents.

PRESSURDIE-2

Abstract PRESSURDIE-2 is an intermediate chromium-tungsten-molybdenum hot die steel possessing excellent combination of properties particularly adapted for use in the aluminum extrusion industry. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on high temperature performance as well as forming, heat treating, and machining. Filing Code: TS-58. Producer or source: Continental Copper & Steel Industries Inc..

Motor transport training schools

The risk estimation presumably is the most crucial part of the entire procedure of assessing hazards/unsafe situations in the work, and especially in the industries’ and constructions’ worksites, where the working conditions are unstable. We can consider the risk as a quantity, which can be estimated and expressed by a mathematical relation, under the help of real accidents’ data. The aim of this work is quadruplicate: (a) the development, elaboration and explanation of two new quantitative risk-assessment techniques, (b) the improvement of specific points of other scientific works, as far as concerns quantitative risk estimation, (c) the application of these techniques on an industrial productive procedure (as a case study) and (d) the comparison of their outcome risk-estimation results. Particularly, we develop and analyze the theoretical background of the two techniques, which we call as “proportional technique” and “decision matrix technique”, and apply them on an aluminum extrusion industry's worksite, which is situated in Greece, by using real data of potential sources of hazards, recorded by safety managers, during the 5.5-year time period of 1999–2004. Comparing the results of the two quantitative risk-assessment techniques, we infer that they are compatible. Therefore, the most important hazard source in the aluminum industry is the “squeezing and hits by dropping objects (transported by derricks)”, and imposes that immediate suppressive measures must be taken place to abolish the danger source.