Why and how Does Extrusion Change with a FEM Approach to Process Simulation

An interview with Tommaso Pinter, from Almax, based in Mori: die engineering is the great step forward which guarantees beforehand the feasibility of aluminium profiles to extruders and end users

by Mario Conserva

It is a well-known fact, widely acknowledged by all industry operators, that dies play a central role as regards the possibility of producing a certain section of an aluminium extrusion, more so today, with the market demanding increasingly complex shapes and final extrusions with more and more remarkable mechanical properties.
Evidence that the contribution of the die manufacturer lies at the heart of the entire process is provided by the enormous changes which occurred during the past few decades as regards extrusion die engineering. We discussed this stimulating topic with Tommaso Pinter, a young representative of a prestigious brand in the field of extrusion dies, Almax, based in Mori (near Trento). Having graduated in Industrial Engineering at Bologna’s University about twenty years ago, studying among other things the mechanisms of heat-induced changes in meals, and an author of numerous technical publications dedicated to aluminium alloys, Tommaso Pinter is the Chief Commercial Officer of Almax Mori and technological manager of the Alumat group which Almax is part of. “I shall introduce the subject with a brief presentation of our company: Almax is part of a group of companies involved in the production of aluminium extrusion dies for the global market. The parent company is Alumat, based in Ciserano near Bergamo; besides Almax Mori we have Matrex in Thessaloniki, in Greece, and Almax Service in Poland, one of our best markets. The group, with just over 140 employees, has overall revenues adding up to more than 25 million euro, we as Almax are worth 11 million euro with 55 employees, 85% on foreign markets, and we are specialized in dies for hard alloys, such as 6082, 6061, 7005, 7108, 7020 and 7075 for structural profiles, even large ones. We produce on average between 350 and 400 dies a month. We consider 1987 to be the date of birth of Almax as we know it and last year we celebrated our thirtieth anniversary, even though the company was actually founded during the second half of the Sixties in Zingonia (near Bergamo) following the experience of the Dutch parent company by the same name. The factory was then relocated to Mori in the beginning of the Eighties and came under the influence of Alcoa, which had purchased the best part of aluminium assets belonging to the Italian State; finally it was purchased in 2004 by the current owners, entrepreneurs who for years had taken care of the company’s management. As a distinguishing feature of the way we work, I would like to mention that we were one of the first manufactures to fit an integrated extrusion simulation into the die manufacturing process; as we shall see in detail later, this means a reduction in production costs, great flexibility, reduction of delivery lead times of the moulds by over 50%, a sharp decrease in correction phases”.

How did this innovative design concept, regarding extrusion die design and production, start and develop?
The starting point is actually quite simple: in the past, the job of die manufactures was based on paper archives and on the individual knowledge of mould makers, extruders and end users who provided basic elements to provide an idea as to the feasibility of a given type of die. Before the introduction of finite element codes, designing extrusion dies was more a matter of art and experience than engineering: to this very day many die manufacturers use the historical experience accrued over time to design dies, using the extruder’s request as an input without questioning it. In other words, it was experience passed on over time to determine whether a given section could be extruded by clients and with what guarantee margins. And it is also a well-known fact that many extruders until recent years were forced to order one or more dies and to carry out different tests only to understand whether or not a new complex section could be provided to the end user and at what production costs. Of course, these approaches may be a great limitation to the development of new extrusion sections: it is indeed easy to guarantee something which worked in the past, while without engineering it may be very expensive and time-consuming to go beyond and to try to seek experimentally on the field the limits of materials and of the process. Today it is possible to refer to digital archives containing all data, from the heat deformability properties of the alloy to the material’s temperature and flow modes during extrusion, to the weight of profiles, knowledge which duly processed allow to determine beforehand the practical feasibility, productivity and production cost of every determined profile. In these terms this may sound easy, in actual fact it is a complex process which in my case began with my studies at University, in Bologna and at the Marche Region Polytechnic, in Professor Luca Tomesani’s group, with research as to the behaviour during hot torsion of different aluminium alloys. After over ten years of work, with the constant cooperation of the University and the concrete help of such institutions as the Autonomous Province of Trento, we were able to get together good calculation instruments which today allow us to carry out an excellent simulation for every single profile.

May we describe, providing some additional technical details, the basic elements of your new method for designing and manufacturing dies?
Finite Element Analysis, FEA, is the key to numeric simulation, integrated by the total knowledge of the variables of the extrusion process. Little more than a decade ago it was understood that the key to satisfy the future demand of extrusion users was integrating design departments with a technology capable of assisting back offices in the feasibility phase. Satisfying a customer for Almax Mori means being able to say, “yes, we can produce a die which in turn can extrude a section just like the one shown in your drawings”, and in order to reach this objective we introduced finite element analysis (FEA). The current state of the art in numeric simulation applied to extrusion processes is defined by a benchmarking conference in various past editions [1,2]. As a consequence, a generally significant increase has been noted in the accuracy of codes for the forecast of the process load, the flow of materials, the pressure and temperature maps. Our technical office in Mori took part several times in the Extrusion Benchmark, FEA is in our DNA.
It has always been a standard practice for extruding companies to ask for the support of die manufacturers in the feasibility phase, especially in the case of complex sections. Before the definition of FEM codes, only empirical formulae were used based on experience to evaluate the feasibility of the details of the dies, while today we are suing FE stress analysis based on an elastoplastic model.

Basically, Columbus’s egg is the control of knowledge and the complete interpretation of the process parameters…
Indeed, with this new approach we were able to reach new limits without running risks at the press, eliminating the cost of expensive die corrections.
During the next few years the growth in the demand for extrusions will be linked significantly to the demand of the automotive industry. Today automotive and High-Speed Rail imply lightweighting so as to require less energy in order to function, and lightweighting means extruding wider and thinner sections. In order to supply recent railway projects, almost all European players updated their large presses to overcome the lack of specific pressure required to extrude the required sections. Force multiplied by displacement is equal to work: extrusion equipment must be adequately redesigned to resist the greater pressure needed to extrude wider and lighter sections. In compliance with this challenge, our Mori technical office got organized so as to provide extruders with clear and precise data as to the possibility of extruding new sections to produce side walls, roofs and floors for railway carriages. In order to be successful we entrusted Italian research centres with different torsion tests so as to obtain an appropriate constitutive equation for each aluminium alloy being used [3]. this is probably the most important aspect which distinguishes a successful extrusion simulation from another, because if we cannot estimate correctly the specific pressure required for the dummy block to push a billet through the die, all other parameters such as temperature and pressure are actually worthless. The second important aspect is the knowledge of the process parameters in use at the press. The fewer assumptions are made, the better results are obtained in terms of accuracy of the forecasts when working with codes on finite elements, for this reason what makes the difference is the cooperation of the extrusion company’s process engineer and the FEM engineer of the die manufacturer.
Given a required section, our simulation team can understand not only whether the aluminium flow will be balanced, but also whether the thickness of the internal walls will respect size allowances. Prior knowledge of these data is absolutely essential especially when the die is to be delivered overseas, because in this case it is no longer necessary to pick up the die to carry out any changes. The innovative and striking power of this approach lies exactly in the fact that for very complex profiles it is possible to foresee whether allowances requested by the end user may or may not be reached during extrusion; profiles which once were refused may today be accepted by extruders based on data obtained using die engineering, and this is a great revolution for the entire extrusion industry. And there’s more: once the value of the technological scrap of the extrusion line is known, our technical department may also provide specifications as to the length of the billet needed to provide a certain length of the section and verify if the press capacity is appropriate to go beyond the specified billet length; by means of a precise calculation of the front end defect, we may estimate the recovery factor precisely enough to provide full warranty of the die even from the standpoint of the extrusion quantities (Figure 1).
The outstanding results reached today are the outcome of work done during ten years of continuous improvement: this is why 10% of the working hours of our engineers are dedicated to research and development activities and to provide feedback to software companies with the appropriate data needed to improve code performance, result precision and, last but not least, the development of new tools. In 2018 we dedicated our efforts to validate our FEM code for the estimate of back end defect, while encouraging every day software houses to implement the best analytical models available in literature to estimate the granulometric changes due to dynamic recrystallization.

From a construction standpoint, what is the state of the art which allows Almax Mori to turn what has been studied on a PC into reality?
An excellent question. Everything is based on a simple but essential principle: the technology I described above is only effective inasmuch as it can produce a die true to the model studied using finite elements. In Mori we eliminated intermediate operations and inserted five-axis milling centres (Figures 2 e 3). In this way we are sure that the die is exactly the same as the one designed and simulated using the computer. The result in the press is true to the one foreseen by the computer. You may take my word for it when I tell you that competitors are not always capable of guaranteeing such standards since they still work largely with manual grinding.

To conclude, it seems to me that these new criteria of die production could change the way extrusions are manufactured, a great step forward to turn an art into science: perhaps by factoring in the creativity and imagination which have always characterised Italian entrepreneurial style, we might reap even more competitive results in a global market context…Undoubtedly as a system we have the opportunity to emerge, making use of the extraordinary experience accrued by Italian extrusion during the past decades. To conclude, regarding the technically relevant data which I tried to introduce in the simplest way, the truth is that the engineering approach to the feasibility of aluminium extrusions is causing most common practices to be forgotten: and it is important to underline that in this new approach the die manufacturer is directly involved not so much and not only during commissioning, but mainly in the design phase of the aluminium section which will be extruded. Today extruders may know whether a profile may be extruded with a given die and may also evaluate precisely the total amount of scrap which might be produced before the die is ordered, and this is providing the entire industry with a great advantage by significantly reducing transformation costs and time to market. By choosing the new approach suggested by Almax, extruders do not run any risks in terms of profitability, after long-term supply contracts have been signed, because the recovery factor may be estimated with a good level of accuracy in the feasibility phase. Working in this way implies reducing the gap between estimated and real production costs, obtaining a competitive advantage with respect to competitors in a market which is growing a significant rate for aluminium extrusions such as the automotive industry, which is more and more demanding. It is understood, given all that has been said so far, that even with this new approach extruders will still have to deal very carefully with downstream operations in order to provide an aluminium section with the desired properties: in other words, the exit from the press, quenching of any type or with any aging machine, profile shipment, cycles and methods of aging, all of this has a great influence on the performance of an extrusion line, irrespective of whether the die was manufactured using state-of-the-art technology.
To conclude, the innovative methods suggested by Almax will definitely provide a significant contribution to broaden the already remarkable employment field of aluminium extrusions, a product range which represents a unique class of semis capable of providing creative solutions to designers in every application field. It is clear that success after over 10 years of studies, research and experiments which we carried out should be attributed to a large extent to our clients who decided to trust this innovative approach to die engineering, believing that “zero die corrections” could be a result within reach for a great relaunch of aluminium extrusion and not just a theoretical and fanciful hypothesis.