Investigation of the Electrohydraulic Forming Process with respect to the Design of Sharp Edged Contours

The overcoming of design constraints with respect to forming of sharply contoured sheet metal workpieces made of high strength steel or other materials which are difficult to form is an important aspect in sheet metal part production. One interesting solution to extend existing forming limits can be the use of electrohydraulic forming as single forming operation or in combination with quasi-static hydroforming. Apart from promising results regarding the feasible part geometries this process allows a quite efficient production due to its potential to reduce equipment expenses. Current research work at the Chair of Forming and Machining Technology (LUF) at Paderborn University deals with a comparison of investigations on both processes, quasistatic and high speed hydroforming. Recent results show an adequate comparison of achievable edge radii using an oblong die geometry and sheet metal made of thin stainless steel. It can be seen that when using electrohydraulic forming an increase of discharge energy leads to smaller radii than achievable by quasi-static hydroforming. An additional potential can be seen in the process characteristic itself because the very short pressure pulse allows a significant reduction of locking forces using only the inertia of the tooling mass

Process reliability and reproducibility of pneumomechanical and electrohydraulic forming processes

A sufficiently high process reliability and reproducibility is mandatory if a high-speed forming process is to be used in industrial production. A great deal of basic research work into pneumo-mechanical and electrohydraulic forming has been successfully performed in different institutions in the past. There, the focus has been more on process related correlations, such as the influence and interaction of different parameters on the course and result of those processes. The aspects of reliability and reproducibility have not been examined to a sufficient extent. Hence, in the case of pneumo-mechanical forming, insufficient investigations have been conducted into the effect that key parameters like the kinetic energy level, the filling height of the working media or the conditions inside the acceleration tube have on the reproducibility and course of the process. For electrohydraulic forming, the repeatability has worsened on occasions up to now. To improve the forming results and, in particular, the reputability of the process, it is necessary to examine the tool parameters associated with the electrodes and the working media. That is why research of this type is currently ongoing at the LUF. One important issue here is examining the options that exist for visualising the way the spark takes hold in the discharge chamber

Combined Working Media-Based Forming on a Pneumo-Mechanical High Speed Forming Machine

Quasi-static working media-based forming processes (WMF) permit the production of complex sheet metal parts with relatively little expense. The associated need for very high pressures and hence complex tools and machines for the production of fine geometrical details is often problematic. The use of high speed forming processes (HSF) can offer many benefits, including a reduced financial outlay on equipment and better part properties in this case. But these processes also have disadvantages, of course, such as if they are used for the production of complex large-surface parts. Consequently, a combination of both approaches would be ideal. This paper describes a new approach to combining high pressure sheet metal forming (HPF) and pneumo-mechanical HSF for the production of complex sheet metal parts

Electromagnetic Compression as Preforming Operation for Tubular Hydroforming Parts

With the aim to extent the forming limits of tube hydroforming a concept of using a previous electromagnetic compression operation will be introduced. One important limit for the possibilities of tube hydroforming is set by the initial circumference and the maximum tangential strain of the used material, whereby the initial circumference is typically determined by the smallest local circumference of the workpiece. The application of an appropriate contoured preform makes it possible to use tubes with a larger initial circumference. In the paper the investigation of the suitability of electromagnetic tube compression for the production of such a preform will be presented. The valuation is based on geometric criteria and material properties of the resulting preform which are strongly influenced by the process parameters. The discussed aspects are the roundness of the preform and the strain hardening of the material

Исследование пневмомеханического высокоскоросного процесса

In the area of metal forming technology, the pneumomechanical high-speed-forming process is a promising approach for manufacturing of thin walled workpieces made of high strength materials. This process uses a pneumatic accelerated plunger that dives into a working media filled pressure chamber for the generation of a short pressure pulse. This pulse can be influenced, on the one hand, by evacuating the acceleration tube and as a consequence higher plunger energy and on the other hand by varying process parameters such as working media characteristics as e.g. density, oxygen content and type as well as the plunger geometry. The influence of these parameters on the process is subject of intense research work at the Chair of Forming and Machining Technology (LUF) at University of Paderborn. Recent results show that pneumomechanical and electrohydraulic forming allows for manufacturing of complex geometrical details in aluminum alloys that cannot be produced by conventional stamping processes. Due to the high homogeneity of the pressure distribution in the pressure chamber, it is possible to achieve high quality workpieces with low dimensional deviations. This paper presents the results of basic research conducted on pneumomechanical high-speed-forming as well as a comparison with electrohydraulic forming.В статье рассматриваются различия обработки листового металла в разных плотностях и видах рабочей среды. В работе было исследовано влияние изменения содержания кислорода в рабочей среде и различных геометрий плунжера на деформацию листового металла. Опытным путем была установлена возможность изготовления сложных геометрических деталей из алюминиевых сплавов с помощью пневмомеханической и электрогидравлической штамповки, обычными способами не производимые. Благодаря точной равномерности распределения давления в радиальном направлении, достигается незначительное геометрическое отклонение заданной формы заготовки. В данной работе представлены результаты фундаментальных исследований пневмомеханической штамповки в сравнение с электрогидравлической формовкой. Результаты исследований были использованы для достижения соответствующих процессов и разработки инструментов для пневмо-механической высокоскоростной штамповки

Исследования высокоскоростного пневмомеханического просесса по формовки сложно структурированых листовых и трубчатых компонентов

У зв'язку з суворими нормами викиду вуглекислового газу і економії ресурсів в автомобільній і аерокосмічній промисловості усе більш вирішальну роль грають полегшені конструкції. Таким чином, на сьогоднішній день необхідність виробництва конструкцій із складною геометрією з високоміцних матеріалів є високоактуальною. У цьому плані, неминуча розробка нових процесів для високоміцних матеріалів тих, що відповідають вищевикладеним вимогам. Процеси високошвидкісного формування показують більш високі показники відносно формування комплексних гострокрайових деталей і є важливим ключем до зниження ваги компонентів, при цьому відповідаючи високим вимогам викиду вуглекислового газу, а також сприяючи збереженню важливих природних ресурсів. Дослідження пневмомеханічного і електрогідравлічного процесу формування металу є важливим предметом інтенсивної дослідницької роботи кафедри формування і обробки технологій університету Падерборн. Для інтеграції вказаних процесів в промисловості, дуже важливе визначення впливу різних параметрів процесу на формування результату, який не лише сприяє оптимізації самого процесу, але і призводить до кращого розуміння явищ цих процесів. У статті розглядається вплив прискорення стислого повітря і рівня заповнення робочого середовища на формування деталей з листової і трубчастої геометрії. Досвідченим шляхом була встановлена можливість виготовлення складних гострокрайових і квадратоподібних геометричних деталей з алюмінієвих сплавів за допомогою пневмомеханічного штампування. Результати дослідження роблять явним факт ефективного впливу тиску стислого повітря і рівня заповнення камери тиску, що змінюється, на формування деталей. У цій роботі представлені результати ґрунтовних досліджень пневмомеханічного штампування в порівняння з конвенціональним гідроформінгом.Lightweight design is playing an increasing role in the automotive and aerospace industries due to the stringent emission regulations. Hence it is necessary to produce parts with complex geometries from sophisticated high-strength materials. In this context, and especially when high strength materials have to be formed into highly complex geometries, it is inevitable that new manufacturing processes will need to be developed which meet these requirements. High speed forming processes have a very high potential when it comes to shaping complex, sharp-edged parts and constitute a key means of reducing a component’s weight and hence of complying with the stringent emission regulations and also saving on essential resources. These processes and, in this case, pneumo-mechanical and electrohydraulic forming in particular, are a major subject of intense research at the University of Paderborn's Chair of Forming and Machining Technology (LUF). To be able to bring these processes into industrial use, it is necessary to identify the influence of different process parameters on the forming result. This will not only help to optimize the process itself, but will also lead to a better understanding of the process phenomena. This paper presents recent results relating to the influence of different process parameters, such as the acceleration pressure and the filling level of the working media, on the forming result of sharp-edged, sheet metal parts and square-formed tube geometries in aluminium using a pneumo-mechanical, high speed forming process. It is seen that the forming result can effectively be influenced by varying the acceleration pressure and the filling level. Furthermore, this paper presents the results of basic research conducted on pneumo-mechanical high speed forming and its comparison with conventional hydroforming.В связи со строгими нормами выброса углекислового газа и экономии ресурсов в автомобильной и аэрокосмической промышленности все более решающую роль играют облегченные конструкции. Таким образом, на сегоднишний день необходимость производства конструкций со сложной геометрией из высокопрочных материалов является высокоактуальным. В этом плане, неизбежна разработка новых процессов для высокопрочных материалов отвечающих вышепоставленым требованиям. Процессы высокоскоростной формовки показывают более высокие показатели относительно формирования комплексных острокраевых деталей и являются важным ключом к снижению веса компонентов, при этом соответствуя высоким требованиям выброса углекислового газа, а также способствуя сохраненю важных природных ресурсов. Исследования пневмомеханического и электрогидравлического процесса формовки металла является важным предметом интенсивной исследовательской работы кафедры формирования и обработки технологий университета Падерборн. Для интеграции указаных процессов в промышленности, очень важно определение влияния различных параметров процесса на формирование результата, который не только способствует оптимизации самого процесса, но и приводит к лучшему пониманию явлений этих процессов. В статье рассматривается влияние ускорения сжатого воздуха и уровня заполнения рабочей среды на формирование деталей из листовых и трубчатых геометрий. Опытным путем была установлена возможность изготовления сложных острокраевых и квадратнообразных геометрических деталей из алюминиевых сплавов при помощи пневмомеханической штамповки. Результаты исследования делают очевидным факт эффективного влияния изменяющегося давления сжатого воздуха и уровня заполнения камеры давления на формовку деталей. В данной работе представлены результаты основательных исследований пневмомеханической штамповки в сравнение с конвенциональным гидроформингом

Investigation of the Process Chain Bending-Electromagnetic compression-Hydroforming on the Basis of an Industrial Demonstrator Part

The increasing significance of lightweight construction concepts requires innovative and adapted production technologies and process chains for the manufacturing of complex parts made of typical lightweight materials. The feasibility and potential of such a process chain consisting of the steps Bending - Electromagnetic compression (EMC) Hydroforming is shown in the present paper on the basis of a demonstrator part similar to a structural component from the automotive industry. Here, special focus is put on the requirements on the production steps and the workpiece properties. Furthermore, the development and testing of EMC-equipment that is optimally adapted to the special forming task is described

Some aspects regarding the use of a pneumomechanical high speed forming process

A promising approach to the production of thin-walled workpieces in high strength materials is the use of a special pneumomechanical high-speed-forming process. This process uses a pneumatically accelerated plunger that dives into a pressure chamber filled with the working media in order to generate a short pressure pulse. Ways in which the pressure pulse can be influenced include e.g. varying the type of working media, the density of the working media, the accelerating pressure distance and the plunger geometry. The influence of these parameters on the process formed the subject of intense technological research at the Chair of Forming and Machining Technology (LUF) at Paderborn University. The results of these investigations were used to achieve an appropriate process and tool design for the pneumomechanical high-speed forming process. It thus proved possible to manufacture complex workpieces and geometrical details from thin-walled, high strength stainless steel or aluminium alloys that cannot be produced by conventional stamping processes. Because of the high uniformity of the pressure distribution in the radial direction, it is possible to achieve just small dimensional or geometrical deviations in respect of the desired shape of the workpiece. The planned paper will present results of the basic research conducted into pneumomechanical high-speed-forming as well as a comparison with electrohydraulic forming

Strength of Tubular Joints Made by Electromagnetic Compression at Quasistatic and Cyclic Loading

Electromagnetic compression of tubular profiles with high electrical conductivity is an innovative joining process for lightweight structures. The components are joined using pulsed magnetic fields which apply radial pressures of up to 200 MPa to tubular workpieces, causing a symmetric reduction of the diameter with typical strain rates of up to 10^4 sec^(-1). This process avoids any surface damage of the workpiece because there is no contact between component and forming tool. The strength of electromagnetically formed joints made of aluminum tubes under cyclic loads is essential to establish electromagnetic forming in automotive structures. In the present paper, the quasi-static performance of tubular joints made by electromagnetic compression produced of different mandrel materials will be analyzed as to the influence of process parameters. Therefore, experimental investigations on aluminum tubes (AA6060) joined on mandrels made of different aluminum, copper, and steel alloys were carried out. Furthermore, the behavior of joints with both mandrel and tube made of AA6060 at swelling cyclic loads (R = δ_ min / δ_ max =0) has been evaluated

Electrografting of BTSE: Zn films for advanced steel-aluminum joining by plastic deformation

This article presents the application of an adhesion promoting highly crosslinked ultrathin organic-inorganic hybrid layer applied to steel which promotes the subsequent joining process based on plastic deformation. The tensile shear results show that a significant increase of the bond strength between low-alloy steel (DC04) and aluminum (AW1050A H111), upon cold-pressure welding (CPW), could be achieved. Electrografting of an ultra-thin film of 1,2-bis(triethoxysilyl)ethane (BTSE) films on the steel surface was done from ethanolic solutions containing zinc ions. Based on surface spectroscopic analysis it is shown that silanol moieties present in the organosilane deposits can form stable chemical bonds with both the iron oxide covered steel and the aluminum oxide covered aluminum alloy. The successful modification of metal oxide surfaces with BTSE has been demonstrated via SEM-EDX, AFM, PM-IRRAS, and XPS measurements. In addition, electrochemical analysis of the BTSE:Zn films showed that the films lead to very good corrosion properties even at low thicknesses