Design and Adaptation of EMF Equipment

Since the electromagnetic forming (EMF) becomes more and more accepted within industrial manufacturing, the methods engineer has to deal with the choice of matching equipment as to perform the task of production in the best possible way. At the present time several manufacturers offer EMF-machines with different characteristics, whereby the machines consist of a pulse power generator and an exchangeable tool coil. The storable energy, the current capability and a high short circuit frequency enable the engineer to adapt tool coils for an optimised pressure course. In the following some aspects of how to dimension direct acting tool coil properties for the EM compression process will be considered. Basically the use of multi-turn coils is advantageous for a good matching. But in a lot of cases the use of a fieldshaper is necessary. It will be shown how the design of a tool coil system including a fieldshaper influences the pressure course. A special case is the application of EM compression in closed spaceframe structures for which a separable tool coil is required. A separable compression coil with non-welding contact elements will be presented

Impulse Hydroforming Method for Very Thin Sheets from Metallic or Hybrid Materials

Forming of very thin metallic and hybrid material foils is a demanding task in several application areas as for example in food or pharmaceutical packaging industries. Narrow forming limits of very thin sheet metals as well as minor process reliability due to necessary exact tool manufacturing (small punch-die clearance), both, causes abiding interest in new and innovative forming processes. In this contribution a new method using high pressure pulses will be introduced to form small geometry elements into very thin metal foils or into hybrid polymer-metal foil. It will be shown how the acting pressure pulse will be generated by electromagnetic acceleration of a certain mass, which initiates a pressure wave within a working media. The effect of different pulse lengths has been compared and evaluated by the forming result. Finally, an outlook concerning suitable pulse power equipment and its industrial capability will be given

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

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

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

On the Significance of the Die Design for Electromagnetic Sheet Metal Forming

Electromagnetic Forming is a high speed forming process using a pulsed magnetic field to form metals with high electrical conductivity, such as copper or aluminium alloys. During the process, typical pressure peaks up to 200 MPa and velocities in the range of 300 m/s can be achieved. As significant process parameters the pressure maximum as well as the local and temporal varying pressure distribution have been identified. As of a certain drawing depth and distance between workpiece and tool coil, the pressure does not act any longer on the workpiece, but the deformation process is still driven by the inertia forces. It has been found out that the velocity distribution within the sheet metal during the forming stages as well as at the time of impact with a die significantly influences the forming result. Additionally, a special undesired effect is the rebound behaviour of flat workpiece areas being in contact with the die. To investigate the influence capability of the die concerning this effect, the parameters stiffness and damping properties have been varied by means of simulation using a mechanical substitute model

Concept of Smart Electrohydraulic Press for Impulse Sheet Forming

Electrohydraulic impulse sheet forming (EHF) method proved its high efficiency at pilot, small-batch, and middle-scale production conditions. As the latest achievement, multielectrode discharge blocks provide effective forming of the middle and large size sheet parts. However, wide application of EHF technology in industry is limited mainly by two problems: instability of impulse pressure fields and lack of literature as well as skilled EHF specialists. Now the problem of instability is solved by a qualified EHF specialist with intermediate disclosing of tooling, inspection of intermediate shapes of blank, making corrections in loading diagram (electrodes’ connections), and setting of new level of discharge energies. New approach to this problem includes solutions based on intellectual computer numerical control of EHF equipment: monitoring of intermediate shape of sheet blank after each discharge and making corrections of loading parameters for the next discharge till the final shape of part. Intermediate shape can be determined by measurements with special sensors built in a die in characteristic places (points). Another subsystem should analyse position of several principal segments of blank, compare them with total strategy of forming procedure for a definite type of sheet part, reveal those places, which need higher pressure to harmonise forming process, and give this information to the subsystem controlling a multicircuit current generator for optimised configuration of activated electrodes and energy level, thus, determining new pressure loading diagram for the next discharge. Now, the tests for blank shape measuring system are planned to solve this principal problem for realisation of the submitted concept. In addition, principal design solutions for multicircuit current generator with special unit for reconnections of electrodes are in work.Спосіб електрогідравлічного імпульсного листового штампування (ЕГШ) довів високу ефективність в умовах пробного, дрібносерійного і середньосерійного виробництва. Новітнє досягнення, – багатоелектродні розрядні блоки, – забезпечує ефективне штампування листових деталів середніх і великих розмірів. Однак широке застосування технології ЕГШ у промисловості обмежується в основному двома проблемами: нестабільністю імпульсних полів тиску і недостачею літератури та кваліфікованих спеціялістів у галузі ЕГШ. У теперішній час проблема нестабільности розв’язується кваліфікованим спеціялістом ЕГШ шляхом розкриття оснащення, оглядом проміжних форм заготованки, внесенням корекцій у схему навантаження (схеми підключення електрод) і встановленням нових рівнів енергії розрядів. Новий підхід до розв’язання цієї проблеми передбачає рішення, які ґрунтуються на використанні інтелектуальної комп’ютерної числової системи керування обладнанням ЕГШ: виявлення проміжної форми листової заготованки після кожного розряду і внесення корекцій у параметри навантаження для кожного наступного розряду до одержання кінцевої форми деталю. Проміжну форму можна визначити шляхом міряння спеціяльними давачами, яких вбудовано в штамп у характерних місцях (точках). Друга підсистема має аналізувати положення декількох принципових ділянок заготованки, порівнювати їх із загальною стратегією процесу штампування для певного типу деталів, виявляти ті ділянки, які потребують більш високий тиск для гармонізації процесу формоутворення, і надавати цю інформацію в підсистеми, які керують багатоконтурним ґенератором струмів для утворення оптимізованої конфіґурації підключених електрод і рівня енергії, таким чином, визначаючи нову схему навантаження для наступного розряду. У теперішній час заплановано досліди по системі міряння форми заготованки для розв’язання цієї принципової проблеми в реалізації запропонованої концепції. Також опрацьовуються принципові конструкторські рішення для багатоконтурного ґенератора імпульсних струмів зі спеціяльним пристроєм для перемикання електрод.Способ электрогидравлической импульсной листовой штамповки (ЭГШ) доказал высокую эффективность в условиях пробного, мелкосерийного и среднесерийного производства. Новейшее достижение, – многоэлектродные разрядные блоки, – обеспечивает эффективную штамповку листовых деталей средних и больших размеров. Однако широкое применение технологии ЭГШ в промышленности ограничивается в основном двумя проблемами: нестабильностью импульсных полей давления и недостатком литературы и квалифицированных специалистов в области ЭГШ. В настоящее время проблема нестабильности решается квалифицированным специалистом ЭГШ путём раскрытия оснастки, осмотром промежуточных форм заготовки, внесением коррекций в схему нагружения (схемы подсоединения электродов) и установлением новых уровней энергии разрядов. Новый подход к решению этой проблемы предусматривает решения, основанные на применении интеллектуальной компьютерной числовой системы управления оборудованием ЭГШ: определение промежуточной формы листовой заготовки после каждого разряда и внесение коррекций в параметры нагружения для каждого последующего разряда до получения окончательной формы детали. Промежуточную форму можно определить путём измерения специальными датчиками, встроенными в штамп в характерных местах (точках). Вторая подсистема должна анализировать положение нескольких принципиальных участков заготовки, сравнивать их с общей стратегией процесса штамповки для определённого типа деталей, выявлять те участки, которые нуждаются в более высоком давлении для гармонизации процесса формообразования, и подавать эту информацию в подсистемы, которые управляют многоконтурным генератором токов для создания оптимизированной конфигурации подключённых электродов и уровня энергии, таким образом, определяя новую схему нагружения для следующего разряда. В настоящее время запланированы опыты по системе измерения формы заготовки для решения этой принципиальной проблемы в реализации предлагаемой концепции. Также прорабатываются принципиальные конструкторские решения для многоконтурного генератора импульсных токов со специальным устройством для переключения электродов

Aspects of Die Design for the Electromagnetic Sheet Metal Forming Process

Within the electromagnetic sheet metal forming process, workpiece velocities of more than 300m/s can occur, causing typical effects when forming into a die, which will be described and discussed in the present paper. These effects make numerous demands regarding the die design. In order to analyze these requirements, experimental as well as numerical investigations have been carried out. Thereby, special focus is put on the possibilities to accomplish these requirements, which are discussed in the following

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

Process Investigation of Tube Expansion by Gas Detonation

The present paper deals with the expansion of tubes by direct application of gas detonation waves, i.e. the gas is both pressure medium and energy source. After an introduction to gas detonation forming, measurements of the motion process and the internal pressures are presented. Results of free expansion and of forming into a die are thoroughly studied and compared to the results of quasi-static burst tests and hydroforming. Using pure aluminum Al99.5 and a medium strength alloy AlMgSi1, expansions by 25 % and 20 % respectively are obtained. A simulation delivers details on the deformation process and specially prepared probes of high-speed tension tests give new insight into metallographic material behavior at different strain rates