Key Engineering Materials Vol. 549

Abstract: This paper describes a knowledge based system (KBS) developed for process planning of axisymmetric deep drawn sheet metal parts. The proposed system is structured into three modules. For the development of proposed system technical knowledge is acquired from different sources of knowledge acquisition and it is represented by using IF-THEN rules. Rules are coded using AutoLISP language and user interface is created using Visual Basic 6. The proposed system automatically models the part geometry in the drawing editor of AutoCAD, calculates blank size, selects the necessary process parameters required for production of deep drawn parts and generates process sequence. The system is flexible because its knowledge base can be extended and modified as old manufacturing facilities are discarded or newer ones are acquired in a particular enterprise. The suitability of proposed system is demonstrated by taking an example of industrial deep drawn sheet metal part. As the system can be implemented on a PC having AutoCAD software and therefore its low cost of implementation makes it affordable for small and medium scale sheet metal industries.

Abstract: In case of sheet metal forming the main dimensional errors are caused by the springback phenomena. The present work deals with numerical simulation related to draw bending and springback of U - shaped parts. The current paper is trying to prove out the important role of the blank holder force variation during the forming process. The Dynaform 5.8 software was used to simulate the forming process, in which the blank holder force varies in four steps between 0 and 50 kN. The factorial simulations test plan was made to cover completely the variation domain and 256 simulations were necessarily to be performed. The part obtained after each simulation is analyzed and measured to quantify the errors caused by springback. Parameters as: angle between flange and sidewall, angle between sidewall and part bottom, chamfer radius between part bottom and sidewall or chamfer radius between sidewall and flange are recorded in a data base. The initial simulations plan together with the generated data base is used as an input for the genetic algorithm optimization method. With the optimized process parameters a new simulation is made and the final shape of the part is compared with the ideal geometry. The shape of the part obtained with the optimized parameters is proving the capability of the proposed method.

Abstract: A servo-driven eccentric press is a synonym for innovative and economic metal forming technology. The path-time-characteristic of the ram of servopresses can be adapted to individual requirements of various forming processes. To achieve a high dynamic, the rotary inertia of the drive train should be as low as possible. Thus, a flywheel is not suitable to provide the energy required for both, the forming process as well as the ram kinematic. Hence the eccentric shaft is driven by the electric motor only. As a consequence, the press force has to be provided completely via the torque of the servomotor. High investment costs resulting from the required size of the drive components is a challenge to be conquered. This pushes the costs for the drive components. Another challenge is the unbalanced power consumption of the servomotor. Energy-converting and energy-storing systems are essential to compensate the power peaks resulting from the forming process and inertia forces. Nevertheless, these systems are expensive and reduce the energy efficiency of the press. Facing these challenges, a novel and innovative drive concept for eccentric presses is being developed at the Institute of Forming Technology and Machines (IFUM). The concept and the results of a first multibody simulation are presented in this paper.

Abstract: Two basic types of load for the tool active elements can be distinguished for the shear cutting process of sheet metal. For high strength, brittle materials, the stamping punch will be exposed to distinctive oscillating axial dynamic loads as a result of abrupt released potential energy, from the tool active elements, the blanking tool and the stamping press, caused by a sudden cracking of the sheet. In contrast, when shear cutting ductile materials, sheet metal will be drawn into the die clearance and the resulting friction between the punch and the cut surface can cause high forces when pulling the punch out of the hole. When using punches featuring a complex cutting peripheral form, - not available as a standard part - it is necessary to decide between head and shank of the punch manufactured out of one part or a shaft without head, which is usually cheaper and can be manufactured by electro-erosive wire-cutting. In the second case, a linking element must be accepted, transferring the load transmission between shaft and tool. This linking element, realized by a form lock or traction, can be the reason for premature failure of the punch. The two described cases of load, in combination with lacking knowledge of the real load on the link as well as eligibility of different punch linking types for each case of loading, cause unnecessary cost in tool manufacturing by oversizing or punch fracture. For this, solid punches as well as joined punches with dowelled or screwed heads have been compared in systematic tests. Brazed and bonded punch heads have been involved in the test series as cost-efficient alternatives to custom punches. Collaterally, characteristic values have been determined for each type of punch in static and dynamic measurements. Especially impact absorption and stiffness of the connection represent non-destructive measureable values allowing a comparison of stamping punches in terms of their dynamic fatigue limit.

Abstract: The productivity of bending on press brakes is strongly affected by the changeover time between consecutive tooling setups. The need for flexible tooling systems that can reduce the setup time is therefore obvious. This is a fortiori true for robot supported bending operations, where the tool system should preferably allow fully automated setup of bending stations. In this article an innovative tooling system concept is presented that can adjust to different punch profiles (from straight tools to deep gooseneck profiles), provide horn tool functionality and allow setups with open punches for collision avoidance during bending. The Leuven bend tooling design can accommodate fully automated changeover between bending jobs. A prototype version of the Leuven bending tool system has been manufactured and extensively tested. Validation results with respect to achievable load levels and stiffness are reported in the article.

Abstract: The press frame vibrations of a stamping press due to the high number of strokes, as well as the vibrations of the ram caused by the cutting impact have a great influence on the economy of a blanking process. The following contribution presents the state of the art regarding the compensation of these and explains the disadvantages of the existent solutions briefly. Based on this overview, two methods are presented to overcome the disadvantages. The first method introduces the vibration compensation of a press body by means of an auto-adaptive mass balancing system. Consisting of four linear motors this system does not increase the inertial forces of the drive train. This is particularly interesting for servo presses. The second method is the compensation of the ram vibrations by using additional forming operations in chad area. This approach enables tool wear reduction with very low investment costs compared to a machine-side solution.

Abstract: This paper presents a low cost knowledge based system (KBS) framework for design of bending die. Considerations for development of KBS are discussed at some length. The proposed framework divides the task of development of expert system into different modules for major activities of bending die design. The procedure of development of KBS modules is also described at length. Production rules for each module are recommended to be coded in the AutoLISP language and designed to be loaded into the prompt area of AutoCAD or through user interface created using Visual Basic. Each module of the proposed framework is user interactive. Development of one module of the proposed framework is also described at length. This module is capable to assess manufacturability of bending sheet metal parts. An illustrative example is also included to demonstrate the usefulness of this module. The proposed system framework is flexible enough to accommodate new acquired knowledge. As the proposed system is implementable on a PC having AutoCAD software, therefore its low cost of implementation makes it affordable even by small scale sheet metal industries.

Abstract: The material for the experiment was a copper-free Al-Zn-Mg-alloy. Because of natural aging after solution treating these materials are not storable at room temperature in T4 temper. Therefore 7xxx series Al alloys are mainly delivered in an artificially aged T6 temper. This state is not proper for a cold formability process, a thermal formability processes like hot working has to be use. In this paper a process chain based on so-called retrogression and re-aging (RRA) treatment was investigated to allow cold forming after a short time treatment. To achieve this tensile test specimens were tested under various retrogression temperatures (220 - 360 °C) and at times (1 - 7 min) to evaluate the flow curve. The properties like strain hardening exponent n and strength coefficient C of the Ludwik-Hollomon equation, a common approximation of the flow curve, are illustrated and the influence of the process parameter is discussed. A re-aging treatment at 130 °C for 16 h after retrogression of non-deformed and deformed material is also examined.

Abstract: Tailor Welded Blanks (TWB) are characterized by the fact that sheets with different material qualities and/or thicknesses are welded together before the forming process. The application of TWBs in the automobile industry brings several advantages, such as the reduction of car body weight and manufacturing costs, as well as the integration of several drawing parts into one part. Despite several established tailor welded blanks types, a new version has emerged: The Tailored Hybrid Blanks (THB). The current investigation focuses on tailored hybrid blanks joined by the CMT-welding technology. The main aim of this study is to specify the mechanical properties as well as the formability of Aluminum Steel Tailored Blanks. Steel (HX340LAD, 0.8 mm) sheets covered by different zinc coat thicknesses were combined with an aluminum alloy (AA6014-T4, 1.2 mm). In order to determine the material properties and to analyze the Heat Affected Zone (HAZ), microhardness measurements were taken transversal and longitudinal to the weld line. Results indicate a change of hardness and a very small HAZ. Tensile tests (perpendicular to weld line) and Nakajima tests with online deformation analyses show that the main formation takes place on the aluminum side.

Abstract: Due to beneficial characteristics such as high specific strength, corrosion resistance and biocompatibility Ti-6Al-4V alloy has become the most important industrially produced titanium alloy during the last decades. Commonly used for aerospace technology and medical products, nowadays Ti-6Al-4V covers 50% of the worldwide produced titanium alloy parts. Different deformation operations as forging and casting as well as machining are used to shape titanium alloy components. For sheet metals, cost and time of fabrication can be reduced significantly via the near net shape technology sheet metal forming. Materials such as the α + β alloy Ti-6Al-4V with high yield stress and comparatively low elastic modules need to be formed at elevated temperatures to increase their formability. Numerical simulations are applied to calculate the forming behavior during the process and conclude the characteristics of the shaped part. Therefore in this paper the mechanical behavior of this titanium alloy is investigated by uniaxial tensile test within elevated temperatures ranging from 250 to 500 °C. Finally, the experimental results are adapted to models which predict the flow response in order to describe material behavior in finite element analysis of the forming process.