Key Engineering Materials Vol. 639

Abstract: 3D optical metrology methods are increasingly used in the research of sheet metal materials and in sheet metal production processes. Optical measuring systems are implemented in different process stages, including design, sheet metal material research and component development, tool making and production as well as series accompanying quality control.Today’s development processes are initially driven from computational methods. Especially for the development of sheet metal components the numerical forming simulation is an important tool. However, performing a reliable forming simulation requires accurate input parameters like 3D geometry data for meshing, material parameters and boundary conditions which can be obtained with optical measuring systems. Further on the validation of these numerical simulations is supported with optical full-field sheet metal forming analysis.In the tool manufacturing phase 3D measurement data contributes in reducing the time frame for CNC machining processes, for the try-out phase, future tool reproduction as well as for repair and maintenance.With automated 3D measuring solutions series accompanying quality control is performed to determine tool wear and to shorten the response time if problems in the production occur.This paper is extending past work [1] and discusses today’s contribution of optical 3D measuring techniques in sheet metal component development and production, covering the areas of determining input parameters for sheet metal forming simulations and its validation, tool manufacturing, including the try-out, and production quality control using automated optical measurement machines.

Abstract: Production of light weight and crash resistant vehicles require extensive use of AHSS (DP,TRIP,TWIP) and Al alloys to form complex shapes. This paper discusses practical determination of material properties and selection of lubricants for forming AHSS using a die set, designed for deep drawing. Tests were conducted in a 300 ton servo press. Thinning at the critical area of the formed part were measured and compared with FE simulation. Prediction of temperatures in deep drawing of selected DP steels and Al alloys in servo press is also discussed.

Abstract: Data-driven quality evaluation in the stamping process of car body parts is quite promising because dependencies in the process have not yet been sufficiently researched. However, the application of data mining methods for the process in stamping plants would require a large number of sample data sets. Today, acquiring these data represents a major challenge, because the necessary data are inadequately measured, recorded or stored. Thus, the preconditions for the sample data acquisition must first be created before being able to investigate any correlations. In addition, the process conditions change over time due to wear mechanisms. Therefore, the results do not remain valid and a constant data acquisition is required. In this publication, the current situation in stamping plants regarding the process robustness will be first discussed and the need for data-driven methods will be shown. Subsequently, the state of technology regarding the possibility of collecting the sample data sets for quality analysis in producing car body parts will be researched. At the end of this work, an overview will be provided concerning how this data collection was implemented at BMW as well as what kind of potential can be expected.

Abstract: In the deep drawing process, the blank-holding force (BHF) is an important process parameter affecting the energy consumption and the successful production of parts. In the present work, both experiments and finite element simulations have been conducted to investigate the influence of constant and time variable BHF on drawing force (DF) and thickness distribution in the deep drawing process of cylindrical and square cups. A finite element model was developed in the AutoForm software and validated with experiments. The developed model has been used for the simulation of deep drawing process of AA6016-T4 aluminum alloy sheet. The experimental and numerical results show that, using a variable instead of a constant BHF, the DF can be decreased in the expense of wall thickening.

Abstract: Product development is complex due to the manifold requirements resulting from various perspectives, such as design, production, safety and sales. A concurrent engineering (CE) approach permits to respect all perspectives in the early development stage. However, in the architecture and construction sector for example, CE is particularly difficult to realize, because the central steering for this collaboration process is missing. Thus, the application of CE in the research sector can promote technical progress and cost reduction. In the specific field of freeform architecture, in most cases an individual shape of single components is unavoidable and the use of standard components impossible. Due to missing universal and mature construction concepts for freeform buildings, they are mostly realized with customized solutions often including material-consuming substructures, while the visible skin has only limited structural and functional properties.In this context the present paper proposes a novel universal panel system made of double-curved sheet metal layers enabling the assembly of self-supporting lightweight structures for the realization of freeform surfaces. The panel system has been developed in cooperation of architects, construction and production engineers, successfully applying an interdisciplinary CE approach. As a result, the concept allows for material and cost efficient solutions applicable for a wide range of freeform applications. The detailed development of the panel system is still in progress.Besides the general panel concept, the paper presents in particular the corresponding manufacturing chain and the tooling concept. Accounting for the varying part geometries in this application a flexible manufacturing chain based on the combination of stretch forming and incremental sheet forming has been developed. The entire production process is implemented in a single machine setup and successfully tested on a small-scale prototype.

Abstract: The continuous need of improved performances in automotive in terms of dynamic behaviour, fuel consumption and safety of passengers, have raised the interest for lightweight alloys as well as for the optimization of the design of the structural components of the car chassis. With this twofold aim, many researches are focused in the evaluation of new car designs, materials, and processes to manufacture even more complex components with increased stiffness-to-weight ratio. From that standpoint, the use of shaped hollow parts in the car body in white appears one of the most promising solutions, due to the elevated stiffness of tubular structures and the reduced weight. However, hydroforming processes that have been traditionally used to shape such components have shown several limitations with lightweight alloys, suffering their reduced formability, the temperature limitations of the forming liquids as well as long process time and complex machines. In this paper the recently introduced technology of Hot Metal Gas Forming (HMGF) has been considered, in order to investigate the influence of the process parameters on the formability of AA6060 tubes. The semi-finished tubes were produced through direct hot extrusion, with different temperatures and feed rates process, and tested by HMGF at elevated temperatures. The properties of the final products are investigated through analyses of the microstructure, micro hardness and thickness measurements.

Abstract: In deep drawing processes sustainability can be increased and processing steps can be omitted by abolishing any lubricants. Tailored tools with locally textured surfaces offer a possibility to compensate higher strains caused by the changed tribological system. Ultrashort pulsed laser machining is an advantageous approach to generate surface features. Thus, very hard and brittle materials can be processed inducing negligible heat affected zones so that the surrounding tool material keeps its initial properties. The material-dependent process parameters for efficient picosecond laser structuring are applied. The effects of features with single feature sizes in the range of 100 µm to 500 µm on friction of the tribological pairing are presented. The dependencies of the friction coefficient on the properties of the micro features - the geometry, the shape, the density and the orientation - are investigated by using a ring-on-disc-tribometer. The ring representing the tool is made out of the cold work steel 1.2379. The zinc-coated deep-drawing steel DC04 is used as disc respectively workpiece material. During the ring-on-disc-tests a constant contact pressure of 2.1 MPa and a mean sliding velocity of 100 mm/s are applied. To obtain the significant influences of micro features on friction, screening tests by varying the parameters according to the Shainin method are carried out. Because of the stochastically occurring high wear observed in reference experiments a changed methodology of ring-on-disc-tests is proposed. Applying this method the effects of textured ring surfaces on friction coefficient of steel-zinc-sliding are evaluated and compared to untextured rings. The latter are tested non-lubricated as well as with lubrication. The screening tests show that the feature orientation is the significant parameter influencing the friction. Selecting this parameter together with the feature density the friction coefficient can be adjusted with regard to untextured surfaces.

Abstract: In order to optimise the material utilisation and improve the lightweight design of automotive parts tailored hollow profiles are needed, especially as semi-finished parts for hydroforming. Internal Flow-Turning is an innovative incremental forming technology which enables the manufacture of tubes featuring a varying wall thickness and a constant outer diameter. These characteristics facilitate the material feed at hydroforming processes significantly. In addition, the spinning-related forming technology improves the mechanical material properties, shape and dimensional accuracy, and the surface quality of parts produced.

Abstract: In recent years, laser forming of round plates into bowl or dome shapes by use of circular, radial and circular-radial patterns have been investigated. Usually formed circular plates using circular or linear patterns are distorted as asymmetric saddle shapes. In this study, a new flower pattern has been proposed to form round plates by laser. To make this pattern, the laser beam scans several petal paths on a circular blank. Laser forming of round plates by the proposed pattern have been studied by three dimensional finite element method. The results have been compared for the flower pattern and other conventional circular and radial pattern. In addition experiments have been conducted to verify the numerical results. The results show that the deformed parts by the petal path are more symmetrical in comparison with circular and radial patterns. It was found that in laser forming of dome-shaped parts, scanning by petal paths prevent distortion and increase the geometrical symmetry of deformed parts by laser. It was shown that laser radiation on petal paths improves the deformation process of laser forming of circular steel sheets.