Key Engineering Materials Vol. 344

Abstract: Quality Management Systems (QMS) of volume production car makers tend to be large. Complexity levels in such structures are difficult to manage. From the design release to the production stage, a manufacturer has to control roughly 9000 parts (including fixings) for a large size car. A large number of subsystems, together with their coupled interactions increase a system’s complexity. Results of the application of a model to manage complexity in some automotive companies in the West Midlands (UK) suggest that complexity reduction leads to quality improvements.

Abstract: A rapid flow of materials with little intermediate buffering between steel mill and hot strip mill has many benefits. One is energy savings due to raised charging temperature in the reheat furnaces of the hot strip mill. Another is that tied capital is freed up, thereby improving mill economy. Still, it is not unusual that average lead-time is in the order of days, or even weeks. The aim of the present work was to show how lead-times from casting to rolling could be improved by changes in the scheduling function. A System Dynamics model of a stainless steel strip production facility with continuous caster and hot rolling mill was created. The model was used to study the dynamics of the system in response to changes in parameters that defined the scheduling configuration. More frequent schedule updating generally resulted in less work in process (WIP) and shorter lead times from casting to rolling, with resulting higher charging temperatures. The amount of oscillation in the system was also reduced. More frequent work roll changes were required when scheduling frequency increased, resulting in an increased fraction of setup time in relation to total processing time. Therefore, a development towards increased scheduling frequency may have to be complemented by efforts to reduce changeover times. The conclusion was that dynamic scheduling routines with frequent schedule updating result in better overall performance of the system due to lower WIP and better heat utilization. Dynamic scheduling routines with frequent updates make the system respond better to changes in the system and give better overall performance. The result is lower WIP, increased energy efficiency and less oscillation in the system.

Abstract: Laser forming of sheet material has been widely investigated for the last 15 years. While researchers encounter severe problems during the forming of a 3D free form shape, at least one category of surfaces can be made with the process of laser forming, namely the developable surfaces, which are widely used in, for example, ship building. Those surfaces show a zero gaussian curvature and can be unrolled onto a plane without distortion. Until now, the forming of such surfaces has been more or less heuristic, but this paper aims to treat the CAD/CAM issues of this problem in a generic way. Once the surface has been defined, in order to obtain a developable surface, the surface is rebuilt into a number of planar flanges. After collision testing, the unfolding of the surface is calculated. The developable surface is scanned on the boundary between two flanges using laser settings that are determined based on efficiency optimisation considerations, keeping in mind the hardware limitations and the possible surface damage for a too high input energy. In this paper, the proposed CAD/CAM procedure is validated by means of a developable parabolic cylinder.

Abstract: Over the past few years both sheet metal process planning and production planning issues received increased attention. For process planning of the laser cutting process, nesting algorithms are developed in order to decrease the waste material. Additionally, algorithms are available for path planning, i.e. determining the best sequence for cutting the different parts. Production planning is mainly performed based on the ability to fill a sheet. For air bending, process planning focuses on bend sequencing and tool selection, while production planning optimization aims at minimizing time consuming setups between the different production layouts at the press brake. However, when integrating both processes, the benefits from individual optimization counteract one another: good nestings at the laser machine can create additional setups at the press brake, hence increasing the makespan. An integrated approach is proposed to verify whether this problem can be solved by already taking into account possible setups at the press brake in the early nesting stage. Integration of both processes aims at an optimal combination of parts on a sheet and minimization of the setups at the press brake. In this paper, an overview of a modeling effort addressing both goals is proposed. When combining parts on a sheet, preference is given to parts requiring the same production layout at the press brake. If this is impossible, production layouts with low changeover times are preferred. Industrial cases are used to verify the applicability of the proposed model. The results are compared to a reference approach where nesting is performed with dedicated software and planning for air bending is based on an operator’s experience. Compared to this reference approach, a makespan reduction and a setup time reduction can be observed. The planning is generated almost instantaneously and no additional sheets are required compared to the reference approach. Future research will focus on expanding the model and verifying its applicability on a larger data-set.

Abstract: The nesting of two-dimensional irregular shapes is a common problem which is frequently encountered by a number of industries where raw material has to be, as economically as possible, cut from a given stock sheet. A frequently recurring problem as far as cutting stock is concerned, is how to obtain the best nesting of some pieces of flat patterns which occupy minimalarea convex enclosure. The area of convex enclosure is related to the convex hull of the union of patterns which can be imagined as a large rubber band surrounding the set of all polygons. Our goal is to automatically obtain the smallest area convex shape containing all the patterns. As a matter of fact, Cheng and Rao have proposed an heuristic “stringy effect” procedure for clustering which follows a descending order of area of patterns. The “stringy effect” is able to put each new piece in a position which minimises the value of the distance between the centroid of each added piece and the centroid of the already formed cluster. The procedures till now shown in literature are quite complex. They make use of sliding techniques, and are not able to effectively work with relatively multiply-connected figures. In particular, the different procedures proposed are based on the No Fit Polygon computation of non-convex polygons, which often generates holes. This work is a proposal for a more efficient method, which can be used in heuristic procedure. In this paper a new procedure for the calculation of “No Fit Polygon” (NFP) of non-convex polygons is presented. Given two non-convex polygons, the algorithm is able to calculate their NFP very quickly and without any approximation by a polygon clipping method. By iterating this procedure with every polygon of our set, and positioning them using the “stringy effect” technique, it is so possible to obtain a convex shape that contains all the patterns, having the minimal area.

Abstract: In contemporary industrial production the ecological aspects have increasingly important role in selection of sheet metal forming process. To produce sheet metal parts with minimal environmental burdening the shortening of forming processes including the procedures for production of appurtenant forming tools as well as decrease use of lubricant is prerequisite. The ecological aspects have to be considered also already in developmental phase where the forming technology is evaluated in digital environment with FEM simulations. In addition, particularly in small and medium batch production the geometrically complex parts are difficult to form economically with conventional forming processes like deep drawing or stretching. Therefore, new concepts like hydro-mechanical forming or incremental sheet metal forming were developed. In order to select the optimal forming process the production costs as well as the environmental aspects like lubrication, noise, pollution and energy per produced part have to be considered. The paper is focused towards the comparison of conventional deep drawing (DD) process aimed for forming the pyramid-shaped part with single point incremental forming technology (SPIF). The economical and ecological aspects affecting the successful forming by both concepts are determined. Comparative evaluation was established in order to present advantages and drawbacks of each analysed technology.

Abstract: Properties and functional behavior of modern products are strongly influenced by their surface characteristics - like their appearance and haptics as well as their optical, tribological and fluidic performance [1]. In present production processes these functional features are mostly generated by surface treatment processes (e. g. grinding, etching, coating). In contrast to these costintensive and complex off-line sequences rolling provides an opportunity to apply functional structures on sheet metal products using non-pollutive synergy-potentials of the process.

Abstract: Boss forming, which is sometimes called hub forming, has attracted its attention as an environment-friendly rotary forming process to form a circular plate with a hole into a boss shape. An experimental study was conducted to survey the technological possibility of boss forming. Boss forming of A1050-O commercially pure aluminum plate of 10 mm thickness was carried out at room temperature under various working conditions. The effects of the working conditions on the metal flow in boss forming were clarified experimentally.

Abstract: This paper deals with an industrial three rolls coater. The behaviour law of the elastomer roll cover in different environments is first established in order to be taken into account in the numerical simulation of the process. Cyclic compression tests are performed and compared to the corresponding numerical simulation to precisely determine the viscoelastic parameters. With the identified parameters, a finite element simulation of the process is then performed to evaluate the meniscus stability in real contact conditions. The influence of the determined elastomer behaviour laws on the free surface position is discussed.