Papers by Keyword: Process Control

Abstract: The transition towards sustainable mobility demands lightweight and modular carrier systems for high-voltage batteries and fuel cells that combine structural efficiency with effective thermal management. This study examines the feasibility of producing thin-walled, large-scale aluminum extrusion profiles for modular battery housings using AA6063. Numerical simulations and experimental trials are conducted to optimize die design and define process limits along the relation between circumscribing circle diameter (CCD) and minimal wall thickness t_min. Furthermore, different quenching methods are used to investigate the influence on surface distortion and final mechanical properties. A streamlined die design with reduced mandrel deflection has enabled defect-free extrusion under controlled conditions for the extrusion of a thin-walled, large-scale profile with a CCD-to-t_min ratio of 138. A narrow process window is identified for extrusion of defect-free profiles. Quenching studies have shown that active cooling methods affect surface deformation but have negligible influence on mechanical properties or microstructure due to efficient heat extraction inherent to thin-wall geometries for the investigated alloy. Scaling experiments using an enlarged cross section by a factor of 2.5 have confirmed similar process stability without wall thickness adjustments, achieving up to 38 % weight reduction compared with conventional designs under industrial conditions.

Abstract: This paper discusses the thickness distributions calculated from surface strain measurements using stereo Digital Image Correlations (DIC) for parts produced with Single Point Incremental Forming (SPIF). The research is carried out on six benchmark cones and pyramids with each convex, straight and concave walls. The accuracy of the thickness calculations, under the assumption of material incompressibility and using the formula for the Green-Lagrange strains, is compared to the thickness distributions measured with a fringe projection scanner. The thickness estimations based on the measured strains proved to be representative for the measured thickness distributions with a mean error of 0.0182 mm, which corresponds to a relative error of 1.47 % of the mean measured thickness. However, errors of up to 0.1688 mm were found in areas of high wall angles and curvatures, corresponding to a relative maximal error of 13.69 % of the mean measured thickness. Hence, the DIC measurements are well suited for characterizing the thickness. Using the thicknesses calculated from the DIC measurements to find the minimal thickness as an indicator of part failure, is possible with relative errors that have an average overestimation of 2.87% of the minimal measured thickness.

Abstract: Despite years of supporting research, commercial use of the Single Point Incremental Forming process remains very limited. The promised flexibility and lack of specific tooling is contradicted by its highly complex deformation mechanics, resulting in a process that is easy to implement but where workpiece accuracy is very difficult to control. This paper looks at geometry compensation as a viable control strategy to increase the accuracy of produced workpieces. The input geometry of the process can be compensated using knowledge about the deformations occurring during production. The deviations between the nominal CAD geometry and the actual produced geometry can be calculated in a variety of different ways, thus directly influencing the compensation. Two different alignment methods and three deviation calculation methods are explained in detail. Six combined deviation calculation methods are used to generate compensated inputs, which are experimentally produced and compared to the uncompensated part. All different methods are able to noticeably improve the accuracy, with the production alignment and closest point deviation calculation achieving the best results

Abstract: The efficiency of porous structure formation in aerated concrete can be improved by including the methods of thermal vacuum compaction or thermal vacuum compaction with vibration into the process as a means of creating high-quality composite cellular concrete. A graphic model of a phase composition change in the aerated concrete mix was developed allowing for an evaluation of the recipe and the mode of bubble porosity generation during hardening. This provides a control over the manufacturing processes and helps to produce aerated concrete with the specified porosity balance, which defines product properties.The effect of temperature and vacuum on molding sand during the initial stage of manufacture is proportional to the bubble porosity volume, which is important for a high-quality porous structure formation. In addition to the above, account must be taken of the combined effect of temperature, vacuum and volume ratio of phases in the base mix when using the proposed methods.Introduction of the developed processing methods into the manufacturing process improves the technology of aerated concrete production and allows for a fabrication of the finest advanced heat insulating and structural and heat insulating products.

Abstract: Theoretical principles of the formation of highly organized porous structure of cellular concrete are developed, based on model concepts of the dynamics of the expanding gas cavity in the liquid phase as a single control cell. The peculiarities of controlling the formation of cellular structure of aerated concrete based on the balance of forces in a three-phase disperse system on the model "gas pore - molding mixture" are revealed and a coalescing-aggregate scheme for porosity formation of the aerated concrete mixture is proposed. It is shown that, in accordance with the refined Rayleigh-Plesset equation, the determining factor in the formation of the cellular structure of aerated concrete is the pressure over the mixture to be poroused, the effect of the porosity being achieved by reducing the external pressure to the vacuum level. The division of pores by size in anaerated concrete mixture is proposed. The maximum pore size is determined by the capillary Laplace constant. The prospects of aerated concrete technology are associated with a decrease in the maximum and average size of cellular pores, as well as methods for eliminating pores of air entrainment and segmented pores. Reducing of the size of the pores will be reflected in the decrease of the Bond quantity and in the increase of the importance of capillary forces in the formation of the porous structure of aerated concrete. The concepts of the types of cellular structures are developed, depending on the average density and their boundaries for cellular concrete are established.

Abstract: Feedback and process control of metalforming processes has received increasing attention the lastdecade. Basically there exist four control philosophies; control ofprocess parameters during the punch stroke, iterative learning control(based on historical data), a combination iterative learning andfeedback control and finally feed-forward control. The present work willpresent three different control schemes which all are based onfeedback philosophy i.e. control during the punch stroke or iterativelearning control, where process parameters are updated according toprocess history. The three control schemes are tested using a non-linear finite element model of a square deep-drawing and finallypros and cons are discussed based on the numerical results.

Abstract: Silicon carbide (SiC) manufacturing is transitioning from 4 inch wafers to 6 inch wafers for production line devices. The main obstacle for SiC manufacturing high yield is defect control. Defectiveness inline control is well established for silicon power device. However, there are two main challenges related to SiC technology. The first challenge is incoming 4H-SiC substrates defectivity and epi layer crystallographic defects. The second challenge is inline defect detection at process steps such as implantation and annealing activation [,]. Defect detection and classification are difficult with current defect inspection tools because of substrate transparency at visible light, color variation, roughness, and wafers’ high warpage. In addition, SiC device integration has been requesting specific optimization. In this paper, collaboration studies have been done to develop solutions to these challenges. Yield correlation analyses have validated the process control flow set to address these two major challenges and to enable the fast ramp of the 6” production line of SiC devices.

Abstract: This paper aims documentary research of theoretical and experimental statistical process control in industrial engineering. The most effective means to reduce process variations against the customer requirements is to implement a quality management system based on statistical process control tools. Cutting regime changes in turning processes are based on careful monitoring of vibration. As soon as it is found in the milling excessive noise or vibration the measure to which it resort is to reduce one or more parameters (speed, feed and depth of cut) to remove the effect. Finally, the measure has a negative impact on performance.

Abstract: The production of irregularly shaped deep drawing parts with high quality requirements, which are common in today’s automotive body shell production, consistently challenge production processes. This challenge results from the high design requirements and automotive lightweight design, and hence the necessary use of high strength steels. Metal forming technology deals with these challenges using highly sophisticated methods to control the material flow. Several control loop methods have existed already in order to control the material flow in deep drawing processes, but only methods with a control intervention between two strokes. However, this kind of control method merely allows control intervention on measurements on the previous part or on measurements of material properties before the actual process. The method developed at the Institute for Metal Forming Technology in Stuttgart makes a control intervention possible during the deep drawing stroke. The used reference variable is the part wall stress and the control variable is the blankholder force, which is manipulated by using the segment elastic blankholder as an actuator. In this paper the experimental setup, the control methods, and the control loop itself will be presented. Furthermore, the developments of the new method will be described.

Abstract: When processing conventional semi-finished metal strips, distinctive changes in the material properties along the strip length are unavoidable. The roller levelling process is sensitive to changes of those strip characteristics. Thus, a process control allowing for an online adaption of the roller levelling machine according to the actual strip characteristics is highly desirable. In order to enable a precise process layout, the calculation by the Finite Element Method (FEM) provides a suited strategy. Furthermore, the coupling of user-subroutines to an FE code offers the possibility to implement and test respective control strategies. This work proposes a control strategy that is based on a force measurement in the first load triangle of a levelling machine. A first FE model including a feedback control is used to calculate the dependence between the force in the first load triangle and the roll intermesh in the last load triangle leading to a flat sheet. The results are transferred to meta models – so called control curves – that give a direct relationship between the measured force and the roll intermesh. Within a second FE setup a feed-forward control based on these control curves is implemented and the proposed control strategy is investigated for varying yield strengths along the strip length. Thus, the time consuming FE simulations that are necessary to obtain the control curves are decoupled from the actual levelling process. According to the obtained results, the introduced approach is able to improve the sheet flatness for thin sheets when a change in the material properties occurs.