Tomasz Bartkowiak

Modeling Performance of a Production Line and Optimizing Its Efficiency by Means of Genetic Algorithm

A production line is a fundament of modern high scale FMCG industry. The performance of the line depends on various factors, out of which breakdowns, cleanings and changeovers play the most important role. The paper describes the idea of modeling production line performance by its decomposition into discrete subsystems. Every machine or workstation together with preceding buffer constitute a single subsystem, which is characterized by statistical distributions of time to repair, time between failures, processing speed and capacity. Time dedicated for cleaning and changing format parts between different production batches is also considered in the model. Subsystems are connected with each other by conveyors. The model was simulated by the given time step. In order to verify the simulation results, the data from the real production line were compared and used for adjusting the parameters of the model. The described specimen consisted of six workstations connected with conveyors. There was one high capacity buffer between the second and third station. The efficiency of the whole line as well breakdown time characterizing every machine was captured by data acquisition system. Based on the given data, the parameters of statistical distributions of time to repair and time between failures were estimated by approximation to known distributions. In addition, statistical distributions of cleaning and changeover time were derived in order to provide general performance of the production line. Genetic algorithm was introduced to optimize the line parameters in order to achieve higher efficiency and to identify potential bottlenecks.Copyright

Validation of simulation model of the filling line failures / Walidacja modelu symulacyjnego uszkodzeń linii napełniania

Abstract The main objective of the article is to present the methodology of validating a simulation model of failures of serial production line. In case of the investigated object, the simulation model was tested to find technological solutions which could compensate for the impact of failures on the operation of important objects present on the line before a failures occurs. A possible solution may be to introduce a new buffer or to adjust the size of existing buffers. Validation is one of the most significant stages in the process of constructing simulation models, as it concerns the credibility of the model. The article presents the use of disturbances modeling, especially breakdowns and micro-stoppages, in the simulation model. It also shows the statistical distribution applied in the model and defines the validation measurement instrument as well as evaluation criteria. All these features are the major strengths of the article. Streszczenie Głównym celem artykułu jest pokazanie metodyki postępowania w procesie walidacji modelu symulacyjnego uszkodzeń linii produkcyjnej pracującej w układzie szeregowym. W przypadku badanego obiektu model symulacyjny był badany po to, aby znaleźć rozwiązania techniczne kompensujące wpływ uszkodzeń na pracę istotnych obiektów znajdujących się w linii przed miejscem wystąpienia uszkodzenia. Takimi rozwiązaniami może być wprowadzenie dodatkowego bufora lub dopasowanie wielkości buforów istniejących. Walidacja jest jednym z najważniejszych kroków w budowaniu modeli symulacyjnych, ponieważ dotyczy ona poziomu wiarygodności zbudowanego modelu. Najważniejszymi atutami artykułu są: wykorzystanie modelowania zakłóceń pracy systemu w modelu symulacyjnym, pokazanie jakie rozkłady statystyczne są do tego wykorzystywane, definicja miernika dla walidacji i kryteriów jego oceny w modelu symulacyjnym.

Computer-aided alignment of castings and machining optimization

The presented publication demonstrates an accuracy assessment method for machine tool body casting utilizing an optical scanner and reference model of the machine tool body. The process allows assessing the casting shape accuracy, as well as determining whether the size of the allowances of all work surfaces is sufficient for appropriate machining, corresponding to the construction design. The described method enables dispensing with the arduous manual operation of marking out as well as shortening the time of aligning and fixing the casting body for machining. For the experimental setup, four rotary indexing table castings were investigated according to the method principles. The geometric accuracy of each casting was examined by comparing their scans with the computer-aided design model, and the machining allowances were evaluated to determine casting qualification for machining. The nominal volume of material to be removed was established and subsequently optimized to reduce the volume to be machined. Thus, a rapid method of aligning a casting in a machine tool according to the planned optimized distribution of machining allowances was developed. For the set of measured castings, it was proven that their poor geometric quality precluded the possibility of further machining according to standard marking out instructions. However, by following the presented methodology, it was possible to successfully process the entire set while reducing the overall volume of the material removed by 4.5–9.6%, as compared with nominal values. The obtained results ultimately confirmed that manual marking out could be eliminated from the casting assessment process.

A Simulative Study Approach for Improving the Efficiency of Production Process of Floorboard Middle Layer

The subject of this paper is the simulation study into the improvement of the production process of floorboard middle layer. The object of our interest in the manufacturing process of wooden floorboard which consists of three layers: lower—made of softwood pieces glued together; middle—in a form a module, made of softwood slats and plywood, and hardwood upper layer. The process improvement involved a better use of raw materials in the form of plats (of variable dimension groups) by reducing losses caused by defects such as wane and knots. A simulation model of the manufacturing process was created by using DES software. Thanks to that model, buffers size and a performance of the designed systems including their anticipated breakdowns were estimated. As a result of the study, a concept of the entire production system meeting the requested production capacity and material efficiency was devised.

Reducing negative impact of machine failures on performance of filling and packaging production line: a simulative study

The paper demonstrates the use of a Discrete Event Simulation tool to reduce the negative impact of machine failures on the performance of a filling line. The buffer allocation problem has received a lot of attention, but still there are examples of unreliable production systems for which a buffer can be allocated in order to increase their productivity. The subject of the study is a filling and packaging production line which consisted of seven machines connected by conveyors. Machine failures are registered by maintenance Data Acquisition system. Those data are used to derive statistical distributions for Time To Repair and Time Between Failures. The model is built using FlexSim simulation software and different allocation scenarios are considered. Introduction of buffers results in an increase in mean line throughput by 15%. The initial results indicate that the proposed approach may lead to the reduction of negative effects of machine failures.

Multi-scale curvature tensor analysis of machined surfaces

Abstract This paper demonstrates the use of multi-scale curvature analysis, an areal new surface characterization technique for better understanding topographies, for analyzing surfaces created by conventional machining and grinding. Curvature, like slope and area, changes with scale of observation, or calculation, on irregular surfaces, therefore it can be used for multi-scale geometric analysis. Curvatures on a surface should be indicative of topographically dependent behavior of a surface and curvatures are, in turn, influenced by the processing and use of the surface. Curvatures have not been well characterized previously. Curvature has been used for calculations in contact mechanics and for the evaluation of cutting edges. In the current work two parts were machined and then one of them was ground. The surface topographies were measured with a scanning laser confocal microscope. Plots of curvatures as a function of position and scale are presented, and the means and standard deviations of principal curvatures are plotted as a function of scale. Statistical analyses show the relations between curvature and these two manufacturing processes at multiple scales.

Kinematics of a Novel Type Positioning Table for Cast Alignment on Machine Tool

The paper presents a study into the kinematics of a novel type of a rotary positioning table based on the constrained parallel mechanism. Fixture and leveling a workpiece on a machine tool table is an essential stage in machining or layout process. In this study, a compact low-height rotary table is presented for automated leveling, which can be mounted directly on the machine tool table without a significant decrease of the workspace. The authors propose a modification of parallel mechanism by introducing four extensible leg design with specific geometrical constraint for workpiece positioning and in order to achieve higher rigidness. The table is driven by four hydraulic linear actuators which are integrated in the linkages. The designed model allows to rotate the table about the sphere center about three independent axis. Procedures using meta-heuristic methods were implemented to optimize the geometrical dimensions of the entire mechanism for the required workspace.Copyright

Characterization of 3D Surface Texture Directionality Using Multi-Scale Curvature Tensor Analysis

Anisotropy of surface texture can in many practical cases significantly affect the interaction between the surface and phenomena that influence or are influenced by the topography. Tribological contacts in sheet forming, wetting behavior or dental wear are good examples. This article introduces and exemplifies a method for quantification and visualization of anisotropy using the newly developed 3D multi-scale curvature tensor analysis. Examples of a milled steel surface, which exhibited an evident anisotropy, and a ruby contact probe surface, which was the example of isotropic surface, were measured by the confocal microscope. They were presented in the paper to support the proposed approach. In the method, the curvature tensor T is calculated using three proximate unit vectors normal to the surface. The multi-scale effect is achieved by changing the size of the sampling interval for the estimation of the normals. Normals are estimated from regular meshes by applying a covariance matrix method. Estimation of curvature tensor allows determination of two directions around which surface bends the most and the least (principal directions) and the bending radii (principal curvatures). The direction of the normal plane, where the curvature took its maximum, could be plotted for each analyzed region and scale. In addition, 2D and 3D distribution graphs could be provided to visualize anisotropic or isotropic characteristics. This helps to determine the dominant texture direction or directions for each scale. In contrast to commonly used surface isotropy/anisotropy determination techniques such as Fourier transform or autocorrelation, the presented method provides the analysis in 3D and for every region at each scale. Thus, different aspects of the studied surfaces could clearly be seen at different scales.Copyright

Numerical and experimental investigations of the dynamics of a variable mass pendulum

In this paper, the numerical and experimental results for the dynamics of pendulum with variable mass were described. Mathematical model was developed taking into account the loss of mass, reactive force, air resistance, and friction. A corresponding test rig was designed and built in order to validate the numerical results. The purpose of the paper is to show that in case of the variable mass systems the second Newton’s law cannot be directly applied in the traditional form. The simple experiment was designed to support the thesis that the modification of Newton’s second law is necessary.