Andrzej Gessner

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

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.

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

Plane Recognition on the Basis of Cloud of Points Determined by Photogrammetry

The article presents the results of research on developing a mathematical model allowing to identify the planes in a measured object, based on a cloud of points located on its walls.A basic mathematical description of surfaces is presented. An algorithm for determining the general equation of the plane on the basis of three points described in the Cartesian coordinate system has been developed. The algorithm has then been used to determine all possible planes in a given set of measured points, which were then subjected to the process of elimination and normalization. Filtered equations of the planes were grouped in order to finally determine the set of the sought-after equations.The designed algorithms have been implemented in a C++ computer program and their effect has been verified on a sample object with 3 methods of measurement: a contact measurement, a structured-light scanner method and with photogrammetry. The calculated equations have been compared with equations developed by a referenced commercial software. The results of the comparison have proved the correctness of the tested algorithms.The mathematical model will be used for rapid assessment of the geometrical parameters of castings and of the size of the machining allowances, as well as in the automatic settings of the casting in the machining space.The research was supported by the National Centre for Research and Development, Poland within the ongoing project No. LIDER / 07/76 / L-3/11 / NCBR / 2012.Copyright

Optimization of Machining Surplus Distribution Relative to Hardness of the Machined Surface

Iron cast machining is nowadays preceded by the process of marking out, ascertaining appropriate casting precision and size of machined surface surpluses. The procedure entails delineating (etching) boundaries of the nominal machining surpluses upon the raw cast surfaces. Their size, standardized according to the ISO 8062 certificate, depends on maximal cast dimensions and the casting method applied. The characteristic machining surplus size of the hereby investigated typical industrial casts ranges between 6 and 8 mm. As casting accuracy is determined by individual foundry standards, the actual machining surplus size values commonly differ from the nominal ones. Thus, in order to ascertain appropriate machining of a given cast, variable surplus distribution is warranted, resulting in actual surplus size values of 2–12 mm.Inherent to the iron casting procedure are variable hardness values within the casting wall cross-section, with the outer wall surface (directly contingent to the mold that rapidly cools the cast) characterized by the highest hardness value, decreasing incrementally towards its center. Verification of surface hardness values takes place after machining and involves selected work surfaces (e.g. base areas of a runner block). Excessive machining of oversized surpluses within the verified areas results in insufficient hardness of their surfaces.Bearing the above considerations in mind, optimization of surplus distribution was attempted, relating to most advantageous hardness values of selected cast work surfaces. The investigation was conducted under industrial conditions, upon milling center framework casts. The selected work surfaces were processed gradually; the surface hardness was measured after each machining step. Results thus obtained were implemented for further machining surplus optimization of equivalent casts.Copyright

Optimizing Machining of Machine Tool Casting Bodies by Means of Optical Scanning

The hereby presented study reports on the results of research funded by the NCBiR improvement grant. The goal of the undertaken experimental effort was to eliminate the laborious process of marking out from the technological procedure of cast machining. Marking out, even in highly automatized machining enterprises, is performed manually. It assesses casting accuracy, as well as denotes surpluses on machining surfaces. The precision of marking out is, therefore, dependent on individual performance of a given worker. Moreover, gauging casts of cylindrical (non-perpendicular) shape is highly problematic. Incorrect marking out generates quantifiable material (cast iron) and machining losses, as well as production interruptions.Herein, we present an innovative cast machining technology based on cast model scanning. Prior to machining, each body is scanned according to the technology guidelines. The subsequent comparison of the cast model and the model of the machined body affords geometrical accuracy assessment of the cast and the determination of optimal machining surpluses. The surplus verifying criteria include: machining volume minimization, tool working motions minimization, and idle tool motion minimization. Moreover, in special cases, high productive cutting (HPC) or high speed machining (HSM) optimization of cast technology, as well as elimination of superfluous procedures (e.g. milling of machining datum surfaces), are possible. The proposed comparative analysis of the aforementioned 3D models additionally affords acquisition of data for positioning (horizontal alignment) of the machined cast, e.g. the required length of technological supports.The hereby presented experimental results (obtained in an industrial setting) confirm the proposed elimination of the marking out process, thereby affording time reduction of preparatory procedures, initial assessment, and positioning of the cast for machining, as well as a decrease of machining volume by approx. 10 % (for the investigated casts). Experimental simulation results allowed us to estimate the machining volume minimization reaching up to 25 % (depending on the cast shape and the machining process specifications). Moreover, our investigation indicated a possibility of detection of casting flaws caused by insufficient surface brushing down. As the casts are painted post-brushing, the interfering sand mold remains are easily overlooked and often cause cutting-tool damage leading to costly production interruptions.Copyright

Application of Optical Scanning and Photogrammetry for Evaluation of Geometrical Tolerance Values

The hereby presented research, funded by the restricted grant LIDER, NCBiR, deals, in part, with the identification of the full implementation potential of the proposed optical measurement techniques in determination of surface flatness parameters, and their comparative assessment. The test methods included the photogrammetric measurement technique (TRITOP, GOM) and the structural light scanning approach (scanner ATOS, GOM), while the CMM measurement (DEA Global Image Clima) was the reference method. The accordingly designed and assembled experimental test stand comprised 2 steel plates. The test surfaces of the plates were appropriately ground; subsequently, the entire test stand was blackened to ascertain efficient optical scanning. Furthermore, the plates were connected by means of 8 screws, thus introducing considerable distortion. A measurement area of 140 × 240 mm was defined on the plate test surface, as determined by CMM, denoting 15 measurement paths of 240 mm in length, distributed every 10 mm, and characterized by measurement point densities of 1, 5, and 20 pt/mm. The reference CMM measurements were conducted on 3 consecutive days at different times (22 measurements in total) to exclude any possible surface modifications. Subsequently, optical scanning was applied and the measurement points lying at the cross-sections of the CMM measurement paths were isolated from the obtained polygon mesh. To further apply the photogrammetric method, the test surface was labeled with markers distributed every 10 mm and coinciding with the CMM measurement paths.Comparative analysis of the flatness parameter for the selected CMM measurement and the measurement values obtained by means of the tested optical methods included:- the entire measurement area,- the sections comprising 80, 60, 50, 45, 40, 30, 20, 15, and 10 % of the entire measurement area, decreasing centrically,- the measurement sub-areas of 30 × 50 mm allotted in the corners and in the center of the test plate.The photogrammetric error of the tested parameter was established at 1.26–19.82 %, depending on the size of the measurement area. The corresponding error value, as determined by the structural light scanning technique, amounted to 0.03–4.31 %.Copyright

Method of Assessment of Casting Accuracy and Minimization of Machining Allowances

The publication demonstrates an accuracy assessment method for machine tool body casting utilizing an optical scanner and a reference design 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 allows dispensing with the arduous manual operation - marking out. Marking out, depending on the size and complexity, might take several working shifts for prototype casting. In case of large and elaborate casts, as those of machine tool bodies, marking out is often restricted only to the first cast of the desired body produced in a given casting mold. Such course of action is based on an assumption that casting is reproducible; hence, no need to assess each and every individual cast. While this approach saves time, it often results in late detection of casting errors (allowance shifts or insufficiencies) during the actual machining process. That, in turn, results in considerable losses due to the disruption of the work process and often demands cast repair. The aim of the hereby presented study is to introduce a new technological premise dispensing with manual marking out as well as allowing fast verification of the cast shapes.Copyright

Backlash Adjustment in Plane Spiroid Gears

Plane spiroid gears currently applied in feed motion rotary drives are roughly described in this paper. The theoretical possible methods of backlash adjustment in this kind of gear are mentioned. Referring to industry experience the only applied method, which uses the eccentric, is described. Its advantages as well as disadvantages related to operation and wearing process are pointed. The disadvantages are mainly connected with changing the gear axis distance while rotating eccentric in order to adjust backlash. A graph depicting the movements of the worm in the direction of backlash reducing and in the perpendicular one, which changes the axis distance, is given. In order to provide some information about the influence of changing axis distance on the mating of face toothing with the worm, mathematical model was created. Some effects of numerical calculations based on that model and showing the bearing contact of the face gear drive supplied with eccentric backlash adjustment are depicted. It can be noticed, how changing the axis distance influences the bearing contact. It can be also estimate if within the chosen range of eccentric rotation the theoretical bearing contact is still acceptable to operate correct. A simplified model presenting the wearing process is also provided. It reveals that after some operating time an edge contact appears while reducing backlash. It significantly decreases the operating time till the next adjustment. There are two methods of backlash reducing described: the first is typical whilst the second is improved and proposed by the author. The advantage of the proposed method is lengthening the operating time between two backlash adjustments. In the end a new type of spiroid gear mating with double-lead worm and deprived of aforesaid disadvantages is mentioned.© 2006 ASME

Theoretical Basis of Generation of Face Worm Gear Drive With Duplex Worm

New type of face worm gear drive with double-lead worm is proposed. The advantages of that gear in comparison to contemporary known gears are also mentioned. The shaping process of the face worm gear is carrying out by means of a single point tool. The same insert is used for cutting the duplex worm. Using a single point tool instead of hobbing cutter considerably reduces the manufacturing cost, in which the share of tool production plays the main role. The shaping process is performed on a CNC milling machine with or without additional equipment. Two main methods of shaping depended on setting up the tool machine are presented. One of them requires no special equipment but a single point tool with insert of specific tool included angle, whilst the second uses a constructed tooling. There are also described 3 methods of shaping the face toothing, which depends on the used technology. Geometry of that face worm gear drive is presented and described. The tooth depth is constant along the whole tooth line. Nominal width of tooth section as well as its location depends on the lead difference of the worm. Provided scheme can be used to calculate those parameters. The total length of the duplex worm is calculated by taking into consideration the internal and external diameters of the worm gear and the additional length which is needed to reduce the backlash. The shape and size of the single point tool is determined according to the worm and the necessary geometric model is provided. There are also given criteria, which limit the maximum length of worm and its maximum lead angle. A complete algorithm describing the designing process of that type of gear is presented in the final part of the article.Copyright