Roman Staniek

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.

Positioning Accuracy Investigations in Face Spiroid Gears

There are two basic methods of forming the face spiroid gears. The first one, well known, is based on cutting the gear with multi-point cutting tool on the gear hobbing machine. The second method is based on machining with single-point cutting tool applying continuous indexing on universal NC machine tool and with application of NC rotary table. The second method is recommended for piece production because of the simple, cheap and universal cutting tool. There is also known the method of forming the face gears with involute tooth line obtained by machining with the inclined tool axis in relation to the face surface of the gear. The methods of forming face toothing in spiroid gear with the tool axis parallel to gear surface (according to author’s proposal) has been presented in the article. In this method the tool axis is located against the machined wheel at the same position as the worm is located in the gear and this is the greatest advantage of this method. For both methods there have been elaborated special machining programs for four axis NC milling machine of FYN 50ND type, together with NC rotary table of FNd-400 type. Then the obtained gears have been tested and investigated. Three types of such gears have been investigated, all of them with ratio 1:90. Two versions of the face spiroid gears have been assembled in the rotary table and then positioning accuracy has been measured. Additionally, for comparison reasons, the double pitch worm gear has been investigated using the same measuring instruments. There have been presented the chosen accuracy investigation of the gears in the range of one full rotation of the spiroid wheel that is connected with table disc (measurement by 4°) and in the range of two worm rotations (measurement by 0,1°) General evaluation of the chosen methods concerning the manufacturing of the face wheels in spiroid gears has been presented too. The data have been obtained from literature and from author’s own researches.Copyright

Research on External and Internal Induction Heating Effectiveness of Injection Molds by Means of Thermovision Measurements

The aim of this work is to compare the effectiveness of two induction heating methods of injection molds by means of thermovision measurement. The problem of selecting external or internal induction heating for thin-walled moldings used in electrical and electronic industry is taken into consideration. At first, the boundary conditions were defined. Then a group of three moldings with different defects were selected. The defects that have been taken to remove by means of induction heating are: weld lines, breaking hinges, air traps and diesel effect. In order to compare the methods of heating two models were created. The first one was made as a block of steel with milled grooves with a width of 2mm and a depth varying from 1 to 12mm. The second model consisted of two parts, one being placed in the second.The research stand consisted of prepared models, induction generator with power of 10kW, specially shaped inductor, thermovision camera and temperature sensor of PT100 type as a reference. First, the surface with milled grooves was heated in four different sectors (because of the shape of inductor) in time of 2s. The area of low-depth grooves heated up to 154°C while the surface with 12 mm grooves heated up to 120°C. It comes from eddy currents flowing. This phenomenon shows that effectiveness of external heating of grooved surface decreases with increasing of grooves depth.In the second case the cavity insert was heated as a coil inside the inductor which was located inside the mold. The measured value was the time of heat transfer from heated area to the forming surface in three configurations.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

Compensation System for Thermal Deformations of Ballscrews

Accurate ballscrews are vital components of precise machine tool drive systems. As determined by direct measurement systems, the ballscrew positioning error has no bearing on the final positioning accuracy of the axis. For economical reasons, however, most machine tools are equipped with indirect measurement systems, in which errors stemming from thermal expansion of the ballscrew constitute approximately 60% of the kinematic chain error sum. Moreover, the currently observed boost in productivity of modern CNC machine tools leads to significant amplification of energy dispersal values in the nut-screw systems, due to the increased positioning velocity of the controlled axes. This, in turn, contributes to a rise of positioning error values through thermal expansion of the aforementioned ballscrews. This article deals with technological and constructional problems of screw lengthening compensation. It enumerates methods of thermal expansion-based error compensation as attained through utilization of indirect measurement systems. Finally, it presents experimental data indicating the possibility of effective screw lengthening compensation, thus proposing an alternative to the currently applied compensation systems.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

Shaping of the Face Worm Gear by Means of the Single Edge Cutting Tool

The theoretical basics of forming the face toothings in flat wheels of spiroid gears by means of a single cutting edge tool, using NC machine tools, have been presented in the paper. Based on kinematics - geometrical formulas, there is described a geometrical model of creating the tooth spaces, as well as a geometrical model of determination of the modification depth along the tooth line. Equations of the tooth line have been calculated, as well as mathematical formulas enabling the determination of the modification depth, assuming the correct matching of the worm with the flat worm wheel of the spiroid gear. Based on geometrical models and mathematical formulas algorithms have been elaborated in order to determine the envelope condition and modification depth of the tooth line. Then, on the basis of the algorithms computer programs have been elaborated that are going to be used to design the flat spiroid gears, as well as to calculate their geometrical dimensions. It has also been possible to illustrate the modification depth along the tooth line. The simulation results have been illustrated by the gear example. Finally two methods are presented of machining the face toothings in spiroid gears with a single edge-cutting tool: accurate and approximate ones. Based on the algorithms and programs a comparative simulation of both methods has been elaborated.© 2008 ASME

Investigations of Thermal Deformations and Their Compensation in CTX 210 V3 Lathe Slide

The accuracy and the repeatability of tool positioning in relation to the work piece is one of the most important features in contemporary NC lathes. Precise lathes are particularly required in the automotive industry. The applied designs of the NC lathe slides do not always assure the required thermal stability of work piece dimensions. It has been observed that during the continuous work time of the one of the world’s famous lathes, the X and the Z axes have been significantly deformed by means of thermal influence. Diagnostic investigations concerning the positioning accuracy have been performed according to the ISO 230/3 standard [7]. While investigations, unpermitted values of thermal deformations in both slide axes, have been observed. The design of the slides has been analyzed and an attempt has been made to minimize the positioning errors that are influenced by thermal deformations. Particular attention has been paid to the errors of the X axis as they influence directly upon the accuracy of the work piece cross dimensions. A new method of deformation compensations for the X axis has been elaborated. The method is based on the elongation measuring of the ball screw applied in cross slides and then programmed compensation in the X axis control system. The practical effectiveness of the introduced compensation method has been confirmed and a five times increase of the machining accuracy has been obtained.Copyright