MECATRONIC EQUIPMENT FOR BEARING RING SURFACE INSPECTION Daniela Cioboata 1, Octavian Dontu 2, Daniel Besnea 2, Robert Ciobanu 2, Adrian Soare 3 1 The National Institute of Research and Development in Mechatronics and Measurement Technique; 2 University POLITEHNICA of Bucharest; 3 SC COMIS SRL Vălenii de Munte E-mail:d_bes@yahoo.com Abstract: This paper presents the integration of rings for bearings control in manufacturing technology to ensure the bearings quality, providing information on processes, and process control by realizing a flexible, open architecture mechatronic equipment for controlling multi-parametric dimensional and geometric rings surfaces of roller bearings with balls and rollers.this equipment will be developed under Partnerships in Priority Areas Programme - PNII supported by MEN-UEFISCDI, in the project PN II-PT- PCCA-2013-4-1671. Keywords: bearings rings control, mechatronic equipment, bearing inspection, bearings precision 1. Introduction Increasing the quality of bearings and efficiency of components manufacturing requires control technologies that are automated, flexible, open architecture, integrated in manufacturing flow. Traditional control systems are costly, have limited functionality and take a long time to adapt to production requirements. Bearing surface geometry and quality are essential for achieving top-class bearings with minimum friction, for increasing energy efficiency of mechanisms, reducing noise and vibration and increasing life. If the bearing component processing technologies have experienced a qualitative progress by using CNC machining centers, total manufacturing flow control still poses major problems for manufacturers, due to the wide variety of shapes and sizes. The paper presents the design, development and implementation of a mechatronic flexible, open architecture equipment, consisting of a positioning 3D system with a precision of 1 µm, a transducer and a specialized software for controlling multi-parametric dimensional and geometric characteristics of surfaces for ball bearing rings and rollers. This equipment must meet the following requirements: rapid and precise calibration; rapid adaptation to the requirements of the manufacturing process; safe and precise detection of parameters deviations resulting in processing for multiparametric control of a wide range (shape and size) of bearing rings; decisional capacity based on predetermined criteria; statistical calculation program for control and streamlining of manufacturing process. [1] 2. The sources of errors in processing Before developing a performance measurement system is necessary to understand the technology of processing bearing rings, sources of errors in processing, requirements for measurable characteristics. Such information shall serve as a basis for developing a control system in optimal quality-cost conditions. Dimensional tolerances Inner and outer diameter tolerances, rings width and bearings width; Inscribed and circumscribed circle tolerances of rolling elements; Bevels dimension tolerances; Width deviations tolerances; Tilt tolerances. Bearings Runout of the inner and outer precision rings; Side runout of the inner ring; Dimensional tolerances of the chamfers; Running Width deviations tolerances; accuracy Tilt tolerances; (precision of The deviation of the inclination of rotation) the external surface generator of the outer ring relative to front surface (outer surface taper of the outside ring); - Race deviations. Fig. 1 Elements that determine precision of the bearings In processing of bearings rings, thanks to the elastic technological system and often imperfect consist of machine tool - piece - tools clamping device and the unevenness of the processing and external factors that accompany this process, it appear both deviations from the nominal size and deviations from the geometric shape and from the position of axes and surfaces. The technological process also affects the quality of machined surfaces. [2] The occurrence of deviations from the micro and macro geometric shape of the surfaces during 262
processing, is a complex process, which is influenced by a number of sources of errors in the manufacturing system that can be categorized into 5 groups: 1. Error sources due to machine tools; 2. Sources of error due to the processing; 3. Sources of error due to fasteners and fed of parts; 4. The error sources that depend on the part; 5. Errors due to environment. In terms of geometry, rings of bearings with ball or roller are characterized by flat surfaces and surfaces with open or closed circular profiles (as defined in ISO 16 610-1: 2006). For ball bearings, besides cylindrical surfaces diameter, an important feature is the rolling diameter of the balls. For ball bearings, the geometry of the raceway is defined in addition to the rolling diameter (measure the diameter of an imaginary circle in a plane perpendicular to the axis of symmetry, in the deepest part of the tread of the inner or outer ring) and the track radius (radius of the profile in the form of an arc of a circle, in a plane through the axis of symmetry). These two parameters are very important because they influence the axial and radial clearance of bearing, contact angle and precision of rolling motion. Track radius is not equal to the radius of the rolling elements. The difference between these diameters defines the curvature of the runway (Figure 2). Fig. 2 Runway curvature f=r/d w Along with dimensional accuracy, machined parts must meet requirements regarding geometrical accuracy. The main deviations that must be taken into account for revolution piece are deviations from cylindrical shape: a. In a cross-section (also called out-of-roundness): ovality, trilobal shape, random irregularities characterized by significant deviations from circular shape, b. In a longitudinal section: concave (drum) shape; convex shape; conical shape; axis curvature. The table below analyzes some specific geometric features of the raceway of the bearing rings and appropriate measurement schemes. [3] Table 1 The parameter indicated on the drawing Measurement scheme Characteristics Deviation from the nominal dimension of a single diameter (diameter) The average diameter deviation from nominal size in a radial plane (diameter, medium) = circularity, respectively circularity in 2 points Standard filter value: 1 500 Standard filter type: Gauss The circularity - after MZCI (Minimum Zone Circle) is the minimum distance between two concentric circles rays including roundness profile inside and outside Deviation of average diameter in different radial plane (parallelism in two points) Wall thickness radial deviation (runout) Individual width deviation from nominal share Width deviation 263
3. Presentation of own solution The conception and design of measurement system of bearing rings must consider the following issues: - device configuration must to be modular as much as possible to increase the versatility of equipment, allowing measurement of a wide range of parts according to the needs of the manufacturer; - measurement system must allowing quick adjustment and calibration in order to be adapted in record time to change of production; - measurement system allowing to measure a greater number of parameters; - measurement system allowing framing of pieces in precision classes; - equipment allow to measure both inner ring and outer ring; - positioning system allowing centering both on the inner ring diameter and outer ring diameter, depending on the control technology of the mark inspected; - measurement system must ensure adequate quality for machined parts. Fig. 3 Presentation of constructive selution for measuring bearing rings: 1- monitor; 2 - PC; 3 - transducer; 4 - bearing ring;5 - transducer support In the projected installation phase has been considered concept of modular construction, as a necessity to increase the flexibility of equipment using devices made of standard elements for the advantages of a qualitative improvement of the construction, reduce the duration and cost of the design and execution. Using electronic modular configuration for measurement and decision on quality of measured parts, it offers the possibility of providing some complex calculation and correlation functions. They are characterized by versatility, speed of response and rapidity in decision and measurement, possibility of informational automation and centralization of decisions, remote control, etc. Figure 4 shows the 3D model for a modular system for measuring inner and outer diameters of the bearing rings. Fastener allows precise centering and rotating parts. The part can rotate and system captures data from points on the outer or inner surface of the workpiece in the same horizontal plane. Fastener can be moved vertically and horizontally due to 3D positioning table, with positioning accuracy of 1 µm, so it can make measurements in as many plans. Reliance pieces on a narrow prism with 120 inclination and uses the force of gravity. This has the advantage of easily placing the workpiece in the measuring post, and fixing the bearing ring by means of a clamp, whose support is fixed on the surface of the 3D positioning table. [4,5] Fig. 4 3D model of the plant for measuring bearing rings: 1-column; 2-prisma; 3-suport fixare prisma;4-3d positioning table; 5-micrometer screw axis X; 6-fixing table; 7-support table; 8-micrometer screw axis Y; 9- micrometer screw axis Z; 10-clamping arbor; 11-arbor; 12-mounting flange bearing ring; 13-bearing ring; 14- transducer; 15-transducer support 264
4. Experimental Results Over the years several methods have been developed to quantify deviations from circularity. Characteristics of method for measuring the deviations from circularity through measurement of radius variation are: axis of the measured part must be aligned with the reference (rotation) axis of the equipment; piece axis must be parallel to the axis of rotation to avoid errors that occur due to the inclination; measuring direction should be concurrent and perpendicular to the rotation axis of the piece; between the feeler and the piece there is relative rotational movement; deviation measured by the transducer is amplified on a chart in the polar coordinates used to assess form deviations of the piece; only shape deviation is amplified, not the radius of the piece, this can introduce distortions in the chart drawn; in order to facilitate the interpretation of results, digital or electronic filters are used (normally low-pass filter) to reduce the influence of the roughness; the part is rotating and transducer and the probe are maintained fixed (fig. 5). Whatever method of evaluating the out-ofroundness deviations must be taken in the following steps: First step is to determine the center of the reference element to which is determined the out-of-roundness deviation. Second step is to determine the circle of the reference element to which is determined the out-ofroundness deviation (circle radius). Third step is to evaluate the out-of-roundness deviation. Result of measurement for out-of-roundness deviation is influenced by the following factors: - the number of points measured; - distribution of measured points; - method of evaluation used. Approximation of reference circle from a number of points «n» measured on the periphery of a circular shape / profile, can be made by: - minimizing the geometric distance from measured point to circle (geometric approximation). - minimizing the mean square distance from the circle at the points measured (eg, orthogonal method of least squares). a. b. Fig. 5 Installation for measuring the bearing rings: a general view;b- constructiv detail 20 15 10 rulment 1 etalon 5 0-40 -20 0 20 40 60 80-5 -10-15 -20 Fig. 6 Distribution of measured points (72 points, considering a rotation of the bearing ring of 5 0 ) on the reference circle 265
36.2 36.15 36.1 maxim 36.05 rulment 1 36 35.95 35.9 etalon minim 35.85 35.8 35.75 0 20 40 60 80 100 120 Figure 7 Distribution of the tolerance field between the maximum and minimum value imposed by ±0.1 mm In figures 6, 7 are presented the diagrams result after measurement of a ring bearing with nominal diameter of 36 mm. 5. Conclusions machines, as optimisation factor of processed surfaces quality BeQuCon, for experimental testing. 6. References The measurement process of the surfaces consist of comparison the real profile with a reference profile. This comparison is done by scanning continuously verified profile in a given section, and record or display the deviation from the ideal circular shape. The part is rotating and transducer and the probe are maintained fixed (fig. 5). Rotating element must describe a "perfect" circle, which is taken as a reference element. These devices use very sensitive transducers for measuring form deviations of the parts. The distance between the axis of rotation and the contact point on the surface of the piece is considered to represent instantaneous radius of the contact surface. The variations of consecutive rays on the circumference, registered from stylus, is the deviation from a perfect circle. By construction, the equipment presented in the figure 5 does not measure the nominal value of the radius, but only the variation of the radial profile in a cross-section of the piece, to a perfect circle. Acknowledgement This mechatronic equipment is developed under Partnerships in Priority Areas Programme - PNII supported by MEN-UEFISCDI, in the project PN II-PT- PCCA-2013-4-1671 Innovative mechatronic system for inspection of the bearing rings machined on CNC [1] Innovative mechatronic system for control rings bearings machined on CNC as a factor in optimizing the quality of machined surfaces BeQuCon, Phase 1. Preliminary analyzes on the process of manufacturing bearing rings for define constructive functional requirements of control equipment. Financing contract no. 268 of 07.01.2014 [2] Cioboată D., Improving control methods for deviations form the bodies of revolution with open or closed circular profile, PhD Thesis, University Politehnica of Bucharest, 2013 [3] Rolling bearing tolerances. Definitions / Measurement principles, Schaffler Group Industrial. [4] Besnea D., Dontu O., and others, Computer aided manufacturing technologies for executing mechatronic components, Ed. Printech, Bucharest, 2008 [5] Mircea M., 3D virtual modeling in machine building (CATIA V5R14), Ed. Printech, Bucharest 2005 [6] Soft-ware developed by MicroTop company [7] www.newport.com [8] www.horst-witte.com 266