Papers by Keyword: Coordinate Measuring Machine

Abstract: Currently the measurement of surface texture in mechanical engineering is traditionally carried out using profilometers. Modern profilometers do not allow measuring of surfaces with complex shapes. This is due to the different sensitivity of the sensor and the discreteness of the movements along the axes of the Cartesian coordinate system. Coordinate Measuring Machines are devoid of such a drawback. However, stylus of the coordinate measuring machine has a diameter many times larger than the diamond stylus of the profilometer. Therefore, there is a mechanical filtering effect, that affects the results of measuring the parameters of the surface texture. In this paper a mathematical model of the contact of the spherical stylus and a rough surface based on analytical geometry is proposed. Influence of the diameter of the spherical stylus on the maximum measurement errors of a amplitude parameters are investigated. Seven amplitude parameters Rp, Rv, Rz, Ra, Rq, Rsk, Rku of the surface texture are modeled. Coordinate measuring machine and profilometer with stylus diameter of 2 μm measurement results are compared. it was concluded that the stylus diameter of the coordinate measuring machine when measuring the surface texture should be no more than 20 μm.

Abstract: Optimization of a flatness error inspection activity on coordinate measuring machine (CMM) is a very crucial problem which demands minimization of a probe path for productive inspection. In the present work, the approach is explained to minimize the total probe travelling length and hence, the time of flatness inspection. Three sampling methods with eight sample sizes have been considered for this work. The ant colony optimization (ACO) algorithm based on travelling salesman problem (TSP) approach was developed in MATLAB environment to find the shortest probe paths. It was verified that the probe path depends on the sampling method used to measure the flatness. The sampling method giving the shortest probe path was selected as the best-suited method for a particular sample size. The results obtained by analyzing an illustrative example shows that the proposed approach is both effective and optimum.

Abstract: The increase of the quality in a productive process allows reduction of costs besides adding value to the product. When manufacturing a product within the tolerances specified in the design it is possible to obtain a correct operation of this product, ensuring the minimum time of use and with a lower risk of early failure. In this sense, machines and equipments involved in the manufacturing and inspection processes must also maintain an acceptable quality of operation by knowing the errors present in the machine structure through the calibration, such as errors due to lack of orthogonality between the axes, caused by inaccurate assemblies. The calibration errors in these machines allow elaborate error compensation plans and thus improve the rate of flawless products in production. The objective of this paper was to identify the influence of errors due to a lack of orthogonality in a bridge type coordinate measuring machine (CMM) through calibration and mathematical modeling of errors. Error calibration is performed with a linear displacement transducer, a granite square and a set support brackets for the granite square. By means of the calibration data and the mathematical modeling of the orthogonality deviation an influence of the measured deviation on the "X" and "Y" directions of the CMM is obtained. The error due to the lack of orthogonality between the "X" and "Y" axes of the CMM was approximately 8.9558 negative arcoseg; in this way, it is evidenced that the angle formed between these axes is 89.9975°. Through this study it can be concluded that orthogonality deviation in the main plane of the machine produces negative components for the axes "X" and "Y", with higher influence on the points collected as it away from machine scales, making greater the error intensity on the results of measurements made at positions farthest from the "X" and "Y" scales.

Abstract: In geometric and dimension tolerance investigations, especially for high precision mechanical parts, the accuracy of measurement is very important. The major equipment for the measurement is the coordinate measuring machine (CMM). However, the recommended strategies for evaluating tolerance values of geometric and dimension cannot be applied with high precision mechanical parts. Hence, in this research, the researcher introduced a new procedure that could evaluate geometric and dimension tolerance values of high precision mechanical parts accurately. This new procedure can determine the minimum sampling point for evaluating geometric and dimension tolerance values by using some performance information on the mechanical parts of the machine. This information was the waviness of the production machine’s motion. In order to evaluate the potential of new procedure, the flatness of test piece was made according to the ISO 10791-7-A160 standard as a case study. This test piece was made from the CNC milling machine (Chevalier 2040 VMC), and the waviness of the CNC milling machine’s motion was counted from the performance testing result measured by the double ball-bar model Renishaw QC10. By comparing flatness obtained by recommended and new procedures, experimental results indicated that the new procedure showed its potential in estimating the flatness.

Abstract: The paper presents a comparison between Coordinate Measuring Machine and 3D white light scanning technologies as applied to the dimensional inspection of turbo-machinery parts such as turbine blade. The results were compared with the CAD model and each other. The results indicate that, even both methods are enough accurate with a slightly better accuracy for CMM, the operational speed and the variety of scanable surfaces give significant advantages to the 3D scanning method when prototypes require dimensional inspection by an alternative rapid route especially when dealing with objects with thin walls or sharp edges.

Abstract: One of the key features of advanced manufacturing technologies is the metrology of geometric quantities. Coordinate measuring machines (CMMs) now are widely used to perform relevant measurements. Normally, the use of CMMs in traditional quality control rooms, isolated from the production floor, often proves unsuitable for effective and timely feedback on the manufacturing process. However, CMMs are sensitive to environmental factors such as humidity, suspended dust and oil, vibrations, and especially temperature. For this reason, measuring machines must to be designed with features that make them more resistant to the environmental influences on shop floor operations. The main goal of this work is to enhance accuracy of a CMM working on the shop floor conditions by design improvements and error compensation. A 3-axis CMM will be built with some improved designed features and a software compensation technique will be applied to enhance the machine accuracy.

Abstract: Currently, geometric deviations of machined parts can be measured following the recommendations outlined in ISO standards such as ISO-12780, ISO-12781, ISO-12180 and ISO-12181. Coordinate measuring machines have now become widely used for inspection hence the tracing and probing strategies recommended in these standards have become much more important. Unfortunately, only minimum number of sections and points are mentioned. Generally, in each section, only a single point will be sampled for the inspection processes. However, the interval between each pair of sampling points has to be smaller than half of the wavelength of the machined surface. Hence, in this research, a method for determining a suitable number of sampling sections and points for geometrical deviation assessment of machined parts made from CNC machining centers is introduced. In this method, the wavelength of a machined surface is predicted from the results of tests used to assess machine performance. Using Finished Test Pieces in ISO 10791-7-A160 as a case study, experimental results indicated that the number of assessed sections and points, calculated according to the introduced method, can be used for accurate measurements of the geometrical deviations of machined parts.

Abstract: This article shows the solution to the problem of designing а neuronetwork component of industrial technical system. This solution lets to provide nominal accuracy of information processing, when technical system is working under conditions of destabilizing factors.Base of designing а neuronetwork component is algorithms of elimination of influence of external and internal noise of artificial neural network developed by authors.

Abstract: The purpose of this paper is to develop mathematical model to investigate the influence of shell casting parameters. Three input parameters such as shell wall thickness (SWT), Pouring temperature (PT) and weight density (WD) were selected to give output in the form of average outer diameter (AOD) as dimensional accuracy. After identification of component, technological prototypes were produced. In this work three dimensional printing (3DP) has been used as rapid shell casting to make shell mould by using Zcast 501 powder with different shell wall thickness for six different light alloy materials. Measurements on a coordinate-measuring machine helped in calculating the dimensional tolerances of the castings produced. For obtaining tight casting tolerances the dimensional accuracy of component is the most important element. The thickness, curing time and orientation of the shell molds, play an important role in providing a high quality of the cast part in time. The dimensional accuracy was found to be more in the case of maximum layer thickness and horizontal position of the component. The investigation has led to conclusions as the Quadratic models were developed for the response. The F - value is 23.93, which implies that the model as well as lack of fit is significant. The value of Prob > F is less then the standard value 0.05, which indicates model terms are significant. With the help of Post curing, shell Mold temperature was not found to affect the dimensional accuracy of the castings, significantly. It was observed that high pouring temperatures also produced castings with better dimensional accuracy. This study will provide main effect of the inputs on average outer diameter as dimensional accuracy in three dimensional printing of light alloys castings. Statistically in this case B, C, A², B², C², AB, BC is the model terms which contributes significantly to the model developed for dimensional accuracy.

Abstract: The paper presents an approach concerning the CMM design. The first stage of this research deals with the acquisition and the development of knowledge about the CMM design. The main mechanical design aspects to achieve a high positioning and measuring accuracy are presented and two main objectives are assigned: high repeatability (design for repeatability) and high predictability of the machine response to the main error sources (design for predictability). In the second stage of this research the dynamic errors states for this CMM design have been analyzed. In high-speed measuring processes dynamic errors will have a great influence on the accuracy. This study has been performed by using finite-element analysis (FEA) of the mechanical frame. The total deformation of the mechanical frame for different accelerations of the moving assemblies has been calculated. The major deflections at the probe position due to the accelerations are obtained by using FEA. These results give a prediction about the dynamic error of the CMM.