Improvement Of Machining Accuracy Research Articles

On‐machine measurement of workpieces with the cutting tool

A new system for on‐machine measurement of workpieces is described. The system is based on a fine touch sensor that enables the cutting tool itself to act as a contact probe to inspect the workpiece. The proposed measurement technology combines the Q‐setter with the fine touch sensor. This low cost measurement system is applied to automatic workpiece setup and improving workpiece dimensional accuracy on a CNC turning center. It is shown that using the proposed measurement system results in workpiece setting time decrease and workpiece machining accuracy improvement. The development of the on‐machine measurement system makes the fine touch sensor extremely attractive for CNC machine retrofitting.

交差格子スケールを用いた超精密ＮＣ工作機械の運動精度の測定と加工精度の改善

The Cross Grid Encoder is a position detector with a grid which crosses at a right angle, superior to conventional optical linear scales which have not been capable, as the Cross Grid Encoder is, of two-dimensional position detection. When this system is applied in the Circular Motion Test, measurement of behavior on a small radius and high feedrate was conducted with high precision, a capability which the DBB test has not offered. In addition, since it can measure the error of not only the circular interpolation but also the linear interpolation, it is possible to obtain information which is very beneficial for the improvement of machine accuracy. This study investigates the causes of the impediments towards machining accuracy improvements by comparing the accuracy measurement of the double-axis feed motion and actual machining accuracy on the ultra-high precision NC machine tool. Finally, by clearing away the ultimate causes of the impediments the improvement of machining accuracy is confirmed.

Articulated Robot Application in End Milling of Sculptured Surface

End milling of a sculptured surface is attempted employing an articulated robot with six degrees of freedom. In this application, the machining error due to the positioning accuracy and elastic deformation of robots should be considered. In order to improve positioning accuracy, a new robot calibration method has been developed and applied. After the calibration, the robot is operated by off-line teaching programs effectively, and experimental end milling is finished with improved machining accuracy. Furthermore, a postprocess error compensation has been realized to minimize the machining error caused by all of factors such as the positioning error, elastic deformation and joint backlash of the robot. Experimental end milling shows that the machining accuracy is improved to near the positioning repeatability of the robot after repeating compensation twice. Additionally, a sensor feedback teaching method which is another way to achieve end milling of a sculptured surface has been developed.

Improvement of Productivity in Aspherical Precision Machining with In-situ Metrology

Summary This paper deals with the development of aspherical machining technology with in-situ metrology using the stylus method for the purpose of improving machining accuracy and reducing machining time. This technique is based on the in-situ measurement of machined geometrical accuracy, which makes it possible to calculate both the deviation of nominal tool diameter from the true one and the tool setting error in tool feed and traverse directions. The machining time can be reduced to a half or one-third with application of this procedure to either aspherical grinding or diamond turning.

A simulation system for improving machining accuracy in milling

The end milling process is used extensively in a variety of manufacturing areas, especially in the aerospace industry, where many of the machined parts are pockets and thin webs. Many of the end milling applications involve machining of thin webs using long and flexible cutters. This leads to the fundamental problem of surface accuracy in milling. The superposition of the tool and the workpiece deflections, which is known as effective system deflection, will cause dimensional errors and irregularities on the finished surface. In the case of thin web machining, using conventional cutting speeds (i.e. 30 to 60 m/min) the surface generation is mainly influenced by the workpiece vibration and to a lesser extent by the tool deflection. The severity of these vibrations depend on the cutting conditions used, as well as material and geometry of the workpiece being cut. In this paper, a simulation system for finish milling of flexible structures is developed. This system includes an improved model for the prediction of the cutting force. This enhanced dynamic model takes into account the deflections of the tool and the workpiece in the calculation of the chip load. A dynamic, 3-D finite element model of the workpiece, which takes into account the effect of material removal, is used in the simulation. An Automatic Mesh Generation program is developed to simulate the material removal during cutting. The simulation results are then compared with the experimental results obtained on a vertical milling machine. Several finishing cuts are performed and the resulting workpiece surface dimensions are compared with the predicted errors.

ワイヤ放電加工の研究 テーパ加工精度の向上

ワイヤ放電加工の研究 テーパ加工精度の向上

Development of Integrated Turning System with Predictive Compensatory Function for Machining Errors

The study presents the development of a personal computer controlled system in turning, consisting of automatic programming function, predictive compensatory function for machining errors, and automatic measurement function of workpieces. The automatic programming function enables the rapid preparation of NC instructions by providing some data related to the final shape of workpiece and cutting conditions. To obtain workpieces with high accuracy, the predictive compensatory function generates modified NC instructions for finishing process on the basis of predicted machining errors. The automatic measurement function is to rapidly evaluate machining errors, utilizing NC instructions for measurement generated by reference to the shape description data. The system is realized on a conventional NC lathe which is upgraded to a BTR-DNC one by connecting it with a personal computer. The BTR-DMC coupling allows NC instructions for machining and measurement to be transferred directly to the NC controller. It becomes apparent that the system developed has potential for improving machining accuracy as well as raising productivity.

Development of turboexpanders with low flow rates

New turboexpanders have been studied with the objective of increasing the slope of usage. The major problems--inadequate life and realization of high speed bearings, and the complex process technology for making small impellers--are considered. Radial axial centripetal reaction turboexpanders are tested with several original solutions to problems developed. The brake, a centrifugal blower, is specified. Gasostatic bearings (designed for rotors) with nozzle balancing were used. The difficulty of the thrust bearings was removed by improving machining accuracy on axial bearing supports and maximum compensation of blower brake. As the efficiency of the twostage turboexpander was found to be 6% higher than singlestage, parameters were compared, and efficiencies equalized. Finally, the problem of a loss of efficiency in smaller size expanders due to scale factors was examined. Coefficient equations using the coefficient of reduced peripheral speed and the Reynolds number resulted in a design for a cryogenic microturboexpander.