Papers by Keyword: Form Error

Abstract: A simulation method for the continuous path controlled grinding process is described in this paper. The process model allows a virtual analysis of the process parameters, different input conditions and their influence concerning workpiece geometry. The machine structure is represented by a structural dynamic system. The dynamic influence of the machine axes is considered by its control system parameters. In this machine model, the positioning error of the axes can be calculated in relation to the reference position. This is used to compute the local engagement numerically. The process force is estimated by means of an empirical grinding force model. Hence, the overall process force can be calculated and fed back into the dynamic model. Closed-loop modeling allows to rate the influence of different parameters with respect to process errors. Finally, a parameter study and the model verification under real conditions are presented on the basis of the wheel head oscillating pin grinding process of crankshafts.

Abstract: An unconstrained optimization model, applicable to radial deviation measurement, is established for assessing cylindricity errors by the minimum circumscribed cylinder evaluation. The properties of the objective function in the optimization model are thoroughly investigated. On the basis of the modern theory of convex functions, it is strictly proved that the objective function is a continuous and non-differentiable and convex function defined on the four-dimensional Euclidean space R4. Therefore, the minimal value of the objective function is unique and any of its minimal point must be its global minimal point. Thus, any existing optimization algorithm, so long as it is convergent, can be used to solve the objective function to get the wanted values of cylindricity errors by the minimum circumscribed cylinder assessment. An example is given to verify the theoretical results presented.

Abstract: An orbital drilling approach is proposed in machining hardened steel hole. In this study, the orbital drilling performance was investigated in connection with deburring, form error and surface roughness. First, the hole machinability of various steels was analyzed to compare an orbital drilling with a vertical drilling; then the orbital drilling experiments of hardened steel were carried out to investigate the effects of orbital drilling parameters such as tool speed, orbital feed and screw-pitch on form error and surface roughness. It is shown that the orbital drilling approach is feasible to machine the hole of hardened steel with smooth surface and little burrs using an AlTiN coating WC drill bite. Moreover, the hole form accuracy and surface roughness can be improved with increasing the tool speed and the working space, or decreasing orbital speed and orbital pitch. It is also found that the hole edge burrs can be reduced by choosing a low orbital speed. It is indicated that the form error may be greatly decreased by using a compensation approach through a new CNC tool orbital path.

Abstract: Optical profiler is a typical modern device for precision form error measurement. In our use of the equipment, we found that the surface form profile after stitching is ambiguous if the lens magnification is changed. The error in terms of PV value can be up to 3200% when the lens magnification changes from 2.5 times to 30 times. This has been confirmed by the equipment supplier. It is worthwhile to offer a comprehensive study as many users may use the instrument of the kind straightforward without detailed investigation of the performance. We found that, among the 6 key parameters studied, 3 independent parameters are more important. For the 3 independent parameters, we recommend to set the magnification A=2.5 times, the resolution r=0.5, and the overlap p=20%. With the recommended settings, the measurement error can be less than 0.5%. Backscan and length for scanning in the vertical direction, and cut off frequency for delivering form profile are less critical compared with the three independent parameters.

Abstract: This paper presents the inspection technology for a freeform surface component which is named F-theta lens. F-theta lens is widely used in laser scanners, printers, etc. Freeform characterization is one of the main approaches to verify the manufacturing precision of freeform surface. At present, there is still a lack of techniques for the characterization of freeform surfaces. This study aimed to explore some approaches to inspect freeform surfaces. Two types of measurement methods, namely contact and non-contact measurement methods, are employed to measure the F-theta lens surface. The pros and cons, the existing problems, different applications and areas for improvement of the two methods are discussed. A series of advanced measuring instruments are used in the measurement process. A brief description of measurement mechanisms of these instruments is also presented. As a whole, this paper contributes to the development of the precision measurement technology for optical freeform surfaces.

Abstract: The aspheric VCD lens is hard to fabricate by injection moulding due to its small volume and high precision requirement. The processing conditions have critical effects on the quality of the moulded lenses. An optic lens needs precisely controlled surface contours, so determination of the processing conditions for lens moulding becomes very complicated. This study’s purpose is to investigate experimentally some effects of the moulding conditions on the form errors of injection moulded lens. An aspheric VCD lens was moulded using polymethyl methacrylate. Different combinations of moulding conditions were used focusing on moulding process parameters of the ram speed, the mould temperature, the melt temperature and the packing pressure, The predicted model of form errors was formulated by orthogonal and regression analysis. Finally, the predicted model is proven to be valid based on the residual diagnostic plots.

Abstract: Evaluation and measurement of form errors distributed on 3D ground curved surface are proposed due to the difficulty of processing measured points of 3D ground curve surface in comparison with axisymmetric curved surface. First form curved surface grinding is conducted by arc-shaped diamond grinding wheel, second ground curved surface is measured by contact measurement to obtain 3D measuring data, next transfer mode from CNC grinding to measuring reference frames is established, then effective and applicable 3D compensation arithmetic for probe sphere error is introduced, finally 3D form errors are investigated in connection with reference frame transfer and probe sphere compensation. It is confirmed that form error PV of is improved form 203 m / 8 cm2 is obtained by using reference frame transfer and probe sphere compensation, enhancing measuring accuracy by about 29 %.

Abstract: A workpiece with a large surface area is likely to be uneven due to form error and waviness. These geometric disturbances can cause inaccurate micro shapes to be formed when micro features are micro-grooved into the surface and cause the resulting workpiece to fail to function as desired. Thus, the real-time monitoring and compensation is required to guarantee the form accuracy of micro features while machining the workpiece with a large surface area. In this study, a method is suggested for real-time measurement and compensation of geometric errors for the micro grooving of a large flat surface using a laser displacement sensor placed ahead of the cutting tool. Experimental results show that the compensated surface profiles fit the measured ones within an allowable tolerance even at cutting speeds as high as 200 mm/s.