Machining Error Model Research Articles

Calculation and Optimization of Cutter Position for Flank Milling Spatial Cam Based on NURBS

In some cases the spatial cam is manufactured with a cutter whose diameter is smaller than that of the roller of cam mechanism, which is defined as nonequivalent manufacture method in the paper. By the analysis for manufacture of contact lines between the cam and the roller, it is indicated that errors caused by the different directions of normal vector are unavoidable for the nonequivalent manufacture method. In order to find the best tool axis vector to minimize the machining error, this paper realized the nonequivalent machining of spatial cam surfaces using the NC flank milling method and proposed a new generation algorithm of the tool path based on NURBS. The NURBS ruled surface of tool axis trajectory is confirmed based on the least square optimization method and the machining error model is given. At last, a numerical calculation and simulation example is described to verify the effectiveness of the algorithm proposed in the paper.

Error compensation for fused deposition modeling (FDM) machine by correcting slice files

PurposeThe purpose of this research is to extend the previous approach to software error compensation to fused deposition modeling (FDM) machines and explores the approach to apply compensation by correcting slice files.Design/methodology/approachIn addition to applying the stereolithography (STL) file‐based compensation method from earlier research; a new approach using the slice file format to apply compensation is presented. Under this approach, the confounded effects of all errors in a FDM machine are mapped into a “virtual” parametric machine error model. A 3D artifact is built on the FDM machine and differences between its actual and nominal dimensions are used to estimate the coefficients of the error functions. A slice file compensation method is developed and tested on two types of parts as a means for further improving the error compensation for feature form error improvement. STL file compensation is also applied to a specific FDM 3000 machine and the results are compared with those of a specific SLA 250 machine.FindingsThe two compensation methods are compared. Although, the slice file compensation method theoretically allows higher compensation resolution, the actual machine control resolution of the FDM machine can be a limitation which makes the difference between STL compensation and slice file compensation indistinguishable. However, as the control resolution is increased, this method will make it possible to provide a higher degree of compensation.Originality/valueCompensation method applied to slice file format is developed for FDM machines and its limitations are explored. Based on the experimental study, dimensional accuracy of parts is considerably improved by the software error compensation approach.

고속카메라를 이용한 절삭공구변형의 보상에 관한 연구

This paper presents an integrated machining error compensation method based on captured images of tool deflection shapes in flat end-milling processes. This approach allows us to avoid modeling machining characteristics (cutting forces, tool deflections and machining errors etc.) and accumulating calculation errors induced by several simulations. For this, a high-speed camera captured images of real deformed tool shapes which were cutting under given machining conditions. Using image processes and a machining error model, it is possible to estimate tool deflection in cutting conditions modeled and to compensate for machining errors using an iterative algorithm correcting tool paths. This corrected tool path can effectively reduce machining errors in the flat end-milling process. Experiments are carried out to validate the approaches proposed in this paper. The proposed error compensation method can be effectively implemented in a real machining situation, producing much smaller errors.

Model-based ‘Chase-the-Ball’ Calibration of a 5-Axes Machining Center

A procedure for model-based calibrating 5-axes machining centers is presented. Machine errors cause relative TCP deviations between a sphere and probing system that can be measured in X, Y and Z simultaneously during a five axes measurement cycle. The exact kinematic configuration of the machine tool can be identified by numerically reproducing the errors that would cause deviations closest to the ones measured. The measuring device, the machine model and the measurement procedure are described briefly. A method well known in robotics is applied to evaluate the mathematical stability of the error identification. With it a suitable number and location of measuring poses and a suitable model setup can be determined. A new general Monte Carlo approach using a full machine error model is applied to determine the expected overall geometric behavior of the machine tool after the calibration. With it uncertainty estimations can be made for any calibration approach. Finally, measurement results before and after the calibration are shown.

Software compensation of rapid prototyping machines

This paper addresses accuracy improvement of rapid prototyping (RP) machines by parametric error modeling and software error compensation. This approach is inspired by the techniques developed over the years for the parametric evaluation of coordinate measuring machines (CMM) and machine tool systems. The confounded effects of all errors in a RP machine are mapped into a “virtual” parametric machine error model. A generic artifact is built on the RP machine and measured by a master CMM. Measurement results are then used to develop a machine error function and error compensation is applied to the files which drive the build tool. The method is applied to three test parts and the results show a significant improvement in dimensional accuracy of built parts.

Assessing Thermally Induced Errors of Machine Tools by 3D Length Measurements

A new measurement technique is proposed for the assessment of thermally induced errors of machine tools. The basic idea is to measure changes of length by a telescopic double ball bar (TDEB) at multiple locations in the machine's workspace while the machine is thermally excited. In addition thermal machine error models are verified and optimised by comparing measured and predicted TDEB length deviations. Validation measurements reveal that more than 60 % of the thermally induced errors can be described by the thermal machine error model proposed at any time and at any position in the machine's workspace.

Assessing geometrical errors of multi-axis machines by three-dimensional length measurements

In this paper a method is presented for assessing geometrical errors of multi-axis machines based on volumetric three-dimensional length measurements. A universal machine error model is proposed since a large variety of machine configurations exists. Such models can be used for software error compensation techniques in order to improve the machine’s positioning behaviour as well as for diagnostic purposes. Length measurements are chosen for the measurement of the positioning errors of a multi-axis machine because these measurements can be executed in a short period of time in a relatively simple way combined with a high accuracy. In order to get comparable results for the geometrical errors as measured with conventional techniques, i.e., laser interferometry, the design of the measurement setup as well as the formulation of the machine error model (including parameter correlation effects) appeared to be of major importance and are subject of this paper.