Drive axis controller optimization of production machines based on dynamic models

The paper deals with the creation and implementation of a methodology for optimizing the parameters of cascade control of the machine tool axis drives. The first part presents the identification of a dynamic model of the axis based on experimental data from measuring the axis dynamics. The second part describes the controller model, selection of optimization objective functions, and optimization of constraint conditions. The optimization of controllers is tuned by simulation using identified state-space model. Subsequently, the optimization procedure is implemented on the identified model, and the found control parameters are used on a real machine tool linear axis with different loads. The implementation of the proposed complex procedure on a real horizontal machine tool proved the advantage of simultaneous tuning of all parameters using optimization methods. The strategy solves the problem of mutual interaction of all control law parameters disabling effective usability of gradual sequential tuning. The methodology was developed on a speed control loop, the tuning of which is usually the most difficult due to the close interaction with the dynamic properties of the machine mechanics. The whole procedure is also applicable to the position and current control loop.

Brass Wire Forming By Friction Stir Back Extrusion: Numerical Modeling and Experiment

Friction stir back extrusion (FSBE) is used to produce brass wires and then, Numerical modeling is developed to simulate the FSBE of brass based on the Coupled Eulerian-Lagrangian technique (CEL) and verified by experiments. Next, the effects of FSBE parameters such as tool rotational and plunging speed on the strain and temperature distributions, microstructure, and patterns of material flow are studied. The results show that, the highest temperature and strain occurs near the tool/workpiece interface, but in a further distance from the tool axis. Additionally, in the cross section of a FSBE wire, the microstructure is finer in the periphery of the sample. A higher rotational speed or a lower plunging speed results in a coarser microstructure. The material flow pattern during the process is conical helix, and does not change meaningfully by the process parameters. The points at the further distance from the tool axis, along with an upward movement, experience an inward spiral movement which is amplified by higher rotational speed. However, the materials very near the tool axis almost take an upward movement and endure a very lower strain.

Five-axis Tri-NURBS Spline Interpolation Method Considering Nonlinear Error Compensation and Correction of CC Paths

In order to improve the accuracy of tool axis vector position and direction in traditional five-axis NURBS interpolation methods and the controlling accuracy of cutter contacting(CC) paths between cutter and work-piece, a five-axis Tri-NURBS spline interpolation method is presented in this article. Firstly, the spline interpolation instruction format is proposed, which includes three spline curves, such as CC point spline, tool center point spline and tool axis point spline. The next interpolation parameter is calculated based on the tool center point spline combined with the conventional parametric interpolation idea. Different from the traditional spline interpolation using the same interpolation parameter for all spline curves, the idea of equal ratio configuration of parameters is proposed in this paper to obtain the next interpolation parameter of each spline curve. The next interpolation tool center point, tool axis point and CC point on the above three spline curves can be obtained by using different interpolation parameters, so as to improve the accuracy of tool axis vector position and direction. Secondly, the producing mechanism of CC paths’ nonlinear error of the traditional spline interpolation is analyzed and the mathematical calculation model of the nonlinear error is established. And then, the nonlinear error compensation and correction method is also put forward to improve the controlling accuracy of CC paths. In this method, the next CC point on the cutter can be firstly obtained according to the next interpolation tool center point, tool axis point and CC point on the three spline curves. And then, the error compensation vector is determined with the two next CC points. To correct the nonlinear error between the next CC point on the cutter and the CC point spline curve, the cutter is translated so that the two next CC points can be coincided. In the end, the new tool center point and tool axis point after translation can be calculated to obtain the motion control coordinates of each axis of machine tool. The MATLAB software is used as simulation of the real machining data. The results show that the proposed method can effectively reduce the CC paths’ nonlinear error. It has high practical value for five-axis machining in effectively controlling the accuracy of CC paths and im-proving the machining accuracy of complex surfaces.

Increasing the Accuracy of Free-Form Surface Multiaxis Milling

This contribution deals with the accuracy of machining during free-form surface milling using various technologies. The contribution analyzes the accuracy and surface roughness of machined experimental samples using 3-axis, 3 + 2-axis, and 5-axis milling. Experimentation is focusing on the tool axis inclination angle—it is the position of the tool axis relative to the workpiece. When comparing machining accuracy during 3-axis, 3 + 2-axis, and 5-axis milling the highest accuracy (deviation ranging from 0 to 17 μm) was achieved with 5-axis simultaneous milling (inclination angles βf = 10 to 15°, βn = 10 to 15°). This contribution is also enriched by comparing a CAD (Computer Aided Design) model with the prediction of milled surface errors in the CAM (Computer Aided Manufacturing) system. This allows us to determine the size of the deviations of the calculated surfaces before the machining process. This prediction is analyzed with real measured deviations on a shaped surface—using optical three-dimensional microscope Alicona Infinite Focus G5.

The method of calculation of the deviation of the tool axis when machining small diameter holes

The article is devoted to an important parameter that characterizes the accuracy of the shape and location of the hole after machining — the displacement of the hole axis. When designing operations for drilling small-diameter holes with a large depth (the ratio of the hole depth to its diameter is more than 10), a method for predicting this parameter is necessary to improve the accuracy of work. The article considers the causes and methods of eliminating this negative impact on hole machining using the example of a small-diameter drill axis runout. Recommendations are given for reducing drill runout: to reduce cutting modes; to perform the drilling operation while rotating the workpiece, which can stabilize the drill position during machining; to use drills made of hard alloy or obtained by powder metallurgy methods, which increases their rigidity; before drilling the workpiece, to center the hole with a more rigid drill.