Three-axis Milling Research Articles

Online identification and feed-forward compensation of nonlinear friction in servo system based on RBF neural network model

In this paper, an online identification and compensation method of nonlinear friction based on radial basis function (RBF) neural network model is proposed for the influence of nonlinear friction on machining accuracy in the low speed process of servo feed system of CNC machine tools. First, a three-layer single-input-output RBF neural network model is established for describing the nonlinear friction of servo feeding system. Second, the neural network online learning algorithm is improved based on adaptive gain, which improves the stability and accuracy of the algorithm. Finally, experiments were carried out on a three-axis milling machine to compensate the friction in the servo feed system in real time based on the online identification results. The results show that the method can effectively improve the online identification accuracy and convergence rate, and effectively improved the low-speed performance of the servo feed system.

Surface quality enhancement by constant scallop-height in three-axis milling operations

The quality of machined part surfaces are under the impact of scallop height which should be analyzed and minimized. Achieving a uniform scallop-height is important for ensuring a smooth surface finish and maintaining consistent material removal across the machined surfaces during CNC machining operations. This approach helps to reduce material waste, tool wear and part production errors while ensuring consistent and high-quality of machined parts. Maintaining a constant scallop height can also help to reduce chatter and vibration during milling operations. The research work develops a virtual machining methodology to produce constant scallops through three-axis milling operations. The proposed approach examines free-form surfaces of workpiece in order to obtain free form surfaces curvatures. Then, free-form surfaces are separated into flat, convex and concave surfaces to provide optimized cutting tool variables in order to provide constant scallop height during CNC cutting tool paths. Achieving a constant scallop height involves optimizing cutting parameters such as feed rate, spindle speed, and step over. To calculate the optimized machining parameters of feed rate, speed of spindle and step over, the Taguchi optimization methodology is utilized in the study. Then, the machining variables of feed rate, speed of spindle and step over are optimized to achieve the uniform scallop height during milling potations of free-form surfaces. As a result, using optimized machining parameters during machining operations, the surface roughness of machined components are reduced by 23.8%. So, the proposed virtual machining method can enhance surface quality of machined parts during CNC milling operations of free-from-surfaces.

Integrated and efficient cutter-workpiece engagement determination in three-axis milling via voxel modeling

Integrated and efficient cutter-workpiece engagement determination in three-axis milling via voxel modeling

Mass Loss and Displacement Modeling for Multi-Axis Milling

During the cutting process, material of the workpiece is continuously being removed by the cutting tool, which results in a reduction of mass as well as a displacement in the center of the workpiece mass. When using workpiece sided force sensors, such as table dynamometers, the total mass and the displacement of the center of mass affects the force measurement due to gravitational and inertial effects. The high flexibility of the milling process leads to a complex change of volume and mass and necessitates the consideration of the engagement conditions between tool and workpiece along the tool path in order to estimate changes in mass and center of mass. This paper proposes a method for estimating the mass loss and the displacement of the center of mass during multi-axis milling processes. In this method the tool gets numerically sliced along the tool axis and the workpiece removal for each slice along an arbitrary tool path gets calculated. To validate the mass loss model, experiments in both three-axis milling as well as multi-axis milling processes have been conducted. Since it is difficult to measure the center of mass, validation for the displacement of the center of mass was done by comparison with data extracted from CAD. The results show good agreement between the simulated and measured mass loss using the proposed approach.

An Efficient Iso-Scallop Toolpath Planning Strategy Using Voxel-Based Computer Aided Design Model

Abstract The primary objective of an efficient computer numerical control (CNC) finishing toolpath strategy is to reduce the machining time and maintain desired surface finish (scallop). Among traditional toolpath planning strategies, iso-scallop gives the shortest toolpath while achieving a uniform surface finish. However, it is computationally complex, time-consuming, and sometimes produces topological inconsistencies in regions of high curvature/gradient. This paper presents a novel voxel-based toolpath planning algorithm to address these issues for the three-axis milling of freeform surfaces. Two strategies have been proposed, namely, iso-scallop and hybrid iso-scallop. Gouge-free cutter location (CL) points are initially computed from the voxel-based model, followed by iso-scallop toolpath generation using a binary search algorithm. The hybrid strategy involves region segmentation to generate an adaptive toolpath in high curvature/gradients regions. The overlapping toolpath is stitched and refined to create an efficient iso-scallop-based tool path. The developed system was extensively tested for complex freeform surface parts and was found to be computationally efficient, robust, and accurate in generating a finishing toolpath.

ВЫПОЛНЕНИЕ ГЕНЕРАТИВНОГО ДИЗАЙНА И АДАПТАЦИЯ К ИЗГОТОВЛЕНИЮ ПОВОРОТНОГО КУЛАКА ЧАСТЬ II

The article describes the creation of a 3D model of the steering knuckle of the “Formula Student” class car using the SolidEdge CAD / CAE system application, named generative design. The initial data are a model of an overly strong steering knuckle, previously calculated load values for various operating modes, information about the properties of the material. In the process of optimization, technological settings are varied in order to obtain a geometry that is as suitable as possible for cutting on a three-axis milling machine with a CNC and without an additional rotary axis. The result of the generative design is used to build a model of a knuckle that can be milled with repositioning and clamped into universal fixtures such as a vise. The construction is carried out using standard solid modeling tools (lofting by sections, adding thickness, etc.). Fastening elements have been added to the part, in the form of rectangular bodies, which will need to be removed using manual cutting and grinding operations after the milling operations are completed. Additionally, holes are removed parallel to the Z axis, which can only be made after cutting the fasteners.

The Effect of the Machining Strategy on the Surface Accuracy When Milling with a Ball End Cutting Tool of the Aluminum Alloy AlCu4Mg

The article discusses the effect of milling strategies on surface quality and geometric deviations during pocket milling when the perpendicular position of the tool is used. For experimental research, an aluminum alloy, AlCu4Mg, was used. For the production, a three-axis milling machine was used, and consequently, the geometric deviations and roughness parameters of the machined surface were evaluated. Also, the surface texture from each strategy was compared. For the production strategy, the constant Z, circular pocket, constant stepover pocket auto border, and spiral strategies were used. The geometric characteristic evaluation showed the influence of the ball end mill used in the machining process. Constant Z strategy achieved the lowest shape deviations. In the spiral strategy, it was possible to observe an effect of plowing, where the cutting tool crushed the material at the tool center. There was a minimal effect on the surface texture in the circular pocket and constant stepover pocket auto border strategies. Using the constant Z strategy, a non-oriented surface texture was obtained. 3D maps of the extracted residual scallop height for each strategy were observed when examining the surface texture. The roughness parameters Ra and Rz for the circular pocket and constant stepover pocket auto border strategies were the lowest.

Dynamic force and stability prediction for milling using feed rate scheduling software and time-domain simulation

This paper describes: 1) the use of feed rate scheduling software to predict the radial depth of cut variation for three-axis milling toolpaths and; 2) the use of the radial depth profile in a time-domain simulation to predict dynamic cutting forces. The time-domain simulation, which also includes the tool tip frequency response functions and force model (which relates the cutting force components to the chip geometry) as inputs, enables dynamic force profiles to be predicted and parameter combinations that cause chatter to be identified. A ramp geometry is selected that provides constantly varying radial depth and force predictions are completed at multiple axial depths for comparison to measured forces. Both stable and unstable (chatter) milling conditions were observed with good agreement between time-domain simulation and measurement results. The value of combining the feed rate scheduling software and time-domain simulation is demonstrated.

Two-sided manual machining method for three-axis CNC milling machine for small and medium-sized enterprises

Small and medium-sized enterprises (SMEs) have a big role in Indonesian economic development. The government has set four strategies in an effort to boost Indonesian economic development. One of the four strategies mentions the SMEs, and the other mentions the use of 4.0 technology. Working capital has been the main issue need to be considered in the SMEs. Thus, the affordability must be considered in the use of 4.0 technology in SMEs. One of the 4.0 technologies that are possible to be used in the SMEs is a three-axis milling machine. One of the limitations of the machine is that it cannot do the back-side machining process. The paper examines the possibility of manual back-side machining on the three-axis milling machine without adding a rotary axis. Four methods were conducted by adding two-point markings on the x-axis, two-point markings on the y-axis, four-point markings on the x- and y-axis, and four-point markings on the x- and y-axis plus a series of offsetting processes. After conducting several qualitative observations and measurements on the mismatched position of the front and the back machining, and also analyzing the problems that emerged during the processes of the four different methods, it is concluded that adding four points markings on the x- and y-axis plus doing a series of offsetting processes is the best method to have two-sided manual machining with three-axis computer numerical control (CNC) milling machine.

Introducing engineering undergraduates to CNC machine tool error compensation

For manually operated machine tools, the accuracy of the machine tool structure limits the accuracy of the parts produced. Such is not necessarily the case with computer numerically controlled (CNC) machine tools. This concept may not be immediately obvious to the engineering undergraduate. The method of error compensation is presented here in a manner that is accessible to the undergraduate engineering student. A homogeneous transformation matrix (HTM) model quantifies the geometric errors of a machine tool, which can be compensated for in software. The mathematical treatment is reduced to only essential elements to emphasize physical understanding. A key feature of this presentation is the application of the model to a three-axis milling machine. This illustration enables the undergraduate student to grasp the concept with ease. Another feature is that the entire model is developed from first principles, which does not require the student to invoke any empirical relationships. Three solved numerical problems illustrate the application of the model to practical situations. Information provided here may be used by the teacher as a template to introduce this subject at the undergraduate level.

MEASUREMENT UNCERTAINTY OF A NEW MACHINE-INTEGRATED, PSD BASED APPROACH FOR THERMO-ELASTIC ERROR MEASUREMENT

[Brecher 2021] presents a new, cost-efficient, machine-integrated measuring method for thermo-elastic errors of three-axis milling machines. The setup consists of a spindle mounted position-sensitive diode and a thermo-stable laser frame on the table. The initial paper contained a rough estimation of the measurement uncertainty and the uncertainty of the measureable errors. This work presents a detailed analysis of the setup’s measurement uncertainty in accordance with GUM 100. In addition the resulting uncertainties for the 13 measureable errors of the kinematic are updated based on the new results by means of a Monte Carlo simulation.

Investigation on Structural Mapping Laws of Sensitive Geometric Errors Oriented to Remanufacturing of Three-Axis Milling Machine Tools

Three-axis milling machine tools are widely used in manufacturing enterprises, and they have enormous potential demands for remanufacturing to improve their performance. During remanufacturing a three-axis milling machine tool, the structure needs to be reconstructed, so it is necessary to identify sensitive geometric errors of the remanufactured machine tool. In the traditional sensitive geometric error identification method, complex error modeling and analysis must be conducted. Therefore, professional knowledge is required, and the process of the identification is cumbersome. This paper focused on the quick identification of sensitive geometric errors for remanufacturing of three-axis milling machine tools. Firstly, sensitive geometric errors of a three-axis milling machine tool were identified based on the multi-body system theory and partial differential method. Then, mapping laws between the sensitive geometric errors and the machine tool structure were firstly presented. According to the proposed mapping laws, the sensitive geometric errors can be identified quickly and easily without complex error modeling and analysis. Finally, the simulation and experiment show that the straightness error of milling is improved up to 0.007 mm by compensating the sensitive geometric errors identified by the proposed mapping laws. The table lookup method based on the mapping laws can quickly identify the sensitive geometric errors of three-axis milling machine tools, which is beneficial for the efficiency and precision of remanufacturing of machine tools.

Machine Learning based quality prediction for milling processes using internal machine tool data

Machine tools are increasingly being equipped with edge computing solutions to record internal drive signals with high frequency. A large amount of available data may be used to develop new data-driven approaches to process optimization and quality monitoring. This paper presents a new approach to predict the quality of finished workpieces for three-axis milling processes with end mills. For this purpose, internal machine tool data provided by an edge computing solution was recorded and used to develop a Machine Learning based method for quality prediction. For the preparation of the data, an introduced domain knowledge-based slicing algorithm is applied, which allows the recorded data to be automatically and precisely assigned to the corresponding geometric elements on the workpiece. During data-driven modeling, 9 Machine Learning algorithms are compared to 4 Deep Learning architectures for multivariate time series classification. The results show that ensemble methods like Random Forest and Extra Trees as well as the Deep Learning algorithms InceptionTime and ResNet reach the best performances for the use case of data-based quality prediction.

A Digital Twin Design for Maintenance Optimization

Digital Twin (DT) is being regarded as a suite of innovative technologies within the Industry 4.0 revolution. DT brings so much excitement to the industries pursuing digitalization. DT, as a real-time representation of a physical object supports manufacturers to enhance the yield from their operations. In particular, it offers a unique and advantageous outlook on the predictive maintenance of complex engineering assets. Along with DT, advanced systems simulation techniques enable industries to efficiently model and analyze real-world problems. In this study, a simulation-based DT design for the operation of a complex engineering asset is developed, in which the virtual model of the critical components is integrated with their degradation model. The DT design aims to understand the components’ degradation status and suggest a suitable maintenance intervention. The mathematical algorithm for the components’ remaining useful life and the related maintenance strategies is integrated with the DT model to determine the optimum service. The user interface is developed within the MATLAB app designer platform. A three-axis milling machine is selected to test the validity of the DT design.

Time-domain simulation and testing for dynamic force and stability prediction in milling: Collaboration with feed rate scheduling software

This paper describes: 1) the use of feed rate scheduling software to predict the radial depth of cut variation for three-axis milling toolpaths and; 2) the use of this radial depth profile in a time-domain simulation to predict dynamic cutting forces. The time-domain simulation, which also includes the tool tip frequency response functions and force model (which relates the cutting force components to the chip geometry) as inputs, enables dynamic force profiles to be predicted and parameter combinations that cause chatter to be identified. A ramp geometry is selected that provides constantly varying radial depth and force predictions are completed at multiple axial depths for comparison to measured forces.

Новый подход к трехкоординатному фрезерованию крупногабаритных поверхностей второго порядка

The study introduces a new approach to precision machining of large-sized surfaces of second order on a three-coordinate horizontal milling machine. The new technology does not require the use of unique large-size boring lathes or five-axis milling machines. Three-axis horizontal milling machines do not need to be equipped with additional equipment that provides the workpiece with the missing rotational and translational movements relative to the machine table. The proposed technology is based on the use of a new approach that combines the geometric parameters of the second-order machined surface, the spherical surface of the cutting tool, i.e. cutter, and their position relative to the working table. The use of the developed technology will improve the efficiency and accuracy of machining the surface of second order, as well as simplify the control program and technological support due to the absence of movable equipment. The study gives an example of practical implementation and shows the possibility of independent control of the machined parabolic surface geometry using a three-coordinate horizontal milling machine.

A Hybrid Approach for Noise Reduction in Acoustic Signal of Machining Process Using Neural Networks and ARMA Model.

Intelligent machining has become an important part of manufacturing systems because of the increased demand for productivity. Tool condition monitoring is an integral part of these systems. Airborne acoustic emission from the machining process is a vital indicator of tool health, however, it is highly affected by background noise. Reducing the background noise helps in developing a low-cost system. In this research work, a feedforward neural network is used as an adaptive filter to reduce the background noise. Acoustic signals from four different machines in the background are acquired and are introduced to a machining signal at different speeds and feed-rates at a constant depth of cut. These four machines are a three-axis milling machine, a four-axis mini-milling machine, a variable speed DC motor, and a grinding machine. The backpropagation neural network shows an accuracy of 75.82% in classifying the background noise. To reconstruct the filtered signal, a novel autoregressive moving average (ARMA)-based algorithm is proposed. An average increase of 71.3% in signal-to-noise ratio (SNR) is found before and after signal reconstruction. The proposed technique shows promising results for signal reconstruction for the machining process.

Experimental Investigation of Dimensional Accuracy in Non-traditional Sheet Metal Spinning Process for Producing Rectangular Spun Part

The non-conventional spinning process was adopted for producing polygons, but one of the process limitations is the error between design and the final product especially with no-mandrel. Dimensional accuracy was adopted for this purpose which gives an indicator of the ability of the formed part to matches the design and checking validated of the adopted methodology for producing rectangular cross-section spun parts, by comparing the coordinating points of real part with the points of the design model. The point of a real part was measured by using a sphere probe fixed on the three-axis milling machine and capturing the data of machine axis movements for the center location of the probe, also, the measurements oppositely took place, by offsetting the points of design along the normal vector for comparison with the real part points. Three parameters were invested for study the effects on the dimensional accuracy, these parameters are spindle speed (48, 68, and 135 RPM), feed ratio (0.16, 0.22, and 0.32 mm/rev), and the ball diameter of the forming tool (16, 22 and 25 mm). The results show that tool ball diameter mainly affecting dimensional accuracy with a higher value of average error reach (6.47mm) when 16mm diameter of tool ball was used, on the other hand, the minimum average error was 1.705mm at low spindle speed.

Optimization of machining parameters based on VERICUT three-axis milling

For the processing of complex parts, it is necessary to determine the optimal processing path and processing technology, in order to ensure its processing accuracy and processing efficiency. Because the complexity of parts, the application of equipment, the method of setting up the process have a direct impact on the processing effect, how to obtain the best processing effect and quality has become the problem that must be solved in the process of intelligent manufacturing. This paper introduces the method of obtaining the best machining parameters of complex parts by using VERICUT software. The experimental results show that the machining parameters obtained by this method can improve the efficiency and quality of machining complex parts by using CAM software. Through this way to complete the processing of complex parts for the complex parts processing technical personnel to provide a certain technical reference and reference role.

Experimental Study of the Volumetric Error Effect on the Resulting Working Accuracy—Roundness

Currently, various types of software compensations are applied to machine tools. Their aim is to increase the working accuracy of the tools. The improvement in working accuracy is then further assessed according to the increase in the dimensional and shape accuracy or the surface quality of the workpiece. This publication describes the effects of the volumetric accuracy of a machine tool on the working accuracy of a workpiece, where total roundness (RONt) is evaluated in multiple cuts. In the experiment, two test workpieces are manufactured on a three-axis milling machining centre. The first is made using a standard machine setup while the second with activated volumetric compensation. The LaserTRACER self-tracking laser interferometer is used to compensate for volumetric accuracy. In the second part, verification measurements are performed with a Ballbar, where roundness error is evaluated according to ISO 230-4. Then two test workpieces are machined, and, in the last part, measurement is performed on Talyrond 595S roundness measuring equipment. Finally, the results are analysed and the dependence between the volumetric accuracy, the circularity error of the machine and the working accuracy of the CNC machine tool is established, represented by the RONt of the workpiece. This paper presents new and unpublished relations between the volumetric accuracy of the machine tool and the RONt of the workpiece.