Cutter-workpiece Engagement Research Articles

Mechanism analysis and prediction of bull-nose cutter wear in multi-axis milling of Ti6Al4V with TiAlN coated inserts

Cutter wear is an unavoidable issue during the milling of difficult-to-machine materials such as Ti6Al4V, which severely affects cutting performance and surface quality. Especially in multi-axis milling, the complex and irregular contact area between cutter and workpiece increases the difficulty of wear prediction. This paper proposes a flank wear prediction model of bull-nose cutter in the multi-axis milling process of Ti6Al4V with TiAlN coated inserts. The cutter workpiece engagement (CWE) zone is analyzed and the wear contact length of cutting edge is obtained, which reveals the uneven distribution characteristics of flank wear. After that, by analyzing the geometric profile properties of cutter wear in multi-axis milling, abrasive and adhesive wear, a flank wear prediction model that takes coating hardness and cutting temperature model into account is established. The proposed model is calibrated and validated by the multi-axis milling experiment of Ti6Al4V with TiAlN coated inserts. The results show that the novel wear model has high accuracy with an average percentage error of 12.76 % and can accurately and quickly predict flank wear in multi-axis milling of Ti6Al4V. Finally, the cutter wear mechanism and chip formation are analyzed, which show that the main wear mechanism is abrasive wear and adhesive wear, and there was no obvious oxidation wear.

A parameter-variant trochoidal-like tool path planning method for chatter-free and high-efficiency milling

Trochoidal milling is known for its advantages in machining difficult-to-machine materials as it facilitates chip removal and tool cooling. However, the conventional trochoidal tool path presents challenges such as lower machining efficiency and longer machining time due to its time-varying cutter-workpiece engagement angle and a high percentage of non-cutting tool paths. To address these issues, this paper introduces a parameter-variant trochoidal-like (PVTR) tool path planning method for chatter-free and high-efficiency milling. This method ensures a constant engagement angle for each tool path period by adjusting the trochoidal radius and step. Initially, the nonlinear equation for the PVTR toolpath is established. Then, a segmented recurrence method is proposed to plan tool paths based on the desired engagement angle. The impact of trochoidal tool path parameters on the engagement angle is analyzed and coupled this information with the milling stability model based on spindle speed and engagement angle to determine the desired engagement angle throughout the machining process. Finally, several experimental tests are carried out using the bull-nose end mill to validate the feasibility and effectiveness of the proposed method.

Efficient Voxel-Based Workpiece Update and Cutter-Workpiece Engagement Determination in Multi-Axis Milling

Abstract This paper presents a new method to efficiently update workpiece and determine cutter-workpiece engagement (CWE) in multi-axis milling simulation based on a uniform voxel modeling space. At each cutter location, a novel algorithm named direct voxel tracing is developed and used to generate a functional cutter surface voxel model to reliably establish the internal space of the milling cutter. The cutter internal space is represented by its voxel boundary with small memory usage. Through the Boolean subtraction between two successive voxel boundaries of the cutter internal space, a minimal voxel deactivation region is attained within which all active workpiece voxels are deactivated (removed) to update the workpiece model. To determine the associated CWE map, a 3D circle voxelization algorithm is employed. By slicing the cutter surface by a sequence of planes perpendicular to and along the cutter axis, CWE can be determined as the sliced 3D circles are voxelized. Quantitative comparisons of the proposed method against existing voxel modeling and vector modeling-based methods have been made. The results have demonstrated much improved computational efficiency of the proposed method in simulating the complex multi-axis milling operations.

A novel method for trochoidal milling tool path tailoring based on curvature variation

Trochoidal milling has gained popularity in high-speed milling owing to its ability to reduce cutting force, accelerate thermal dissipation, and increase tool life. Nevertheless, it has the drawbacks of poor cutting efficiency and longer machining time due to decreased cutter-workpiece engagement (CWE). This paper studied the tailoring of trochoidal milling tool path curves subjected to improve machining efficiency by controlling curvature variation while meeting predefined CWE angle criteria. The relationship between the instantaneous CWE angle and the curvature variation of the tool path curve was quantitatively established. Then, a negative exponential function-based governing function was introduced to regulate the curvature variation. Finally, the proposed method was experimentally validated via trochoidal milling of curved slots by evaluating machining efficiency and surface quality. The results showed that compared with the circular, elliptical, and polynomial tool path, the tailored tool path-related average CWE angle increased by 40.5 %, 17.9 %, and 6.3 %; while the machining efficiency improved by 25 %, 16 %, and 14 %, respectively. Although the surface quality (surface roughness varies within 5 % and flatness raised by 27 %) is worse than that of the other three tool path patterns, benefiting from the highly improved machining efficiency, it is still applicable in high-efficiency rough milling of components.

Fast extraction of cutter-workpiece engagement for milling force prediction in multi-axis machining

The paper proposes a fast extraction method for cutter-workpiece engagement (CWE), which greatly facilitates the milling force prediction during multi-axis machining. One of the key cores of the method is to reconstruct the nearby cut-off material of workpiece using a set of past neighboring cutter location points (CLPs), and obtain the CWE entity through local Boolean operation among the current tool, workpiece blank, and reconstructed entity. Moreover, by performing 2-dimensional (2D) image mapping, the engagement boundary of CWE entity will be quickly obtained. Combining with the analytical formula of instantaneous undeformed chip thicknesses (IUCTs), the composite IUCT for tool side and bottom cutting edges during actual immersion is further derived. Finally, accurate and fast prediction of milling force with consideration of tool attitude, corner feature and bottom cutting effect is achieved. The results reveal that the method can predict milling force with an excellent performance of first-order computation complexity.

Deformation prediction in flank milling of thin-walled parts based on cutter-workpiece engagement

Due to the weak rigidity of thin-walled parts, deformation inevitably occurs due to the influence of cutting forces during the machining process, making it challenging to achieve high machining accuracy. To address the above problem, it is necessary to conduct advanced predictions to determine the machining errors in thin-walled parts. This paper proposes a force-induced deformation prediction model based on cutter-workpiece engagement (CWE). The thin-walled structure is divided into two substructures, removal volume and workpiece. The finite element (FE) model of removal volume between any two discrete feed positions can be constructed based on CWE. At each feed position, the birth-death element method is employed to simulate actual material removal, updating the workpiece's stiffness. In the simulation process, utilizing node offset techniques to modify the cutter-workpiece contact zone, ensuring a high level of geometric consistency between the workpiece's FE model and its actual machining shape. Finally, the proposed method is proven via flank milling experiments. The machining errors predicted using the method proposed in this paper exhibit higher accuracy.

Investigation of the tool flank wear influence on cutter-workpiece engagement and cutting force in micro milling processes

Cutting force modeling is essential for comprehending the dynamic mechanics of the micro-milling process. Accurate calculation of the cutter-workpiece engagement is crucial for predicting cutting force accurately. This study proposes an accurate analytical model of cutter-workpiece engagement that comprehensively incorporates tool flank wear, tool edge radius, and tool runout for predicting cutting forces in the micro-milling process. Based on the actual tool radius model, which takes into account tool flank wear and tool edge radius, a fast real-time online method for accurately calculating the entry and exit angles is presented. This method involves the trochoidal trajectories of the current cutting edge and all passing cutting edges from the previous cycle under the influence of tool runout. Then the cutter-workpiece engagement is determined. Based on this, the cutting force is predicted combined with instantaneous uncut chip thickness and cutting force coefficients considering tool flank wear and tool runout. Through micro-end milling experiments, the validity of the cutting force model is confirmed. The statistical analysis of the predicted cutting forces further demonstrates the effectiveness of accounting for the impact of tool flank wear on the cutting forces throughout the entire micro-milling process. Through case analysis, it is concluded that tool flank wear leads to increased cutter-workpiece engagement and significantly affects the cutting forces in three directions. This work could offer a theoretical foundation and practical guidance for predicting tool life and controlling surface quality during the machining process.

Analytical Modelling of the Cutter Workpiece Engagement and the Undeformed Chip Thickness for Circular Ball end Milling Path for Adaptive Feed Rate

Analytical Modelling of the Cutter Workpiece Engagement and the Undeformed Chip Thickness for Circular Ball end Milling Path for Adaptive Feed Rate

BOOLEAN OPERATION-BASED FAST CALCULATION OF CUTTER-WORKPIECE ENGAGEMENT DURING PERIPHERAL MILLING

The cutter-workpiece engagement (CWE) is an important basis for accurately predicting milling force and vibration of machining system, which can be dramatically affected by the complex tool path, variable part allowance and various tool profiles. The paper presents a fast calculation method of CWE during peripheral milling process based on the Boolean operation. A second-developed simulation environment embedded the kernel program with the aid of commercial CAM is established. In the computing model, the locally past-cut material entity of the workpiece is replaced by a set of neighboring tools, and the geometric entity of CWE is quickly obtained through the Boolean operation between the tool, workpiece blank, and past-cut entities. The instantaneous uncut chip thickness (IUCT) is further obtained after extracting the tooth start and end cutting angles. Thanks to the first-order computation time complexity, the method has a significant advantage of fast computing speed when compared to the traditional method with a globally updated workpiece. In the milling case of S-shaped workpiece, the results indicate that the method can effectively calculate the CWE status along the entire tool path, and achieve the fast prediction of milling force under a long-time machining condition.

Identification of milling information and cutter-workpiece engagement in five-axis finishing of turbine blades based on NURBS and NC codes

Five-axis milling is frequently used for machining of turbine blades. Cutting force can cause deformation and vibration of blades, which will eventually affect the milling accuracy and surface quality. Modeling of cutter-workpiece engagement (CWE) is a key process to predict cutting force, especially for complex tool geometries and workpiece surfaces. In this paper, a method to modeling ball-end cutter CWE boundaries for blades with free-form surfaces is presented. Firstly, the NURBS theory is employed to get the surfaces before and after finishing. Secondly, milling information such as coordinate systems is extracted from NC codes. Thirdly, the CWE boundaries are extracted based on the NURBS surfaces and extracted information. The proposed model is a combination of discrete and analytical method. Finally, the performance of CWE model is examined from computational accuracy and efficiency, and is verified through milling test. The proposed method provides a visualization of complex engagement between tool and blade in five-axis milling process, and can be further used in simulation of milling force, vibration and deformation.

Virtual Dynamics Model for 5-axis Machining of Thin-Walled Blades

Abstract The five-axis ball-end milling dynamics of thin-walled blades is presented. The cutting forces are predicted from the ball end mill–blade geometry engagement maps along the tool path. The Frequency Response Function (FRF) of the thin-walled blade is predicted using Finite Element shell elements, and it is updated along the toolpath as the metal is removed. The predicted cutting forces are applied on both the workpiece and tool FRFs to predict the forced vibrations and chatter stability at each tool location. A simplified method to update the cutter–workpiece engagement (CWE) is used to obtain the three-dimensional stability lobe diagram at each desired point on the blade. The integrated model is used to simulate the 5-axis machining of thin-walled blades in the digital environment. The proposed digital model is experimentally validated by machining a series of thin-walled rectangular plates and a twisted fan blade.

An optimized milling force prediction method for multi-axis ball-end finish milling

By accurately predicting milling force in finish milling, simulation of the milling process can be effectively conducted, followed by the provision of effective recommendations on optimization of machining process parameters. The prediction of ball-end milling force poses a significant challenge due to the influence of the cutter workpiece engagement (CWE) calculation and cutting force coefficient identification. This paper proposes a precise approach for predicting milling force, which involves an improved calculation method of CWE and an optimized identification approach for cutting force coefficients based on a mechanistic model. In the calculation of CWE, an optimization method considering the dynamic change of undeformed slice thickness and CWE boundary calculation is proposed. Furthermore, an improved approach incorporating interference signal removal and multiple nonlinear regression fitting methods is utilized for cutting force coefficient identification. Subsequently, the resulting prediction is validated through comparison with measurements and demonstrates a prediction accuracy exceeding 94%. The conclusion drawn is that the proposed prediction method for multi-axis ball-end finish milling force exhibits high accuracy in its predictions.

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

Prediction of Chatter Stability in Bull-Nose End Milling of Thin-Walled Cylindrical Parts Using Layered Cutting Force Coefficients

During the bull-nose end milling operations of thin-walled structures, chatter usually occurs and adversely affects cutter performance, finished surface quality, and production efficiency. To accurately predict chatter stability, a suitable dynamic model with effective system parameters is required. In this article, a three-degree-of-freedom (3-DOF) dynamic model is developed to analyze the milling stability of the thin-walled cylinders, in which the dynamics of the bull-nose end mill along the x-axis and y-axis directions and the dynamic of the workpiece along the z-axis direction are taken into account. Then, the cutter-workpiece engagement (CWE) is extracted by employing a slice-intersection-based approach. And the layered cutting force coefficients are identified by considering the influences of varying cutter diameters on the cutting speed. Thereafter, the semi-discretization method (SDM) is adopted to compute the stability lobe diagram (SLD). In the end, a group of milling tests are carried out on a thin-walled cylinder to validate the accuracy and reliability of the proposed model, and the results show that the model predictions agree well with the experimental data.

Tri-dexel-based cutter-workpiece engagement: computation and validation for virtual machining operations

Tri-dexel-based cutter-workpiece engagement: computation and validation for virtual machining operations

Stability analysis of pocket machining with the spiral tool path using the discontinuous Galerkin method

Pocket machining is widely used in the aerospace and automotive industries. The spiral tool path ensures smooth and consistent pocket machining. However, high-efficiency pocket machining places great demand for the stability of the milling processes. In this paper, the mechanics and dynamics of pocket machining along the spiral tool path are modeled, and a time-domain method is proposed to predict the stability of pocket machining in the framework of the discontinuous Galerkin method (DGM). The mechanics of pocket machining is modeled on the basis of computing the varying cutter-workpiece engagement. The cutting forces are predicted and experimentally verified. Further, the dynamic model of pocket machining is established and the stability of the pocket machining process is predicted with the stability lobes of representative feed directions along the spiral tool path. The DGM based time-domain method is proposed to improve the computational accuracy and efficiency of the stability analysis. The predicted stability of pocket machining along the spiral tool path is validated by the experimental results.

A double-NURBS approach to the generation of trochoidal tool path

Trochoidal milling becomes a popular strategy in high-speed rough milling, thanks to its advantages in lowering cutting force (and tool wear) and increasing tool life. However, it also suffers from the disadvantages of low cutting efficiency and prolonged machining time due to its reduced cutter-workpiece engagement in the cutting area and the idle tool path in the non-cutting area. In this paper, a new trochoidal tool path generation method is proposed based on a double-NURBS curve. Unlike traditional circular trochoidal tool path that combines circular and linear paths to approximate the trochoidal path, the double-NURBS tool path can truly represent a trochoidal path with C2 continuity throughout the entire tool path. In the front cutting area, the control points of the NURBS are modified to increase the cutter-workpiece engagement angles; in the rear non-active area, the NURBS curve is modified to shorten the non-cutting distance and the machining time. Degree elevation of the NURBS circle from 2 to 3 maintains C2 continuity to ensure the machining is smooth throughout all transitions. Cutting force simulations and pocket machining experiments are carried out to validate that the proposed double-NURBS approach deliver the expected result and performance.

A Parameter Optimization Method for Chatter Stability in Five-Axis Milling

Chatter is a dynamic instability caused by the regeneration of waviness on the workpiece surface and damages the machining efficiency and product quality. For five-axis milling, the chatter stability analysis is more complicated because the cutter-workpiece engagement and the direction of the dynamic cutting force vary along the tool path. This paper presents a parameter optimization method to avoid chatter in the five-axis milling process. The dynamic milling system is modeled in each tool-path segment, and the stability is analyzed by introducing the semi-discretization method to solve the delay differential equation. In addition, the multi-frequency solution to the stability prediction for the multiple degrees of freedom spindle-cutter system and workpiece system is presented. Considering the speed and acceleration constraints of the spindle system and the feeding system, the spindle speed optimization iterative method is applied based on the chatter prediction. The verification experiment is conducted on the five-axis milling of the S-curve part to show the predictive accuracy of the chatter model and the validity of the proposed optimization method.

복셀 기반 NC 밀링가공 절삭력 고속 시뮬레이션

With the advent of the 4th industrial revolution, advanced digital manufacturing technologies are actively developed to strengthen manufacturing competitiveness. Smart factories require a real-time digital twin including a Cyber-Physical System (CPS) of machines and processes and intelligent technologies based on the CPS. To predict machining quality and optimize machines and processes, it is necessary to analyze the cutting force during machining. Therefore, for real-time digital twin, a fast cutting force simulation model that receives information such as the positions of the feed axes in short time intervals from the CNC and calculates the cutting force until the next information is input is required. This paper proposes a voxel-based fast cutting force simulation in NC milling for real-time digital twin. The proposed simulation model quickly calculates the cutting force by using only information of voxel elements removed by each tool edge without complicated Cutter-Workpiece Engagement (CWE) and chip thickness calculations in previous studies. To verify the performance of the developed simulation, experimental machining was performed and the measured cutting force and simulated cutting force were compared. It was demonstrated that the proposed model can successfully predict the cutting force 3.5 times faster than the actual process.

CWE identification and cutting force prediction in ball-end milling process

Ball-end milling of sculptured surfaces is an efficient and cost effective manufacturing technique when compared with other methods. However, an accurate cutting force prediction is still challenging when the Cutter Workpiece Engagement (CWE) and Instantaneous Undeformed Chip Thickness (IUCT) vary simultaneously. In order to predict the milling force accurately, an algorithm is designed to obtain the CWE boundaries with the variable tool orientations. Inspired by the main idea of analytical CWE model, an improved Z-map method is developed, which is based on the classic Z-map method. The point cloud of tool envelope surface method is generated based on the classic Z-map and the points of the CWE are screened according to the chosen criteria. Afterwards, the IUCT is calculated numerically by the accurate cutting thickness model. In order to overcome the drawbacks of the IUCT method, a simplified IUCT model is proposed to eliminate the iterative calculation. Related milling experiments were carried out on Al7075 workpiece to validate the proposed models showing a good agreement with errors smaller than 12.5%. It can be concluded from simulation results that tool postures have a significant effect on the machining process. This contributes to in-depth understanding the material removal process and optimizing the process parameters of multi-axis machining processes.