The form error reduction in side wall machining using successive down and up milling

In this paper, the form error reduction method is presented in side wall machining. Cutting forces and tool deflection are calculated considering surface profile generated by the previous cutting such as roughing and semi-finishing. Using the form error prediction from tool deflection curve, the effects of tool teeth numbers, tool geometry and cutting conditions on the form error are analyzed. The characteristics and the differences of generated surface shape in up and down milling are also discussed and over-cut free condition in up milling is presented. The form error reduction method through successive down and up milling has been suggested. The effectiveness and usefulness of the suggested method are verified from a series of cutting experiments under various cutting conditions. It is confirmed that the form error prediction from tool deflection in side wall machining can be used in proper cutting condition selection and real time surface error simulation for CAD/CAM systems. This research also contributes to cutting process optimization for the improvement of form accuracy in die and mold manufacture.     

机器学习辅助下的五轴数控铣削刀轨优化

针对铣削加工过程中刀具挠度变形的自动补偿问题,提出了一种用于五轴数控加工的刀轨自优化方法.首先,该方法从铣削加工材料去除仿真中获得工艺条件,且将计算出的切削条件与相应的形状误差测量相关联;其次,采用基于统计学习理论的支持向量回归(Support Vector Regression,SVR)来预测所产生的形状误差,并进行...     

Geometric adaptive straightness control system for the peripheral end milling process

A relationship between the tool deflection and the feed rate is modelled by a modified Taylor's tool-life equation. An off-line Geometric Adaptive Control (GAC) system to compensate for machining straightness error in the finished surface due to tool deflection and guideway error generated by the peripheral end milling process is proposed.

Without a priori knowledge of the variations of the cutting parameters, the time-varying parameters are estimated by an exponentially windowed recursive least squares method with only post-process measurements of the straightness error through a gap sensor. The location error is compensated by moving the milling bed through a numerical control command before cutting. The waviness error is regulated by using optimal feed rate manipulation as obtained from the proposed GAC method during machining although the parameters do not converge to fixed values.

Experimental results show that the location error is controlled within the range of fixturing error of the milling bed on the guideway, the waviness accuracy can be increased to more than three times that of the case with no control action. A single-pass milling operation can become feasible through practical application of the proposed GAC system for finish cutting conditions.     

Roughness and texture generation on end milled surfaces

Plane surface generation mechanism in flat end milling is studied in this research. The bottom of a flat end mill has an end cutting edge angle that plays an important role in surface texture. Surface texture is produced by superposition of conical surfaces generated by the end cutting edge rotation. The machined surface is cut once again by the trailing cutting edge. This back cutting phenomenon is frequently observed on surfaces after finishing. Tool run-out and tool setting error including tool tilting and eccentricity between tool center and spindle rotation center are considered together with tool deflection caused by cutting forces. Tool deflection affects magnitude of back cutting and the surface form accuracy. As a result, the finished surface possesses peaks and valleys with form waviness. Surface topography parameters such as RMS deviation, skewness and kurtosis are used for evaluating the generated surface texture characteristics. Through a set of cutting tests, it is confirmed that the presented model predicts the surface texture and roughness parameters precisely including back cutting effect.     

Estimation of cutter deflection and form error in ball-end milling processes

This paper presents a method to analyze the 3-dimensional form error of a ball-end milled surface due to the elastic compliance of the cutting tool. In order to estimate the form error in various cutting modes, the cutting force and the cutter deflection models including the effect of the surface inclination were established. The cutting forces were calculated by using the cutter contact area determined from the Z-map of the surface geometry and the current cutter location. The tool deflection responding to the cutting force was then calculated by considering the cutter and the holder stiffness. The cutter was modeled as a cantilever beam consisting of the shank and the flute. The stiffness of the holder was measured experimentally. Various experimental works have been performed to verify the validity of the proposed model. It is shown that the proposed method is capable of accurate prediction of cutting forces and the surface form error.     

Optimum orientation of a torus milling cutter: Method to balance the transversal cutting force

In this paper, a new method for tool positioning in milling on torus cutters with round inserts is presented. A new criterion associated with balancing of the transversal cutting force is used to compute a tool orientation. The considered tool inclination is towards the back of the tool. In this case, all inserts work simultaneously and generate a continuous cutting phenomenon. Each of the inserts produces a transversal cutting force; some being positive while others are negative. A small tool axis inclination angle leads to balancing the transversal cutting force exerted on the tool and then reducing deflection and vibrations in milling operations. Firstly, this approach to the dynamic aspects relating to cutting forces in the milling process is significant for mould and die manufacturing since it allows polishing time to be reduced. In addition, as vibrations are reduced, enhanced surface quality can be obtained directly on free-form surfaces such as aeronautic fittings.     

Tool deflection compensation in peripheral milling of curved geometries

This paper presents compensation of surface error due to cutting force-induced tool deflections in a peripheral milling process. Previous research attempts on this topic deal with error compensation in machining of straight geometries only. This paper is concerned with peripheral milling of variable curvature geometries where the workpiece curvature changes continuously along the path of cut. In the case of curved geometries, both process geometry and the cutting forces have shown to have strong dependence on workpiece curvature and hence variation of surface error along the path of cut. This calls for a different error compensation strategy than the one which is normally used for machining straight geometries. The present work is an attempt to improve accuracy in machining of curved geometries by use of CNC tool path compensation. Mechanistic model for cutting force estimation and cantilever beam model for cutter deflection estimation are used. The results based on machining experiments performed on a variety of geometries show that the dimensional accuracy can be improved significantly in peripheral milling of curved geometries.     

The prediction of dimensional error for sculptured surface productions using the ball-end milling process. Part 2: Surface generation model and experimental verification

This paper presents a surface generation model for sculptured surface productions using the ball-end milling process. In this model, machining errors caused by tool deflections are studied. As shown in Part 1 of this paper, instantaneous horizontal cutting forces can be evaluated from the cutting geometries using mechanistic force models. In this paper, a tool deflection model is developed to calculate the corresponding horizontal tool deflection at the surface generation points on the cutter. The sensitivity of the machining errors to tool deflections, both in magnitude and direction, has been analyzed via the deflection sensitivity of the surface geometry. Machining errors are then determined from the tool deflection and the deflection sensitivity of the designed surface. The ability of this model in predicting dimensional errors for sculptured surfaces produced by the ball-end milling process has been verified by a machining experiment. In addition to providing a means to predict dimensional accuracy prior to actual cutting, this surface generation model can also be used as a tool for quality control and machining planning.     

The prediction of dimensional error for sculptured surface productions using the ball-end milling process. Part 1: Chip geometry analysis and cutting force prediction

The study of machining errors caused by tool deflection in the balkend milling process involves four issues, namely the chip geometry, the cutting force, the tool deflection and the deflection sensitivity of the surface geometry. In this paper, chip geometry and cutting force are investigated. The study on chip geometry includes the undeformed radial chip thickness, the chip engagement surface and the relationship between feed boundary and feed angle. For cutting force prediction, a rigid force model and a flexible force model are developed. Instantaneous cutting forces of a machining experiment for two 2D sculptured surfaces produced by the ball-end milling process are simulated using these force models and are verified by force measurements. This information is used in Part 2 of this paper, together with a tool deflection model and the deflection sensitivity of the surface geometry, to predict the machining errors of the machined sculptured surfaces.     

Virtual cutting and optimization of three-axis milling processes

This paper presents generalized process simulation and optimization strategies to predict and improve the performance of three-axis milling operations. Cutter-part engagement conditions are extracted from a solid modeling system, which can handle free form part surfaces found in dies and molds. The cutting force distribution along the engaged cutting edge-part surface is evaluated based on the laws of mechanics of milling. By integrating the distributed force along the cutting edge, total forces, torque and power are either predicted analytically using closed-form solutions, or numerically if the cutting tool shape is discontinuous. Simulation results are then used in a constraint-based optimization scheme to maximize the material removal rate (MRR) by calculating acceptable feedrate levels. The proposed virtual milling system is demonstrated experimentally in milling a stamping die with free form surfaces.     

Experimental investigation and simulation of machining thin-walled workpieces

An enhanced simulation model is presented in this paper to predict form deviations in end milling processes of thin-walled structures. The calculation of tool engagement is based on level curves representing surface geometry of the workpiece and the NC code driven sweep volume. To consider influences of force-induced deflections resulting in static form errors on machined surface of the workpiece, a model for superposed stresses is enclosed. Derived from the tool engagement, the cutting force is predicted using a parametric force model. The experimental investigations within the measuring of static and dynamic form errors during processing and afterwards are shown and measurement results are compared with results of the cutting simulation to verify the proposed method. The presented achievements are deduced from research activities aiming at an increased understanding of shape deviation induced by interactions between tool, workpiece and clamping device during machining.     

Analytical models for high performance milling. Part I: Cutting forces, structural deformations and tolerance integrity

Milling is one of the most common manufacturing processes in industry. Despite recent advances in machining technology, productivity in milling is usually reduced due to the process limitations such as high cutting forces and stability. If milling conditions are not selected properly, the process may result in violations of machine limitations and part quality, or reduced productivity. The usual practice in machining operations is to use experience-based selection of cutting parameters which may not yield optimum conditions. In this two-part paper, milling force, part and tool deflection, form error and stability models are presented. These methods can be used to check the process constraints as well as optimal selection of the cutting conditions for high performance milling. The use of the models in optimizing the process variables such as feed, depth of cut and spindle speed are demonstrated by simulations and experiments.     

An advanced FEA based force induced error compensation strategy in milling

The study introduces a multi-level machining error compensation approach focused on force-induced errors in machining of thin-wall structures. The prediction algorithm takes into account the deflection of the part in different points of the tool path. The machining conditions are modified at each step when the cutting force and deflection achieve a local equilibrium. The machining errors are predicted using a theoretical flexible force-deflection model. The error compensation is based on optimising the tool path taking into account the predicted milling error. The error compensation scheme is simulated using NC simulation package and is experimentally verified.     

基于开放式系统的曲面加工误差动态补偿控制

将基于传感器信息的智能型开放加工系统应用于曲面的高精度加工,提出了曲面加工误差的动态补偿方法。为预测加工误差的补偿量,建立了刀具弯曲模型,分析了刀具弯曲对加工误差的影响。实验结果表明,本系统可有效地提高加工精度,使加工误差降低1／3－1／4。     

Predictive force model for ball-end milling and experimental validation with a wavelike form machining test

This paper presents a predictive force model for ball-end milling based on thermomechanical modelling of oblique cutting. The tool geometry is decomposed into a series of axial elementary cutting edges. At any active tooth element, the chip formation is obtained from an oblique cutting process characterised by local undeformed chip section and local cutting angles. This method predicts accurately the cutting force distribution on the helical ball-end mill flutes from the tool geometry, the pre-form surface, the tool path, the cutting conditions, the material behaviour and the friction at the tool-chip interface. The model is applied for a complex surface which is a wavelike form used as a validation machining test. The results are compared with experimental data obtained from ball-end milling tests performed on a 3-axis CNC equipped with a Kistler dynamometer.     

Active integration of tool deflection effects in end milling. Part 2. Compensation of tool deflection

This study presents a compensation method in milling machining in order to take into account tool deflection during tool-path generation. Tool deflection that occurs during machining, and especially when flexible tools such as end mills are used, can result in dimensional errors on workpieces. The study presented here is part two of a two-part paper. In part one the cutting force models and the surface prediction method have been presented.Here the focus is on tool deflection effects' integration during the generation of the tool path. A strategy is proposed that modifies the nominal tool trajectory, compensates for the machining errors due to tool deflection, without degrading the production performance and the machined accuracy. The methodology allows optimization of the tool path trajectory in order to achieved a specified tolerance. Some experimental results are presented.     

An improved cutting force and surface topography prediction model in end milling

During the milling operation, the cutting forces will induce vibration on the cutting tool, the workpiece, and the fixtures, which will affect the surface integrity of the final part and consequently the product's quality. In this paper, a generic and improved model is introduced to simultaneously predict the conventional cutting forces along with 3D surface topography during side milling operation. The model incorporates the effects of tool runout, tool deflection, system dynamics, flank face wear, and the tool tilting on the surface roughness. An improved technique to calculate the instantaneous chip thickness is also presented. The model predictions on cutting forces and surface roughness and topography agreed well with experimental results.     

On cutter deflection surface errors in peripheral milling

Cutter deflections induce significant amount of surface error on machined components and it is one of the major obstacles towards achieving higher productivity in peripheral milling operation. These surface errors do not take one particular form and their shape and profile measured along axial direction, varies significantly with cutting conditions. The understanding and characterization of all possible surface error types is of immense value to process planners as it forms a basis for controlling and compensating them. This paper presents a methodology to classify surface error profiles and to relate the same with cutting conditions in terms of axial and radial engagement between cutter and workpiece. The proposed characterization scheme has been validated using computational studies and machining experiments. The importance of proposed characterization is further demonstrated in understanding peripheral milling of curved geometries where workpiece curvature influences radial engagement of the cutter that often changes surface error shape both qualitatively and quantitatively. Computational and experimental studies undertaken to study machining of curved geometries underline the importance of proposed characterization scheme in identifying correct cutting conditions for a given machining situation.     

球头碗球面加工组合机床设计

根据球面形成原理,利用铣刀和工件的两个圆运动,合成球头碗的不完整内球面。采用组合机床,结构简单,调整、维护方便,主轴弹性卡头便于工件装卸。对零件尺寸、形状和位置误差进行了分析。通过对铣刀和主轴电机的变频调速,找出最佳切削参数,实现了内球面的高效率高精度加工。     

Analysis and simulation of size effects in micromilling

In this paper the influence of a downscaling of the tool diameter and of the machining parameters on the milling process is analyzed. Starting with an analysis of the cutting edge radius of the tools, the influence of the downscaling on the process is determined by analyzing the surface quality and the cutting forces. The simulation system NCChip, which has been developed at the ISF, is used to simulate the cutting forces when using small tool diameters. This simulation is also used to predict the cutting forces for more complex engagement conditions, like increasing radial immersion or milling of a slot pocket. Additionally, the effects of a downscaling on the tool deflection are analyzed, and strategies to reduce these effects are investigated.