复杂形状工件的端铣切削力模型

以传统的端铣切削力模型为基础，提出了一种新的端铣加工中静态切削力的预报模型。该模型考虑了复杂的工件形状和不同的铣刀进给轨迹。给出了一种新的工件和铣刀接触算法。     

Three-dimensional process stability prediction of thin-walled workpiece in milling operation

High-speed machining of thin-walled workpiece is widely used in aerospace industry. To optimize the machining parameters in milling operations, the related process stability is required to be predicted. Compared to the existing two-dimensional (2D) milling stability model, a more completed three-dimensional (3D) regenerative process stability prediction model of thin-walled workpiece is presented based on the newly developed dynamic model. The efficiency and accuracy of the regenerative milling stability can be improved in the presented 3D model. The analysis procedure of the stability of flexible dynamic milling is developed in details. The 3D stability lobes are calculated according to the full discretization method and direct integration scheme. To verify the accuracy of presented 3D stability model, the thin-walled workpiece milling sound pressure signal and surface quality are determined in experiments.     

Optimal fixture design in peripheral milling of thin-walled workpiece

In order to optimize the positions of the locators in peripheral milling of a thin-walled workpiece, a finite element model along with an accurate cutting forces model is proposed in this paper. The finite element model takes into account the thickness variations of the workpiece in peripheral milling. The locators on the secondary locating surface directly influence the surface errors in peripheral milling of thin-walled workpiece, so this paper deals with the optimization of the positions of the locators on the secondary locating surface. A method including two steps is presented. In the first step, the initial positions of the locators are determined by adding the locators at the position with the maximum deformation. In the second step, a heuristic algorithm is proposed to optimize the positions of the locators. Finally, a simulation example is used to illustrate the method.     

薄壁零件的高速铣削稳定性研究

薄壁结构零件在加工过程中极易发生变形和切削振动,这对提高加工质量和加工效率十分不利.在考虑刀具和工件两个方向自由度的基础上,分析了薄壁零件的动态铣削模型.针对2A12铝合金薄壁结构零件,利用MIKRON UCPDUR0800 高速加工中心和相关仪器、软件,通过铣削力辨识实验和模态实验,进行了高速铣削薄壁零件的稳定域分析和实验验证.     

Quadtree-array-based workpiece geometric representation on three-axis milling process simulation

A workpiece hybrid representation method based on quadtree-array is presented to improve the geometric simulation efficiency on three-axis milling process. The method takes the advantages both of Z-Map and quadtree in simulation model representation. The discrete points managed by using Z-Map algorithm is to represent the whole model, while the points used to represent the simulated surface detail are managed with quadtree-array. The method can reduce the levels of a quadtree without losing simulation accuracy. A dynamic optimization algorithm to the quadtree structure is highlighted to reduce its total nodes in simulation process. As a result, the simulation efficiency can be improved significantly. A three-axis milling process simulation system based on quadtree-array representation was developed and used to evaluate the performance of the presented method. The evaluated results show that quadtree-array-based hybrid representation method of workpiece can improve the simulation efficiency significantly, and reasonable division number of array cells is also recommended.     

Virtual workpiece: workpiece representation for material removal process

In this paper, an efficient methodology to generate a virtual workpiece (VWP) is presented. VWP is a workpiece in a virtual environment in which the geometric, kinematic, and thermo-mechanical effects of the process and resources can be reflected. VWP encompasses not only the macro-information corresponding to the shape of the “virtually” machined intermediate workpiece, but also the micro-information, such as the surface roughness, scallop heights, chatter mark, etc. To represent VWP, swept volume (SV) of geometrically defined cutters is generated first by envelope profiles which are calculated by the intersection of the Tool map with the Contact map of the tool moving direction. Then SV is tessellated to conduct elementary 1D Boolean subtraction of SVs from the IPW. The Boolean subtraction is realized by means of an efficient ray-triangle intersection test using Barycentric coordinates. Finally, VWP is reconstructed as a triangular mesh (STL, stereolithography data format) from the orthogonal triple-dexel model (TDM) which predicts machined surface quality, such as surface roughness, gouging and sharp edges and is reused for further operations, e.g., tool path generation, simulation and geometric metrology, etc. To demonstrate the validity of VWP modeling, several material removal processes, e.g., milling and micro-EDM operations, have been tested and the proposed approach has been proven to be applicable to enhance the quality of NC simulation and verification.     

刀具和工件的子系统动态特性对铣削稳定性的影响

针对目前铣削稳定性研究的状况,建立一个新的动力学模型,该模型同时考虑刀具子系统和工件子系统的动态特性,并借助MATLAB/Simulink软件开发了一个仿真模型,通过仿真实验和铣削实验,研究如何改善铣削稳定性,并发现通过改变刀具子系统和工件子系统刚度的相互关系可以起到抑制颤振的目的。     

Extracting cutter/workpiece engagements in five-axis milling using solid modeler

Predicting cutting forces in milling process simulation requires finding cutter/workpiece engagements (CWEs). The calculation of these engagements is challenging due to the complicated and changing intersection geometry between the cutter and the in-process workpiece. In this paper, a solid modeling based methodology for finding CWEs generated in five-axis milling of free form surfaces is presented. The proposed methodology is an extension of the solid modeler based three-axis CWE extraction method given in [21]. At any given instant of the five-axis tool motion, the velocity vectors along the cutter axis may move in directions that do not lie in the same plane, and therefore the cutter envelopes need to be approximated by spline surfaces. Considering the spline surface approximations, the CWE methodology described in [21] does not work properly for the five-axis milling. Therefore in the proposed method, the in-process workpiece is used instead of the removal volume for extracting the CWEs. A terminology the feasible contact surfaces (FCS), defined by the envelope boundaries, is introduced. To extract the CWEs at a given cutter location, first the BODY entity, obtained by offsetting the FCS with an infinitesimal amount, is intersected with the in-process workpiece. Then, the resultant removal volume is decomposed into faces. Finally, the surface/surface intersections are performed between those faces and the FCS to obtain the CWE boundaries. To be used in the force model, the CWE boundaries are mapped from Euclidean 3D space to a parametric space defined by the engagement angle and the depth-of-cut for a given tool geometry.     

Chatter prediction utilizing stability lobes with process damping in finish milling of titanium alloy thin-walled workpiece

Machining chatter often becomes a big hindrance to high productivity and surface quality in actual milling process, especially for the thin-walled workpiece made of titanium alloy due to poor structural stiffness. Aiming at this issue, the stability lobes are usually employed to predict if chatter may occur in advance. For obtaining the stability lobes in milling to avoid chatter, this article introduces an extended dynamic model of milling system considering regeneration, helix angle, and process damping into the high-order time domain algorithm which can guarantee both high computational efficiency and accuracy. Via stability lobes, the reasonability and accuracy of the proposed method are verified globally utilizing specific examples in literature. More convincingly, the time-domain numerical simulation is also implemented to predict vibration displacement for partial stability verification. In this extended model, process damping is well-known as an effective approach to improve the stability at low spindle speeds, and particularly, titanium alloy as typical difficult-to-machine material is generally machined at low spindle speeds as well due to its poor machinability. Therefore, the proposed method can be employed to obtain the 3D stability lobes in finish milling of the thin-walled workpiece made of titanium alloy, Ti-6Al-4V. Verification experiments are also conducted and the results show a close agreement between the stability lobes and experiments.     

对刀及工件测头在数控铣床上的应用

在南通XK5 0 2 5 /4数控铣床上使用触发式测头 (英国雷尼绍的OMP40工件测头和TS2 7R对刀测头 )实现工件定位和刀具的测量 ,进一步完善该铣床的功能 ,促进了加工的自动化。     

虚拟加工过程薄壁工件铣削变形模型研究

在薄壁工件的切削加工中,工件的受力变形是影响加工过程的一个主要因素,文中针对薄壁工件侧面的立铣加工,建立了不同复杂度的切削过程模型,以仿真工件薄壁在加工中受到切削力发生的变形,虚拟实现受到工件变形影响下的切削过程。通过仿真创成的工件表面形貌与实际切成的工件表面的比较,对文中各模型进行了验证。     

FEM-based prediction of workpiece transient temperature distribution and deformations during milling

In high-speed dry milling of thin-walled parts, the cutter-workpiece temperature rises asymptotically with cutting speed, causing excessive cutter tooth wear and workpiece thermal expansion, which in turn reduces the cutter life and produces dimensional and geometrical variabilities in the machined part. Therefore, a basic understanding of the thermal aspect of machining and the effecting parameters is essential for achieving better part quality with improved productivity. This paper presents a transient milling simulation model to assist manufacturing engineers in gaining in-depth understanding of the thermomechanical aspects of machining and their influence on resulted part quality. Based on the finite-element method approach, the model can predict transient temperature distributions and resulted elastic-plastic deformations induced during the milling of 2.5D prismatic parts comprising features like slots, steps, pockets, etc. The advantages of the proposed model over previous works are that it (1) performs feature-based machining simulation considering transient thermomechanical loading conditions; (2) allows modeling the effects of coolant on convective heat transfer rate; and (3) considers the nonlinear behavior of the workpiece due to its changing geometry, inelastic material properties, and flexible fixture–workpiece contacts. The prediction accuracy of the model was validated with experimental results obtained during the course of the research work. A good agreement between the numerical and experimental results was found for different test cases with varying part geometries and machining conditions.     

Optimization of the number and positions of fixture locators in the peripheral milling of a low-rigidity workpiece

In this paper, a method is proposed to optimize the fixture layout in the peripheral milling of a low-rigidity workpiece. Because the locators on the secondary locating surface directly influence the deformation of the workpiece in peripheral milling, this paper deals with the optimization of the number and positions of the locators on the secondary locating surface. The method proposed in this paper includes two stages. In the first stage, the initial number and positions of the locators are determined by adding the locators at the position with the maximum deformation. In the second stage, the number and positions of the locators are optimized. Using the method proposed in this paper, the number of locators is reduced, while the machining accuracy of the workpiece is retained.     

Stability improvement and vibration suppression of the thin-walled workpiece in milling process via magnetorheological fluid flexible fixture

In aerospace industry, thin-walled workpiece milling is a critical task. Also, the machining vibration is a major issue for the accuracy of the final part. In this study, a new dynamic analytical model is proposed to determine the effect of damping factor on the dynamic response of thin-walled workpiece in machining. A complex structure workpiece is equivalent to a thin plate. The fixture constrains and the damping factor are crucial elements of this thin plate. Therefore, the magnetorheological fluid flexible fixture is designed to suppress the machining vibration in machining process. Then, the general dynamic cutting force model and the damping force model are proposed for the key dynamic equation for the prediction of dynamic response to evaluate the stability of the milling process with and without the damping control. Finally, the feasibility and effectiveness of the proposed model is validated by machining tests. The predicted values match on the experiment results.     

Tool–workpiece interaction in deformational cutting

A method is developed for the comparison of deformational cutting and traditional cutting in terms of the force and energy consumption. The force required is less in deformational cutting than in traditional cutting.     

一种新型盘铣刀——阶梯状分屑盘铣刀

数控铣床和普通铣床非常重要的工作之一是铣削平面,传统盘铣刀的切削深度较小,此时可以设计一种可以阶梯状分屑的盘铣刀,使其在铣削平面时阶梯状分屑,从而加大了一次切削的切削深度,提高了切削效率。     

Cutter workpiece engagement region and surface topography prediction in five-axis ball-end milling

Based on the machining tool path and the true trajectory equation of the cutting edge relative to the workpiece, the engagement region between the cutter and workpiece is analyzed and a new model is developed for the numerical simulation of the machined surface topography in a multiaxis ball-end milling process. The influence of machining parameters such as the feed per tooth, the radial depth of cut, the angle orientation tool, the cutter runout, and the tool deflection upon the topography are taken into account in the model. Based on the cutter workpiece engagement, the cutting force model is established. The tool deflections are extracted and used in the surface topography model for simulation. The predicted force profiles were compared to the measured ones. A reasonable agreement between the experimental and the predicted results was found.     

涡轮叶盘数控加工优化方法的研究与实现

为提高涡轮叶盘的加工效率和质量，提出了涡轮叶盘数控加工工艺方案，在粗加工阶段，采用插铣方法代替传统的点铣加工，分层加工，减小加工变形。采用UGNX进行涡轮叶盘建模，NERC-Max数控编程，VERICUT刀轨仿真。结果表明，采用插铣方法，切削效率高，刀具和叶片未发生干涉，加工阶段划分、刀轨设计合理。提出的涡轮叶盘数控加工工艺方案可行。     

Improvement of flatness error in milling plate-shaped workpiece by application of side-clamping force

To improve flatness error of plate-shaped workpieces in milling under side clamp holding mechanisms, appropriate magnitudes of clamping forces and method of application are studied in this paper. The effect of side-clamping force on workpiece deformation is investigated by experimental and computational analyses for the case where the workpiece is clamped at a position higher than the neutral plane of bending of the plate-shaped workpiece. It is found that the thermal deformation and elastic deformation caused by clamping force are in two opposite directions. Then, an appropriate method is proposed to compensate for the workpiece thermal deformation caused by cutting heat with the opposite elastic deformation caused by the side-clamping force, so as to keep the machined top surface of the workpiece flat as much as possible. The proposed method has been confirmed through computational analyses and experiments. © 2000 Elsevier Science Inc. All rights reserved.     

基于知识的高速面铣刀设计系统研究

高速面铣刀是知识密集型产品,传统设计方法存在设计周期长且不能很好地利用已有知识和经验的问题。本文采用基于知识的高速面铣刀设计方法,提出了基于知识的高速面铣刀设计框架模型,创建了基于规则的高速面铣刀设计知识库和基于特征相似度的高速面铣刀实例库,并在UG／NX平台上开发了基于知识的高速面铣刀设计系统,实现了知识驱动的切削铝合金高速面铣刀模型的快速设计。最后,通过对铣刀模型的应力场分析和实际切削试验验证了该方法的可行性和推理的正确性。