Enhanced virtual machining for sculptured surfaces by integrating machine tool error models into NC machining simulation

Sculptured surface machining is a time-consuming and costly process. It requires simultaneously controlled motion of the machine axes. However, positioning inaccuracies or errors exist in machine tools. The combination of error motions of the machine axes will result in a complicated pattern of part geometry errors. In order to quantitatively predict these part geometry errors, a new application framework ‘enhanced virtual machining’ is developed. It integrates machine tool error models into NC machining simulation. The ideal cutter path in the NC program for surface machining is discretized into sub-paths. For each interpolated cutter location, the machine geometric errors are predicted from the machine tool error model. Both the solid modeling approach and the surface modeling approach are used to translate machine geometric errors into part geometry errors for sculptured surface machining. The solid modeling approach obtains the final part geometry by subtracting the tool swept volume from the stock geometric model. The surface modeling approach approximates the actual cutter contact points by calculating the cutting tool motion and geometry. The simulation results show that the machine tool error model can be effectively integrated into sculptured surface machining to predict part geometry errors before the real cutting begins.     

Swept volumes of toroidal cutters using generating curves

Modelling the volume swept by a tool as it moves from one programmed position to another in three, four and five-axis milling is a challenging task. In this paper, a technique for generating the volume swept by a toroidal cutter in its motion along a given tool path, is presented. This technique is based on identifying “generating curves” along the path and connecting them into a solid model of the swept volume. The swept volume simulations are verified experimentally for three test pieces. These are also compared with the simulation results from the Z-map technique. The results of the experimental verification show the method to be accurate to within 10 μm for the three test pieces. Furthermore, the computation time for the new technique is significantly less than the Z-map method. It is concluded that the proposed method has the potential of allowing fast simulation and verification of multi-axis tool paths.     

并联机床数控加工的刀具瞬时包络面轮廓线研究

文章对用并联机床进行曲面加工,处于两个加工刀位之间的刀具的平移和旋转的运动速度进行了分析.通过引入在一般运动情况下(包括旋转和平移),通用锥形刀具的瞬时包络面轮廓线的求解公式,得到了用并联机床数控加工中刀具的瞬时包络面轮廓线的解法.对这些轮廓线进行放样处理就可以创建刀具的包络面体.应用上述研究成果可以模拟并联机床曲面加工中已加工表面的形状,文中最后给出了计算实例并进行了验证.     

虚拟加工过程模型研究

现有的对加工过程的研究都只侧重于它的几何特性，而忽略了它的物理特性。而由切削力引起的零件的变形将直接影响到零件的加工质量。这些因素是不能忽略的。本文对虚拟加工过程模型进行了研究，详细讨论了零件在加工过程中的基于Z-Buffer的中间模型的建立和计算方法并在该模型的基础上研究了材料切出过程中产生的瞬时切削力模型。该研究所依据的平台包括：SolidWorks,CAMWorks,Cosmos/Works。     

Chip volume prediction using a numerical control verification model

This paper presents a prediction model of chip volume per tooth in milling operations using a numerical control (NC) verification model that can describe actual cutting. This is important from the viewpoint of cutting force calculation and prediction of the chip load on a cutter tooth. In this paper, the cutter swept volumes along the path were calculated from the information obtained from NC codes as well as the feed-rate. The chip volume per tooth was kinetically modeled for the machining state of free-formed surfaces with flat, ball and round endmills, respectively. To investigate the effectiveness of the proposed model, simulation studies were conducted. Following this simulation, the chip volume per tooth precisely mimicked real machining.     

Swept surface determination for five-axis numerical control machining

This paper presents a closed-form solution of the swept profile of a generalized cutter in five-axis numerical control (NC) machining. The machine configurations and tool movements defined in NC programs are considered to model the true machine tool trajectory, which includes the linearly translational and rotational movements. Based on the machine tool trajectory and the cutter geometry, the cutter’s instantaneous swept profile is determined. By integrating the intermediate swept profiles, the cutter’s swept envelope can be constructed and applied to NC verification. The proposed method provides the explicit solution of the swept profile of a generalized cutter, which is important but not possible in the existing methods for five-axis NC verification. The computer implementations show that the approach developed is superior to the traditional methods.     

Surface finish visualisation in high speed, ball nose milling applications

High speed milling systems are capable of producing complex parts that require little or no hand finishing operations. The machined surfaces are smooth to the touch and they are within the required machining tolerances. However, the visual surface appearance of the parts can be a quality issue because the surface patina is generated by a rotating, multi-flute, ball nose milling cutter as it moves over the surface of the part. Current CAM systems provide good simulating procedures to view the overall surface geometry with swept volume procedures, but they do not consider the micro pattern pertaining to the cutting action of individual cutter flutes. The work presented in this paper addresses this consideration and assesses two new methods to satisfy the need to account for, and predict, the surface machining effects from a ball nose milling cutter.     

数控刻楦中刀轴矢量平滑化及仿真

为了解决数控刻楦中刀轴矢量方向相对鞋楦表面法向频繁变换而造成冲击或发生干涉等问题,提出一种刀轴矢量平滑化插值方法。在确定刀触点的情况下,根据鞋楦表面的微分几何性质确定刀轴矢量方向。采用空间矢量光滑插值方法获得一系列中间位置刀轴矢量使刀轴变化较均匀：根据鞋楦误差要求,采用几何变换方法分析切削工步的起始和结束刀触点处的刀轴矢量变化状况。据此估计刻楦误差。以某规格鞋楦数控刻制过程为例对刀轴矢量光顺化方法进行仿真。结果表明,该方法可以避免刀轴方向频繁变换,并有效地提高加工精度。     

Formulating the swept envelope of rotary cutter undergoing general spatial motion for multi-axis NC machining

Based on the tangency condition in envelope theory and the body velocity representation in spatial kinematics, a closed-form solution of the swept envelope of a general rotary cutter moving along a general tool path defined in the NC programs is derived. No additional moving frames or local frames are required, and the computational formulas are independent of the types of the machines. The results can be applied to NC machining simulation, tool path optimization, and CAD/CAM of spatial cams.     

Modelling the machining dynamics of peripheral milling

The machining dynamics involves the dynamic cutting forces, the structural modal analysis of a cutting system, the vibrations of the cutter and workpiece, and their correlation. This paper presents a new approach modelling and predicting the machining dynamics for peripheral milling. First, a machining dynamics model is developed based on the regenerative vibrations of the cutter and workpiece excited by the dynamic cutting forces, which are mathematically modelled and experimentally verified by the authors [Liu, X., Cheng, K., Webb, D., Luo, X.-C. Improved dynamic cutting force model in peripheral milling—Part 1: Theoretical model and simulation. Int. J. Adv Manufact Tech, 2002, 20, 631–638; Liu, X., Cheng, K., Webb, D., Longstaff, A. P., Widiyarto, H. M., Jiang, X.-Q., Blunt, L., Ford, D. Improved dynamic cutting force model in peripheral milling—Part 2: Experimental verification and prediction. Int. J. Adv Manufact Tech, 2004, 24, 794–805]. Then, the mechanism of surface generation is analysed and formulated based on the geometry and kinematics of the cutter. Thereafter a simulation model of the machining dynamics is implemented using Simulink. In order to verify the effectiveness of the approach, the transfer functions of a typical cutting system in a vertical CNC machine centre were measured in both normal and feed directions by an instrumented hammer and accelerometers. Then a set of well-designed cutting trials was carried out to record and analyse the dynamic cutting forces, the vibrations of the spindle head and workpiece, and the surface roughness and waviness. Corresponding simulations of the machining processes of these cutting trials based on the machining dynamics model are investigated and the simulation results are analysed and compared to the measurements. It is shown that the proposed machining dynamics model can well predict the dynamic cutting forces, the vibrations of the cutter and workpiece. There is a reasonable agreement between the measured and predicted roughness/waviness of the machined surface. Therefore the proposed approach is proven to be a feasible and practical approach analysing machining dynamics and surface roughness/waviness for shop floor applications.     

螺旋锥齿轮数控铣齿加工过程几何仿真研究

利用面相对象技术和CAD系统的三维建模功能及其ObjectARX技术，根据螺旋锥齿轮的加工原理，提出了CNC铣齿机、齿坯和刀具三维模型的构建方法以及基于全局光照明的加工环境光照计算的具体方法。利用齿坯实体模型和刀具实体模型做布尔减运算，来实现模拟工件材料的去除过程；同时，采用全局光照明模型建立了具有真实感的数控加工虚拟现实环境。实际应用表明，该系统不但实现了螺旋锥齿轮的计算机辅助铣齿，提高了加工效率，降低了加工成本；而且还提供了非常真实的仿真效果。所获仿真结果可为齿面接触分析、有限元应力分析、齿轮的数控加工等提供精确的三维几何模型。     

虚拟加工设备的建模和加工过程物理仿真

介绍了虚拟加工设备建模的常用软件，并对虚拟数控机床和刀具的建模进行了讨论。着重研究了虚拟加工过程物理仿真，利用有限元（FEM）法建立了切削力仿真模型，利用多体系统运动学理论建立了虚拟数控机床的运动模型。最后，提出虚拟加工物理仿真技术发展中存在的问题以及未来的研究方向。     

基于OpenGL的刃磨加工仿真模型的建立方法

仿真模型的建立是数控加工过程仿真的核心部分.本文通过对旋转锉刃磨加工过程的分析,以OpenGL为开发工具,通过由刀具形状和刀具轨迹产生的刀具扫描体与离散的工件模型进行布尔运算的方法来建立仿真模型,并给出了仿真结果.     

基于RBF-ARX模型的绞吸挖泥船横移过程模型设计

由于绞吸挖泥船横移过程的影响因素众多,具有明显的非线性和时变性特征,难以精确建模来描述其动态特性。因此在对挖泥船产量形成过程详细分析的基础上,针对传统神经网络收敛速度慢、隐含层较多、训练阶段无法自适应调整网络结构的缺点,采用RBF-ARX模型结构进行绞吸挖泥船产量和横移速度的建模。通过结构化非线性参数优化方法SNPOM,离线识别出RBF-ARX模型的线性和非线性参数,并利用仿真对所建模型和真实数据的误差进行对比。仿真结果表明:所建立的绞吸式挖泥船横移过程模型能够比较准确描述系统在全局范围内的动态特性,与挖泥船的实际产量输出拟合较好。     

准双曲面齿轮数控加工仿真系统设计

根据准双曲面齿轮数控加工原理,提出了CNC铣齿机、齿轮毛坯和盘铣刀实体模型的具体构建方法;利用简化的齿轮毛坯实体模型和盘铣刀实体模型做布尔减运算,在计算机上实现了模拟工件材料的去除过程;通过加工仿真结果和实际加工结果对比,验证了加工仿真方法的正确性.所获得的仿真结果可为齿面接触分析和有限元应力分析提供精确的实体模型.     

Broaching tool design through force modelling and process simulation

Tool design is the most critical part of broaching operations as the key process parameters are permanently defined by the cutter geometry. The main objective of this study is to develop methods for increased productivity of broaching processes through improved tool design based on force simulations. A thermo-mechanical force model is applied to broaching operations with complex tool geometries. Intermediate teeth definition and generation algorithms which are essential parts of broaching process simulations are developed. Simulation results are experimentally verified, and improved tool designs are demonstrated.     

齿轮仿真加工在UG中的实现

文章简要介绍了UG二次开发的常用接口,阐述了齿轮切齿仿真加工的原理,并且在UG NX3.0中,实现了MFC类库的调用,解决了如何在UG二次开发中融入MFC的问题.然后,以齿轮仿真加工为例,计算出了相应的刀具参数,采用参数化设计的思想,建立了齿轮刀具与齿轮毛坯的简化模型,根据齿轮加工原理,对齿轮切齿过程进行动态的仿真,完成了参数设计计算与仿真加工的一体化,为UG的其它二次开发提供参考与借鉴.