凸曲面拼接模具球头铣刀的瞬时铣削力预测

在曲面模具拼接区域球头铣刀铣削过程中,刀具载荷变化大,瞬态铣削力有突变现象,影响模具拼接区域的加工精度和表面质量。为了预测拼接区域球头铣刀的瞬态铣削力,首先,建立考虑冲击振动的球头铣刀三维次摆线轨迹方程,得到瞬时未变形切屑厚度模型;然后,基于铣削微元的思想,建立凸曲面双硬度拼接模具球头铣刀的瞬态铣削力模型,该模型能够综合考虑拼接区冲击振动、硬度变化、刀具工件切触角度变化对瞬态铣削力的影响;最后,进行凸曲面拼接区域球头铣刀铣削加工实验。实验结果表明,预报的瞬态铣削力和实验测量结果在幅值上和变化趋势上具有一致性,在平稳切削时最大铣削力预测误差值基本在15%以内,验证了该模型能有效地预报凸曲面模具拼接区域球头铣刀的瞬态铣削力。     

多硬度拼接淬硬钢铣削动力学分析

颤振是金属切削加工过程中由于刀具和工件之间相互作用所产生的一种强烈的自激振动现象,会导致切削力幅值增加且发生剧烈波动,进而降低工件表面质量和刀具使用寿命。针对此问题,基于铣削过程稳定性预测分析方法建立多硬度拼接工件的动态铣削系统,对多硬度拼接模具铣削过程稳定性进行深入研究,实现了对拼接模具铣削加工过程颤振稳定域的仿真,进而研究了模态参数对稳定性叶瓣图形状的影响。最后通过时域分析、表面形貌和刀具磨损的研究,综合验证了稳定性预测曲线的精度。研究结果为多硬度拼接模具铣削加工提供理论基础,并设置合理的加工参数来实现金属最大切除率,为大型汽车覆盖件模具铣削加工提供理论依据及技术指导。     

CVD金刚石刀具的微细铣削仿真及试验研究

为研究切削参数对CVD金刚石微铣刀切削性能的影响,运用扩展有限元法对CVD金刚石微刀具的铣削加工和刀具损伤应力进行仿真模拟,研究了铣削加工后工件的表面粗糙度随切削参数的变化规律,分析了切削参数对微铣刀失效的影响,并通过试验验证了仿真结果的正确性。研究结果表明:在CVD金刚石微铣刀加工TC4钛合金时,铣削深度和每齿进给量的增加不利于工件加工质量的改善;铣削速度增加对工件加工表面粗糙度影响较小;铣削深度是影响刀具失效的主要因素,铣削速度和每齿进给量是影响刀具失效的次要因素。     

拼接模具过缝区域切削力建模与表面质量

针对汽车覆盖件拼接模具铣削过程中刀具易磨损破损、已加工表面精度低的问题,对铣削拼接缝过程进行了切削力微元建模。根据加工材料硬度的不同,把每一切削周期的切屑厚度建成切削角度的函数关系,得到不同切削角度下剪切力和犁耕力模型。通过引入单自由度斜体碰撞模型,运用霍普金森压杆试验得到不同主轴转速下刀-工碰撞的弹性变形量δ,进而得到过缝处刀具受到的冲击力。结合剪切力、犁耕力模型与冲击力模型得到过缝区域铣削力预测模型。切削试验与仿真结果具有很好的一致性,证明所建立模型的正确性。研究了不同进给方向下的表面质量,对已加工表面质量、表面粗糙度及工件间高度差进行分析,结果表明,由高硬度切向低硬度工件时可以获得较好的表面质量。所得结果为汽车覆盖件拼接模具铣削加工的工艺优化提供了理论支持。     

基于MATLAB的圆周铣削力仿真对铣刀参数的选择分析

针对圆周铣削加工中工件和机床的偏移使得铣削力对工件精度有较大影响的现状,通过对圆周动态铣削力模型理论进行研究,然后利用MATLAB函数通过改变参与加工的铣刀参数对圆周铣削力进行仿真分析,并通过对照仿真实验进行模型验证,研究结果表明在铣削过程中铣削力分布对工件已加工部分的尺寸精度有重要影响,通过对不同参数的仿真结果对比表明在生产加工前通过铣削力仿真可以选择出较为合理的铣刀加工参数从而减少机加工误差,提高加工效率。     

高速面铣加工的动态铣削力和刀具振动研究

基于力学式切削力预测方法建立了面铣刀动态铣削模型,该模型充分考虑切削厚度、刀具前角和刀具后刀面磨损对铣削力的影响.在Matlab/Simulink环境下,进行了动态铣削力和刀具振动仿真及其频谱分析,并根据仿真结果对转速、齿数、刀具磨损量等影响因素进行了分析验证,该模型有利于揭示各切削参数对动态铣削力和刀具振动的影响规律,从而为实现切削加工参数优化提供理论支持.     

面向铣削力控制的凸曲面拼接模具硬态铣削工艺优化

机械加工对于模具结构的要求日益复杂,导致在模具自由型面上存在大量沟槽、凸凹等结构,容易出现磨损严重、拉毛拉裂等问题。对于模具不同位置所需要的应力特征不同,多采用镶块式模件拼接后整体铣削加工。而拼接处存在铣削力的突变导致刀具磨损过快和型面精度不高问题。本文通过阐述球头刀铣削凸曲面拼接模具表面形成机理,分析了铣削过程中不同位置的刀具-工件的接触关系;并且以球头铣刀加工不同硬度的淬硬钢Cr12MoV凸曲面拼接模具试验为对象,揭示切削深度、切削速度、每齿进给量及刀具铣削方向对拼接处铣削力突变的影响规律;以铣削力突变最小为目标进行正交试验研究,得到考察指标的主次影响规律和最优参数组合。     

变密度微织构球头铣刀切削性能多目标优化

为深入研究微织构排列形式对微织构理刀具的抗磨减摩机理的影响,分别从理论、仿真及试验等方面对最优的微织构排布形式进行研究。首先,建立微织构在刀具前刀面的数学模型及仿真模型。其次,通过试验验证仿真结果的准确性。仿真及试验研究均发现,变密度微织构球头铣刀的铣削性能优于均匀分布密度的微织构球头铣刀。最后,运用模糊评价法优选最优的铣削性能的微织构球头铣刀,优化结果表明,两排织构间距先为200 μm,再为150 μm,最后为175 μm的微织构球头铣刀的铣削性能最好。该项研究使刀具具有良好的抗磨减磨性,提高加工效率及被加工工件的表面质量。     

PCD直刃波齿铣刀加工复合材料的切削性能研究

在切削碳纤维增强复合材料(CFRP)时,大前角的切削刃可以有效减少毛刺,提高加工表面质量,但是前角的增加会影响刀具寿命.本文研究开发了一种PCD直刃波齿立铣刀,设计了不同前角的铣刀进行铣削对比试验,并进行了不同切削距离的磨损试验.通过对比不同切削长度的刀具前刀面、后刀面磨损形貌以及工件上下表面的毛刺,研究了不同前角的铣刀对加工质量的影响.结果 表明,7°前角的铣刀可以有效切断碳纤维,从而减少毛刺的产生,而0°前角的毛刺较多;随着切削距离的增长,7°前角的铣刀比0°前角铣刀前后刀面磨损更小.     

五轴曲面铣削的通用表面纹理形貌建模方法

为进一步提高五轴铣削加工曲面纹理形貌仿真建模方法的通用性,同时为考虑刀具姿态角影响及分类的曲面纹理质量评定提供参考,提出了一种基于刀具结构通用参数和通用曲面刀触点坐标系的五轴铣削曲面纹理形貌建模及仿真方法。基于具有通用性的环形铣刀,采用刀具倾斜角?和旋转角θ定义刀具位姿,建立了能够适用于不同刀具及曲面的五轴铣削表面纹理过程的刀具切削刃点表达式。基于离散化思想,结合刀具切削刃点表达式,提出通过几何关系寻找瞬时扫掠四边形内工件网格点来实现曲面纹理形貌仿真。建立了平面和球面两类常用不同几何特征曲面以及不同类型自由曲面在不同刀具姿态角下表面纹理形貌仿真模型,并将平面仿真形貌分为?=0°、?≠0°两类,同时通过平面仿真时间对比验证了该仿真方法的效率更高。最后进行平面切削实验,结果表明,θ=-40°、?=20°及θ=15°、?=60°组合下实际切削与仿真表面纹理特征基本一致,同时实际切削表面纹理形貌特征与仿真分类结果一致,验证该曲面纹理形貌建模和仿真方法正确有效。     

基于Z-MAP方法的球头铣刀铣削力的建模

瞬时刚性切削力的建模是铣削加工物理仿真的基础,然而,球头铣刀的刀齿形状复杂,加工过程中姿态多变,瞬时刚性铣削力的建模难度较大。在考虑刀具姿态调整的情况下,通过齐次坐标变换建立了刀齿的运动轨迹,提出了一种识别刀具和工件瞬时接触区的改进Z-MAP算法,通过计算当前刀齿的参考线与工件的边界面或刀齿扫掠面的交点求出瞬时未变形切屑厚度,并采用非线性回归的方法辨识了切削力系数,在此基础上使用微元积分法建立了瞬时切削力的计算模型。为了验证仿真模型的可靠性,分别进行了垂直加工和倾斜加工试验,试验和仿真结果具有较高的一致性,表明该建模仿真方法是有效的,可以为实际加工中参数的选择和优化提供理论依据。     

整体球头铣刀参数化设计技术

球头铣刀广泛用于各种复杂型面工件的加工,而对于不同的工件材料、加工型面及切削参数需要合理地选取铣刀的几何参数。本文基于UG二次开发技术和数据库等技术开发了整体球头铣刀参数优化设计系统,实现了整体球头铣刀的自动高效参数化设计,为不同加工工况要求下的球头铣刀设计提供了设计手段。     

车铣加工切削机理分析

车铣加工通过将车刀更换为铣刀,增加铣刀转动自由度,基于工件转动和铣刀转动的合成运动,完成对工件的加工.车铣加工具有断屑更容易、切削温度低、切削力小等优点,即使工件低速旋转,也能实现高速切削.对车铣加工的切削机理进行了分析,具体包括刀具磨损机理、切屑形成机理、工件表面质量、难加工材料切削等.     

Process modeling and toolpath optimization for five-axis ball-end milling based on tool motion analysis

In free-form surface machining, the prediction of five-axis ball-end milling forces is quite a challenge due to difficulties of determining the underformed chip thickness and engaged cutting edge. Part and tool deflections under high cutting forces may result in poor part quality. To solve these concerns, this paper presents process modeling and optimization method for five-axis milling based on tool motion analysis. The method selected for geometric stock modeling is the dexel approach, and the extracted cutter workpiece engagements are used as input to a force prediction. The cutter entry?Cexit angles and depth of cuts are found and used to calculate the instantaneous cutting forces. The process is optimized by varying the feed as the tool?Cworkpiece engagements vary along the toolpath, and the unified model provides a powerful tool for analyzing five-axis milling. The new feedrate profiles are shown to considerably reduce the machining time while avoiding process faults.     

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.     

自由曲面数控加工用刀具

从刀具有效半径和切削速度的角度,分析比较了球头立铣刀在三坐标和平头立铣刀在五坐标自由曲面加工中的加工效率与切削性能,提出了球头立铣刀和平头立铣刀的优化刀具尺寸,并对叶片曲面的刀具轨迹进行了仿真模拟。     

Swept surface-based approach to simulating surface topography in ball-end CNC milling

The parts, in automotive, aerospace, die/mold industry, which have extremely high demands on the quality and integrity of the surface, are usually milled by CNC machine tools. In order to obtain the desirable surface quality, it is an effective way to choose the appropriate cutting parameters before machining by simulating the surface topography formed in the milling process. To do so, this paper develops a model based on the swept surface of the cutting edge and N-buffer model for predicting the surface topography and studies the effect of various cutting parameters. In this developed model, the mathematical equation of the cutting edge is first given, and then based on the relative motion between the cutter and the workpiece, the swept surface of the cutting edge along the tool path is accurately analyzed and modeled from the perspective of kinematics, which is used to describe realistically the cutting interaction between the cutter and the workpiece. Subsequently, the milling process is simulated by an improved N-buffer model by means of the proposed accurate interpolation method for calculating the cusp height. This procedure presents the advantage of not requiring any numerical iteration or approximation to gain the cusp height of any point on workpiece. On basis of the model, the effect of the cutting parameters such as spindle speed, feedrate, inclination angle, path interval, and cutter runout is investigated. Finally, the real machining experiments are performed and compared with the predicted results. The simulated surface topography shows a good agreement with the experimental one. This demonstrates that the developed model can predict accurately the surface topography and also provide the great potential for the surface quality control and the cutting parameter selection in actual production.     

Modeling and Analytical Solution of Chatter Stability for T-slot Milling

T-slot milling is one of the most common milling processes in industry. Despite recent advances in machining technology, productivity of T-slot milling is usually limited due to the process limitations such as high cutting forces and stability. If cutting conditions are not selected properly the process may result in the poor surface finish of the workpiece and the potential damage to the machine tool. Currently, the predication of chatter stability and determination of optimal cutting conditions based on the modeling of T-slot milling process is an effective way to improve the material removal rate(MRR) of a T-slot milling operation. Based on the geometrical model of the T-slot cutter, the dynamic cutting force model was presented in which the average directional cutting force coefficients were obtained by means of numerical approach, and leads to an analytical determination of stability lobes diagram(SLD) on the axial depth of cut. A new kind of SLD on the radial depth of cut was also created to satisfy the special requirement of T-slot milling. Thereafter, a dynamic simulation model of T-slot milling was implemented using Matlab software. In order to verify the effectiveness of the approach, the transfer functions of a typical cutting system in a vertical CNC machining center were measured in both feed and normal directions by an instrumented hammer and accelerators. Dynamic simulations were conducted to obtain the predicated SLD under specified cutting conditions with both the proposed model and CutPro?. Meanwhile, a set of cutting trials were conducted to reveal whether the cutting process under specified cutting conditions is stable or not. Both the simulation comparison and experimental verification demonstrated that the satisfactory coincidence between the simulated, the predicted and the experimental results. The chatter-free T-slot milling with higher MRR can be achieved under the cutting conditions determined according to the SLD simulation.