基于约束融合机理的薄壁件高效加工刀轨规划理论与方法

The problem of cutting stability is often a key challenge needed to be solved urgently in high efficient machining of thin-walled parts. In order to solve this problem, the research of new toolpath generation methods will be carried out for five-axis high efficiency machining based on multi-constraints fusion. Theoretical modeling, algorithm design and experimental verification are integrated to study and verify the new developed toolpath considering the combining effect of cutting dynamics and vibration stability theory. Firstly, the thin-walled parts surfaces are divided and coupling reconstructed smoothly according to the geometric features. The geometric representation mechanism will be explored for high quality toolpath. Then, the velocity field and steady-state stiffness field will be introduced to toolpath design because of low efficiency and weak stiffiness in thin-walled parts machining. The characteristics of cutter motion constraints in tool axis trajectoy will be analyzed, and the model of tool motion optimization will be built and solved. The nonlinear mapping and its evolution between variable stiffness and cutting stabilty are studied under the effect of dynamic cutting forces. The high-speed cutting stability model will be built in the toolpath surface. Finally, the fusion methods between the tool orientations optimization and stable toolpath planning will be studied considering the combining effect of kinematics and dynamics besides geometry. The dynamic bayesian networks reasoning models are uesd to study the coupling relevance between geometric and physical constraints. The optimization mechanism and mapping rules will be clarified clearly for constraints coupled and decoupled on tool axis trajectory. Based on this, the software module will be developpd and verified by examples in engineering project. The expected research achievements will have very important application value for high efficiency and precise machining technology, and will also enrich the toolpath planning strategies for five-axis high performance machining.

薄壁件加工中的切削稳定性问题一直是高效精密制造中迫切需要解决的难题。本项目基于申请人前期研究成果，融合切削动力学和振动稳定性理论，采取理论建模、算法设计和实验验证相结合的思路，提出多元约束融合驱动的薄壁件高效加工刀轨控制新原理和新方法。首先通过研究薄壁零件曲面划分及光滑耦合重构，探索高品质五轴刀路的几何表达机制；接着针对薄壁件加工效率低和弱刚性的特点，研究将速度场和稳态刚度场引入刀轨设计的操控方法，分析刀轴在轨迹面上的运动约束特性，并建立其运动优化求解模型。研究动态切削力激励下，工艺系统变刚度特性与切削稳定性之间的非线性映射及演化关系，构造刀轨面上的高速切削稳定性模型；最后借助混合约束的动态贝叶斯网络推理，研究几何学、运动学及动力学综合作用下的刀具位姿优化与稳定性设计融合方法，阐明约束耦合与解耦对刀轴轨迹的优化机理与映射规律。预期研究成果将为薄壁零件的高效精密制造提供科学方法与实践依据。

本项目于2013年8月批准立项，2014年1月开始实施，计划2016年12月结题。项目研究内容包括四个方面：薄壁件多曲面耦合重构及刀轨线性化方法、刀具轨迹中物理约束引入方法和建模分析、混合约束下五轴加工刀轨控制优化求解策略、软件开发和工程应用。项目研究按原计划实施，主要完成了以下几项研究工作：（1）提出基于高斯球面优化的五轴加工等距双NURBS刀具路径生成及其同步插补算法，解决等距双NURBS刀具路径插补过程中两条NURBS曲线参数的同步问题；（2）针对五轴刀路的线性不连续性问题，提出在刀具中心点路径和刀轴点路径的相邻拐角处，构建满足精度约束且达到G2连续的三次NURBS曲线，实现五轴线性路径的拐角光顺；（3）研究基于球面角度插补的五轴联动非线性误差控制方法，提高加工精度，实现薄壁零件等厚加工；（4）研究基于刚度模型的刀具轨迹优化方法，运用机床弹性变形的等效位移变换算法，和工件表面几何特征调整优化刀具轨迹，实现零件加工的表面质量补偿；（5）针对所给定的五轴联动数控机床以及机床各轴的伺服能力约束下，推导五轴联动等距双 NURBS 刀路插补中进给速度和进给加速度的可行范围，使插补器的输出命令满足机床各轴伺服能力的约束；（6）提出基于稳定性的球头刀刀轴方向优化方法，采用频域稳定性方程对五轴加工过程进行描述，应用离散Nyquist法判断其稳定性；（7）开发基于RTX平台的连续小线段高速平滑插补软件，应用于薄壁件五轴加工中，加工效率提高30%以上，系统软件满足数控加工的实时性任务和精度要求。（8）在项目资助下，已发表论文8篇，其中SCI收录3篇，EI收录4篇，正在撰写SCI论文1篇；已授权发明专利2项，申请软件著作权1项。