A dynamic priority-based approach to concurrent toolpath planning for multi-material layered manufacturing

This paper presents an approach to concurrent toolpath planning for multi-material layered manufacturing (MMLM) to improve the fabrication efficiency of relatively complex prototypes. The approach is based on decoupled motion planning for multiple moving objects, in which the toolpaths of a set of tools are independently planned and then coordinated to deposit materials concurrently. Relative tool positions are monitored and potential tool collisions detected at a predefined rate. When a potential collision between a pair of tools is detected, a dynamic priority scheme is applied to assign motion priorities of tools. The traverse speeds of tools along the x-axis are compared, and a higher priority is assigned to the tool at a higher traverse speed. A tool with a higher priority continues to deposit material along its original path, while the one with a lower priority gives way by pausing at a suitable point until the potential collision is eliminated. Moreover, the deposition speeds of tools can be adjusted to suit different material properties and fabrication requirements. The proposed approach has been incorporated in a multi-material virtual prototyping (MMVP) system. Digital fabrication of prototypes shows that it can substantially shorten the fabrication time of relatively complex multi-material objects. The approach can be adapted for process control of MMLM when appropriate hardware becomes available. It is expected to benefit various applications, such as advanced product manufacturing and biomedical fabrication.     

Boundary-conformed toolpath generation for trimmed free-form surfaces

In this paper, we adopt a 2D reparameterization procedure to regenerate boundary-conformed toolpaths. Three methods for the 2D reparameterization of trimmed boundaries in parametric space are examined and compared. They are the Coons method, the Laplace method, and a newly developed boundary-blending method. These three methods represent three different approaches to 2D surface parameterization, namely, the algebraic interpolation approach, the partial differential equation approach, and a geometric offsetting approach, respectively. Complete algorithms for surface reparameterization and toolpath generation are developed and implemented. The results showed that the Coons method is relatively simple yet might cause anomalies when the complexities of the boundary are high. The Laplace method is robust but takes relatively more computational time and also has the problem of uneven distribution of iso-parametrics. For the newly developed boundary-blending method, both the computational efficiency and parameterization robustness are quite good, in addition, it alleviates the uneven distribution problem appeared in the Laplace results.     

Part accuracy improvement in two point incremental forming with a partial die using a model predictive control algorithm

As a flexible forming technology, Incremental Sheet Forming (ISF) is a promising alternative to traditional sheet forming processes in small-batch or customised production but suffers from low part accuracy in terms of its application in the industry. The ISF toolpath has direct influences on the geometric accuracy of the formed part since the part is formed by a simple tool following the toolpath. Based on the basic structure of a simple Model Predictive Control (MPC) algorithm designed for Single Point Incremental Forming (SPIF) in our previous work Lu et al. (2015) [1] that only dealt with the toolpath correction in the vertical direction, an enhanced MPC algorithm has been developed specially for Two Point Incremental Forming (TPIF) with a partial die in this work. The enhanced control algorithm is able to correct the toolpath in both the vertical and horizontal directions. In the newly-added horizontal control module, intensive profile points in the evenly distributed radial directions of the horizontal section were used to estimate the horizontal error distribution along the horizontal sectional profile during the forming process. The toolpath correction was performed through properly adjusting the toolpath in two directions based on the optimised toolpath parameters at each step. A case study for forming a non-axisymmetric shape was conducted to experimentally validate the developed toolpath correction strategy. Experiment results indicate that the two-directional toolpath correction approach contributes to part accuracy improvement in TPIF compared with the typical TPIF process that is without toolpath correction.     

基于PartMaker的多任务车铣复合加工编程

概述了当前复合机床存在多任务加工编程的难题.比较几种编程方法介绍了PartMaker编程软件特征,着重阐述了PartMaker中进行多任务车铣复合加工编程和NC程序生成方法.结果表明运用PartMaker较好地解决了当前多任务复合加工编程复杂性问题,大大简化了编程过程和提高了编程效率,提高了工件加工精度,缩短了生产周期.     

Guide curve based interpolation scheme of parametric curves for precision CNC machining

Real-time parametric interpolation has played a key role in the computer control of machine tools. To achieve highest quality parts, generated trajectories not only describe the desired toolpath accurately, but also have smooth dynamics profiles. This paper presents a novel parametric interpolator based on guide curve. The relationships between geometric properties and kinematic properties are firstly discussed. Then, with a consideration of the important effect of the curvature of curvilinear path on the machining dynamics, a corresponding formula, which describes the relation of the maximum allowed feed acceleration/deceleration and the maximum allowed rate of change of curvature radius of paths, is built. Thus, based on a near arc parameterization and through modifying the curvature radius curve to deal with corners, key regions and other cases, adaptive feedrate schedule is completed according to the reconstructed smooth curvature radius curve. Consequently, confined chord errors, corners on the path and the acceleration/deceleration capabilities of the machine tool are simultaneously considered and incorporated into the guide curve based parametric interpolation system without using look-ahead scheme. Simulation results indicate the feasibility and precision of the proposed interpolation method.     

数控铣削中刀具路径的拓扑分析

针对计算机辅助制造中数控铣床上常用的三种刀具路径进行了拓扑分析，给出了不同路径拓扑的残留高度计算公式，并对影响粗糙的因素进行了讨论，该公式可用于表面粗糙度的预测，最后，提出了一种自适应刀具的路径的设想。     

数控恒力铣削刀路设计

在切削加工物理分析的基础上探讨铣削力和切削加工参数之间的关系,建立铣削非圆曲线的力学模型,采用单因素试验法设计铣削试验,通过最小二乘法确定铣削力模型系数。以非圆曲线为例,完成了数控恒力切削测力实验,试验结果表明:该方法能够使切削力在非圆曲线的加工中基本保持不变,改善了曲线的加工质量,缩短了加工时间,在提高加工效率和精度方面具有优势。     

Toolpath planning algorithm for the ablation process using energy sources

Ablation processes using various energy sources such as lasers, electrical power and ultrasonic sources have been widely used in industry to ablate workpieces made of hard-to-cut and temperature resistive materials. Even though the cutting mechanism of the ablation process is different from that of the mechanical cutting process, an identical toolpath of the mechanical cutting process has been applied to the ablation process. An inappropriate toolpath for the ablation process may result in a lower dimensional accuracy of the ablated part. Therefore, a new toolpath planning algorithm considering the characteristics of the energy source is required. In this paper, a toolpath planning algorithm for the ablation process is proposed. The proposed algorithm consists of three steps: (1) The generation of a valid toolpath element, (2) the storage of toolpath elements and the creation of sub-groups, (3) the linking of sub-groups. New guidelines on the toolpath demanded by the ablation process are studied. A new idea involving the use of a storage matrix is applied to the storage of toolpath elements and the creation of sub-groups. In order to verify the applicability of the proposed algorithm, the proposed toolpath planning algorithm has been implemented and tested with practical examples.     

Optimization-based non-equidistant toolpath planning for robotic additive manufacturing with non-underfill orientation

Additive manufacturing (AM) technology has achieved universal application in a great number of fields, such as aerospace, medicine, and military industry. As a significant factor causing weak mechanical properties and part flaws, underfill is inevitable in AM based on the conventional equidistant toolpaths with a limited extra cost. To eliminate underfill caused by sharp corners and voids, this paper develops an optimization-based non-equidistant toolpath, i.e., isoperimetric-quotient-optimal toolpath (IQOP). Firstly, an optimization problem minimizing the isoperimetric quotient of toolpaths is designed to generate smooth toolpaths and is convexified. Then, a unilateral rolling circle method is proposed to guarantee the well-defined condition of the optimization-based toolpath planning process. Finally, the application of the depth tree makes the IQOP method adopt slices with complex boundaries and topological structures. The experimental results show that the proposed IQOP achieves an average 88.5% lower underfill rate than the contour-parallel toolpath (CP). IQOP significantly outperforms the dense CP (DCP) on toolpath smoothness and printing efficiency, with better performance on underfill. With obvious advantages on toolpath smoothness and underfill rate, IQOP achieves higher printing quality than CP in the real world. The proposed approach also provides a general framework of non-equidistant toolpath planning for complex slices in AM and computer numerical control (CNC) milling.     

复杂型腔行切轨迹生成算法研究

复杂型胶类零件的加工是数控编程中的一个难点.本文从提高加工算法的稳定性和加工效率的角度出发.提出了一个复杂平面型腔数控加工的优化算法.即通过二维环的等距、自交、集合等基本运算.按“端点同环最短距离优先剖面线算法”规划并优化刀具轨迹.最后给出了应用实例.