Pengcheng Hu

Improving the dynamics of five-axis machining through optimization of workpiece setup and tool orientations

Existing works in optimization of five-axis machining mainly focus on the machining efficiency and precision, while the dynamic performance of the machine tools has not been fully addressed, especially in high-speed machining, in which the rotary actuators have limited dynamic ability. In this paper, a study is reported on how to generate a tool path so that the maximal angular accelerations of the rotary axes of the five-axis machine can be reduced. Two independent methods are proposed for this task: (1) by optimizing the setup of the workpiece on the machines table, and (2) by finding better tilt and yaw angles for the tool orientations. In this paper, the setup parameters of the workpiece are incorporated into the inverse kinematic equations, and angular acceleration functions are established according to the numerical solutions of those equations. While varying the tool orientations unquestionably would affect the surface quality of the machining, we introduce the so called Domain of Geometric Constraints that will restrict the allowable tilt and yaw angle of the tool at the cutter contact points on the part surface, so to ensure the satisfaction of the requirement of both local-gouging-free and cusp-height. For the first method-finding the optimal workpiece setup-a heuristic-based approach, i.e., the Genetic Algorithm (GA), is adopted, whereas for the second method-the constrained optimization of tool orientations-we present an elaborate algorithm based on the results from the analysis conducted by the authors. At the end of the paper, computer simulation experiments are reported that demonstrate the effectiveness of our proposed methods and algorithms.

Five-axis tool path generation based on machine-dependent potential field

Traditional methods for improving machining efficiency in five-axis machining mainly concentrate on two frontiers. One seeks to minimise the total length of the tool path, while the other aims at maximising the feedrate. These two optimisations are carried out independently at different stages of a machining process and often conflict each other. Explicitly, a tool path with minimum total tool path length may turn out to be inferior when the specific machine tool’s capacities are considered, and, in order not to exceed the limits of those capacities, the machine’s controller has to keep the feedrate under an inordinately low level, thus actually prolonging the real machining time. In this article, by considering the local geometry of the part surface and the speed and acceleration limits of the machine’s axes, a vector field called machine-dependent potential field is proposed to characterise the relationship between the material removal rate and the feed direction. Based on this introduced potential field, and combined with the well-known iso-cusp height expansion method, a new five-axis tool path generation algorithm is proposed. Preliminary experiments show that this new algorithm can sometimes achieve substantial savings in total machining time over the existing methods.

Global obstacle avoidance and minimum workpiece setups in five-axis machining

The state-of-the-art tool path computation algorithms for five-axis machining consider only the workpiece and clamping device for collision avoidance. However, in a real five-axis machining process, there are many other types of obstacles beyond workpiece and clamps that the tool assembly must avoid, e.g., sensors and other intrusive devices. In such cases, the only solution at present is by means of computer simulation of the machining process after the tool path has been computed. If collision is found, it requires re-computing the tool path and/or changing the setup of the workpiece. This process is then re-iterated until all the collisions are resolved. As a result, the process is time consuming and requires excessive human intervention. In this paper, we present rigorous analyses of the obstacles in five-axis machining and propose efficient numerical algorithms for calculating and representing them. Using our results, the obstacle-free tool orientations can be determined completely at the tool path planning stage, rather than relying on the simulation afterward. In addition, as a direct application of our mathematical modeling, we present a heuristic-based solution to the optimal workpiece setups problem: finding a minimum number of workpiece setups for an arbitrary sculpture part surface so that it can be machined completely on a given five-axis machine without colliding with the obstacles. We use orthogonal table-table five-axis machines as an example and work out a numerical experiment using the proposed solution.

Efficiency-optimal iso-planar tool path generation for five-axis finishing machining of freeform surfaces

Abstract Traditional works in five-axis iso-planar tool path generation mainly aim at finding the best direction of the parallel drive planes so that the total length of the tool path is minimized. However, an iso-planar tool path optimized this way is often found to be inferior in improving the machining efficiency, as it ignores the kinematic constraints of the specific machine tool. In this paper, we present an efficiency-optimal iso-planar tool path generation algorithm for multi-axis machining of freeform surfaces that takes the kinematic capacities of the machine tool in full consideration. Rather than trying to maximizing the cutting strip width alone, the proposed algorithm aims at globally maximizing the material removal rate which considers both the cutting strip width and the machine’s kinematic capacities and hence is a more comprehensive reflection of machining efficiency. In addition, we further enhance the machining efficiency by automatically adjusting the tool orientation along the tool path. Both computer simulation and physical machining experimental results show that, when compared with the traditional iso-planar tool path generation algorithms, the proposed method is often able to substantially improve the machining efficiency.

Automatic generation of efficient and interference-free five-axis scanning path for free-form surface inspection

As a new contacting surface inspection technology, five-axis continuous sweep scanning enables a much higher inspection efficiency compared with the traditional three-axis point-by-point inspection. However, currently how to plan an interference-free scanning path for an arbitrary free-form surface still heavily depends on human intervention and the scanning path thus obtained lacks severely in inspection efficiency since the unique kinematic characteristics of the five-axis inspection are ignored. Motivated by these deficiencies, this paper proposes a practical algorithm for automatically generating an interference-free and efficient five-axis continuous scanning path for an arbitrary free-form surface. The algorithm adopts the guiding-path + trajectory-curve paradigm for the generation of scanning curves while the collision-free constraint on the stylus is taken care of by considering the aggregate accessibility of the reference curves. A digraph is then constructed on the aggregated accessibility domains of the sample points of the guiding path and the stylus orientation along the guiding path is determined by finding the shortest path in this graph. A simple surface partitioning scheme is also introduced in case a surface cannot be scanned in a single pass and needs to be divided into suitable smaller patches. Preliminary experiments in both computer simulation and physical inspection of the proposed algorithm validate that, when compared with the two leading commercial solutions, the proposed algorithm not only is fully automatic without relying on human intervention but also achieves a much higher inspection efficiency. A concept called aggregate admissible orientation domain (AAOD) is proposed.A method based on AAOD is presented to partition the surface of inspection.Stylus orientation is determined based on a digraph defined from AAOD.Experiments verify the superior efficiency and automation level of our method.

Automatic Generation of Five-Axis Continuous Inspection Paths for Free-Form Surfaces

Continuous five-axis sweep scanning is an emerging technology for free-form surface inspection, which, unlike the traditional three-axis inspection that works in a point-by-point manner, keeps the stylus tip in constant contact with the surface during the scanning, and thus could tremendously improve the inspection efficiency. However, at present, it mostly depends on humans to plan a five-axis inspection path, which severely affects the potential use of this new technology. In this paper, we report a practical algorithm, which is able to automatically generate a five-axis inspection path for an arbitrary free-form surface. The crux of this algorithm is that the unique kinematic characteristics of the five-axis inspection machine are fully considered and utilized when a path is planned. As a direct result of this consideration and utilization, the inspection efficiency is tremendously increased, often 20–30 times better than an inspection path obtained by any traditional path planning algorithm that disregards the inspection machine itself. The experiments performed by us have fully validated this point.

Boundary-Conformed Tool Path Generation Based on Global Reparametrization

In this paper, a boundary-conformed tool path generation method for either compound or trimmed surfaces are proposed, based on two powerful reparametrization schemes- the discretized harmonic mapping and the convex combination mapping. By globally mapping a 3D surface onto a 2D unit square and then planning an iso-parametric curve in the 2D domain, the corresponding Cutter Contact (CC) curve on the original 3D surface is easily generated which conforms with the boundary of the surface. Based on this CC curve generation strategy, a CC curve expansion algorithm for covering the entire surface is designed which takes into account the machining accuracy requirement, i.e., The specified maximum cusp height. Tool paths generated in this way for compound or trimmed surfaces are boundary-conformed, smooth, and guarantee the required machining accuracy.

Five-axis finishing tool path generation for a mesh blade based on linear morphing cone

Abstract Blisk is an essential component in aero engines. To maintain good aero-dynamic performance, one critical machining requirement for blades on blisk is that the generated five-axis tool path should be boundary-conformed. For a blade discretely modeled as a point cloud or mesh, most existing popular tool path generation methods are unable to meet this requirement. To address this issue, a novel five-axis tool path generation method for a discretized blade on blisk is presented in this paper. An idea called Linear Morphing Cone (LMC) is first proposed, which sets the boundary of the blade as the constraint. Based on this LMC, a CC curve generation and expansion method is then proposed with the specified machining accuracy upheld. Using the proposed tool path generation method, experiments on discretized blades are carried out, whose results show that the generated tool paths are both uniform and boundary-conformed.