Hongyao Shen

A generic uniform scallop tool path generation method for five-axis machining of freeform surface ☆

Abstract In this paper, a generic uniform scallop tool path generation method for five-axis machining is presented. Unlike the conventional methods which are based on the local surface geometry assumptions, this method is inspired by cutting simulation. Initially, the designed surface is planted with dense grasses. If a cutter is put onto the surface, the affected grasses will be cut short. All the affected grasses form a grass ring on the surface. When the cutter moves along the previous tool path, the envelope of the grass rings will form a machining band. Based on the machining band, cutter contact points can be found on the surface to ensure that the cutting edge touches exactly on the side of the band. These cutter contact points are fitted to construct the next tool path. In this way, all the tool paths can be generated recursively. An optimization is also developed to improve the computing efficiency of the path generation process. The proposed uniform scallop tool path generation method is generic. It can be popularized to (1) any kind of end mill with various sizes, (2) any kind of parametric surface and (3) directional- or contour-parallel tool path topologies. Another salient feature of this method is that it is free of local surface geometry assumptions, so the obtained tool paths are more precise. The proposed method is implemented and evaluated with several freeform surface examples. The feasibility of the method is also verified by actual cutting experiment.

Five-axis tool path generation in CNC machining of T-spline surfaces

Abstract Because of its flexible topology and robust data structure, the T -spline surface has become the trend of free-form surfaces representation in the realm of CAD design, animation and CAE. Yet its application in manufacturing has not been fully explored. In this work, the possibility of direct tool path generation on the T -spline surface has been discussed. An improved space-filling curve (ISFC) tool path planning algorithm has been proposed to exploit the advantage of T -spline as a mathematical representation of free-form surfaces in CAM process, as well as to overcome its disadvantages such as irregular boundaries and holes in the pre-image. The turning problem in traditional SFC has been tackled using Hermite compensation curves. Finally, a prototype system has been developed to implement the proposed algorithm and actual machining has been conducted. The result shows the feasibility as well as the efficiency of the proposed method for T -spline surfaces tool path generation compared to commercial CAM system.

Tool path generation for multi-axis freeform surface finishing with the LKH TSP solver

In freeform surface finishing, there are three major types of tool path topologies: the direction-parallel type, the contour-parallel type and the space-filling curve (SFC) type. The SFC topology is capable of covering the whole surface with only one path. In this paper, we present a new way of planning the SFC type tool path by formulating the planning task as a traveling salesman problem (TSP). The optimal path is generated in two steps. Firstly, a set of regular cutter contact (CC) points is generated on the input surface. A cutting simulation method is developed to evaluate the scallop error and determine the position of the next CC point in cross-feed direction. This method is free of local surface curvature assumptions and is therefore accurate for big cutters. Secondly, the obtained CC points are input into an efficient TSP solver LHK for the optimal CC point linking sequences. To stop the CC points from diagonal linking or penetrating linking, the Euclidean distance evaluation function for two CC points is redefined in LHK. The proposed tool path generation method is verified with several freeform surface examples; the results show that the method can automatically find the optimal feed direction and it can generate shorter tool path than the traditional SFC method. The feasibility of the proposed method is also verified by a cutting experiment. A new way of planning SFC type tool path is proposed.Cutting simulation method is proposed to evaluate the scallop error.Tool path planning task is formulated as a TSP and LKH is applied for solution.In LKH, the distance function is redefined to avoid incorrect linking problem.

Generating HSM-adapted pocketing tool path by region subdivision

High-speed machining (HSM) is an effective manufacturing process to produce parts. In HSM, it is required that the tool path should be smooth and the material removal rate should be constant. However, in geometry, it is nearly impossible to cover an arbitrary pocket with a single form of curves that satisfy both the above two requirements. In this paper, a compromise is made by subdividing the pocket into two kinds of regions: the HSM regions and the low-speed machining (LSM) regions. The HSM regions are selected to be the maximum inscribed circles (MICs) of the pocket. These MICs are calculated in an offset manner. Inside each HSM region, successive concentric circles are filled. The radii of the circles are controlled so that the material removal rate remains constant. The obtained concentric circles are then smoothly linked with pairs of arcs and used as the HSM tool path. For the rest LSM regions, conventional contour parallel tool paths are filled and low cutting speed is applied considering that there might be sharp angles on the pocket boundary. As the HSM regions could take up to 50% of the whole pocket and the cutting speed in HSM regions can be set very high, the average cutting speed for the whole pocket can be enhanced. Several pocket examples are used to verify the feasibility of the proposed HSM tool path generation method.

Five-axis trajectory generation based on kinematic constraints and optimisation

This paper proposed a five-axis trajectory generation method based on kinematic constraints and optimisation. The optimisation algorithms based on double solutions filtering and singularity determination are designed during inverse kinematics, which can choose the appropriate solution set within the movement ranges of rotary axes. Trajectory generation with kinematic constraints for each axis is significant in high speed machining, however, the component acceleration for each drive does not only depend on the value of tangential velocity (feed), but also on its changing rate. It is inefficient to deal with this problem by using general iterative methods. This paper proposes an approximate constraint method which keeps constant feed for each small segment by eliminating the effect from feed changing, and then connects the constant feed stages by trapezoidal acceleration transition. Simulation for a five-axis tool path in impeller machining is implemented. The results show that the solution profile which overruns the angle movement range is filtered, and both the velocity and acceleration on each axis are confined.

A Novel Method of Efficient Machining Error Compensation Based on NURBS Surface Control Points Reconstruction

A novel method to improve the efficiency of error compensation in free-form surface machining based on the Non-Uniform Rational B-Splines (NURBS) surface control points reconstruction is proposed in this article. With the presented method, a relatively small number of inspection points are needed to be measured for error compensation. The machined surface is obtained by reconstructing the control points of the designed surface based on the on-machine measurement data. The machining error of the surface is obtained by calculating the difference between the machined surface and the designed one. Then a compensate surface is achieved using the mirror symmetry model and surface modification method to compensate the machining error. Experimental validation for the milling of a NURBS surface shows that the machining accuracy of the surface is improved by 62.57% through use of the proposed method.

Self-Sensing of Position-Related Loads in Continuous Carbon Fibers-Embedded 3D-Printed Polymer Structures Using Electrical Resistance Measurement

Condition monitoring in polymer composites and structures based on continuous carbon fibers show overwhelming advantages over other potentially competitive sensing technologies in long-gauge measurements due to their great electromechanical behavior and excellent reinforcement property. Although carbon fibers have been developed as strain- or stress-sensing agents in composite structures through electrical resistance measurements, the electromechanical behavior under flexural loads in terms of different loading positions still lacks adequate research, which is the most common situation in practical applications. This study establishes the relationship between the fractional change in electrical resistance of carbon fibers and the external loads at different loading positions along the fibers’ longitudinal direction. An approach for real-time monitoring of flexural loads at different loading positions was presented simultaneously based on this relationship. The effectiveness and feasibility of the approach were verified by experiments on carbon fiber-embedded three-dimensional (3D) printed thermoplastic polymer beam. The error in using the provided approach to monitor the external loads at different loading positions was less than 1.28%. The study fully taps the potential of continuous carbon fibers as long-gauge sensory agents and reinforcement in the 3D-printed polymer structures.

Fused deposition modeling five-axis additive manufacturing: machine design, fundamental printing methods and critical process characteristics

Purpose The staircase effect and support structure under overhanging geometry are two inherent weaknesses that reduces the surface quality and induces material waste. This paper aims to design a five-axis fused deposition modeling system with interference-free nozzle to solve the problems. Design/methodology/approach To facilitate the application of five-axis printing machine, three new printing methods are proposed according to different geometries and application requirements, which include tangential direction printing, normal sculpture printing and compatible printing. Findings The static flow beading characteristic is researched to establish the criterion for switching the mode between three-axis printing and five-axis printing. Experiment proves the critical point existing and 51° is the critical point at the given parameters. The concept of dynamic flow beading is proposed. The relationship between equivalent volume and roughness is established based on elaborate experiments, which helps to figure out the boundary between safe area and beading area under different parameters of layer thickness and nozzle diameter. Originality/value Three new printing methods are proposed according to different geometries and application requirements, which include tangential direction printing, normal sculpture printing and compatible printing. Considering the special movement situation during five-axis printing process, the dynamic flow beading issue is proposed. The relationship between equivalent volume and roughness is established based on elaborate experiments, which helps to figure out the boundary between safe area and beading area under different parameters of layer thickness and nozzle diameter.

Smooth non-uniform rational B-spline (NURBS) machining with kinematic limit for short linear segments

Set of methods based on non-uniform rational B-spline (NURBS) are proposed in this article, which are adopted to improve the smoothness during short linear numerical control (NC) codes machining. The smoothness refers to two aspects: the contour fairness of CL trajectory and the machining stability of the machine tool. To obtain contour fairness, the optimised knots combination strategy (OKCS) is proposed in least square NURBS fitting from short linear segments, which generates NURBS curve for the next interpolating process. Sequentially, an axis-based look-ahead NURBS interpolator (ALANI) is designed for NURBS interpolation in order to improve the machining stability according to the kinematic limit. Both OKCS and ALANI are simulated and compared with congener algorithms, respectively. Furthermore, algorithms are implemented on digital signal processor (DSP) platform, and actual machining examples are presented at last.

A polygons Boolean operations-based adaptive slicing with sliced data for additive manufacturing

In order to increase the efficiency of additive manufacturing, this paper proposes a novel adaptive slicing approach of sliced data with minimum thickness based on Boolean operations of polygons. It can greatly handle the balance between the build time and the surface precision of additive manufacturing. The proposed adaptive slicing is available for the single solid model, the support of additive manufacturing, and simultaneously manufactured multiple models. At first, the Boolean operations of polygons are used to gain the relationship of the adjacent layers to serve as the topological information. Second, two parameters are proposed to evaluate the precision of sliced surface: the ameliorative area ratio and variation of the cusp height. Ameliorative area ratio overcomes the drawbacks of original area deviation ration criteria and can work on the large and complex models. Variation of the cusp height makes the calculation of cusp height suitable for sliced data of model, and it is independent of the normal vector of surfaces. Third, the adaptive slicing is realized by removing unnecessary layers based on two parameters and the maximum allowable thickness. The thicknesses are times of the minimum thickness. Moreover, the adaptive slicing for support of additive manufacturing is developed through dividing the support into two parts according to its height and location. Slicing of multiple models is also proposed by choosing the maximum ameliorative area ratio and variation of the cusp height among all models in the same z level as the two parameters. Finally, the adaptive slicing for the three types is tested with some special models, and corresponding models are printed with FDM technology based on slicing results of the proposed approach. Results show that the proposed adaptive slicing approach is effective.