Continuous Tool Path Research Articles

Continuous Toolpath Optimization for Simultaneous Four‐Axis Subtractive Manufacturing

Continuous Toolpath Optimization for Simultaneous Four‐Axis Subtractive Manufacturing

Jerk limited continuous tool path generation for flexible systems in non-cartesian coordinate systems

Inspired by computer numerical control (CNC) technology and drastic changes in the world of electronics and microcontrollers, the idea of using non-cartesian coordinate system for CNC machines became a topic of interest. Non-cartesian coordinate systems provide freedom of movement in systems with large working spaces where high dimensional accuracy is not a prime concern. Applications of such systems can be found in murals, where a painting is applied to a large wall of any arbitrary build material. In the present paper, a new design was introduced to automate the process of drawing murals on large surfaces. The proposed mechanism utilized chain and sprocket to overcome the size limitations of traditionally available x-y tables. In addition to that, the developed mechanism does not utilize the common robust structures used in the conventional CNC systems and the tool motion is created using flexible arms that are not heavily constrained. The effect of systems unwanted vibration has been eliminated using continuous trajectory and kinematic profiles. Parametric curve interpolation algorithms for trajectory planning were implemented to increase the flexibility of drawing complex curves. Parametric curves such as B-spline and non-uniform rational B-spline (NURBS) were employed to generate a jerk limited trajectory for motion control and extraction of kinematic profiles. Such trajectory constrains the jerk of the system and guarantees a smooth motion free of feed-rate fluctuations. Compared to other methods available for extracting the kinematic profiles, jerk limited method decreases the travel time and trajectory error. Ultimately, motion commands were produced by using kinematic profiles and the second order Taylor interpolator. STM32746ZG card was used as the main processor and two stepper motors controlled by a Bit Pattern interpolation algorithm were utilized to drive the proposed mechanism. The input pulses of stepper motors were stored as binary bits and transmitted to drivers in real-time. The feedback was also evaluated by two rotary encoders, placed at the end of the motors’ shafts. Encoder data were acquired and transmitted using a TCP/IP protocol to guarantee zero data loss during the transmission.

Generation of continuous and sparse space filling toolpath with tailored density for additive manufacturing of biomimetics

A method of generating a continuous toolpath that can be biased in a user-specified direction of travel is proposed for the fabrication of density-based functionally graded parts through Additive Manufacturing (AM). The methodology utilizes Lin Kernighan's (LK) Travelling Salesman Problem (TSP) solver over a digitized grid within the contour domain to generate a toolpath with minimal lifts and a common start and end point. Three force-based methods of digitization, namely rectangular, circular, and contour adaptive, are proposed in this work. Each of these methods initialize from a structured or an unstructured grid, where the grid points are assumed to be connected with either linear (rectangular digitization) or a combination of linear and torsional springs (circular and contour adaptive digitization). Enforcing an equilibrium amongst the spring forces and appropriately selecting the ideal spring length, the necessary configuration of grid points can be generated for a desired toolpath.The density of grid points (consequently, part density) can be varied through the user-defined input function or an image-based density map imposed on the ideal spring length over the contour domain. The proposed toolpath, as a case study, was implemented for printing a bone with density prescribed through a CT scan image stack. The CT scan of the printed part qualitatively establishes the conformity of the toolpath to the user-specified density gradient.

Study of optimization of blade non-uniform allowance process and chatter stability domain

In addressing the phenomenon of chatter during the machining of thin-walled components, a machining strategy involving the implementation of a continuous non-uniform toolpath has been proposed as a remedy for chatter suppression. The methodology commences with a meticulous determination of machining allowances, accomplished by utilizing fitting functions. Subsequently, the stiffness coefficients and natural frequencies inherent to the workpiece-tool system are extracted through modal analysis. A stability lobes diagram is formulated, employing the principles of regenerative chatter analysis. This diagram encompasses both uniform toolpath scenarios and non-uniform continuous toolpath scenarios, with the latter established via the least squares method. The resultant stability lobes diagram effectively delineates the boundaries within which chatter remains stable, under varying depths of cut. The stability lobes diagrams substantiate the effectiveness of the non-uniform continuous toolpath constructed via the least squares method in significantly augmenting the inherent stiffness coefficient of the workpiece-tool system, thereby mitigating chatter. This approach serves as a valuable guide for the manufacturing of intricate curved thin-walled components.

Concurrent Design of Composite Structure and Continuous Toolpath for Additive Manufacturing of Fiber-Reinforced Polymer Composites

Concurrent Design of Composite Structure and Continuous Toolpath for Additive Manufacturing of Fiber-Reinforced Polymer Composites

Stress-based continuous planar path planning for additive manufacturing

This paper presents a novel continuous planar path planning algorithm based on principal stress orientation field to improve structural performance of the products fabricated with additive manufacturing. For a given 3D shape, it is first sliced into planar layers with specified layer thickness, which are discretized into grids for the optimization of tool-paths. Then, the principal stresses and the corresponding orientation field are calculated with the finite element analysis method, which are projected onto grids. Since the principal stress orientations of elements with principal stress values close to zero are arbitrary, a weighted filtering strategy is applied to generate a smooth principal stress orientation field. Finally, the tool-paths are generated with genetic algorithm through minimizing the idle travel distance of the nozzle. Furthermore, the tool-path width is adaptively adjusted according to the tool-path orientation to avoid the overfill issue caused by the discretization. Additionally, a method is introduced to achieve global continuous tool-paths, aiming at eliminating idle travel completely. The optimized tool-paths are simulated and compared with the state-of-the-art methods. Experimental results demonstrate that the objects fabricated with the proposed method have superior structural performance.

Fiber Reinforcement of 3D Printed Concrete by Material Extrusion Toolpaths Aligned to Principal Stress Trajectories

Additive manufacturing of cementitious materials is a rapidly growing branch of manufacturing both in research and industry, particularly the variant of material deposition by extrusion. This process results in a strong anisotropy in mechanical properties, owing largely to the interfaces between adjacent filaments. This anisotropy is even more pronounced when fiber reinforced mortars or continuous entrained reinforcement components such as cables are used. To exploit orientation-dependent performance, the print path can be designed to align with the principal (tensile) stress trajectories. However, obtaining an appropriate print path based on this concept poses several challenges, related to the filling of intermediate spaces between two trajectories. In this paper, an approach for planning such a robot toolpath is presented, elaborated, and illustrated by means of a case study on a well-known reference case. The main features of the tool planning method are the relaxation of the offset width, the avoidance of toolpaths with acute angles by intersecting offset curves, and a continuous toolpath.

A continuous toolpath strategy from offset contours for robotic additive manufacturing

Toolpath planning is an essential component of robotic additive manufacturing. An efficient toolpath strategy allows parts to be made that are geometrically accurate, free of defects, have good mechanical properties and have low residual stress. Toolpaths for cold spray additive manufacturing have some technical constraints that need to be considered compared to their counterpart designed for conventional 3D printing machines. This study presents an automated toolpath planning method based on offset contours. The generated toolpath is globally continuous, layer-wise setting, making it suitable for robotic cold spray additive manufacturing. The toolpath algorithm was tested on a variety of geometries to demonstrate its robustness. One model was selected for printing using a commercial high-pressure cold spray system. The experimental results show that our method is applicable to cold spray robotic additive manufacturing for near-net shape construction. The method is particularly good for web-rib structures.

Global Continuous Toolpath Planning with Controllable Local Directions

Toolpath planning for Continuous fiber reinforced thermoplastic composites (CFRTPCs) 3D printing is a challenging task, which is vital to decrease the process complexity. In this paper, we propose a global continuous path planning method for CFRTPCs. First, for the set of 2D connected regions generated by slicing, we establish an optimized print sequence with a minimum idle stroke under interference constraints. Second, a continuous Zigzag path generation algorithm with controlled deposition direction is constructed for each 2D connected region, and path optimization is used to lessen the uneven deposition spacing. Finally, A separation axis theorem is used to prevent interference during the printing process, and we use a genetic algorithm to choose the connection points between 2D paths in a given spatial printing sequence to make the minimum idle stroke, creating a global continuous path with controllable deposition direction. The method proposed in this paper can provide the ability to customize the local deposition path direction and ensure the continuity of the global path to avoid interference and reduce the post-processing workload, so it is suitable for continuous path planning and multi-physics field optimization of complex structures, which can fully utilize the advantages of high-performance fibers to improve the customization ability and the performance of the fabricated parts for 3D printing and provide support for the manufacturing of high-performance structures in different fields.

Accurate TCP Position and Orientation Trajectory Generation in 6DOF Robotic Manipulators and CNC Machine Tools using FIR Filtering and Haversine Synchronisation

The use of robotics in manufacturing is rapidly growing. One promising application in particular is the use of robots as machining platforms. Robotic machining offers many advantages such as large operating envelopes, flexibility in operations and low installation and running costs. Robotic machining platforms much like computer numerically controlled (CNC) machine tools are commanded by numerical controllers (NCs) using the well established G-code part programming language (ISO-6983). Toolpaths are defined in the work piece coordinate system (WCS) as a series of discrete tool centre point (TCP) positions and tool orientations. The role of the NC is to generate smooth feed drive or robot joint commands such that the tool or end effector travels along the commanded toolpath whilst satisfying TCP position and orientation tolerances and robot/machine tool kinematic constraints. Interpolating tool orientations directly in the WCS requires complex real-time spherical interpolation computations. Overcoming this challenge, this paper introduces a C4 continuous tool path trajectory generation method for 6DOF motion. The tool centre point position is smoothed in the WCS, however, the tool orientation is smoothed directly in the rotary coordinate system without the requirement for spherical interpolation. The interpolated tool orientation trajectory follows the path of the great circle arc using the modified Haversine method eliminating non-linear interpolation errors present in linear interpolation of rotary axis positions (machine coordinate system interpolation). The proposed method is validated by simulation of a 6DOF robotic manipulator.

Thermal Scalar Field for Continuous Three-dimensional Toolpath Strategy Using Wire Arc Additive Manufacturing for Free-form Thin Parts

Wire Arc Additive Manufacturing (WAAM) is revolutionizing the field of Additive Manufacturing (AM) by being the technological solution to manufacture thin-walled structures of large dimensions and medium geometric complexity at reduced cost with an excellent buy-to-fly ratio. Manufacturing parts with this technology is nowadays done through 2.5D strategies. This type of strategy consists in cutting a 3D model using planar layers parallel to each other. This 2.5D technique limits the complexity of the geometries that can be produced in WAAM without taking advantage of height deposit modulation. It also requires several start/stop phases of the arc during the transition from one layer to another, which leads to poor quality. This paper presents a new fast and efficient path planning strategy aiming at creating a continuous manufacturing path, thus increasing poor part quality. This strategy so called “Scalar Thermal Field for Continuous Toolpath” is generating a continuous spiral manufacturing toolpath for thin shaped parts. The modulation of deposition, by controlling the welding torch travel speed at constant wire feed rate, allows continuous deposition of material throughout the manufacturing process. The keypoint of the method is the use of a thermal scalar field associated with a 6-axis robotic arm kinematics which allows the manufacturing of closed parts after optimal closure point determination or direct manufacturing of opened parts with non-planar free edges. Validation of the presented method is performed by manufacturing three distinct parts : an opened, a closed part and a multi-branch part. The fabrication of these parts and their precise measurement have shown the reliability and the restitution capacity of our method which is clearly superior to 2.5D strategies nowadays commonly used in WAAM technology. • Presents a new and easy to compute continuous toolpath generation method. • Describes a path planning strategy using 5-axis with modulation of the deposit. • Uses thermal scalar field for the generation of continuous toolpaths. • Reduces the arc start/stop phases by using a continuous toolpath strategy. • Validates the method by manufacturing and measuring three different types of parts.

A path smoothing scheme for micro-line tools using cubic B-spline fitting with dominant points

To obtain higher order continuous tool path, a cubic B-spline curve fitting method is presented in this paper to process the linear tool path. First, a local cubic polynomial fitting with bidirectional scanning scheme is proposed to determine some initial dominant points. Based on these dominant points, the initial knot vector is generated by average method, and the initial B-spline is constructed. To constrain the fitting error, a Newton’s method based fitting error estimation scheme and a fitting error based dominant point insertion scheme are proposed to modify the B-spline. Simulation results prove that our method can compress data and smooth tool path. Compared with another existing curve fitting method, the number of control point has decreased by 9.43%, and the machining time has decreased by 94.45% compared with traditional point-to-point (P2P) motion.

Continuous tool-path planning for optimizing thermo-mechanical properties in wire-arc additive manufacturing: An evolutional method

Continuous tool-path is often chosen to improve deposition efficiency and forming quality in wire-arc additive manufacturing. However, the concentration of adjacent tool-path fragments makes the thermo-mechanical properties of continuous tool-paths tend to be poor, resulting in performance degradation and other defects. This work focuses on the efficient planning of the continuous tool-path with fine thermo-mechanical properties and proposes an evolutional method based on genetic algorithm. All the key operations of the proposed method, such as crossover and mutation, are designed based on the characteristics of the research object. Thereinto, the fitness of a continuous tool-path is evaluated within several seconds by using the rapid thermo-mechanical field prediction model, which ensures the efficiency of the whole planning process. Additionally, the formability constraint is introduced to ensure the forming quality of the part fabricated with the planned tool-path. The experiments demonstrated that the thermo-mechanical properties of the planned tool-path improves by more than 87 % and the average residual Von Mises stresses of it decreases by more than 32 MPa. Meanwhile, the time cost of a single planning process is at the hour level, which is acceptable when considering that it takes several hours for the numerical simulation method to calculate one thermo-mechanical field.

Air-to-Liquid Heat Exchanger Fabricated Using Deposition-Based Additive Manufacturing Processes

Abstract This work describes the use of deposition-based additive manufacturing (AM) techniques to fabricate air-cooled, two-fluid heat exchangers. The project focused on a Heating, Ventilation and Air Conditioning application and used an industry-standard copper/aluminum heat exchanger manufactured with conventional technology as the basis for assessing performance. The manufacturing constraints associated with using deposition-based AM technology for this application include the need for a continuous tool path within each build layer that allows uninterrupted extrusion and therefore defect-free water channel walls that correspond to a reliably leak-tight heat exchanger. A geometry that respects these constraints was developed, simulated, optimized and finally manufactured and tested. The material used was a composite of polymer filled with conductive flakes in order to provide high conductivity in the direction that heat must flow in this heat exchanger, across the wall separating the fluids. The measured performance for several test coupons matched the predicted performance and the test coupons exhibited performance that approach and in some cases exceeds conventional technology

A graph-based path planning method for additive manufacturing of continuous fiber-reinforced planar thin-walled cellular structures

PurposeComposite cellular structures have wide application in advanced engineering fields due to their high specific stiffness and strength. As an emerging technology, continuous fiber-reinforced polymer additive manufacturing provides a cost-effective solution for fabricating composite cellular structures with complex designs. However, the corresponding path planning methods are case-specific and have not considered any manufacturing constraints. This study aims to develop a generally applicable path planning method to fill the above research gap.Design/methodology/approachThis study proposes a path planning method based on the graph theory, yielding an infill toolpath with a minimum fiber cutting frequency, printing time and total turning angle. More specifically, the cellular structure design is converted to a graph first. Then, the graph is modified to search an Eulerian path by adding an optimal set of extra edges determined through the integer linear programming method. Finally, the toolpath with minimum total turning angle is obtained with a constrained Euler path search algorithm.FindingsThe effectiveness of the proposed method is validated through the fabrication of both periodic and nonperiodic composite cellular structures, i.e. triangular unit cell-based, Voronoi diagram-based and topology optimized structures. The proposed method provides the basis for manufacturing planar thin-walled cellular structures of continuous fiber-reinforced polymer (CFRP). Moreover, the proposed method shows a notable improvement compared with the existing method. The fiber cutting frequency, printing time and total turning angle have been reduced up to 88.7%, 52.6% and 65.5%, respectively.Originality/valueA generally applicable path planning method is developed to generate continuous toolpaths for fabricating cellular structures in CFRP-additive manufacturing, which is an emerging technology. More importantly, manufacturing constraints such as fiber cutting frequency, printing time and total turning angle of fibers are considered within the process planning for the first time.

Numerical investigation of incremental forming process of AISI 304 stainless steel

ABSTRACT In recent years, sheet metal forming has gained great importance in the production process. To improve the quality of the manufactured products and reduce the production cost, incremental forming, particularly that adapted to small pieces, can be a good alternative. It is within this scope that the present study was carried out. This research work deals with the finite element simulation of the incremental forming process applied to achieve a trunk cone. It also examines the effects of the geometrical parameters of the tool and of the sheet on the forming force, stress distribution and thinning of the sheet. The obtained results show that the thinning of the sheet is more important in the case of the continuous tool path (about 0.2 mm), compared to that in the discontinuous one.

Continuous contour-zigzag hybrid toolpath for large format additive manufacturing

Large format additive manufacturing (LFAM) has witnessed rapid development in recent years and facilitated digital fabrications of geometrically intricate structures. However, there has been limited research on toolpath optimization tailored for LFAM. This paper presents a novel framework to generate a globally continuous toolpath for both solid and partial infill designs in LFAM. For solid infill, outward contour and double offset schemes are used to generate smooth curves as the primary volume-filling paths; the remaining unfilled areas are covered by extending zigzag lines from the closest contours. Subsequently, a contour layer-wise connection is carried out based on the depth-first-search algorithm to formulate a globally continuous path. A post-processing step is also presented to optimize the coverage and curvature of the toolpath design. The concept is extended for partial infill settings by trimming and joining rectangular grid lines. Compared with other state-of-the-art methods in the literature, the proposed algorithm is superior in delivering better print quality, fewer sharp turns, and enhanced fabrication efficiency. Finally, two interesting experiments demonstrate how LFAM of topology optimized structures can benefit from the proposed continuous toolpath: topology optimized table printed from thermoplastic polyurethane (TPU) and topology optimized chair printed from 3D concrete printing (3DCP).

Tool Path Generation Algorithm Based on Rough Machining of Jade Carving Surface

To improve the quality of tool paths in surface machining, different machining requirements are considered in the tool path generation algorithm. In the traditional tool path generation algorithm, due to the lack of a unified mathematical calculation framework, these requirements often need to be considered separately, but they often compete with each other, so that different requirements cannot be satisfied at the same time and the tool path cannot achieve the optimal. To resolve this issue, an extensive tool path generation algorithm framework for arbitrary surfaces was proposed. The proposed algorithm transforms the tool path calculation framework into a constrained functional optimization problem by establishing an optimization function based on the potential energy field and an inequality function based on the gradient field in the machining area. By establishing finite element approximation, the functional optimization problem is transformed into a numerical optimization problem, which reduces the difficulty of solving. According to the machining requirements of die surface such as tool path smoothness, line width constraint and cutting direction constraints were transformed into the constraints of potential energy field isopotential line, and the method of generating reciprocating cutter path and cutter contact path isosection cutter path was proposed by optimizing the method. It is evident from the simulation and machining experiments results that continuous and smooth tool paths can be generated by using this algorithm, and machining quality and machining efficiency can be improved. By adding different machining requirements into the framework, a tool path with different optimization objectives can be generated.

A C3 continuous toolpath corner smoothing method for a hybrid machining robot

A high-order continuity of a five-axis toolpath helps avoid problems such as equipment resonance, allowing high-quality and high-efficiency machining to be achieved. This paper presents a semi-analytical C3 continuous toolpath corner smoothing method for a 5-DOF (degree of freedom) hybrid robot. Based upon curvature derivative continuity conditions, the tool position and orientation paths can be directly smoothed by inserting quintic B-splines. Benefitting from an analytical error expression, orientation error can be accurately predicted and controlled with improved computational efficiency. Then, by converting the remaining position and orientation segments into the specially designed 7th-degree B-spline, the C3 continuity of the geometrically smoothed toolpath is mathematically guaranteed without iterative calculations. Additionally, a path adjustment strategy is developed to enhance the performance of the proposed approach. Finally, simulations and experiments are carried out on the TriMule-800 mobile robot machining system by incorporating a jerk-continuous feedrate profile. The feasibility of the proposed approach in addressing a general five-axis toolpath is verified.

Toolpath planning for cold spray additively manufactured titanium walls and corners: Effect on geometry and porosity

Cold spray additive manufacturing (CSAM) is a solid-state deposition process well-suited to titanium that has the potential to make large, near-net-shape parts at high productivity. However, further research is required to truly accomplish the freedom of design expected from CSAM and, in particular, to address how to manufacture a specific 3D object with minimal porosity. Therefore, this paper focuses on understanding how tool path planning strategy and robot kinematics affect the geometry and porosity distribution in a 3D object. Square titanium frames were manufactured layer-by-layer using a continuous tool path planning strategy in which the contour spray angle, traverse speed and corner smoothing radius were varied selectively. The sample geometry was analysed by 3D laser scanning, and the capacity to produce straight, vertical walls and square corners were demonstrated. The total porosity in the manufactured objects was measured using the Archimedes’ principle, further investigated by metallographic cross-section analysis, and then validated by X-ray computed tomography on selected samples. Porosity was distributed layer by layer, creating a fishbone structure in the cross-section with higher porosity between the layers and near the edges of the walls and corners. The influence of robot kinematics and toolpath planning on forming underbuilt and overbuilt structures and how they influenced porosity development are also discussed. The knowledge generated from this research can significantly influence the development of tool path planning strategies in CSAM, providing the means to produce improved near-net-shapes with controlled porosity formation.