Tool Path Planning Research Articles

Interlacing Infills for Multi-Material Fused Filament Fabrication Using Layered Depth Material Images

One major concern regarding multi-material additive manufacturing (MMAM) is the strength at the interface between materials. Based on the observation of how nature puts materials together, this paper hypothesizes that overlapping and interlacing materials with each other enhance the interface bonding strength. To test this hypothesis, this research develops a new slicing framework that can efficiently identify the multi-material regions and develop interlaced infills. Based on a ray-tracing technology, we develop layered depth material images (LDMI) to process the material information of digital models for toolpath planning. Each sample point in the LDMI has an associated material and geometric properties that are used to recover the material distribution in each slice. With this material distribution, this work generates an interlocking joint and an interlacing infill in the regions with multiple materials. The experiments include comparisons between similar materials and different materials. Tensile tests have shown that our proposed infill outperforms the interlocking joint in all cases. Fractures occur even outside the interlacing area, meaning that the joint is at least as strong as the materials. The experimental results verify the enhancement of interface strength by overlapping and interlacing materials. In addition, existing computational tools have limitations in full use of material information. To the best of our knowledge, this is the first time a slicer can process overlapped material regions and create interlacing infills. The interlacing infills improve the bonding strength, making the interface no longer the weakest area. This enables MMAM to fabricate truly functional parts. In addition, the new LDMI framework has rich information on geometry and material, and it allows future research in multi-material modeling.

Tool path planning of consecutive free-form sheet metal stamping with deep learning

Sheet metal forming technologies, such as stamping and deep drawing, have been widely used in automotive, rail and aerospace industries for lightweight metal component manufacture. It requires specially customised presses and dies, which are very costly, particularly for low volume production of extra-large engineering panel components. In this paper, a novel recursive tool path prediction framework, impregnated with a deep learning model, is developed and instantiated for the forming sequence planning of a consecutive rubber-tool forming process. The deep learning model recursively predicts the forming parameters, namely punch location and punch stroke, for each deformation step, which yields the optimal tool path. Three series of deep learning models, namely single feature extractor, cascaded networks (including state-of-the-art deep networks) and long short-term memory (LSTM) models are implemented and trained with two datasets with different amounts of data but the same data diversity. The learning results show that the single LSTM model trained with the larger dataset has the most superior learning capability and generalisation among all models investigated. The promising results from the LSTM indicate the potential of extending the proposed recursive tool path prediction framework to the tool path planning of more complex sheet metal components. The analysis on different deep networks provides instructive references for model selection and model architecture design for sheet metal forming problems involving tool path design.

Reconfigurable Modular System of Prefabricated Timber Grids

To coordinate the old wisdom of modular systems and the emerging paradigm of Industry 4.0, the latest digital discretism has worked on combinatorial assembly for open-ended field conditions. Considering oriented to small-scale semipermanent timber buildings, this paper introduces a reconfigurable modular timber grid inspired by the traditional East Asian timber architecture. The system only requires minimum cuts on a dimensional timber to produce serialized components. As a result, the timber components dismantled from previous buildings can be easily reprocessed for other structures of different configurations. This recycling scheme facilitates serial manufacturing and reduces resource consumptions. Such a reconfigurable system relies on the grid geometry and the local topology of connections. The formalism of Bravais lattice from crystallography facilitates the analysis of the symmetry in various regular grids. Our prototype of the timber grid is self-standing (without connections to the ground) and creates a large overhang. A finite element method is developed to evaluate the structural performance of timber structures with semirigid joints on the basis of the direct stiffness method. Traditional East Asian architecture uses the interlocking mechanism for wood connections, whereas our system uses shallow-notched joints on the wood. A robotic milling system is adopted to prefabricate the wood components. The shallow notches are modeled as Boolean operations between a pair of cuboid components, which greatly simplifies the toolpath planning of the robotic system. System design, serial production of components, assembly, and recycling are integrated within a consistent and open system. • The reconfigurable timber grid optimizes material supply and energy consumption. • Bravais lattice from crystallography reveals the symmetry in regular timber grids. • Timber components from previous buildings can be easily reprocessed for reuse. • Finite element method models the semirigid connections in timber grid. • Robotic milling system is adopted to prefabricate the wood components.

Uniform Coverage Tool Path Generation for Robotic Surface Finishing of Curved Surfaces

We provide a novel solution to the problem of robot tool path generation to uniformly cover the surface area of a curved surface with varying curvatures by using a circular, flat finishing tool. We first develop a local contact shape descriptor using tools from differential geometry to estimate the contact shape and its area between the finishing tool and the workpiece surface under an applied normal force. Based on this varying contact area as the tool moves on the surface, we describe a tool path planning strategy that provides full and uniform coverage of a free-form or curved surface with the least amount of overlap. As opposed to fixed spacing paths with point contact in most existing approaches, we provide a novel path generation method where the interval spacing between neighboring path segments is determined by the contact area, which is position-dependent and varies along the surface in accordance with its principal curvatures. An efficient bisection method is employed in the proposed off-line path planning strategy. Numerical studies were conducted for ruled and general curved surfaces to compare the contact areas and coverage of the resulting path with paths generated using two other approaches from the literature. Real-time surface finishing experiments with a six degree-of-freedom robot equipped with a surface finishing tool were also conducted for both these surfaces to validate the proposed approach. Results from the numerical studies and experiments are presented and discussed.

Investigations on the trochoidal toolpath for processing the biomaterial through magnetorheological fluid assisted finishing process

Magnetorheological fluid assisted finishing (MFAF) is a super-surface finishing technique to achieve a mirror-like polished surface that is required in several fields such as biomedical implants, microchannels, optics, etc. The optimal process parameters and appropriate toolpath planning can significantly improve the surface quality of the parts produced by an MFAF process. This paper presents the trochoidal toolpaths for polishing the surface of a biomaterial: Duplex stainless steel (DSS) via the MFAF process. First, an analytical model has been developed to study the forces applied on the magnetorheological fluid chain of the MFAF tool while scanning on a trochoidal path. This model shows that the polishing time reduces and process efficiency increases with the proposed toolpath compared with the conventional ZIG-ZAG toolpath. Then, the experiments are performed to study the geometrical description of the asperities such as surface roughness (Ra), skewness (Rsk), and kurtosis (Rku) on the polished surface via trochoidal toolpath. Developing an analytical model to study the input variables' impact over the responses includes multiphysics and nonlinearity, making it complex. Hence, the response surface methodology (RSM) is used to analyze and optimize the effect of different process parameters over the surface roughness parameters. Finally, the wettability, corrosion, and wear tests are performed to investigate the biocompatibility of the polished surface.

Autonomous robotic additive manufacturing through distributed model‐free deep reinforcement learning in computational design environments

The objective of autonomous robotic additive manufacturing for construction in the architectural scale is currently being investigated in parts both within the research communities of computational design and robotic fabrication (CDRF) and deep reinforcement learning (DRL) in robotics. The presented study summarizes the relevant state of the art in both research areas and lays out how their respective accomplishments can be combined to achieve higher degrees of autonomy in robotic construction within the Architecture, Engineering and Construction (AEC) industry. A distributed control and communication infrastructure for agent training and task execution is presented, that leverages the potentials of combining tools, standards and algorithms of both fields. It is geared towards industrial CDRF applications. Using this framework, a robotic agent is trained to autonomously plan and build structures using two model-free DRL algorithms (TD3, SAC) in two case studies: robotic block stacking and sensor-adaptive 3D printing. The first case study serves to demonstrate the general applicability of computational design environments for DRL training and the comparative learning success of the utilized algorithms. Case study two highlights the benefit of our setup in terms of tool path planning, geometric state reconstruction, the incorporation of fabrication constraints and action evaluation as part of the training and execution process through parametric modeling routines. The study benefits from highly efficient geometry compression based on convolutional autoencoders (CAE) and signed distance fields (SDF), real-time physics simulation in CAD, industry-grade hardware control and distinct action complementation through geometric scripting. Most of the developed code is provided open source.

Study of deterministic surface micro-texture generation in ultra-precision grinding considering wheel oscillation.

Ultra-precision grinding is crucial for manufacturing high-end optics and molds, while the unbalanced wheel vibration is inevitable and becomes even more critical in surface generation, which resulted in undesired waviness and micro-texture on the ground surface. In this paper, to understand and control the micro-texture generation, a theoretical model has been developed to predict the deterministic surface micro-texture generation resulted from unbalanced tool vibration in ultra-precision grinding, in which the overlap trajectories of grinding wheel with an arc cutting edge were analyzed and calculated. The simulation work was performed and a double phase mechanism involved in deterministic textural pattern and structure has been revealed. Both theoretical and experimental results proved that phase shift is an important factor to determine micro-texture evolution in the ultra-precision grinding process. On this basis, a novel tool path strategy has been proposed to fabricate deterministic micro-structure by coordinating oscillation motion of the grinding wheel and phase shift control, in which a rhombus-shaped micro-structure array can be generated. A small adjustment for the phase shift was conducted and it was found that the more complex micro-texture with different textural patterns and micro-structure can be machined. The results indicated that the phase control for the tool path planning is an effective method to fabricate flexible and tunable micro-texture surfaces in ultra-precision grinding.

Influence of tool path planning on process stability and deposition accuracy in laser material deposition with coaxial wire feed

Laser material deposition (LMD) is a laser-based additive manufacturing process that is widely used for fabrication, diversification, and repair of parts in various industries. LMD processes can be distinguished by the form of the filler material. In terms of availability, storage, safe handling, and price, filler material in wire form often has advantages over powdered materials. In this work, the influence of tool path planning on the deposition accuracy and the process stability of LMD with coaxial wire feed is studied. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of an annular shaped laser beam without any shadowing. While the process is completely directionally independent, the stability is linked to the wire feed rate, laser power, and process feed rate. Additionally, the ratio between the wire and the laser beam diameter affects the stability. Movement of the wire inside the annular beam may result in shadowing and process abort. Changes in the working distance (defocusing) lead to changes in the beam diameter, which affects the process stability. This can result in imperfections, i.e., bonding defects, or pores in the tracks and layers that will add up in the built components and must be avoided for imperfection-free three-dimensional geometries. On even surfaces, the geometry of the deposited tracks is controlled by changing the laser power, the wire feed speed, and the process speed. When building three-dimensional parts, critical points of the tool path planning are acute angled corners and crossing points. In the experiments, boundaries for the process stability in critical points are established and track geometries are compared to previous results. Furthermore, different strategies for the avoidance of material accumulation at the start, end, and crossing points are investigated. The different approaches are discussed, and finally an outlook for further use and possible applications is given.

Recent advances in additive manufacturing for current challenges, materials and their applications

Additive Manufacturing (AM) technology in 3-D printing has grown into a great field in today’s technological world, especially in manufacturing sectors. Various AM technologies have been developed presently and their advancement has beenprocessed worldwide is presented. Their advancement included usability and compatibility of the different types of material. Moreover, the applications of 3-D printing via different AM technologies in biomedical applications, dental implants, pharmaceutical industries, chemical processing equipment, structural components, automotive industries, marine sectors, aerospace sectors, sports equipment and food processing industries have been presented. However, suggested applications viadifferent AM technologies have also been reported. Further, the challenges in development of the 3D structure via different AM technologies have also been discussed. The remedial/treatment like pre and post processing operations, tool path planning, and slicing orientation have also been suggested in printing of the sound 3D complex structure.

Adaptive contour based printing of a propeller using hybrid-wire arc additive manufacturing

In this paper, we discuss our approach to printing a propeller blade using the hybrid wire arc additive manufacturing set up at the Singapore University of Technology and Design. This setup can perform both additive and subtractive processes within an integrated work cell. The propeller additive tool path planning is done using the adaptive level-set contour method. Together with a hybrid method, it enabled us to build a propeller with minimum material spillage and without the need to use overhang calculations, which shows the benefits of using both processes to overcome some limitations of WAAM printing. The same propeller was printed without using the hybrid method and compared to the hybrid one, the comparison shows the effect of the subtractive method -as the hybrid method- in printing consistently and more accurately.

Constant Load Toolpath Planning and Stiffness Optimization for Robot Milling of Freeform Surfaces

Constant Load Toolpath Planning and Stiffness Optimization for Robot Milling of Freeform Surfaces

Toolpath Planning for Manufacturing of Complex Parts Through Incremental Sheet Forming

Abstract Incremental sheet forming (ISF) offers great flexibility in producing complex sheet parts as compared with conventional sheet forming processes where part-specific die sets are required to form a product. While there are many potential applications of ISF in various industries, toolpath planning for multifeature parts remains a leading challenge hindering the wide adoption of ISF. In this study, a criterion based on the gradient of the target surface was established for determining the appropriate feature forming sequence. Based on the analysis of the gradients of the surface, multifeature geometries were separated into two categories: “plane-referenced” and “surface-referenced.” Experimental investigations of forming a multifeature air intake as an example were carried out to demonstrate the proposed criterion and feature forming sequence. The results show that the choice of the optimal sequence depends on the type of geometry formed. The proposed criterion extends existing toolpath strategies for relatively regular geometries, where features are formed from flat or inclined bases to more complex geometries with features on a curved basis. This work will be of interest to both design and manufacturing communities.

Printing Ready Topology Optimization for Material Extrusion Polymer Additive Manufacturing.

Additive manufacturing-oriented topology optimization features in the extreme geometric complexity that magnifies the product functional performance. However, the increased geometric complexity makes postprocessing of the designs technically nontrivial and sometimes inefficient because of too many structural details. To address this issue, this article presents a novel printing-ready topology optimization method whereby the topological designs can be directly exported in the format of a printing-ready G-code, which saves the postprocessing efforts of stereo lithograph (STL) model generation, model slicing, and tool path planning. More importantly, the slicing and tool path information can be tracked all the time during optimization to facilitate the evaluation of the tool path-related material constitutive model, for example, the fiber-reinforced composites, so as to improve the numerical analysis accuracy and the design result optimality. Finally, three case studies are performed to test the postprocessing efficiency of the printing-ready approach and the multi-scale design case, which demonstrates the outstanding high efficiency characteristic of the proposed approach.

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.

Iso-scallop tool path planning for triangular mesh surfaces in multi-axis machining

• A robust and universal isoscallop tool path planning method for multi-axis machining is proposed. • The tool path with the constant scallop height is generated from the first contour of a normalized geodesic distance field (GDF) on triangular mesh surfaces. • The proposed algorithm starts from the boundary curve and runs forward recursively to ensure that the surface is covered completely by the isoscallop tool path. • The feasibility and superiority are studied by several simulations and experiments. Triangular mesh enables the flexible construction of complex surface geometry and has become a general representation of 3D objects in computer graphics. However, the creation of a tool path with constant residual scallop height on triangular mesh surfaces in multi-axis machining is not a convenient task for current algorithms. In this study, an isoscallop tool path planning method for triangular mesh surfaces, in which the tool path is derived directly from the contours of a normalized geodesic distance field (GDF), without any post-processing is proposed. First, the GDF is built to determine the shortest geodesic distance from each vertex to the mesh boundary. Then, the normalizing process is performed on the GDF to ensure that its first contour meets the isoscallop height requirement considering the mesh curvature and effective cutter radius. To improve the computational efficiency, the GDF is only built in the mesh area related to the first contour by specifying a stop distance. Moreover, an adaptive refinement process is conducted on the mesh to improve the smoothness and accuracy of the tool path. Finally, the triangular mesh is trimmed along this first contour for a new round of tool path planning. The proposed method is organized recursively and terminated when no new paths are generated. Simulations and experiments are conducted to verify the effectiveness and superiority of the proposed tool path planning method.

SFCDecomp: Multicriteria Optimized Tool Path Planning in 3D Printing using Space-Filling Curve Based Domain Decomposition

We explore efficient optimization of toolpaths based on multiple criteria for large instances of 3D printing problems. We first show that the minimum turn cost 3D printing problem is NP-hard, even when the region is a simple polygon. We develop SFCDecomp, a space filling curve based decomposition framework to solve large instances of 3D printing problems efficiently by solving these optimization subproblems independently. For the Buddha model, our framework builds toolpaths over a total of 799,716 nodes across 169 layers, and for the Bunny model it builds toolpaths over 812,733 nodes across 360 layers. Building on SFCDecomp, we develop a multicriteria optimization approach for toolpath planning. We demonstrate the utility of our framework by maximizing or minimizing tool path edge overlap between adjacent layers, while jointly minimizing turn costs. Strength testing of a tensile test specimen printed with tool paths that maximize or minimize adjacent layer edge overlaps reveal significant differences in tensile strength between the two classes of prints.

Real-time toolpath planning and extrusion control (RTPEC) method for variable-width 3D concrete printing

Extrusion-based 3D concrete printing (3DCP) is one of the most widely used methods for the digital fabrication of concrete material. For variable thickness components, inner cavity or internal toolpath can occur when using constant-width filament. Printing with variable-width filament is a possible solution to reduce the inner toolpath and enhance the integrity of the components. However, the conventional open-loop control method requires pre-calibration of materials and extrusion equipment and relies on the fine control of the material properties and the stability of the pump system. This paper presents a variable-width 3DCP method using real-time toolpath planning and extrusion control (RTPEC). In this paper, the material requirement, extrusion system, and real-time control algorithm are discussed. A controlled experiment is performed to verify the feasibility of the algorithms and the real-time control system. The printing accuracy in the horizontal and vertical directions is analyzed by 3D scanning. The result shows better horizontal accuracy and surface quality by using the RTPEC method. The result is well within the tolerance of the building scale component and demonstrates the potential applications in 3D concrete printing of building scale components.

Research on three-section type tool path planning algorithm for tooth hot pressing model cutting

In the process of automatic cutting of the tooth hot-pressed model, there are problems that the gingival line feature point data obtained by scanning is not suitable as a cutting route data and the tool path planning methods also lack universality. A trajectory conversion algorithm based on Bézier curve is proposed to process the feature points of gingival line by dividing the points to be optimized into four categories, which also uses the morphological characteristics of the gingival line to divide the hot-pressed model into three parts: anterior sides, posterior sides, left and right posterior sides. Each part adopts a different tool path planning method. The data analysis shows that if the density parameter ρ is 4, the number of optimized feature points can be increased by 3.5 times, and included angle of straight-line can be increased by about 16.5% on average. The path and posture of the tool changes continuously and smoothly, and the transition is natural at the junction. Cutting experiments further show that it takes 50 s for the machine to obtain an invisible orthotics. Regarding product quality as a criterion, the burrs of machine-cut products are both less and small. In a nutshell, the research effectively improves the stability of product quality and promotes production efficiency.

Fabrication of Sinusoidal Microstructures on Curved Copper Surface by Ultra-Precision Diamond Cutting with a Rotary B-Axis and Fast Tool Servo System

While curved surface microstructures have wide applications in optical components and devices, how to achieve high machining accuracy of the microstructures is crucial for their applications. In the present work, we fabricate sinusoidal modulation microstructures on a curved copper surface by ultra-precision diamond cutting, with the combination of a rotary B-axis and a fast tool servo system. Specifically, tool path planning, together with the consideration of a curved, sinusoidal surface meshing and tool tip arc segmentation compensation, is carried out. Preliminary cutting experiments are firstly carried out on a homemade four-axis ultra-precision lathe, which demonstrates the advantages of additionally applying the rotary B-axis in suppressing burr formations and over-cutting phenomenon over the sole utilization of the fast tool servo system. Subsequent experiments are carried out to evaluate the effects of feed rate and the number of sampling points on the machining accuracy of the microstructures under the combination of a rotary B-axis and a fast tool servo system. With the optimized machining parameters, sinusoidal modulation microstructures, which have a wavelength of 700.6 μm, a peak-to-valley of 18.7 μm, a surface roughness of 18.9 nm and a deviation of profile tolerance of 4.326 μm, are successfully fabricated on a curved copper surface with a face radius of 10 mm and a curvature radius of 500 mm.

Toolpath Planning and Generation for Multi-Stage Incremental Forming Based on Stretching Angle.

To solve the problems that exist in the multi-stage forming of the straight wall parts, such as the sheet fracture, uneven thickness distribution, and the stepped feature sinking, a new forming toolpath planning and generation method for the multi-stage incremental forming was proposed based on the stretching angle. In this method, the parallel planes that were used for forming toolpath generation were constructed by using the stretching angle so that the distances between the parallel planes and the forming angles were gradually reduced. This makes the sheet material flow become changed and the thickness thinning is relieved. The software system for the toolpath generation was developed by using C++, VC++, and OpenGL library. In order to verify the feasibility of the proposed method, numerical simulation and forming experiments were carried out for the single stage forming, the traditional multi-stage forming, and multi-stage forming based on the proposed forming toolpath, using 1060 aluminum sheets. The comparative analysis of the thickness distribution, profile curve, strain curve, and sheet material flow shows that the proposed method is feasible, and the profile dimension accuracy is better, the thickness distribution is more uniform, and the sinking and bulging are significantly reduced. The formed sheet part with the stretching angle of 15° has higher dimensional accuracy, smaller bottom subsidence, and larger thickness than that of the stretching angle 5°.