Tool Path Generation Research Articles

Optimal tool path generation and cutter geometry design for five-axis CNC flank milling of spiral bevel gears

Abstract Computer numerical control milling provides greater flexibility and universality for machining complex gears compared to dedicated gear manufacturing. A critical challenge in popularizing the use of five-axis flank milling to spiral bevel gears is to achieve acceptable machining accuracy that ensures the meshing performance of the finished gears. Previous studies, which used approaches such as gear design modification, using multiple tool paths, and end milling, failed to resolve this issue. Thus, this paper proposes a computational scheme to improve the machining accuracy of five-axis flank milling of spiral bevel gears by optimizing the tool path and cutter geometry. The scheme minimizes the geometric deviations between the machined surface and original design using heuristics and optimization algorithms. A simplified tooth contact analysis method was developed to quantitatively evaluate the contact path of the meshing gears. The simulation results of real gears show that the proposed scheme outperforms previous methods in reducing machining errors and further enhance the meshing performance by optimizing the design of form cutters. This work developed an effective approach for flexible and low-cost manufacturing of complex gears.

Fabrication of high aspect-ratio aspheric microlens array based on local spiral diamond milling

Ultraprecision mold machining combined with precision glass molding is the most promising technology for the mass production of glass microlens arrays (MLAs). However, fabricating an MLA with a high aspect-ratio (AR) (ratio of height to aperture), submicron scale profile accuracy, nanoscale surface finish, and good consistency remains a considerable challenge. A local spiral diamond milling (LSDM) method is proposed to generate a high AR MLA on a nickel-phosphorous (Ni-P) plated mold. A spiral toolpath generation algorithm that considers the tool edge radius and performs profile error (PV) compensation is developed. Each lenslet at any local position can be precisely machined by controlling the servo motions of the three translational axes. Then, the entire MLA can be generated by shifting the toolpath to go through the centers of all lenslets according to the MLA layout. The tool parameters are optimized to avoid local and global tool interference during machining. The generated toolpath provides steady slide axis movements to avoid dramatic changes in cutting speed and acceleration. An MLA with an AR of 0.166 is fabricated. The results show that the fabricated mold and the molded lenses have a profile accuracy (PV) of less than 1 μm and a surface roughness (Ra) of less than 14 nm. The cross-sectional profiles indicate that the fabricated MLA has high machining consistency.

Toolpath generation for ultraprecision machining: Freeform surface blending

This paper is the final part in a two-part series investigating toolpath generation for freeform optics manufacturing. Building on the surface generation techniques already presented, this paper introduces a 3D blending surface that has the form of a continuous polynomial curve and is used to smoothly fill in the space between two non-intersecting, polar boundaries and two surfaces of the form Z(X,Y). The proposed blending surface renders it possible to smoothly join two surfaces defined over different domains together, as well as to smooth over the discontinuity created where two surfaces intersect. It is shown that increasing the order of the blending polynomial increases the continuity of the overall piecewise, blended surface. As a corollary, it is possible to increase the overall continuity of a toolpath along its cutting direction. To illustrate the robustness of the proposed surface blending technique, experimental data is presented for the toolpath generation, diamond machining, and measurement of a freeform microlens array. Designed with no exploitable symmetries or simplifications and very difficult to model with traditional CAD software, this surface is comprised of an array of freeform lenslets superimposed and blended onto a freeform base surface. All lenslets are individually tilted about the X and Y-axes such that they are normal to the base surface at their respective locations, and all blends have the same form as the intersection curve between each respective lenslet and base surface. Machined in brass to optical quality, this C3 continuous surface represents a general case of the proposed surface generation and blending techniques.

A machining digital twin for hybrid manufacturing

Hybrid manufacturing consisting of metal additively manufactured preforms and computer numerical control (CNC) machining has been established to be an effective method for high material use rates. However, hybrid manufacturing introduces unique challenges. Near-net shape designs are typically selected, which result in a smaller margin for part placement within the stock and stringent requirements for work coordinate system identification. Additionally, less stock material reduces the preform stiffness, which limits the material removal rates during machining. This paper demonstrates a digital twin for CNC machining of a wire arc additively manufactured preform that implements: 1) structured light scanning for stock model identification and tool path generation; 2) a fused filament fabrication apparatus to attach temporary fiducials and scan targets to the preform that enable coordinate system definition for both the CAM and CNC machine; 3) preform and tool tip frequency response function measurements to enable stable milling parameter selection; and 4) post-manufacturing measurements of geometry, surface finish, and structural dynamics to confirm designer intent. These efforts define key components of the machining digital twin for hybrid manufacturing.

A 3D printing tool-path generation strategy based on the partition of principal stress field for fused filament fabrication

A 3D printing tool-path generation strategy based on the partition of principal stress field for fused filament fabrication

Offset-tool-servo diamond end flycutting multi-layer hierarchical microstructures

Microstructural functional surfaces inspired by nature have been widely applied in the fields of optics, aerospace, electronics and communication. There function not only originates from a single layer of surface microstructures, but also depends largely on the combined effect of hierarchical structures. Hierarchical microstructures are generally overlapped by two or more layers to generate a functional complementary and combined surface. Fast/slow tool servo technology is usually employed to fabricate micro/nanostructures. However, it is challenging to fabricate multi-layer hierarchical microstructures with sharp edges using only a commercial three-axis ultra-precision lathe. In the present study, a novel ultra-precision offset-tool-servo end flycutting (OTSEF) system was developed. Considering the geometry and installation pose of the diamond tool, a tool path based on the OTSEF system was planned, and different hierarchical microstructures could be fabricated using a compensated linear tool trajectory. Furthermore, a mathematical modeling for tool path generation for complex multi-layer hierarchical microstructures, overlapping micro-lens units with secondary pyramid structures, was established. After determining and compensating for the misalignment between the center of the diamond tool and workpiece, hierarchical microstructures with high precision and quality were successfully fabricated. The theoretical and experimental results demonstrate that the OTSEF system has unique advantages in the fabrication of multi-layer hierarchical microstructures. The present research not only provides a deep insight into tool path modeling but also a machining method for multi-layer hierarchical microstructures.

A deep-learning-based in-situ surface anomaly detection methodology for laser directed energy deposition via powder feeding

Laser Directed Energy Deposition via Powder Fed (LDED-PF) based Metal Additive Manufacturing suffers from inferior dimensional accuracy mainly due to thermal cycling, localized heat accumulation, inconsistency in the powder stream, deviation in the speed of the motion system and powder focus, etc. In-situ monitoring, along with defect detection algorithms, can be used for avoiding unpredictable build failures while minimizing the time and cost of exhaustive ex-situ characterization techniques. Existing surface quality assessment techniques for LDED-PF mainly focus on intermittent process monitoring, data acquisition, data post-processing, feature extraction, and error identification. The present work investigates the development of a novel in-situ monitoring software platform that can be used for the surface anomaly detection of LDED-PF parts using machine learning techniques. Despite the existing methods in the literature, this technique has shown high robustness and high confidence in defect detection regardless of the geometry, and varied density of point clouds. First, a novel method is developed to calibrate the laser line scanner with respect to the robotic end-effector with the sub 0.5 mm accuracy. Subsequently, 2D surface profiles obtained from the LDED-PF built part surface using the laser scanner are stitched together to create an accurate 3D point cloud representation. Further, the point cloud data is processed, and defect detection is carried out using unsupervised learning and supervised (deep) learning techniques. The overall accuracy and mean IoU of 91.3 % and 83.3 % are achieved, respectively. The study paves the way for the development of automatic tool path generation for the LDED-PF process to build high-quality components.

Minimization of Nonproductive Time in Drilling: A New Tool Path Generation Algorithm for Complex Parts

In computerized tool path programming, the operator/user can generate the tool path based on the shape and geometry of the part to be produced by choosing from a set of predefined strategies available in the library of Computer Aided Manufacturing (CAM) software. These tool paths are typically not optimum, specifically for complex geometries. This paper employed Travelling Salesman Problem (TSP) as a foundation to propose a new tool path optimization algorithm for drilling to minimize the tool path length and subsequently reduce the time spent on nonproductive movements. The proposed algorithm was solved using local search approach in the presence of multiple constraints including geometric obstacles and initial location of tool origin. The outcome was a near-optimum tool path for drilling operations with no collision with workpiece features. The computational efficiency of the proposed algorithm was also compared with other methods in available literature using a standard workpiece as a benchmark. The results confirmed that for given examples, the near-optimum collision-free tool paths using the developed model in this paper were almost 50% shorter than the tool path generated by a commercial CAM software.

블록 오버랩 기반 CNC의 사이클 타임 예측

This paper proposes a cycle time estimation algorithm of a CNC machine tool, using a block overlap based tool path generation algorithm. Velocity profile generation algorithm of CNC interpolator is proposed to compute the cycle time of the G-Code block. Because the CNC blends adjacent velocity profiles to reduce the cycle time and smooth the tool path, the cycle time is adjusted considering the block overlap. The in-position time of rapid traverse is compensated to improve the cycle time estimation accuracy. The simulation model was designed to estimate the cycle time of the CNC machine tool. A three-axis feed drive testbed was used to evaluate the cycle time estimation accuracy of the proposed algorithm.

A grammar-based algorithm for toolpath generation: Compensating for material deformation in the additive manufacturing of concrete

In architecture, AM technologies have been used for rapid prototyping since the early 1990s. However, using AM for automated building construction represent a revolution for the industry that requires modeling the complex relationships between materials, printing system, and designs. An important aspect of research in this area is the deformation of concrete during printing and how it affects shape accuracy and structural stability of the printed geometries. A previous experimental study proposed a series of equations to predict material deformation for a specific concrete mix. This study incorporates these equations in a shape grammar-based algorithm to decompose complex geometries into simpler ones, slice the simpler geometries, and generate compensated toolpaths. The algorithm was implemented in Grasshopper, a Rhino plugin, and it can be used as a 3D slicer specifically for 3D printing concrete purposes. The slicer is validated with two printing experiments, involving a simple and a complex shape. The algorithm can be extended to other material mixes by developing similar experimental studies and incorporating the resulting equations.

Efficient Toolpath Generation Method for High-Quality and High-Accuracy Machining of Curved Surfaces

Currently, there is no function in commercial CAM systems to generate optimal quality machining for curved surfaces. In computer-aided manufacturing (CAM) systems, the toolpath (cutter location data) is derived as an approximately straight-line segment based on a plane approximation surface instead of a free-form surface from the designed shape. Due to this approximation, machining accuracy and quality are decreased, especially in the region with characteristic lines like in an outer automobile covering part. This paper presents an algorithm procedure for toolpath generation to process complex parts with characteristic curves with high-quality and high-accuracy machining by dividing the surface into different regions, the region where machining accuracy is not required as a plane approximation surface and the remaining region where accuracy is required as free-form surfaces. The proposed method was confirmed by machining experiments that actual machining realized high machining quality and accuracy compared to the conventional CAM system.

Optimisation of tool path shape in trochoidal milling using B-spline curves

In recent years, trochoidal milling has become greatly widespread since it provides high productivity and long tool life, especially when cutting difficult-to-machine materials. Numerous studies have dealt with the analytical description and the experimental investigation of the evolution of cutting force, temperature, tool wear, chatter stability, etc. However, most of these analyses are focusing on the conventional circular and cycloid-shape trajectories. Only a few studies address the potential of improving the efficiency by modifying the tool path shape, leaving significant reserves untapped. If the mathematical formulation of the trajectory cannot be described easily, then a sophisticated optimisation algorithm is needed to determine the appropriate tool path shape. To overcome these difficulties at trochoidal milling of straight slots, the present work proposes a new tool path generation algorithm that can maximize the average material removal rate (MRR) while controlling the tool load. In this approach, the tool path is modelled by a B-spline curve whose control points are optimised using a differential evolution algorithm. The developed tool path generation strategy was compared through simulations and experiments with two widely used solutions viz the traditional cycloid-shaped tool path and a modern approach used in computer-aided manufacturing (CAM) systems. The results reveal that the developed method is able to control the tool load and the smoothness of the tool path, and most importantly, also exceeds the existing methods in terms of productivity.

A Comprehensive Review on Experimental Conditions, Strategies, Performance, and Applications of Incremental Forming for Deformation Machining

Abstract The demand for product customization and flexible manufacturing techniques is growing day by day to meet the rapid changes in customer requirements. The current review presents the developments in the domains of incremental sheet forming (ISF) and deformation machining (DM) strategies to obtain thin monolithic geometries. The study focuses on the literature on room temperature single point incremental forming that can be applied to the DM. Thin structural parts are challenging to produce by machining because they have inadequate static and dynamic stiffness and low thermal stability. Significant research work on the evolution of diverse theories that emerged to address the fundamental mechanisms of ISF and DM processes has been reported in the literature. This paper presents an outline of the significant process and response parameters, experimental strategies, deformation mechanics and fracture behavior, toolpath generation techniques, and processes’ applications. The paper reports the motivation, research directions, existing gaps, and expansion in the domains of DM processes. The paper also outlines the evolution of incremental forming for deformation machining in the context of future critical applications in the domains of biomedical, aerospace, and automotive engineering.

Integrated Interface System of STEP Data Models for the Tool Path Generation

The STEP (STandard for the Exchange of Product model data) is a worldwide standard for exchanging products between diverse computer systems and industrial applications. STEP files (ISO 10303) contain 3D data in the universal data format with a boundary representation (B-rep) that allows the exchange of data models between CAD, CAM, and CNC systems. Traditionally, G-code generation relies on CAM software as an add-on, which incurs significant installation costs. The purpose of this paper is to describe the development of an Integrated Interface System (I2S) for Tool Path Generation (TPG) for the CNC milling operations utilizing neutral STEP files.The algorithm was interpreted in Hypertext Preprocessor (PHP) programming and produced a computer interface system that is capable to convert STEP file geometric data to G-code format.The geometric features of the sample block were modeled using a 3D CAD model. The result was validated using machining simulation, and the machining is performed on a three-axis CNC milling machine with a PC-based controller.In modern manufacturing systems based on Open Architecture Controller (OAC), the development of the I2S provides an alternative to generating machining tool paths and G-code by intercepting CAM software.

A new algorithm for optimal process parameters based on minimum building time in additive manufacturing

BackgroundAdditive manufacturing method is used for manufacturing of solid three-dimensional parts. It requires less human efforts and manufacturing time for parts is less. Different process parameters such as layer thickness, building orientation, infill type, and infill percentage affect the building time, model cost, mechanical properties, and surface roughness. The presented paper develops an algorithm for adapting layers and generating tool-paths. This algorithm can improve the fabrication efficiency and geometrical accuracy in the additive manufacturing (AM) of complex models. The proposed algorithm consists of three modules that identify the optimal process parameters, named as part building orientation, layer thickness, strategy type for internal filling, and slope of the tool-path.ResultsThe input is the PTS file that contains the points of the layers contour of the computer-aided design (CAD) model. All the modules for the proposed algorithm were implemented using the MATLAB R2019a programming language software. The main finding results showed that the fabrication with an adaptive layer thickness was more time-efficient. The build time was reduced up to 47.3%. The developed tool-path generation strategies (contour offset and zigzag line tool-path) can effectively balance the AM surface quality and fabrication efficiency requirements.ConclusionIn this research, the AM users can benefit by saving the cost and time. The parts were fabricated with a high degree of accuracy, and the surface finish was suitable for determining the optimal process parameter.

Kinematics of a 5-axis hybrid robot near singular configurations

• A method based on kinematics modification for singularity avoidance is proposed. • A criterion for choosing the appropriate inverse kinematic solution is presented. • A semi-analytical algorithm for forward kinematic analysis is developed. • An algorithm is developed by modifying C -axis instructions. • Both simulations and experiments are carried out to verify the proposed approach. This paper proposes a method for non-singular tool path generation based on inverse kinematics modification in joint space to deal with the singularity problem of a 5-axis hybrid robot in machining process. Firstly, a criterion for choosing the appropriate solution of inverse displacement analysis is presented, that enables the avoidance of mechanical interference and enlargement of the task workspace. As a counterpart of inverse displacement analysis, a semi-analytical algorithm for forward displacement analysis is developed with high computational efficiency. These works lay a comprehensive and solid foundation for motion control and tool path simulation of the hybrid robot. Then, it reveals that at a singular configuration that varies with the system configurations, sudden changes occur in both rotation of the C -axis of the 2-DOF wrist and lengths of three telescopic legs within the 3-DOF parallel mechanism. This finding leads to an effective method for non-singular tool path planning by directly modifying the C -axis commands in the joint space using linear interpolation technique. Finally, both simulation and experimental results on a prototype machine show that in the neighborhood of singularity, continuous and smooth joint motions and acceptable tracking accuracy can be ensured after the modification.

Build Strategies Based on Substrate Utilization for 3-Axis Hybrid Wire Arc Additive Manufacturing Process

The hybrid wire arc additive manufacturing (H-WAAM) process is one of the prominent methods for realizing large near-net-shaped metallic objects. In this process, a CAD model of the component is sliced into a set of 2D contours followed by the generation of toolpaths. An arc welding torch then follows these toolpaths for adding material over a substrate to realize the near-net shape of the object. These near-net-shaped objects are then followed by a machining operation to convert them into a fully functional part. It is always anticipated that the near-net shape of an object is produced quickly and upholds a high geometrical accuracy. Conventionally, the deposition rate is increased to reduce the build time but with a compromisation in the geometrical accuracy and material integrity. Therefore, in this work, the authors have investigated three substrate utilization methods, viz., (i) reusable substrate, (ii) embedded substrate, and (iii) integrated substrate to achieve the same goal. The build strategies for these three substrate utilization methods are illustrated through several examples. Also, a case study was performed for fabricating an impeller-like structure through a 3-axis H-WAAM setup. It has been observed that the embedded substrate method exhibits superior geometrical accuracy and takes less time to build the part as compared to other methods. A maximum of 64.34% of the material and 89.17% of build time is saved by adopting proposed build strategies compared with the traditional subtractive process.

Digital Programming of Liquid Crystal Elastomers to Achieve High-Fidelity Surface Morphing

Morphable surfaces have the potential to enable new kinds of adaptive systems, but existing fabrication methods have limited ability to achieve high resolution morphing into arbitrarily specified shapes. This work presents a platform and algorithms for toolpath generation to enable freeform structures capable of high-resolution surface morphing. The morphing surfaces were composed of liquid crystal elastomer (LCE), with nematic domains aligned using a scratch post capable of applying adjustable pressure and shear velocity, offering the ability to locally tune actuation strains and thus bending curvature radii from 1.8 mm to 14.4 mm. Patterning toolpaths for multi-layer structures were generated using two alternative algorithms, the results of which were compared using example structures capable of morphing from flat sheets into domes and models of a human faces. This process resulted in morphed human face shapes with structural similarities of up to 84.5% when compared to the original model, demonstrating the high fidelity and reconfigurability of this approach for fabricating complex morphable LCE structures.

Automatic generation of 3d spiral tool path for incremental sheet metal forming of mechanical parts with complex geometry

Incremental sheet metal forming is a flexible manufacturing technology that allows to form of various components on the same milling machine, without expensive tools. A hemispherical tool moves along a CNC-controlled tool path and deforms the sheet into the desired shape. The tool path has a significant role in the geometric accuracy of the final part. There has been very little research on the problem of the forming of sophisticated parts with asymmetric wall angles. This paper presents a new approach to generating optimized tool paths for single-point incremental sheet forming (SPIF). At first, a strategy is proposed for the automatic generation of a 3D tool path during forming in a single-step operation. Then, a systematic technique of creating intermediate shapes is investigated by defining tool paths interpolated from the final part shape. The proposed methodology is applied to form a hip cup prosthesis. This part has a complex asymmetric geometry with important angles, a multi-step approach is used. The proposed methodology to define the different tool paths was implemented in Matlab. A numerical simulation of the incremental forming process is performed to predict the final geometry of the aluminum sheet. A comparison of desired and predicted geometries shows the reliability of the proposed method.

In-process adaptive dimension correction strategy for laser aided additive manufacturing using laser line scanning

Additive manufacturing (AM) technologies have seen rapid growth in the past decade. Achieving high-quality consistency and accuracy remains a challenge in the fabrication of large-format metallic parts using the directed energy deposition AM processes. An efficient dimension correction strategy is required to prevent build failure during the AM process. In this paper, a laser line scanning sensor was integrated into a robot-based laser aided additive manufacturing (LAAM) system to realise the on-machine measurement of the part geometry. With this system, an in-process adaptive dimension correction strategy was proposed. The dimensional deviations in the intermediate layers could be corrected immediately after they were detected during the LAAM process, thus avoiding excessive dimensional deviation leading to build failure. A tool-path generation process for dimension correction was proposed which did not rely on traditional time-consuming CAD reconstruction. Only 3D point cloud was used directly, enabling the quick response of the LAAM system in restoring the dimensional accuracy. The deviated surface could be automatically filled up, and the subsequent deposition processes were resumed after each cycle of the dimension correction. To facilitate the proposed dimension correction strategy, a Robot Operating System (ROS)-based software platform was developed. Experimental comparisons between the part built with and without correction were conducted. The results demonstrated a significant improvement in dimensional accuracy when the correction strategy was applied.