Workpiece Model Research Articles

A robust assessment method of point cloud quality for enhancing 3D robotic scanning

Point clouds are widely used to construct models of workpieces using 3D scanners, especially where high-quality robotic and automatic 3D scanning is required in industries and manufacturing. In recent years, Point Cloud Quality Assessment (PCQA) has garnered increasing attention as it provides quality scores for entire point clouds, addressing issues such as downsampling and compression distortions. However, current PCQA methods cannot provide specific and local quality scores, which are necessary to facilitate rescanning and recompletion in 3D robotic scanning. Additionally, 3D data produced by robotic view-planning algorithms are usually considered the final result, where PCQA is typically not involved. In this paper, we bridge the gap between PCQA methods and practical robotic 3D scanning. We propose a no-reference PCQA method that recognizes sparse regions during 3D scanning, providing both local and overall quality scores. Unlike traditional methods that primarily consider density as a key metric, our method assumes that an expected 3D scan will have a uniformly distributed point cloud on surfaces. We analyze the quality of points by using geometric information from surfaces fitted to these points, which are mapped to a 2D distribution based on specified distances and angles. We conducted experiments on various datasets, including both synthetic and public datasets, to evaluate the accuracy and robustness of our method. The results show that our method can represent the quality on surfaces more accurately and robustly than density calculation methods. Additionally, it outperforms most existing PCQA methods in scenarios of downsampling, which is a common challenge in high-quality 3D scanning applications. The performance of our quality enhancement experiments on practical 3D scanning, conducted towards the end of our study, demonstrates significant potential for real-world applications. The related code is released at https://github.com/leihui6/PQA.

Efficient Voxel-Based Workpiece Update and Cutter-Workpiece Engagement Determination in Multi-Axis Milling

Abstract This paper presents a new method to efficiently update workpiece and determine cutter-workpiece engagement (CWE) in multi-axis milling simulation based on a uniform voxel modeling space. At each cutter location, a novel algorithm named direct voxel tracing is developed and used to generate a functional cutter surface voxel model to reliably establish the internal space of the milling cutter. The cutter internal space is represented by its voxel boundary with small memory usage. Through the Boolean subtraction between two successive voxel boundaries of the cutter internal space, a minimal voxel deactivation region is attained within which all active workpiece voxels are deactivated (removed) to update the workpiece model. To determine the associated CWE map, a 3D circle voxelization algorithm is employed. By slicing the cutter surface by a sequence of planes perpendicular to and along the cutter axis, CWE can be determined as the sliced 3D circles are voxelized. Quantitative comparisons of the proposed method against existing voxel modeling and vector modeling-based methods have been made. The results have demonstrated much improved computational efficiency of the proposed method in simulating the complex multi-axis milling operations.

Deep learning assisted fabrication of metallic components using the robotic wire arc additive manufacturing

PurposeBecause of the advantages of high deposition efficiency and low manufacturing cost compared with other additive technologies, robotic wire arc additive manufacturing (WAAM) technology has been widely applied for fabricating medium- to large-scale metallic components. The additive manufacturing (AM) method is a relatively complex process, which involves the workpiece modeling, conversion of the model file, slicing, path planning and so on. Then the structure is formed by the accumulated weld bead. However, the poor forming accuracy of WAAM usually leads to severe dimensional deviation between the as-built and the predesigned structures. This paper aims to propose a visual sensing technology and deep learning–assisted WAAM method for fabricating metallic structure, to simplify the complex WAAM process and improve the forming accuracy.Design/methodology/approachInstead of slicing of the workpiece modeling and generating all the welding torch paths in advance of the fabricating process, this method is carried out by adding the feature point regression branch into the Yolov5 algorithm, to detect the feature point from the images of the as-built structure. The coordinates of the feature points of each deposition layer can be calculated automatically. Then the welding torch trajectory for the next deposition layer is generated based on the position of feature point.FindingsThe mean average precision score of modified YOLOv5 detector is 99.5%. Two types of overhanging structures have been fabricated by the proposed method. The center contour error between the actual and theoretical is 0.56 and 0.27 mm in width direction, and 0.43 and 0.23 mm in height direction, respectively.Originality/valueThe fabrication of circular overhanging structures without using the complicate slicing strategy, turning table or other extra support verified the possibility of the robotic WAAM system with deep learning technology.

Modelling and Optimization of Machined Surface Topography in Ball-End Milling Process.

In order to optimize machined surface topography, this paper presents a novel algorithm for simulating the surface topography and predicting the surface roughness of a ball-end milling process. First, a discrete workpiece model was developed using the Z-map method, and the swept surface of a cutter edge was represented using triangular approximation. The workpiece surface was updated (i.e., material removal process) using the intersection between the vertical reference line and the triangular facet under a cutting judgement. Second, the proposed algorithm was verified by comparing the simulated 3D surface topography as well as 2D surface profile and average roughness (Sa) with experimental measurements. Then, numerical simulation examples planed by the Box-Behnken design methods were carried out to investigate the Sa in the ball-end milling operation. The correlations of Sa and cutting parameters were represented by a response surface reduced quadratic model based on the ANOVA results. Finally, the feed per tooth, radial depth of cut, and tilt and lead angles were optimized for improving the machining efficiency under the Sa constraints. This study presents an effective method for simulating surface topography and predicting the Sa to optimize the cutting parameters during ball-end milling process.

Coupling numerical simulation of plasma arc channel evolution and particle dispersion process

Arc discharge plasma (ADP) technology can be applied to disperse easily aggregated materials, such as the carbon nanotubes and Fe3O4. To investigate the evolution of the plasma arc channel and particle dispersion effect during the ADP process, a coupled electrode–plasma channel–workpiece (Fe3O4 clusters) and particle dispersion heat transfer model was established. The simulation results exhibited that the plasma arc formed at 0.05 s acted on the workpiece surface, forming a conical bottle-shaped structure with a wide arc column near the workpiece region and a narrow arc column near the electrode region due to the plasma column–workpiece interaction. With the continuous discharge, a discharge crater was formed on the workpiece surface due to the thermal-pressing effect of the plasma arc, and the dynamic pressure exerted by the arc column on the workpiece center increased continuously, driving the dispersion of the particles. In addition, ADP dispersion experiments were carried out on Fe3O4 to verify the simulation results. The experimental results showed that the morphologies of plasma arc channel evolution and discharge crater agreed with the simulation results. Moreover, the Fe3O4 particles dispersed by the ADP showed good dispersion morphology, which will further promote the spread of ADP technology in the dispersion and application of materials.

Analysis on mechanism of material removal rate and surface flow machining process

A novel finishing technique called abrasive flow machining (AFM) uses abrasive particles as the instrument for material removal. The term "self-deformable stone" refers to the abrasive particle-containing carrier medium, and AFM is commonly known as "no-tool" precision finishing procedure. AFM involves passing a semi-solid polymer-based medium through the work piece at a specific pressure while adding abrasive particles in a specific amount. The three main parts of the AFM are the machine, the medium, and the tooling or fixture. The machine is made up of a media cylinder, hydraulic cylinder, control system, and frame structure. A typical AFM method uses extrusion pressures ranging from 15 bars to 110–210 bars. Tooling and fixtures serve the purpose of positioning the workpiece and giving instructions to the media as they go over the finished product. A carrier, some additives, and an abrasive powder make up the medium. Since the finite volume approach deals with fluid flow, it can be used to represent the flow of media. For the modelling and simulation in this work, the ANSYS 15 software package's FLUID FLOW FLUENT was utilised. Together with the fixtures, 2D model of a cylindrical workpiece and 3D model of 4 rotating dies have been created. Using the available experimental data, the two models have been validated. For varying volume fractions and media speeds, the most influential flow output characteristics, such as velocity, strain rate, and dynamic pressure have all been examined. The granular and non-granular flows were both simulated using the 3D model. The impact of various abrasive particles with varying volume fraction and diameter on the Skin friction coefficient and granular pressure, two flow output characteristics that have been researched. The outputs' flow analysis provides a forecast for the effectiveness of material removal.

Real-time pose correction and registration of complex workpiece in robotic machining considering normal consistency constrains

Efficient and precision model registration of complex workpiece with arbitrary pose is a challenging task that determines the effects of intelligent robotic machining. Aiming at the problems of limited field of view of 3D vision sensors such as surface structured light and the complexity of scanning-splicing-registration algorithm, in this paper a real-time pose correction and registration algorithm of complex workpiece in robotic machining considering normal consistency constrains is proposed. Specifically, the operations on ellipse feature detection and center point extraction are performed based on the arc-support line segment, and then the actual three-dimensional coordinate of the ellipse is obtained by the camera conversion matrix. Furthermore, considering the constrained normal consistency of the center points set of ellipses on the model surface, the pose of the target workpiece is corrected in real-time by the improved ICP registration algorithm. Taking the automotive flywheel shell as a typical application object, the experimental results demonstrate that the registration correction time of the proposed algorithm is 0.5 s, and the registration accuracy can reach 0.35 mm. The repetitive correction time of the algorithm after arbitrarily changing the workpiece pose is less than 1 s, and the positioning accuracy of the guiding robot is less than 1.5 mm. On the premise of satisfying the robotic machining quality requirements, the pose of the complex workpiece model can be corrected in real-time for subsequent robotic machining.

Effect of tool pin profile on the heat generation model of the friction stir welding of aluminium alloy

Abstract The present work aims to model the three-dimensional heat transfer coupled with the material flow model of 7075-T6 aluminium alloy material using the three tool pin profiles, square, pentagon, and hexagon, in the friction stir welding process. The temperature rise and fluid flow behaviour from the top to the bottom of the tool were evaluated. Also, the strain rate and dynamic viscosity variation were found near the tool pin and shoulder region. The results showed that the frictional contact heat between the shoulder surface and workpiece was responsible for the maximum heat generation. The probe area was minimum in the square tool pin geometry, which results in high heat generation due to the maximum shoulder surface contact area with the workpiece model. Furthermore, the analytical formula for calculating the heat generation on the tool shoulder/workpiece interface and the tool pin/workpiece contact region were also evaluated. The numerical modelling of heat generation was evaluated by COMSOL Multiphysics V5.3a software.

Analysis of crystal structure transition of polycrystalline 3C-SiC in nanocrystalline grinding based on molecular dynamics simulation

In order to study the grain/grain boundary crossing mechanism of polycrystalline 3C-SiC materials under nano-grinding, molecular dynamics(MD) method was used to simulate the grinding process of polycrystalline 3C-SiC materials under diamond abrasive particles. Through the coupling method of Voronoi construction of polycrystalline 3C-SiC workpiece model and MD construction process, the nano-grinding process of polycrystalline 3C-SiC material was established, the potential function field parameters were optimized, and the residual stress in polycrystalline 3C-SiC was eliminated. The energy transition equation is modified to reduce the time for the system to enter dynamic equilibrium. The crystal structure and dislocation generation of polycrystalline 3C-SiC were analyzed by post-processing methods such as defect analysis and crystal structure recognition. The results found that: there are cubic lattice, simple cubic lattice, hexagonal lattice and graphene mechanism type atoms at the grain boundary. During the machining process, the cubic lattice type atoms are converted to other types atoms, and other types structure atoms are converted to each other. The internal structure atoms of grains are converted to the grain boundary structure atoms during the machining process, and the crystal atoms near the grain boundary have low structural stability. The grinding force mainly acts on the forward direction and just below the grinding grain, and also has a small amount of distribution at the grain boundary, but it is relatively weak. The dislocation caused by grinding mainly occurs at grain boundaries. The resulting debris was monolithic, and a few were granular. The interconversion between grains and different structural atoms at the grain boundary is mainly from the crystal lattice atoms in grains to other atoms at the grain boundary. The force is transferred to the grain through the grain boundary, which hinders the transboundary transfer of force and protects the grains. The shearing force plays a dominant role in the grinding process.

Enhancing Robotic-Based Propeller Blade Sharpening Efficiency with a Laser-Vision Sensor and a Force Compliance Mechanism.

The edge sharpness of a propeller blade plays a vital role in improving energy transmission efficiency and reducing the power required to propel the vehicle. However, producing finely sharpened edges through casting is challenging due to the risk of breakage. Additionally, the blade profile of the wax model can deform during drying, making it difficult to achieve the required edge thickness. To automate the sharpening process, we propose an intelligent system consisting of a six-DoF industrial robot and a laser-vision sensor. The system improves machining accuracy through an iterative grinding compensation strategy that eliminates material residuals based on profile data from the vision sensor. An indigenously designed compliance mechanism is employed to enhance the performance of robotic grinding which is actively controlled by an electronic proportional pressure regulator to adjust the contact force and position between the workpiece and abrasive belt. The system's reliability and functionality are validated using three different workpiece models of four-blade propellers, achieving accurate and efficient machining within the required thickness tolerances. The proposed system provides a promising solution for finely sharpened propeller blade edges, addressing challenges associated with the earlier robotic-based grinding studies.

Stability and Bifurcation Analysis in Turning of Flexible Parts with Spindle Speed Variation Using FEM Simulation Data

This study investigates the effect of variable spindle speed with sinusoidal modulation on chatter vibrations generated in turning of flexible parts. The Euler–Bernoulli beam theory is assumed for mathematical modeling of the slender workpiece that is clamped at the chuck and pinned at the tailstock. The induced force as interaction between tool and workpiece (A2024-T351) during chip formation is calculated using finite element simulation. Numerical-based semi-discretization approach is utilized to seek stability regions and chatter frequencies regarding coupled dynamic model of tool and workpiece, in the form of delay differential equations with time varying delay term. The simulated data are validated and compared with those for a rigid part. The results indicate the efficiency of periodic modulation in improvement of machining stability especially for low spindle speeds. The stability charts for different interaction location and also time history response are studied, extensively. Finally, detection of period-one, flip and secondary Hopf bifurcations for different spindle speeds at instability borders are analyzed and discussed by solving corresponding eigenvalue problem.

Establishment of Straight Profile Hourglass Worm under Virtual Reality

Virtual workpiece is widely used in dynamic simulation and can be imported into the Virtual Gear Measuring Center (VGMC) to be virtually measured. The tooth surface of hourglass worm is complicated, so the dynamic meshing performance is often improved by modification of the tooth surface. The design cycle of traditional tooth surface modification without digital virtual workpiece is long, and the dynamic meshing performance only can be judged by getting meshing spots with sample parts. In this paper, based on the direct digital modeling, the working tooth surface and the non-working tooth surface are processed respectively for the straight profile enveloping worm, and the errors introduced by the turning tool in the modeling process are eliminated. Segmental cutting and inversion methods are proposed to greatly improve the modeling efficiency. By writing software and parameterizing modeling process, the virtual workpiece model of the hourglass worm with controllable accuracy and no holes and redundant faces can be obtained conveniently and quickly. The model can improve the design efficiency and shorten the design cycle.

Triple-ray-rep model based geometric modeling simulation with voxelized removal volumes in NC machining

Geometric modeling techniques presented in this study target the important problem of improving the quality of milling processes through simulation-assisted research and development. Geometric modeling capabilities include generating the tool swept volumes for each tool motion, subtracting these from a dynamically changing in-process workpiece model, and calculating the instantaneous cutter engagements. In this study, the workpiece has been represented with a series of evenly distributed vectors oriented in three directions of the Cartesian coordinate system. Thus, sampling in multiple directions, called the triple-ray rap-based method, overcomes the problems associated withz-Map-based techniques, in which sampling only along one direction misses surface portions such as sharp edges and vertical walls. In addition, since the tool-swept volumes are regarded as envelope surfaces in the vector model-based techniques, the intersection calculations have been reduced to line/surface intersections. In the tool engagement extractions, the tool removal volumes represented by the vectors have been utilized instead of the in-process workpiece to reduce memory usage and the program runtime. Later, these removal volumes were voxelized at the predetermined resolutions for performing the arc and voxel intersections. In this research, the milling tools have been modeled as the surface of revolutions. Thereby, the method has been broadened to use more than just the APT type cutters, and it can be generalized for other types of cutting tools.

Automated process planning in milling of hybrid components

Hybrid material composites can meet the increasing demands for high strength and low weight due to their different workpiece properties. Usually, hybrid components require post-machining after their fabrication. Due to the different material properties, new challenges arise in the machining process. It is essential to recognize the course of the material boundary in order to adapt the process planning accordingly and to enable a uniform material transition during machining. This paper presents a method for automated material recognition and automatic adaptation of the process parameters considering a uniform force level during the milling of hybrid materials. This way, the load on the milling tool in the material transition area can be reduced by up to 71%, which prevents premature tool failure. An optical laser line scanner is used to localize of material transitions within hybrid components. This enables a digital mapping of the material distribution in the discretized workpiece model. In combination with an empirical force model, it is possible to predict the cutting forces of the different materials and determine the material transition area for adapting them to specified target values.

Reconstruction of 3-D CAD Model of Workpiece With Internal Defect Based on Industry CT Image

A 3D CAD model of workpiece with internal defect can effectively evaluate the effect of internal defect on the use performance of the workpiece by digital simulation, and the analysis result can provide technical support for optimizing manufacturing process, but how to obtain the model has always been a difficult problem. A reconstruction approach is proposed for 3D CAD model of workpiece with internal defect based on industrial CT image in this paper. Firstly, the CT image data is achieved by use industry CT scan the workpiece with internal defect, then the internal defect is segmented from the volume data composed of industrial CT images. The STereoLithography (STL) model of the workpiece (excluding defect) and the STL model of the internal defect are obtained via the 3D surface reconstruction of volume data. Then, in order to obtain the correct position of internal defect in the nominal CAD model of the workpiece, the STL model of the workpiece (excluding defect) is registered with the nominal CAD model. Finally, the CAD model of internal defect is reconstructed, and then the 3D CAD model of workpiece with internal defect is achieved by Boolean operation with the entity model of internal defect and the nominal CAD model of workpiece. The reconstructed CAD model of workpiece with internal defect is imported into the finite element simulation software, and the simulation analysis can be carried out according to the needs, which proves the effectiveness of the method in this paper. The proposed method make full uses the nominal CAD model of workpiece, and only need to reconstruct the CAD model of internal defect, which is simple and efficient.

Digital model reconstruction through 3D Stereo Depth camera: a faster method exploiting robot poses

In industrial robotic contact-based operations it is necessary to have a detailed geometrical knowledge of the work-piece to automate the generation of the working trajectory. In many cases, the digital model is not available or it differs from its as built actual conditions. Vision sensors, especially 3D vision sensors allows to scan the work-piece and reconstruct its digital copy that is used for the generation of the robotic working trajectory. In this paper we compare two algorithms for the generation of the 3D model of an unknown work-piece based on the use of the RGB-D images taken from different perspectives. The first technique, based on standard image reconstruction methods commonly used for reconstruction of indoor scenes where error in the order of few centimeters is negligible, is exploited in this work in order to be exploited in contact-based robotic operations where the geometrical error has to be limited to few millimeters. It is based on the analysis of the images to estimate the camera pose taking each image. Based on the pose, the algorithm integrates then the information contained in the images in a unique volume representing the scene. The second algorithm directly uses the known poses of the robot, stored while capturing each image, to integrate the information to create the model. The two algorithms are compared to evaluate the accuracy, acquisition time and elaboration time. The analysis is done considering two kinds of objects, the first one with regular shape, the second one corresponding to an actual industrial object.

Simulation and Study on Surface Residual Stress Influence of TC4 Titanium Alloy

To study the residual stress distribution on the machining surface of TC4 titanium alloy and its influence on the milling stability, a three-dimensional milling model of TC4 titanium alloy workpiece milling with carbide end milling cutter was established based on Abaqus finite element software. Constraints were imposed according to the actual machining conditions. The distribution of residual stress on the machined surface of TC4 titanium alloy with different milling parameters was investigated by using the angular velocity and feed velocity of the tool as input load variables. The simulation results show that along the tool feed direction for reference, its residual stress was generally greater than the left side of the milling groove on the right side of the milling groove residual stress, cutting tool feed direction on the normal direction of the farther distances from the center of the tool axis of the residual stress value, the greater the residual stresses in longitudinal depth was as the smaller the farther distance milling surface stress value.

Research on the effect of cutting parameters on the machinability of polycrystalline Fe-Cr-W alloy by molecular dynamics simulation

Molecular dynamics simulation has become a major theoretical analysis method for ultra precision machining of various materials. Large Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) is used to construct a molecular dynamics model for cutting polycrystalline Fe-Cr-W alloy with CBN tool. The geometric parameters of the tool model are: the rake angle is −10°, the clearance angle is 7°, and the tool tip radius is 1.5 nm, including 8570 atoms. The size of the workpiece model is 24 nm × 10 nm × 10 nm, including 203,893 atoms. Ovito is used to visually analyze the influence of cutting parameters on the machinability of workpieces. The results show that the extrusion of the tool on the workpiece makes the atoms of the workpiece move and become chips and machined surfaces. Excessive cutting speed and depth will produce large hydrostatic stress, large cutting force, high cutting temperature and deteriorate the machined surface.

Chatter suppression for milling of thin-walled workpieces based on active modal control

Owing to the low stiffness of workpiece, chatter easily occurs in milling of thin-walled structures, which may cause poor surface quality and uncontrolled machining accuracy. For suppressing milling chatter of thin-walled workpieces, this paper presents an active control method with a piezoelectric patch actuator. As a flexible body, thin-walled workpieces have more than one modals participating in milling vibration, and its dynamic characteristics vary with tool position. This paper establishes dynamic model of the thin-walled workpiece with a semi-analytical method. Considering three order modals of workpiece, actuator position is optimized and active controller is designed. The varying dynamic characteristics of workpiece are overcome by designing controller with the parameters on the maximum vibration position to stabilize the whole process. Experiments verify the necessity of considering more than one modals of workpiece in active control through various chatter characteristics dominant by different modals. With the designed control method, the stable cutting depth improves from 0.2 mm to 1 mm.

A Reverse Modeling Method Based on CAD Model Prior and Surface Modeling

Reverse engineering is an important process of real model digitization. However, the existing methods are limited by the characteristics of the modeling object; the modeling is low efficient, has poor versatility, and unstable accuracy. To complete the reverse engineering of a real workpiece with irregular deformation based on the ideal computer-aided design (CAD) model, a high-precision reverse engineering method of the workpiece based on the CAD model prior was presented. Through the registration of the ideal CAD model and the point cloud model of the real workpiece, the geometric feature position information and feature constraint information contained in the CAD model are transmitted to the modeling process, which helps to improve the accuracy and efficiency of reverse engineering. This method is applied to the reverse engineering process of the engine compartment with slight irregular deformation, the modeling accuracy reaches 0.04 mm, and the high-precision reverse engineering of the engine compartment is successfully realized.