Scallop Height Research Articles

The generation of supplementary toolpaths for surface machining based on rapid prediction of scallop height distributions

The generation of supplementary toolpaths for surface machining based on rapid prediction of scallop height distributions

A novel tool path planning method for 5-axis single-point diamond turning

5-Axis single-point diamond turning adds two linked axes based on 3-axis single-point diamond turning, which can smoothly and continuously process complex surfaces. Compared to 3-axis turning, tool path planning for 5-axis single-point diamond turning is a complex decision-making process, which is a novel problem in the existing studies and a difficulty in multi-axis turning. In this study, a novel path planning method for 5-axis single-point diamond turning is proposed. Firstly, the mapping relation from scallop height to the distribution of cutter contact (CC) points is established in the non-uniform rational B-spline (NURBS) parameter space, thereby the planning of CC points is quickly achieved under fewer constraints. Furthermore, the local interference and global interference generation mechanism of 5-axis single-point diamond turning are revealed by geometrical analysis, combining diamond tool parameters and tool shank parameters. By transforming the motion of the cutter axis posture in 3D space into swings in two planes, the posture accessibility diagram of the cutter axis is efficiently constructed. Finally, the feasibility and effectiveness of the tool path planning method are verified by 5-axis single-point diamond turning experiment. And the contour accuracy is improved through the quadratic planning of the CC points (the contour accuracy after compensation is 3.2 μm compared to normal one 9.6 μm). This study extends the traditional 3-axis turning to 5-axis turning, providing a new perspective for the machining of complex surfaces.

An assessment of effective slope as a parameter for turbulent drag prediction over multi-scaled roughness

The streamwise effective slope (ESx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm ES}_x$$\\end{document}), which is the mean absolute streamwise gradient of the roughness, is considered to be a key parameter in predicting the drag penalty of rough-wall turbulent boundary-layers. However, many real-world rough surfaces are multi-scaled. For such surfaces, ESx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm ES}_x$$\\end{document} can be unbounded and its value can be dominated by scales of the topography that are invisible to the flow. To illustrate this, a campaign of drag balance measurements was conducted with a set of machined surfaces. A baseline surface is prepared with fine machining parameters. By coarsening the machining precision, artefacts called ‘scallops’ are introduced which increases the ‘measured’ ESx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm ES}_x$$\\end{document} without changing other geometrical statistics. The drag of the ‘scalloped’ surfaces is higher than the baseline surface, with the relative drag increase scaling with the viscous scaled scallop height, but only when their height exceeds 2∼3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2\\sim 3$$\\end{document} times the viscous length scale. Further, the drag of one of the ‘scalloped’ cases, even when the scallop height is O(10)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {O}(10)$$\\end{document} viscous units, is seen to be much lower (∼28\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 28$$\\end{document}%) than a case with matched ESx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm ES}_x$$\\end{document}, but where the ESx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm ES}_x$$\\end{document} results from larger scale features. These findings confirm that for multi-scaled surfaces, ESx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm ES}_x$$\\end{document} may be a misleading topographical metric for drag (or ks\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k_s$$\\end{document}) prediction and one must consider which scales contribute to the average slope of a surface.

Surface quality enhancement by constant scallop-height in three-axis milling operations

The quality of machined part surfaces are under the impact of scallop height which should be analyzed and minimized. Achieving a uniform scallop-height is important for ensuring a smooth surface finish and maintaining consistent material removal across the machined surfaces during CNC machining operations. This approach helps to reduce material waste, tool wear and part production errors while ensuring consistent and high-quality of machined parts. Maintaining a constant scallop height can also help to reduce chatter and vibration during milling operations. The research work develops a virtual machining methodology to produce constant scallops through three-axis milling operations. The proposed approach examines free-form surfaces of workpiece in order to obtain free form surfaces curvatures. Then, free-form surfaces are separated into flat, convex and concave surfaces to provide optimized cutting tool variables in order to provide constant scallop height during CNC cutting tool paths. Achieving a constant scallop height involves optimizing cutting parameters such as feed rate, spindle speed, and step over. To calculate the optimized machining parameters of feed rate, speed of spindle and step over, the Taguchi optimization methodology is utilized in the study. Then, the machining variables of feed rate, speed of spindle and step over are optimized to achieve the uniform scallop height during milling potations of free-form surfaces. As a result, using optimized machining parameters during machining operations, the surface roughness of machined components are reduced by 23.8%. So, the proposed virtual machining method can enhance surface quality of machined parts during CNC milling operations of free-from-surfaces.

Efficient cutting path planning for a non-spherical tool based on an iso-scallop height distance field

Iso-scallop height machining means, when machining a freeform surface, the scallop height between any two neighboring tool paths on the surface will be a constant (i.e., the given threshold), which is preferable among various freeform surface machining strategies due to its high machining efficiency as well as better machine tool’s dynamics. However, all the existing iso-scallop height path planning methods pertain to only the ball-end or flat-end types of tools. In recent years, the non-spherical cutting tool has become more and more popular, especially for five-axis machining of complex freeform surfaces, majorly owing to its non-constant curvature which can be utilized to adaptively fit the tool to the surface to both avoid the local gouging and enlarge the cutting width. However, there have been no reported works on iso-scallop height five-axis tool path generation for a non-spherical tool, and, in this paper, we present one. Specifically, we first define and construct two fields on the surface to be machined-the collision-free tool orientation field (vector) and the iso-scallop height distance field (scalar). The iso-lines of the scalar field and their associated tool orientation field vectors then naturally serve as potential iso-scallop height five-axis tool paths, and we present a propagation-based algorithm to construct the desired tool path from the iso-lines. The computer simulation and physical cutting experiments confirm that everywhere on the surface, except maybe near the saddle curves of the scalar filed, the scallop height is exactly the given threshold. By adding the saddle curves as extra tool paths, the final machined surface then is assured of the required scallop height requirement.

A novel tool path planning method for machining triangular mesh surfaces based on geodesics in heat theory

Tool path planning is a critical technology in aerospace and gear manufacturing, where triangular meshes commonly model these complex surfaces. However, current tangential geometry-based tool path planning methods suffer from problems such as excessive assumptions, high computational complexity, and low machining accuracy. In this manuscript, a novel tool path planning method for machining triangular mesh surfaces, offsetting-based the heat-geodesic field (HGF) to obtain tool path, is proposed. Firstly, an initial heat source curve (IHSC, i.e., master path) extraction method is proposed to consider cutter motion and part geometry characteristics. Based on this, a robust modeling method for HGF with a linear process is established. Finally, an efficient determination method for adjacent paths based on HGF is established, which utilizes geodesic distances as metrics, as opposed to the traditional Euclidean distances. Simulations and experiments under various conditions are carried out to validate the proposed method. Compared to zigzag paths, the proposed method improves machining efficiency by 24.28 % while maintaining the same scallop height constraint. Furthermore, it has significant advantages in machining accuracy, such as avoiding corner errors caused by particular surface boundaries. Consequently, the proposed tool path planning method, with highly efficient and robust, is expected to improve the machining accuracy and efficiency for complex surfaces.

Investigation of stochastic toolpath strategy in three-axis ball-end milling of 2D and free-form surfaces

The machining of free-form components by ball-end milling inherently produces surface error in the form of scallops. The objective of any free-form toolpath strategy is to balance productivity while minimizing scallop height to reduce surface error. Conventional machining strategies produce repeatable material patterns (constant scallop height) that may limit workpiece function in areas such as lubricity, directional anisotropy, and aesthetic appearance. These strategies also involve steady-state cuts, which allow accumulation of temperature, restrict the permissible depth and speed. In the present paper a novel complex stochastic toolpath strategy has been proposed that comprises pseudo-random circular contours concatenated into a smooth path. The approach enables continuous variation of chip load, force, and direction, and avoids conditions of continuous, periodic high cutting loads and heat accumulation. Based on initial testing, it has been observed that stochastic toolpaths are longer than conventional toolpaths. However, a decrease in average cutting loads enable reduction in cutting time with feed optimization. Additionally, the proposed strategy resulted in lower scallop height than conventional machining, thereby improving surface condition.

Effect of Wheel Path in Raster Grinding on Surface Accuracy of an Off-Axis Parabolic Mirror

Off-axis parabolic mirrors have extensive applications in X-ray optics, with the precision of their curvature directly impacting grazing-incidence focusing performance. Notably, the off-axis parabolic surface has non-rotating and non-symmetrical characteristics. Ultra-precision raster grinding utilizing a diamond wheel is a common method. Crucially, establishing an optimal wheel path stands as the key to ensuring surface accuracy during off-axis paraboloid grinding. In this study, according to the double curvature property of an off-axis parabolic surface, two different wheel paths were compared: one tracing the meridian direction (parabolic generatrix) and the other following the arc vector direction (arc). The results showed that the wheel path in raster grinding stepping along the arc vector direction can obtain a smaller scallop height and higher surface accuracy. The surface accuracy of one step along the arc vector direction is 9.6 μm, and that of the other step along the meridian direction is 32.6 μm. A model of the scallop height was established based on the relative relationship between adjacent wheel paths, and the error is within 5%. According to the correlation between scallop height and shape error, we conducted an analysis of the spatial distribution of shape errors under varying wheel paths. The wheel path that steps along the arc vector is more suitable for raster grinding of the off-axis paraboloid. The above study can provide theoretical guidance for the wheel path planning of off-axis parabolic mirrors with high surface accuracy.

Grinding marks suppression strategy based on adjusting grinding traces distribution

For the grinding marks phenomenon formed in cross grinding of plane, spherical and aspheric optical elements would reduce the surface quality, surface strength and optical performance of workpiece, which would increase subsequent polishing time and wastage of polishing resources, the suppression strategies of grinding marks based on adjusting grinding traces distribution simulation was investigated. According to the distribution equations of grinding traces and the scallop height, the possibility of two grinding marks suppression strategies was discussed, one of strategy was based on matching grinding parameters and the other one was on grinding traces superposition without depth of cut. Based on the two strategies, the grinding verification experiments were carried out. The results showed that the grinding marks were suppressed by the matching parameters strategy, which cracks and deep grinding traces were less, surface roughness and its homogeneity were better, surface waviness was smaller when ground by matching parameters with the phase shift of 0.618. Besides, when grinding traces superposition strategies were used to process experiments, the morphology and surface roughness did not change much, but all homogeneity of surface roughness were fine with the increasing of superposition times. Moreover, the surface waviness significantly decreased from 90 to 30 nm after 3 superposition times, the grinding marks were also suppressed by the grinding traces superposition without depth of cut. This research would provide references and ideas for grinding aspherical surface with high surface quality and efficiency, and low energy.

Ultra-precision Ductile Grinding of Off-Axis Biconical Free-Form Optics with a Controllable Scallop Height Based on Slow Tool Servo with Diamond Grinding Wheels

Ultra-precision Ductile Grinding of Off-Axis Biconical Free-Form Optics with a Controllable Scallop Height Based on Slow Tool Servo with Diamond Grinding Wheels

Tool Path Planning with Confined Scallop Height Error Using Optimal Connected Fermat Spirals

Tool Path Planning with Confined Scallop Height Error Using Optimal Connected Fermat Spirals

Method for Keyhole-Free High-Aspect-Ratio Trench Refill by LPCVD.

In micro-machined micro-electromechanical systems (MEMS), refilled high-aspect-ratio trench structures are used for different applications. However, these trenches often show keyholes, which have an impact on the performance of the devices. In this paper, explanations are given on keyhole formation, and a method is presented for etching positively-tapered high-aspect ratio trenches with an optimised trench entrance to prevent keyhole formation. The trench etch is performed by a two-step Bosch-based process, in which the cycle time, platen power, and process pressure during the etch step of the Bosch cycle are studied to adjust the dimensions of the scallops and their location in the trench sidewall, which control the taper of the trench sidewall. It is demonstrated that the amount of chemical flux, being adjusted by the cycle time of the etch step in the Bosch cycle, relates the scallop height to the sidewall profile angle. The required positive tapering of 88° to 89° for a keyhole-free structure after a trench refill by low-pressure chemical vapour deposition is achieved by lowering the time of the etch step.

The Effect of the Machining Strategy on the Surface Accuracy When Milling with a Ball End Cutting Tool of the Aluminum Alloy AlCu4Mg

The article discusses the effect of milling strategies on surface quality and geometric deviations during pocket milling when the perpendicular position of the tool is used. For experimental research, an aluminum alloy, AlCu4Mg, was used. For the production, a three-axis milling machine was used, and consequently, the geometric deviations and roughness parameters of the machined surface were evaluated. Also, the surface texture from each strategy was compared. For the production strategy, the constant Z, circular pocket, constant stepover pocket auto border, and spiral strategies were used. The geometric characteristic evaluation showed the influence of the ball end mill used in the machining process. Constant Z strategy achieved the lowest shape deviations. In the spiral strategy, it was possible to observe an effect of plowing, where the cutting tool crushed the material at the tool center. There was a minimal effect on the surface texture in the circular pocket and constant stepover pocket auto border strategies. Using the constant Z strategy, a non-oriented surface texture was obtained. 3D maps of the extracted residual scallop height for each strategy were observed when examining the surface texture. The roughness parameters Ra and Rz for the circular pocket and constant stepover pocket auto border strategies were the lowest.

Effect of Ball End Cutter Tilt Milling on Path Interval of Blade Surface

Different milling posture of ball-end cutter will alter path interval and affect surface scallop-height, which was an important problem to be considered to enhance the quality and efficiency of blade surface. In view of ball end cutter tilt milling of blade surface, the relation equation between path interval and scallop-height was established by constant scallop-height method, based on the determination of collision boundary and milling sensitivity, the optimal tilt angles and path interval of blade surface milling were solved, moreover, by means of cutting simulation method, the differences between tilt milling and traditional non-tilt milling were compared and analyzed from the perspective of scallop height and processing time, and verified through comparative experiments. The results show that the optimal tilt angles of blade surface milling is 36.9°, when the path interval is fixed, the surface roughness of non-tilt milling and tilt milling are 0.719 µm and 0.561 µm respectively, the surface processing quality of tilt milling is 28.2% higher than that of non-tilt milling, when scallop-height is fixed, the total time of non-tilt milling and tilt milling are 31.21 min and 25.46 min respectively, the machining efficiency of tilt milling is 17.1% higher than that of non-tilt milling. The effectiveness of tilt milling method is verified, which can provide reference basis for high-quality and efficient machining of similar blade surfaces.

A framework from point clouds to workpieces

Combining computer-aided design and computer numerical control (CNC) with global technical connections have become interesting topics in the manufacturing industry. A framework was implemented that includes point clouds to workpieces and consists of a mesh generation from geometric data, optimal surface segmentation for CNC, and tool path planning with a certified scallop height. The latest methods were introduced into the mesh generation with implicit geometric regularization and total generalized variation. Once the mesh model was obtained, a fast and robust optimal surface segmentation method is provided by establishing a weighted graph and searching for the minimum spanning tree of the graph for extraordinary points. This method is easy to implement, and the number of segmented patches can be controlled while preserving the sharp features of the workpiece. Finally, a contour parallel tool-path with a confined scallop height is generated on each patch based on B-spline fitting. Experimental results show that the proposed framework is effective and robust.

Numerical simulation of femtosecond laser ablation of quartz glass and silicon nitride.

The ablation threshold and depth models were established based on the electron density evolution equation of dielectric and ionization theory. The volume model was then deduced, and the models were validated. For quartz glass and silicon nitride, the dependences of the threshold with pulse duration, ablation depth, and volume with fluence were analyzed. Also, the relations of scallop height and scanning velocity were predicted. The results show that the thresholds of quartz glass at durations of 12, 35, and 220 fs were 3.3, 2.9, and 2.3J/cm2, respectively, while the thresholds of silicon nitride at the same durations were 2.0, 1.8, and 1.4J/cm2, respectively. The ablation depth of quartz glass decreased with the increase of duration when the fluence deviated from the threshold. The depth of silicon nitride was opposite to it, and the ablation volume of silicon nitride was larger than that of quartz glass in the same condition. When the scanning velocity and fluence were determined, the scallop height decreased with the increase of duration. However, when the velocity and duration were determined, the scallop height increased with the increase of fluence. The shorter the duration was, the greater the variation of the scallop height.

A novel method to predict surface topography in robotic milling of directional plexiglas considering cutter dynamical displacement

Recently, industrial robots have been applied to the machining of non-metallic materials because of the advantages of low cutting force requirements, low cost, and high flexibility, etc. Due to the limited static/dynamic stiffness of robot joints and links, the accuracy of robotic machining, especially the surface topography, is more susceptible to the cutting forces and dynamic vibrations, compared with CNC machining. To provide clear insights into the formation process of surface topography in robotic machining of oriented Plexiglas and choose reasonably the machining parameters, a method to predict the surface topography in the robotic machining of oriented plexiglas is presented, considering fully the tool dynamic vibrations. In this method, the dynamic intersection behavior in the cutting zones of the robotic machining process is first modeled, which is then used to determine the dynamic displacements. The gained vibration displacements are integrated into the sweep surfaces of the cutter cutting edges by changing the theoretical equations of cutting edges, in order to more accurately calculate the machining scallop points in the presence of tool vibrations. After that, between the discrete sweep surfaces and the workpiece, a mapping-based intersecting method is proposed to compute the intersections with the lowest scallop heights, and these intersections are used to construct the 3D graph, which can represent the topography of the resulting machined surface. Finally, the computer simulation and machining experiments are conducted, and it is shown that the predicted and physically measured surface topography have a good agreement.

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.

Towards understanding and controlling of the surface texture pattern in 5-axis ball-end milling using fast texture simulation

Surface texture is critical for the functionality of industrial parts. This work aims to effectively control the surface texture by applying the phase difference angle between adjacent cutting passes using 5-axis ball-end milling. Because the texture pattern is complicated and is formed by combining feed-interval and step-interval scallops, we propose a level-contour-based fast simulation method to effectively generate the surface texture by inputting the phase difference angle with tilt and lead angles of the cutter. After clarifying the influence of these three parameters on the texture pattern, the desired texture was controlled by modifying the tool path according to the simulated phase difference angle. As a result, the milled surface texture corresponded well with the simulation. The details of the cutting features were efficiently and comprehensively simulated. The mechanism underlying the sudden change in the texture ridge direction was clarified as the major-minor ridge transition when the phase difference angle increased to a certain level, wherein the surface roughness could be decreased because the rearrangement of the cutting region reduced the scallop height. The proposed fast simulation method was also applied to the optimization process with a case study to demonstrate the benefits it can bring to the surface texture design and control.

Elliptical torus cutter tool path generation based on minimum distance computation

In mould manufacture the elliptical torus cutters are used for their high cutting velocity, but the special geometry also brings issues in tool path generating and machining quality controlling. In this paper a guide curve tool path generating method for elliptical torus cutters is presented with the cutter location points computed by a minimum distance algorithm and the path spacing determined by an adaptive method. In the minimum distance algorithm, the calculation is resolved into an iterative process from point to freeform surface and an algebraic calculation process from point to elliptical torus surface considering the geometry of the cutter, which reduces the iterative process and improves the computing speed. In the adaptive path spacing method, the contacting geometry between the elliptical cutter and the workpiece surface is analysed and the relations among the scallop height, the tool tilt angle and the path spacing are deduced, based on which the guide curves are adjusted in advance to control the scallop height. Calculating examples and experiments are carried out, showing that the consuming time of cutter location (CL) points computation algorithm is reduced by 30% comparing to earlier method, and the adaptive path spacing method performs better than constant method in both scallop height controlling and tool path shortening. The results indicate that the presented tool path generating method can help to reduce both the machining and machine waiting time as well as ensuring the machining quality.