Random adaptive tool path for zonal optics fabrication.

Deterministic optics fabrication using sub-aperture tools has been vital for manufacturing precision optical surfaces, industrial robotic polishing, which is a more economical and intelligent method is required in modern fabrication process. However, the challenge of robotic polishing lies in the widely used spiral and raster paths, which may leave excess waviness from the tool path, and the unavoidable constant removal layer is added to obtain positive dwell time which cause low polishing accuracy. The waviness can be removed by either using smoothing tools sequentially or randomizing the tool path. However, process efficiency and accuracy are not well considered in the existing tool-path planning. A density adaptive path based on a stacked rotation convolution model to ensure polishing accuracy and efficiency while avoiding waviness generation is proposed in this study, and then the dwell time is calculated by anti-aliasing space-variant deconvolution. The robotic polisher experimental results confirm that the root mean square (RMS) of the final surface figure has been successfully reduced and stabilized at 7.355 nm, and the convergence effect at unit wavelength has been significantly augmented with an improvement of 367%, reducing the measurement from 28% to 131%; in addition, no obvious mid-spatial frequency (MSF) peak was generated in the PSD analysis of density adaptive path polishing results. Henceforth, the polishing accuracy, efficiency, and MSF error of robotic polishing can be greatly enhanced.

By analysis of the validity of tool path, tool path planning is divided into two processes, the choice of curves on surface and the design of effective and rational path arrangement. On this basis, a spiral topology toolpath for continuous cutfing is developed in order to reduce the number of interruptions and rapid traversals during high-speed machining (HSM) process. Based on the isoparametric toolpath, the contour-parallel isoparametric path is firstly created, and then a spiral path is generated as a kind of diagonal curve between the isoparametric offset curves. Experimental results demonstrate that the proposed method is straightforward and avoids the self-intersection of the toolpath, especially suitable for HSM.

Analysis and development of elliptical tool path in trochoidal milling

Tool path generation is an important task in end milling. In the existing literature, the tool path pattern/style is determined based on geometric analysis. However, there is little analysis from the viewpoint of machining dynamics/cutting force, which is more related to the final manufacturing performance. Although there are many types of tool paths (e.g., zigzag, spiral, and ISO-scallop tool path), they can be decomposed into a number of circular tool paths with various path radii and cutting angles. Firstly, by investigating chip formation mechanism, the effect of tool path radius on uncut chip thickness is obtained. Analysis shows that tool path radius has a significant influence on uncut chip thickness, thus affecting the cutting force, especially when the tool path radius is small. Then, the effect of cutting angle on cutting force distribution is analyzed. It is found that the feed direction could vary the distribution of cutting force in X and Y direction in 3-axis end milling. Based on such analysis, the cutting force prediction model considering tool path effect is established. To validate the proposed model, various experiments have been carried out based on well-designed tool paths. The comparative results show that (1) tool path has great effect on cutting force through the tool path radius, rotation direction, and start/end point, and (2) the proposed model is capable of providing accurate cutting force prediction considering tool path effect. From a physical viewpoint, the proposed method provides huge potential in automated/intelligent tool path optimization towards better surface quality via minimizing cutting force, which significantly contributes to the state of the art in tool path generation.

ABSTRACTWhile 5-axis CNC machines improve the manufacturing productivity, the tool-path programming demands human expertise and tremendous time investment to generate collision-free optimal tool trajectories. To address the challenge of multi-axis CNC programming, this work presents a new discrete volume based geometry representation that naturally enables highly parallel geometry processing. Then it formulates and discusses a methodology for tool path planning algorithms designed around the formulated geometric representation for 5-axis CNC milling machines and ball end tools. This paper is the first of two papers that deals with finding the XYZ locations of ball end mill centers that govern the tool trajectories. The experimental 5-axis machining using the resulting tool paths demonstrates that the designed algorithms are capable of producing collision- and gouge- free tool paths with a desired surface quality for a given target geometry by using the selected ball end tools.

A realtime curvature-smooth interpolation scheme and motion planning for CNC machining of short line segments

Tool path generation is a fundamental problem in 5-axis CNC machining, which consists of tool orientation planning and cutter-contact (CC) point planning. The planning strategy highly depends on the type of tool cutters. For ball-end cutters, the tool orientation and CC point location can be planned separately; while for flat end cutters, the two are highly dependent on each other. This paper generates a smooth tool path of workpiece surfaces for flat end mills from two stages: Computing smooth tool orientations on the surface without gouging and collisions and then designing the CC point path. By solving the tool posture optimization problem the authors achieve both the path smoothness and the machining efficiency. Experimental results are provided to show the effectiveness of the method.

Spiral tool path optimization method for fast/slow tool servo-assisted diamond turning of freeform surfaces with highly form accuracy

Difficult-to-machine material thin-walled parts with curved surface are widely used in industrial applications, and the shape accuracy is a basic requirement for ensuring the usability. Due to the low rigidity of the thin-walled curved surface parts, the cutting force becomes a sensitive factor for the machining deformation. In addition, high speed milling, that has an obvious attribute of small cutting force comparing with the traditional one, provides an effective way to process the thin-walled curved surface parts made by difficult-to-machine materials like titanium alloy. Moreover, the rigidity of the thin-walled curved surface parts is constantly changing along with the machining process, which leads to a more complex machining deformation when choosing different tool paths and affects the machining quality. To reduce the machining deformation, a proper cutting parameters combination which influences the machining deformation directly is obtained based on the established cutting force model, and then a deformation control strategy by planning tool path is put forward. At the same time, an efficient compensation method based on modifying cutter location point is proposed. Taking TC4 thin-walled arc-shaped parts as an example, experimental studies indicate that the largest deformation values reduce to 49 μm after compensation. Compared with the former 104 μm, the deformation degree decreases by 52.88 % when the thickness of the thin wall is 200 μm. The research provides an effective approach to reduce the machining deformation induced error for difficult-to-machine material thin-walled parts with curved surface.

The direction of the end-effector is fixed in most of industrial robot applications, such as grinding, welding and spraying. The sixth axis of 6R industrial robot is the redundant freedom for these applications. This paper uses the redundant freedom to make orientation planning. In addition, most of time tool paths for these applications may be composed of some short and complex curves. It is difficult and time-consuming for online teaching method to make tool path planning. Therefore, an off-line programming(OLP) method was adopt to solve these problems in this paper. The path planning strategy and the orientation planning strategy were proposed and applied into the OLP system to generate the tool path automatically for these applications.

The present contribution focuses on finishing operations in machining. Finishing operations belong to the most time-consuming and surface quality-critical machining tasks. High-quality tools are available nowadays for choosing optimal tool paths for finishing. Yet, the finishing options for general shaped surfaces are still severely limited. Although CAM systems can efficiently generate tool paths, none of them offers the combination of finishing tool paths, modern productive methods and adaptive tool paths. Increasing the productivity while maintaining dimensional accuracy and the quality of finished surfaces is the key point in finishing. One of the ways to improving productivity is the use of constant cutting speed. The aim of this article is to present experimental verification of these assumptions and demonstrate the impact on the quality of the finished surface

Cube-machining test is a possible method for evaluating the accuracy of five-axis machining centers. Although the geometric errors of rotary axes can be evaluated by measuring the height and inclination errors of the machined surfaces, other error sources, such as tool length and profile errors, influence the machining accuracy. Clarifying the factors that influence the machined result is necessary to correctly evaluate the machine tool accuracy based on the cube-machining test results. In this study, the effect of tool path and Z-axis reversal error motion on the cube-machining test accuracy was investigated. Actual machining tests were conducted with three types of the reversal error conditions of Z-axis. The Z-axis reversal error directly affected the results owing to different Z-axis motions for each surface of the workpiece. Based on the investigation, for the machining, a tool path pattern, which can reduce the influence of the Z-axis reversal errors by restricting the motion direction changes of Z-axis for all surfaces, was proposed. According to the Z-axis reversal error test results, the surfaces machined using the proposed tool path were not affected by the reversal error.

Diamond turning based on a fast tool servo (FTS) is widely used in freeform optics fabrication due to its high accuracy and machining efficiency. As a new trend, recently developed high-frequency and long-stroke FTS units are independently driven by a separate control system from the machine tool controller. However, the tool path generation strategy for the independently controlled FTS is far from complete. This study aims to establish methods for optimizing tool path for the independent control FTS to reduce form errors in a single step of machining. Different from the conventional integrated FTS control system, where control points are distributed in a spiral pattern, in this study, the tool path for the independent FTS controller is generated by the ring method and the mesh method, respectively. The machined surface profile is predicted by simulation and the parameters for the control point generation are optimized by minimizing the deviation between the predicted and the designed surfaces. To demonstrate the feasibility of the proposed tool path generation strategies, cutting tests of a two-dimensional sinewave and a micro-lens array were conducted and the results were compared. As a result, after tool path optimization, the peak-to-valley form error of the machined surface was reduced from 429 nm to 56 nm for the two-dimensional sinewave by using the ring method, and from 191 nm to 103 nm for the micro-lens array by using the mesh method, respectively.

When machining thin-walled workpieces like turbine blades, the parts are prone to be bent by the cutting forces due to its low rigidity. The workpiece deflection during the machining process of the thin-walled workpiece is a critical issue that is likely to jeopardize the finish surface quality. Traditionally, in order to control the machining error caused by deflections, conservative machining parameters are adopted as constants for each cutter locations which are determined by simply taking the weakest spot as the reference. As the residual thickness left on the thin-walled part surface usually cannot be removed with a single cut, multi-pass machining is necessary to be used by removing the residual thickness with several rounds of cuts. For a given thin-walled workpiece, the primary objective in this thesis research is to develop optimized process planning strategies for five-axis machining including both end milling and flank milling aiming at improving the machining time efficiency to educe the total machining time while maintaining the acceptable machining errors. For five-axis end milling, the optimization process to achieve this goal is divided into two parts. Firstly, the optimization of machining parameters for thin-walled workpiece is accomplished by a novel variable depth-of-cut machining strategy for semi-finish and finish machining based on the workpiece deflection constraints. It strives to maximize the depth-of-cut locally for each cutter contact (CC) point while respecting a calibrated threshold of the normal cutting force 𝐹<sub>𝑛</sub> which is the major cause of the workpiece deflection. The maximum allowed depth-of-cut 𝑑<sub>𝑚𝑎𝑥</sub> of each CC point is determined adaptively according to the calibrated maximum allowed 𝐹<sub>𝑛</sub> of the thin-walled workpiece. The multi-pass semi-finishing tool path is generated by offsetting the finishing tool path with the computed variable depth-of-cut. Next, we integrate the optimization of finishing tool path and machining parameters together to further improve the machining efficiency of the multi-pass machining for the thin-walled workpiece. A five-axis tool path generation method is developed to automatically generate a finishing tool path that reduces the total machining time of the multi-pass tool path expanded from the generated finishing tool path for an arbitrary thin-walled workpiece. A cutting area potential field on the given part surface of a thin-walled workpiece is first established to indicate the principle feed direction for any point on the part surface. Based on this field, the finishing tool path is planned through the iso-scallop height tool path expansion scheme. For the flank milling of thin-walled workpieces, a new multi-pass adaptive machining parameters optimization method for flank milling of thin-walled workpiece is developed that generates the multi-pass tool path from an input finishing tool path, with the optimized radial depth-of-cut and feedrate assigned to each cutter location. Both radial depth-of-cut and feedrate are simultaneously optimized by solving a minimization problem formulated based on the cutting force model subject to the deflection constraints and machine’s kinematical constraints. Finally, computer simulations and physical cutting experiments are reported to clarify the improvements achieved in machining efficiency by the proposed strategies.

Off-axis aspheric surface is an indispensable optical device for the high precision measurement and manufacturing equipment, and the tool path generation is a very important factor for the manufacturing to obtain the surface with high precision form and nanometric surface finish. In this paper, the systemic description of tool path generation method about the off-axis parabolic surface with ultra-precision single point diamond turning is processed. Two effective methods of generating the accurate spiral tool path are proposed and compared. The proposed methods are mainly based on mathematical calculation directly from analytic surfaces, including the general process of tool path generation, cutting-tool compensation and avoiding tool interference. This work can provide the theoretical basis of choosing the cutting tool path for off-axis parabolic surface and can improve the efficiency and precision of machine. Finally, some cutting simulations are implemented to prove the proposed methods.