A new optimization tool path planning for 3-axis end milling of free-form surfaces based on efficient machining intervals

Five-axis machining of free-form surfaces has one major advantage over three-axis machining, i.e. a greater degree of flexibility in positioning the cutting tool relative to the surface. In five-axis machining of free-form surfaces there are three major phases in creating the tool path: (i) generation of the cutter contact (CC) points; (ii) formation of the cutter location (CL) points that define the path followed by the cutting tool reference point; and (iii) the creation of the specific machine tool part program (G-code file). In this paper, the free-form surface is defined as a triangular polyhedral mesh. The CC-points are created from the surface mesh definition employing a cutting plane technique. Additionally, the CC points are positioned based on an examination of several important factors: geometric constraints derived from the machine tool axis limits, gouging (undercutting) of the free-form surface by the cutting tool and collision of the tool with either the machining stock or machine. The CL points can then be generated along the resulting CC points by consideration of specific machining strategies, such as cusp height and a smooth change in tool posture. The critical issues addressed in this work concern the avoidance of machining problems (machine limit, collision, and gouging) in the tool-path generation phase. Therefore, this technique avoids inefficient five-axis machining practices by automatically creating and verifying a feasible tool-path prior to the actual metal cutting.

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.

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.

The development of CAD/CAM technology has significantly increased efficiency in each individual area. Tool path generation is an important step for the machining of freeform surface. A number of algorithms have been proposed by different researchers for the accurate and efficient tool path generation for the machining of the freeform surface. In this research the study is focus on developed algorithm for generates tool path based freeform features recognition by using the one of the important surface property (Curvature), where has been using the sign of the curvature for recognize the freeform features. The developed algorithm is implemented using multi patches construction of non-uniform B-Spline surface. And the algorithm includes two components, first is the forward-step function that determines the maximum distance between two cutter contact points with a given tolerance. The second components are the side-step function which determines the maximum distance between two adjacent tool paths with a given scallop height. The result of the algorithm (G-Code) is obtained by using MATLAB software and it's simulated and verification by using CIMCO software, where the freeform features has machined severally. The main aim of machining the freeform features severally is avoiding the changing in the machining setup. Hence the CNC milling selects the suitable setup to machine each feature. And therefore, the algorithm has been able to reduce the machining time.

The selection of the right tool path trajectory and the corresponding machining parameters for end milling is a challenge in mold and die industries. Subsequently, the selection of appropriate tool path parameters can reduce overall machining time, improve the surface finish of the workpiece, extend tool life, reduce overall cost, and improve productivity. This work aims to establish the performance of end milling process parameters and the impact of trochoidal toolpath parameters on the surface finish of AISI D3 steel. It especially focuses on the effect of the tool tip nose radius deviation on the surface quality using precision measurement techniques. The experimental design was carried out in a systematic manner using a face-centered central composite design (FCCD) within the framework of response surface methodology (RSM). Twenty different experiment trials were conducted by changing the independent variables, such as cutting speed, feed rate, and trochoidal pitch distance. The main effects and the interactions of these parameters were determined using analysis of variance (ANOVA). The optimal conditions were identified using a multiple objective optimization method based on desirability function analysis (DFA). The developed empirical models showed statistical significance with the best process parameters, which include a feed rate of 0.05 m/tooth, a trochoidal pitch distance of 1.8 mm, and a cutting speed of 78 m/min. Further, as the trochoidal pitch distance increased, variations in the tool tip cutting edge were observed on the machined surface due to peeling off of the coating layer. The flaws on the tool tip, which alter the edge micro-geometry after machining, resulted in up to 33.83% variation in the initial nose radius. Deviations of 4.25% and 5.31% were noted between actual and predicted values of surface roughness and the nose radius, respectively.

This paper studies the development of cutting strategy in the fabrication of freeform surface in ultra-precision raster milling (UPRM). The tasks of developing cutting strategy in freeform machining involve in the selection of cutting parameters and the planning of tool paths. An integrated system is built in this study to develop the cutting strategy, automatically generate NC program, simulate the tool paths and machining process, as well as make predictions for the machining time and the surface quality of the raster milled freeform surface. Experiment is conducted to verify the developed system and the experimental results show that the system is applicable for the machining of freeform surface in UPRM. This study therefore contributes to avoiding the need to conduct expensive and time consuming trial cutting tests to ensure the product quality in the freeform machining.

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.

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

A Practical Approach to Generating Accurate Iso-Cusped Tool Paths for Three-Axis CNC Milling of Sculptured Surface Parts

Partition-based five-axis tool path generation for freeform surface machining using a non-spherical tool

The fabrication of high-quality freeform surfaces is based on ultra-precision diamond turning with fast tool servo (FTS) technology which allows direct machining of the freeform surfaces with sub-micrometric form accuracy and nanometric surface roughness. Surface roughness is an important factor in evaluating the performance of the optical freeform surfaces. This paper presents a theoretical and experimental analysis of surface generation in ultra-precision single-point diamond turning. In this model, we take into consideration the basic machining parameters as well as the relative vibration between the workpiece and the tool in both the cutting and feeding directions. Theoretical model is built to predicting the surface roughness of machined flat surface as well as freeform surfaces. A series of experiments have conducted and the results show good correlation between the theoretical model and the fabricated surfaces.

Shortening total length of tool path is preferred in numerical control (NC) machining since it can reduce machining time effectively. Compared with iso-planar tool path, iso-scallop tool path is shorter in length due to the pursuing of maximum interval values. However, the process of iso-scallop tool path generation is more complicated and time-consuming. To simplify the computing process and improve efficiency, this paper presents an efficient iso-scallop tool path generation method for three-axis scattered point cloud machining. Avoiding offsetting points or fitting surface, scallop points and iso-scallop cutter location (CL) points are directly calculated based on scattered data points by iterative algorithms. In order to reduce the times of iterative calculations, initial scallop-height points and CL points are calculated to be closer to the wanted theoretical points. Only a small number of key data points are searched for use so as to reduce calculation amount, and the number gradually decreases with the increase of iterations. Two typical point clouds are used to test the presented method. The experiment results indicate that the scallop height on the machined surface is uniform, and total length of the generated tool paths is much shorter than that of iso-planar tool paths. Moreover, the computation efficiency is also improved and is higher than our previous method (Int J Adv Manuf Technol 63: 137–146, 2012).

The selection of the optimal tool path strategy and appropriate cutting conditions, especially in the machining aspects of free form surfaces are important to achieve higher productivity. In this work, optimal tool path selection for machining concave surfaces is carried out to achieve minimum surface roughness (Ra), cutting forces and machining time in ball-end milling of aluminium alloy 6061 (Al 6061). Various tool path strategies including 3D offset, raster, concentric, radial zig-zag, zig, and concentric zig-zag are employed. The cutting parameters considered were feed rate, spindle speed and step over. Design of experiments (DoE) along with the statistical analysis of variance (ANOVA) and mean plots are used to determine the significant parameters and their levels for each tool path strategy. Conflicting results were obtained from the ANOVA and the mean plot analyses, to achieve optimum levels that led to lower surface roughness, cutting forces and machining time. It is observed that lower values of surface roughness and cutting forces are obtained with the low level of feed rate and step over in all six tool path strategies. However, high feed rate and step over the lead to decreased machining time. Hence, grey relational analysis is carried out considering multiple performance characteristics such as minimum surface roughness, cutting forces and machining time, and optimal combinations of the milling process parameters for each tool path strategies are identified.KeywordsBall-end millingTool path strategyAluminium alloy 6061Surface roughnessCutting forcesMachining timeGrey relation analysis

An adaptive tool path generation algorithm for precision surface machining

In two-dimensional (2D) free-form contour machining by using a straight (flat) end mill, conventional contour parallel paths offer varying cutting engagement with workpiece, which inevitably causes the variation in cutting loads on the tool, resulting in geometric inaccuracy of the machined workpiece surface. This paper presents an algorithm to generate a new offset tool path, such that the cutting engagement is regulated at a desired level over the finishing path. The key idea of the proposed algorithm is that the semi-finish path, the path prior to the finishing path, is modified such that the workpiece surface generated by the semi-finish path gives the desired engagement angle over the finishing path. The expectation with the proposed algorithm is that by regulating the cutting engagement angle along the tool path trajectory, the cutting force can be controlled at any desirable value, which will potentially reduce variation of tool deflection, thus improving geometric accuracy of machined workpiece. In this study, two case studies for 2D contiguous end milling operations with a straight end mill are shown to demonstrate the capability of the proposed algorithm for tool path modification to regulate the cutting engagement. Machining results obtained in both case studies reveal far reduced variation of cutting force, and thus, the improved geometric accuracy of the machined workpiece contour.