Pocket Machining Research Articles

Spiral tool path generation method for complex pocket machining based on electrostatic field theory

Spiral tool path generation method for complex pocket machining based on electrostatic field theory

Impact of smoothing interpolations on the non-conventional machining of pockets

Smoothing curves have been used in computer aided design software for years. This is the reason why machinists very early wondered about the possibilities of creating toolpaths directly generated from this type of mathematical curves. In addition, in recent research work, we have shown that the non-uniform rational Bspline interpolation is the most favorable towards high-speed machining of complex shapes. As a result, we are thinking of simulating by this type of interpolation the pocket recess machining strategies proposed by a computer aided manufacturing software, currently developed in linear and circular interpolations only. In this article we propose a study of the influence of the parameters of Bspline curves on the hollowing out of pockets by smoothing initial cutting methods. To do this, we chose the smoothing of the zigzag method by Bspline and NURBS while varying the order and the discretization parameters to know the impact on the dynamics of the high-speed machining mechanism and on the non-conventional machining precision. This work has shown that parametric curves are favored for this type of machining provided that this tool is mastered.

A Study of Machining Characteristics during Continuous Machining of Circular Pockets Using A6061-T651 High-Speed Steel-Conducting Coated End Mill Tools

A Study of Machining Characteristics during Continuous Machining of Circular Pockets Using A6061-T651 High-Speed Steel-Conducting Coated End Mill Tools

Determination of the Feasibility of Using Eco-Friendly Walnut Shell Abrasive Particles for Pocket Milling of Titanium Workpieces by Abrasive Waterjet Technology

Abrasive waterjet technology is nowadays a well established non-conventional method with significant capabilities for material removal with high productivity and minimum environmental impact compared to other processes. However, in order to be in line with the green transition directives, further steps are required to ensure the sustainability of manufacturing processes and reduce the risk of material depletion by employing recyclable materials. For this purpose, an eco-friendly abrasive material such as walnut shell is employed for pocket machining of a titanium alloy workpiece. Due to the relatively low hardness of this material, compared to common abrasive materials such as garnet or alumina, it is required to determine the appropriate range of process parameters in order to obtain high-quality pockets with high productivity. Thus, in this work, a comprehensive experimental study is conducted in order to determine the effect of various process parameters on pocket depth, pocket width, material removal rate, flatness and parallelism error of produced pockets. The results prove the feasibility of using walnut shell as abrasive material for pocket milling, although MRR is almost an order of magnitude lower than the values commonly obtained for usual abrasives. Moreover, it is not recommended to use jet pressure values over 250 MPa so dimensional accuracy, flatness and parallelism error are maintained in acceptable values.

Stability analysis of pocket machining with the spiral tool path using the discontinuous Galerkin method

Pocket machining is widely used in the aerospace and automotive industries. The spiral tool path ensures smooth and consistent pocket machining. However, high-efficiency pocket machining places great demand for the stability of the milling processes. In this paper, the mechanics and dynamics of pocket machining along the spiral tool path are modeled, and a time-domain method is proposed to predict the stability of pocket machining in the framework of the discontinuous Galerkin method (DGM). The mechanics of pocket machining is modeled on the basis of computing the varying cutter-workpiece engagement. The cutting forces are predicted and experimentally verified. Further, the dynamic model of pocket machining is established and the stability of the pocket machining process is predicted with the stability lobes of representative feed directions along the spiral tool path. The DGM based time-domain method is proposed to improve the computational accuracy and efficiency of the stability analysis. The predicted stability of pocket machining along the spiral tool path is validated by the experimental results.

Novel Tool Path Generation Method for Pocket Machining Using Sound Field Synthesis Theory

Contour parallel tool paths have been proved to be a preferred machining strategy for their advantage of less tool retractions and less sharp turns. The traditional geometrical algorithm-based tool path generation method often makes it hard to simply and simultaneously solve the problems of self-intersection, no residual, and smoothness at the same time due to their contradictions. To address this issue, a contoured parallel tool path generation method for pocket machining is developed in this study. It is based on sound field synthesis theory inspired by the phenomenon of sound wave propagation. Firstly, the simplified medial axis (SMA) tree of the pocket is extracted and the propagation direction of each SMA segment is calculated on account of the geometric characteristics of the pocket boundary. Secondly, the final tool path is obtained through the synthesis of the sound field. Finally, the novel method is verified on five different pockets to generate a contoured parallel milling tool path. After machining these pockets and measuring the machining time, roughness, and cutting force, the experimental results demonstrate that the tool path obtained by the novel method has advantages in improving machining quality and efficiency.

A double-NURBS approach to the generation of trochoidal tool path

Trochoidal milling becomes a popular strategy in high-speed rough milling, thanks to its advantages in lowering cutting force (and tool wear) and increasing tool life. However, it also suffers from the disadvantages of low cutting efficiency and prolonged machining time due to its reduced cutter-workpiece engagement in the cutting area and the idle tool path in the non-cutting area. In this paper, a new trochoidal tool path generation method is proposed based on a double-NURBS curve. Unlike traditional circular trochoidal tool path that combines circular and linear paths to approximate the trochoidal path, the double-NURBS tool path can truly represent a trochoidal path with C2 continuity throughout the entire tool path. In the front cutting area, the control points of the NURBS are modified to increase the cutter-workpiece engagement angles; in the rear non-active area, the NURBS curve is modified to shorten the non-cutting distance and the machining time. Degree elevation of the NURBS circle from 2 to 3 maintains C2 continuity to ensure the machining is smooth throughout all transitions. Cutting force simulations and pocket machining experiments are carried out to validate that the proposed double-NURBS approach deliver the expected result and performance.

Обратная задача циклографического моделирования пространственной кривой

The objective of the present study is to justify the possibility of constructive and analytic solution to the inverse problem of cyclographic modeling of a curve of space R3 and development of a respective algorithm. The orthogonal projection and the two components of the cyclographic projection of a spatial curve form a triad of elements in plane z=0. These elements are the result of the direct problem solution and constitute the basis for the inverse problem solution. The direct problem consists in construction in plane z=0 of a cyclographic projection (a model) of a given spatial curve, while the inverse problem consists in determination of a spatial curve given its cyclographic projection. Insufficient knowledge on the inverse problem as well as its relevance in practical applications, e.g. in cutting tool trajectory calculation for pocket machining of mechanical engineering products on NC units, make urgent the definition and the solution of the inverse problem. In the present paper a simple convex closed curve is considered as the given cyclographic projection. It is proven that there exists a unique spatial curve, for which the given curve constitutes a cyclographic projection. The algorithm for the inverse problem solution is demonstrated on examples.

Error modelling\u2013based machining sequence optimization of a pocketed beam milling: part A, end supported beam

This paper, on the basis of error modelling, proved the optimal pocket machining sequences of a simply end supported pocketed beam using mathematic induction method. The optimal pocket machining sequence with the minimum pocket floor height error is the machining from both ends to the middle and the optimal sequence is not unique because of the symmetric supports about the central plane; meanwhile, the optimal pocket machining sequence with the minimum wall position error is the machining from the fixed end to the free end and the optimal machining sequence is unique. A beam of Al7075 (744 mm in length, 172 mm in width, and 100 in thickness ) with 9 pockets was used to demonstrate the optimal sequences. One of the optimal sequence with minimum floor height error was used in pocketing (roughing), and the maximum distortion was 0.693 mm in the middle and the maximum floor height error appeared on both sides rather than the middle, which were 0.477 mm and 0.388 mm, and part growth produced maximum wall position error was 0.719 mm. On the same part, further demonstrated the optimal sequence with minimum wall position error in finishing (with 1 mm dimension in stock for all surfaces) and the wall position errors were fully removed. The pocketed beam machining is a typical and representative case and the results and conclusion can be extended to pocketed plate/board machining and even surfacing.

On smoothness of connection of spatial curve cyclographic projection segments

The correlation between smoothness of connection of segments of a spatial curve and the respective cyclographic projection is considered. The sufficient condition for smoothness at the point of connection of segments of cyclographic projection of a spatial curve described by a polynomial spline of order k +1 is formulated and verified. It has been demonstrated that despite the derivative of order k +1 of the spline function describing the spatial composite curve along with all the higher-order derivatives not being continuous, it is possible to connect segments of the cyclographic projection with smoothness , where r = k + i, i = 0,1,2,…. Achieving smoothness , through the formulated condition of sufficiency is demonstrated on numeric examples. The obtained results of the study can serve as the basis of development of effective algorithms of cyclographic formation of geometric objects applied in geometric optics, road surface form design, and optimal cutting tool trajectory design in pocket machining.

Optimal selection of milling cutting tools for machining of triangular pockets

Minimizing machining time is an objective that must be taken into account when choosing the cutting tool. The diameter of the cutting tool is one of the parameters which greatly influences the machining time of different geometric shapes, especially pockets. In this study, a methodology for optimizing the choice of milling cutting tools for machining triangular pockets was proposed. An analytical model expressing the length of cutting tool paths has been optimized using sequential quadratic programming. the study carried out in this work leads to the conclusion that the spiral contour strategy makes it possible to have a minimum length for the machining of triangular shaped pockets.

Quasi-Optimal Tool Trajectories for High Speed 2.5D Process Based on Morphological Transformation

2.5D processes are ubiquitous in pocket machining of structural parts as well as layer based additive manufacturing. Modern manufacturing systems are mostly integrated with high-speed motion capacity, which conventionally generated tool path cannot fully exploit due to large path stepover variation and sharp turnings at degenerated corners. Advanced geometric approaches strived to increase the local smoothness of the trajectory without taking care of the stepover variation, which could cause uneven material deposition in layered additive process and excessive load impact in cutting process. To liberate the high-speed capacity in 2.5D process, we developed a brand new scheme for tool trajectory planning, by taking advantage of image morphology. A morphological transformation of the target 2D shape, termed medial core, is defined and identified in this paper, which serves crucially to generate stepover constrained tool paths. The utilization of medial core facilitates a parameterization of the 2D shape, where qualified iso-curves can be easily propagated to satisfy in the high speed context. By comparing with other state-of-the-art tool path generation methods, our method outperformed in both additive process and cutting process, with noticeably reduced processing time, better surface quality in additive process and stabilized milling force in pocket cutting process.

A Universal Pocket Plunge Milling Method to Decrease the Maximum Engagement Angle

Abstract Plunge milling has been proven to be an efficient strategy for machining of pockets with deep cavities and difficult-to-cut material. Previous work generates the plunge toolpath mainly by controlling the radial cutting width within the given value. However, uneven tool engagement angles may lead to excessive tool load and tool load fluctuations, which has a negative influence on tool life. In this study, a universal plunge milling toolpath generation method is proposed to improve tool life by decreasing the maximum tool engagement angle. A series of concentric circles with constant radius increment is utilized to generate a toolpath with constant cutting radial depth. Center of the concentric circle is determined based on the pocket contour. New detailed algorithms to generate plunge toolpath for basic cases have been developed. An automatic pocket subdivision algorithm has been developed by dividing the pocket into several subregions that are easy to be machined. Without loss of generality, the method is applicable for both open and closed pockets. It also works for pockets with and without islands inside. The method is implemented and verified successfully by machining experiments. The results provide strong evidence that the proposed method can reduce the maximum engagement angle over the entire toolpath and thus improve the tool life.

Analysis and trimming operations in the problem of spatial formation of a family of offset curves given an area with islands

In the present paper an algorithm of determination and trimming of non-working segments of offset curves generated for an area and a number of islands within it is considered. The algorithm is based on cyclographic method of spatial formation of offset curves given curvilinear boundary contours of an area and islands within it. Methods of analysis and corresponding algorithms of trimming of non-working segments of offset curves are considered for the cases of self-intersection of offset curves. The analysis and trimming operations form the basis of the proposed algorithm of spatial formation of offset curves. The calculations that accompany every stage of formation process are exact and not based on iteration algorithms. The acquired analytical solution to the problem of generation of a family of offset curves significantly facilitates cutting tool trajectory calculation and control programming in pocket machining on NC units.

Spiral toolpath generation method for pocket machining

Spiral toolpath plays a significant role in 2.5D pocket machining with the advantages of free of sharp corners and without unwanted un-cutting materials. Technically, efficiency of pocket machining toolpath is determined by its smoothness and total length. Most of existing spiral toolpath generation methods pay more attention on acquiring a smooth toolpath without tool retractions, lacking consideration of total length minimization. In this work, an improved spiral toolpath generation method based on medial axis (MA) transformation is developed to decrease the total length of toolpath, so as to improve the machining performance. The proposed method can be applied to pockets with arbitrary geometries. To avoid unwanted interference between cutting tool and pocket boundary, cutting tool accessibility analysis is firstly conducted. MA sub-cycle for each layer is acquired by trimming the original MA of the pocket. Toolpath of each layer is determined by the envelope curve of a set of disks with various diameters that located on its MA sub-cycle. Toolpath between adjacent layers is guaranteed to be free of intersections. The spiral toolpath is generated by connecting the isolated toolpaths of all layers based on partially linear morphing. Then a toolpath modification algorithm is developed to smooth the spiral toolpath around root node of pocket MA. Finally, machining experiment is conducted to validate the advantages of the proposed method on machining efficiency improvement.

A Study on Dimensional Accuracy in Circular Pocket Machining of SCM415 Steel

A Study on Dimensional Accuracy in Circular Pocket Machining of SCM415 Steel

A Study on the Squareness of Circular Pocket Machining of SCM415 Steel

A Study on the Squareness of Circular Pocket Machining of SCM415 Steel

A Study on Surface Roughness in Circular Pocket Machining of SCM415 Steel

A Study on Surface Roughness in Circular Pocket Machining of SCM415 Steel

Development of Direction-Parallel Strategy for Shorting A Tool Path in The Triangular Pocket Machining

The machining strategy is one of the parameters which practically influences the time of the different manufacturing geometric forms. The machining time directly relates to the machining efficiency of the tool paths. In area milling machining, there are two main types of tool path strategies: a direction-parallel milling and contour-parallel milling. Then direction-parallel milling is simple compared with a contour-parallel strategy. This paper proposes a new model of the direction-parallel machining strategy for triangular pockets to reduce the tool path length. The authors develop an analytical model by appending additional the tool path segments to the basis tool path for cutting un-machined area or scallops, which remained along the boundary. To validate its results, the researchers have compared them to the existing model found in the literature. For illustrating the computation of this model, the study includes two numerical examples. The results show that the proposed analytic direction-parallel model can reduce the total length of machining. Thus, it can take a shorter time for milling machining.

Use of a virtual milling system to generate power-aware tool paths for 2.5-dimensional pocket machining

Traditional (direction-parallel and contour-parallel) and non-traditional (trochoidal) tool paths are generated by specialized geometric algorithms based on the pocket shape and various parameters. However, the tool paths generated with those methods do not usually consider the required machining power. In this work, a method for generating power-aware tool paths is presented, which uses the power consumption estimation for the calculation of the tool path. A virtual milling system was developed to integrate with the tool path generation algorithm in order to obtain tool paths with precise power requirement control. The virtual milling system and the tests used to calibrate it are described within this article, as well as the proposed tool path generation algorithm. Results from machining a test pocket are presented, including the real and the estimated power requirements. Those results were compared with a contour-parallel tool path strategy, which has a shorter machining time but has higher in-process power consumption.