Freeform surfaces, also called sculptured surfaces, have been widely used in various engineering applications. Freeform surfaces are primarily manufactured by CNC machining, especially 5-axis CNC machining. Various methodologies and computer tools have been developed in the past to improve efficiency and quality of freeform surface machining. This paper aims at providing a state-of-the-art review on recent research development in CNC machining of freeform surfaces. This review primarily focuses on three aspects in freeform surface machining: tool path generation, tool orientation identification, and tool geometry selection. For each aspect, first concepts, requirements and fundamental research methods are briefly introduced. The major research methodologies developed in the past decade in each aspect are presented with details. Problems and future research directions are also discussed.

Review: Recent development in CNC machining of freeform surfaces: A state-of-the-art review

The iso-planar (Cartesian) tool path generation method has been used for several decades. However, it suffers an inherent drawback: in the region where the direction of the surface normal is close to that of the parallel intersecting planes, the intersecting plane intervals have to be reduced because of the influence of surface slopes. This causes redundant tool paths in the associated flatter regions and results in lower machining efficiency. This paper presents an algorithm that overcomes the disadvantage of the iso-planar method while keeping its advantages of robustness and simplicity. In this algorithm, the concept of isophote is applied to partition the surface into different regions. In each region the tool path side steps are adaptive to the surface features. Therefore redundant tool paths are avoided. By applying the region-by-region or global-local machining strategy, the machining efficiency is increased.

Adaptive iso-planar tool path generation for machining of free-form surfaces

The effects of cutter path strategies on surface roughness of pocket milling of 1.2738 steel based on Taguchi method

The aim of this paper is to propose a pocketing tool path improvement method by adapting the geometry of the tool path to the kinematic performance of high speed machining machine tools. The minimization of the machining time is a major objective, which should be taken into account for the tool path computation. In this way the tool path length can be reduced or the real feedrate increased. The described method proposes modification of the values of the corner radii in order to increase real feedrate. In the same way, this method checks the radial depth of cut variations along the tool path. The computed tool path presents a smaller length and the machine tool produces a higher average feedrate at the same time. In addition, the use of Bspline for the tool path computation is a significant improvement compared with straight lines and circle arcs for the machining time reduction. Several tests are realized on various machine tools in order to quantify the benefits: the proposed method can reduce the machining time by approximately 25% compared with classical tool paths computed using a CAM system.

Corner optimization for pocket machining

This article proposes a new method of 2D curve interpolation using non-uniform cubic B-splines particularly adapted to the interpolation of sequences of straight lines and circle arcs. The purpose of this method is to calculate C2 continuous curves adapted to high feedrate pocket machining. Industrially machined pockets usually present simple forms. Generally, the tool path is defined by circle arcs and line segments that introduce slowdowns during machining. Thus, a method for approximating a sequence of line segments and circle arcs using Bspline curves is proposed. The proposed method ensures exact line interpolation, to approach the tool path precisely, to reduce the number of control points and to avoid thickening and oscillation at the connections between line segments and circle arcs. Various applications are presented and numerous tests on machine tools allow the advantages of this method to be illustrated.

Bspline approximation of circle arc and straight line for pocket machining

Automatic CNC milling of pockets: geometric and technological issues

Offsetting 3D contours on parametric surfaces is used in various design and manufacturing purposes such as shrinking and expanding trimmed surfaces, tolerancing and NC machining. The approach presented in this paper is coordinate-reference independent and allows the iterative calculation of interference-free 3D offset contours. The main elements in this approach are the iterative offset of parametric segments, their trimming and connection, and the handling of loops. The preliminary offsetting is achieved in the Cartesian domain associated with the surface. The interferences are then handled in parametric space.

Offsetting 3D Contours on Parametric Surfaces

In practical surface design, most of the surfaces are trimmed surfaces resulting from Boolean manipulations. Avoiding damage to adjacent surfaces in the generation of tool paths for their machining is a fundamental problem. This paper presents an efficient method for representing and generating tool paths for the NC machining of trimmed surfaces considering this constraint. After 3D offsetting of surface contours, the method derives suitable tool paths from 2D pocket filling and then maps them onto the surface space either as isoparametric or iso-scallop patterns. As the method can deal efficiently with degenerate surfaces, it can be considered as a tool for CAM software integration.

NC Machining of Trimmed Surfaces Maintaining Adjacent-Surfaces Integrity

Rolling ball blending techniques are widely used for rounding edges and corners of mechanical parts in computer aided design. The techniques of computing trim curves for blending are used in this paper to delimit the domains of machinability of parametric surfaces. Whereas the principle of the rolling ball can be used for machining single or compound surfaces, the focus here is only on compound surfaces. A survey of existing methods is given followed by an application for a new approach for the generation of flow line tool paths.

Surface blending for machining purposes: A brief survey and application for machining compound surfaces

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Papers

Automatic CNC milling of pockets: geometric and technological issues

Offsetting 3D Contours on Parametric Surfaces

NC Machining of Trimmed Surfaces Maintaining Adjacent-Surfaces Integrity

Surface blending for machining purposes: A brief survey and application for machining compound surfaces