Claire Lartigue

A new format for 5-axis tool path computation, using Bspline curves

Abstract This article presents a new format of tool path polynomial interpolation in 5-axis machining. The linear interpolation usually used produces tangency discontinuities along the tool path, sources of decelerations of the machine tool whereas polynomial interpolation reduces the appearance of such discontinuities. The new format involves a faster tool path and a better surface quality. However, it imposes a modification of the process so as to take the interpolation format and the inverse kinematics transformation (necessary to 5-axis machining) into account. This article deals with the geometrical problem of tool path calculation. Validation tests are detailed. They show that profits concern the reduction of machining time as well as the quality of the machined surfaces. Indeed, the trajectory continuity avoids the appearance of marks and facets.

Tool path deformation in 5-axis flank milling using envelope surface

This paper deals with assessment and correction of tool path in 5-axis machining. The tool trajectory is described using two curves; each one corresponding to the trajectory of two particular points of the tool axis. The assessment of the tool path is performed via the calculation of the envelope surface, which is calculated using a kinematics approach. The geometrical deviations between the envelope surface and the nominal surface are calculated. When necessary, the tool path is corrected, so that the envelope surface fits the ideal surface as much as possible. This correction is carried out by the deformation of both curves that are representative of the tool trajectory. We choose to illustrate our purpose through flank milling of sculptured surfaces.

CNC tool path in terms of B-spline curves

Abstract We present an accurate and efficient method to generate a CNC tool path for a smooth free-form surface in terms of planar cubic B-spline curves which will be fed into a free-form curve interpolator. We assume the use of a three-axis CNC machine tool with a ball end-mill cutter. We first interpolate break points, which are generated by computing the offset surface – driving plane intersection curve reflecting the curvature, by a planar cubic B-spline curve. We then evaluate the maximum scallop height along a scallop curve by computing the stationary points of the distance function between the scallop curve and the design surface. Furthermore, we compute the maximum pick feed such that the maximum scallop height along a scallop curve coincides with the prescribed tolerance. Illustrative examples show the substantial improvements this method achieves over conventional methods where the tool path consists of linear or circular paths.

Optimization of 5-axis high-speed machining using a surface based approach

This paper deals with optimization of 5-axis trajectories in the context of high-speed machining. The objective is to generate tool paths suited to high speed follow-up during machining in order to respect cutting conditions, while ensuring the geometrical conformity of the machined part. For this purpose, the optimization of the tool axis orientations is performed using a surface model for the tool path, which allows integrating kinematical limits of the machine tool as well as classical geometrical constraints. The illustration of the optimization through an example highlights the gain in machining time, thereby demonstrating the feasibility of such an approach.

Scale Space Meshing of Raw Data Point Sets

This paper develops a scale space strategy for orienting and meshing exactly and completely a raw point set. The scale space is based on the intrinsic heat equation, also called mean curvature motion (MCM). A simple iterative scheme implementing MCM directly on the raw point set is described, and a mathematical proof of its consistency with MCM is given. Points evolved by this MCM implementation can be trivially backtracked to their initial raw position. Therefore, both the orientation and mesh of the data point set obtained at a smooth scale can be transported back on the original. The gain in visual accuracy is demonstrated on archaeological objects by comparison with several state of the art meshing methods.

High-Performance NC for HSM by means of Polynomial Trajectories

This paper summarises works carried out for defining tool trajectory formats well adapted to High Speed Machining (HSM). Advantages in using native polynomial formats, calculated directly from the CAD model, are highlighted. In particular, polynomial surface formats are presented as a generic format for tool trajectory. Illustrations show that surface formats represent a good compromise between smoothness machining time, and surface quality.

Digitised point quality in relation with point exploitation

This paper deals with the quality of digitised points obtained with noncontact probes. The digitising system is analysed so that each source of inaccuracy can be isolated. In particular, for systems such as triangulation laser sensors, the use of the CCD camera is not influence free, and generates nonhomogeneous errors. All sources of inaccuracy of the digitising system lead to a point cloud, the quality of which is described through indicators. These indicators correspond to the digitising noise and the density of the data. In addition to those usual indicators, we suggest qualifying the point cloud through completeness and accuracy. The completeness identifies the dimension of the digitising gaps, while the accuracy is associated with the measurement uncertainty of a 3D point. For each indicator, an evaluation method is presented and then applied. However, the use of those quality indicators only makes sense if they are related to the point exploitation.

Characterization of 3D surface topography in 5-axis milling

Within the context of 5-axis free-form machining, CAM software offers various modes of tool-path generation, depending on the geometry of the surface to be machined. Therefore, as the manufactured surface quality results from the choice of the machining strategy and machining parameters, the prediction of surface roughness in function of the machining conditions is an important issue in 5-axis machining. The objective of this paper is to propose a simulation model of material removal in 5- axis based on the N-buffer method and integrating the Inverse Kinematics Transformation. The tooth track is linked to the velocity giving the surface topography resulting from actual machining conditions. The model is assessed thanks to a series of sweeping over planes according to various tool axis orientations and cutting conditions. 3D surface topography analyses are performed through the new 3D roughness parameters proposed by recent standards.

A New Concept for the Design and the Manufacturing of Free-Form Surfaces: The Machining Surface

Abstract This paper deals with a modeling method of free-form surfaces based on the new concept of the machining surface. The machining surface is built so that design intents and manufacturing requirements are ensured and so that it completely defines the tool movement necessary to produce a part. Therefore, approximations appearing during the elaboration process (CAD modeling, tool path calculation and free-form machining) are minimized. The concept of the machining surface described here relies on an analysis of the process quality.

Scan planning strategy for a general digitized surface

As new functional requirements of products lead to the definition of more complicated shapes, reverse engineering is playing a more important role. The process consists in defining a CAD model of the object surfaces from the measurement of the real object. Reverse engineering takes advantage of new advances in noncontact measuring systems leading to a representation of the surfaces as large clouds of points. Nevertheless, scanning without path planning may affect completeness and accuracy of the measured data. This paper addresses the problem of intelligent scan planning within the context of reverse engineering. A measuring system allows us to acquire a cloud of points, which represents the first measurement of the free-form object. This incomplete and locally inaccurate cloud of points is used as a basis to generate an intelligent scan planning. A pretreatment of the point cloud is performed to determine the quality of the first scan and to find out the characteristic edges. The method relies on a voxel representation of the data. According to given thresholds of quality criteria (noise and completeness), unsatisfactory quality zones and digitizing gaps are identified. The new scan paths for an optimal digitizing are then calculated including optimal orientation search. An experimental application of the presented work is described through the digitizing of a face mask.