Emmanuel Duc

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.

The Domain of Admissible Orientation concept: A new method for five-axis tool path optimisation

This work deals with the optimisation of tool paths in five-axis machining. The objective is to improve the kinematic behaviour of machine tools during milling. The orientation of the tool axis at each point of a tool path is optimised while ensuring quality constraints. These are modelled using the Domain of Admissible Orientation (DAO) concept expressed in the P-System and transformed into the M-System. This article aims at defining the DAO and presents an example of optimisation using this concept. This optimisation is a minimisation of the movement generated by each rotation axis and is applied to two test parts.

New approach to 5-axis flank milling of free-form surfaces: Computation of adapted tool shape

This paper develops a new approach to solve the problem of interferences during the flank milling of a non-developable ruled surface. Many articles propose to modify the tool path to reduce this problem. A novel approach is proposed here, Computation of Adapted Tool Shape (CATS), which computes and optimizes the tool shape to reduce these interferences. The aim of this CATS method is to maintain a standard CAM system thanks to the tool shape modification. This method is presented for the machining of an industrial part and for a numerical experimental design of nine surfaces.

Tool path smoothing of a redundant machine: Application to Automated Fiber Placement

Automated Tape Laying and Fiber Placement of composite materials are the two principal automated processes used for fabrication of large composite structures in aeronautical industry. The aluminum parts produced by High Speed Machining tend to be replaced by carbon fiber composite parts realized with these processes. However, structural parts present reinforcement zones which disturb the tool path follow-up and generate an increase of the manufacturing time. Thus, this paper deals with the optimization of tool paths of a 7-axis machine tool of Fiber Placement with the objective of reducing the manufacturing time while ensuring the requested quality of the final part. In this paper, two complementary methods are detailed. The first method takes advantage of the degree of redundancy of the machine tool to decrease the kinematic loads of the control joints. The second method aims to smooth the orientation of the machine head along the tool path while ensuring quality constraints. These two methods are then applied on a test tool path and bring to a significant decrease of the manufacturing time (32.9%).

Machining of free-form surfaces and geometrical specifications

Abstract The machining process of free-form surfaces with computer aided design:manufacture (CAD:CAM) systems has to be in accordance with the geometrical specifications. Usually, the cutter path strategy is defined in order to respect these specifications (essentially, form deviation and roughness) as much as possible. Unfortunately, there is no obvious link between geometrical specifications and the CAM parameters that characterize the cutter path strategy. The aim of this paper is to propose links between CAM parameters and geometrical specifications so that the machined surface has the desired quality. These links cannot be made without taking the influence of the form convexity into account. In addition, the parameter values can be optimized with respect to the machining time.

An analytical method for obtaining cutter workpiece engagement during a semi-finish in five-axis milling

In five-axis milling, determining the continuously changing Cutter Workpiece Engagement (CWE) remains a challenge. Solid models and discrete models are the most common methods used to predict the engagement region. However, both methods suffer from long computation times. This paper presents an analytical method to define the CWE for toroidal and flat-end cutters during semi-finish milling of sculptured parts. The staircase workpiece model that resulted from rough milling was used to verify the method. The length of each cut at every engagement angle can be determined by finding two points: the lower engagement (LE) point and the upper engagement (UE) point. An extension of the method used to calculate the grazing point in swept envelope development was utilized to define the LE-point. The test showed that the existence of an inclination angle significantly affected the location of the LE-point. For the UE-point, it was first assumed that the workpiece surface was flat. A recalculation of the CWE was then performed to obtain a more accurate engagement profile with the actual surface. A technique called the Toroidal-boundary method was employed to obtain the UE-point when it was located on the toroidal side of the cutting tool. Alternatively, a method called the Cylindrical-boundary method was used to calculate the UE-point for a flat-end cutter on the cylindrical side of the toroidal cutter. The proposed model was successfully used to generate CWE data for two model parts with different surface profiles. The accuracy was verified twice: first, by comparing the coordinates of the UE-points with respect to the workpiece surface and second, by using Siemens-NX. The results proved that the proposed method was accurate. Moreover, because this method is analytical, it is more efficient in terms of computation time compared with discrete models.

HSM-ADAPTED TOOL PATH CALCULATION FOR POCKETING

High-speed milling imposes a precise choice of cutting conditions, because the feed rate and the radial depth of cut influence the maximum forces on cutting edges. But the control of these cutting conditions for pocket machining is very difficult due to the complex tool path shape. Our work is focused on the improvement of the geometrical definition of the tool path, in order to ensure a better respect of the cutting conditions required for HSM. Initially, we study variations in the radial depth of cut and the real feed rate, when the tool follows usual tool paths for pocketing. Numerical simulations and experimental measurements are used. Next, a new tool path computation method that increases the real feed rate and respects radial depth of cut requirements is proposed. The computation takes into account both the geometrical requirements and the HSM dynamic requirements. Such tool paths reduce machining time and respect initial cutting parameters which are favorable for process reliability and tool life.

Modeling and Analysis of Five-Axis Milling Configurations and Titanium Alloy Surface Topography

Five-axis milling with a ball-end cutter is commonly used to generate a good surface finish on complex parts, such as blades or impellers made of titanium alloy. The five-axis milling cutting process is not straight forward; local cutting conditions depend a lot on the geometrical configuration relating to lead and tilt angles. Furthermore, the surface quality is greatly affected by the cutting conditions that define the milling configuration. This study presents a geometrical model of five-axis milling in order to determine the effective cutting conditions, the milling mode, and the cutter location point. Subsequently, an analysis of surface topography is proposed by using the geometrical model, local criteria, and a principle component analysis of experimental data. The results show the effects of local parameters on the surface roughness, in relation to the lead and tilt angles.

Geometric and Kinematic Modelling of a New Parallel Kinematic Machine Tool: The Tripteor X7 Designed by PCI

Today, Parallel Kinematic Machine tools (PKMs) appear in automotive and aeronautic industry. These machines propose high kinematic performances allowing a higher productivity than Serial Kinematic Machine tools (SKMs). However, this kinematic behaviour is anisotropic and a particular study is then necessary to locate the part in a workspace where the kinematic performances are well exploited. The study presented in this article deals with the determination of geometric and kinematic models of a new PKM : the Tripteor X7 designed by PCI. The inverse kinematic model expresses the joint coordinates with regard to the cartesian coordinates. The kinematic model which takes into account velocity, acceleration and jerk limits axis, allows computing the displacement time between two tool positions. Finally, this model can be used to determine the workspace where Non Effective cutting Times (TNE) are minimum. The method is applied for an automotive part machining

Analytical Method for Obtaining Cut Geometry of Helical Toroidal Cutter during Semi-Finish in 5-Axis Milling

Cut geometry data is an essential information in current machining simulation and optimization. The tool orientation changed continuously during free-form machining become a challenge in predicting cut geometry in 5-axis milling. This paper present an extended analytical method to define cut geometry during semi-finish milling. The algorithm was developed by taken into account the existence of helical angle. The developed model was successfully implemented to generate the shape and the length of cut. From the test it was found that helical angle gives significant effect to the cut geometry.