Christophe Tournier

Automatic polishing process of plastic injection molds on a 5-axis milling center

The plastic injection mold manufacturing process includes polishing operations when surface roughness is critical or mirror effect is required to produce transparent parts. This polishing operation is mainly carried out manually by skilled workers of subcontractor companies. In this paper, we propose an automatic polishing technique on a 5-axis milling center in order to use the same means of production from machining to polishing and reduce the costs. We develop special algorithms to compute 5-axis cutter locations on free-form cavities in order to imitate the skills of the workers. These are based on both filling curves and trochoidal curves. The polishing force is ensured by the compliance of the passive tool itself and set-up by calibration between displacement and force based on a force sensor. The compliance of the tool helps to avoid kinematical error effects on the part during 5-axis tool movements. The effectiveness of the method in terms of the surface roughness quality and the simplicity of implementation is shown through experiments on a 5-axis machining center with a rotary and tilt table.

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.

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.

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.

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.

The Concept of the Machining Surface in 5-Axis Milling of Free-form Surfaces

The concept of the machining surface (MS) is an approach to the process of design and manufacturing of free form surfaces. The machining surface is the surface representation of the tool path, integrating functional design specifications and machining constraints. By definition, it is a surface including all the information necessary for the driving of the tool, so that the envelope surface of the tool movement sweeping the MS gives the expected free-form. In this paper, we study the building of the MS for 5-axis end milling with usual cutting tools, ball, flat and filleted endmill. We make so that the design and manufacturing constraints taken into account by the machining surface are completely uncoupled within the MS.

TOOL PATH GENERATION AND POST-PROCESSOR ISSUES IN FIVE-AXIS HIGH SPEED MACHINING OF HYDRO TURBINE BLADES

As a core part of aerospace, space, and steam turbine plants, blades are generally machined via 5-axis linkage processing to satisfy the high precision requirements of the rigorous surface. To save costs in blade machining, many small- and medium-sized enterprises often combine standard 3-axis computer numeric control machines with the automatic indexing turntable. The traditional 4-axis machining method adopts a constant feed rate, which causes overcutting near the leading and trailing edges of the blade because of the rapid changes in tool orientation. To solve this problem, we propose a speed optimization method that utilizes variational speed to ensure that the decomposition velocity and acceleration of each axis do not exceed the allowable values. First, we guarantee the correct tool lead angle. Second, a corrected speed model is established to obtain the component speed of each axis and to determine the constraint conditions of maximum and accelerated speed. Third, a 4-axis post processor for blade processing is developed using Java advanced language combined with the optimization algorithm. The cutting experiment reveals that our proposed speed optimization method effectively controls the precision of the surface profile and overcomes the overcut phenomenon that often occurs in traditional 4-axis machining.

Direct duplication of physical models in discrete 5-axis machining

This paper deals with the feasibility of direct duplication of physical objects with regard to a classical approach based on reverse engineering. The object surface acquisition is performed using optical devices. Algorithms for tool path generation directly from the cloud of points have been developed in 3-axis machining. A n-buffer simulation completed by the real machining emphasises that direct duplication is efficient in terms of conformity to the geometry. As the surface reconstruction step is removed, the proposed process is faster and simpler to implement. The last step is concerned with the extension to discrete 5-axis machining. The main issue is related to the determination of the part set-ups and the corresponding point cloud segmentation.

Performance evaluation of CUDA programming for 5-axis machining multi-scale simulation

5-Axis milling simulations in CAM software are mainly used to detect collisions between the tool and the part. They are very limited in terms of surface topography investigations to validate machining strategies as well as machining parameters such as chordal deviation, scallop height and tool feed. Z-buffer or N- buffer machining simulations provide more precise simulations but require long computation time, especially when using realistic cutting tools models including cutting edges geometry. Thus, the aim of this paper is to evaluate Nvidia CUDA architecture to speed-up Z-buffer or N-buffer machining simulations. Several strategies for parallel computing are investigated and compared to single-threaded and multi-threaded CPU, relatively to the complexity of the simulation. Simulations are conducted with two different configurations including Nvidia Quadro 4000 and Geforce GTX 560 graphic cards.

PERFORMANCE OF OFF-LINE POLYNOMIAL CNC TRAJECTORIES WITHIN THE CONTEXT OF HSM

The objective of the article is to present various off-line calculation methods to calculate polynomial tool trajectories, format well adapted to High-Speed Machining. In particular, we are interested in comparing machining performances of various polynomial calculation algorithms such as interpolation, association or inter-approximation with energy minimization. This comparison is achieved using a test part through simulations and machining tests to justify the efficiency of the calculation methods. Measurements of velocity and position during machining highlight differences between the different association methods. Attention is also paid to the visual and geometrical quality of the machined surfaces.