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Concept# Découpe laser

Résumé

thumb|Machine de découpe laser en train de couper des formes géométriques sur du polystyrène expansé.
thumb|Machine de découpe laser à l'exposition "".
La découpe laser est un procédé de fabrication qui consiste à découper la matière grâce à une grande quantité d’énergie générée par un laser et concentrée sur une très faible surface. Cette technologie est majoritairement destinée aux chaînes de production industrielles, mais peut également convenir aux boutiques, aux établissements professionnels et aux tiers-lieux de fabrication.
Les performances de la découpe laser sont en constante évolution : diversification des matériaux, augmentation de l'épaisseur de la découpe, finalisation du rendu. Ces critères d’amélioration sont liés notamment aux progrès réalisés en matière de sources laser.
Le laser peut être pulsé (source de type YAG), continu (source CO2 ou azote).
Principe
La focalisation d'un rayon laser permet d'élever la température d'une zone réduite de matière, ju

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MICRO-520: Laser microprocessing

The physical principles of laser light materials interactions are introduced with a large number of industrial application examples. Materials processing lasers are developing further and further, the lecture presents the physical limitations of the processes.

MICRO-426: Laser fundamentals and applications for engineers

The course will cover the fundamentals of lasers and focus on selected practical applications using lasers in engineering. The course is divided approximately as 1/3 theory and 2/3 covering selected applications.

MICRO-435: Quantum and nanocomputing

The course teaches non von-Neumann architectures. The first part of the course deals with quantum computing, sensing, and communications. The second focuses on field-coupled and conduction-based nanocomputing, in-memory and molecular computing, cellular automata, and spintronic computing.

Séances de cours associées (62)

Concepts associés (19)

Laser

thumb|250px|Lasers rouges (660 & ), verts (532 & ) et bleus (445 & ).
thumb|250px|Rayon laser à travers un dispositif optique.
thumb|250px|Démonstration de laser hélium-néon au laboratoire Kastler-Bro

Numerical control

Numerical control (also computer numerical control, abbreviated CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a comp

Impression 3D

alt=Une grenouille en plastique bleue est en cours de construction par une imprimante 3D|vignette|Objet imprimé en 3D par une Ultimaker 2 Go
vignette|Imprimante 3D dans un fab lab béninois.L'impressio

Although used in a very large variety of applications, drilling is one of the most complex and least understood manufacturing processes. Most of the research on drilling was done in the field of metal cutting for mechanical parts since, in this case, high precision and quality are needed. The use of composite materials in engineering applications has increased in recent years, and in many of these applications drilling is one of the most critical stages in the manufacturing process. This is because it is among the last operations in the manufacturing plan of composite parts. Delamination and extensive tool wear are among the problems which drilling of composite materials are currently facing. A major difference between metallic and composite plates is their structure: isotropic for metals and anisotropic for composite materials; meaning that while for metallic materials all the structure will respond in a similar manner under the machining loads, the composite structure will have localized responses from the same loads, leading to defects in the internal structure of the remaining work-piece material (i.e. delamination). Delamination can lead to failure in use and parts with such defects are usually discarded. Delamination is not usually visually detectable and special testing is necessary, affecting the costs of the final parts. Delamination during drilling was found to occur at tool entry (peel-up) or tool exit (push-out) and depends on the loads at inter-laminar level. The work presented in the current thesis focuses in providing reliable information about the thrust and torque distribution along the drill radius (and work-piece thickness) during drilling for varying cutting parameters, drill geometry and work-piece material. Such data should assist in the development of delamination models capable of capturing the influence of the drill geometry and cutting parameters on delamination onset and propagation during both exit and entry of the drill in the work-piece. A cutting force model is proposed to obtain the elementary cutting force distribution along the drill radius which is able to account for changes in axial feed rate and drill geometry. Based on oblique cutting, forces are considered on both rake and relief faces. A generic relationship in the form of a transformation matrix is developed to relate oblique cutting to drilling, valid for any drill geometry. The mathematical description of the drill geometry in the scope of cutting force modeling has been revised. The kinematics of the drilling process is now taken into account for (i) all geometrical parameters of the drill and for (ii) the elementary cutting forces decomposition. Additionally, a new drill type and its geometric features have been described mathematically and the definition of the geometrical parameters has been generalized so that other drills types or variations could be easily implemented into the model. It proved therefore possible to adopt simpler expressions for the empirical force coefficients of the cutting force model. Up to four empirical coefficients are used, which are calculated from experiments for each work-piece material and drill type. Most experimental investigations on drilling fiber reinforced composites analyze only the total thrust and torque generated during drilling or separately the forces caused by the chisel edge and cutting lips by drilling with or without a pilot hole. The later type of analysis suggested that is possible to obtain more detailed information about the distribution of the loads in drilling from the analysis of the forces variation during tool entry into the work-piece. Pursuing this direction, an experimental analysis method is proposed to obtain the axial and tangential elementary cutting force distribution along the tool radius or work-piece thickness. The cutting force distribution obtained experimentally was used to calibrate the cutting force model, rather than the total thrust and torque. The experimentally obtained cutting force distribution can also be used alone for analyzing the drilling process (i.e. the loads distribution among the plies of the composite laminate and how this load is influenced by changes in the drill geometry and the cutting conditions).

Milling is a most common type of material removal process by rotating tools to create a variety of features on a part. The material is removed in a controlled way by sweeping a rotating cylindrical tool along the specific trajectory known as milling tool path. For any specified shape and volume of material to be removed, there are a variety of possible tool paths and cutting conditions. These different possibilities can be evaluated based on various geometric as well as process related factors. Milling time is one of the most important factors in evaluating the process efficiency, which depends upon the tool path planning and the behavior of the physical machine tool. Tool path planning usually considers factors such as limitations of cutting tools, tolerance requirement and workpiece geometry etc., which directly influence the milling process time. Further, as milling process involves physical interaction between tool and workpiece, the wear and tear of milling tools is an important issue. As the breakdown of cutting tools is detrimental for productivity; the tool paths must be evaluated based on other important physical considerations like cutting forces and chatter. A number of cutting force models on the preselected cutting parameters with high reliable prediction capability are already available in the literature, however, a simplified category of constant engagement zones are usually assumed to exist. Engagement zone may vary along the tool path as it depends on instantaneous in-process workpiece geometry and hence imparting a change in the cutting forces also. Thus one of the objectives of this work is to present a system to verify a milling process plan to incorporate arbitrary tool paths and in-process changes in workpiece geometry. Among the available tool paths, contour parallel tool paths are the most widely used tool paths for 2D milling operations. A number of exact as well as approximate methods are available for offsetting a closed boundary in order to generate a contour parallel tool path; however, most of methods are inherently incapable of dealing with complex problems (change in topology and self intersecting feature) during offsetting and require highly efficient computational routines to identify and rectify these problems. In this work, a boundary value formulation of the offsetting problem is studied and a fast marching method based solution for tool path generation is presented. This method handles the topological changes during offsetting naturally and deals with the generation of discontinuities in the slopes by including an "entropy condition" in its numerical implementation. A number of examples are presented and computational issues are discussed for tool path generation. Although, the tool path generation methods discussed earlier guarantee to generate a geometrically feasible tool path the in-process engagement is still not constant or its variation is not minimized. This leads to variation of actual radial depth of cut especially at the sharp corners or high curvature profiles, the usual problems encountered due to this variation are (i) left over material at corners (ii) sudden increment in cutting forces. These conditions force the process planner to add more tool passes to the original tool paths or adhere to conservative feed values respectively. In either case, it renders the process plan inefficient. This work presents a method based on signed distance function to generate spiral-out contour parallel tool path generation. This proposed method and algorithms avoids the leftover material at the corners and minimizes the variation of radial depth of cut at each level of contour milling and consequently maintains the same cutting conditions specified as starting cutting parameters which are favorable for process reliability, part quality and tool life. Finally the second type of contour parallel tool path i.e. spiral-in milling is investigated for milling tool path generation with an aim to generate "efficient" geometrically feasible spiral in tool paths which minimize the variation of the milling process from its steady state while minimizing the curvature of the tool path. Further, the tool path for non-convex geometry are developed which are optimized for the stepover and the engagement with no tool retraction involved, which is highly desirable for high speed milling of arbitrary pockets.

Adaptive optics is used to abate aberrations with a wavefront correction. It is widely used in astronomy and is starting to expand into applications of laser focusing and imaging with high numerical apertures, e.g. microscopy. The physical background of focusing laser light and imaging is the same, so we can use the same methods. In both cases, light is propagating through a lens; either it becomes focused into a small region or light from a small region becomes imaged on a camera. Modulations applied on the lens to implement wavefront corrections behave similarly in both applications. A powerful simulation tool was created to characterize the impact of those modulations. As an example, we validated a design for a Fresnel lens produced on a glass fibre tip to focus its emitting light. We have developed solutions mainly for three different problems. First, a high depth of focus enables keeping a laser beam focused within a larger length or imaging objects from different positions simultaneously. In photography, this can be attained by stopping down the aperture, which introduces a huge loss of light. State-of-the-art for focusing into a line segment also shows an inefficient performance. We present an elegant lens design, which enables highly efficient elongation of the depth of focus. Preliminary studies have shown that it might be a feasible alternative for current intra-ocular lens implants in ophthalmology or for 3D visualization in imaging and microscopy. A high depth of focus also has a large potential in optical lithography and data storage, because the focal position is enlarged and does not have to be adjusted precisely to obtain a useful spot. Second, specimen-induced aberrations can affect even a perfectly adjusted, diffraction limited lens system. A planar refraction index mismatch introduces spherical aberrations, degrading the optical resolution. As a first step to correct them, we were able to characterize simultaneously the refractive index and the thickness of an unknown medium that is placed between the lens and its focal region. This was done by clever manipulation of the beam angles with the same adaptive optics element in the focusing and in the imaging system. Finally, the medium-induced spherical aberrations were corrected based on the characterization results. The point spread function degradation of a focused laser beam was completely removed, which might be useful in optical tweezers or in laser processing of biological samples. While imaging through the planar refractive index mismatch, the bending of the object field was corrected and the diffraction limited performance restored.