Automatic tool path generation for numerically controlled machining of sculptured surfaces

This dissertation presents four new tool path generation approaches for numerically controlled machining of sculptured surfaces: TRI\sb-XYINDEX, FINISH, FIVEX\sb-INDEX, FIX\sb-AXIS\sb-INDEX. All of the above systems index the tool across the object surface in the Cartesian space so that evenly distributed tool paths are accomplished. TRI\sb-XYINDEX is a three-axis tool path generation system which uses a surface triangle set (STS) representation of the surface for tool position calculations. Surface edges are detected with local searching algorithms. Quick tool positioning is achieved by selecting candidate elements of polygons. Test results show that TRI\sb-XYINDEX is more efficient when machining surfaces which are relatively flat while the discrete point approach is faster for highly curved surfaces. FINISH was developed for generating three-axis ball-end tool paths for local surface finishing. It was based on the SPS. Given a surface with excess material represented by a set of discrete points, FINISH automatically identifies the undercut areas. Results show that FINISH provides significant improvements in machining efficiency. FIVEX\sb-INDEX is developed for generating five-axis flat-end tool paths. It uses an STS approximation. Contact points on the surface are derived from edge lists obtained from the intersections of vertical cutting planes with the polygon set. The distances between adjacent end points set an initial step-forward increment between surface contact points. To verify tool movements, some intermediate tool positions are interpolated. The key features of FIVEX\sb-INDEX are: (1) a polygon set representing an object which may be composed of multiple surfaces; (2) Surface contact point generation by cutting plane intersection; (3) simple tool incrementing and positioning algorithms; (4) minimal user interaction; (5) user controlled accuracy of resulting tool paths. FIX\sb-AXIS\sb-INDEX is a subsystem of FIVEX\sb-INDEX, generating tool paths for a tool with fixed orientations. Surface contact points are generated similar to FIVEX\sb-INDEX while tool positions are corrected with the highest point technique along the tool axis direction. Linear fitting is applied to output tool positions. FIX\sb-AXIS\sb-INDEX is preferred for machining surfaces curved in one direction, such as ruled surfaces. Test results show that FIX\sb-AXIS\sb-INDEX can serve as a three-axis tool path generation system but a five-axis machine is required to do it. (Abstract shortened by UMI.)

Rapid prototyping of micro-optics for brightness restoration of diode lasers

Abstract unavailable please refer to PD

Analysis of the influence of surface modifications on the fatigue behavior of hot work tool steel components

Hot work tool steels (HWS) are widely used for high performance components as dies and molds in hot forging processes, where extreme process-related mechanical and thermal loads limit tool life. With the functionalizing and modification of tool surfaces with tailored surfaces, a promising approach is given to provide material flow control resulting in the efficient die filling of cavities while reducing the process forces. In terms of fatigue properties, the influence of surface modifications on surface integrity is insufficiently studied. Therefore, the potential of the machining processes of high-feed milling, micromilling and grinding with regard to the implications on the fatigue strength of components made of HWS (AISI H11) hardened to 50 ± 1 HRC was investigated. For this purpose, the machined surfaces were characterized in terms of surface topography and residual stress state to determine the surface integrity. In order to analyze the resulting fatigue behavior as a result of the machining processes, a rotating bending test was performed. The fracture surfaces were investigated using fractographic analysis to define the initiation area and to identify the source of failure. The investigations showed a significant influence of the machining-induced surface integrity and, in particular, the induced residual stress state on the fatigue properties of components made of HWS

The integration of geometric information within design and manufacture

Imperial Users onl

Compensation of Relevant and Compensable Volumetric Errors for Five-Axis Machine Tools Based on Differential Kinematics

RÉSUMÉ Les erreurs géométriques d’une machine-outil ont un impact direct sur la précision des pièces usinées. Cette thèse traite de la compensation d'erreur des machines-outils CNC à cinq-axe. Dans la première phase, une formulation générale de l’erreur volumétrique et un système de compensation hors ligne sont proposés pour améliorer la précision de la pièce. En utilisant la cinématique des corps rigides et les paramètres d'erreur estimés de la machine, les commandes de position de la machine contenues dans un code G standard sont utilisées pour calculer l’erreur de position de l'outil. Le Jacobien, exprimant le différentiel entre l’espace articulaire et l'espace cartésien, est également développé et utilisé pour calculer les modifications de commande articulaire de telle sorte que l'effet des erreurs de la machine peut être annulé par de petits changements directement sur le code G. Lorsque la compensation est implémentée, sa validation est requise. Des machines à mesurer tridimensionnelles (MMT) ou d'autres dispositifs de mesure externes sont couramment utilisés pour mesurer la précision de la pièce usinée à des fins de validation. Dans ce travail, une série de tests de défauts surfaciques issus de l’usinage sont proposés pour comparer la précision d'usinage avant et après la compensation en utilisant des mesures sur machine seulement. Les écarts sur les surfaces produites découlent de l'erreur volumétrique et proviennent d’erreurs géométriques spécifiques de la machine qui sont mesurées en utilisant un palpeur placé sur la machine erronée elle-même. L'effet de la stratégie de compensation est ensuite validé en comparant l’écart entre les surfaces avec usinage compensé et non compensé. Les résultats des mesures sont compatibles avec les valeurs d'erreur volumétrique prévues et montrent une amélioration de la précision (réduction de décalage) d'environ 90% après compensation. Finalement, deux nouvelles notions, la pertinence de l'erreur et l’aptitude à la compenser, sont introduites et quantifiées pour la machine-outil. La compensation des erreurs pertinentes et compensables seulement conduit à une compensation optimisée dans laquelle des modifications de commandes minimales mais efficaces sont faites. Une pièce est conçue spécialement pour le test, contenant des caractéristiques communes est usinée, en utilisant les cinq axes d’usinage simultanément, pour la validation expérimentale. Les résultats de simulation montrent jusqu'à 75% de réduction dans la 1-norme des compensations linéaires et angulaires alors que les erreurs pertinentes demeurent efficacement corrigées.----------ABSTRACT Machine tool geometric errors directly impact on the accuracy of machined parts. This thesis addresses the error compensation in five-axis CNC machine tools. In the first phase, a general volumetric error formulation and an off-line compensation scheme are proposed to improve part accuracy. Using rigid body kinematics and estimated machine error parameters, the machine position commands contained in a standard G-code are used to calculate the tool erroneous location. The Jacobian, expressing the differential joint space to Cartesian space relationship, is also developed and used to calculate minute joint command modifications so that the effect of machine errors can be canceled by making small changes directly to the G-code. When compensation is implemented, its validation is sought. Coordinate measuring machines (CMM) or other external measurement devices are commonly used to measure the accuracy of the machined part for validation purpose. In this work, a series of surface mismatch producing machining tests are proposed to compare the machining accuracy before and after the compensation using only on-machine measurements. The produced surface mismatches that represent the volumetric error and come from specific machine geometric errors are measured using touch probing by the erroneous machine itself. The effect of the compensation strategy is then validated by comparing the surface mismatch value for compensated and uncompensated slots. The measurement results are compatible with the predicted volumetric error values and show an accuracy improvement (mismatch reduction) of about 90 % after compensation for the machine tested. Finally, two new notions, error relevance and error compensability, are introduced and quantified. Compensation of only relevant and compensable errors leads to an optimized compensation in which minimal but effective command modifications are made. A specially designed test part containing common features is machined, using up to five-axis simultaneous machining, for the experimental validation. Simulation results show up to 75% reduction in the 1-norm of the linear and angular compensations while the relevant errors are still effectively corrected

Manufacturability analysis for non-feature-based objects

This dissertation presents a general methodology for evaluating key manufacturability indicators using an approach that does not require feature recognition, or feature-based design input. The contributions involve methods for computing three manufacturability indicators that can be applied in a hierarchical manner. The analysis begins with the computation of visibility, which determines the potential manufacturability of a part using material removal processes such as CNC machining. This manufacturability indicator is purely based on accessibility, without considering the actual machine setup and tooling. Then, the analysis becomes more specific by analyzing the complexity in setup planning for the part; i.e. how the part geometry can be oriented to a cutting tool in an accessible manner. This indicator establishes if the part geometry is accessible about an axis of rotation, namely, whether it can be manufactured on a 4th-axis indexed machining system. The third indicator is geometric machinability, which is computed for each machining operation to indicate the actual manufacturability when employing a cutting tool with specific shape and size. The three manufacturability indicators presented in this dissertation are usable as steps in a process; however they can be executed alone or hierarchically in order to render manufacturability information. At the end of this dissertation, a Multi-Layered Visibility Map is proposed, which would serve as a re-design mechanism that can guide a part design toward increased manufacturability

Characterising the dynamic response of ultrasonic cutting devices

The current work begins by considering a range of common high power ultrasonic components in order to establish a standardised approach to tool design for optimum performance. The vibration behaviour of tuned components resonating longitudinally at ultrasonic frequencies around 35 kHz is modelled via finite element analysis and measured by experimental model analysis. Significant improvements in experimental validation of the models are achieved by the use of a 3D LDV, which allows modal analysis from both in-plane and out-of-plane measurement, which is critical in proposing alternative designs. The vibration characteristics of complex multiple-component systems used in ultrasonic cutting of food products are also investigated. Commonly, the design approach for ultrasonic systems neglects to account for the mutual effects of physically-coupled components in the system vibration. The design of systems also neglects the nonlinear dynamic effects which are inherent in high power systems due to the nonlinearities of piezoelectric transducers. The first issue is tackled by considering the vibration behaviour of the whole system and the influence of individual components and, particularly, offers design improvements via modification of block horns and cutting blade components, which are modelled and validated. The issue of nonlinearity is addresses by identifying the mechanisms of energy leakage into audible frequencies and characterising the common multimodal responses. For this study, design modifications focused on reducing the number of system modes occurring at frequencies below the tuned system frequency. As a consequence of these approaches, insights for the design of multiple-component systems in general are provided

Micromachining

To present their work in the field of micromachining, researchers from distant parts of the world have joined their efforts and contributed their ideas according to their interest and engagement. Their articles will give you the opportunity to understand the concepts of micromachining of advanced materials. Surface texturing using pico- and femto-second laser micromachining is presented, as well as the silicon-based micromachining process for flexible electronics. You can learn about the CMOS compatible wet bulk micromachining process for MEMS applications and the physical process and plasma parameters in a radio frequency hybrid plasma system for thin-film production with ion assistance. Last but not least, study on the specific coefficient in the micromachining process and multiscale simulation of influence of surface defects on nanoindentation using quasi-continuum method provides us with an insight in modelling and the simulation of micromachining processes. The editors hope that this book will allow both professionals and readers not involved in the immediate field to understand and enjoy the topic