Analysis of Different Tool Path Strategies for Free Form Machining with Computer Aided Surface Milling Operations

[EN] Free form surfaces are commonly used to generate aesthetic parts. These parts can be manufactured directly by material removal techniques or indirectly with molding or forming techniques. In any case, these surfaces must be commonly machined with traditional processes, at least until certain degree of surface finishing, and the tool path must be generated with computer aided applications. In doing so, developers are implementing new theoretical strategy operations for controlling tool path and trajectories. These new options have so many combinations that it is difficult to know which is the best one to choose when defining the tool movements. Apart from the traditional strategies fixed angle method, principal axis method and multipoint machining, combined with tool orientation, there are many other strategies to explore due to machine tool and numerical control improvements. What is need now is a validation of these new strategies in computer aided applications regarding time minimizing and how the cutting parameters affects in the surface final result.The authors would like to thanks Universitat Politècnica de València, La Fondation Dassault Systèmes, Carolina Foundation and the National Polytechnic School for the support of this article through the 2017 call and project PIS 16-15 - PIS 16-22.Vila, C.; Ayabaca-Sarria, C.; Torres Carot, R.; Gutiérrez, SC.; Meseguer, M.; Yang, X. (2019). Analysis of Different Tool Path Strategies for Free Form Machining with Computer Aided Surface Milling Operations. Procedia Manufacturing. 41:843-850. https://doi.org/10.1016/j.promfg.2019.10.006S8438504

Experimental Study And Modeling Of Mechanical Micro-machining Of Particle Reinforced Heterogeneous Materials

This study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles. This research is motivated by increasing demands of miniaturized components with high mechanical performance in various industries. Mg-MMCs become one of the best candidates due to its light weight, high strength, and high creep/wear resistance. However, the improved strength and abrasive nature of the reinforcements bring great challenges for the subsequent micro-machining process. Systematic experimental investigations on the machinability of Mg-MMCs reinforced with SiC nano-particles have been conducted. The nanocomposites containing 5 Vol.%, 10 Vol.% and 15 Vol.% reinforcements, as well as pure magnesium, are studied by using the Design of Experiment (DOE) method. Cutting forces, surface morphology and surface roughness are characterized to understand the machinability of the four materials. Based on response surface methodology (RSM) design, experimental models and related contour plots have been developed to build a connection between different materials properties and cutting parameters. Those models can be used to predict the cutting force, the surface roughness, and then optimize the machining process. An analytical cutting force model has been developed to predict cutting forces of MgMMCs reinforced with nano-sized SiC particles in the micro-milling process. This model is iv different from previous ones by encompassing the behaviors of reinforcement nanoparticles in three cutting scenarios, i.e., shearing, ploughing and elastic recovery. By using the enhanced yield strength in the cutting force model, three major strengthening factors are incorporated, including load-bearing effect, enhanced dislocation density strengthening effect and Orowan strengthening effect. In this way, the particle size and volume fraction, as significant factors affecting the cutting forces, are explicitly considered. In order to validate the model, various cutting conditions using different size end mills (100 µm and 1 mm dia.) have been conducted on Mg-MMCs with volume fraction from 0 (pure magnesium) to 15 Vol.%. The simulated cutting forces show a good agreement with the experimental data. The proposed model can predict the major force amplitude variations and force profile changes as functions of the nanoparticles’ volume fraction. Next, a systematic evaluation of six ductile fracture models has been conducted to identify the most suitable fracture criterion for micro-scale cutting simulations. The evaluated fracture models include constant fracture strain, Johnson-Cook, Johnson-Cook coupling criterion, Wilkins, modified Cockcroft-Latham, and Bao-Wierzbicki fracture criterion. By means of a user material subroutine (VUMAT), these fracture models are implemented into a Finite Element (FE) orthogonal cutting model in ABAQUS/Explicit platform. The local parameters (stress, strain, fracture factor, velocity fields) and global variables (chip morphology, cutting forces, temperature, shear angle, and machined surface integrity) are evaluated. Results indicate that by coupling with the damage evolution, the capability of Johnson-Cook and Bao-Wierzbicki can be further extended to predict accurate chip morphology. Bao-Wierzbiki-based coupling model provides the best simulation results in this study. v The micro-cutting performance of MMCs materials has also been studied by using FE modeling method. A 2-D FE micro-cutting model has been constructed. Firstly, homogenized material properties are employed to evaluate the effect of particles’ volume fraction. Secondly, micro-structures of the two-phase material are modeled in FE cutting models. The effects of the existing micro-sized and nano-sized ceramic particles on micro-cutting performance are carefully evaluated in two case studies. Results show that by using the homogenized material properties based on Johnson-Cook plasticity and fracture model with damage evolution, the micro-cutting performance of nano-reinforced Mg-MMCs can be predicted. Crack generation for SiC particle reinforced MMCs is different from their homogeneous counterparts; the effect of micro-sized particles is different from the one of nano-sized particles. In summary, through this research, a better understanding of the unique cutting mechanism for particle reinforced heterogeneous materials has been obtained. The effect of reinforcements on micro-cutting performance is obtained, which will help material engineers tailor suitable material properties for special mechanical design, associated manufacturing method and application needs. Moreover, the proposed analytical and numerical models provide a guideline to optimize process parameters for preparing and micro-machining of heterogeneous MMCs materials. This will eventually facilitate the automation of MMCs’ machining process and realize high-efficiency, high-quality, and low-cost manufacturing of composite materials

A CAD/CAM concept for High Speed Cutting compatible rough machining in die, mould and pattern manufacturing

Die, mould and pattern manufacturing plays a central role in the production of capital and consumer goods. Ever-shorter product life cycles and the expanding diversity of features require continued cuts in production lead times. Recently, these developments in the market, accompanied by a simultaneous demand for improved quality at a lower cost, are becoming clearly noticeable. Along with the streamlining of organizational structures and advanced technological developments, it is above all the introduction of CAD/CAM software that offers great potential for reducing lead times for components with free surfaces. The role of milling in the integrated process chain of die, mould and pattern manufacturing is steadily gaining importance. This is due to the ongoing further development of milling-machine technology, the cutting tools and their coatings, and of the CAD /CAM systems themselves. Generally speaking, the milling process is divided into the operations of roughing and finishing. For rough milling, efficient machining means high stock-removal rates together with close contour approximation and low tool wear. Rough milling is normally carried out layer by layer, i.e. in a 2.SD machining operation with constant depth per cut because the rate of material removal and process reliability are usually highest when this method is used. High-speed cutting (HSC), which has been the subject of extensive university research for far more than ten years, has meanwhile become established as a finishing process in many companies. However, the application of HSC demands the observance of geometric and, above all, technological constraints. A considerable degree of optimization can be achieved when these constraints are applied to rough milling. In the integrated process chain, the CAD/CAM system performs the task of calculating NC programs based on CAD data which meet the requirements posed by rough and finish machining operations. While general interest was focused on the development of CAM strategies for HSC finish machining, advanced development of technology-oriented CAM modules for upstream roughing operations was neglected. The paper at hand deals with the development of a CAM module for rough-machining complex components in die, mould and pattern manufacturing. It provides an insight into the process-technological demands made on HSC operations and their application in rough machining, from which guidelines and requirements on technologically oriented NC functions for CAM software were derived. These encompass both the complete development of an interactive, dialogue-based user guidance function and the algorithmic conversion of the calculation routines. The concept at hand was almost entirely implemented and integrated in the CAD/CAM system developed by Tebis AG, Germany, which was conceived especially for die, mould and pattern manufacturing and is scheduled for introduction to the free market starting in April 2001

Automated CNC Tool Path Planning and Machining Simulation on Highly Parallel Computing Architectures

This work has created a completely new geometry representation for the CAD/CAM area that was initially designed for highly parallel scalable environment. A methodology was also created for designing highly parallel and scalable algorithms that can use the developed geometry representation. The approach used in this work is to move parallel algorithm design complexity from an algorithm level to a data representation level. As a result the developed methodology allows an easy algorithm design without worrying too much about the underlying hardware. However, the developed algorithms are still highly parallel because the underlying geometry model is highly parallel. For validation purposes, the developed methodology and geometry representation were used for designing CNC machine simulation and tool path planning algorithms. Then these algorithms were implemented and tested on a multi-GPU system. Performance evaluation of developed algorithms has shown great parallelizability and scalability; and that main algorithm properties are required for modern highly parallel environment. It was also proved that GPUs are capable of performing work an order of magnitude faster than traditional central processors. The last part of the work demonstrates how high performance that comes with highly parallel hardware can be used for development of a next level of automated CNC tool path planning systems. As a proof of concept, a fully automated tool path planning system capable of generating valid G-code programs for 5-axis CNC milling machines was developed. For validation purposes, the developed system was used for generating tool paths for some parts and results were used for machining simulation and experimental machining. Experimental results have proved from one side that the developed system works. And from another side, that highly parallel hardware brings computational resources for algorithms that were not even considered before due to computational requirements, but can provide the next level of automation for modern manufacturing systems

Continuous improvement of a machining process by designing a new jig

This thesis report gives an insight on how an often overlooked, jig and fixture used as a manufacturing aid to produce a product and essential for delivering products reliably and repeatedly with high quality. This continuous improvement project of an exciting machining process of winding cones used overhead garage doors. The improvement was a necessity with a forecast for 2019 estimating the need for 43% faster production cycle (takt time) compared to the previous year. Hence, the main objective was to reduce the machining time required per part by designing a modular jig system, ideally with 12 parts per cycle. To make the work in an organized structure the project was dived into four phases namely: research, design, machining and implementation. The research phase included in the study of the old jig in use, analysing the process and sketching the basic requirements. The design phase was based on the methodology of Design for Six Sigma methodology for the fixture. Different kind of jig components was designed and assembled using SOLIDWORKS CAD model. The critical review of design iteration was analysed using SWO analysis (short version of the standard SWOT analysis) for design. The machining of most components of the jig was done in-house with tacit knowledge of the machinist instead of using CAM software’s making it first of its kind project in developing knowledge management in the company for future jig requirements. The critical outcomes of the project were harvested from the implementation phase. The newly machined modular jig system proved to have increased the number of parts machined per day by 32% with expected savings of more than €6000 per annum. The added benefit of a modular jig system was that one base (skeleton of the jig) could be used in machining different products. Also, future projects now have the intellectual and physical resources of making jigs and fixtures in-house. This drastically reduces the lead times for new parts, which is crucial for a small-medium enterprise stay competitive.Este relatório dá uma visão sobre como um acessório usado pode auxiliar na produção de forma a produzir um produto e os elementos essenciais para a sua entrega de forma confiável e repetida com alta qualidade. Este é um projeto de melhoria contínua de um processo de maquinagem de cones de enrolamento, usados em portas de garagem suspensas. A melhoria surjiu de uma necessidade com a previsão para 2019, estimando a necessidade de um ciclo de produção 43% mais rápido (takt time) em comparação com o ano anterior. Assim, o objetivo principal passava por reduzir o tempo de maquinagem necessário por peça, projetando um sistema de gabarit modular, idealmente com 12 partes por ciclo. Para realizar o trabalho numa estrutura organizada, o projeto foi dividido em quatro fases: pesquisa, projeto, maquinagem e implementação. As fases de pesquisa foram incluídas no estudo do antigo gabarit em uso, analisando o processo e esboçando os requisitos básicos. A fase de projeto foi baseada na metodologia de Design for Six Sigma para um dispositivo. Foram projetados e montados diferentes tipos de componentes de gabarit usando o modelo SOLIDWORKS CAD. A revisão crítica da iteração do projeto foi analisada usando a análise SWO (versão reduzida da análise SWOT convencional) para projeto. A maquinagem da maioria dos componentes do gabarit foi feita internamente com conhecimento tácito do responsável técnico, recorrendo ao software CAM, tornando-o o primeiro de seu tipo no desenvolvimento da gestão do conhecimento na empresa para futuros requisitos de gabarit. Os principais resultados e conclusões dos projetos foram descritos na fase de implementação. O sistema de gabarit modular recém-maquinado provou ter aumentado o número de peças maquinadas por hora em 32%, com economias comprovadas de mais de € 6.000 por ano. O benefício adicional de um sistema de gabarit modular consiste de criar uma base (esqueleto do gabarit) usada na maquinagem de diferentes produtos, e projetos futuros, permitindo à empresa deter os recursos intelectuais e físicos de criar gabarits e acessórios internos. Assim, foi reduzido drasticamente o tempo de espera para novas peças, o que é crucial para uma pequena média empresa permanecer competitiva

DESIGN AND MICROFABRICATION OF EDGE-LIT OPTICAL LIGHT CURTAINS

Plastic optical light guides can be used for a variety of interior and exterior vehicle light curtains such as cabin illuminators and automotive tail lights. The edge-lit wave guide is an optically transparent substrate coupled with one or more energy efficient light emitting diodes (LEDs). The light rays from the source travel through the substrate based on the principle of total internal reflection. If a surface of the optical wave guide is patterned with optical microstructures then the light rays will scatter and refract throughout the medium, primarily exiting opposite to the patterned surface. Uniform illumination over this active surface region is a function of the individual optical microstructure\u27s shape and the spatial distribution of the microstructures. The goal of this research is to investigate the light dispersion characteristics in both smooth and micro-patterned optically transparent substrates, and utilize optical simulation software to develop viable design approaches for fabricating small and medium sized light curtains. The study first identifies an appropriate optical microstructure (i.e. cylindrical indentations) that can be reliably imprinted on the surface of an optically transparent polymethyl-methacrylate (PMMA) substrate using a multi-axis micromilling machine. The optical simulation software Light Tools is then used to determine the most appropriate microstructure radius and spatial positioning of elements for uniform light distribution. The key design and fabrication parameters for near optimal performance are summarized and used to establish the process plan for the high-speed precision micromilling operations. Experiments are performed on several 100 mm x 100 mm x 6 mm polymer light guide panels (LGPs) including a customized design with a hexagonal arrangement of microstructures. Both interior and boundary regions of the sample LGPs are investigated for intensity distribution, optical transmission efficiency, and light loss. Although the experiments involve relatively small flat PMMA LGPs, the optical design and microfabrication methods can be readily extended to larger surface areas or curved optically transparent polymer substrates for contoured light curtains

FEM-based prediction of workpiece transient temperature distribution and deformations during milling

In high-speed dry milling of thin-walled parts, the cutter-workpiece temperature rises asymptotically with cutting speed, causing excessive cutter tooth wear and workpiece thermal expansion, which in turn reduces the cutter life and produces dimensional and geometrical variabilities in the machined part. Therefore, a basic understanding of the thermal aspect of machining and the effecting parameters is essential for achieving better part quality with improved productivity. This paper presents a transient milling simulation model to assist manufacturing engineers in gaining in-depth understanding of the thermomechanical aspects of machining and their influence on resulted part quality. Based on the finite-element method approach, the model can predict transient temperature distributions and resulted elastic-plastic deformations induced during the milling of 2.5D prismatic parts comprising features like slots, steps, pockets, etc. The advantages of the proposed model over previous works are that it (1) performs feature-based machining simulation considering transient thermomechanical loading conditions; (2) allows modeling the effects of coolant on convective heat transfer rate; and (3) considers the nonlinear behavior of the workpiece due to its changing geometry, inelastic material properties, and flexible fixture-workpiece contacts. The prediction accuracy of the model was validated with experimental results obtained during the course of the research work. A good agreement between the numerical and experimental results was found for different test cases with varying part geometries and machining condition

A Probabilistic-Based Approach to Monitoring Tool Wear State and Assessing Its Effect on Workpiece Quality in Nickel-Based Alloys

The objective of this research is first to investigate the applicability and advantage of statistical state estimation methods for predicting tool wear in machining nickel-based superalloys over deterministic methods, and second to study the effects of cutting tool wear on the quality of the part. Nickel-based superalloys are among those classes of materials that are known as hard-to-machine alloys. These materials exhibit a unique combination of maintaining their strength at high temperature and have high resistance to corrosion and creep. These unique characteristics make them an ideal candidate for harsh environments like combustion chambers of gas turbines. However, the same characteristics that make nickel-based alloys suitable for aggressive conditions introduce difficulties when machining them. High strength and low thermal conductivity accelerate the cutting tool wear and increase the possibility of the in-process tool breakage. A blunt tool nominally deteriorates the surface integrity and damages quality of the machined part by inducing high tensile residual stresses, generating micro-cracks, altering the microstructure or leaving a poor roughness profile behind. As a consequence in this case, the expensive superalloy would have to be scrapped. The current dominant solution for industry is to sacrifice the productivity rate by replacing the tool in the early stages of its life or to choose conservative cutting conditions in order to lower the wear rate and preserve workpiece quality. Thus, monitoring the state of the cutting tool and estimating its effects on part quality is a critical task for increasing productivity and profitability in machining superalloys. This work aims to first introduce a probabilistic-based framework for estimating tool wear in milling and turning of superalloys and second to study the detrimental effects of functional state of the cutting tool in terms of wear and wear rate on part quality. In the milling operation, the mechanisms of tool failure were first identified and, based on the rapid catastrophic failure of the tool, a Bayesian inference method (i.e., Markov Chain Monte Carlo, MCMC) was used for parameter calibration of tool wear using a power mechanistic model. The calibrated model was then used in the state space probabilistic framework of a Kalman filter to estimate the tool flank wear. Furthermore, an on-machine laser measuring system was utilized and fused into the Kalman filter to improve the estimation accuracy. In the turning operation the behavior of progressive wear was investigated as well. Due to the nonlinear nature of wear in turning, an extended Kalman filter was designed for tracking progressive wear, and the results of the probabilistic-based method were compared with a deterministic technique, where significant improvement (more than 60% increase in estimation accuracy) was achieved. To fulfill the second objective of this research in understanding the underlying effects of wear on part quality in cutting nickel-based superalloys, a comprehensive study on surface roughness, dimensional integrity and residual stress was conducted. The estimated results derived from a probabilistic filter were used for finding the proper correlations between wear, surface roughness and dimensional integrity, along with a finite element simulation for predicting the residual stress profile for sharp and worn cutting tool conditions. The output of this research provides the essential information on condition monitoring of the tool and its effects on product quality. The low-cost Hall effect sensor used in this work to capture spindle power in the context of the stochastic filter can effectively estimate tool wear in both milling and turning operations, while the estimated wear can be used to generate knowledge of the state of workpiece surface integrity. Therefore the true functionality and efficiency of the tool in superalloy machining can be evaluated without additional high-cost sensing

E -commerce for the metal removal industry

The popularity of outsourcing fabrication introduces a problem, namely an inevitable loss of data as information is translated from design to fabrication or from one system to another. Unsatisfactory information, delivered to the outsourcing facility, and inefficient communications between design and fabrication certainly cause enormous economic losses from late product delivery or bad product quality. To overcome these data transferring problems and to improve communications between the design and fabrication sides, a design and manufacturing methodology for custom machined parts in E-Commerce is suggested and implemented in this dissertation. This methodology is based on the idea of a Clean Interface like the Mead-Conway approach for VLSI chip fabrication [MEAD81]. Essential design information for fabricating parts properly with NC (Numerical Controlled) milling machines is expressed in machining/manufacturing features, fabrication friendly terminologies, and is represented by a new language called NCML (Numerical Control Markup Language). NCML is based on XML (Extensible Markup Language)---the document-processing standard proposed by the World Wide Web Consortium (W3C). NCML is designed to include the minimum requisite information necessary for the manufacturer to produce the product. The designer defines NCML, which overcomes geographical separation between design and manufacturing, and minimizes unnecessary interactions caused from lack of information. To prove the possibility of custom machine part fabrication and E-Commerce with NCML, three software systems are implemented. These three systems are FACILE/Design, FACILE/Fabricate, and E-Mill. FACILE is a prototype CAD/CAM system developed to verify NCML feasibility as an Electronic Data Interchange (EDI) format. FACILE/Design is a system based on manufacturing features like holes, contours, and pockets. It can be used to create geometric models, verify the design, and create NCML files. The NCML file is imported by FACILE/Fabricate and turned into G-codes by applying appropriate cutting conditions. Simplified machining simulation and cost estimation tools using NCML inputs are also developed to show some examples of NCML applications that can help design and manufacturing activities. To demonstrate how NCML could be used in a web-based application, an E-Business model called E-Mill has been implemented. E-Mill is a market place for machined parts whose data is encoded in NCML. To make E-Mill a feasible E-Commerce model, two-way communication based on NCML data and the visualization of 3D geometric models in the Virtual Reality Modeling Language (VRML) are equipped with a competitive matchmaking mechanism. In this dissertation, a whole system based on NCML bridges the gap between design and manufacturing. As a part of the NCML validation process for the new system, the pros and cons of NCML design features are discussed. A system for cost estimation is calibrated and compared to real cutting results for the purpose of validation