Contour parallel milling tool path generation for arbitrary pocket shape using a fast marching method

Contour parallel tool paths are among the most widely used tool paths for planer 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, the applicability of various offsetting methods is restricted because of limitations in dealing with pocket geometry with and without islands, the high computational costs, and numerical errors. Generation of cusps, segmentation of rarefied corners, and self-intersection during the offsetting operations and finding a unique offsetting solution for pocket with islands are among the associated problems in contour tool path generation. Most of methods are inherently incapable of dealing with such problems and use complex computational routines to identify and rectify these problems. Also, these rectifying techniques are heavily dependent on the type of geometry, and hence, the application of these techniques for arbitrary boundary conditions is limited and prone to errors. In this paper, a new mathematical method for generation of contour parallel tool paths is proposed which is inherently capable of dealing with the aforementioned problems. The method is based on a boundary value formulation of the offsetting problem and a fast marching method based solution for tool path generation. 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. The appropriate modifications are carried out to achieve higher accuracy for milling operations. A number of examples are presented, and computational issues are discussed for tool path generatio

Integrated process planning for a hybrid manufacturing system

A hybrid manufacturing system integrated CNC machining and laser-aided layered deposition and achieves the benefits of both processes. In this dissertation, an integrated process planning framework which aims to automate the hybrid manufacturing process is investigated. Critical components of the process planning, including 3D spatial decomposition of the CAD model, improvement of the toolpath generation pattern, repairing strategies using a hybrid manufacturing system, etc., are discussed --Abstract, page iv

Repair of metallic components using hybrid manufacturing

Many high-performance metal parts users extend the service of these damaged parts by employing repair technology. Hybrid manufacturing, which includes additive manufacturing (AM) and subtractive manufacturing, provides greater build capability, better accuracy, and surface finish for component repair. However, most repair processes still rely on manual operations, which are not satisfactory in terms of time, cost, reliability, and accuracy. This dissertation aims to improve the application of hybrid manufacturing for repairing metallic components by addressing the following three research topics. The first research topic is to investigate and develop an efficient best-fit and shape adaption algorithm for automating 3D models\u27 the alignment and defect reconstruction. A multi-feature fitting algorithm and cross-section comparison method are developed. The second research topic is to develop a smooth toolpath generation method for laser metal deposition to improve the deposition quality for metallic component fabrication and repair. Smooth connections or transitions in toolpath planning are achieved to provide a constant feedrate and controllable deposition idle time for each single deposition pass. The third research topic is to develop an automated repair process could efficiently obtain the spatial information of a worn component for defect detection, alignment, and 3D scanning with the integration of stereo vision and laser displacement sensor. This dissertation investigated and developed key technologies to improve the efficiency, repair quality, precision, and automation for the repair of metallic components using hybrid manufacturing. Moreover, the research results of this dissertation can benefit a wide range of industries, such as additive manufacturing, manufacturing and measurement automation, and part inspection --Abstract, page iv

Pengoptimuman jarak laluan mata alat menggunakan algoritma koloni semut untuk proses pengisaran poket

Pada masa kini, proses pemesinan kisar poket menggunakan mesin Kawalan Komputer Berangka (CNC) banyak digunakan dalam pemotongan logam. Terdapat dua langkah pemesinan di dalam proses pengisaran poket iaitu pemesinan kasar dan kemasan. Pemesinan kasar mengambil masa lebih 50 % dari keseluruhan masa pemotongan kerana sejumlah besar bahan kerja dipotong sehingga hampir menyerupai bentuk yang dikehendaki. Oleh itu, adalah penting untuk mempercepatkan masa pemesinan kasar. Pemesinan kontur selari dapat menghasilkan masa pemesinan kasar yang lebih rendah berbanding zigzag dan satu hala. Walau bagaimanapun, terdapat satu masalah di dalam pemesinan kontur iaitu berlaku bahagian lebihan tidak terpotong pada bahagian bucu dan tengah. Kawasan lebihan tidak terpotong ini berlaku kerana penetapan nilai selang antara kontur (ω) yang melebihi jejari mata alat (r). Salah satu cara untuk memotong kawasan lebihan ini adalah dengan menambahkan satu laluan mata alat tambahan (Llt) ke atas laluan asal, iaitu laluan kontur selari. Kaedah penghasilan laluan mata alat tambahan yang diperkenalkan kajian terdahulu berjaya untuk memotong keseluruhan kawasan lebihan ini. Namun, laluan yang dihasilkan oleh kajian sebelum ini tidak mempertimbangkan pergerakan mata alat yang menyumbang kepada peningkatan jarak laluan mata alat dan masa pemesinan kasar. Oleh itu, objektif kajian ini adalah untuk mengoptimumkan laluan mata alat bagi menentukan jarak laluan mata alat yang minimum di dalam proses pengisaran poket berdasarkan pemesinan kontur selari menggunakan kaedah cerdik buatan (AI). Algoritma kontur selari (Algo-KS) dibina bagi menghasilkan laluan mata alat secara kontur selari dan untuk menentukan kawasan lebihan tidak dipotong. Algoritma Koloni Semut berdasarkan aturan peralihan baru (ACO-PB) telah diperkenalkan untuk menentukan pergerakan mata alat bagi memotong kawasan lebihan berdasarkan aturan peralihan dan jarak minimum di antara dua kawasan lebihan. ACO-PB telah diuji keberkesanannya ke atas dua model iaitu model pertama dan model kedua bagi menentukan masa pemesinan kasar (Tmk). Seterusnya, Tmk yang diperoleh ini disahkan keputusannya menggunakan proses uji kaji pemesinan. Uji kaji dilakukan dengan mempraktikkan laluan mata alat yang dihasilkan berdasarkan ACO-PB ke dalam mesin kisar CNC tiga-paksi. Bahan kerja Aluminium 6061 dan mata alat jenis keluli laju tinggi (HSS) hujung rata yang bersalut Titanium Nitrida digunakan sepanjang proses pemesinan kasar. Hasil kajian mendapati terdapat perbezaan Tmk sebanyak 7.2 % di antara Tmk ACO-PB dan uji kaji. Keputusan ini telah mengesahkan bahawa ACO-PB yang dibangunkan berupaya untuk meminimumkan jarak laluan mata alat dan dapat dipraktikkan di dalam proses pemesinan sebenar. Llt dan Tmk yang dihasilkan ACO-PB juga telah dibandingkan dengan Llt dan Tmk yang diperoleh berdasarkan kajian terdahulu. Keputusan simulasi menunjukkan ACO-PB telah menghasilkan laluan mata alat yang lebih pendek sebanyak 23.7 % dan pengurangan Tmk sebanyak 4.95 % berbanding kajian terdahulu. Kajian ini juga telah membandingkan Tmk yang diperoleh menggunakan ACO-PB dan Mastercam dan mendapati ACO-PB berjaya mengurangkan Tmk sebanyak 46.5 %. Sebagai kesimpulan, kajian ini telah berjaya membangunkan algoritma ACO-PB yang berupaya untuk meminimumkan jarak laluan mata alat di dalam pemesinan kontur selari dan mengurangkan masa pemotongan bagi proses pemesinan kasar

Time-Optimal Feedrate Planning for Freeform Toolpaths for Manufacturing Applications

Optimality and computational efficiency are two desired yet competing attributes of time-optimal feedrate planning. A well-designed algorithm can vastly increase machining productivity, by reducing tool positioning time subject to limits of the machine tool and process kinematics. In the optimization, it is crucial to not overload the machining operation, saturate the actuators’ limits, or cause unwanted vibrations and contour errors. This presents a nonlinear optimization problem for achieving highest possible feedrates along a toolpath, while keeping the actuator level velocity, acceleration and jerk profiles limited. Methods proposed in literature either use highly elaborate nonlinear optimization solvers like Sequential Quadratic Programming (SQP), employ iterative heuristics which extends the computational time, or make conservative assumptions that reduces calculation time but lead to slower tool motion. This thesis proposes a new feedrate optimization algorithm, which combines recasting of the original problem into a Linear Programming (LP) form, and the development of a new windowing scheme to handle very long toolpaths. All constraint equations are linearized by applying B-spline discretization on the kinematic profiles, and approximating the nonlinear jerk equation with a linearized upper bound (so-called ‘pseudo-jerk’). The developed windowing algorithm first solves adjacent portions of the feed profile with zero boundary conditions at overlap points. Afterwards, using the Principle of Optimality, connection boundary conditions are identified that guarantee a feasible initial guess for blending the pre-solved adjacent feed profiles into one another, through a consecutive pass of LP. Experiments conducted at the sponsoring company of this research, Pratt & Whitney Canada (P&WC), show that the proposed algorithm is able to reliably reduce cycle time by up to 56% and 38% in two different contouring operations, without sacrificing dynamic positioning accuracy. Benchmarks carried out with respect to two earlier proposed feedrate optimization algorithms, validate both the time optimality and also drastic (nearly 60 times) reduction in the computational load, achieved with the new method. Part quality, robustness and feed drive positioning accuracy have also been validated in 3-axis surface machining of a part with 1030 waypoints and 10,000 constraint checkpoints

Pengoptimuman jarak laluan mata alat menggunakan algoritma koloni semut untuk proses pengisaran poket

Pada masa kini, proses pemesinan kisar poket menggunakan mesin Kawalan Komputer Berangka (CNC) banyak digunakan dalam pemotongan logam. Terdapat dua langkah pemesinan di dalam proses pengisaran poket iaitu pemesinan kasar dan kemasan. Pemesinan kasar mengambil masa lebih 50 % dari keseluruhan masa pemotongan kerana sejumlah besar bahan kerja dipotong sehingga hampir menyerupai bentuk yang dikehendaki. Oleh itu, adalah penting untuk mempercepatkan masa pemesinan kasar. Pemesinan kontur selari dapat menghasilkan masa pemesinan kasar yang lebih rendah berbanding zigzag dan satu hala. Walau bagaimanapun, terdapat satu masalah di dalam pemesinan kontur iaitu berlaku bahagian lebihan tidak terpotong pada bahagian bucu dan tengah. Kawasan lebihan tidak terpotong ini berlaku kerana penetapan nilai selang antara kontur (ω) yang melebihi jejari mata alat (r). Salah satu cara untuk memotong kawasan lebihan ini adalah dengan menambahkan satu laluan mata alat tambahan (Llt) ke atas laluan asal, iaitu laluan kontur selari. Kaedah penghasilan laluan mata alat tambahan yang diperkenalkan kajian terdahulu berjaya untuk memotong keseluruhan kawasan lebihan ini. Namun, laluan yang dihasilkan oleh kajian sebelum ini tidak mempertimbangkan pergerakan mata alat yang menyumbang kepada peningkatan jarak laluan mata alat dan masa pemesinan kasar. Oleh itu, objektif kajian ini adalah untuk mengoptimumkan laluan mata alat bagi menentukan jarak laluan mata alat yang minimum di dalam proses pengisaran poket berdasarkan pemesinan kontur selari menggunakan kaedah cerdik buatan (AI). Algoritma kontur selari (Algo-KS) dibina bagi menghasilkan laluan mata alat secara kontur selari dan untuk menentukan kawasan lebihan tidak dipotong. Algoritma Koloni Semut berdasarkan aturan peralihan baru (ACO-PB) telah diperkenalkan untuk menentukan pergerakan mata alat bagi memotong kawasan lebihan berdasarkan aturan peralihan dan jarak minimum di antara dua kawasan lebihan. ACO-PB telah diuji keberkesanannya ke atas dua model iaitu model pertama dan model kedua bagi menentukan masa pemesinan kasar (Tmk). Seterusnya, Tmk yang diperoleh ini disahkan keputusannya menggunakan proses uji kaji pemesinan. Uji kaji dilakukan dengan mempraktikkan laluan mata alat yang dihasilkan berdasarkan ACOPB ke dalam mesin kisar CNC tiga-paksi. Bahan kerja Aluminium 6061 dan mata alat jenis keluli laju tinggi (HSS) hujung rata yang bersalut Titanium Nitrida digunakan sepanjang proses pemesinan kasar. Hasil kajian mendapati terdapat perbezaan Tmk sebanyak 7.2 % di antara Tmk ACO-PB dan uji kaji. Keputusan ini telah mengesahkan bahawa ACO-PB yang dibangunkan berupaya untuk meminimumkan jarak laluan mata alat dan dapat dipraktikkan di dalam proses pemesinan sebenar. Llt dan Tmk yang dihasilkan ACO-PB juga telah dibandingkan dengan Llt dan Tmk yang diperoleh berdasarkan kajian terdahulu. Keputusan simulasi menunjukkan ACO-PB telah menghasilkan laluan mata alat yang lebih pendek sebanyak 23.7 % dan pengurangan Tmk sebanyak 4.95 % berbanding kajian terdahulu. Kajian ini juga telah membandingkan Tmk yang diperoleh menggunakan ACO-PB dan Mastercam dan mendapati ACO-PB berjaya mengurangkan Tmk sebanyak 46.5 %. Sebagai kesimpulan, kajian ini telah berjaya membangunkan algoritma ACO-PB yang berupaya untuk meminimumkan jarak laluan mata alat di dalam pemesinan kontur selari dan mengurangkan masa pemotongan bagi proses pemesinan kasar

Automatic compensating cleanup operation

Journal ArticleToday's part geometries are becoming ever more complex and require more accurate tool path to manufacture. Machining process efficiency is also a major consideration for designers as well as manufacturing engineers. Although the current advanced CAD/CAM systems have greatly improved the efficiency and accuracy of machining with the introduction of Numerically Controlled (NC) machining, excessive material may still be left on the finished part due to machining constraints, including the inaccessibility of the designed part geometry with respect the cutter, machine motion constraints like ramp angles, specific cutting patterns, etc. Polishing operations such as grinding and hand finishing are quite time consuming and expensive and may damage the surface of the part or introduce inaccuracies because of human errors. Although most of the existing machining approaches attempt to reduce such excessive restmaterials by modifying NC tool paths, none of them is satisfactory. They can be time consuming, error prone, computationally intensive, too complicated to implement, and limited to certain problem domains. A compensating cleanup tool path will be developed in this research to automatically remove these excessive material from the finish part. This method greatly reduces the burden of hand finishing and polishing and also reduces the error and complexities introduced in manually generating cleanup tool paths in the shop floor. More important, the tool path generated by this method will reduce the machining time and increase tool life compared with optimized tool path which left no excessive material behind

Computer aided process planning for rapid prototyping using a genetic algorithm

This thesis presents a new method for Computer Aided Process Planning (CAPP) for a subtractive Rapid Prototyping (RP) process. The CNC-RP process uses a 4-axis CNC machining center to create parts with flat end-mills. The objective is to determine the optimal system parameters for the RP process - those that enable parts to be created in a shorter amount of time. Two main contributions make this possible. First, a method of generating different machining orientation sets enables the part to be created with the same level of safety and quality available with the current system. Second, machining time is related to tool selection. These two contributions are combined into a single objective function. A Genetic Algorithm technique is implemented to determine the best machining tool sizes and machining orientations. The results show that a Genetic Algorithm can be applied to a RP process plan to reduce the total processing time

A unified rough and finish cut algorithm for NC machining of free form pockets using a grid based approach

http://www.worldcat.org/oclc/4333435

From computer-aided to intelligent machining: Recent advances in computer numerical control machining research

The aim of this paper is to provide an introduction and overview of recent advances in the key technologies and the supporting computerized systems, and to indicate the trend of research and development in the area of computational numerical control machining. Three main themes of recent research in CNC machining are simulation, optimization and automation, which form the key aspects of intelligent manufacturing in the digital and knowledge based manufacturing era. As the information and knowledge carrier, feature is the efficacious way to achieve intelligent manufacturing. From the regular shaped feature to freeform surface feature, the feature technology has been used in manufacturing of complex parts, such as aircraft structural parts. The authors’ latest research in intelligent machining is presented through a new concept of multi-perspective dynamic feature (MpDF), for future discussion and communication with readers of this special issue. The MpDF concept has been implemented and tested in real examples from the aerospace industry, and has the potential to make promising impact on the future research in the new paradigm of intelligent machining. The authors of this paper are the guest editors of this special issue on computational numerical control machining. The guest editors have extensive and complementary experiences in both academia and industry, gained in China, USA and UK