22,173 research outputs found

    Topological model for machining of parts with complex shapes

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    Complex shapes are widely used to design products in several industries such as aeronautics, automotive and domestic appliances. Several variations of their curvatures and orientations generate difficulties during their manufacturing or the machining of dies used in moulding, injection and forging. Analysis of several parts highlights two levels of difficulties between three types of shapes: prismatic parts with simple geometrical shapes, aeronautic structure parts composed of several shallow pockets and forging dies composed of several deep cavities which often contain protrusions. This paper mainly concerns High Speed Machining (HSM) of these dies which represent the highest complexity level because of the shapes' geometry and their topology. Five axes HSM is generally required for such complex shaped parts but 3 axes machining can be sufficient for dies. Evolutions in HSM CAM software and machine tools lead to an important increase in time for machining preparation. Analysis stages of the CAD model particularly induce this time increase which is required for a wise choice of cutting tools and machining strategies. Assistance modules for prismatic parts machining features identification in CAD models are widely implemented in CAM software. In spite of the last CAM evolutions, these kinds of CAM modules are undeveloped for aeronautical structure parts and forging dies. Development of new CAM modules for the extraction of relevant machining areas as well as the definition of the topological relations between these areas must make it possible for the machining assistant to reduce the machining preparation time. In this paper, a model developed for the description of complex shape parts topology is presented. It is based on machining areas extracted for the construction of geometrical features starting from CAD models of the parts. As topology is described in order to assist machining assistant during machining process generation, the difficulties associated with tasks he carried out are analyzed at first. The topological model presented after is based on the basic geometrical features extracted. Topological relations which represent the framework of the model are defined between the basic geometrical features which are gathered afterwards in macro-features. Approach used for the identification of these macro-features is also presented in this paper. Detailed application on the construction of the topological model of forging dies is presented in the last part of the paper

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

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    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

    A Review of State-of-the-Art Large Sized Foam Cutting Rapid Prototyping and Manufacturing Technologies.

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    Purpose – Current additive rapid prototyping (RP) technologies fail to efficiently produce objects greater than 0.5?m3 due to restrictions in build size, build time and cost. A need exists to develop RP and manufacturing technologies capable of producing large objects in a rapid manner directly from computer-aided design data. Foam cutting RP is a relatively new technology capable of producing large complex objects using inexpensive materials. The purpose of this paper is to describe nine such technologies that have been developed or are currently being developed at institutions around the world. The relative merits of each system are discussed. Recommendations are given with the aim of enhancing the performance of existing and future foam cutting RP systems. Design/methodology/approach – The review is based on an extensive literature review covering academic publications, company documents and web site information. Findings – The paper provides insights into the different machine configurations and cutting strategies. The most successful machines and cutting strategies are identified. Research limitations/implications – Most of the foam cutting RP systems described have not been developed to the commercial level, thus a benchmark study directly comparing the nine systems was not possible. Originality/value – This paper provides the first overview of foam cutting RP technology, a field which is over a decade old. The information contained in this paper will help improve future developments in foam cutting RP systems

    Feature recognition & tool path generation for 5 axis STEP-NC machining of free form / irregular contoured surfaces

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    This research paper presents a five step algorithm to generate tool paths for machining Free form / Irregular Contoured Surface(s) (FICS) by adopting STEP-NC (AP-238) format. In the first step, a parametrized CAD model with FICS is created or imported in UG-NX6.0 CAD package. The second step recognizes the features and calculates a Closeness Index (CI) by comparing them with the B-Splines / Bezier surfaces. The third step utilizes the CI and extracts the necessary data to formulate the blending functions for identified features. In the fourth step Z-level 5 axis tool paths are generated by adopting flat and ball end mill cutters. Finally, in the fifth step, tool paths are integrated with STEP-NC format and validated. All these steps are discussed and explained through a validated industrial component

    Surface roughness variation of thin wall milling, related to modal interactions

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    High-speed milling operations of thin walls are often limited by the so-called regenerative effect that causes poor surface finish. The aim of this paper is to examine the link between chatter instability and surface roughness evolution for thin wall milling. Firstly, the linear stability lobes theory for the thin wall milling optimisation was used. Then, in order to consider the modal interactions, an explicit numerical model was developed. The resulting nonlinear system of delay differential equations is solved by numerical integration. The model takes into account the coupling mode, the modal shape, the fact that the tool may leave the cut and the ploughing effect. Dedicated experiments are carried out in order to confirm this modelling. This paper presents surface roughness and chatter frequency measurements. The stability lobes are validated by thin wall milling. Finally, the modal behaviour and the mode coupling give a new interpretation of the complex surface finish deterioration often observed during thin wall milling

    Pembangunan dan keberkesanan kit penyongsang dalam proses pengajaran dan pembelajaran (PDP) di kolej vokasional

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    Pembangunan Alat Bahan Bantu Mengajar (ABBM) untuk menggalakkan guru menggunakan Kit Penyongsang dalam proses pengajaran dan pembelajaran (PdP). Kajian ini bertujuan untuk membangun dan menguji keberkesanan Kit Penyongsang dalam PdP di Kolej Vokasional. Pembangunan Kit Penyongsang adalah berdasarkan model ADDIE dan kajian ini menggunakan pendekatan kuantitatif berbentuk kuasi eksperimental. Kajian ini menggunakan kaedah ujian pra-pasca yang melibatkan seramai 42 orang pelajar Teknologi Elektrik daripada dua buah Kolej Vokasional. Instrumen kajian merangkumi ujian pra, pasca dan soal selidik. Data dianalisis menggunakan kekerapan, skor min dan ujian-t. Hasil kajian menunjukkan bahawa pembangunan Kit Penyongsang dapat berfungsi dengan baik dan penggunaan Kit Penyongsang ini meningkatkan pencapaian pelajar dalam topik penyongsang. Berdasarkan hasil kajian dengan penggunaan Kit Penyongsang menunjukkan peningkatan sebanyak 44.9% berbanding menggunakan kaedah konvensional iaitu 9.67%. Secara kesimpulan menunjukkan Kit Penyongsang ini dapat menarik perhatian pelajar untuk mempelajari subjek ini

    From 3D Models to 3D Prints: an Overview of the Processing Pipeline

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    Due to the wide diffusion of 3D printing technologies, geometric algorithms for Additive Manufacturing are being invented at an impressive speed. Each single step, in particular along the Process Planning pipeline, can now count on dozens of methods that prepare the 3D model for fabrication, while analysing and optimizing geometry and machine instructions for various objectives. This report provides a classification of this huge state of the art, and elicits the relation between each single algorithm and a list of desirable objectives during Process Planning. The objectives themselves are listed and discussed, along with possible needs for tradeoffs. Additive Manufacturing technologies are broadly categorized to explicitly relate classes of devices and supported features. Finally, this report offers an analysis of the state of the art while discussing open and challenging problems from both an academic and an industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and Innovation action; Grant agreement N. 68044

    Reconstruction of freeform surfaces for metrology

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    The application of freeform surfaces has increased since their complex shapes closely express a product's functional specifications and their machining is obtained with higher accuracy. In particular, optical surfaces exhibit enhanced performance especially when they take aspheric forms or more complex forms with multi-undulations. This study is mainly focused on the reconstruction of complex shapes such as freeform optical surfaces, and on the characterization of their form. The computer graphics community has proposed various algorithms for constructing a mesh based on the cloud of sample points. The mesh is a piecewise linear approximation of the surface and an interpolation of the point set. The mesh can further be processed for fitting parametric surfaces (Polyworks® or Geomagic®). The metrology community investigates direct fitting approaches. If the surface mathematical model is given, fitting is a straight forward task. Nonetheless, if the surface model is unknown, fitting is only possible through the association of polynomial Spline parametric surfaces. In this paper, a comparative study carried out on methods proposed by the computer graphics community will be presented to elucidate the advantages of these approaches. We stress the importance of the pre-processing phase as well as the significance of initial conditions. We further emphasize the importance of the meshing phase by stating that a proper mesh has two major advantages. First, it organizes the initially unstructured point set and it provides an insight of orientation, neighbourhood and curvature, and infers information on both its geometry and topology. Second, it conveys a better segmentation of the space, leading to a correct patching and association of parametric surfaces.EMR

    Analytical models for high performance milling. Part I: cutting forces, structural deformations and tolerance integrity

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    Milling is one of the most common manufacturing processes in industry. Despite recent advances in machining technology, productivity in milling is usually reduced due to the process limitations such as high cutting forces and stability. If milling conditions are not selected properly, the process may result in violations of machine limitations and part quality, or reduced productivity. The usual practice in machining operations is to use experience-based selection of cutting parameters which may not yield optimum conditions. In this two-part paper, milling force, part and tool deection, form error and stability models are presented. These methods can be used to check the process constraints as well as optimal selection of the cutting conditions for high performance milling. The use of the models in optimizing the process variables such as feed, depth of cut and spindle speed are demonstrated by simulations and experiments

    Rapid manufacturing- state of the art, analysis and future perspectives

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    Layer based manufacturing system often referred to as Rapid Prototyping (RP) have been in existence for 22 years, in the past 5 years Rapid Manufacturing (RM) has emerged from these RP systems to produce functional and structural customer focused end use components and products. This keynote paper will review the current range of technologies for metallic systems, it will also evaluate the operating principles, features, potential and limitations of current commercially available systems. Rapid Manufacture is increasingly being used for high value difficult to manufacture components with a new set of design rules required to fully exploit the RM systems inherent characteristics. A case studies approach will be used to show the benefits and pitfalls this new design freedom can provide designers
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