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

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

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.)

An Integrated Approach to Finish Machining of RP Parts

An integrated approach to finish machining of RP parts and tools has been developed at the University of Rhode Island. Pre-processing operations, including surface offsets to add machining stock, and post-processing operations, including CNC tool-path generation, have been combined into one integrated set of software algorithms to make possible the effective finishing of near-net parts and tools from RP. An in-depth description of the uniquely developed STL vertex offset algorithm will be explored as well as an automatic method for adaptive raster milling, sharp edge contour machining and hole drilling from STL files. The time involved and surface finish benefits of the developed methodology will be compared to alternative approaches.Mechanical Engineerin

A multi-perspective dynamic feature concept in adaptive NC machining of complex freeform surfaces

This paper presents a new concept of feature for freeform surface machining that defines the changes in feature status during real manufacturing situations which have not been sufficiently addressed by current international standards and previous research in feature technology. These changes are multi-perspective, including (i) changes in depth-of-cut: the geometry of a feature in the depth-of-cut direction changes during different machining operations such as roughing, semi-finishing and finishing; (ii) changes across the surface: a surface may be divided into different machining regions (effectively sub-features) for the selection of appropriate manufacturing methods for each region such as different cutting tools, parameters, set-ups or machine tools; and (iii) changes in resources or manufacturing capabilities may require the re-planning of depth-of-cuts, division of machining regions and manufacturing operations (machines, tools, set-ups and parameters). Adding the above dynamic information to the part information models in current CAD systems (which only represent the final state of parts) would significantly improve the accuracy, efficiency and timeliness of manufacturing planning and optimisation, especially for the integrated NC machining planning for complex freeform surfaces. A case study in an aircraft manufacturing company will be included in this paper

Superquadrics and Angle-Preserving Transformations

Over the past 20 years, a great deal of interest has developed in the use of computer graphics and numerical methods for three-dimensional design. Significant progress in geometric modeling is being made, predominantly for objects best represented by lists of edges, faces, and vertices. One long-term goal of this work is a unified mathematical formalism, to form the basis of an interactive and intuitive design environment in which designers can simulate three-dimensional scenes with shading and texture, produce usable design images, verify numerical machining-control commands, and set up finite-element meshwork for structural and dynamic analysis. A new collection of smooth parametric objects and a new set of three-dimensional parametric modifiers show potential for helping to achieve this goal. The superquadric primitives and angle-preserving transformations extend the traditional geometric primitives-quadric surfaces and parametric patches-used in existing design packages, producing a new spectrum of flexible forms. Their chief advantage is that they allow complex solids and surfaces to be constructed and altered easily from a few interactive parameters

Multi-Axis Planning System (MAPS) for Hybrid Laser Metal Deposition Processes

This paper summarizes the research and development of a Multi-Axis Planning System (MAPS) for hybrid laser metal deposition processes. The project goal is to enable the current direct metal deposition systems to fully control and utilize multi-axis capability to make complex parts. MAPS allows fully automated process planning for multi-axis layered manufacturing to control direct metal deposition machines for automated fabrication. Such a capability will lead to dramatic reductions in lead time and manufacturing costs for high-value, low-volume components with high performance material. The overall approach, slicing algorithm, machine simulation for planning validation, and the planning results will be presented

Analytical and experimental investigation of orthogonal turn-milling processes

Machining of hard-to-cut materials is challenging due to their high strength resulting in reduced productivity and high manufacturing cost. Conventional machining processes are commonly used for production of these parts where cutting speed, and thus the material removal rate, is limited due to high tool wear rate. Because of the increasing market demands for higher quality, reduced lead times and cost, alternative techniques are required in order to increase productivity in machining of these materials. An increase in potential production capacity was observed in the recent years due to advancements in machine tools that offer high precision, increased flexibility and spindle speed. Multi-axis machining, which can be a remedy for these demands, have been continuing to spread rapidly in many industries particularly in aerospace and defense. These processes are generally performed on multi-tasking machines through simultaneous cutting operations on the same part or machining of more than one part simultaneously. Turn-milling, which is a promising multi-axis cutting process combining two conventional machining operations; turning and milling, can offer high productivity for difficult-to-cut materials such as Ti and Ni alloys as well as parts with large diameters which cannot be rotated at high speeds on conventional lathes. However, the work done on analysis and modeling of turn-milling operations is very limited. On the other hand, due to the high flexibility and capability of turn-milling operations, there are numerous process parameters which need to be selected properly to utilize the full potential offered by these processes. In order to achieve this, process models which consider all cutting parameters are required. In this thesis, analytical models for turn-milling process geometry, chip formation and cutting force including eccentricity effects are presented. Furthermore, circularity, cusp height and surface roughness are modeled and simulated. Model predictions are verified by experiments carried out on a multi-tasking machine tool under different process conditions. Tool wear tests for hard-to-machine materials are also performed on the same machine where effects of turn-milling process conditions on tool life are shown. Simulation and experimental results show that substantial increase in productivity can be achieved using turn-milling in machining of difficult-to-cut materials when process conditions are selected properly

Surface roughness prediction in milling based on tool displacements

In this paper, an experimental device using non-contact displacement sensors for the investigation of milling tool behaviour is presented. It enables the recording of high frequency tool vibrations during milling operations. The aim of this study is related to the surface topography prediction using tool displacements and based on tool center point methodology. From the recorded signals and the machining parameters, the tool deformation is modeled. Then, from the calculated deflection, the surface topography in 3D can be predicted. In recent studies, displacements in XY plane have been measured to predict the surface topography in flank milling. In this article, the angular deflection of the tool is also considered. This leads to the prediction of surfaces obtained in flank milling as well as in end milling operations. Validation tests were carried out: the predicted profiles were compared to the measured profile. The results show that the prediction corresponds well in shape and amplitude with the measurement

Robotic polishing of large optical components

Lightweight space mirrors have been widely used in earth observation and astronomy applications. Many organizations and companies, such as NASA in America, ESA in Europe, SSTL in UK as well as CASC in China, have spent a lot of money and effort on researching new materials for larger size space mirrors to meet both the payload weight constraints of launch and the increased advanced manufacturing process demanded for higher observations quality. This project is aimed at robot neutral polishing of lapped, ground and polished optical substrates using an industrial FANUC robot system. The project focused on three main fields which were: robot polishing with polyurethane tool and cerium oxide, pitch polishing with pitch tool and cerium oxide, as well as polishing of a 400mm ULE component. The polishing process targets were to achieve: 1) a surface roughness (Ra) of 10 nm and a surface profile (Pt) of 6 µm and 2µm on lapped and ground substrates respectively with polyurethane based tools and 2) a surface roughness (Ra) of 2nm with a surface profile (Pt) unchanged on robot neutral polished substrates using pitch based tools. This thesis comprises four main sections: a literature review, an experimental implementation, metrology and analysis, and the final conclusions. The experiment results measured with the metrology equipment selected were analysed. Conclusions of the relationship between the polishing performance of a specific sample and the selected polishing tool, polishing slurry, tool pressure, polishing time and other parameters were drawn. Results obtained from robot neutral polishing were surface roughness (Ra) of 8-10nm and surface profile (Pt) of 6µm for 100mm square lapped and ground parts. The process scalability was demonstrated from robot neutral polishing in 45hours, a 400mm square ground component from a surface roughness (Ra) of 200nm to 10nm. There is additional work to be implemented in the future, such as the development of robot pitch polishing of robot neutral polished parts to achieve 2nm Ra